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a Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545 USA
b Hudsonia, Ltd., Bard College Field Station, Annandale, NY 12504 USA
groffmanp{at}ecostudies.org
Calcareous wetlands are of great interest in conservation biology. Previous research has suggested that there are significant differences in soil microbial N cycle processes between calcareous wetlands developed on organic vs. mineral soils. In the study presented here, we measured potential net N mineralization and nitrification, denitrification enzyme activity and soil inorganic N levels at 25 calcareous wetland sites with variable substrate types. We also evaluated the response of N cycling to livestock grazing by sampling at two sites with heavy grazing activity. All N cycle variables were significantly higher in organic soils than mineral soils on a weight basis; however, there were very few differences when results were expressed on an areal (volume) basis because of the low bulk density of the organic soils. The areal results suggest that organic and mineral soil calcareous wetland sites have similar N water quality maintenance values, that is, the ability to absorb N from upland land areas. Heavily grazed sites had significantly decreased pH and increased NO-3 levels relative to undisturbed sites, but the differences were small. The lack of strong differences in N cycle variables between mineral and organic soil sites raises questions about the need to make a classification distinction between calcareous peatlands (fens) and calcareous mineral soil wetlands in nutrient cycling and water quality maintenance contexts.
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