7/31/2019 BIOL432 - Abstract and presentation

1/4

Why the research was of interest: - humic substances might influence planktonic food chains in lakes in 2ways: (i) by altering the physical and chemical environment and thus modifyingautotrophic primary production and the dependent food web and (ii) by acting as adirect carbon and/or en ergy source to the food web (Steinberg et al. 2006.Dissolved humic substances ecological driving forces from the individual to theecosystem level? Freshwater Biology 51: 1189-1210.)

- DOC influences lake plankton metabolism through physical , chemical, andbiological processes: humic DOC affects the underwater light climate by reducing thedepth of the trophogenic layer and competes with phytoplankton for light. DOC hasalso been shown to scavenge limiting nutrients, including Fe and othermicronutrients, from the water. These physical and chemical processes may depressprimary production. At the same time, DOC can also serve as a carbon source forbacteria and indirectly for other heterotrophic components of the plankton, so DOCshould contribute to plankton community respiration. Jones reviewed theseprocesses and hypothesized that planktonic P:R ratios should generally increase withtrophy in lakes and that, at comparable nutrient or chlorophyll concentrations,

colored lakes should have lower P:R ratios than clear- water lakes. (del Giorgio, P.A.,R.H. Peters. 1994. Patterns in planktonic P:R ratios in lakes: Influence of lake trophyand dissolved organic carbon. Limnol. Oceanogr. 39: 772-787.)

- Phytoplankton productivity in l akes, estuaries and oceans plays an essentialrole in element cycling and food supply to heterotrophs. (Oduor, S.O., and M.Schagerl. 2007. Phytoplankton primary productivity characteristics in response tophotosynthetically active radiation in three Kenyan Rift Valley saline- alkaline lakes.Journal Of Plankton Research 29: 1041-1050.)

- Primary production by phytoplankton, the base of the food web in aquaticsystems, regulates energy availability to higher trophic levels as well as carbon andoxygen fluxes between the ocean and the atmosphere. (Forget, M. -H. et al. 2007.Extraction of photosynthesis-irradiance parameters from phytoplankton productiondata: demonstration in various aquatic systems. Journal Of Plankton Research 29:249-262.) Note: I copied from the papers so please write this info. in yourown words if you are using it.

Background/Previous studies I have a few other papers, but I haven't read them yet, as they sort of repeat what those aresaying. I also copied the papers, so change the wording!

Carignan, R., D. Planas and C. Vis. 2000. Planktonic production and respiration inoligotrophic Shield lakes. Limnology Oceanography 45(1): 189-199.

o Balance between production and resipiration lies at the basis of ourunderstanding of carbon flow and food web structure in marine and freshwaterecosystems

Photosynthesis exceeds total planktonic respiration: are netautotrophic, they are net sinks for CO2 and net producers of O2 andorganic matter Conversely, P < R, net heterotrophic, net sources of CO2 and netconsumers of organic carbon

7/31/2019 BIOL432 - Abstract and presentation

2/4

Several studies have suggested that respiration systematicallyexceeds photosynthesis in the epilimnion of oligotrophic lakes, estuaries,and oceans (Sorokin 1971; Findlay et al. 1992; del Giorgio and Peters1993, 1994; Coveney and Wetzel 1995; del Giorgio et al. 1997; Duarteand Agusti 1998).

Ideally, gross photosynthesis and community respiration shouldbe compared by measuring the uptake or release of products orsubstrates common to both reactions (O2, CO2). Here, we use high-precision metabolic rate measurements in theepilimion of 12 Canadian Shield lakes to test the heterotrophyhypothesis. We show that in such lakes, gross photosynthesis nearlyalways exceeds planktonic respiration. The detection limits for NP and R were 0.7 and 0.5 mgC m23 h21,respectively. Gross photosynthesis during the incubation (GP) wascalculated as NP 1 R, assuming equal dark and light algal respiration; the

validity of this assumption is not critical to our conclusions since algalrespiration is small (5 15%) compared to GP and community respiration(Bidwell 1977; Stone and Ganf 1981). Volumetric (VR) and areal (AR) 24-hcommunity respiration rates were calculated assuming that respirationrates measured on water collected in the morning ( R), wererepresentative of the entire day

Carignan, R., A. Blais and C. Vis. 1998. Measurement of primary production andcommunity respiration in oligotrophic lakes using the Winkler method. Canadian Journalof Fisheries and Aquatic Sciences 55: 1078-1084.

