Organic matter turnover along a nutrient gradient in the Everglades

Organic matter accumulation in wetlands represents a potential long-term sink and source for organic carbon (C) and associated nutrients and contaminants. Turnover of organic C was measured in a nutrient-impacted sawgrass and cattail marsh in Everglades Water Conservation Area 2A (WCA-2A). Controlled laboratory incubations and a microcosm study were conducted to determine potential rates of C mineralization in plant litter and peat along a gradient of phosphorus (P) enrichment. Field incubations at 10 sites along the nutrient gradient measured in situ organic matter decomposition rate throughout the floodwater, litter and peat profile.; Organic C mineralization in wetland microcosms was significantly enhanced by interactive effects of increased P availability and decreasing water table. Approximately 90% of the variability in potential organic C mineralization in peat and plant litter, measured under aerobic and anaerobic conditions, was explained by total P and lignocellulose content of the organic substrate. Anaerobic mineralization rates were 32% of the rates measured under aerobic conditions. In situ organic matter decomposition rate was higher in nutrient-enriched areas of WCA-2A than in the low-nutrient interior marsh. Decomposition rate typically was at a maximum in the floodwater and litter layer and decreased with depth in the peat profile. Field studies provided evidence that microbial decomposers obtain nutrients, especially P, from the surrounding floodwater and soil porewater as well as from the organic substrate.; Results of laboratory and field studies indicate that organic C turnover in WCA-2A is strongly affected by P availability, although O{dollar}sb2{dollar} availability is the major controlling factor. Availability of C (substrate quality) and nitrogen (N) may limit turnover rate under P-enriched conditions. Experimental findings from these studies provide insight into the effects of accelerated nutrient loading on C cycling and net accumulation of organic matter and nutrients in wetlands.