Spatial distribution of soil nutrients in a northern Everglades marsh: Water conservation area 1

The Florida Everglades developed as a nutrient-poor, rain-fed ecosystem. However, for the past 30 yr, the Everglades have received nutrient-enriched surface water runoff from the adjacent Everglades Agricultural Area (EAA). This study examines the response of a pristine wetland, Water Conservation Area 1 (WCA I), part of the northern Florida Everglades, to nutrient loading as documented by soil nutrient concentrations. During 1979 to 1988, WCA 1 received 138 t total P (TP) and 4919 t total N (TN), retaining 53% of the TP load and 58% of the TN load. Analyses of the spatial distribution of soil N and P showed steep gradients of TP along the western canal boundary, adjacent to inflow points importing EAA runoff. Surficial soils (0-10 cm depth) at interior marsh sites had a mean TP concentration of 368 mg kg(-1), compared with 1028 mg kg(-1) measured at sites adjacent to the western canal. Similar trends were observed for soil Ca and Mg, while C and N did not show the same boundary effects on spatial enrichment. Nutrient-enriched sites also had higher porewater soluble reactive P (SRP; 0.15 mg L-1) and NH4-N (1.65 mg L-1) than unenriched sites (SRP = 0.02 mg L-1 NH4-N = 0.85 mg L-1). Of the 90 sites sampled, 66 sites consisted of sloughs and sawgrass (Cladium jamaicense Crantz); the remaining 24 sites were either cattail (Typha spp.) dominated or had a significant cattail presence. These 24 cattail sites were closest to the nutrient inflow areas and had the highest soil nutrient concentrations.