3. RECENT ENVIRONMENT OF LAKE GOS´CIAZ AND CONNECTED … · 3. recent environment of lake gos´cia z and connected lakes 3.1. geological structure and relief in the surroundings

3. RECENT ENVIRONMENT OF LAKE GOSCIAZAND CONNECTED LAKES

3.1. GEOLOGICAL STRUCTURE AND RELIEF INTHE SURROUNDINGS OF THE NA JAZACHLAKE SYSTEM

Bogumi Wicik

Quaternary substratum

The substratum of the Pleistocene deposits in theP ock Basin consists of Pliocene clays and, locally, ofMiocene brown coals, sands, and carbonaceous clays aswell as of calcareous sandstones and marls of the Creta-ceous (Mapa Geologiczna Polski 1978). Discontinuitiesof the Tertiary sediments and their variable thickness re-sult from erosional and glacitectonic processes (Skom-pski 1971, Madeyska, Chapter 2.2). In the area of lakesNa Jazach the topography at the top of the Tertiary de-posits is fairly complicated. Between Lake Mielec andthe western part of Lake Gosciaz the top of the Tertiarydeposits forms a meridional ridge at the height of 40 ma.s.l. East of the ridge the surface of the Pliocene claysforms an oval depression. The isoline closing this de-pression at the height of 30 m a.s.l. runs through the east-ern part of Lake Gosciaz and through lakes Mrokowo andWierzchon. In the bottom of this depression, occurring ca.0.6 km to the east of Lake Gosciaz, the Tertiary depositsare found below 20 m a.s.l. Small funnel-like depressions(with a diameter of ca. 300 m) at the top of the substra-tum have also been registered north of lakes Na Jazach.The surface of the Tertiary occurs there between 30 mand 20 m a.s.l. (So onowicz 1987, Tkaczyk 1987). Thepresence of weakly permeable deposits is documented bygeoelectrical measurements (Churski & Marszelewski,Chapter 3.3). Ca. 0.6 km NE of Lake Wierzchon theMiocene brown coals and thick fine-grained sands withcoal dusts have been found directly under the fluviogla-cial deposits at the depth of 27 m (ca. 40 m a.s.l.). At thenorthern shore of Lake Gosciaz (ca. 200 m east of To-by ka Bay) the Quaternary deposits reach thickness of17 m. The Pliocene clays below occur to a depth of 30 m,and the underlying carboniferous series of the Miocenereach an elevation of ca. 27 m a.s.l. The top of this seriesis built of brown coals (2 m), while its lower parts consistof fine-grained sands with coal dust. Ca. 0.4 km south of

Lake Gosciaz the surface of the Pliocene clays occurs atthe height of 31 m a.s.l., and the top of the Miocene coalsat ca. 25 m a.s.l. The basin of Lake Gosciaz intersects theMiocene deposits at an elevation of 26–24 m a.s.l.

The Pliocene clays contain siderite and pyrite concre-tions, and the Miocene marly clays contain crystals ofgypsum and pyrite (Skompski 1971). The ash (67%) ob-tained after burning the sample of the Miocene coals ofthe surrounding of Lake Gosciaz contained 0.23% Mg,0.61% Fe, and ca. 0.32% SO4.

The discontinuities in the isolating layer of thePliocene clays play the role of hydrogeological windows(Churski & Marszelewski, Chapter 3.3). Mixing of theTertiary (and older) waters with the Quaternary waterstakes place. Direct seepage of the Miocene waters to thelake could have occurred in the initial period of the lakeexistence. Movement of waters within hydrological win-dows favours microbiological activation of the chemi-cally active components of the Miocene coals such ascarbon and sulphur. Their removal, especially in the ga-seous form (CO2, CH4, H2S), from the Miocene series re-sults in a decrease in volume, which may cause the sub-sidence of the overlying geological layers. Such pro-cesses probably gave rise to the “karstic” character of thesurfaces of the Tertiary deposits and also possibly to thefunnel shape of the central deep in Lake Gosciaz. Thus, itcan be supposed that the development of the Late-Glacialmeltwater morphology was modified by the local hydro-geological conditions (Wicik & Wieckowski 1991).

Pleistocene sediments and forms

Lakes Na Jazach occur within the linear depressionproduced in fluvioglacial deposits (Madeyska 1991,1993, Chapter 2.2). Within the P ock Basin these depositsform several terrace levels descending as indistinct stepstowards the north. In that part of P ock Basin the flat sur-face of fluvioglacial sediments is dissected by the systemof subglacial troughs and meltwater depressions (Fig.3.1).

The fluvioglacial deposits of the terrace 67–70 m a.s.l.near lakes Na Jazach exhibit small differences in grainsizes. The patches of gravels and sands with boulders upto 15 cm in diameter occur only SE of Lake Wierzchon

Ralska-Jasiewiczowa M., Goslar T., Madeyska T. & Starkel L. (eds), 1998. Lake Gościąż, central Poland. A monographic study. Part 1. W. Szafer Institute of Botany, Polish Academy of Sciences, Kraków.

(Skompski 1971). These deposits are to 1.1 m thick. Theirgrain-size composition is given in Table 3.1. Generally, inthe near-surface zone of the surrounding of lakes NaJazach, medium and fine sands with a few pebbles (Tab.3.1) predominate. At the NE shore of Lake Gosciaz,under these deposits at a depth of ca. 3 m is a layer offine and medium sands with a few crumbs of carboneoussubstance in the basal part (61.5 m a.s.l.). At the northernshore of Lake Gosciaz, under fine and varigrained sandsat the elevation of 60 m a.s.l. are fine sands with chunksof coal, and below at the depth of 7 m are varigrainedsands with gravels. At the southern shore of LakeGosciaz fine sands occur to the depth of 2–3 m abovevarigrained sands with gravels and then, from 8 m on,fine sands again. The western section of the shore ofLake Gosciaz to a depth of ca. 5 m is built of differen-tiated sands with gravels. Below, at the height of 59.5 ma.s.l., fine sands with chunks of lignite and lamellae ofbogheads have been found. The eastern part of the south-ern shore of Lake Gosciaz to a depth of ca. 4–5 m belowthe lake water level is built of sands and gravels with finerounded pebbles, underlain by fine and medium sands. At0.5–1 km to the north of the lakes, between 67–64 ma.s.l., the surface is folded (Fig. 3.1), with features of anerosional edge in places. Actually, this is the surface of

the slope dipping to the north, with fragments of shallowvalleys and fine dunes.

The lower fluvioglacial terrace, located at 64–60 ma.s.l., is built of varigrained sands with an admixture ofgravels and fine pebbles. Within this terrace, NE of LakeWierzchon, in the near-surface layer, fine sands with gra-vels occur to the depths of 2.5–5 m, and fine sands to thedepths of 11 m. Black and steel-grey clays (Miocene?)have been found there at 57 m a.s.l.

Meltwater depressions occupied at present by thelakes reach depths of 13–17 m (51–47 m a.s.l.). Greaterdepths (20–40 m) occur only in three hollows of LakeGosciaz (see Chapter 5.1). At the sites of the presentpeatlands the original depths of the depressions were 6–10 m. In the bottoms of meltwater depressions, fine sandsusually occur under limnic sediments. The underwatersill separating Lake Gosciaz from Tobyłka Bay at thewater depth of ca. 4 m is built of differentiated sands withgravel and pebbles.

After accumulation of fluvioglacial deposits had beencompleted, the surface with buried dead ice was sub-jected to eolian processes. In the zone of meltwater de-pressions Na Jazach there was a border between the areasof deflation and accumulation. North of these depressionsdeflation was small and did not completely mask the ero-

Fig. 3.1. Geomorphic map of the area of lakes Na Jazach. Pleistocene forms: 1 – subglacial channels, 2 – fluvioglacial terrace 70–67 m a.s.l.,3 – fluvioglacial terrace 64–60 m a.s.l., 4 – edges of terrace levels, 5 – erosional valleys, 6 – dead-ice depressions, 7 – deeps and steps in lakebottoms, 8 – meltwater depressions, 9 – plains of lacustrine deposition, 10 – dunes. Holocene forms: 11 – bog plains in dead-ice depressionsand in the river valley floors, 12 – undercuts, 13 – landslide slopes, 14 – spring niches, 15 – alluvial fans.

36 LAKE GOSCIAZ

sional edge between the terraces. South of lakes NaJazach the dune complexes are usually arcuate and reachto 12 m in height. At the southern and eastern margins ofthe meltwater depressions there are only singular smalldune ridges stretching from NW to SE. Probably thedunes originally overlaid the dead ice, and because ofthat some of these dunes end abruptly at the edges of thelake basins. At the base of the dunes the layers of fossilsoils and weathering zones are lacking. The dunes arebuilt of fine sands (Tab. 3.1) containing locally fairamount of muscovite.

Melting of dead ice and formation of outwash tookplace after cessation of the eolian processes. Because ofthe lack of free surface runoff, marginal fragments ofmeltwater depressions played the role of reservoirs oflimnic sedimentation. The plains related to this episodeare covered with fine sands or silty sands with thin siltyinterbeddings (Fig. 3.1). These deposits exhibit an indis-tinct horizontal lamination (Kotarbinski & Urbaniak-Biernacka 1975).

Holocene deposits and forms

In the deeper meltwater depressions, limnic sedimen-tation started in the Bølling or Allerød and took placewithout major interruptions also at the beginning of theHolocene. However, in the eastern part of Lake Gosciazgeomorphological and sedimentological changes oc-curred. In the borings located directly at the easternshore, it was found that the limnic sediments accumu-lated around 11,800 14C BP became covered with a finesand layer 4.4–6 m thick. The surface of the lake terracethere is adjacent to a landslide slope. Formation of thelatter took place after deposition of the limnic sediments.The change in the shore morphology caused intensifiedsedimentation in the nearby part of the lake. The slopesand spring-niches at the southern shore of Lake Gosciazand at the springs of the Ruda stream are much younger.The 5–7 m steep scarp of the lake that incises the aquiferis subject to landslide processes. The beach is built of thesands transported towards the lake from numerous springs.

The Holocene limnic sediments of the present-daylakes Na Jazach consist of carbonate and carbonate-sul-phide gyttjas. The latter are common in Lake Gosciaz.The meltwater depressions occupied at present by thepeatlands, are filled with carbonate gyttjas being up to 4

m thick. The peats overlying the gyttjas are 1.2–4 mthick. Swamp peats with Phragmites and wood peats pre-dominate there. The peats of the transitional peatlands are1.5–2 m thick and occur in the meltwater depressions lo-cated mainly on the northern side of the system of lakesNa Jazach. Lake Mrokowo is surrounded by moss peat.

When the activity of the Ruda stream began, thegyttjas became locally covered with deposits of the allu-vial fans. These deposits consist of sands of various grainsizes and with plant detritus and chunks of charcoal.

3.2. BATHYMETRY AND MORPHOMETRYOF LAKE GOSCIAZ

Zygmunt Churski

Lake Gosciaz was sounded for the first time by Jaczy-nowski in 1925 (Lencewicz 1925). The depths weremeasured every 20 or 30 meters by means of a stringwith a weight. Distances between sounding points weremarked on a rope extended on floats. Positions of tran-sects were determined by geological compass. The watertable of the lake during the measurements was at a levelof 63.9 m a.s.l. As a result of this sounding the maximumdepth was determined as 25.8 m, with the lake area as46.9 ha. Moreover, Jaczynowski (1929) worked out thelake morphometry based on the established grid.

After initiation of the studies on the deposits of LakeGosciaz, which required precise determination of sound-ing coordinates, new measurements were undertaken inorder to obtain an up-to-date and a very detailed grid ofthe lake and its surrounding. Torun Military Unit No.1440 under the supervision of Lt. J. Ciuba, M. E., per-formed bathymetric (echosounding) and topographicmeasurements, which allowed for working out a newplan (Fig. 3.2).

Application of echosounding and modern surveyingtechniques enables precise positioning of sites of sound-ing and levelling as well as for precise determination ofdepths from water table to the surface of the bottom de-posits. When a weighted line (sounding line) is used, itssubmergence into the upper layer of lake deposits, evendown to 0.5 m, has to be taken into consideration. More-over, Jaczynowski’s measurements of 1925 did not in-clude large parts of the lake. Thus, a new plan wasnecessary.

Table 3.1. Grain-size composition of deposits in the area of the lakes Na Jazach.

Type of depositGrain sizes in %

above 2.5 mm 2.5–1.0 mm 1.0–0.5 mm 0.50–0.25 mm 0.25–0.10 mm below 0.1 mm

Residual glacial deposits 24.0 12.1 37.0 23.8 2.3 0.8

Glacifluvial sands 0.2 2.7 38.2 41.4 9.9 0.6

Fluvial sands 0.4 0.9 12.3 48.5 19.7 12.2

Eolian sands 0.0 0.3 6.2 31.2 49.1 13.2

Recent environment 37

The plan with isobaths and contour lines every 1 mprovides a detailed picture of relief of the bottom andsurroundings of the lake. In the relief of the lake basinthere are two distinct deep hollows, with steep westernslopes and gentle eastern ones. Asymmetry also extendsto the basin slopes above the lake. The southern slope ofthe lake is steep, with well-defined landslides and under-water landslide lobes. On the other hand, the northernslope is much lower and more gentle. Large contrast alsois apparent between the relief of the bottom and surround-ings of the lake due to different origin of these units.

When analysing the present plan of the lake bottomone should bear in mind that the lake basin has beenfilled with lacustrine deposits. The sediment cores andcross-sections in which primary bottom is included(Wieckowski 1993) show that the initial outline of thelake bottom is only partially preserved in the present re-lief of the lake. Despite the fact that the deposits are sev-eral meters thick (up to 20 m), two well-defined deephollows remained in the central and western parts. Thesehollows have existed since the lake formation and pro-vide evidence of calm sedimentation. On the other hand,the hollows have been neither preserved in the northernbay (Tobyłka) nor in the eastern part, where sedimenta-tion was intensified due to the stream flowing from LakeBrzózka to Lake Mielec as well as due to landslide pro-cesses.

Analyses of the sediment cores provide evidence forthe existence of five definite deep hollows at the initialphase of the lake development (Wieckowski 1993). Themaximum depth of the lake was at the site of the presentdeepest spot and reached ca. 44 m. Thus, morphometricdata presented below refer to the present bottom relief,which preserved the original outline in the central partonly.

The plan provides evidence that Lake Gosciaz occu-pied much larger area and was confluent with the neigh-bouring lakes. A higher elevation of the original watertable is evidenced by wetlands in the vicinity of lakes andby the fragments of preserved terraces, which are well-defined east of the lake.

The morphometric data of the lake are as follows:Area (A) 41.7 haMaximum length (L) 1168 mMaximum width (B) 735 m Mean width (A/B) 357.2 mElongation (L/B) 1.59Volume (V) 2 073⋅103 m3

Maximum depth (Dmax) 24 mMean depth (V/A) 4.97 mRelative depth (Dmax/√A) 0.04Depth index (Dmean/Dmax) 0.21Shore line length (S) 3 452 mDevelopment of shore line 1.51

Fig. 3.2. Bathymetric plan of Lake Gosciaz. 1 – isobaths, 2 – shoreline, 3 – contour lines, 4 – wetlands, 5 – scarps, 6 – springs, 7 – streams,8 – elevation in m a.s.l.

38 LAKE GOSCIAZ

Elevation of water table 64.3 m a.s.l.Mean bottom gradient 4o29’Mean gradient of the slope fromthe isobath of 16 m to 24 m 11o21’The comparison of the above data with the corre-

sponding parameters of Jaczynowski (Lencewicz 1925)proves that the lake area is now smaller by ca. 5 ha andshallower by ca. 2 m. The change in the area can resultfrom permanent overgrowing of the lake. The differencein the depths can be partly attributed to the low accuracyof earlier measurements.

Analysis of morphometric data shows that LakeGosciaz can be assigned to the medium-sized lakes of theGostyninskie Lake District. It is the second deepest lakein the region (after Lake Białe). If the original basin(without lake deposits) were considered, however, LakeGosciaz would be the deepest one in the region (44 m).Lake Gosciaz is also unique with respect to gradient ofthe slopes. Although the average bottom gradient (4o29’)can be accepted as a high mean value, the gradient of thedeep hole, below 16 m, reaches 11o21’, which is an ex-treme value rarely encountered. The average gradients ofother lakes vary from 2o to 5o. Moreover, relative depth(ratio of maximum depth to the square root of the area) ofLake Gosciaz is 0.04, a rather large value as well. Thisvalue allows comparison of vertical and horizontaldimensions of the lake basin, and is more characteristicfor cirque than for lowland lakes.

