Nutrient profiles in the everglades: examination along the eutrophication gradient.
We examined the concentration profiles of nutrients in the surface water, 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 showed an exponential decrease downstream of the inflow structures attaining background values of 7-12, 7-9 and 5-6 micrograms l-1 of TP, TDP and PO4-P, respectively, at distances of 8-10 km. The pore water PO4-P concentration in the oligotrophic areas ranged between 5 and 10 micrograms l-1. Molar ratios of dissolved inorganic N and P suggest a possible switch in nutrient limitation in the surface water from P in the oligotrophic areas to N in the eutrophic areas (DIN:DIP approximately 5). External nutrient loading has also contributed to a three- to four-fold increase in soil TP concentration and enhanced pore water PO4-P in the northern marshes. Unlike P, C and N concentration in the soils remained fairly uniform along the eutrophication gradient. 210Pb dating of soil cores suggests that the increase in soil P concentration (from < 500 to 1500 micrograms 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 inflow structures in 1960-1963 through which agricultural drainage from the Hillsboro canal enters the marshes. Organic P makes up 70-90% of the total P in the soils as uptake by algae and macrophytes is the primary 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.
Vaithiyanathan
P
P
Duke University Wetland Center, Loxahatchee, FL 33470, USA.
Richardson
C J
CJ
D002118:Calcium / Q000032:analysis; D002244:Carbon / Q000032:analysis; D005068:Eutrophication; D005431:Florida; D005618:Fresh Water / Q000032:analysis*; D009566:Nitrates / Q000032:analysis; D009573:Nitrites / Q000032:analysis; D010710:Phosphates / Q000032:analysis; D011786:Quality Control; D000644:Quaternary Ammonium Compounds / Q000032:analysis; D012987:Soil / Q000032:analysis*
D009566:Nitrates; D009573:Nitrites; D010710:Phosphates; D000644:Quaternary Ammonium Compounds; D012987:Soil; D002244:Carbon; D002118:Calcium