Organic nitrogen and carbon transformations in a stream network of Chesapeake Bay watershed

Abstract

Increased export of anthropogenically-derived nitrogen in streams has contributed to increased water quality problems. I investigated in-stream transformations of nitrogen and carbon at the benthic habitat and reach network scale. Both indicated large transformations of dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) along the Gwynns Falls urban stream network. In-stream transformation of DON and DOC declined from headwaters to outflow, with a mean 23% removal of DOC and 57% removal of DON. Transformation rates ranged from in-stream internal loading of 28 g/m<super>2</super>/day to in-stream removal of 740 g/m<super>2</super>/day for DOC (mean: uptake 64 g/m<super>2</super>/day) and in-stream internal loading of 4.8 g/m<super>2</super>/day to in-stream removal of 74 g/m<super>2</super>/day for DON (mean: uptake 3.5 g/m<super>2</super>/day). Urban stream networks may act as both "transporters" and "transformers" of nitrogen and knowledge regarding in-stream N transformations is critical in predicting the sources and removal of nitrogen en route to adjacent tidal waters.