Hydrobiologia 510: 53–66, 2003.© 2003 Kluwer Academic Publishers. Printed in the Netherlands.

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The influence of habitat structure and flow permanence on invertebratecommunities in karst spring systems

H. Smith1, P.J. Wood2 & J. Gunn3

1Pennine Water Group, School of Engineering, Design and Technology, University of Bradford, Bradford,West Yorkshire BD7 1DP, U.K.Tel: 1274-235470. E-mail: h.smith5@bradford.ac.uk2Department of Geography, Loughborough University, Loughborough, Leicestershire LE11 3TU, U.K.3Limestone Research Group, Geographical Sciences, University of Huddersfield, Queensgate, Huddersfield,West Yorkshire HD1 3DH, U.K.

Received 6 June 2002; in revised form 19 June 2003; accepted 30 June 2003

Key words: flow variability, spring ecology, groundwater, habitat structure, crenobiology

Abstract

The macroinvertebrate fauna of five karst (limestone) springbrook systems with contrasting physical habitat anddischarge patterns were investigated to examine the role of flow permanence and habitat structure on macroin-vertebrate community composition. Clear physical differences were identified between perennial and intermittentsprings and individual sampling stations. However, flow permanence, water temperature and the input of leaflitter exerted a greater influence on the aquatic invertebrate community than habitat structure. Perennial sites werecharacterised by a greater abundance of macroinvertebrates and greater Ephemeroptera, Plecoptera and Trichoptera(EPT) richness than intermittent sites. The fauna of all of the springbrook systems examined were dominated byrelatively common and ubiquitous taxa (e.g. Gammarus pulex) although a number of taxa displaying life cycleadaptations to ephemeral aquatic habitats (e.g. Limnephilus auricula and Stenophylax permistus) were recorded atintermittent sites.

Introduction

Springs are unique freshwater ecosystems providingan interface between hypogean (subterranean) andepigean (surface water) habitats, and represent ideallocations to examine the relationships between faunalcommunities and the environmental parameters thatinfluence their distribution. Spring and springbrookcommunities demonstrate the majority of the struc-tural and functional properties seen in other lotic com-munities, yet are significantly less complex (Williams& Williams, 1998). Despite their obvious importanceto freshwater ecology, the study of the relationshipbetween spring macroinvertebrate communities andenvironmental variables is relatively poorly under-stood (Williams et al., 1997; Botosaneanu, 1998;Hoffsten & Malmqvist, 2000).

Springs and their associated habitats usually con-tain a limited number of macroinvertebrate speciesof diverse origin, including a number of spring-specialists (Danks & Williams, 1991). Most ground-water dominated springs are protected from largeoscillations associated with climatic variability, andrelict species have persisted in many areas of theworld (Ponder, 1985; Ito, 1998). Many springs exhibitthermal stability throughout the year (van der Kamp,1995). The area around a spring’s source, known asthe eucrenal zone, has been delineated according toits thermal regime. The boundary of the eucrenal zonewith the hypocrenal (downstream - springbrook) zoneis generally defined as the point where the annualvariation in water temperature does not exceed 2 ◦C(Erman & Erman, 1995). Thermal stability is a biolo-gically important characteristic and the eucrenal zonemay represent a highly stable ecological environment

54

(Williams, 1991). However, such constant conditionsare not present in all spring systems and water temper-ature, chemical composition, suspended-solid content,and discharge may exhibit either gradual (seasonal) orsudden (incidental and storm-related) variations (Ryen& Meiman, 1996; Webb et al., 1998).

Thermal variability of springwater is dependent onthe mode of flow, and the duration that water is un-derground significantly influences the temperature ofthe resurgent water (Pitty, 1976). Pulses of allogenicwater (water entering from a point source, e.g. surfacerunoff and streams) that move rapidly through openjoints after precipitation will differ from autogenicwater that seeps slowly through a diffuse network ofnarrow joints and fissures. In autogenic-fed systems,the temperature of karst springwater may vary littlethroughout the year, with the mean water temperaturenearly equal to the mean annual air temperature for thearea (van der Kamp, 1995).

A wide range of lotic and riparian habitats maybe present within an individual springbrook and as aresult a wide variety of resources may be availablewithin a small geographical area (Gooch & Glazier,1991). Common macroinvertebrate species in springshave been associated with specific chemical (Webb etal., 1998) and physical factors, including pH (Glazier,1991), alkalinity and macrophyte cover (Glazier &Gooch, 1987). In some instances the physical habitat,most notably substratum composition (size of clastsand heterogeneity) and the presence of aquatic veget-ation, have been found to be the dominant controlson community composition (Williams & Williams,1999). However, in others it has not been possible torelate any instream habitat characteristics to the faunalcommunity structure (Lindegaard et al., 1998).

