Dissolved organic nitrogen budgets for upland, forested ecosystems in New England

Relatively high deposition of nitrogen (N) in the northeastern United State s has caused concern because sites could become N saturated. In the past, m ass-balance studies have been used to monitor the N status of sites and to investigate the impact of increased N deposition. Typically, these efforts have focused on dissolved inorganic forms of N (DIN = NH4-N + NO3-N) and ha ve largely ignored dissolved organic nitrogen (DON) due to difficulties in its analysis. Recent advances in the measurement of total dissolved nitroge n (TDN) have facilitated measurement of DON as the residual of TDN - DIN. W e calculated DON and DIN budgets using data on precipitation and streamwate r chemistry collected from 9 forested watersheds at 4 sites in New England. TDN in precipitation was composed primarily of DIN. Net retention of TDN r anged from 62 to 89% (4.7 to 10 kg ha(-1) yr(-1)) of annual inputs. DON mad e up the majority of TDN in stream exports, suggesting that inclusion of DO N is critical to assessing N dynamics even in areas with large anthropogeni c inputs of DIN. Despite the dominance of DON in streamwater, precipitation inputs of DON were approximately equal to outputs. DON concentrations in s treamwater did not appear significantly influenced by seasonal biological c ontrols, but did increase with discharge on some watersheds. Streamwater NO 3-N was the only fraction of N that exhibited a seasonal pattern, with conc entrations increasing during the winter months and peaking during snowmelt runoff. Concentrations of NO3-N varied considerably among watersheds and ar e related to DOC:DON ratios in streamwater. Annual DIN exports were negativ ely correlated with streamwater DOC:DON ratios, indicating that these ratio s might be a useful index of N status of upland forests.