DISTRIBUTION OF SOIL AND PLANT NUTRIENTS ALONG A TROPHIC GRADIENT IN THE FLORIDA EVERGLADES

Historically, atmospheric precipitation has been the primary source of N and P to the Florida Everglades. Alterations to the natural hydrology, surface water runoff from agricultural lands, and controlled releases from take Okeechobee have increased nutrient loading to the Everglades. A nutrient front encompassing approximately 8000 ha has developed in a northern Everglades marsh, Water Conservation Area 2A (WCA-2A; 44 684 ha), during the last three decades from surface water P and N loading, in addition to atmospheric inputs. Soil cores (0-60 cm) and plant tissue were collected from sawgrass, Cladium jamaicense Crantz, and cattail, Typha domingensis Pers., stands at a distance of 1.6, 5.6, and 9.3 km south of major surface water inflows in WCA-2A: Site N (northern), Site C (central), and Site S (southern), respectively. Although N loading was approximately 10-fold greater at Site N compared with Sites C and S, no significant difference in total N was found between sites at any soil depth. In contrast, P accumulated threefold in soils at Site N compared with Site S (P < 0.05). Organic P accounted for approximately 75% of the total P. Acid-extractable inorganic P (HCl-P(i)), as an indicator of Ca-bound P, accounted for 80% of the inorganic P and was significantly correlated to dissolved P concentrations of the soil pore water (r = 0.89). Alkali-extractable inorganic P (NaOH-P(i)), as an indicator of the Feand Al-bound P, comprised 20% of the total inorganic P. High pH values (> 8.0) were measured from pore water associated with benthic algal mats. Interstitial P concentrations were 2 to 3 orders of magnitude higher at Site N (> 1000 mug L-1) than at Site S (< 4 mug L-1) and plant tissue N/P ratios at Site N and C were lower, 11:1 compared with 40:1 at Site S. These data suggest P may be an important nutrient limiting primary productivity in the Everglades and that Ca-P precipitation, catalyzed by algal photosynthesis, may be an important mechanism for soil P assimilation.