Nitrate Source Tracking: Combining Isotopic, Microbial, and Chemical Tracers in a Mixed Land-Use Watershed

Nitrate is a wide-spread source of contamination to ground and surface waters worldwide. Since nitrate has many diverse sources in the environment and is affected by a suite of biological and chemical transformation processes, tracing the source of nitrate to streams is quite difficult, especially when using traditional pollutant accounting methods in mixed land-use watersheds.

15N and 18O nitrate isotopes have been used to resolve organic vs. inorganic stream nitrate sources, but have limited use in mixed land-use watersheds due to problems with source signature overlap for human and animal nitrate sources and with in-stream nitrogen transformations. Microbial source tracking using E. coli may help improve the success of nitrate source discrimination with isotopes, especially with regard to discriminating between human and animal nitrate sources. Inorganic chemicals such as sodium and chloride may help further discriminate among human sources of nitrate.

The objective of this project is to identify point and non-point nitrate pollution sources by monitoring isotopic, microbial, and inorganic chemical tracers in stream water. Specific project objectives include identifying tracer signatures of all major nitrate sources in the watershed, determining E. coli genotype characteristics to aid in separating human, sewage and animal agricultural sources, establishing tracer variations among seasons and flow regimes, and studying the spatial variations of tracer relationships within nested subwatersheds with dominant urban/suburban, forest, agricultural, and mixed land-uses.

The investigators from Penn State University are: Anthony R. Buda, Ph. D. candidate, School of Forest Resources; Dr. David R. DeWalle, School of Forest Resources; Dr. Chitrita DebRoy, Gastroenteric Disease Center, and Dr. Michael A. Arthur, Department of Geosciences.