Large relative depth of similar order of magnitude hasbeen recorded in the case of Lake Dzielno (0.042) andLake Kocioł (0.082) (see Churski, Chapter 2.4). For com-parison, the relative depth of Lake Zdworskie is 0.003and that of Lake Rakutowskie 0.0013 (Jaczynowski1929).

It should be emphasized that the present plan can con-stitute background for tracing further changes in depth,area, and shore line. In order to make such surveyingpossible, a network of benchmarks corresponding to thepresent-day topographic framework was established atthe lake.

3.3. HYDROLOGY AND SEDIMENTATIONCONDITIONS IN LAKE GOSCIAZ

Zygmunt Churski & Włodzimierz Marszelewski

Lake Gosciaz is located in the Vistula River valleyand belongs to the drainage basin of the Ruda, which isthe left tributary of the Vistula. The topographic catch-ment of Lake Gosciaz occupies an area of ca. 588 ha, in-cluding the Lake Gosciaz area of 41.7 ha, i.e. 7.1%(Fig. 3.3). The highest site in the lake drainage basin islocated on the watershed in the southern part of the catch-ment (97.5 m a.s.l.), while the lowest point occurs wherethe Ruda flows out of the lake (64.3 m a.s.l.). The abso-

lute difference in elevation reaches 33.2 m. The surfaceof the lake drainage area reveals a slope from SE to NWand therefore controls directions of surface and ground-water drainage. Directions of groundwater flow havebeen determined on the basis of groundwater contourlines (Fig. 3.3). Surface deposits of the drainage basin aremainly highly permeable loose sands. Almost the entirearea of the drainage basins is covered with forest.

Maximum depth of the lake at the period of its forma-tion was 44 m. At present the lake basin is half-filledwith nearly 20 m of sediments. Mean rate of accumula-tion is more than 1 mm per year. Regarding that the lakeoccurs in flat, forested terrain and that no large river en-ters it, this rate is large. The nature of the deposits pro-vides evidence of continuous sedimentation (Goslar,Chapter 6), which indicates permanent water supply tothe lake and exceptional regularity of seasonal changes inthermal regime and water dynamics.

In order to describe the lake hydrology as well as itsthermal regime and water dynamics, systematic fieldstudies (in monthly intervals) were performed in 1990–1993. Hydrogeological, hydrological, and limnologicalinvestigations have been organized to elucidate lake sta-bility and formation of laminated deposits.

The field studies, lasting only three years, were at-tempted to explain conditions of water supply to the lakeand their seasonal and multi-year stability, as well as toexplain variability in water level, thermal conditions, andchemistry of lake water and to gain insight into waterbalance and water regime in the lake catchment. Particu-lar emphasis was placed on the contribution of ground-water to the lake budget. In order to determine conditionsat the contact of groundwater and lake water, geoelectri-cal measurements were performed at 40 spots along 4meridional and parallel transects on each side of the lake.The layout of gauging spots allowed the study of aquifersin the direct vicinity of the lake, and evaluation of possi-bilities of water supply to the lake from deeper aquifers.The measurements were taken by vertical electroresist-ance sounding method in the symmetric scheme ofSchlumberger. Power line separations AB/2 were of 120to 200 m, which facilitated penetration to a depth of ca.70 m. The network of measurement sites is presented inFig. 3.3.

The main stream in the drainage basin of LakeGosciaz is the Ruda stream, which flows out fromswamps in the trough upstream of Lake Wierzchon, ca.2.7 km upstream from Lake Gosciaz. The Ruda flowsthrough four lakes (Wierzchon (Jazy), Brzózka, Gosciaz,and Mielec) and discharges into the Włocławek Reser-voir. The Ruda is 9 km long. In its middle course it isdammed by a weir ca. 3 m high, which is also a waterdischarge gauging site. The backwater affects the uppercourse of the Ruda, including Lake Gosciaz itself. Des-pite the damming some seasonal variability in water level


and discharge is noticeable in this reach of the Ruda.Maximum discharges were recorded in winter and springseasons and reached to 36 dm3/s upstream and to82 dm3/s downstream of Lake Gosciaz (data for hydro-logic year 1992 and 1993), respectively. During summer(from June to August) discharges of the Ruda were de-creasing. A subsequent increase in discharges was ob-served in autumn (Tab. 3.2). Changes in specific runoffof the Ruda were as follows: in the upper reach they var-ied from 1.3 dm3/s⋅km2 in August to 6.7 dm3/s⋅km2 inMarch, while in the lower reach (downstream of the lake)from 3.7 dm3/s⋅km2 to 10.5 dm3s⋅km2, respectively (Tab.3.2). This proves a strong contribution of groundwater toLake Gosciaz.

Alimentation of Lake Gosciaz by groundwaters isfully confirmed by geoelectrical measurements per-

formed in the vicinity of the lake. Based on the relation-ships between resistivity of deposits and their lithologyas well as on the information from the borings located inthe neighbourhood, geological analysis of the resultsshowed the location of strongly and weakly permeablelayers in the surrounding of Lake Gosciaz. Geoelectricalcross-sections illustrate the position of the lake basinwith respect to the layers of various resistivity (Fig. 3.4).

Geoelectrical investigations (carried out by the Hydro-consult Company) proved the existence of 3 to 5 com-plexes differing in specific resistance and occurring atdepths from 50 to 70 m. In a subsurface zone up to ca.10 m thick, a layer of extremely high resistivity (from1000 to over 10,000 Ohm-metres) was identified as drysands in the aeration zone. Below is a complex of sandywater-saturated deposits with resistance from 100 to 1000

Fig. 3.3. Map of the Lake Gosciaz drainage basin. 1 – watershed of the catchment and the Ruda stream; 2 – watershed of Lake Gosciaz; 3 –streams and lakes; 4 – swamps; 5 – discharge gauging sites (a) and temperature measurement sites (b); 6 – water-level staffs; 7 – gauging spotson Lake Gosciaz; 8 – piezometer; 9 – profiles of geoelectrical measurements; 10 – groundwater contours (partly after R. Glazik 1978).

40 LAKE GOSCIAZ

Ohm-metres. Characteristic differentiation of resistanceprovides evidence of variation in grain size of sandy de-posits belonging to this complex. The total thickness ofthe complex ranges from 10 to 40 m. The whole complexmay be interpreted as the Pleistocene terrace and dunedeposits.

The basal limit of these deposits (marked on the cross-sections in Fig. 3.4) is the interface between the Tertiaryand Quaternary deposits. The data allowed for determina-tion of geometry and layout of the complex of the weaklypermeable deposits that separate the Quaternary and Ter-tiary aquifers. It has been stated that the entire basin ofLake Gosciaz occurs within these two aquifers. In the in-itial phase of development, Lake Gosciaz was water-fed

by both the aquifers. At present, due to a significant fill-ing of the lake basin with deposits, the Tertiary watersmay reach the lake only through hydrological windows,the presence of which has been confirmed by differencesin the water temperature (Gierszewski 1993, Wicik &Wieckowski 1991, Churski et al. 1993). The Tertiary wa-ters are strongly perched and feed the lake only peri-odically, as evidenced by measurements of water tem-perature on 12 July 1990 (see Fig. 3.6). Waters of thePleistocene deposits contribute most significantly to thesupply of the lake. These waters infiltrate from the up-land through the highly permeable layers of coarse sandsand gravels. They also feed the lake through natural inletsoccurring on the southern shore ca. 0.4 m above the lakewater table. Their efficiency during a year does not varytoo much, but their influence on hydrological conditionsof the lake is particularly evidenced by the ice cover,which forms much more slowly at the southern shore

than in the other parts. Location within the aquifer facili-tates abundant recharge of the lake by groundwater. Di-rection of the Pleistocene water outflow is shown bygroundwater contour lines (Fig. 3.3), while movement ofthe Miocene waters follows the orientation of the Vistulavalley.

Alimentation with groundwater directly controls waterlevel, physical features of the lake, and dynamics of thelake water. Due to groundwater alimentation and the weirexisting on the Ruda downstream of the lake, annualchanges in the lake water level are small and reach onlya few centimetres.

The seasonal changes in thermal conditions of LakeGosciaz are directly associated with changes in air tem-

peratures. Nevertheless, an important role in modificationof water temperature is played by such factors as theshape and depth of the lake basin and especially the man-ner of alimentation, including the contact between thelake and groundwater.

In spring-summer season Lake Gosciaz features ther-mal stratification typical of dimictic lakes. The thicknessof epilimnion varied from 6 m in August of 1990 and1992 to 3 m in 1994, indicating good mixing of the upperwater layer of the lake (Fig. 3.5). The thickness of themetalimnion varied from 3.5 m to 4.0 m. The metalim-nion was characterized by high gradients of water tem-peratures, which often exceeded 4oC/m. Such situationsmost frequently occurred in the deep holes. In the shal-lower parts (above 10 m) such a strong stratification hasnot been observed. During summer stagnation (August) atypical stratification was observed both along longitudi-nal and transverse profiles (Figs 3.6 A, B, D). The results

Table 3.2. Comparison of water inflow and outflow by Ruda stream to and from Lake Gosciaz with the atmospheric precipitation in thehydrological year 1993.

Month Inflow (in m3) Outflow (in m3) Precip. (mm)Discharge (dm3/s⋅km2)

Above lake Below lake

XI 19 440 221 620 41 2.5 10.0

XII 24 110 265 160 36 3.0 10.4

I 32 140 267 840 44 4.0 10.5

II 46 570 241 920 25 6.3 10.5

III 53 560 268 000 20 6.7 10.5

IV 42 770 197 000 19 5.5 8.0

V 31 470 175 440 23 4.0 6.8

VI 20 740 150 980 67 2.7 6.1

VII 15 400 115 170 66 2.1 4.5

VIII 10 040 93 750 90 1.3 3.7

IX 35 640 241 060 150 4.6 9.8

X 37 500 230 300 8 4.7 9.1

Total 369 380 2 468 240 589 – –

Mean – – – 3.7 8.3


of the temperature measurements of 12 July 1990 shouldbe particularly emphasized. The temperatures recorded inthe eastern part were lower (by ca. 4.5–5.0oC) than thosein the other parts of the lake (Fig. 3.6 C). Thermal anom-alies of this type could have occurred due to a suddensupply of the Tertiary waters through the hydrologicalwindows described above.

Regular monthly hydrological observations allowedidentification of variability in vertical distribution of tem-perature in subsequent months (Fig. 3.7). Investigationsin the deepest site of the lake proved that in Lake Gosciazperiods of spring homothermal conditions were short andthat summer stratification was initiated in the second halfof April. The above is the evidence of bradymictic fea-tures of this lake. The bradymictic type of lake is charac-terized generally by weak circulation, resulting from suchfactors as: extended ice-cover and persisting snow-cover(sheltered location of lake), thermal and chemical stratifi-cation arising the very early spring, very short and weakvernal circulation and early formation of summer stratifi-cation (Paschalski 1963, Choinski 1995). During themajor part of the observation period the deeper layers ofwater (below 10 m) were characterized by slight oscilla-tions in temperature and therefore by weak circulation. It

is confirmed by very low coefficients of thermal stratifi-cation, from 0.44 in August 1994 to 0.56 in August 1992.

Periods of autumn homothermal conditions wereslightly longer when compared with the spring ones (ca.by 6 weeks), and their duration depended on timing ofice-cover formation.

During frost periods typical reverse stratification wasobserved, and water temperature close to the bottom var-ied from 3.9oC to 5.0oC. This is additional evidence ofthe influence of groundwater on thermal conditions anddynamics of lake waters as well as of heat accumulatedin bottom deposits. The temperature of the surface layerof bottom sediments was almost identical to water tem-perature at the bottom. However, the temperature of thebottom sediments was higher by a few oC already at adepth of several tens of centimetres.

Based on the results of these studies Lake Gosciazmay be assigned to the lakes of eumictic type, with pre-vailing features characteristic for bradymixis.

Thermal phenomena in the lake directly affect oxygencirculation. Fast summer stratification reduces the possi-bility of oxidation of the deeper water layers. In LakeGosciaz at depths below 8–10 m a strong deficit ofoxygen increases from the decline of spring (saturation of

Fig. 3.4. Geoelectrical cross-sections of Lake Gosciaz surroundings (see Fig. 3.3) with hydrogeological interpretation. 1 – measurement sites;resistivity in Ohm-metres.

42 LAKE GOSCIAZ

water with oxygen varied from 20% to 30%), leading tothe lack of oxygen in August. Transparency of water israther low as well. During spring and summer watertransparency measured by Secchi disks reached from1.2 m to 2.0 m. The highest transparency occurred inwinter especially during the presence of ice cover andreached 5.0 m.

The properties given above provide evidence of an ad-vanced eutrophy of Lake Gosciaz, whose shores are sub-jected to intensive overgrowth. Increased eutrophicationof the lake can be associated with artificial damming ofthe Ruda stream and thus with the reduced rate of waterexchange in the lake, as well as with fisheries.

The studies have confirmed that the lake is perma-nently fed by groundwater and that this supply is not dis-turbed by inflow of surface waters. Moreover, exception-ally well preserved rhythm of thermal changes have beenidentified, with a definite stratification in summer andtwo periods of homothermal conditions in spring andautumn. These regular thermal changes conditioned weakcirculation in summer and winter as well as verticalmovement of water particles, which supported sedimen-tation in periods of homothermal conditions. Due tolonger duration of autumn homothermal conditions the

2 – weakly permeable sediments; 3 – boundaries of the geoelectrically distinguished units; 4 – base of highly permeable sediments; 5 – specific

Fig. 3.5. Vertical distribution of water temperature in the lake duringthe full summer stagnation. A – 12 Aug 1992; B – 08 Aug 1990; C –10 Aug 1994.


Fig. 3.6. Distribution of water temperature (in oC) along longitudinal profile of the lake (A – August 1990, B – August 1992, C – July 1990)and transverse profile of the lake (D – August 1990).

44 LAKE GOSCIAZ

accumulation of sediments was most intensive duringthat time of the year.

Summarizing, it can be said that the sedimentation de-velops best during autumn homothermal conditions andeventually during spring homothermal conditions. Theseperiods of intensified dynamics of water movement wereassociated with thermal homogenization and with the in-crease in alimentation. Summer and winter periods arecharacterized by extreme calmness, interrupted only byinflow of the cool Tertiary waters. Inflow of water anddissolved substances to Lake Gosciaz is controlled byvariability in alimentation and is rather small in compari-son to the lakes located on the plateau. Such situation re-sults from lake location in the valley and from its intensi-fied feeding by groundwater.

At present the basin of Lake Gosciaz is filled withsediments which constitute ca. 50% of its capacity. In1925 Jaczynowski determined the maximum depth as25.8 m (Lencewicz 1925). At present the maximumdepth is 24 m. It would indicate that ca. 2 m of the bot-tom deposits could have accumulated in the deepest partfor 70 years, assuming that the earlier measurementswere precise enough.

Due to overgrowing, the area of Na Jazach lake com-plex diminishes, though in Lake Gosciaz, with steepslopes, this process is very slow. A larger extent of thelake in the past is evidenced by lake terraces in certain lo-cations. The process of overgrowing is currently beingstopped by artificial damming, which disturbs the rhythmof water-level oscillations in the lake and can inducechanges in sedimentation conditions.

3.4. CHEMISTRY OF GROUNDWATERS IN THENA JAZACH LAKES AREA

Bogumił Wicik

Lakes Na Jazach and the connecting Ruda stream aswell as adjacent peatlands form a hydrological systemfed by groundwaters of the Quaternary aquifer. Thethickness of this aquifer in the area exceeds 20 m. Be-neath the Quaternary aquifer are Pliocene clays and lo-cally Miocene coals and carbonaceous sands or even Cre-taceous limestones.

The pressure of the Cretaceous waters, in which min-eralization does not exceed 0.5 g/dm3, is 900–1200 kPa(Fabianowski & Olczak 1988). Near Lake Wierzchonthese waters stabilized at the level of 54 m a.s.l. in wells.Waters of the Miocene brown coal series are also weaklymineralized and are under subartesian pressure of 250–1300 kPa. When bored near Lake Wierzchon these watersstabilize at ca. 39 m a.s.l. They contain up to 0.4 mg/dm3

of manganese and in certain cases over 10 mg/dm3 of iron.The Quaternary waters in this part of the Płock Basin

flow northward with an hydraulic gradient of ca. 1.5–2‰Fig

. 3.

7. V

aria

bilit

y in

the

rmal

con

diti

ons

(o C)

in t

he d

eepe

st s

ite o

f L

ake

Gos

ciaz

in

1990

–199

2.