The faunal composition of springbrook systemsmay be strongly related to the persistence of aquatichabitats, rather than structure (Smith et al., 2001).Macroinvertebrate community abundance and di-versity is usually higher in perennial springs, althoughin some intermittent springs the abundance of someinsect taxa (e.g. Ephemeroptera and Diptera) may begreater due to their ability to rapidly colonise waterbodies following the resumption of flow (Glazier &Gooch, 1987).

Instream habitat structure and the temporal vari-ability of discharge within a spring and its brook isdependent upon a number of factors including precip-itation, catchment area, topographic relief, bedrock,adjacent landuse and the relationship of the spring tothe underlying aquifer (Gooch & Glazier, 1991). This

paper examines the influence of habitat characteristics,water chemistry and flow permanence on the macroin-vertebrate communities within five limestone springsystems within a single catchment in the English PeakDistrict. Sampling stations along each springbrook areinvestigated to examine the spatial variability of themacroinvertebrate community and the environmentalparameters that influence them.

Study area and methodology

The springbrook systems examined were all locatedwithin the River Wye catchment in the Peak DistrictNational Park (Derbyshire) England (Fig. 1). The cli-mate of the region is temperate, with a mean annualrainfall of c. 1200 mm. The area has an averageJanuary air temperature of 1.7 ◦C and a mean Julytemperature of 14.5 ◦C, with a mean annual air tem-perature of 8.0 ◦C. A broad anticline of Carboniferouslimestone underlies the area, outcropping over 540km2 (Gunn et al., 1998) and is commonly referred toas the ‘White Peak’. In contrast to other British Car-boniferous limestone regions, the White Peak formsa compact area, 40 km long (north-south) and up to20 km wide, surrounded by lithologies that supportsignificant surface drainage.

The study sites comprised 2 intermittent springs(Sites 1 and 4), 2 perennial springs (Sites 2 and 5) andone linear spring (Site 3), encompassing the range ofdischarge regimes within limestone springs (Fig. 1).Linear springs are characterised by erosion in a chan-nel in which the upper end is usually dry for at leastfour-months of the year and the area of groundwateremergence fluctuates up or down this channel depend-ing on local precipitation and groundwater levels. As aresult the position of the spring source is often difficultto clearly define. A summary of the physical character-istics of the five springs investigated is given in Table1.

Water temperature (◦C), pH, conductivity (µScm−1) and dissolved oxygen concentration (mg l−1)of springwater at source (point of groundwater emer-gence), were measured using portable meters. Bi-carbonate concentrations (mg l−1) were analysed inthe field using a Camlab Ltd. digital titrator. Wa-ter samples were collected at each spring-source, andanalysed in the laboratory for calcium, magnesium,iron, potassium and sodium using an atomic absorp-tion spectrometer (AAS), and for chloride, nitrate andsulphate through ion chromatography. Substrate com-

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Figure 1. Location map of: (a) the White Peak study area and; (b) the River Wye indicating the location of the springbrooks (1–5) examined.

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Table 1. Physical characteristics of the karstic spring sample sites in the River Wye valley (all measurements taken at spring source)

Site Elevation (m) Mean Length Land Mean water T.var Mean Q Q.var RIoP

width (m) (m) use Temp. (◦C) (L/sec)

1 203 2.5 30 sparse 8.2 0.3 3.5 100 6

woodland

2 158 0.5 180 dense 8.4 0.2 2.3 69 7

woodland

3 154 3.5 30 sparse 8.5 0.9 3.1 80 7

woodland

4 148 5.0 100 grazed 8.6 0.6 1.8 100 9

pasture

5 145 6.0 60 grazed 8.8 1.8 21.6 71 2

pasture

T.var = annual variation in water temperature (◦C); Q.var = annual variation in discharge (%); RIoP = Relative Index of Permanence (valuesderived from 8 samples at 6-weekly intervals over the study period, total n = 37; 3 samples not collected due to desiccation).

position (percentage cobble, gravel, sand and silt)and percentage cover of instream leaf litter, woodydebris, and vegetation cover (bryophyte and macro-phytes) were determined using a visual estimationprocedure (Armitage et al., 1995). Spring dischargewas measured at the source employing the standardvelocity-area technique (Gordon et al., 1992) using anelectromagnetic flowmeter. The percentage variationin discharge was calculated for the entire study periodusing the following formula:(

maxQ − minQ

maxQ

)× 100

An alternative measure of permanence was providedby deriving a relative index of permanence (RIoP).This was calculated by ranking the springs accordingto their mean discharge, and then ranking the springsaccording to their minimum discharge at summerbaseflow. The two separate ranks were then summedto provide a RIoP for each spring site (adapted fromFeminella, 1996).

