PEAT ACCRETION AND N, P, AND ORGANIC C ACCUMULATION IN NUTRIENT-ENRICHED AND UNENRICHED EVERGLADES PEATLANDS

Recent (1964-1989) rates of peat accretion and nitrogen (N), phosphorus (P), and organic carbon (C) accumulation were measured in Everglades soils to characterize the effects of altered hydroperiod and nutrient regimes on the nutrient storage capacity of the Everglades ecosystem. Peat accretion was related to hydroperiod and phosphorus loading. Accretion rates were highest in areas of extended hydroperiod (2.8-3.2 mm/yr) and/or phosphorus enrichment (4.0 mm/yr) and lowest in areas of reduced hydroperiod (1.6-2.0 mm/yr). Rates of accumulation of nitrogen were 3.8-11.6 g-m-2.yr-1 (chiBAR = 8.2 g.M-2-yr-1) and those of organic C were 54-161 g-m-2.yr-1 (chiBAR = 104 g.M-2.yr-1). Accumulation rates of N and organic C were primarily a function of peat accretion rates. Phosphorus accumulation was controlled by both peat accretion and increased soil P content. Soil P concentrations (1248 mug/g) in an area receiving N and P enriched agricultural runoff were 2-3 times higher than P levels at unenriched locations (432-764 mug/g). As a result, rates of P accumulation at this site (0.46 g.m-2.yr-1) were 2-8 times greater compared to unenriched Everglades soils (0.06-0.23 g.m-2-yr-1). Inputs of P (0.53 g.M-2. yr-1) and N (15.5 g.m-2-yr-1) to the nutrient-enriched area of Water Conservation Area (WCA) 2A (via rainfall and surface flow) were nine and twelve times higher than inputs to the unenriched part of WCA 2A. As a result, the efficiency of P removal was lower at the enriched site (87%) than at the unenriched location (100%). Nitrogen removal efficiencies also were lower in the enriched area (75%) as compared to the unenriched area, where N accumulation in peat was 290-450% of the input. The difference in N storage efficiencies between the two sites may reflect differences in N fixation and denitrification in nutrient-enriched and unenriched Everglades peatlands. Our findings suggest that nutrient-enriched agricultural drainage has contributed to increased rates of peat accretion and phosphorus accumulation in areas of the northern Everglades that have been receiving agricultural drainage for the past 25-30 yr. The affected area has functioned effectively as a phosphorus sink, primarily due to increased organic P storage. However, the effects of nutrient loading, especially P, on the long-term stability of the Everglades ecosystem and on the long-term P storage potential of Everglades peats are poorly understood and are currently under investigation.