(Fig. 3.8, Churski & Marszelewski, Chapter 3.3). Thusthe lakes are located on the route of the groundwaterflowing from the anticlinorium ridge of the older substra-tum towards the Vistula valley. The discontinuities in theisolating layer of the Pliocene clays serve as hydrologicwindows, where a direct contact between the Quaternarywaters and confined waters of the older geological hori-zons occurs.

Dynamics of groundwater exchange near the lakes de-pends on magnitude of surface runoff. In periods of lowprecipitation or large moisture losses due to evaporation,the losses of groundwaters inflowing from the south arecompensated through the hydrologic windows. As a re-sult, if no significant changes occur in the thickness ofaeration zone, the top part of the aquifer contains “old”waters of a long-lasting hydrological circulation and aconstant temperature of ca. 7.5–8.5oC, which discharge tothe lakes.

During the periods of high water levels and cessationof the drainage zone at the southern side of the lakes, themain water mass feeding the water bodies exhibits highrate of flow, similar to the mean infiltration coefficientfor this part of Płock Basin (0,00036 m/s; Sierzega &Narwojsz 1988). These are waters of seasonally variabletemperature, low mineralization, and rich in substancesderived from the soil zone.

The waters of the Quaternary aquifer in the lakes Na

Jazach area are differentiated by their chemical composi-tion. In the bottom parts of this aquifer at the zone ofcontact with the Pliocene clays the waters are alkaline,with pH 8.5–10.5 and ca. 15 mg Ca/dm3, 55 mgNa+K/dm3, and ca. 100 mg HCO3 and CO3/dm3. Theirtotal hardness is 2.0oGer. They can mix with the waters ofthe upper parts of this aquifer. In boreholes to a depth of12 m, waters of similar chemical properties have notbeen found.

In the top parts of the Quaternary aquifer, which re-main in contact with the aeration zone, thin layers ofnatural or slightly acid waters occur, with mineralizationnot exceeding 0.12 g/dm3. These waters contain colloidalhumus-mineral complexes and occur locally at the north-ern side of the lake system Na Jazach and also west ofLake Mielec, for they contribute to Lake Mrokowo. Mostwaters of the Quaternary aquifer feeding the lakes andthe Ruda stream exhibit diverse chemical properties. Thecomposition of groundwaters inflowing from the south issignificantly modified near the lakes.

East of Lake Gosciaz, gradients of the groundwatertable are from 2 to 5‰. Low values occur near LakeMrokowo and peatlands occupying depressions north ofthe lake. The top part of the aquifer shows seasonalchanges in temperature, it is neutral or weakly acidic, andits mineralization slightly exceeds 0.1 g/dm3 (Fig. 3.9).The present-day bottom deposits of Lake Mrokowo are

Fig. 3.8. Hydrographic sketch of the area of lakes Na Jazach. 1 – springs, 2 – elevations in m a.s.l., 3 – geological profiles, 4 – lakes, 5 – mires,6 – hydroisohypses.

46 LAKE GOSCIAZ

fed by such waters and consist of non-calcareous algal-gyttja saturated with methane (CH4). An oligotrophicmire is developed beside the lake. Waters strongly over-saturated with H2S occur in closed depressions to the NWand SE of Lake Mrokowo and in its littoral part belowpeat and limnic deposits at the depth of 7–9 m. Waterswith no hydrogen sulphide appear in springs and seeps inthe Ruda valley upstream of Lake Wierzchon. Moreover,hydrogen sulphide is not found in groundwaters belowthe peat deposits near the stream valley and east of LakeGosciaz. In general within the area limited by hydroi-soline of 67 m a.s.l. (Fig. 3.8), by the Ruda stream valley,and by the southern bank of Lake Wierzchon, the ground-water without H2S exhibits slightly reducing properties.The waters contain ca. 55 mg Ca/dm3, ca. 180 mgHCO3/dm3, and 0.1–0.8 mg Fe/dm3 at pH 7.3–7.6. Theirmineralization (0.30–0.34 g/dm3) is usually higher thanthat of waters feeding lakes Gosciaz and Mielec (Fig.3.10). Due to permanent feeding with such waters, gyttjasdeposited in lakes Wierzchon and Brzózka contain over90% CaCO3. High accumulation of carbonates, whichhas been proceeded since both the lakes were formed, isan effect of continuous supply of waters of stable physi-cal and chemical properties. In the carbonate deposits ofthese lakes iron is practically lacking. Ferruginous or-ganic soil complexes are supplied with groundwatersfrom the south and they have stabilized in the eastern partat the height of Lake Mrokowo.

At the northern side of the Ruda valley and of LakeWierzchon, the groundwaters contain ca. 0.2 g ions/dm3,24–40 mg Ca/dm3, and 80–150 mg HCO3/dm3.

In the western part, including lakes Gosciaz and Mie-lec, the gradients of groundwater table are 5–12 ‰. Highgradients occur also in the 200–300 m wide zone of in-tensive drainage that adjoins the lake in the south. Steepslopes of the lake basins cut across the aquifer at theheight of ca. 65 m a.s.l. The waters outflowing there fromnumerous springs and seeps exihibit constant temperature(7.5–8.5oC) and constant ionic composition, regardless ofseason or water level (Fig. 3.10). In periods of low levelsof the water table the total content of ions in spring wa-ters is larger by ca. 25–30 mg/dm3 than at high water le-vels. On the other hand, changes in acidity are signifi-cant: from pH 6.7–7.1 in spring months to pH 7.2–7.8 inthe remaining seasons. In the 8 km wide belt south to thelakes the groundwaters exhibit the same properties as thewaters in the springs and in the eastern part (Fig. 3.10). Arelatively intensive horizontal exchange of waters in thewestern part, forced by the draining influence of the lakesand of the stream, does not eliminate moderate reducingconditions in the aquifer. At pH 7.2–8.2, up to 2.5 mgFe/dm3 occurs in groundwaters mainly in form ofFe(HCO3)2. Thus a very strong contrast exists betweenthe properties of the aeration and saturation zones. Thereduced forms of Fe, transported with weakly alkalinegroundwaters towards the lakes, are subjected to intens-ive transformation to Fe(OH)3 in the zone of contact with

Fig. 3.9. Ionic composition of snow water (1), lake water of Lake Mro-kowo (2), and groundwaters of aeration zone (continuous lines).

Fig. 3.10. Ionic composition of the groundwaters of saturation zone.1 – dominant values, 2 – extreme values, 3 – springs at the shore oflakes Gosciaz and Mielec.


the oxygenized and carbonate-free layer of aeration. Insuch conditions in the top parts of the aquifers the strong-ly ferruginous layers occur (Fig. 3.11). The abundant pre-

cipitates of iron hydroxides in form of nest-like accumu-lations as well as iron and manganese concretions arefound there. Thickness of the oxidation layers is 0.4–1.2m. These layers occur in the zones of seasonal fluctua-tions of the groundwater levels, and they are places ofpartial concentration of the elements leached from thesoils.

Locally levels of precipitates of iron compounds, andless frequently of manganese, are found at the depth of2–3 m below the groundwater table or lake water level(Fig. 3.11). In such situations the groundwaters exhibitslightly higher pH (7.7–7.9) and presence of gases, espe-cially CO2. The pressure of these waters at the depth ofca. 3 m below the water table was ca. 140 kPa and didnot vary during measurements lasting up to twenty hours.The iron concretions occurring in the carbonate sandsreach 3–8 mm in diameter. They are usually oval orspindle-shaped; their interior is filled with spherically ar-ranged ochre. The concretions of iron hydroxides wereforming when the groundwater table at the southern sideof Lake Gosciaz occurred 3–4 m below the present-daylevel. The waters within such horizons, after beingbrought to the surface, become yellow-red. They containover 10 mg Fe/dm3. In the samples of waters occurringbelow and above the layers with concretions the contentof total iron is definitely smaller. The waters below the“ferrugination” zones are greenish, but after oxidation ofthe ferrous compounds they become rusty orange.

Waters of some springs feeding the lakes Gosciaz andMielec contain more substantial amounts of iron inautumn and spring seasons only (0.9–1.4 mg Fe/dm3).The jelly-like precipitates of ferruginous mineral com-plexes deposited at seepages contain, besides iron andmanganese, many other chemical elements. The substan-tial enrichment in other elements occurs in the beachsands (Tab. 3.3). The groundwaters infiltrating into thelake within the beach and littoral shoals feature weak hy-drostatic pressure. If bored at the depth 2–6 m thesegroundwaters usually stabilize at ca. 0.3–1 m above thelake water table. While the temperature of the lake wateris 23oC (in summer), the water temperature in shoal zoneat the depth of 1.5 m is 12oC. The cold groundwaters mixthere with lake waters, the pressure of gases contained inthe groundwaters decreases, and CaCO3 crystallizesabundantly. In Lake Mielec intensive accumulation ofcarbonates makes development of the underwater plants

Fig. 3.11. Lithological profiles (I, II, III) of the southern shore of LakeGosciaz (see Fig. 3.8). 1 – fine-grained and medium-grained sands,2 – coarser sands with gravel, 3 – sulphur-calcareous gyttja, 4 – levelof groundwater, 5 – horizons of Fe and Mn precipitation.

Table 3.3. Content of selected chemical elements in deposits of littoral zone of Lake Gosciaz.

Type of depositLoss on

ignition in %Organic C

%

mg/kg of ash

Fe Cd Pb Ni Co As Zn Sr Mn

Beach sands 0.4 0.2 9500 0.10 0.5 0.9 0.34 6.3 0.2 2.1 270

Ferruginous depositsprecipitated in spring

33.6 4.3 110050 0.24 9.1 24.2 6.10 20.6 5.9 31.0 6000

48 LAKE GOSCIAZ

impossible. The underwater plants covered with carbo-nate crust, die out in the beginning of June. Strong reduc-ing conditions, usually with H2S, occurring within shoalsand beaches favour stabilization of numerous chemicalelements (in the form of sulphides) brought here with thegroundwaters. Some of these elements, e.g. Mn and Fe,after oxidation change into hydroxides. Beyond the litto-ral zone, in Lake Mielec the deposits are of carbonatefacies, while in Lake Gosciaz the deposits of sulphide-carbonate facies are accumulated (Wicik 1993). Waters ofthe lakes and the Ruda stream linking these lakes havestrong affinity to groundwaters (Fig. 3.12). They areslightly hard, calcium bicarbonate waters. The streamwaters at the inlet to Lake Wierzchon contain more Caand HCO3 ions than waters being in contact with aerationzone in its source area. In lakes Wierzchon and Brzózkathe waters of the Ruda stream lose 20 mg Ca/dm3 and ca.70 mg HCO3/dm3. At the entrance to the Tobyłka Bay thetotal content of the main ions in the stream waters de-creases by ca. 85 mg/dm3.

In lakes Gosciaz and Mielec, further transformation ofchemical properties of the waters of the stream as well asof the springs takes place, and ca. 2 km downstream ofthe outlet from Lake Mielec the Ruda waters are poorerin Ca and sulphate ions but enriched in HCO3 ions whencompared to the stage at the inflow to the lakes.

3.5. HYDROBIOLOGICAL CHARACTERISTICSAND MODERN SEDIMENTATION OF LAKEGOSCIAZ

Andrzej Gizinski, Andrzej Kentzer, Tomasz Mieszczankin,Janusz Zbikowski & Roman Zytkowicz†*

The discovery of laminated sediments in LakeGosciaz has initiated interdisciplinary studies of the lakeand its surroundings, including palaeoecology and eco-logy (Ralska-Jasiewiczowa 1993). The varved sedimentscontain a specific chronological record of environmentalchanges during ca. 13,000 years. Such a record cannot beread without profound knowledge of the modern struc-tures and functions of the lake ecosystem, in particularthe phenomena and processes determining the formationof lacustrine sediments. Sedimentation in lakes respondsto external and internal forcing (Sly 1976). Gizinski et al.(1992) demonstrated that the functioning of particularlake ecosystems, even in lakes of the same limnologicaltype, appeared to be very different. The “individuality” oflakes shows that the common hydrobiological informa-tion is not sufficient for dependable description of thespecific ecological situation of lakes at any given timeand place.

The investigations, which have been carried out since1988, aimed at hydrobiological recognition of the struc-tures and functions of the Lake Gosciaz ecosystem. Thepalaeoecological character of the whole program dictatedthat the main attention be given to modern sedimentation,i. e. to phenomena and processes influencing the charac-ter of sediments and lamination. Within these processesboth resuspension and redeposition have not been wellstudied. The importance of sediment transportation andtranslocation was already emphasized by Zytkowicz(1982, 1989). A rapid development of interest in resus-pension and its function both in the ecosystem and in theformation of laminated sediments has been observed inrecent years (Wisniewski 1995).

3.5.1. HYDROBIOLOGY

In studies of abiotic parameters of Lake Gosciaz muchemphasis was put on studying:

1. The effect of water dynamics on the thermal andoxygen regime.

2. The budget of the most important biogens (nitrogenand phosphorus). Such investigations are the expressionof the holistic approach to the lake ecosystem as the dy-namic structure. It is likely to be the most reliable source

Fig. 3.12. Ionic composition of the surficial water. 1 – Ruda upstreamof Lake Wierzchon, 2 – outlet to Lake Gosciaz, 3 – source area of Rudastream, 4 – Lake Mielec, 5 – Lake Gosciaz, 6 – Ruda downstream ofLake Mielec, 7 – Lake Wierzchon.

* The authors are grateful to Dr. M. Luscinska and M. Sc. E. Kudełko forproviding their phytoplankton data and to M. Sc. P. Napiórkowski forhelpful comments on the zooplankton section. We are most indebted toJ. Mielczarek, P. Wachniew, M. Piwowarczyk, and I. Jabłonska for muchhelp during the field work. Also, we thank many students of the Depart-ment of Hydrobiology who contributed to this work in different ways.


of information regarding the efficiency of the ecosystem(Kentzer et al. 1990, Gizinski et al. 1991).

3. The chemistry of different phosphorus fractions inlake sediments. In Golterman’s (1988) opinion sedimentsas a “black box” play a crucial role in the understandingof the phosphorus cycle in lakes. Phosphorus is the factorresponsible for the trophy of water bodies (Vollenweider1968). The trophy, in turn, determines intensity of pri-mary production, especially of phytoplankton, one of theprincipal components of the matter accumulating on thelake bottom.

The lake is surrounded by fresh conifer forest. Therewere still field crops until ca. the year 1950. The lake isfed by groundwater (ca. 90% of inflow). The Rudastream supplies only 10% of inflow (Gierszewski 1993,Chapter 3.3). The groundwater discharges in springs nearthe shore line on the southern side of the lake. The phy-tolittoral zone is poorly developed (Kepczynski & Nory-skiewicz, Chapter 3.7). Among emergent plants Typhaangustifolia and Phragmites australis predominate. Sub-

mergent plants are mainly represented by Potamogetonfiliformis, P. praelongus, and P. perfoliatus. The lake sur-roundings are used for recreation, mainly by anglers. Dueto the situation of the lake within the Landscape Park thetouristic pressure has recently diminished.

An accurate description of Lake Gosciaz and its drain-age basin have been presented in previous chapters.

Following Wetzel & Likens (1990) the morphologicalparameters are essential for assessing the thermal sta-bility, biological productivity, and many other structuraland functional constituents of the lake ecosystem. Gizins-ki (1978) stressed the morphological features of the lakebasins that determined water dynamics. They affect theoxygen regime and particularly the disturbance of thenear-bottom oxymicrostratification. In Lake Gosciaz(Fig. 3.13, Tab. 3.4) the real thickness of epilimnion (5.4m) is bigger than that calculated according to Patalas(1960) formula (4.3 m). Thus the water dynamics ishigher than expected, probably due to western winds fre-quently blowing along the axis of the lake. Also, a verylarge difference between the maximum and mean depthsuggests a distinct division of the lake basin into twoparts:

– the shallow part (5–6 m), featured by the flat bottomand high water mass dynamics;

– the deep one, with high steep slopes and “stagnant”water.

In the shallow part one would expect good oxygenconditions, and in the deep part poor conditions. Theshallow part is the zone of resuspension, and the deeppart is the zone of accumulation.

The particularly steep slope occurring in the deep partof the lake basin is an uncommon feature in Polish lakes,which usually reveal a steeper slope in the sublittoral anda rather flat profundal zone.

