Wetland nitrogen dynamics in an Adirondack forested watershed

Wetlands often form the transition zone between upland soils and watershed streams, however, stream–wetland interactions and hydrobiogeochemical processes are poorly understood. We measured changes in stream nitrogen (N) through one riparian wetland and one beaver meadow in the Archer Creek watershed in the Adirondack Mountains of New York State, USA from 1 March to 31 July 1996. In the riparian wetland we also measured changes in groundwater N. Groundwater N changed significantly from tension lysimeters at the edge of the peatland to piezometer nests within the peatland. Mean N concentrations at the peatland perimeter were 1Ð5, 0Ð5 and 18Ð6 μmol L 1 for NH4C, NO3 and DON (dissolved organic nitrogen), respectively, whereas peatland groundwater N concentration was 56Ð9, 1Ð5 and 31Ð6 μmol L 1 for NH4C, NO3 and DON, respectively. The mean concentrations of stream water N species at the inlet to the wetlands were 1Ð5, 10Ð1 and 16Ð9 μmol L 1 for NH4C, NO3 and DON, respectively and 1Ð6, 28Ð1 and 8Ð4 μmol L 1 at the wetland outlet. Although groundwater total dissolved N (TDN) concentrations changed more than stream water TDN through the wetlands, hydrological cross-sections for the peatland showed that wetland groundwater contributed minimally to stream flow during the study period. Therefore, surface water N chemistry was affected more by in-stream N transformations than by groundwater N transformations because the in-stream changes, although small, affected a much greater volume of water. Stream water N input–output budgets indicated that the riparian peatland retained 0Ð16 mol N ha 1 day 1 of total dissolved N and the beaver meadow retained 0Ð26 mol N ha 1 day 1 during the study period. Nitrate dominated surface water TDN flux from the wetlands during the spring whereas DON dominated during the summer. This study demonstrates that although groundwater N changed significantly in the riparian peatland, those changes were not reflected in the stream. Consequently, although in-stream changes of N concentrations were less marked than those in groundwater, they had a greater effect on stream water chemistry—because wetland groundwater contributed minimally to stream flow. Copyright  2004 John Wiley & Sons, Ltd.