| Research
Nutrients in the Swan-Canning
Estuary || Stream
restoration of Wilson Creek Ohio River ecosystem study The Ohio River ecosystem study is a collaborative research effort with a fellow faculty member, Dr. Jeff Jack, initiated while I was at the University of Louisville. Diverse projects were supported through funding from various sources, including comparative work on the Ohio, Tennessee and Cumberland rivers with funding from the Department of Energy through Murray State Center for Reservoir Research, and studies of drinking-water contaminants, funded by the Environmental Protection Agency through Western Kentucky University Technical Assistance Program. Most recently we have received funding to participate in EPA’s Environmental Monitoring and Assessment Program focusing on great river ecosystems. Much of the credit for the work we have accomplished goes to three of my former Ph.D. students: Debbie Guelda and Rick Koch, now at Bemidji State University, and Tim Sellers at Keuka College. Dr. Kumud Acharya joined our research group in January 2004 and has initiated new work focusing on nutritional energetics of riverine zooplankton. Information presented below highlights some of our forthcoming findings. Effects of point source loadings, sub-basin inputs and longitudinal variation in material retention on C, N and P delivery from the Ohio River basin. Bukaveckas et al. (forthcoming in Ecosystems; due 2005).
Spatial variability in material fluxes within large river basins may arise from point source inputs, variable contributions from sub-basins and longitudinal variation in material transformation and retention. By measuring instantaneous fluxes throughout the Ohio River basin, we were able to draw inferences about the importance of these factors in determining the overall export of C, N and P from the basin. Our study spanned the lower 645 km of the Ohio River and included all tributaries that contributed at least one percent of the volume of the Ohio River at its confluence with the Mississippi. The intensively cultivated northern sub-basin (Wabash River) contributed a large fraction of N and P entering the Ohio River. In the southern sub-basins (Tennessee and Cumberland rivers), impoundments and less intense cultivation appear to diminish and delay material delivery, particularly with respect to N. The southern rivers account for a proportionately larger fraction of the water entering the Mississippi River during low discharge conditions and this fraction has increased during the past 50 years. The upper portion of the study reach was found to be a net source of CHLa and DOC and a net sink for inorganic N, suggesting that this portion of the river provided a generally favorable environment for autotrophic production. Point source loadings of NH4 were significant inputs to the upper sub-reach but a relatively small component of the overall budget for dissolved inorganic N.
Experimental evidence for density-dependent effects and the importance of algal production in determining population growth rates of riverine zooplankton. Guelda et al. (forthcoming in River Research and Applications; due in 2005)
Food limitation effects on life-history traits of lake zooplankton have been well documented, but few studies have examined linkages between population growth rates and food resources in riverine environments. In rivers, allochthonous inputs of particulate organic matter may mitigate food limitation effects allowing density-independent mechanisms associated with washout (discharge) and feeding interference (turbidity) to assume greater importance. We experimentally manipulated densities of commonly occurring riverine zooplankton, Bosmina longirostris and cyclopoid copepods, within 2000 L mesocosms containing ambient or algal-enriched food resources. The experiment was repeated through time (July, August, September) to represent the range of zooplankton densities and food-resource levels observed in the Ohio River during warm-water, low-flow conditions. High growth rates and low sensitivity to density-dependent effects were observed during July when POC and chlorophyll concentrations were highest. Lower growth rates and stronger response to density-dependent effects were observed during August and September experiments when POC and chlorophyll concentrations were lower. Direct manipulations of algal abundance resulted in higher growth rates when gains in chlorophyll were accompanied by increases in the edible size fraction (September experiment). Algal C concentrations were found to be a significant predictor of variation in population growth rates for Bosmina but not cyclopoids. Algal C concentrations in the Ohio River rarely fell below experimentally derived minimum food thresholds but were often below saturation thresholds, suggesting that population growth rates were constrained by autochthonous food resources despite the prevalence of allochthonous carbon.
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