Spatial and temporal patterns of dissolved nitrogen in a Coastal Plain woodland stream

We describe spatial and temporal patterns of dissolved inorganic and organic nitrogen concentrations (DIN and DON) from Payne Creek, a small woodland stream located in the Gulf Coastal Plain physiographic province of west-central Alabama. This region is characterized by low gradient, geomorphically complex drainage systems, which have received little attention from the standpoint of nitrogen biogeochemistry. Unlike observations made in most woodland streams, the DIN pool in Payne Creek is dominated by ammonium (NH₄-N). From 2002-2008, monthly average NH₄-N concentration ranged from 15.5 to 61.3 ppb (overall mean = 28.7 ppb), representing 60-87% of DIN. Average nitrate (NO₃-N) concentration varied among months from 3.0 to 20.8 ppb (mean = 9.1 ppb). Concentrations of both forms of DIN were greatest in summer, lowest in winter, and were inversely related to seasonal changes in discharge. DON concentration varied over time from 16.1 to 126.8 ppb (mean = 66.3 ppb) and on average accounted for 60% of total dissolved nitrogen. Longitudinal changes in DIN and DON concentrations point to the potential for in- and near-stream processes to influence nitrogen export, and appear to be related to the distribution of nitrogen-fixing riparian plants, as well as changes in local geomorphic structure and hydrologic residence time.