Macroinvertebrate sampling and water chemistrymeasurements were undertaken at the sites at ap-proximately six-weekly intervals from March 1999 toFebruary 2000. Five stations (a–e) were establishedon each spring. This was the minimum number ofstations required to encompass all of the major meso-habitats in the most heterogeneous spring. The firststation was located at the point of groundwater emer-gence (source), the second 2.5 m downstream, andthe third approximately 10 m from source. Stationsd and e at each site were spaced in such a way thatthey corresponded to the major habitat changes in thelower reaches of the springbrook. At each sampling

station a 1-minute Surber sample (0.1 m2 with a 250µm mesh net) was used to collect invertebrate fauna,disturbing the substratum to a depth of 50 mm. Extens-ive sampling of small habitats such as springs shouldnot be undertaken on a regular basis. The samplingstrategy employed maximised the data obtained whilstavoiding excessive disturbance of the spring sourceand its brook (Zollhöfer, 1999). Macroinvertebratesamples were preserved in the field with 70% in-dustrial methylated spirit (IMS) and returned to thelaboratory for sorting and processing. Identificationwas undertaken to species where possible, althoughsome early instar larvae and some taxonomically de-manding groups such as Chironomidae (identified tosub-family), Tipulidae, and Oligochaeta were notidentified to species level.

To examine differences between the invertebratecommunities of the springs, and individual stationswithin a single spring the Shannon-Wiener, Simpson,and Marglef diversity indices and the Berger-Parkerdominance index were calculated using the α SpeciesDiversity and Richness software (Pisces Conserva-tion, 1998). In addition, species richness (numberof taxa), Ephemeroptera, Plecoptera and Trichopterarichness (EPT) and invertebrate abundance (individu-als m−2) were calculated and offered as independentvariables within a t-test to assess any significant dif-ferences between the invertebrate communities of per-ennial and intermittent springs. Environmental datawere analysed using Principal Components Analysis(PCA). Combined environmental and macroinverteb-rate community data were analysed using CanonicalCorrespondence Analysis (CCA) within the program

57

CANOCO 4.0 (ter Braak & Šmilauer, 1998). An un-restricted random Monte Carlo permutation test wasperformed to determine the significance of individualenvironmental variables and canonical axes. All spe-cies data were transformed (log e +1) prior to analysesto reduce the clustering of common and abundanttaxa at the centre of the ordination plot, and there-fore allow examination of qualitative differences in thecommunity composition (Castella et al., 1995).

Results

Environmental characteristics

The temperature regimes of the five spring sourceswere broadly similar and within 0.8 ◦C of the meanannual air temperature for the Buxton area (8.0 ◦C)(Table 1). Sampling stations downstream of the sourceexperienced much greater variability in water tem-perature (>2 ◦C) over the study period and generallyreflected prevailing meteorological conditions at thetime of sampling. Water chemistry parameters werecomparable for all of the springs, with a small vari-ation in the mean ionic concentrations of bicarbon-ate, calcium, magnesium, sodium, potassium, nitrate,sulphate, chloride and iron between the five sites(Table 2). Mean conductivity varied by 55 µS cm−1

(range 533–588 µS cm−1), dissolved oxygen levelsby 1.9 mg l−1 (range 8.2 – 10.1 mg l−1) and pH byonly 0.4 (range 7.1–7.5) (Table 2). Since preliminaryanalyses indicated that water chemistry had relativelylittle influence on springbrook macroinvertebrate com-munity composition, due to low inter-spring variationcompared to other environmental parameters, it wasnot included in further analyses.

Examination of physical habitat characteristicswithin PCA clearly identified perennial (Sites 2 and 5)and intermittent (Sites 1 and 4) springs on the first axis(Fig. 2). Sampling stations within the linear spring(Site 3) were clearly arranged longitudinally on thefirst and second axes, reflecting variation in discharge(Q.var) and downstream changes in water temperat-ure (T.var). The cumulative percentage of varianceexplained by the first four PC axes was 74.5%, withthe first axis accounting for 21.9% of the variation, andthe second axis explaining a further 20.6%. Variationin discharge (Q.var) was most closely correlated withaxis 1 (r = −0.726; P ≤ 0.01), and resulted in theclear differentiation of spring source and springbrooksampling stations with an intermittent flow regime

from the perennial stations. Intermittent springbrookstations (Site 1c–e and 4c–e) were typically charac-terised by silty substrates, and low vegetation cover.In contrast, the source and upstream stations (a–b) ofthe majority of the springbrooks were characterisedby cobble or gravel substrates, with the exception ofSite 4 and sampling station 5b. The downstream sta-tions in one perennial (Site 5) and the linear spring(Site 3) were characterised by instream vegetation(macrophytes and bryophytes) and sandy substrates.Site 2 had the lowest variability of discharge over thestudy period (69%) and as a result the majority of thespringbrook sampling stations were characterised bycobble and gravel substrates and appeared to sharethe physical characteristics of many source samplingstations.

