Presented By:

Dr. Troy Rasbury, Ph. D., Associate Professor

Stony Brook University - Department of Geosciences

Subterranean groundwater discharge (SGD) has been shown to be a substantial flux of water volume and accompanying ions and pollutants to the Long Island Sound (LIS). Shallow groundwater on Long Island can have elevated nitrate due to fertilizer, septic water, and animal waste. In summer months addition of nitrate to the LIS can result in eutrophication and damage to the ecological systems.  Efforts to mitigate nitrate flux to the LIS have focused on surface run off and point sources, whereas the SGD input is poorly quantified and potentially at least as important. Nitrogen (N) and oxygen (O) isotopes define fields that overlap, and particularly since processes along the path change the nitrogen isotopes, it can be impossible to know the source of this contaminant. We used boron (B) isotopes, which are a known conservative tracer of source in non-coastal settings, to aid in the identification of nitrate to LIS.  While the fields defined by N and O isotopes of mineral fertilizer and septic water overlap, they are entirely separated in fields defined by N and B. We find that that the nitrate to the LIS from the sites we have studied can be shown to be entirely from mineral fertilizer even though one of the sites was down gradient of a residential area.

Bio For: Dr. Troy Rasbury, Ph. D.