The Lethal and Sublethal Effects of Elevated Groundwater Nitrate Concentrations on Infaunal Invertebrates in the Central Sand Plains

Background/need: In many regions in Wisconsin, and throughout the world, ground water is elevated in nitrate concentration. 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 ground water 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). There is also a large need to determine how nitrate is processed in Wisconsin ecosystems that receive
high amounts of nitrate in groundwater. In addition to nitrate toxicity, this project also addressed removal of nitrate, and denitrification in particular, in a Wisconsin stream ecosystem that receives groundwater with high nitrate concentration.

Objectives: The main objectives of the research project were: 1) to assess the lethal and sublethal effects of elevated nitrate concentrations in shallow ground water on aquatic infaunal invertebrates in the Central Sand Plains of Wisconsin, and 2) to determine how groundwater nitrate processing and profiles changed with sediment depth in a sand plains stream.