Environmental influences on community structure

A total of 83 taxa from 52 families were recordedfrom the five springs during the study period (Table3). Gammarus pulex (L.) was the most abundant andfrequently occurring taxa (present in 132 of a totalof 169 samples and 30% of all individuals), althoughits density in individual samples was highly variable.Insects comprised 59.4% of the macroinvertebrateabundance (34.7–78.7%) and 84.3% (70.4–89.1%) ofspecies richness across the five sites. However, eachspring appeared to have a distinctive community (av-erage Jaccard Similarity between two sites = 40.5%)despite the geographical proximity of some sites. Thesites most similar over the study period were springs 2and 3 with a Jaccard’s Similarity Coefficient and Bray-Curtis Similarity of 60.8% and 72.2% respectively.

The mean abundance (individuals m−2), speciesrichness, dominance, equitability and diversity indicesfor each of the 25 sampling stations are presented inTable 4. A significant difference in the mean abund-ance (individuals m−2) (t-test t = −3.22; p =<

0.05), number of taxa (t-test t = −3.60; p =< 0.05)and the EPT richness (t-test t = −2.90; p =<

0.05) between perennial and intermittent spring com-munities was recorded. However, no significant dif-ferences were recorded between the Shannon-Wiener,Simpson or Margalef diversity indices or the Berger-Parker dominance index for perennial and intermittentsprings. The mean abundance of macroinvertebrateswas greater (>1000 m−2) at perennial sites (2a–e,3c–e and 5a–e) compared to intermittent sites. Spe-cies richness was lower in the intermittent source and

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Table 2. Summary of the mean conductivity (C µS cm−1), pH, dissolved oxygen (DO mg l−1), bicarbonate (HCO3 mg l−1), calcium (Camg l−1), magnesium (Mg mg l−1), sodium (Na mg l−1), potassium (K mg l−1), nitrate (NO3 mg l−1), sulphate (SO4 mg l−1), chloride(Cl mg l−1) and iron (Fe mg l−1) recorded at source within the five limestone springs sampled within the River Wye valley (March 1999 –February 2000

C µS cm−1 pH DO mg l−1 HCO3 mg l−1 Ca mg l−1 Mg mg l−1 Na mg l−1 K mg l−1 NO3 mg l−1 SO4 mg l−1 Cl mg l−1 Fe mg l−1

Site mean SD mean SD mean SD mean SD mean SD mean SD mean SD mean SD mean SD mean SD mean SD mean SD

1 536 51 7.1 0.2 10.1 0.9 212 8 91.3 3.5 4.1 0.2 16.1 2.1 0.7 0.1 24.2 4.2 34.9 5.4 29.2 0.9 0.5 0.12 588 18 7.4 0.3 9.1 3.4 224 12 94.5 4.9 5.8 1.1 15.3 2 0.8 0.1 30.5 2 43.7 3.9 31.3 1.7 0.5 0.13 586 22 7.5 0.3 9.1 0.9 218 10 96.7 2.9 6.8 1.4 14.7 2.8 1.5 0.4 21.1 3.1 43.3 5 31.9 2.2 0.4 0.14 533 30 7.4 0.2 8.2 0.5 213 6 92 3.9 5.9 0.9 10.2 0.3 1.2 0.3 26.2 1.9 39.8 1.5 25.3 1.2 0.4 0.15 563 43 7.3 0.1 10.1 0.3 226 26 96.2 7.5 6.2 0.3 10.6 0.7 0.8 0.4 18.4 6.7 40.8 5.8 22.2 0.6 0.9 0.1

SD = standard deviation (mean and SD values based on 8 replicate samples collected at 6-weekly intervals over the study period, total n = 74;6 samples not collected due to desiccation). All analyses were conducted in triplicate.

springbrook stations, although no clear longitudinalpatterns could be distinguished in the data.