Physical and chemical parameters of water

During the summer a distinct thermal stratificationwas observed. The temperature gradient was high, reach-ing 4oC per 1 m. So the thermocline effectively separatedsurficial, warm, frequently mixed water layer from thedeeper, less moving, and much colder one. Strong windscan generate an intensive mixing and lowering of thethermocline. On the other hand, lack of winds and warmweather can initiate the formation of a new shallow ther-mocline. Such a situation could have been observed inLake Gosciaz on August 4, 1994. The basic thermoclineexisted at the depth of 6 to 9 m, and the new additionalone at a depth of 2 to 5 m (Fig. 3.14). Another anomalywas the displacement of the thermal stratification pro-duced by appreciable sudden inflows of groundwater inthe eastern part of the lake (Churski et al. 1993, andChapter 3.3).

Parallel to the thermocline, the oxycline was also

Fig. 3.13. Bathymetry of Lake Gosciaz and the division of lake basininto two parts. 1 – sampling station, 2 – the zone of accumulation,3 – the zone of resuspension (ca. 50% of the whole lake area).

Table 3.4. Some morphometric parameters of Lake Gosciaz.

Area 41.7 ha

Volume 2073 tys. m3

Maximum depth 24 m

Mean depth 4.97 m

Maximum length 1.168 km

Maximum width 0.735 km

Depth of the epilimnion1) 4.3 m

Index of mixing (Im)2) 0.87

Slope factor (αp)3) 12.5%

1) Depth of the epilimnion (in metres) = 4.4√⎯⎯D, where D = effective fetch (in kilometres) (after Patalas 1960)2) Im (Index of mixing) =

4.4√⎯⎯Dmean depth

(after Gizinski 1974)

3) For definition of αp see Håkansson & Jansson (1983: 195)

50 LAKE GOSCIAZ

formed. This resulted from condensation and decomposi-tion of settling seston particles in the metalimnion. Theoxygen concentrations in the hypolimnion decreased tozero at the end of the summer. That is a typical feature ofeutrophic lakes. The oxygen conditions strongly in-fluenced the zooplankton and the distribution of bottomfauna in Lake Gosciaz.

An average Secchi disc visibility (SD) reached ca. 2 m(range – 1.2 to 4.2 m). Kudełko (unpubl.), using this par-ameter, obtained a trophic state index (TSI(SD)), accordingto the Carlson (1977) formula:

TSISD = 10(6 – ln SDln 2

)

where SD is in meters. TSISD assumes values from 0to 100; 0–42 means oligotrophy, 43–55 mesotrophy and56–100 eutrophy. TSISD for Lake Gosciaz was 53, i. e. itappeared rather mesotrophic. Other trophic parameters(see below) clearly demonstrated an eutrophic characterof the lake. Thus in this case the Carlson index was notvery helpful.

Hydrochemical studies have shown that Lake Gosciazis highly eutrophic. The mean total phosphorus (Ptot) was0.524 mg/dm3, and organic nitrogen (Norg) was 7.241mg/dm3. The N:P ratio (14:1) was typical for eutrophiclakes. The dominant form of mineral nitrogen was am-monium (N-NH4), with a mean concentration of 0.432mg/dm3, whereas mean concentrations of nitrate (N-NO3)and nitrite nitrogen (N-NO2) were respectively 0.038 and0.012 mg/dm3 (Tab. 3.5). The concentration of com-pounds in the lake water did not differ from that recordedin other highly eutrophic lakes (Golachowska 1971, Gi-zinski et al. 1991). Likewise, high concentration of the

compounds in the groundwater was similar to that in thelake itself (Tab. 3.5).

The nutrient loading originating from the drainagebasin was very high (3.5 g P/m2year, 40 g N/m2year in1991–92, and 2.9 g P/m2year, 42.5 g N/m2year in 1992–93). Such a load exceeded the level regarded as danger-ous (Vollenweider 1968). It should be stated that in theyears 1991–1994 the nutrient concentration in the lakes,especially of phosphorus, systematically diminished.Mean annual Ptot concentrations (mg/dm3) in the follow-ing years were: 1991/92 – 0.600; 1992/93 – 0.499;1993/94 – 0.205.

On the basis of results of hydrochemical investiga-tions in the two following years (1991/92 and 1992/93),the budget was made for the two major nutrients (phos-phorus and nitrogen, Tab. 3.6). The accumulation of theseelements in the lake was estimated with respect to dif-ferences between their “import” and “export”. In the firstyear of examinations, the accumulation of P was 575 kg(35% of an annual import), and of N 1484 kg (11%). Nu-trient accumulations were similar to those noted in the ef-ficiently functioning ecosystem of the eutrophic LakeParteczyny Wielkie (Kentzer et al. 1990). It can be con-cluded that the nutrient-balance calculations revealed hy-drochemical stability for Lake Gosciaz and the high effi-ciency of its self-regulatory mechanisms.

The stability of phosphorus deposition in the bottomsediments depends on the chemical character of phospho-rus binding (fractions). A mobile fraction NaOH-P (Pbound to aluminium and organic matter) constituted ca.80% of Ptot. An appreciable contribution of this fractioncorresponds to potential intensity of P exchange at thewater-mud interface. More detailed hydrochemical ana-

Fig. 3.14. Distribution of tempetrature (in oC) with depth and time in Lake Gosciaz (measurements performed by Churski, Marszelewski& Mieszczankin).


lyses (Kentzer 1995) have proved that the real exchangeintensity between water and sediment was not so high. Itwas estimated that the phosphorus particles are recycledat the water-mud interface 3–4 times before the definitiveburial in the sediment or leaving the lake with outflowingwater.

Changes of P concentration in the surface layer ofsediments had a cyclic character (Fig. 3.15). Kentzer(1995) presented the alternating occurrence of two peri-ods. The first is spring-summer season with the high Ptot

concentration, when the P deposition prevented its re-lease. In autumn-winter, P release predominated over de-position (low P concentration in sediments).

The phosphorus accumulation in the lake was the re-sult of the character and the quantity of sedimentingmaterial as well as the processes occurring in the sedi-ments.

Phytoplankton

Phytoplankton of Lake Gosciaz has only been identi-fied during the vegetation season of the year 1993 (Ku-dełko 1994). In the phytoplankton under study 268 taxawere identified in the Cyanophyta, Dinophyta, Chryso-phyceae, Bacillariophyceae, Chlorophyta, Cryptophy-ceae, Xantophyceae, and Euglenophyta. The largest as-semblage of species was reported in April (142 taxa) and

Table 3.6. The phosphorus (Ptot) and nitrogen (Ntot) budget in Lake Gosciaz for 2 years (1991/92 and 1992/93).

Years Input, kg Output, kgAccumulation in the lake

Kg % of input

Ptot1991/92 1573 998 575 36%1992/93 1340 998 342 25%

Ntot1991/92 18017 16533 1484 8%1992/93 19162 17078 2048 11%

Fig. 3.15. Changes of Ptot concentrations (mg/g dry weight) in sedi-ments of Lake Gosciaz, from March 1992 to September 1993 (afterKentzer 1995).

Table 3.5. The chemical composition of water in Lake Gosciaz in its surficial inflow and in the groundwaters (mg/dm3) – 1991/1993.x – mean values, r – range.

Lake*) water Ground water Surficial inflow Surficial outflow

Ptotx 0.524 0.474 0.355 0.430

r 0.070–1.380 0.115–1.430 0.050–1.032 0.060–1.040

P–PO4x 0.133 0.179 0.156 0.068

r 0.015–0.310 0.060–0.438 0.015–0.590 0.013–0.235

Norgx 7.241 6.786 5.650 7.092

r 1.800–13.050 1.900–16.000 1.900–11.690 1.800–13.050

N–NH4x 0.432 0.148 0.222 0.225

r 0.000–1.300 0.000–0.466 0.000–0.413 0.000–0.536

N–NO3x 0.038 0.065 0.050 0.042

r 0.000–0.111 0.011–0.155 0.011–0.190 0.000–0.152

N–NO2x 0.012 0.021 0.014 0.009

r 0.000–0.045 0.001–0.049 0.001–0.080 0.000–0.019

Ca2+ x 44.1 49.3 41.9 43.6

r 32.2–58.1 38.1–60.0 20.1–68.0 39.7–54.5

Mg2+ x 11.7 9.8 10.7 11.2

r 3.2–21.6 4.0–18.4 4.8–19.2 3.2–17.6

Cl–x 15.1 20.0 16.1 14.5

r 7.2–24.9 10.1–29.5 7.2–24.5 7.2–22.3

*) the mean values for the whole column of water; usually concentrations were higher near the bottom

52 LAKE GOSCIAZ

in June (144 taxa), the smallest in July (64) and in August(62). The dominant group were diatoms (158 taxa), greenalgae (66 taxa) and blue-green algae (23 taxa). The list ofspecies reaching over 80% stability is given in Table 3.7.Besides these widespread species two species rarely re-ported in Poland were found: Surirella suecica Grun. inVan Heurck and Oestrupia zachariassi (Reich.) Hust.

The mean phytoplankton biomass was 1.35 mg/dm3

(range 0.18–3.11 mg/dm3). Diatoms predominated andconstituted about 41% of total biomass. The highest phy-toplankton biomass was observed in the summer (up to3.11 mg fresh weight per dm3 in July, Tab. 3.8). The lo-west biomass was recorded in November (0.182mg/dm3), but species diversity at that time was very high(127).

Based on species composition, Lake Gosciaz can beclassified as a eutrophic lake, whereas based on the meanbiomass it is mesotrophic.

Phytoplankton examinations have demonstrated a cy-clic occurrence of species in the lake. Seasonal type offluctuations was also observed in the youngest part ofsediments (Goslar 1993). Obviously, phytoplankton liv-

ing or dead settles down. In Table 3.9 diatom taxa notedin the water and in the sediments were set together. Oc-currence at the same time of some species in the waterand in the sediment does not have to be a rule. Such asituation resulted from either the annual changes of phy-toplankton development or resedimentation of previouslyresuspended sediments.

Zooplankton

The preliminary results of studies on the zooplanktonof Lake Gosciaz were published by Błedzki (1993) andthey are summarized below.

In the pelagic and the littoral zones 14 taxa of Rotato-ria, 21 taxa of Cladocera, and 7 taxa of Copepoda (Tab.3.10) have been found. The number of Rotatoria rangedfrom 66 to 269 ind/dm3 (mean – 170 ind/dm3) and thenumber of Crustaceae ranged from 19 to 177 ind/dm3

(mean – 118 ind/dm3). The number of reported taxa inLake Gosciaz (42) was high compared to that in otherlakes of northern Poland (the average 32, Gizinski et. al.1992). The vertical distribution of zooplankton in the

Table 3.7. The list of the most important (over 80% of stability) and some rare phytoplankton species in Lake Gosciaz (from Kudełko1994).

Important phytoplankton taxa

CYANOPHYTA

Microcystis aeruginosa Kütz.

Microcystis wesenbergii Kom.

Gleocapsa limnetica (Lemm.) Holl.

Gleocapsa minima (Keiss.) Holl.

Woronichinia naegeliana (Unger) Elenk.

Phormidium mucicola Hub.-Pest. et Neum.

Phormidium tenue (Ag. et Gom.) comb. Agan et Kom.

Anabaena flos-aquae Breb. ex Born. et Flah.

DINOPHYTA

Ceratium hirundinella (O.F.Müll.) Bergh.

Peridinium cinctum (O.F.Müll.) Ehr.

CHRYSOPHYCEAE

Dinobryon divergenes Imhof

BACILLARIOPHYCEAE

Aulacoseira granulata (Ehr.) Simonsen

Cyclotella meneghiniana Kütz.

Cyclotella atomus Hust.

Cyclotella bodanica Grun. in Shneid.

Stephanodiscus alpinus Hust. in Huber-Pestall.

Stephanodiscus hantzschii Grun. (in Cleve et Grun.)

Diatoma tenuis Agardh

Asterionella formosa Hass.

Fragillaria crotonensis Kitton

Fragillaria reicheltii (Voigt) Lange-Bert.

Fragillaria ulna (Nitzsch) Lange-Bert.

Fragillaria pinnata Ehr. var. pinnata

Fragillaria brevistriata Grun in Van Heurck

Navicula cari Ehr.

Navicula schoenfeldii Hust.

Gyrosigma attenuatum (Kütz.) Rabenh.

Cymbella silesiaca Bleish. in Rabenh.

Amphora inariensis Kramm.

CHLOROPHYTA

Phacotus lenticularis (Ehr.) Stein

Eudorina elegans Ehr.

Pediastrum boryanum (Turp.) Menegh

Pediastrum duplex Meyen

Oocystis lacustris Chod.

Monoraphidium subclavatum Nyg.

Coelastrum microporum Nag. in A.Br.

Staurastrum pseudopelagicum W. et G.S. West

Rare phytoplankton taxa

CRYPTOPHYCEAE

Cryptomonas marssonii Skuja

XANTOPHYCEAE

Characiopsis sp.

EUGLENOPHYTA

Trachelomonas sp.

Colacium vesiculosum f. arbuscula (Stein) Huber-Pest.


summer (Tab. 3.11) differed significantly for differentstrata due to oxygen depletion. Considering the smallarea and the low diversity of littoral zone, zooplankton ofthat area did not play an important role in the functioningof the lake ecosystem.

A substantial element of zooplankton in Lake Gosciazwere the “effective filtrators” (Gliwicz 1977). In periodsof maximal productivity their contribution to the totallake zooplankton biomass was ca. 80% (Tab. 3.12). Therich assemblages of “effective filtrators” limiting thephytoplankton development were related to the high effi-ciency of the functioning of the ecosystem. The pelagicmechanisms of the lake functioning were also very effi-cient.

Zoobenthos

The benthic fauna of Lake Gosciaz was studied byZbikowski (1993, 1995). In this chapter the summary ofhis investigations is presented.

The taxonomic composition and distribution ofzoobenthos in Lake Gosciaz were typical for highly eu-trophic lakes (Tables 3.13 and 3.14). The taxonomicdiversity and abundance of the majority of bottom faunagroups (except Chaoboridae and Ceratopogonidae larvae)were the highest in the littoral zone and clearly decreasedwith depth.

Larvae of 23 Chironomidae taxa were noted in the lit-toral part of the lake, with the dominance of Pseudochi-ronomus e.g. prasinatus and Cladotanytarsus e.g. man-

Table 3.8. Biomass of the dominant phytoplankton taxa (mg/dm3) in Lake Gosciaz in 1993 (from Kudełko 1994). (+) taxa with the mini-mum biomass.

Taxon 20.04 23.05 19.06 16.07 10.08 03.09 24.09 10.11

CYANOPHYTA

Microcystis aeruginosa Kütz. + 0.008 + 0.006 0.008 0.024 + +

M.wesenbergii Kom. + 0.015 + 0.078 0.004 + + +

Gleocapsa limnetica (Lemm.) Holl. + + + 0.005 0.052 0.022 + +

Woronichinia naegelina (Unger) Elenk. + 0.221 + + + + + 0.005

Phormidium tenue (Ag.et Gom.) comb. Agan et. Kom. + 0.063 + 0.103 0.225 0.667 0.321 +

Aphanizomenon flos-aquae (L.) Ralfs + 0.002 0.02 0.044 +

Anabaena flos-aquae Breb. ex Born. et Flah. 0.038 + 0.134 0.53 0.347 0.016 0.001

DINOPHYCEAE

Ceratium hirundinella (O.F.Müll.) Bergh. 0.029 0.073 + 1.969 0.006 0.017 0.176 +

BACILLARIOPHYCEAE

Cyclotella bodanica Grun. in Shneid. 0.097 0.128 + 0.008 0.147 0.016 0.1 0.017

Stephanodiscus hantzschii Grun. (in Cleve et Grun.) 0.316 0.005 + 0.002 0.013 0.006 0.03 0.014

Asterionella formosa Hass. 0.003 0.002 + 0.215 0.418 0.035 0.045 0.008

Fragilaria crotonensis Kitton 0.103 0.009 + 0.17 0.341 0.254 0.17 0.007

Fragilaria reicheltii (Voigt) Lange-Bert. 0.003 + + 0.365 0.385 0.107 0.075 0.003

Fragilaria ulna (Nitzsch) Lange-Bert. 0.038 0.002 + 0.006 0.241 0.096 0.137 0.006

CHLOROPHYTA

Pediastrum boryanum (Turp.) Menegh. 0.087 0.021 + + 0.167 + + 0.02

Biomass of specificated taxa 0.676 0.585 3.063 2.557 1.635 1.07 0.075

Total biomass of phytoplankton 0.795 0.868 3.114 2.792 1.773 1.285 0.182

Table 3.9. Seasonal changes of selected species of phytoplankton found in water (from Kudełko 1994) and in the youngest part of theLake Gosciaz laminated sediments (from Goslar 1993).

