Distribution of Soil P In Everglades Stormwater Treatment Area Wetlands.

Stormwater Treatment Areas of the Everglades were developed to treat agricultural discharge from the Everglades Agricultural Area.  In order to assess the P status of the STAs, we measured different labile and non-labile forms of P to determine the soil allocation of retained P in the ecosystem. Multiple cells of two STAs (STA-5 and 6) were sampled and soil fractionated into labile, Fe-Al bound, Ca-Mg bound, humic-fulvic acid, and residual P pools..  Total P was an average of 53% higher for STA-5 than STA-6.  STA-5 had 314, 17, 55, 58, and 77% higher P than STA-6 for KCl, NaOH-Pi, NaOH-Po, HCl-Pi, and residual fractions, respectively.  The labile P fraction (KCl-extractable) was low for both STAs, averaging less than 1 mg P/kg.  The NaOH-Pi fraction averaged 51 mg P/kg, and overall had the 2^nd lowest P concentration of all fractions.  An average of 154 mg P/kg was found in the humic-fulvic acid fraction, while the HCl-Pi pool contained 108 mg P/kg.  Residual P contains P that is stable and somewhat resistant to decomposition, and this pool contained an average of 68 mg P/kg.   STA-5 showed higher P concentrations in both labile and non-labile pools than STA-6, probably because of higher historic P loading which increased total P.  The similar percentage increase of P in STA-5 compared to STA-6 suggests that P loading only increased the concentrations of the fractions but not the distribution of P among the fractions.  Cells closer to inflow structures generally differed from cells near the outflows, through higher P concentrations in most fractions near inflow points.