Canonical Correspondence Analysis (CCA) clearlyseparated perennial and intermittent sampling sites onthe first axis, primarily based on variation in dis-charge (Q.var) (Fig. 3a). Annual variation in tem-perature (T.var) and the presence of leaf litter (L.lit)from adjacent trees were strongly associated withthe second axis. The first four canonical axes ex-plained 34.1% of the species and 70.1% of the speciesenvironment relationship, and both were significant(p ≤ 0.005) (Table 5). Three environmental vari-ables (Q. var, T. var. and L. lit) were found to besignificant when examined using a Monte Carlo ran-dom permutations test within the forward selectionprocedure of CANOCO 4 (Table 5). Examinationof the taxon biplot clearly indicated a greater num-ber of macroinvertebrate taxa associated with per-ennial sampling stations [e.g. Plecoptera: Nemurellapicteti (Klapálek,); Trichoptera: Drusus annulatus(Stephens), Agapetus fuscipes (Curtis), Beraea pullata(Curtis), Beraea maura (Curtis), Plectrocnemia con-spersa (Curtis), Crunoecia irrorata (Curtis); the riffle-beetle Elmis aenea (Müller), and Asellus aquaticus(L.)] (Fig. 3b). The intermittent sampling stationswere characterised by Stagnicola palustris (Müller),three limnephilid Trichoptera [Limnephilus auricula(Curtis), L. lunatus (Curtis) and Stenophylax permis-tus (McLachlan)], Tipulidae and several other Dipteralarvae commonly associated with semi-aquatic habit-ats and waterlogged soils [Fannidae and Bibionidae:Bibio Johannis (L.)].

Discussion

Instream habitat structure and substratum compositionhave been shown to be dominant factors influencingthe distribution of invertebrate taxa within many river-ine systems (Harper et al., 1995), and distinct faunalassemblages may be associated with individual hab-itats (e.g. Pardo & Armitage 1997; Wood & Armit-age, 1999). However, the results obtained from thesprings and springbrooks examined within the RiverWye catchment suggest that discharge variability hasa greater influence on macroinvertebrate communitycomposition than instream habitat structure. This al-most certainly reflects the overriding importance ofdischarge variability in shaping instream habitat struc-ture. The presence and volume of organic debris(leaf litter) was the only physical habitat variable thatsignificantly influenced the springbrook community.Riparian vegetation structure and landuse around thespring source may therefore have a strong influence onthe community structure and overall abundance. Theinput of leaf-litter from the surrounding vegetationforms an important source of organic matter and maybe the primary source of energy for the invertebratecommunity within many springs where autochthonousproduction is naturally low (Rosi-Marshall & Wallace,2002).

Detailed analysis of the macroinvertebrate com-munity indicated that discharge variability (Q.var) andvariation in water temperature (T.var) were the dom-inant factors influencing the macroinvertebrate com-munities within the springbrook systems examinedwithin the River Wye valley. The perennial and in-termittent sites were clearly differentiated within mul-tivariate analyses (PCA and CCA). The role of thermalvariability in shaping groundwater-dominated eco-systems has been widely acknowledged (Arscott et

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Figure 2. Principal Components Analysis (PCA) of the environmental parameters from the five springbrooks examined in the River Wye Valleyindicating perennial � and intermittent stations �. Abbreviations of environmental variables are: Cob – percentage cobble substratum; Grav –percentage gravel substratum; Sand – percentage sand substratum; Silt – percentage silt substratum; Veg – percentage macrophyte cover; Moss– percentage bryophyte cover; Q.var = percentage annual variation in discharge; T.var = annual variation in water temperature (◦C); L.lit =percentage leaf litter cover; Wood – percentage woody debris cover.

al., 2001). However, at a greater spatial resolution(between catchments) it is recognised that springsfed by water from different geological sources maysupport markedly different communities as a resultof local physical and chemical characteristics (Wil-liams et al., 1997). Limestone (karstic) springs mayprovide relatively buffered environments as long asflow persists.

Hydrological variability within aquatic ecosystemsis one of the primary factors controlling the distri-bution of lotic fauna (Townsend et al., 1987; Woodet al., 2001). Benthic communities within intermit-tent aquatic systems have been found to differ fromthose within nearby perennial systems (Wiggins et al.,1980; Williams, 1996). The majority of the faunawithin intermittent springs in the Wye valley werecommon, ubiquitous and opportunistic species, manyof which have also been recorded in the mainstemriver or at neighbouring perennial spring sites (Smith,2000; Smith et al., 2001). However, the perennialspring sampling stations in this study were character-ised by at least twice the abundance of invertebratesand greater EPT diversity (particularly Trichoptera lar-vae) than intermittent source and springbrook stations(Table 4). However, none of the diversity or domin-

ance indices differed significantly between perennialand intermittent sites.

