Occurrence and Generation of Nitrite in Ground and Surface Waters in an Agricultural Watershed

The goal of the proposed research is to better understand the extent of nitrite (NO2-) occurrence in groundwater, and the conditions that promote the accumulation of this potentially toxic form of nitrogen in both groundwater and surface waters of agriculturally-dominated catchments. The proposed study will (1) examine temporal patterns of groundwater and surface water chemistry and NO2- occurrence along four upland-to-stream transects, (2) measure NO2- generation in a series of controlled laboratory experiments to quantify rates and likely pathways of NO2- formation; and (3) conduct a survey of groundwater chemistry to determine if NO2- is present in groundwater at diverse locations in Wisconsin. This mixture of monitoring, surveys, and field and lab experiments should substantially expand our understanding of the processes and conditions leading to NO2- accumulation in water, and provide insights into a poorly understood pathway of nitrogen cycling: dissimilatory nitrate reduction to ammonium. This work is motivated by the occurrence of relatively high concentrations of NO2- in several Wisconsin streams and similar reports of elevated NO2- in N-enriched groundwater and interstitial riverine environments elsewhere. If NO2- exists at high concentrations in groundwater, it could pose a health risk to individuals who rely on this drinking water source. Further, discharge of N-rich groundwater leading to NO2- accumulation in streams creates similar stresses on sensitive aquatic communities, even at low concentrations. Thus, this proposal will provide valuable information on the extent of this chemical and the environmental circumstances in which it can occur- critical first steps for dealing with issues of nitrite contamination. We expect this work to be of broad interest to researchers interested in nitrogen biogeochemistry, particularly with respect to groundwater-surface water interactions, as well as to management agencies responsible for protecting in-stream habitats and communities and protecting vulnerable groundwater drinking water sources in agricultural landscapes.