FACTORS AFFECTING PHOSPHATE-UPTAKE BY PEAT SOILS OF THE FLORIDA EVERGLADES

The Florida Everglades constitutes a unique, historically oligotrophic ecosystem threatened by the effects of phosphate (PO4) pollution resulting from agricultural runoff. The present study was designed to determine its capacity to remove PO4 from solution and to study the effects of total P content of the soil, PO4 concentration of the water, autoclaving, and glucose and ammonium addition on PO4 removal by neutral peats of the Florida Everglades. Samples of peat soils were obtained from an area impacted by water with a high total P content and an unimpacted area, both within Everglades National Park. PO4 removal was determined by passing a solution containing a known PO4 concentration (0 to 12.5-mu-M) through a soil column and measuring the difference in concentration between the influent and effluent solutions over time. Removal rates for both soils were nearly constant with time at the lower PO4 concentrations but decreased with time at higher PO4 concentrations. The initial rate and the extent of removal increased linearly with PO4 concentration; these values were consistently higher for the soil from the unimpacted site than for the impacted site. Autoclaving the unimpacted soil diminished the initial rate and extent of PO4 removal by the soil. Addition of 100-mu-M NH4Cl to the unimpacted soil increased the removal of P from 1.0 and 10.0-mu-M solutions. Glucose (15 mg C L-1) had no effect on the removal from 2.5 and 10.0-mu-M PO4 by the unimpacted soil. PO4 removal in natural peats is controlled by a combination of biotic and abiotic processes, the relative importance of which is determined by the concentration of PO4 in the water.