Document: JOH-3-60-10

Effects of drawdown on phosphorus dynamics of a subtropical wetland.

WHITE, J.R.*, K.R.REDDY and I.CALZADA-BUJAK

University of Florida, Gainesville, Fl USA ¹

Abstract:
Accretion of organic matter can constitute a major sink for phosphorus (P) in wetlands. Alternating flooded-drained conditions in organic soils have demonstrated increased soluble P floodwater concentrations in some wetlands. Phosphorus retention/release of newly accreted soils should be evaluated under various hydrologic conditions to guide management policy and to forecast the potential efficiency of treatment wetlands. We investigated the influence of hydrology on P release from soils of the Everglades Nutrient Removal Project (ENRP), a treatment wetland designed to reduce P levels in agricultural drainage waters flowing into the Everglades. Intact soil cores were collected, 9 each at inflow, interior, and outflow stations. A 20 cm floodwater depth was aerated and replaced every 30 days to simulate the wetland's hydraulic retention time. Treatments investigated were: 90 days continuous flooding, 30 days drawdown-drying, and 30 days drawdown followed by 90 days flooding. Soluble reactive P and soluble total P concentrations were measured in the floodwater over time as well as changes in the microbial pool and activity. Highest P flux occurred under continuous flooding at the inflow, decreasing towards the outflow. P flux decreased significantly upon drawdown-reflooding suggesting this management strategy increased P retention in these soils. Consequently, implementing a short-term drawdown may be a beneficial management tool for the ENRP resulting in both soil consolidation and P flux reduction from recently accreted organic soils.

Keywords: phosphorus, constructed wetland, Everglades

This abstract is being presented at: 1:45 PM in session:
Oral Session #13: N Fixation and Biochemical Patterns.