Lentic Ecology I
Presiding: D DeNicola, Slippery Rock University; A Hershey, University of North Carolina at Greensboro
NB32D-01 10:30h
Long-term Changes in del 13C in DOC-based Benthic Food Webs in Arctic Lakes
Arctic regions are rapidly warming, resulting in warmer summer lake temperatures and increased slumping of organic soils. In Lake NE-12, del 13C of primarily benthivorous lake trout has declined over eleven years. Two important lake trout prey, the caddisfly Grensia and the snail Lymnaea, also became more 13C-depleted. In Lake E-1, the deposit-feeding chironomid, Stictochironomus, also shifted toward lower del 13C, while filter-feeding Tanytarsini did not. Pelagic zooplankton did not show a trend toward 13C depletion overall, but were less consistent. Recent and concurrent studies have shown that DOC is an important resource for the benthic foodweb. Methanotrophy is part of the DOC-based foodweb. Our recent studies have shown that macrobenthos use some methanotroph production. Methane has very low del 13C, thus incorporation of a small amount of methane-based production has a large effect on del 13C. We suggest that climate-driven changes in the carbon pools available to microbes are resulting in increased importance of methanotrophs in macroinvertebrate diets, contributing to the observed long-term del 13C changes. Increased algal fractionation could also be important, but this mechanism has less support because zooplankton and filter-feeding chironomids did not show the same pattern, and previous studies have shown very limited benthic-pelagic coupling.
NB32D-02 10:45h
Response of Submersed Macrophyte Communities to Selective Removal in Eurasian Watermilfoil Dominated Systems
Invasive species such are thought to dominate communities through competitive superiority. When invasive species are controlled, revegetation by native plants is desired, but often difficult. The response of submersed macrophytes communities to selective removal of Eurasian watermilfoil (Myriophyllum spicatum) and native plants was investigated in three lakes: a lake with high water clarity and few herbivores, a lake with poor clarity and few herbivores, and a clear lake with a high density of milfoil herbivores. At each lake, 16 to 20 2mX2m plots were identified and delineated with a pvc frame on the bottom and each plot was assigned to one of 4 treatments in a randomized block design. Treatments were: remove all plants, remove Eurasian watermilfoil, remove all non-milfoil plants or remove no plants. Prior to treatment duplicate biomass samples were collected from each plot. Visual estimates of plant cover were made every 2-4 weeks and biomass samples were collected at the end of the summer. Plots were resampled similarly in the year following the manipulation. The treatments were successful at manipulating the plant community in each lake, but overall did not reveal dramatic shifts or competitive interactions. Within one year the communities reverted to their premanipulation state.
NB32D-03 11:00h
Associations of aquatic invertebrates and water quality in the ecology of an emerging tropical disease
Mycobacterium ulcerans Infection is commonly called Buruli ulcer, a rapidly emerging skin disease that is often disfiguring and causes severe and lasting morbidity in developing nations of the tropics and sub-tropics. Outbreaks of BU are nearly always associated with slow-flowing aquatic habitats affected by human-mediated landscape changes, and biting aquatic insects are thought to play a role in transmission. As a part of a World Health Organization initiative, we are determining landscape factors that determine water quality conditions conducive for enhanced M. ulcerans growth and abundance in the aquatic environment. In June 2004 we collected water quality and invertebrate data from 12 water bodies near Accra, Ghana, Africa. Preliminary analyses found predator-dominated communities (from 47% - 64%) with Hemiptera (e.g., Belostomatidae and Naucoridae) most often collected. Using exploratory canonical correspondence analysis, sites separated out by functional feeding groups and water quality variables. Higher water hardness and total suspended solids was most associated with scrapers (i.e., snails) and shrimp, respectively. PCR evidence suggests that M. ulcerans is found among snails, fish and invertebrates. Future studies are proposed that take a multi-scale, multidisciplinary approach for identifying disturbance metrics that can be used to predict human Buruli ulcer incidence near monitored water bodies.
NB32D-04 11:15h
Does Climate Change Confound Lake Recovery?
Four acidified (pH < 6) and nine reference lakes have been sampled since 1988 for chemistry and benthic macroinvertebrates of the littoral, sublittoral and the profundal habitat. Many lakes showed positive trends in pH, reflecting recently decreasing SO4 deposition but negative trends in sublittoral and profundal species richness and diversity. Littoral species richness and diversity, however, increased in both lake types during this time period. In multiple stepwise regression TN, conductivity and NAOwinter index, and pH were the best predictors of species richness, diversity, and CA axis 1 scores against physico-chemical variables. The processes generating these patterns are unclear, but we speculate that decreasing conductivity and increasing water color indicating the influence of 'wet' years might increase allochthonous DOM inputs, which may negatively affect periphyton communities and in turn benthic macroinvertebrate richness and community composition. Positive phases of the NAO winter index bring warmer, wetter winters to Scandinavia, this may cause longer summer stratification, and thus an increase of hypolimnetic anoxia. Furthermore, a deeper thermocline in shallow lakes caused by warmer climate may particularly effect the sublittoral fauna due to e.g. enhanced nutrient turnover leading to internal eutrophication and thus lack of oxygen.
NB32D-05 11:30h
Periphyton Response to Nutrient Manipulation in 3 Lakes of Different Trophic Status: Effects on Density, Taxonomic Composition and Size Spectra
Nutrient-diffusing substrata were used to examine nutrient limitation of periphyton communities in 3 Irish lakes that differ in periphyton productivity. Phosphorus addition treatments had significantly higher algal biovolume density than nitrogen addition or control. Canonical correspondence analysis using nominal variables to define treatments indicated both nutrient addition and lake productivity significantly affected taxonomic composition. The flora of the least productive lake was dominated by diatoms characteristic of low alkalinity and Bulbochaete. Phosphorous addition increased Bulbochaete in this lake, but increased Phormidium and Stigeoclonium in the two more productive lakes. Size spectra of algae were significantly affected by either nitrogen or phosphorus in the most productive lake because Stigeoclonium increased relative to smaller cyanobacteria and diatoms. Although nutrient addition increased large filamentous chlorophyte taxa in the two less productive lakes, it did not significantly affect size spectra. The results indicate that increased nutrient loading should increase periphyton area- specific biovolume, increase filamentous chlorophytes, and potentially shift size spectra to larger classes in lakes over a broad range of benthic productivities. The peak size class was smallest in the most productive lake suggesting that size spectra maybe more useful to indicate nutrient changes within a lake rather than define differences between lakes.