Spring Summer Autumn

Water (1993) Stephanodiscus hantzschii Aulacoseira spp. (= Melosira spp.)Asterionella formosaFragilaria crotonensisFragilaria ulna (= Synedra ulna)

Fragilaria crotonensisFragilaria ulna (= Synedra ulna)

Sediments(ca. 1870–1960)

Stephanodiscus hantzschiiAsterionella formosaAsterionella f. var. gracillima

Fragilaria crotonensisSynedra acus (= Fragilaria ulna var. acus)

Melosira ssp. (= Aulacoseira spp.)

54 LAKE GOSCIAZ

cus. Mollusca were noted only in the littoral zone. Thisgroup was represented by Pisidium sp. (the most numer-ous genus), Dreissena polymorpha, Valvata naticina, andLymnaea peregra. The Chironomidae larvae were themost numerous (44% of all zoobenthos and nearly 2

times more than Oligochaeta – 27%). Larvae of midgespredominated also in biomass of all zoobenthos (excl.Mollusca) (32%).

In the sublittoral zone, in comparison with the littoralzone, a significantly lower taxonomic diversity was

Table 3.10. The list of species of zooplankton in Lake Gosciaz (from Błedzki 1993).

ROTATORIA

Asplanchna priodonta Gosse Karatella quadrata (O.F.Müller)

Brachionus angularis Gosse Polyarthra dolichoptera (Jol.)

Conochilus hippocrepis Ehrenberg Polyarthra euryptera (Wierz.)

Filinia longiseta (Ehrb.) Polyarthra vulgaris (Carl.)

Kellicottia longispina Kell Synchaeta pectinata (Ehrb.)

Karatella cochlearis cochlearis Gosse Trichocerca birostris (Minkiewicza)

Karatella cochlearis tecta Gosse Trichocerca similis (Wierz.)

CLADOCERA

Acroperus harpae (Baird) Diaphanosoma brachyurum (Liév.)

Alona affinis* (Leydig) Daphnia cucullata Sars

Alona quadrangula* (O.F.M.) Daphnia longispina (O.F.M.)

Alonella nana* (Baird) Disparalona rostrata (Koch.)

Bosmina coregoni (Baird) Eurycercus lamellatus* (O.F.M.)

Bosmina longirostris (O.F.M.) Graptoleberis testudinaria* (Fisher)

Bosmina longispina (Leydig) Leptodora kindti (Foche)

Camptocercus sp.* (O.F.M.) Pleuroxus aduncus*(Jurine)

Ceriodaphnia pulchella (G.O. Sars) Pleuroxus uncinatus* (Baird)

Ceriodaphnia quadrangula (O.F.M.) Peracantha truncata* (O.F.M.)

Chydorus sphaericus (O.F.M.)

COPEPODA

Cyclops kolensis Lillj. Thermocyclops oithonoides (Sars)

Cyclops vicinus Uljamn Eudiaptomus gracilis (Sars)

Eucyclops serulatus (Fisher) Eudiaptomus graciloides (Lillj.)

Mesocyclops leuckarti (Claus)

* recorded only in surficial layer of lake sediments

Table 3.11. The vertical distribution of zooplankton in Lake Gosciaz (Błedzki 1993). N – ind/dm3; B – μg/dm3 dry weight.

Epilimnion Metalimnion Hypolimnion0.5m above the

bottom

N B N B N B N B

Rotatoria 175 61 70 4 65 5 6 1

Crustacea 325 1168 200 397 85 192 25 41

Total zooplankton 500 1229 270 401 150 197 31 42

Table 3.12. The contribution (% of biomass) of the effective filtrators in the total of zooplankton of Lake Gosciaz (Błedzki 1993).

MonthIV VIII XI

Crustacea total zoopl. Crustacea total zoopl. Crustacea total zoopl.

Epilimnion 18 14 80 78 80 73

Meta- and hypolimnion 29 12 79 69 74 74


found (Tab. 3.14). The number of Chironomidae is 15times lower, and Oligochaeta nearly 7 times lower. In theextralittoral zone of the lake Oligochaeta were repre-sented only by Potamothrix hammoniensis. No Epheme-roptera or Mollusca were found. The taxonomic compo-sition of Chironomidae larvae was typical for eutrophiclakes. Ceratopogonidae larvae were the most frequent inthe sublittoral zone, and the Chaoboridae larvae werefound there. They would have been more characteristic ofthe deep profundal zone. Oligochaeta were more numer-ous than Chironomidae, but Chironomidae had higherbiomass than Oligochaeta.

In the upper profundal zone, the bottom fauna wasstill poorer (in quality and in number) except Chaobori-dae larvae, which were dominant in this zone – 1175ind/m2. They constituted 87% of individuals and 73% ofbiomass of all the bottom fauna. Large Chironomus plu-

mosus was frequently found among Chironomidae. Cera-topogonidae larvae were rare.

In the lower profundal zone Chaoboridae still domi-nated. The rest of the bottom fauna was represented onlyby a few Oligochaeta and Chironomidae. The most im-portant forms among Chironomidae larvae were preda-tors, but not any specific forms were recorded for thatzone.

In the whole extralittoral zone (i.e. sublittoral, upperand lower profundal) of the lake, the highest abundanceof macrozoobenthos was observed during spring andautumn circulation, and the lowest one during the sum-mer stratification. It is argued that the abundance ofzoobenthos in the lake was limited mainly by oxygendeficiency. The eubenthos (fauna living in the surface ofthe bottom sediment) was not abundant enough (below0,5 g/m2) to have any influence on the formation and the

Table 3.13. The taxonomic composition and the number of chironomids larvae (ind/m2) in the particular zones of Lake Gosciaz. Meanvalues of five study years (1988–92). L – littoral, S – sublittoral, UP – upper profundal, LP – lower profundal.

Chironomidae L S UP LP

Procladius spp. 38 79 13 9

Chironomus f.l. plumosus L. – 51 35 –

Cryptochironomus sp. 116 2 – –

Cladotanytarsus sp. 480 1 – –

Pseudochironomus prasinatus Staeg. 763 – – –

Tanytarsus sp. 453 – – –

Microtendipes e.g. chloris Mg. 212 – – –

Polypedilum e.g. nubeculosum Meig. 198 – – –

Tanypus kraatzi Kieff. 40 6 – –

Tanypus vilipennis Kieff. 10 7 – –

Endochironomus e.g. dispar Mg. 77 – – –

Endochironomus e.g. tendens. F. 46 – – –

Glyptopendipes e.g. gripecoveni Kieff. 50 – – –

Chironomus f.l. semireductus Lenz – 10 1 –

Polypedilum e.g. convictum Walk. 13 – 1 –

Polypedilum e.g. bicrenatum Schr. 15 – – –

Strictichironomus psammophilus Tshern. 15 – – –

Cladopelma sp. – 9 1 –

Ablabesmyia sp. 13 – – —

Dicrotendipes tritomus Kieff. 10 – – –

Dicrotendipes e.g. nervosus Staeg. 10 – – –

Cladopelma viridula 10 – – –

Cricotopus latidentatus Tshern. 10 – – –

Chironomus f.l. anthracinus Zett. 10 – – –

Demicryptochironomus sp. 7 – – –

Einfeldia e.g. carbonaria Mg. – 8 – –

Cryptochironomus e.g. pararostratus Lenz. – – – 2

Microchironomus sp. – 1 – –

Chironomidae – X* 7 – – –

Chironomidae n.d. 47 – – –

Chironomidae “pupae” 38 1 1 –

* unidentified forms of chironomids, different from the mentioned above

56 LAKE GOSCIAZ

transformation processes of the bottom sediments, i. e. ondisturbance of laminations. The eubenthos should be200-times more frequent to disturb the lamination effec-tively.

To recapitulate, the bottom fauna of Lake Gosciaz hada rather “predator” character (domination of Chaobori-dae, numerous Ceratopogonidae larvae, and the main roleof Procladius spp. larvae among Chironomidae), whichcould disturb the biocoenosis balance. Unexpectedlysmall quantity of eubenthos below the 11 m depth couldbe a symptom of that disturbance in the deepest part ofthe lake.

Concluded lake characteristics

Hydrobiologic studies of Lake Gosciaz have provedthat it is a dimictic, strongly thermally stratified eutrophiclake. The occurrence of the thermocline and oxycline,dictated the distribution of zooplankton and zoobenthos.The lake ecosystem is stable and efficient with relationto: 1) the high diversity of phytoplankton and zooplank-ton, 2) the high contribution of “effective filtrators” inzooplankton, which could effectively control algal devel-opment, 3) the high phosphorus accumulation in the lakesediments (to 35% of the total annual input). The lowabundance of benthic fauna found at maximum depth in-dicated the lack of sediment mixing (bioturbation) anddiminished exchange in the water-mud interface.

3.5.2. MODERN SEDIMENTATION

Tomasz Mieszczankin

Modern sedimentation studies qualify the functioningefficiency of water ecosystems and the manner in whichsediments are formed. The ecosystem is stable when ex-ternal inflows do not bring about changes in its biologicalstructures, and the primary sedimentation (net sedimenta-tion) reflects its productivity. Sedimentation is closely re-lated to the parameters controlling the water dynamics,which influences wind/wave action, and it is also relatedto the morphology of the lake basin (morphological fea-tures were discussed previously). In many lakes the se-dimentation rate is determined by processes of resuspen-sion, which can play a fundamental role in the palaeoeco-logical aspects of sedimentation in lakes (Davis et al.1984).

The measurements of sedimentation rate in LakeGosciaz were done in 1991 (Kentzer & Zytkowicz 1993)and 1993–1994. Sedimentation rate was measured by cy-linders (10 cm in diameter and 30 cm height) with an as-pect ratio (height/diameter) of 3:1 (Blomqvist & Håkans-son 1981). Modern sedimentation studies in Lake Gos-ciaz were started by Zytkowicz (1982), who describedsome details of methodology of investigations elsewhere.Funnel traps with a diameter of 70 cm and a height of120 cm were used so that material for chemical analyses

Table 3.14. Number of individuals (N, ind/m2), number of taxa (NT) and biomass (B, g/m2) of the bottom fauna in Lake Gosciaz, inparticular zones; values from 1988–1992 years. x – mean, min. – minimum, max. – maximum, BwM – biomass without Mollusca (g/m2).

TaxaLittoral Sublittoral Upper profundal Lower profundal

x min. max. x min. max. x min. max. x min. max.

Chironomidae NT 23* 3 9 10* 1 7 5* – 3 2* – 2

N 2688 739 6401 175 26 487 52 – 154 11 – 52

B 488 2.1 18.7 2.15 0.11 10.5 1.32 – 4.52 0.02 – 0.15

Oligochaeta N 1554 337 2736 239 46 1077 119 – 303 36 – 103

B 136 0.54 3.33 0.85 0.02 4.5 0.26 – 0.7 0.1 – 0.53

Chaoboridae N – – – 385 – 3402 1175 51 7169 4213 51 16897

B – – – 1.51 – 11.33 4.36 0.2 28.01 14.19 033 65.94

Ceratopogonidae N 165 – 755 340 26 1026 5 – 26 – – –

B – – – 0.67 0.05 1.15 0.01 – 0.05 – – –

Ephemeroptera N 957 – 2075 – – – – – – – – –

B – – – – – – – – – – – –

Mollusca N 448 – 2075 – – – – – – – – –

B 22.76 – 43.36 – – – – – – – – –

Total zoobentos N 5812 1479 9434 1139 359 3813 1351 205 7238 4260 154 16975

B 37.9 4.09 6266 518 1.24 15.89 5.95 0.88 28.07 14.31 0.6 65.98

BwM 15.14 3.04 36.56 518 1.24 15.89 5.95 0.88 28.07 14.31 0.6 65.98

Dominant taxa amongChironomidae (%)

Pseudochironomusprasinatus

29Procladius spp.

45Ch. plumosus

69Procladius spp.

82

Cladotanytarsuse.g. mancus

18Chironomusplumosus

29Procladius spp.

25Cryptochironomuse.g. pararostratus

18

* – sum of taxa


(also stable-isotope analyses, see Wachniew & Rózanski,Chapter 3.6) could be obtained quickly and effectively.Sediment traps were deployed at the maximum-depth sta-tion (1.5 m), and 10 m above the bottom for 1 to 10weeks. The collected material was dried under dim-inished pressure at 20oC. Organic matter was determinedas a loss on ignition at 520oC for 3 hours. CaCO3 was es-timated through the treatment of ash remaining aftercombustion with 1 N HCl and titration of Ca2+ by 0.01 NEDTA with murexide. The results of calcite estimationwere verified by re-combustion at 900oC (Geyh et al.1971).

In the period of investigation, minimum sedimentationrate was 1.84 g/m2d, and maximum – 40.0 g/m2d (Fig.3.16). Mean sedimentation rate was 5.9 g/m2d in uppertraps and 13.1 g/m2d in bottom traps (Tab. 3.15). Meanannual net sedimentation in upper traps was ca. 2150g/m2 and 4780 g/m2 1.5 m above the bottom. Sedimenta-tion was higher during spring and autumn circulationsthan during summer stagnations. During periods withoutice-cover sedimentation remained high. However, eventhe short duration of ice-cover in March 1993 and Fe-bruary 1994 caused considerable decrease of accumula-tion rate respectively to 4.52 and 3.8 g/m2d. In traps ex-posed for a longer time (Jan. 13 to March 29, 1994) se-dimentation was much higher (see Fig. 3.16 and Tab.3.16). It could be assumed that before freezing over and

directly after ice melting the sedimentation rate was veryhigh.

During overturns the sedimentation recorded in upperand bottom traps differs considerably (see high value ofb-a in Tab. 3.15).This was probably result of resedimen-tation. In periods of summer stratification these differen-ces were much smaller, and in 1996 even negative. Itseems to be the result of mineralization during settling.The average differences between upper and bottom trapswere 13.72 g/m2d during circulation and 0.68 g/m2d insummer.

Sedimentation of CaCO3 was closely correlated withtripton sedimentation. The maximum values occurredduring circulation and the minimum in the summer stag-nation periods (Fig. 3.17). The lowest concentration ofcalcite (37%), reported as the weight percent in tripton(not considering ice-cover occurrence), was observed atthe moment of the strong thermocline formation (Fig.3.18). Thereafter there was a slow increase of calcite con-centration until it reached its maximum (ca. 56%) at theend of the vegetation season. The contribution of CaCO3

in tripton had declined through the winter to reach itsminimum at the end of spring, when the new thermoclinewas formed.

The composition of tripton under ice in the years 1993and 1994 was different (Tab. 3.16). In April 1993 afterthe ice melted, the composition of sedimenting seston

Fig. 3.16. Tripton sedimentation (g/m2d) 1.5 m and 10 m above the bottom in Lake Gosciaz in years 1991 and 1993–1994, as measured in traps.Mean values for upper and bottom traps were 5.9 g/m2d and 13.1 g/m2d, respectively.

Table 3.15. Mean sedimentation (g/m2.d) 10 and 1.5 m above the bottom during circulation (C) and stratification (S) periods in LakeGosciaz.

Depth1991 1993 1994 Mean Mean for period

1991–1994C S C S C S C S

a – 10 m 4.44 5.36 5.35 6.37 8.85 5.15 6.21 5.63 5.90

b – 1.5 m 15.86 7.36 18.72 7.10 25.20 4.47 19.93 6.31 13.12

b–a 11.42 2.00 13.37 0.73 16.35 –0.68 13.72 0.68 7.22

58 LAKE GOSCIAZ

was very similar to that observed a month before, underice. However, in the year 1994 directly after ice melting,i.e. in March, the tripton composition appeared distinctlydifferent from that in February under ice.

Mean annual sedimentation in Lake Gosciaz in theyears 1991 and 1993–1994 (3500 g/m2year) was muchhigher than in other lakes with laminated sediments: 300g/m2year in meromictic Lake Fayetteville (Brunksill1969) and 410–550 g/m2year in dimictic Elk Lake(Nuhfer et al. 1993). Such differences could have resultedfrom the lower trophy of the compared lakes and/or fromthe high contribution of re-sedimenting matter. LakeGosciaz is a dimictic lake also. The cyclic character ofsedimentation in Lake Gosciaz in the period of investiga-tion depends on the alternate occurrence of circulationand stagnation periods. During winter without ice-covertripton sedimentation is also high.