A number of Trichoptera taxa recorded at the in-termittent sites in this investigation display life cycleadaptations associated with the colonisation of tem-porary aquatic habitats, such as an extended flightperiod from spring into autumn or aestivation as adultsduring the dry summer (e.g. Limnephilus auricula,Limnephilus lunatus, Micropterna sequax (McLach-lan) and Stenophylax permistus (Sommerhäuser et al.,1996). Given the differences in the Trichoptera faunarecorded in perennial and intermittent spring systems,it may be possible to use them as relatively rapid andeffective indicators of flow persistence in both springsand other types of water bodies (Erman & Erman,1995; Meyer & Meyer, 2000).

Ephemeral aquatic habitats may be character-ised by pioneer insect taxa that may emerge fromdesiccation-resistant eggs or that are able to survivein small moist (semi-aquatic) microhabitats within theriver bed or banks (Boulton, 1989). These refugia mayinclude mats of leaf litter, rotting wood and pocketsof damp substratum beneath the surface in the hy-porheos (Boulton & Lake, 1992). However, in otherstudies few, if any, macroinvertebrate taxa recorded

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Table 3. Aggregated annual macroinvertebrate data indicating presence or absence and abundance for the 5 springbrooks (total n = 169 samples,31 samples not collected due to desiccation). Key to abundance: P = present (1 individual collected); R = rare (2 – 10 individuals); O = occasional(11 – 50 individuals); C = common (51 – 250 individuals); A = abundant (> 250 individuals)

Sampling stations 1a 1b 1c 1d 1e 2a 2b 2c 2d 2e 3a 3b 3c 3d 3e 4a 4b 4c 4d 4e 5a 5b 5c 5d 5e

TURBELLARIAPlanariidae Crenobia alpina O R P A A C A C O C C C C O C O O AOLIGOCHAETA P O R R R R O P O R R R R O C C C O R R R R RHIRUDIDAEGlossiphoniidae Glossiphonia complanata R R P P R RErpobdellidae Erpobdella octoculata P PPiscicolidae Piscicola geometra P RMOLLUSCAAncylidae Ancylus fluviatilis RHydrobiidae Potamopyrgus jenkinsi P P PLymnaeidae Lymnaea peregra P P R P R R O O O C

Stagnicola palustris R PLymnaea truncatula O P R O P

Sphaeriidae P OCRUSTACEAGammaridae Gammarus pulex A R O O O A A A A A C C A A A R O A A A A AAsellidae Asellus aquaticus R P R P R R R PPLECOPTERANemouridae Nemurella picteti P C C O O P R R P R C A C A A

Nemoura erratica O R O C O R R O O O RNemoura cambrica O P O C C O O P R O O C O R

Chloroperlidae Chloroperla torrenttium P O RPerlidae Isoperla grammatica PEPHEMEROPTERABaetidae Baetis rhodani R P O R R R R R O O O R R O R R R O C C O CEphemerellidae Ephemerella ignita R R R RTRICHOPTERARhyacophilidae Rhyacophila dorsalis PLimnephilidae Limnephilidae sp. P P C P R O R R O P P R O R R R

Limnephilus lunatus O O O O R O R RLimnephilus vittatus PLimnephilus extricatus PLimnephilus auricula P R RHalesus radiatus PDrusus annulatus O O R O R R R R R R O O O OMicropterna sequax R R R R O O O C O R R O O OPotamophylax cingulatus P P R R R OPotamophylax rotundipennis PPotamophylax latipennis P P P R R P R RChaetopteryx villosa R R R P R P R R R PStenophylax permistus R R P

Glossosomatidae Agapetus fuscipes A A A A C R R C R R O A O C CLeptoceridae Ceraclea albimucula PLepidostomatidae Lepidostoma hirtum P P

Crunoecia irrorata OGoeridae Silo pallipes P P P R PBeraeidae Beraea pullata P R O R P

Beraea maurus O R O O P R O R O PPolycentropodidae Plectrocnemia conspersa R R R R P R R O R PHETEROPTERAVeliidae Velia caprai PNotonectidae Notonecta obliqua PCorixidae Sigara lateralis P

Sigara nigrolineata R

Continued on p. 61

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Table 3. contd.

Sampling stations 1a 1b 1c 1d 1e 2a 2b 2c 2d 2e 3a 3b 3c 3d 3e 4a 4b 4c 4d 4e 5a 5b 5c 5d 5e

COLEOPTERAElmidae Elmis aenea R R P P P R R R P

Limnius volkmari P R P RRiolus subviolaceus P

Hydrophilidae Megasternum obscurum PCoelostoma orbiculare PAnacaena lutescens PHelophorus brevipalpis P P R R P P A R C CHydrobius fuscipes P PLaccobius truncatellus P PLaccobius aequalis P P P

Hydraenidae Hydraena riparia PDytiscidae Dytiscidae (larvae) R R P R P R R P R P

Agabus bipunstulatus R PAgabus biguttatus PAgabus guttatus RHydroporus obsoletus R

