Lentic Ecology II Posters
Presiding: E Marti, Centre d'Estudis Avancats de Blanes (CSIC); C Hoagstrom, South Dakota State University
NB33R-01 1330h
Comparison of Grazing Intensity & Diets of Native and Invasive Amphipods in Lake Erie
Echinogammarus ischnus, an invasive amphipod originating from the Ponto Caspian Basin, was first discovered in the Detroit River in 1995 and has migrated through the lower Great Lakes displacing the native amphipod, Gammarus fasciatus. Both amphipods seek food and refuge by inhabiting substrata encrusted with zebra mussels and/or filamentous macro-algae. The filamentous green alga Cladophora, along with its epiphytic communities, are an important food source and refuge from predators and physical stresses. We examined the gut content of both amphipod species to determine their preferred food in their natural habitats, and conducted a laboratory experiment to determine each amphipod's grazing effects on algal biomass. Gut analysis was completed by taking grab samples from 4 study sites located along the western shore of Lake Erie every two weeks July through September, 2004. Amphipods were separated by species and preserved in 90% alcohol for later dissection. Algal taxa from amphipod guts were identified and enumerated using brightfield microscopy. In the lab experiment, algal biomass prior to and after two weeks of amphipod grazing was determined using ash-free dry mass and chlorophyll-a. Preliminary results indicate that E. ischnus and G. fasciatus exert approximately equal grazing pressure on the Great Lakes food web.
NB33R-02 1330h
Young Sub-Arctic Lakes: Are They Valuable as Records of Recent Climate Change?
Arctic and sub-arctic regions, which are among the most rapidly warming regions on the planet, are model ecosystems for studying potential impacts of anthropogenic climate change. As the initial part of a larger, multi-regional paleolimnology-climatology project, we measured various features of the lake waters to establish differences among six young and previously unstudied lakes on the Matanuska Glacier, Alaska. Two dystrophic lakes, ~300 yr old, developed atop stagnated, forested ice had high concentrations of dissolved organic carbon (mean 18.7 mg C/L). Two oligotrophic lakes, ~30 yr old, developed atop ice-cored moraines had lower DOC concentrations (mean 3.4 mg C/L). Two ~30 yr old silt-laden, proglacial lakes near the margin had the lowest DOC concentrations (mean 1.1 mg C/L). Nitrate and ammonium concentrations varied across lakes, but were generally higher in the two dystrophic lakes. Zooplankton communities were well established in the dystrophic lakes, but were less abundant or absent in the other lakes. We concluded that the lakes are different in carbon profiles and trophic interactions, which will be beneficial in our paleolimnology study. Changes in carbon isotopes and plankton assemblages stored within the sediments can be used to evaluate the impact of warming in sub-arctic lakes.
NB33R-03 1330h
A Diatom-based, Paleolimnological Study Of Rush Lake, Wisconsin
Rush Lake, located in Winnebago County, Wisconsin, is a shallow, eutrophic, lake/wetland dominated by cattails. This system has historically been important for fishing and waterfowl production. But recently the general public view the lake as degraded from increased sedimentation, contamination from lead shot, and perceived reduction in fish and wildlife. A sediment core (374cm) was taken by employing a modified Livingstone piston corer. The core sample was dated with carbon-14 yielding a date at the base of the core of 4110 +/- 40 yr. B.P. The core sediments were sampled for diatoms starting at 5cm for every 10cm after that (37 samples). Diatoms were counted for a total of 300 per sample. Typical of shallow lakes, the core showed signs of being extensively reworked. Despite this, multivariate analysis of diatoms (PCA) suggests that this system has become more eutrophic. This is consistent with a pollen analysis and is likely due to agricultural activities in the watershed. There is no evidence (i.e., increase in % planktonic diatoms) that the lake had ever developed a pelagic zone for an extended period of time. Results of this study may be useful in making future management decisions to restore Rush Lake.
NB33R-04 1330h
Storm Induced Changes in Turbidity, Chlorophyll, and Rotifer Abundance in Acton Lake, Ohio
Storms are natural disturbances that can alter several processes in lakes. However, the magnitude of the disturbance caused by storms in reservoirs may be unnaturally large due to land use practices within the watershed. Daily to weekly limnological sampling was conducted during spring and summer 2001-2003 and changes in turbidity (measured as non-volatile suspended solids, NVSS) and algal biomass (measured as chlorophyll a) as well as rotifer abundance was analyzed. Storms varied in both magnitude of peak discharge and frequency. During storms in which daily samples were taken, changes in turbidity were strongly correlated to storm intensity. Overall, turbidity was higher during periods of increased discharge than during periods exhibiting base flow or near base flow conditions. Chlorophyll levels decreased in association with storms due to increased turbidity and discharge. In general, chlorophyll levels were highest during the periods between storm events. The response of rotifer abundance seemed to be related to both magnitude of peak discharge and frequency of storm events, with high frequency and discharge causing decreases in abundance and low frequency or discharge causing increases in abundance. Overall, however, rotifer abundance was greater during calm periods.
NB33R-05 1330h
Status of Lake Superior Benthic Macroinvertebrates, 1994-2003
Recently documented changes to benthic communities in the lower Great Lakes have created concerns about the status of benthic macroinvertebrates in Lake Superior. This lakewide study was conducted to ascertain their status in U.S. nearshore waters of Lake Superior. Benthic macroinvertebrates were collected from 27 sites representing the U.S. nearshore waters (20 to 110 m) of Lake Superior in 1994, 2000, and 2003. No significant differences in total benthic macroinvertebrate abundance, or abundances of oligochaetes, clams or chironomids were detected between years. Abundance of the amphipod Diporeia spp. was lower in 2000 than in 1994 and 2003. The oligochaete trophic index, a measure of relative abundance of species tolerant of varying degrees of organic enrichment, did not differ between years. Diporeia exhibited a bimodal depth distribution, with peaks in abundance at depths of 30 to 40 and 60 to 70 m. Oligochaetes were most abundant at 50 to 60 m depth, clams between 30 and 70 m, and chironomids at less than 30 m, with a secondary peak at 50 to 60 m. The spatial and temporal variability observed in Lake Superior benthic macroinvertebrate communities has implications for sampling design for environmental assessment. This abstract does not necessarily reflect USEPA policy.
NB33R-06 1330h
Lake Disruptions on Sediment Mobility and Effects on Benthic Chlorophyll
Watershed structure can have a profound effect on physical, chemical, and biological characteristics of streams. We investigated stream reaches above and below lakes in three watersheds that varied in the size and numbers of lakes in the Sawtooth Mountains to address how lakes affect sediment mobility and how this in turn affects algal biomass. During base flow, we gathered physical data such as pebble counts, stream geometry, and gradient to calculate sediment mobility. Chlorophyll a was measured as the biological response variable. We found that excess shear stress in lake outflows was <1, while excess shear stress was >1 in inflows, indicating that inflow sediments were mobile. Chlorophyll a concentrations were at least 10X greater at outflow sites compared to inflow sites. At one watershed where chlorophyll a was measured at a variety of sites on rocks of median sediment size (D50), there was a positive correlation between D50 and algal biomass (R2 =0.31, p=0.02). Other experiments indicated that lower chlorophyll a at inflow sites was due to increased bed mobility and not due to abrasion by bedload. Together, these results support the hypothesis that sediment trapping by lakes leads to increased substrate stability, and in turn allows increased periphyton growth.