The low sedimentation rate in the summer (Fig. 3.16)

depends on the thermocline (Fig. 3.14), which is a naturalbarrier for the sedimenting matter (Lastein 1976). The in-crease of tripton flux started from the beginning of thewater mixing and extension of the resuspension zone.The considerable difference between upper and bottomtraps during mixing periods (Tab. 3.15) demonstrated thatresuspension and resedimentation initiated increasingflux of particulate matter. Bottom traps measured net se-dimentation plus resedimentation, while traps under thethermocline measured only net sedimentation (Bloesh1994, Håkansson 1994). During the summer stagnation,when in the lower profundal resuspension was not regis-tered, somewhat higher sedimentation (12%) in bottomtraps (Tab. 3.15) should have been connected with the“funnel effect” (Ohle 1962).

The morphology of the lake basin, described earlier,let us distinguish two zones: the shallow one of resuspen-sion and the deep one of accumulation, with a high slope

Fig. 3.18. Calcite sedimentation (in g/m2d) 1.5 m and 10 m above the bottom in Lake Gosciaz.

Fig. 3.17. Concentrations of calcite and organic matter (in %) in tripton from Lake Gosciaz.


factor (17.5%), which was a very substantial feature forthe processes of sediment transportation and deposition(Håkansson 1977).

A high dynamics of sedimentation during circulationperiods clearly showed that the sediment formation inLake Gosciaz depended first on the processes of sedi-ment distribution and focusing. The separation of twoparts (Fig. 3.13) facilitated understanding of sedimenta-tion mechanisms in the lake. The shallow part was af-fected by resuspension practically over the whole year,except for ice-cover periods. Most of the particles re-cycled back to the water column were mainly depositedin the deep part, in the zone of accumulation. The highdepth and the occurrence of the lamination excluded bot-tom resuspension in the deepest central part of the laketill recent times.

The influence of the shallows on sedimentation isgreater where the area of this zone is larger (Håkansson& Jansson 1983). Because in Lake Gosciaz the area ofthe shallows was 50%, occurrence of resuspension seemsto be certain. If sedimentation near the bottom (13.1

g/m2d) was twice higher than the amount recorded inupper traps (5.9 g/m2d), in the deep part sediments couldhave been accumulated from the area twice as large. Alsoin Elk Lake (Nuhfer et al. 1993) sediment resuspensioninduced over twice the sedimentation rate, from ca. 500 to1154 g/m2year.

To disclose the profound effect of the pollen assemb-lages finally incorporated in sediments, tripton wasexamined palynologically (Mieszczankin & Noryskie-wicz unpubl.). It was demonstrated that in the central partof Lake Gosciaz pollen sedimentation in bottom trapswas much higher than in the upper ones. That “excess”had to be a result of redeposition. The more obviousproof was that bottom traps were influenced by thegreater portion of resuspended material, like the registrat-ing of maximum pollen assemblages after freeze-up,when suspended particles could have been “calmly” set-tled (Fig. 3.19). Pollen grains of plant taxa out of theirflowering season were also found in tripton. The numberof species was much higher in the bottom traps too.Davis (1973) showed that the intensification of pollen se-

Fig. 3.19. Sedimentation of pollen grains per square centimetre per day 1.5 m (black) and 10 m (white) above the bottom in Lake Gosciaz.

Table 3.16. Sedimentation rate (g/m2d) and composition (%) of tripton in Lake Gosciaz under ice cover (in March 1993 and February1994). Funnel-shaped traps were set up 10 and 1.5 m above the bottom; exposure time – 24 h.; (–) lack of data.

Sedimentation of Depth 11.03.1993 28.02.1994

Tripton 10 m – 1.09 (100%)

1.5 m 4.52 (100%) 3.80 (100%)

Organic matter 10 m – 0.38 (34.6%)

1.5 m 1.20 (26.5%) 1.39 (36.5%)

Calcite 10 m – 0.05 (4.9%)

1.5m 1.82 (40.2%) 0.11 (10.4%)

60 LAKE GOSCIAZ

dimentation was a result of bottom-sediment resuspen-sion and downward transport, with deposition in the pro-fundal zone.

Apart from wind/wave-induced resuspension Hilton etal. (1986) distinguished other mechanisms related tosediment redistribution (translocation), such as currenterosion (turbidity currents) and slumping or sliding onslopes. The occurrence of such events in Lake Gosciazwas highly probable due to ground-water inflow (Churskiet al. 1993) and high slopes (Tab. 3.4). Neverthless, in thewhole 18 m profile of laminated sediment, the occurrenceof turbidites was not observed (Goslar, Chapter 6.1,Wieckowski et al., Chapter 5.1).

Calcite was the main constituent of tripton in LakeGosciaz. Its maximum sedimentation (Fig. 3.17) and highpercentage contribution in seston settling during circula-tion (Fig. 3.18) was the evidence that sediments depositedin the shallows tend to be carried into deeper areas.

The maximum precipitation of CaCO3 was observedin the middle of summer (Wachniew & Rózanski, Chap-ter 3.6). Thus on the whole area of the lake bottom, thelayer enriched in calcite should have been created in thesummer and the dark one during the cooler periods, whencalcite formation was limited. During circulation, sedi-ment deposited in the shallows was resuspended andresedimented downward in the lake basin. The examin-ation confirmed that in the deep parts of the lake the for-mation of a layer with higher concentration of CaCO3

took place by the end of the thermal stratification and im-mediately afterwards (compare Fig. 3.14 and 3.17). Sea-sonal changes of sedimentation would have indicated theformation of laminations. It was also established that icecover contributed to calm sedimentation, thus conduciveto the formation of the specific layer (Tab. 3.16). Thelack of ice cover, the extension of time of water mixing,and the high sedimentation rate probably precluded theaccumulation of the specific sediment layer in winter, andas a consequence the absence of lamination in such ayear. In the last few years persistent ice cover was not ob-served, but that did not apply in the last 30 years, whenGoslar (1993) did not detect laminations. Accordingly,winter with or without ice cover probably was not criticalfor the disappearance of the varves in Lake Gosciaz. It islikely that reasons can be found in the increase of the se-dimentation dynamics during circulation periods.

If sediment lamination was not a secondary phenome-non resulting from diagenesis, probably the followingreasons apply for the absence of sediment stratification inLake Gosciaz:

1) Disturbances of periodicity in those processes fa-vourable for sediment lamination.

2) Intensification of resuspension and redeposition.The resuspension and the homogenization of sedimentlayers diminished the differentiation of the resedimentingmaterial.

Water dynamics and sediment resuspension

Morphological and hydrobiological parameters showthat the lake could be divided into two parts (Fig. 3.13),with different water dynamics: the shallow (depth 5–6 m)dynamic part, with resuspension and the deep static partwith oxygen deficits (the zone of accumulation). Theirindividual character determined the structure and thefunction of the lake ecosystem. The distinct thermoclineseparated these two parts during the summer stagnation,and it was a barrier for sedimenting tripton. The lake tothe depth of 5–6 m is shallow and polymictic. The mod-ern sedimentation studies proved that resuspension in theshallows induced approximately double sedimentationrate in the deep part. Mechanisms of sediment transloca-tion (turbidity currents, slumping and sliding) and its fo-cusing are also expected. These assumptions were con-firmed by the morphological parameters of the lake basinand the measures of pollen sedimentation. The most in-tensive pollen sedimentation was recorded after freeze-upas a result of previous sediment resuspension. It wasprobable that seasonal variations in the character of trip-ton were too small to observe the formation of clear var-ves. The lack of ice-cover prolonged the water circulationand supported the high sedimentation rate. It was likelythat increase in the water dynamics and sedimentationwas the cause for the lamination decay in recent years.

The sedimentation studies are continued. A lot of ma-terial has not been worked out yet. Further investigationswill emphasize the tripton palynology, crystallography,and microscopic analyses (particularly phytoplankton).All those topics will be presented in the separate publica-tions.

3.6. ISOTOPIC COMPOSITION OF CALCITEDEPOSITED IN LAKE GOSCIAZ UNDERPRESENT CLIMATIC CONDITIONS

Przemysław Wachniew & Kazimierz Rózanski*

Isotopic record of lacustrine calcite in the sediments

Information preserved in isotopic composition of la-custrine calcite plays a very important role in studiesaimed at reconstruction of past climates on continentalareas. Since their very beginning the interdisciplinarystudies of Lake Gosciaz have included attempts to recon-struct past climatic conditions with the carbon- andoxygen-isotope ratios of calcite obtained from the sedi-ment cores. A very good correlation between abruptchanges of the δ13C and δ18O values (Rózanski et al.1992, Kuc et al. 1993) and changes of other paleoclimatic

* We thank T. Mieszczankin for delivering the sediment trap samples.


indicators (e. g. pollen record, Ralska-Jasiewiczowa et al.1992) at the Late-Glacial/Holocene transition prove thatthe isotopic composition of calcite reflects climatic con-ditions, at least in part of the record. On the other hand,the isotopic record preserved in the sediments of LakeGosciaz reveals some features that cannot be unequivo-cally assigned to any documented climatic or environ-mental changes (Rózanski et al., Chapter 8.6). Therefore,a thorough understanding of the processes controllingisotopic composition of calcite formed nowadays in thisparticular lake system is required. This chapter is aimedat presenting the principal patterns of calcite formation inLake Gosciaz in relation to environmental conditionsboth from chemical and isotopic points of view.

Laminated sediments of Lake Gosciaz consist mainlyof calcite which occurs in form of crystals of differentshape and size. Of microorganisms developing carbonatetests only green algae Phacotus were found in the lake(Kudełko 1994) but their contribution to calcite sedimen-tation is negligible. Lack of carbonate rocks in the catch-ment of the lake ensures that the sediments contain nocarbonates of detrital origin. This assumption has beenproven by the mineralogical studies of the sediments.Among other carbonates only small amounts of rhodoch-rosite and siderite are present in the sediments (Łacka etal., Chapters 7.3 and 8.2). The mean residence time ofwater in the lake is 1–2 years (Wachniew 1995). Sincethe lake is fed mainly by groundwaters, δ18O of its watersshould reflect the mean isotopic composition of precipita-tion over the catchment area slightly modified by evap-oration. Finally, Lake Gosciaz and its catchment havebeen for last forty years almost free from direct anthro-pogenic influences (Goslar, Chapter 9.2.1). The above-mentioned properties make Lake Gosciaz a convenientsite to investigate in detail the processes controlling iso-topic composition of calcite deposited in a natural lakesystem located in a temperate climatic zone.

In mesotrophic to eutrophic hard-water lakes photo-synthesising microorganisms utilize vast quantities ofCO2 dissolved in water. This leads to supersaturation ofthe epilimnic waters with respect to calcite and to its sub-sequent precipitation. The isotopic composition of pre-cipitating calcite is determined by the isotopic composi-tion of dissolved inorganic carbon (DIC), which in thesurface lake waters consists mainly (>95%) of bicarbo-nate (HCO3

–), and by the isotopic fractionation associ-ated with the precipitation process. Under equilibriumconditions the extent of this fractionation for carbon iso-topes only slightly depends on water temperature, chang-ing by few hundreds of permil per 1oC for temperaturerange observed in mid-latitude lakes. Thus, one can ex-pect δ13C of precipitating calcite to reflect in the first in-stance δ13C of DIC pool in the lake. During photosyn-thesis phytoplankton preferentially removes 12CO2 fromwater, while precipitating calcite is enriched in 13C with

respect to DIC. The exchange of CO2 between the atmos-phere and a lake usually results in the enrichment of 13Cin DIC. Other sources of DIC are surface and ground-water inflows to a lake, and decomposition of organicmatter both in the water column and in the sediments, as-sociated with liberation of strongly 13C-depleted CO2 incase of aerobic respiration or strongly 13C-enriched CO2

in case of methanogenesis. δ18O of DIC is controlled byδ18O of water because most of oxygen atoms involved inthe H2O – CO2 – CaCO3 system are contained in watermolecules. The temperature dependence of the 18O equili-brium fractionation factor between water and calcite(change of -0.25‰ per 1oC, O’Neil et al. 1969) is largeenough to imprint water temperature in δ18O of auth-igenic calcite. Generally, δ18O of bulk lacustrine calcitecan be used as an indicator of paleoenvironmental condi-tions but accurate reconstruction of past temperatures isimpossible due to the number of interfering factors.

Sampling and measurement procedures

Regular sampling campaigns on Lake Gosciaz werecarried out monthly between April and October 1993.The lake waters were sampled at several depths (usually1, 3, 5, 8, 13, and 18 meters) for chemical and isotopeanalyses. Sediment samples were collected by use of thesediment traps installed at 10 m above the bottom, in thedeepest part of the lake (for details see Gizinski et al.,Chapter 3.5). The chemical analyses of water samples(pH, alkalinity, Ca2+ concentration) were performed inthe field laboratory within few hours after sampling byuse of the ion selective electrodes. Analytical reproduci-bilities for the chemical analyses (1σ) were better than0.03, 4%, 1% respectively. Equilibrium equations wereused to calculate the concentrations of the DIC species(CO2, HCO3

-, CO32-) (Stumm & Morgan 1981). The pH

and SI values were recalculated for the in situ tempera-tures of water. The isotopic compositions of water, DIC,and calcite deposited in the sediment traps weremeasured. The carbon-isotope ratios of DIC were deter-mined in CO2 liberated from the water samples afteracidification (Wachniew 1995). The calcite and watersamples were prepared for mass-spectrometry analysesby the use of standard methods. The overall precision ofδ18O determination was better than 0.1‰ for water and0.2‰ for calcite. The overall precision of δ13C determi-nation was better than 0.3‰ for DIC and 0.1‰ for cal-cite. The isotope ratios are expressed versus the VPDBstandard for calcite samples and versus the VSMOWstandard for water samples.

Chemical and isotopic observations of calcite precipitation

The seasonal changes of the monitored chemical andisotopic parameters in the lake waters follow to some ex-

62 LAKE GOSCIAZ

tent the pattern of water temperature changes (see Gizins-ki et al., Chapter 3.5). At the beginning of April, duringthe spring overturn, pH values in the water column wererelatively constant. Later, significant differences were ob-served, with elevated pH values in the epilimnion persist-ing until the beginning of September (Fig. 3.20a). The in-crease of pH in the surface waters was caused by photo-synthetic assimilation of CO2. On the other hand, decom-position of organic matter in the bottom waters and in thesediments, accompanied by the release of CO2, led to adecrease of pH in the hypolimnion. A gradual breakdownin the thermal gradient enabled partial mixing of thewater column, thus making the differences of pH be-tween the surface and bottom waters in October less pro-nounced than in the preceding months. The maximumobserved pH values were lower than the values reportedin the literature for some eutrophic lakes during planktonblooms (>9, e.g. Emerson 1975, Herczeg & Fairbanks1987).

The pH values of the lake waters is affected in severalprocesses, e.g. photosynthesis and respiration (Stumm &Morgan 1981). Therefore, the saturation index (SI)should be a better indicator of the intensity of calcite pro-

duction than pH. The saturation index reflects the degreeof saturation of the solution with respect to calcite:

SI = log (Ca2+ ) (CO3

2−)KC

where parentheses denote activities of the ions, andKC is the equilibrium constant. Calcite precipitates onlyat positive SI values. During the studied period the sur-face waters of Lake Gosciaz were always supersaturatedwith respect to calcite while the bottom waters were tem-porarily undersaturated, what facilitated calcite dissolu-tion (Fig. 3.20b). The highest SI values were recorded on29 April. Surprisingly, that SI maximum was accompa-nied by the lowest fluxes of sedimentating organic matterand calcite (Gizinski et al., Chapter 3.5). Calcite precipi-tates only from the supersaturated waters but the degreeof supersaturation evidently does not determine the rateof precipitation. The fluxes of organic matter and calciteevaluated with the aid of sediment traps are positivelycorrelated (r2 = 0.92) and their ratio is 1:0.62 (Wachniew1995). This strong correlation suggests that withdrawalof CO2 by phytoplankton, causing saturation of lake wa-ters with calcite, is not the only way the phytoplanktonaffects formation of calcite crystals. A strong correlationbetween the occurrence of phytoplankton and calcite pro-duction was reported for many lakes (reviewed in Küch-ler-Krischun & Kleiner 1990). In natural waters growthof calcite crystals is predominantly initiated by heteroge-neous nucleation on the surfaces of other solid substrates(Stumm & Morgan 1981). Phytoplankton, its remnants,and other particles may serve as heteronuclei. The SEMphotographs of material collected in the sediments trapsprove that calcite crystal growth is often initiated on thesurface of diatom valves (Starnawska, pers. comm.). In-teractions between biological and physicochemical pro-cesses leading to precipitation of calcite in lake watersmight, through kinetic effects, result in isotopic disequili-brium between precipitate and solution.