Scirtidae Scirtidae (larvae) R R R R R R R C C C R C C C C CNoteridae Noteridae (larvae) PDIPTERATipulidae R O O P R R R O R O O R O O O O R R O R R O O O OChironomidae Orthocladiinae C C C C C O C A O A O C C C O O O O O R R O C C C

Diamesinae C C A R A P R R C R R O C R O R P R RTanypodinae P O R P R R P R O O R R R R R O OChironominae

Tanytarsini O P C C P A C P R R P C RPodonominae P

Prodiamesinae P R O OCeratopogonidae P P P R R PSimuliidae P O C C P P R R R C O O O R O C C A APsychodidae R R R R O R R C R O O O O C P O O C C OEmpididae P PDixidae R R R P R R R P P O R R RPtychopteridae R R PStratiomyidae P R O O O R P R R R P P P C C C RBibionidae Bibio johannis OFannidae OAthericidae Atherix sp. P RSyrphidae Eristalis P PSciaridae R R R P O C O O RHYDRACARINA P

within intermittent streams displayed any adaptationsto the cessation of flow (e.g. Gray, 1981; Feminella,1996). The dominant insect taxa associated with manyseasonally wet and dry habitats are thought to persistfrom year to year by virtue of repeated colonisationfrom nearby perennial habitats rather than throughphysiological tolerance (Batzer & Resh, 1992). Withinheadwater springs systems subject to regular desicca-tion, aerial dispersal is thought to be the dominantrecolonisation mechanism utilised by aquatic insects(Zollhöfer, 1999). The ability of Diptera larvae, andespecially Chironomidae, to utilise freshwater habit-

ats prone to extreme hydrological variability has beenwidely noted (e.g. Lindegaard, 1995; Langton & Cass,1998). However, the wider use of Diptera larvae in thecharacterisation of springs has been poorly developedin most areas due to the taxonomically demandingnature and the high person-hours required for theiridentification.

Within the River Wye valley, insect taxa contributean important component of the community abundance(mean value 59.4%) and species richness (mean valueof 84.3%). The majority of insect taxa probably flyin from nearby perennial water bodies to oviposition

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Table 4. Summary of species richness, mean abundance, Shannon-Wiener diversity index, Simpson diversity index, Margalef diversity index,Berger-Parker dominance index and EPT (Ephemeroptera, Plecoptera and Trichoptera) richness for all 25 spring and springbrook samplingstations. Data represents aggregated macroinvertebrate samples for the entire study period (March 1999 – February 2000)

Species Mean Shannon– Simpson Margalef Berger– EPT

richness abundance Wiener diversity diversity Parker richness

(S) (N m−2) diversity (H) dominance

(d)

1a 16 720 1.63 3.61 2.28 0.44 6

1b 13 497 1.22 2.63 1.93 0.46 3

1c 14 609 1.34 2.75 2.03 0.52 3

1d 14 497 1.47 3.50 2.10 0.38 3

1e 14 843 1.28 2.59 1.93 0.58 2

2a 20 1754 1.74 3.91 2.55 0.43 8

2b 24 1751 1.86 4.40 3.08 0.39 12

2c 27 1544 1.93 5.04 3.54 0.29 12

2d 25 2445 2.10 5.57 3.07 0.34 9

2e 29 2524 1.73 3.92 3.57 0.40 15

3a 22 335 1.96 3.86 3.61 0.48 10

3b 22 451 1.71 3.41 3.27 0.48 9

3c 36 1384 1.77 2.96 4.70 0.55 15

3d 30 1438 1.79 3.26 4.13 0.52 11

3e 33 1069 1.91 3.13 4.59 0.54 13

4a 24 294 2.42 7.93 4.20 0.28 5

4b 13 471 1.45 2.91 1.95 0.50 3

4c 12 198 2.03 6.11 2.10 0.29 2

4d 20 234 2.25 7.41 3.48 0.23 4

4e 13 128 1.99 5.02 2.68 0.37 2

5a 31 1035 1.72 2.97 4.46 0.53 10

5b 28 3732 2.05 5.58 3.40 0.26 11

5c 32 2098 2.10 4.88 3.92 0.40 11

5d 28 2911 2.14 5.62 3.51 0.25 10

5e 32 5434 1.79 4.16 3.60 0.32 12

when flow resumes in the intermittent springs. Therepeated colonisation of the springs may result in atemporally dynamic community, reflecting wider nat-ural and anthropogenic changes occurring in the urbanand agricultural landscape and management activitieswithin adjacent water bodies.

