State Water Resources Research Institute Program

Project ID: 2009WI217B
Title: The Lethal and Sublethal Effects of Elevated Groundwater Nitrate Concentrations on Infaunal Invertebrates in the Central Sand Plains
Project Type: Research
Start Date: 3/01/2009
End Date: 2/28/2010
Congressional District: 6
Focus Categories: Nitrate Contamination, Groundwater, Ecology
Keywords: groundwater, nitrate, aquatic invertebrates, Wisconsin
Principal Investigator: Stelzer, Robert Scott
Federal Funds: $ 15,649
Non-Federal Matching Funds: $ 3,753
Abstract: This proposed project addresses the University of Wisconsin System Groundwater Research Program priority of identification and characterization of chemical pollutants in groundwater and their threats to ecosystems and human health, including the type, toxicity and persistence of degradation products.

GROUNDWATER PROBLEM TO BE ADDRESSED: In many regions of Wisconsin and throughout the world, groundwater has elevated nitrate concentrations. Although the threats of high groundwater nitrate (> 10 mg NO3-N/L) to human health are well understood, much less is known about effects on animals in groundwater dominated habitats, such as the sediments of gaining streams. Shallow groundwater associated with streams in the Central Sand Plains of Wisconsin has nitrate concentrations as high as 100 mg NO3-N/L. In these systems, infaunal (sediment dwelling) invertebrates, such as amphipods, are exposed to nitrate concentrations that exceed those known to cause lethal and sublethal toxic effects in a variety of animals (fishes, amphibians, aquatic invertebrates).

RELEVANCE OF PROPOSED RESEARCH: Little is known about the toxic effects of elevated nitrate concentrations on invertebrates in shallow groundwater dominated sediments. Information about the sublethal effects of nitrate on aquatic invertebrates is particularly scarce even though sublethal affects of elevated nitrate may be more pervasive than lethal effects in freshwater ecosystems. The proposed research will help fill these important gaps in the understanding of nitrate toxicity in freshwater ecosystems.

OBJECTIVE: The main objective of the proposed research is to assess the lethal and sublethal effects of elevated nitrate concentrations in shallow groundwater on aquatic infaunal invertebrates in the Central Sand Plains of Wisconsin.

APPROACH: The investigators will use combined laboratory and field approaches to determine acute and chronic effects of elevated groundwater nitrate on mortality, growth rates, respiration rates and tissue nitrogen content of Gammarus pseudolimnaeus, a ubiquitous and locally abundant infaunal invertebrate found in streams throughout the Wisconsin Central Sand Plains and the Upper Midwest. In laboratory experiments, they will expose Gammarus to nitrate concentrations (1 to 512 mg NO3-N/L) encompassing the range which has resulted in toxic effects in other animals, including insects and fishes. A number of indicators of toxicological stress, including LC10s, LC50s, no-observed-effect concentrations (NOECs) and lowest-observed-effect concentrations (LOECs), will be determined. In field experiments, Gammarus will be exposed to different in situ porewater nitrate concentrations in the shallow sediments of Radley Creek (Waupaca County, Wis.), which exhibits very large spatial variation in porewater nitrate concentrations (0.3 to 100 mg NO3-N/L). In addition to the principal response variables described above, porewater nitrate concentration and other variables that may affect amphipod performance (dissolved oxygen concentration, water temperature, sediment organic matter) will be measured and incorporated in multiple regression models. The aim of the models will be to assess the influence of porewater nitrate and other variables on Gammarus mortality and performance in nature.

USERS OF PROJECT FINDINGS: The results of this project will be useful to toxicologists, biogeochemists, limnologists, stream ecologists, and entomologists who are interested in nitrate toxicity, nitrogen cycling or invertebrate ecology in freshwater ecosystems. The outcomes of the project will also help inform decision makers about nutrient management in watersheds and about the management of stream food webs.

Progress/Completion Report, 2009, PDF

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