An isotopic investigation of nitrate processing in shallow groundwater in the White Clay Creek watershed, Pennsylvania

Abstract

Nitrate (N03-) input from fertilizer contaminates surface and groundwater, which can be detrimental to the functioning of ecosystems, decrease biodiversity in streams, as well as cause health problems in humans. In this study, we investigated N03- processing in 2nd and 3rd order streams in the White Clay Creek watershed in southeastern Pennsylvania to determine if denitrification in riparian zones was responsible for decreasing N03- concentrations in groundwater. Isotopic abundances of 15 N and 18 0 can be utilized to investigate the processing of N03-. We found varying N03- concentrations in groundwater wells that were close in proximity to each other (0.076 mg N/L- 2.814 mg N/L). In most sites, we observed an enrichment of 0 15 N as In[N03-] decreased, suggesting that denitrification may be one of the processes that N03- undergoes in groundwater. In order to further elucidate the processes that N03-undergoes, however, it is important to continue isotopic investigations and conduct other water chemistry analyses. These studies can be useful to identify the impact of agricultural input of N03- on stream ecosystems, as well as to determine biological processes that alter these inputs, thereby minimizing the negative effects of N03- on stream ecosystems.