Gammaridae are frequently the most abundant taxarecorded within many perennial lotic spring systems(e.g. Gooch & Glazier, 1991; Lindegaard et al., 1998).In the Wye Valley springs, Gammarus pulex was themost widely distributed and numerically most abund-ant taxon. Within both of the perennial springs andthe linear spring G. pulex was the most common andfrequently occurring taxa in the springbrook stations.In contrast, within both intermittent springs the highestabundances were recorded at the source stations whilst

flow continued. At both intermittent sites the down-stream springbrook stations became dry before thespring-head and remained dry for some time follow-ing the resumption of flow at the source. The greaterabundance of G. pulex was particularly pronouncedduring the late spring and early summer as dischargebegan to decline and may reflect the migration ofindividuals towards the spring-source (Williams &Williams, 1993). However, it is unlikely that G. pulexisolated at the source would survive prolonged periodsof dewatering (Ladle & Bass, 1981). Some individualsmay have followed the retreating water undergroundand persisted within hypogean habitats (e.g. interstitialhabitats or cave streamways) where sufficient waterwas present, although the ability of these individu-

63

Figure 3a. Canonical Correspondence Analysis (CCA) of the five springbrooks examined in the River Wye valley: (a) site biplot – indicatingperennial � and intermittent stations �, and environmental parameters; Abbreviations of environmental variables are: Cob – percentage cobblesubstratum; Grav – percentage gravel substratum; Sand – percentage sand substratum; Silt – percentage silt substratum; Veg – percentagemacrophyte cover; Moss – percentage bryophyte cover; Q.var = percentage annual variation in discharge; T.var = annual variation in watertemperature (◦C); L.lit = percentage leaf litter cover; Wood – percentage woody debris cover; and; b) taxon biplot.

als to recolonise the spring and springbrook with theresumption of flow is unknown.

Conclusions

The limestone spring systems of the River Wye val-ley support distinct macroinvertebrate communitiesthat can be clearly differentiated based on the dis-charge variability, thermal variability and the volumeof organic leaf litter within the aquatic environment.Perennial source and springbrook sampling stationssupported a greater abundance of invertebrate taxa andhad a greater diversity of Ephemeroptera, Trichopteraand Plecoptera (EPT) than intermittent sampling sites,although some taxa displayed features thought to beadaptive in aquatic habitats with intermittent flow(e.g. Limnephilus auricula and Stenophylax permis-tus). Aquatic habitat structure exerted relatively littleinfluence on spring and springbrook community struc-

Table 5. Summary of CCA eigen values, cumulative percent ofvariance explained on the first four canonical exes, significance ofcanonical axes and significant environmental variables identifiedusing the Monte Carlo random permutation test

Axis 1 Axis 2 Axis 3 Axis 4

Eigenvalue 0.269 0.162 0.135 0.101Species environment correlation 0.969 0.918 0.947 0.907Cumulative% variance:

of species data explained 13.7 22.0 29.0 34.1of species-environment relation 28.2 45.3 59.5 70.1

F ratioSignificance of first canonical axis 2.39∗∗Significance of all canonical axes 1.58∗∗Significant environmental variables:Q.var 3.11∗∗T.var 1.59∗L.lit 1.70∗∗

Q.var = annual variation in discharge (%); T.var = annual variationin water temperature (◦C); L.lit = percentage leaf litter cover; ∗p ≤ 0.01; ∗∗ p ≤ 0.005.

64

Figure 3b. (Continued)

ture or composition, with the exception of leaf litterderived from marginal vegetation. Insect taxa werethe most abundant and diverse faunal group withinall of the springs investigated. However, in commonwith many studies of spring ecosystems an amphipodcrustacean (Gammarus pulex) was the most widelydistributed and abundant species recorded (e.g. Gooch& Glazier, 1991; Lindegaard et al., 1998).

Stream and spring discharge variability may lead tosignificant temporal variability in aquatic communityabundance and structure (Wood et al., 2001; Smith& Wood, 2002). The markedly different macroinver-tebrate communities that characterise intermittent andperennial springs provide a valuable tool to monitorthese poorly studied systems. There is an increas-ing need to recognise the vulnerability of these sys-tems to groundwater pollution (Williams et al., 2000),groundwater abstraction (Petts et al., 1999) and landmanagement practices so that appropriate polices andpractices can be developed for the sustainable man-

agement of these spatially and temporally variablephenomena.

Acknowledgements

HS acknowledges the support of a research student-ship from the Division of Geographical Sciences,University of Huddersfield. Thanks to Paul Hard-wick, Margaret Scott, Mike Kelly, and the numerouspeople who helped with the fieldwork. Thanks to DrM.D. Agnew and Dr J.C. Green for comments ondrafts of this manuscript and to Mark Szegner andClive Cartwright (Loughborough University) for theproduction of figures.

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