NITROGEN ALTERATION OF SURFACE AND SUBSURFACE WATER IN TWO ADIRONDACK WETLANDS

Changes in subsurface and in-stream nitrogen (N) water chemistry were measured through two riparian wetlands within the Archer Creek watershed in the Adirondack Mountains of New York State from March 1–July 31, 1996. Both of the wetlands contained well-defined surface water inlets and outlets. This research was conducted to determine whether changes in subsurface water chemistry within the wetlands had a significant impact on the N chemistry of stream water passing through the wetlands. One wetland was dominated by Sphagnum herbaceous growth and had peat depths that ranged from 0-3.5 m. A second wetland had herbaceous growth dominated by a variety of grasses and sedges and peat depths that ranged from 0-0.5 m. Average N concentrations at the wetland perimeter were 1.5, 0.5, and 18.6 µ mol L^-1 for NH₄⁺, NO₃^-, and DON, respectively, while wetland groundwater N chemistry was 56.9, 1.5, and 31.6 µ mol L^-1 for NH₄⁺, NO₃^-, and DON, respectively. The average concentrations of stream water N species at the inlet to the wetlands were 1.5, 10.1, and 16.9 µ mol L^-1 for NH₄⁺, NO₃^-, and DON, respectively and 1.6, 28.1, and 8.4 µ mol L^-1 at the wetland outlet. The change in total dissolved N (TDN) was greater for subsurface wetland water than for surface water flowing through the wetlands. Nonetheless, hydrologic cross-sections for the Sphagnum wetland showed minimal wetland groundwater contribution to stream flow during the study period. Therefore, in-stream N transformations through the wetlands had a greater influence on surface water N chemistry than groundwater N transformations because in-stream changes affected a greater volume of water. Surface water N input-output budgets indicated that the Sphagnum wetland retained mainly organic N and the sedge wetland retained mostly inorganic N during the study period. Although subsurface N water chemistry was significantly altered as it passed through riparian wetlands, those changes were not reflected in the stream. Consequently, although in-stream N water chemistry transformations were less than groundwater N transformations, they had a greater impact on stream water chemistry.