Soil Phosphorus Release and Storage Capacity from an Impacted Subtropical Wetland
- Jehangir H. Bhadhaa,
- Willie G. Harrisb and
- James W. Jawitz *b
Cattle-based agriculture on sandy soils has generated concern over P leaching within the basin of Lake Okeechobee, Florida. Elevated P concentrations in surface and groundwater relate to P retention capacity of soils. To evaluate P release and storage capacity of impacted soils with fluctuating water tables, four intact soil cores were analyzed (one upland and three wetland) to determine their maximum sorption capacity (S max), equilibrium P concentration (EPC0), and soil P storage capacity (SPSC) up to 160-cm depth. Sorption isotherms were measured for samples at 10-cm depth increments and data fitted to a Langmuir model (r 2 ≥ 0.88). Both EPC0 and water-soluble P were higher at the surface and decreased with depth. Oxalate-extractable Fe and Al correlated with (i) oxalate-extractable P (r 2 = 0.83), and (ii) S max (r 2 = 0.71). In situ pore water concentrations collected using multisamplers were consistently higher than EPC0 values. This discrepancy was much greater for near-surface horizons for which the difference may partially be due to redox-induced release of P previously scavenged by Fe under anaerobic (flooded) conditions. The SPSC values were positive, however, even when discounting Fe (i.e., assuming in situ chemical reduction) for samples from deeper horizons, suggesting that the small discrepancies for these horizons are not attributable to Fe oxidation. All cores had negative SPSC at the surface and high EPC0, suggesting that neither wetland nor upland soils safely sequester additional P. High pore water P values in the surface horizons are consistent with the inference of the surface soils potentially being a source for P.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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