Microbial enzyme activities in a freshwater marsh after cessation of nutrient loading

Accurate assessment of perturbation and recovery from anthropogenic nutrient inputs in wetland ecosystems is important for resource management decisions. Nutrient availability affects detrital decomposition and sediment accumulation rates, contributing to and helping to maintain changes in plant community structure. In this paper we report patterns of microbial enzyme activities as indicators of change in areas of a subtropical wetland 8 yr after cessation of nutrient loading. Select enzyme (acid phosphatase, beta-glucosidase, and dehydrogenase) activities were assayed on detrital material and surface soils collected from different vegetation communities within impacted and reference (unimpacted) areas. Acid phosphatase activity (APA) did not vary as dramatically as total P (TP) in soil, but was distinctly different in detritus of impacted and reference vegetation communities. The APA in soil and detritus was greatest in the reference sites, particularly in the Panicum area. Beta-glucosidase activity was highest in Typha areas and demonstrated significant temporal variation. Differences in the timing and length of inundation may play a role in observed trends, since the NW Panicum and Cladium reference sites flooded and reached anaerobiosis later in the growing season than did impacted areas. Data from this study indicate ongoing changes in biogeochemical cycling of nutrients in soils and detritus associated with vegetation communities in areas of historic nutrient loading.