Study site Carignan, R., D. Planas and C. Vis. 2000. Planktonic production and respiration inoligotrophic Shield lakes. Limnology Oceanography 45(1): 189-199.= o ns ="urn:schemas-microsoft-com:office:office" />

o Area is underlain by a granitic or anorthosic bedrock covered by 1-5m of glacial tillso Soils are mostly Orthic Ferro-Humic Podzol (Canadian classification)o Catchments are forested (>95%) primarly with sugar maple ( Acer saccharum , yellow birch ( Betula alleghaniensis ) beech ( Fagus grandifolia , and

poplar ( Populus tremulodes o Annual precipitations: 1,100 mm per year, 30% falling as snowo = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />LakeCromwell has relatively high DOC and TP concentrations owing to its largedrainage ratio and to the presence of extensive wetlands in its watersheds.o Lakes Cromwell has well-developed (;25% of lake area) macrophytebeds dominated by Nymphea odorata, Nymphoides cordata, Potamogeton sp.,and Utricularia vulgaris

7/31/2019 BIOL432 - Abstract and presentation

3/4

Lake Location

LA(km2)Lakearea

CA(km2)catchmentarea

Zm(m)meandepth

Hydraulicresidencetime

Totalp (mgperm3)

TotalN

DOC Lightattenuationcoefficient

Croche

458599N,748019W

0.19 0.88 0.51 1.91 3.8 211 3.52 0.65

Cromwell

458599N,748009W

0.10 9.94 2.9 0.06 9.6 313 5.17 1.09

o

Carignan, R., A. Blais and C. Vis. 1998. Measurement of primary production andcommunity respiration in oligotrophic lakes using the Winkler method. Canadian Journalof Fisheries and Aquatic Sciences 55: 1078-1084.

o Altitude 340 mo 70 km north of Montrealo The two lakes exhibit contrasting limnological conditionsencountered in unperturbed Shield lakes. Croche Lake is a small (20 ha)headwater seepage lake with a mean depth of 4.8 m, a drainage ratio of 5.1, and

a water residence time of 2.3 years. Macrophytes are virtually absent in the lake.Its water chemistry is typical of oligotrophic Shield lakes, with an average totalphosphorus, chlorophyll a , and dissolved organic carbon of 4 mg?L 1, 1.1 mg?L 1, and 3.5 mg?L 1, respectively. In contrast, Cromwell Lake (11 ha) has a meandepth of 2.6 m, a large drainage ratio (91), and a much shorter residence time(0.07 years). The lake receives water from two larger lakes (Croche and Pilon)and from several extensive marshes and beaver dams. As a result, CromwellLake has higher concentrations of total phosphorus (10 mg?L 1), chlorophyll a(3.8 mg?L 1), and dissolved organic carbon (5.2 mg?L 1); it also has a well-developed littoral macrophyte belt dominated by Utricularia vulgaris andNymphoides cordata .

So The 21 Laurentian lakes are located in the southeastern part of thePrecambrian Shield, 80 km north of Montreal (468N, 748W). The bedrock in thisregion is mainly gneiss and granite, and it is covered by morainic soils and borealforests.

Results

7/31/2019 BIOL432 - Abstract and presentation

4/4

A few of the key points from the data...Gross photosynthesis and Humic Content

- light levels decrease with depth in both lakes; Cromwell - decrease wasstrongly exponential (R2=0.9767), Croche - decrease was more linear (R2=0.901)

- gross photosynthesis also decreases with depth in both lakes, probablybecause of lowered light levels (significant data)- gross photosynthesis is lower in the humic lake (Cromwell) probably becausethe humic content attenuates light (not significant data)- gross photosynthesis did not decline any faster in the humic lake than theclear lake (not significant data)- (based on Carignan article) Cromwell appears to have a shallowertrophogenic/euphotic zone, probably due to the presence of humic matter

Zooplankton and Gross Photosynthesis- on average, respiration was higher and gross photosynthesis was lower

when zooplankton were present i.e. non-fractioned bottles (not significant)- the effect of zooplankton seems to be the same in both lakes (significant)

How the results relate to the literature:

A study showed that primary productivity was inversely related to total dissolved organiccarbon andThe results suggest that humic matter depressed primary productivity (Jackson,T.A., and R. E. Hecky. 1980. Depression of Primary Productivity by Humic Matter in Lake andReservoir Waters of the Boreal Forest Zone. Can. J. Fish. Aquat. Sci. 37: 2300-2317.)

Arst et al. 2008 Although light attenuation coefficients varied widely between lakes, the difference betweenprimary production was not significant. Observed a decrease in primary production with depth,but most started low, had a peak and then decreased to zero. At low irradiance, maximum wasseen at surface and then decreased. The peak primary production is a short distance belowsurface of water.

Carignan et al. 2000 Gross photosynthesis was most at surface, had peak at lower irradiance and decreased with depthto 0. Also observed significant decrease in production with depth. The peak in grossphotosynthesis is a short distance below surface of water, with the exception when irradiencewas low, there was a peak at the surface of the water.