SPATIAL-DISTRIBUTION OF SOIL NUTRIENTS IN A NORTHERN EVERGLADES MARSH - WATER CONSERVATION AREA 2A

Increased nutrient loading to the northern Everglades from the nearby Everglades Agricultural Area (EAA) has raised concerns of eutrophication of this oligotrophic wetland. A field study was conducted to determine the influence of nutrient loading on spatial distribution of P, N, C, and related physico-chemical parameters in the peat soils (Histosols) of Water Conservation Area 2A (WCA-2A) in the northern Everglades. Field sampling of the top 30 cm of soil was performed at 74 sites across WCA-2A. Isarithmic plots of N and P forms based on geostatistical analyses revealed widespread enrichment of P, especially in areas proximal to surface inflows importing nutrient-laden water from the EAA. Enrichment of less magnitude was shown for soil N, while spatial variability of C, bulk density, ash content, and pH were minimal. Concentration of soil porewater NH4+-N was typically in the 1.5 to 2.5 mg L-1 range in the interior (less impacted) region of WCA-2A, compared with 4 to 8 mg N L-1 near surface inflows at the northern end of WCA-2A. In contrast, soluble reactive P in the Porewater varied from almost-equal-to 100 mug L-1 or less in the interior marsh to >1000 mug L-1 near inflow structures. Mean soil total P at a depth of 0 to 10 cm was 473 mg kg-1 in the interior marsh, compared with 1338 mg kg-1 in the areas adjacent to inflows. Results of this study show that WCA-2A soil has served as a net storage for the increased load of P in nutrient-laden surface inflows. Much of the additional soil P is available for plant uptake, based on the magnitude of P enrichment across a large area. Nutrient enrichment in the soil corresponded with the occurrence of cattails (Typha domingensis Pers. and T. latifolia L.) in areas previously dominated by sawgrass (Cladium jamaicense Crantz).