, Volume 48, Issue 2, pp 165-184

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

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Abstract

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, USA. At the Arbutus Lake outlet dissolved organic nitrogen (DON), NO3 - and NH4 + 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 NH4 - 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 NH4 + 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.