The Ca2+ concentrations in the surface waters werelower than in the bottom waters (Fig. 3.20c), and de-creased from April to September. This decreasing trendreflects constant removal of calcium from the water col-umn through precipitation of calcite. The epilimneticconcentrations of DIC did not show such an unequivocaltrend, fluctuating in a wide range (Fig. 3.21a). The largenegative shifts of Ca2+ and DIC concentrations observedfrom 5 July to 5 August both in the surface and bottomwaters did not correspond to any significant increase ofprimary production rates (see Gizinski et al., Chapter3.5). Considering relatively constant rates of calcite andbiomass production, the rates of Ca2+ and DIC supplyfrom other sources of DIC, such as decomposition of or-ganic matter, waters feeding the lake, and dissolution ofcalcite had to vary considerably over that time.

Precipitation of calcite in the surface waters may beFig. 3.20. Monthly profiles of: a) pH, b) SI, c) Ca2+ concentration.


caused by the decrease of CO2 concentration due tophotosynthetic assimilation or by other physicochemicalprocesses, for example changes of water temperature(Kelts & Hsü 1978). CO2 utilization by phytoplankton isthe most important process affecting saturation of LakeGosciaz surface waters with calcite, water temperaturechanges have minor influence on the SI values (Wach-niew 1995). Calcite was present in the sediment trapsduring the whole studied period in 1993, always beingthe main component of the collected material (35–55%by weight, Gizinski et al., Chapter 3.5). No distinct maxi-ma of calcite sedimentation were observed except theperiods of resuspension during the spring and autumnwater column overturns. Results obtained from the sedi-ment traps point to a rather uniform, intense deposition ofcalcite between mid-April and mid-September 1993. Re-suspension and resedimentation of the sediments mightaccount for the significant portion of calcite depositedoutside the period of thermal stratification. Calcite trans-ported from shallow parts of the lake contributes to sedi-ments deposited in the deepest parts. Therefore the iso-topic signal preserved in annual layer may not entirelycorrespond to isotopic composition of calcite producedduring the corresponding year.

Figure 3.21b shows the monthly profiles of δ13CDIC inthe lake. At the beginning of April the δ13CDIC valueswere almost constant in the water column. This isotopicparameter followed characteristic patterns of other physi-cochemical parameters in the well-mixed lake (see Figs3.20 and 3.21). During thermal stratification (May – Sep-tember) DIC in the epilimnion was enriched in 13C com-

paring to the bottom waters. The gradual decrease in the13C content in the bottom waters was due to the release of13C-depleted carbon during the microbial decay of or-ganic matter. The October profile reflects partial mixingof the bottom and surface waters resulting from the grad-ual vanishing of thermal stratification. The δ13CDIC valuesin the epilimnion varied between -6‰ and -4‰ and inthe hypolimnion between -10‰ and -6‰. The volume-tric ratio of the epilimnion to the hypolimnion is approxi-mately 2.5:1. Therefore, the final δ13CDIC value resultingfrom the autumn mixing is closer to the epi- than hypo-limnic value. From late autumn to early spring, whenphotosynthetic activity is low, the isotopic compositionof DIC is probably affected mainly by the release of DICfrom the sediments, by the exchange of CO2 with the at-mosphere (when the lake is free of ice cover), and bycarbon brought to the lake by inflowing waters. Unfortu-nately there are no isotope data available for the winterperiod. However, judging from the April and Octoberprofiles (Fig. 3.21b) the δ13CDIC values should not changesignificantly during winter. Also for the eutrophic LakeGreifen (Switzerland) no considerable change of theδ13CDIC values between December and May was reported(McKenzie 1982). Given only minor changes of the carb-on isotope ratio of DIC during thermal stratification (lessthan 2%), its initial value at the onset of thermal stratifi-cation determines to a large extent the δ13CDIC values forthe whole period of calcite precipitation.

The carbon- and oxygen-isotope compositions of cal-cite collected in 1993 in the sediment traps during one tosix week periods are presented in Fig. 3.22. The carbon-isotope ratios vary in a much narrower range (<1‰) thanthose of oxygen (<3‰). The carbon-isotope ratios of cal-cite samples collected during thermal stratification gener-ally follow the pattern of δ13CDIC changes (Fig. 3.22a).The weighted mean δ13C of calcite for the whole studiedperiod was -1.7‰. The 13C enrichments between calciteand HCO3

- were determined for the calcite samples col-lected during 24 hours and for DIC sampled prior to thecalcite collection period. The values observed in summeramount to 2.9‰ (5 Jul), 3.0‰ (5 Aug), and 2.8‰(7 Sept), being in general agreement with the calculatedequilibrium enrichments and with the values observed inlaboratory experiments (Turner 1982). The apparent en-richment values in spring and autumn were higher: 3.3‰(29 Apr), 3.7‰ (4 Jun), and 4.1‰ (19 Oct) but close tothe values observed during production seasons in Swisslakes (Hollander & McKenzie 1991) and Canadian lakes(Turner 1982). However, in case of Lake Gosciaz thesehigher values correspond to the periods when the occur-rence of intensive resuspension was evident (29 Apr, 19Oct) or probable (4 Jun) (see Gizinski et al., Chapter 3.5).δ13C of resuspended calcite is higher than for calcite pro-duced in the water column (Wachniew 1995). The appar-ent isotopic enrichments between calcite and HCO3

- may

Fig. 3.21. Monthly profiles of a) DIC concentration, b) δ13CDIC.

64 LAKE GOSCIAZ

differ from the actual values, because δ13CDIC and watertemperature vary considerably within the epilimnion.Collected bulk calcite samples consist of portions withdifferent isotopic composition, whereas DIC was sam-pled only immediately before exposition of the traps.

The oxygen-isotope ratios of the collected calcitesamples vary in a wide range. This may be partly due tothe worse overall precision of δ18O determinations(0.2‰). Calcite precipitated during April to June wasconsiderably more depleted in 18O than calcite precipi-tated in summer and winter. This change exceeds in-crease in δ18O of lake waters caused by evaporation. Theweighted mean δ18O of calcite for the studied period is-8.6‰ while δ18O of lake waters for the same period is-7.4‰. For the period from 29 April to 19 October whencontribution of resuspended material was probably smallthe corresponding values are -8.8‰ and -7.3‰, respec-tively. Assuming equilibrium fractionation of oxygen iso-topes between water and calcite (O’Neil et al. 1969) thesevalues give average water temperature 22oC while the ac-tual value was 17oC. The expected δ18O values of calcitecalculated for this period is -7.5‰. Calcite precipitated inthe lake seems to be depleted in 18O comparing to iso-topic equilibrium with lake water at least on a scale ofone year. As in the case of δ13C the calculated δ18Ovalues of calcite should be weighted by the intensities ofcalcite precipitation at the corresponding depths. How-ever, spatial and temporal variations of water temperatureand its isotopic composition within the euphotic zonecannot account for the discrepancies between the calcu-

lated and observed δ18O values of calcite because the es-timated temperature of water (22oC) is higher than ob-served at the lake surface for most of the studied period.

Implications for paleoenvironmental reconstructions

Precipitation of calcite in Lake Gosciaz was observedduring the whole studied period of 1993. Supersaturationof surface waters with respect to calcite was caused bythe intensive assimilation of CO2 by phytoplankton or-ganisms during photosynthesis. The fluxes of calcite andorganic matter evaluated with the aid of sediment trapswere strongly correlated. The high degree of supersatura-tion alone does not suffice to induce precipitation of cal-cite. Apparently, the growth of calcite crystals took placein the presence of phytoplankton or its remnants, whichserved as nucleation centers.

The carbon-isotope ratios of calcite collected in sedi-ment traps were relatively constant, reflecting changes ofδ13CDIC. Variations of δ13C of calcite in the sedimentaryrecord might be thus interpreted as a result of changes inthe lake system affecting its carbon budget. Results ofnumerical modelling of DIC evolution (Wachniew &Rózanski 1997) show that DIC originating from decom-position of organic matter is a crucial element of thecarbon budget of the lake. Large amounts of organiccarbon must be transported into Lake Gosciaz becausedecomposition of organic matter within the lake appearedto be at least by one third higher than its production.Generally, sources of isotopically light carbon (DIC con-tained in groundwaters feeding the lake and organic carb-on from the cachment) are associated with water input.Increased water input (e.g. due to higher precipitationrate over the catchment) should result in lowering ofδ13CDIC. The same might be effect of deforestation lead-ing to increased surface runoff and larger amounts of par-ticulate organic carbon transported into the lake. On theother hand, escape of 13C depleted CO2 and CH4 into theatmosphere increases δ13CDIC. Intensity of transport ofgases through the water-air interface is wind-controlled.Variations of δ13C of calcite observed in the sedimentaryrecord can also result from gradual filling of the lakebasin with sediments which leads to lowering of themean residence time of water in the lake.

The oxygen-isotope ratios of calcite collected in thesediment traps during the studied period show that pre-cipitated calcite was depleted in 18O with respect to theexpected equilibrium values especially for samples col-lected in spring. The reasons for this apparent disequili-brium remain unknown. On the other hand, data availablefrom the Late-Glacial, and early Holocene (Kuc et al.,Chapter 7.6) and youngest parts (Goslar & Wachniew1995) of the sediment cores extracted from Lake Gosciazclearly show that the recorded changes of the δ18O valuesof authigenic calcite remain a useful proxy indicator of

Fig. 3.22. A comparison of the monthly and mean isotopic compositionsof calcite from the upper trap and: a) δ13C of DIC b), δ18O of water.Points denote the observed values, lines represent the weighted averages.


the climatic changes, with the temporal resolution of theisotope signal in the order of several years.

3.7. MACROPHYTE VEGETATION OF NA JAZACHLAKES AND THE DISTRIBUTION OF THESURROUNDING PLANT COMMUNITIES

Klemens Kepczynski† & Andrzej Noryskiewicz

The complex of four lakes (Wierzchon, Brzózka,Gosciaz, and Mielec) called Na Jazach, and the streamRuda connecting the lakes were the object of the floristicand phytosociological field research, together with thesurrounding forest areas and the nearest peatbogs. The fieldstudies were started in 1987 and continued until 1994.

The flora of the Na Jazach lake complex

The flora of the Na Jazach lake complex includes 560species of vascular plants belonging to 81 families. Itsrichness is the consequence of the considerable diversityof habitats. An essential part of the flora is composed ofspecies adapted to aquatic, submerged, and moist habi-tats. Another significant group is formed by species oc-curring in various forest and brushwood habitats. On theother hand, there are comparatively few representativesof xerothermic grasslands.

The most numerous components of the flora representthe following families: Compositae (60 species), Grami-neae (49), Cyperaceae (39), Caryophyllaceae (32), Rosa-ceae (29), Papilionaceae (24), Scrophulariaceae (22), andLabiatae (20). 26 families of the plant list are representedby only one species, and 24 families by 2 or 3 species.Among the taxa found in the study area native speciespredominate, while alien species, including 42 archeo-phytes and 13 kenophytes, constitute only a low percent-age of the flora.

The majority of the kenophytes come from NorthAmerica, less frequently from Asia, and taxa comingfrom the Mediterranean area in a wide sense predominateamong archeophytes. The fairly common kenophytes areAcorus calamus, Solidago serotina, Senecio vernalis,Padus serotina, Erigeron canadensis, and Acer negundo.To the most frequently occurring archeophytes belongCapsella bursa-pastoris, Geranium pusillum, Erodiumcicutarium, Herniaria glabra, Bilderdykia convolvulus,Spergula arvensis, Anchusa officinalis, and Scleranthusannuus.

Many floristic rarities have been noted in the flora ofthe Na Jazach lake complex and the adjacent areas. Theyinclude plants under full protection (16 species) or par-tial protection (10 species), and 49 species are rare in thewhole Płock Basin. The following species are fully pro-tected: Lycopodium annotinum, L. clavatum, Diphasiumcomplanatum, Dianthus superbus, Pulsatilla pratensis, P.patens, Nuphar luteum, Drosera rotundifolia, Hedera

helix, Chimaphila umbellata, Lilium martagon, Orchisfuchsii, Epipactis helleborine, E. palustris, Listera ovata,and Liparis loeselii. Under partial protection are Polypo-dium vulgare, Nymphaea alba, Ribes nigrum, Frangulaalnus, Primula officinalis, Ledum palustre, Arctostaphy-los uva-ursi, Viburnum opulus, Helichrysum arenarium,and Convallaria majalis.

The following rare species are particularly interesting:Ophioglossum vulgatum, Cystopteris fragilis, Dryopteriscristata, D. dilatata, Alnus incana, Salix nigricans, Violaepipsila, Agrimonia procera, Trifolium lupinaster,Angelica archangelica subsp. litoralis, Andromeda poli-folia, Myosotis laxa ssp. caespitosa, Utricularia minor,U. intermedia, Teucrium scordium, Scheuchzeria palus-tris, Potamogeton praelongus, Rhynchospora alba, Cla-dium mariscus, Carex diandra, C. remota, C. limosa, andSparganium minimum. Other floristic peculiarities aresome relict moss species: Camptothecium nitens, Thui-dium lanatum, Meesia triquetra, Paludella squarrosa,and Scorpidium scorpioides.

Due to the absence of fields under crop in the areaconsidered, the synanthropic species are very poorly rep-resented in the present-day flora. The economicallyutilized plants are generally only forest trees. The mostcommon tree species is pine (Pinus sylvestris), occurringin all kinds of forests. In extremely poor habitats thisspecies develops dwarf forms.

Plant communities

Basing on the analysis of 600 phytosociological relevéscarried out in the area under study, 64 syntaxonomic unitsof 14 classes have been characterized (Tab. 3.17). Thenomenclature and classification have been adoptedmainly after Matuszkiewicz (1967, 1981), some otherauthors being also referred to (Pałczynski 1975, Jasnowska& Jasnowski 1983, Neuhäuslova & Neuhäusl 1985).

The full classification of plant associations distin-guished is contained in Tab. 3.17. The simplified map ofplant communities is presented in Fig. 3.23.

The vegetation is differentiated according to the pre-vailing habitat conditions (hydrologic conditions, typesof soils and their nutrient resources, topographic fea-tures). Five basic groups of plant communities can bedistinguished here, i. e. aquatic, reedswamp, mire, brush-wood, and forest vegetation groups. In addition, “saum”and synanthropic, mainly ruderal, communities occurover small areas, developing in the vicinity of seasonallyused human settlements and along roads and roadsides.One of the principal factors affecting the vegetationdiversity of the area in question is water, deriving fromthe small (66 km2) catchment area of the stream Rudaand stored in four lakes (Gosciaz, Wierzchon, Brzózkaand Mielec) and in the stream flowing through them anddischarging into the Vistula River near Dobiegniewo.

66 LAKE GOSCIAZ

The distribution and development of the typical aqu-atic vegetation depend mainly on the configuration of thelake bottoms and their depth as well as on their fertility.The largest bottom surfaces occupied by vegetation arefound in shallow lakes with little water motion, whosebottom sediments, rich in organic matter, favour intensiveplant growth (lakes Wierzchon and Brzózka). Muchpoorer development of aquatic vegetation is found inLake Gosciaz, where plants grow only in its shallowestparts. However, also in the shallow Lake Mielec (maxi-mum depth 1.5 m), only small areas are occupied by aqu-atic communities, because its bottom is formed by thickbeds of carbonate gyttja (Wicik & Wieckowski 1991,Wicik 1993, Wieckowski 1993), outgasing with great in-tensity. It is suggested that the poor development of aqu-atic vegetation in Lake Mielec is due to considerablewater turbulence (gas), poor oxygen supply, and poor sta-bility of the lake bottom.

In the lake complex Na Jazach 12 aquatic-plant asso-ciations of three syntaxonomic classes have been found.The associations Ceratophylletum demersi, Myriophylle-tum spicati, and Ranunculetum circinati occupy the lar-gest areas in lakes Brzózka (90% of lake area) andWierzchon (more than 60%). They develop in welllighted, considerably shallowed places on muddy substra-tum. Their development and spread of Elodeetum ca-nadensis and communities with Potamogeton crispus, P.compressus, and P. pusillus, is restricted to small areasonly on the bottoms of these lakes. Comparatively smallareas are occupied by the associations Hydrocharitetummorsus-ranae, Lemno-Spirodeletum polyrrhizae, andCharetum fragilis. Small stands of Hydrocharitetum mor-sus-ranae occur mainly in lakes Wierzchon and Mielecand in low frequency in Lake Gosciaz and the streamRuda. Lemno-Spirodeletum polyrrhizae has been foundin all the water bodies. Charetum fragilis occurs only inlakes Wierzchon and Brzózka. Stands of the associationPotamogetonetum natantis develop only in the southernpart of Lake Wierzchon, where it covers altogether thearea up to 200 m2.

