Tuesday, November 14, 2006
184-1
Potential Phosphorus Dissolution From a Restored Wetland.
C.S. Brownfield, D.H. Hesterberg, and M.J. Vepraskas. North Carolina State University, Department of Soil Science, Box 7619, Raleigh, NC 27695-7619
When agricultural land is converted to a wetland, reduction of the soil will potentially increase the mobility of phosphorus. Our objectives were to measure reductive P dissolution in soil samples ranging from organic to mineral soils collected from a drained, 250 ha Carolina bay that had been farmed for up to 30 years before wetland conditions were restored. Total soil P concentrations ranged between 8 and 19 mmol P kg-1 (250 and 600 mg P kg-1) in the whole soil and 19 and 90 mmol P kg-1 (602 and 2800 mg P kg-1) in the silt + clay fractions, with 57% to 78 % being organic P in the latter fraction. Aqueous suspensions of the silt + clay fractions of field moist, surface-soil samples were subjected to microbial reduction in a continuously-stirred reactor while monitoring pH , redox potential (Eh), dissolved reactive P (DRP), dissolved total P, dissolved organic carbon (DOC), dissolved Fe, Al, and Mn, and evolved CO2 (microbial activity). Eh decreased from an average of 510 mV to -20 mV (pH 4.5-6.4) within 20d of reduction. During 25 d of reduction, there was no change in DRP in five of the six soil samples, while DRP doubled in the suspension of silt + clay from a deep, organic soil. Our short-term incubation results suggest that dissolution and off-site movement of P from this restored wetland will not be a problem, except perhaps from the area of the deep, organic soil, a <100 ha area located in the center of the wetland.