NUTRIENT PROFILES IN THE EVERGLADES - EXAMINATION ALONG THE EUTROPHICATION GRADIENT

We examined the concentration profiles of nutrients in the surface wat er, soil and pore water along the eutrophication gradient of the Water Conservation Area-2A (WCA-2A) in the northern Everglades. Phosphorus levels in the surface waters contributed by the agricultural runoff sh owed an exponential decrease downstream of the inflow structures attai ning background values of 7-12, 7-9 and 5-6 mu g l(-1) of TP, TDP and PO4-P, respectively, at distances of 8-10 km. The pore water PO4-P con centration in the oligotrophic areas ranged between 5 and 10 mu g l(-1 ). Molar ratios of dissolved inorganic N and P suggest a possible swit ch in nutrient limitation in the surface water from P in the oligotrop hic areas to N in the eutrophic areas (DIN:DIP similar to 5). External nutrient loading has also contributed to a three-to four-fold increas e in soil TP concentration and enhanced pore water PO4-P in the northe rn marshes. Unlike P, C and N concentration in the soils remained fair ly uniform along the eutrophication gradient. Pb-210 dating of soil co res suggests that the increase in soil P concentration (from < 500 to 1500 mu g g(-1)) and P accumulation rate (from 0.06 to 0.46 g P m(-2) per year) at the eutrophic site correlates with the installation of in flow structures in 1960-1963 through which agricultural drainage from the Hillsboro canal enters the marshes. Organic P makes up 70-90% of t he total P in the soils as uptake by algae and macrophytes is the prim ary mechanism of P removal in these wetlands. Calcium supply from the underlying bedrock suggested from the surface and pore water chemical profiles has important consequences for P-cycling in the Everglades as Ca-bound P is the major form of inorganic P storage in the soils. (C) 1997 Elsevier Science B.V.