Response of biogeochemical indicators to a drawdown and subsequent reflood

Temporal oscillations in hydrology are a common occurrence in wetlands and can result in alternating flooded and drained conditions in the surface soil. These oscillations in water levels can stimulate microbial activities and result in the mobilization and redistribution of significant amounts of carbon (C), nitrogen (N), and phosphorus (P). The goal of this study was to experimentally simulate a drawdown and reflood of marsh soil from a nutrient-enriched site and a reference site of a wetland (Blue Cypress Marsh Conservation Area, Florida). The goal was to better understand the changes in biogeochemistry and microbial activities present in these soils as a result of hydrological fluctuations. Measurements of dissolved reactive phosphorus (DRP), ammonia, and nitrate in the floodwater indicated significantly higher (alpha = 0.05) NH4+ and DRP fluxes from the nutrient-enriched site; floodwaters in the cores from both sites contained significant NO3- concentrations (9.6 mg N L-1), which was rapidly consumed over the core incubation period (30 it). Water level drawdown and reflooding initially stimulated the soil microbial biomass, methanogenic rates, and extracellular enzyme activities (acid phosphatase and beta-glucosidase). The anaerobic microbial metabolic activities (CO2) where initially significantly (a = 0.05) enhanced by the reflood, resulting in roughly equivalent rates as the aerobic respiratory activities (CO2), presumably as a function of the high water column NO3- levels. This study illustrates that the reflood event in the hydrological cycles in a wetland can significantly stimulate the activities of hydrolytic enzymes and microbiological communities in these soils.