Nitrogen solutes in an Adirondack forested watershed: Importance of dissolved organic nitrogen

Nitrogen (N) dynamics were evaluated from 1 June 1995 through 31 May 1996 within the Arbutus Lake watershed in the Adirondack Mountains of New York State, U.S.A. At the Arbutus Lake outlet dissolved organic nitrogen (DON), NO3 and NH + 4 contributed 61%, 33%, and 6% respectively, to the total dissolved nitrogen (TDN) flux (259 mol ha−1 yr−1). At the lake inlet DON, NO3 , and NH + 4 constituted 36%, 61%, and 3% respectively, of TDN flux (349 mol ha−1 yr−1). Differences between the factors that control DON, NO3 , and NH4 stream water concentrations were evaluated using two methods for estimating annual N flux at the lake inlet. Using biweekly sampling NO3 and NH + 4 flux was 10 and 4 mol ha −1 yr−1 respectively, less than flux estimates using biweekly plus storm and snowmelt sampling. DON flux was 18 mol ha−1 yr−1 greater using only biweekly sampling. These differences are probably not of ecological significance relative to the total flux of N from the watershed (349 mol ha−1 yr−1). Dissolved organic N concentrations were positively related to discharge during both the dormant (R2 = 0.31; P < 0.01) and growing season (R2 = 0.09; P < 0.01). There was no significant relationship between NO3 concentration and discharge during the dormant season, but a significant negative relationship was found during the growing season (R2 = 0.29; P < 0.01). Biotic controls in the growing season appeared to have had a larger impact on stream water NO3 concentrations than on DON concentrations. Arbutus Lake had a major impact on stream water N concentrations of the four landscape positions sampled, suggesting the need to quantify within lake processes to interpret N solute losses and patterns in watershed-lake systems.