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Material Fluxes Across Wetland Ecotones in Northern Landscapes
Author(s) -
Johnston Carol A.
Publication year - 1993
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.2307/1941912
Subject(s) - wetland , ecotone , environmental science , hydrology (agriculture) , snow , snowmelt , ecosystem , permafrost , spatial variability , ecology , surface water , spatial ecology , physical geography , geology , habitat , geography , geomorphology , statistics , geotechnical engineering , mathematics , environmental engineering , biology
The spatial and temporal distribution of sediment, nutrients, and cations in a 2—ha wetland near Shawano, Wisconsin (USA) was used to evaluate the effect of wetland ecotones on water— and windborne fluxes at ecosystem and landscape scales. Within the wetland ecosystem the ecotones studied were beach ridges deposited by post—glacial White Clay Lake, and stream levees deposited by a second—order stream flowing through the wetland. Snow, soil, and surface water data collected from a 52—point sampling grid were geostatistically analyzed to derive contour plots of within—wetland concentrations. Wind—blown snow form the frozen lake surface accumulated in the wetland behind a low beach ridge to a depth of >65 cm, nearly 7 times the depth at wind—protected areas of the wetland. As a result of this snow accumulation, areas to the lee of the beach ridge annually received 10% more water and 1.5% more inorganic N from direct precipitation than did other areas of the watershed. The use of geostatistical plots to analyze wetland surface waters revealed that: (1) within—wetland spatial variability was high on every sampling date except early snowmelt; (2) on a given sampling date, concentration patterns differed for different elements, sometimes substantially; (3) with the exception of NO 3 —N, the spatial patterns for a given material changed considerably over time; and (4) many of these spatial patterns were interpretable on the basis of observed water flow patterns and wetland ecology. In general, there was a decrease in the concentrations of inorganic solids and most ions, and an increase in Ca + + and chemical oxygen demand with distance from the stream. Overbank fluxes contributed P to the wetland during spring and fall floods, but diluted ambient P concentrations during snowmelt events. During snow—free periods there was a sharp gradient in NO 3 —N concentrations from a streamside value of °5 mg/L to <0.4 mg/L in wetland areas >45 m from the stream. Measurement of the concentration gradient perpendicular to the stream indicated NO 3 —N disappearance rates of 6.6 g/100 m of distance during the spring flood. Soil concentrations of mineral matter and P were highest in areas of the wetland closest to the stream; soil concentrations of ammonium and nitrate were spatially disaggregated, and related to levee elevation. At the watershed scale the wetland retained and/or denitrified 15.2% of the total solids, 13.7% of the N, and 14.2% of the P fluxes from the watershed, thus benefitting the water quality of White Clay Lake.