In Lake Gosciaz the aquatic vegetation develops onlyin its shallow offshore parts and in the very shallow bayTobyłka. Besides Lemno-Spirodeletum polyrrhizae andHydrocharitetum morsus-ranae, stands of Elodeetum ca-nadensis and Potamogetonetum pectinati have beenfound there. Particularly interesting is the presence of therare association Potamogetonetum filiformis, developedas a facies with Potamogeton praelongus. Stands ofPotamogetonetum perfoliati, developed in its southwest-ern offshore part, have been also found in Lake Gosciazonly.

The rather poor aquatic vegetation of Lake Mielec isrepresented by Ceratophylletum demersi, Hydrocharite-tum morsus-ranae and Lemno-Spirodeletum polyrrhizae,growing only in its western part.

The reedswamp vegetation is most differentiated onthe shores of Lake Gosciaz, where it occupies compara-tively large areas in its shallow, slightly muddy offshoreparts. Stands of Phragmitetum communis, Typhetum an-gustifoliae, Acoretum calami, Glycerietum maximae andEleocharitetum palustris occur solely in Lake Gosciaz.The largest surfaces are occupied by Phragmitetum com-munis and Typhetum angustifoliae. They usually developon slightly muddy mineral substratum, forming belts ofvarious widths. Much smaller areas are occupied byGlycerietum maximae, Eleocharitetum palustris andAcoretum calami, which form patches of different size,usually within belts of other reedswamp communities.Typhetum latifoliae, sporadically found in Lake Gosciaz,occurs frequently in the offshore, heavily muddy parts oflakes Wierzchon and Mielec.

Patches of the rare association Scirpetum taber-naemontanii develop solely on the eastern shore of LakeMielec, and Scirpetum lacustris have been observed onlyin the stream Ruda, at its outflow from Lake Mielec.Communities of sedge rush develop in all the lakes stu-died and along the banks of the stream Ruda. In LakeGosciaz the stands of Caricetum rostratae, Caricetumpaniculatae, and Caricetum gracilis were most com-monly found. Phytocoenoses of Caricetum rostratae de-velop as belts of varying width and poorly developed pat-ches in the shallow offshore parts of the lake on mineralslightly mud-covered substratum. Small agglomerationsof that association occur in lakes Mielec and Wierzchonand sporadically on the banks of the stream Ruda. Pat-ches of Caricetum paniculatae occur mainly in sub-merged places and are most commonly found in the vi-cinity of wet alderwoods, which are one of the more ad-vanced links in the succession series. Stands of that asso-ciation have been observed only on the northeasternshore of Lake Gosciaz and on Mielec shores. Stands ofCaricetum gracilis have been found only on the shore ofLake Gosciaz, at the inflow of the stream Ruda. Patchesof Caricetum elatae occur on the shores of lakes Wierz-chon and Brzózka, where they form very narrow belts inthe shallowest places. The remaining associations ofsedge rushes are found in most of lakes and on the riverbanks. Thelypteridi-Phragmitetum community shows aparticularly luxuriant growth on the swampy shores oflakes Mielec and Wierzchon. The associations Caricetumripariae, Caricetum appropinquatae, and Phalaridetumarundinaceae and a small fragment of the associationCladietum marisci occur solely on the banks of thestream Ruda, while Cicuto-Caricetum pseudocyperi andIridetum pseudacori (Kepczynski & Noryskiewicz 1993)develop only on seasonally submerged shores of LakeWierzchon. In a shallow hollow near Lake Gosciaz asmall stand of Sparganietum minimi, rare in that area, hasbeen found.

Aquatic and reedswamp communities occur also on


Table 3.17. Classification of plant communities of the Na Jazach Lake complex.

LEMNETEA R. Tx. 1955 LEMNETALIA R. Tx. 1955

Lemnion minoris R. Tx. 1955 1. Lemno-Spirodeletum polyrrhizae W. Koch 1954 em.

Müll. et Görs 1960 2. Hydrocharitetum morsus-ranae Langendonck 1935

CHARETEA (Fukarek 1961) Krausch 1964 CHARETALIA Sauer 1937

Charion fragilis Krausch 1964 3. Charetum fragilis Fijałkowski 1960

POTAMOGETONETEA R. Tx. et Prsg 1942 POTAMOGETONETALIA Koch 1926

Potamogetonion Koch 1926 em. Oberd.1957 4. Potamogetonetum pectinati Carstensen 1955 5. Potamogetonetum filiformis Koch 1926 6. Ranunculetum circinati (Bennema et West.1943)

Segal 1965 7. Elodeetum canadensis (Pign. 1953) Pass. 1954 8. Ceratophylletum demersi Hild. 1956 9. Myriophylletum spicati Soe 1927 10. Potamogetonetum perfoliati Koch 1926 em. Pass. 1964

Nymphaeion Oberd. 1957 11. Potamogetonetum natantis Soo 1927 12. Nupharo-Nymphaeetum Tomasz.1977

UTRICULARIETEA INTERMEDIO-MINORIS Den Hertog etSegal 1964 em. Pietsch 1965

UTRICULARIETALIA INTERMEDIO-MINORIS Pietsch 1965 Sphagno-Utricularion Müll. et Görs 1960

13. Sparganietum minimi Schaaf 1925PHRAGMITETEA R. Tx. et Prsg 1942

PHRAGMITETALIA Koch 1926Phragmition Koch 1926

14. Scirpetum lacustris (Allorge 1922) Chouard 1924 15. Typhetum angustifoliae (Allorge 1922) Soo 1927 16. Eleocharitetum palustris Sennikov 191917. Phragmitetum communis (Gams 1927) Schmale 1939 18. Typhetum latifoliae Soo 192719. Acoretum calami Kobendza 194820. Glycerietum maximae Hueck 193121. Scirpetum maritimi (Br.-Bl. 1931) R. Tx. 1937

Magnocaricion Koch 1926 22. Thelypteridi-Phragmitetum Kuiper 1957 23. Cicuto-Caricetum pseudocyperi Boer. et Siss. in Boer 1942 24. Iridetum pseudacori Eggler 1933 25. Caricetum ripariae Soo 1928 26. Caricetum acutiformis Sauer 1937 27. Caricetum paniculatae Wangerin 191628. Caricetum rostratae Rübel 1912 29. Caricetum elatae Koch 1926 30. Caricetum appropinquatae (Koch 1926) Soo 1938 31. Caricetum gracilis (Graebn. et Hueck 1931) R. Tx. 1937 32. Caricetum vesicariae Br.-Bl. et Denis 1926 33. Phalaridetum arundinaceae (Koch 1926 n.n.) Libb. 1931 34. community with Calla palustris

Sparganio-Glycerion fluitantis Br.-Bl. et Siss. in Boer 1942 35. community with Berula erecta

BIDENTETEA TRIPARTITI R. Tx. Lohm. et Prsg 1950 BIDENTETALIA TRIPARTITI Br.-Bl. et R. Tx. 1943

Bidention tripartiti Nordh. 1940 36. Polygono-Bidentetum (Koch 1926) Lohm. 1950

MOLINIO-ARRHENATHERETEA R. Tx. 1937 MOLINIETALIA Koch 1926

37. community with Deschampsia caespitosa Molinion Koch 1926

38. community with Molinia coerulea Calthion R. Tx. 1936 em. Oberd. 1957

39. Epilobio-Juncetum effusi Oberd. 1957 40. Scirpetum silvatici Knapp 1946

SCHEUCHZERIO-CARICETEA FUSCAE (Nordh. 1936) R. Tx. 1937SCHEUCHZERIETALIA PALUSTRIS Nordh. 1936

Rhynchosporion albae Koch 1926 41. Caricetum limosae Br.-Bl. 1921 42. Rhynchosporetum albae Koch 1926

Caricion lasiocarpae Vanden Bergh. ap. Lebrun et all. 1949 43. Caricetum lasiocarpae Koch 1926 44. Caricetum diandrae Jon. 1932 em. Oberd. 1957 45. Sphagno-Caricetum rostratae (Steff. 1931) em. Dierss. 1978 46. community with Eriophorum angustifolium47. community with Juncus effusus

CARICETALIA FUSCAE Koch 1926 em. Nordh. 1936 Caricion fuscae Koch 1926 em. Klika 1934

48. Carici-Agrostietum caninae R. Tx. 1937 49. Calamagrostietum strictae (Steff. 1931) Tołpa 1956 50. community with Carex fusca

OXYCOCCO-SPHAGNETEA Br.-Bl.et R. Tx. 1943 SPHAGNETALIA MAGELLANICI (Pawł. 1928) Moore (1964) 1968

Sphagnion magellanici Kästner et Flössner 1933 em. Dierss. 1975 51. Eriophoro vaginati-Sphagnetum recurvi Hueck 1929

PLANTAGINETEA MAIORIS R. Tx. et Prsg 1950 PLANTAGINETALIA MAIORIS R. Tx. (1947) 1950

Polygonion avicularis Br.-Bl. 1931 52. Lolio-Plantaginetum (Lincola 1921) Beger 1930

ARTEMISIETEA Lohm.GALIO-CALYSTEGIETALIA SEPIUM (R. Tx. 1950) Oberd. 1967

Senecion fluviatilis R. Tx. 1947 53. Eupatorietum cannabini R. Tx. 1937 em. Falinski 1966

ONOPORDETALIA ACANTHII Br.-Bl. et R. Tx. 1943 Eu-Arction lappae R. Tx. 1937 em. Siss. 1950

54. Tanaceto-Artemisietum vulgaris Br.-Bl. (1931) 1949 ALNETEA GLUTINOSAE Br.-Bl. et R. Tx. 1943

ALNETALIA GLUTINOSAE R. Tx. 1937 Alnion glutinosae (Malc. 1929) Meijer Drees 1936

55. Sphagno squarrosi-Alnetum Sol.-Górn. 1975 56. Ribo nigri-Alnetum Sol.-Górn. 1975 57. Salicetum pentandro-cinereae (Almq. 1929) Pass. 1961 58. community with Calamagrostis canescens

VACCINIO-PICEETEA Br.-Bl. 1939 VACCINIO-PICEETALIA Br.-Bl. 1939

Dicrano-Pinion Libb. 1933 59. Peucedano-Pinetum Mat. (1962) 1973 60. Querco roboris-Pinetum J. Mat. 1981

QUERCO-FAGETEA Br.-Bl. et Vlieg. 1937 FAGETALIA SYLVATICAE Pawł. 1928

Alno-Padion Knapp. 1942 em. Medw.-Korn. ap. Mat. et Bor. 1957 61. Circaeo-Alnetum Oberd. 195362. Carici remotae-Fraxinetum Koch 1926

Carpinion betuli Oberd. 1953 63. Tilio-Carpinetum Tracz. 1962

RHAMNO-PRUNETEA Rivas Goday et Carb. 1961 PRUNETALIA SPINOSAE R. Tx. 1952

Rubion subatlanticum R. Tx. 1952 64. Pruno-Crataegetum Hueck 1931

68 LAKE GOSCIAZ

mires situated around the lakes. Only one aquatic com-munity with Nymphaea alba has been found there, whilereed vegetation is represented by different communitiessuch as Typhetum latifoliae, a community with Phrag-mites australis and Acoretum calami, Thelypteridi-Phrag-mitetum, Iridetum pseudacori, Caricetum paniculatae,Caricetum acutiformis, Caricetum vesicariae, Caricetumrostratae, Caricetum elatae, and a community with Callapalustris.

Among the least frequent mire associations in the sur-roundings of lakes Na Jazach are those usually occurringon transitional peatbogs: Rhynchosporetum albae, Ca-ricetum limosae, Caricetum lasiocarpae, and Caricetumdiandrae. They develop on acid peat substratum in placessubmerged during the periods of heavy rainfall andspring thaw. On transitional peatbogs develop also rarephytocoenoses of Sphagno-Caricetum rostratae andEriophoro vaginati-Sphagnetum recurvi. Patches of thelatter association usually occur in complexes of raisedbogs; in the investigated transitional moors (Kepczynski& Noryskiewicz 1992) they form one of the developmen-tal phases. The association frequently found in the 11 stu-died mires was Carici-Agrostietum caninae. It usuallydevelops on fens, with a steady horizontal water supply,but is also found in marginal parts of transitional peat-bogs. Drier parts of peatbogs are overgrown by com-munities from Molinio-Arrhenatheretea classes (Epilo-bio-Juncetum effusi, Scirpetum sylvatici, and com-munities with Molinia coerulea and Deschampsia caespi-tosa).

Brushwood communities, represented mainly by Sa-licetum pentandro-cinereae, occur on submerged shoresof the lakes, by the stream Ruda, and in the surroundingsof peatbogs. Stands of a community with Calamagrostiscanescens, without trees or shrubs, occur in the vicinityof willow brushwoods and wet alderwoods.

The distribution of forest communities dependsmainly on the character of soil and on hydrologic condi-tions. Wet alderwoods (Carici elongatae-Alnetum sensulato) develop in submerged habitats in direct contact withsurface water. They are distinctly differentiated into twoassociation types: Sphagno squarrosi-Alnetum and Ribonigri-Alnetum. The first one occurs in places withoutdrainage and occupies comparatively small land surfaces,and the other occupies large areas in the surroundings ofall the lakes and of the stream Ruda. In recent years thearea occupied by the black current alderwood (Ribonigri-Alnetum) decreased due to the lowering of ground-water level. Similar but slightly more elevated habitatsare occupied by various forms of the association Circaeo-Alnetum. Particularly interesting are patches with numer-ous occurrences of Orchis fuchsii and Listera ovata.Those phytocenoses grow on the southern shores of allthe lakes, and they are particularly well developed nearlakes Brzózka and Mielec. In places of seepage water

flowing from the southern elevated slopes (mainly bylakes Gosciaz and Mielec), impoverished forms of Cariciremotae-Fraxinetum have developed. That association israre in northern Poland.

At some distance from the lakes, associations of Tilio-Carpinetum and Querco roboris-Pinetum adjoin the carrcommunities. Stands of Tilio-Carpinetum cover largerareas on the southeastern side of Lake Wierzchon (Fig.3.32), and on the slope on the southern side of LakeGosciaz they form a narrow belt bordering upon Cariciremotae-Fraxinetum towards the lake and on Querco ro-boris-Pinetum forest on the other side. Northwest of LakeGosciaz on elevated slopes small fragments of Pruno-Crataegetum occur. It is a vicarious communities forTilio-Carpinetum developing after the forest stand hasbeen destroyed by man.

The surroundings of lakes Na Jazach are dominatedby pine forests. Their composition depends on the fer-tility of the habitats. In more humid places richer in nu-trients near water bodies, stands of Querco roboris-Pine-tum develop, and dry dunes are overgrown by Peuceda-no-Pinetum.

The distribution of vegetation around the lakes NaJazach depends mainly upon the natural conditions.There are no apparent damages resulting from human ac-tivity to be observed there nowadays. Most natural fea-tures can be found in aquatic, reedswamp, and mire plantcommunities, and among forest communities in wet al-derwood and riverside forests.

To the contrary, a distinct effect of human manage-ment is visible in the formation of pine forests. Duringforest management pine has been protected for manyyears, being introduced even on mixed deciduous foresthabitats. That is evidenced by the species composition ofunderstory and herb layer in many stands of mixed pineforests.

During several years’ studies we observed the gradualdecrease of the area occupied by alderwoods to the ad-vantage of the alder carr. That process can be observeddistinctly on the southern shores of lakes Wierzchon,Brzózka, Gosciaz, and Mielec. It is the result of the grad-ual lowering of the groundwater level, caused mainly bythe low annual rainfall in recent years.

From the present-day patterns and diversity of plantcommunities as well as from their continuous dynamictransformations it can be presumed that in the past thewater bodies occupied larger areas than recently. Such aconclusion is substantiated by the present-day develop-ment of plant communities, particularly spectacular in theeastern and western parts of the lake complex, where alarge area is occupied by Ribo nigri-Alnetum and Cir-caeo-Alnetum, developing on a substratum formed ofpeats. The presently observed intense shallowing of lakesWierzchon, Brzózka, and Mielec will soon result in com-plete disappearance of those water bodies and in the de-


velopment of reedswamp and mire vegetation, and finallyof wood communities in their place. The pattern and suc-cession of plant communities in the area of the lake com-plex Na Jazach does not basically differ from those ob-served in other areas of lowland Poland with little humaninterference.

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3. RECENT ENVIRONMENT OF LAKE GOS´CIAZ AND CONNECTED … · 3. recent environment of lake gos´cia z and connected lakes 3.1. geological structure and relief in the surroundings