Influence of phosphorus loading on biogeochemical cycling of nitrogen in northern Everglades soils

The northern Everglades ecosystem has been affected by phosphorus (P) loading from agricultural drainage waters resulting in a distinct eutrophic gradient with high total soil P in areas proximal to surface water inflow points. In addition, the vegetative community has shifted from the natural sawgrass (Cladium, spp)-open water system to dense, monotypic cattail (Typha, spp.) affecting ecosystem function. These effects were distinctly seen in the Water Conservation Area 2A (WCA-2A) of the Everglades.; I sought to investigate the influence of P on the biogeochemical cycling of nitrogen (N) along the eutrophic gradient. The availability and cycling of N in wetlands can affect ecosystem productivity and water quality. Rates of organic N mineralization, nitrification, and denitrification were measured on soil collected from three depths at eight sites along eutrophic gradient. A series of laboratory and field studies were conducted to discern the influence of P on the biogeochemical cycling of N.; Organic N mineralization was significantly increased with P additions in both short term (days) and long term (months) studies. Aerobic mineralization rates were two times higher than rates measured under anaerobic conditions. The size/activity of the microbial pool was significantly increased by P loading, leading to an increase in inorganic N release. Initial nitrification rates appeared to be regulated by the availability of oxygen, while potential rates were influenced both by the microbial pool size and substrate concentration. The activity of denitrifying enzymes in the soil was found to be influenced by nitrate concentrations. However, denitrifying potential appeared to be higher in soils with high total P content.; The results of laboratory and field studies indicate that mineralization, or net release of inorganic N is affected by P availability to the microbial pool. Potential rates of denitrification also appeared to increase with increasing P concentration, however only after the NO3- limitation was exceeded. The increased concentrations of NH4 + may provide a stimulatory effect on the growth of macrophytes in the wetland. Greater macrophyte growth may then alter both ecosystem structure and function by continually cycling N back into organic forms (macrophytes) and re-releasing the inorganic N through decomposition.