Wednesday, November 15, 2006 - 2:30 PM
307-6

Long-term Phosphorus Immobilization by a Drinking-water Treatment Residual.

Sampson Agyin-Birikorang1, George O'Connor1, and Lee W. Jacobs2. (1) Univ of Florida, 106 Newell Hall, Gainesville, FL 32611, (2) Dept of Crop & Soil Sciences, Michigan State Univ, East Lansing, MI 48824-1325

Excessive soluble P in runoff is a common cause of eutrophication in fresh waters. Abundant evidence indicates that drinking-water treatment residuals (WTRs) can reduce soluble P concentrations in P-impacted soils in the short term (days to weeks). The long-term (years) stability of WTR-immobilized P has been inferred, but validating field data are scarce. This study was undertaken at two Michigan field sites with a history of heavy manure applications to study the longevity of alum WTR (Al-WTR) effects on P solubility over time (7.5 yr). Amendment with Al-WTR reduced water-soluble P (WSP) concentration by ≥ 60 % of those of the control plots, and the WTR immobilized P (WTR-P) remained stable 7.5 yr after WTR application. We also utilized rainfall simulation techniques to investigate P losses in runoff and leachates from surface soils of the field sites, 7.5 yr after the one-time Al-WTR application. Amendment with WTR reduced dissolved P and bioavailable P (BAP) by > 50 % from both sites, showing that even 7.5 yr after WTR amendment of the sites, the WTR-immobilized P remained non-labile. Thus, WTR-immobilized P would not be expected to dissolve into runoff and leachates to contaminate surface waters or groundwater. Even if WTR-P erodes to surface waters, the bioavailability of the immobilized P will be minimal and will have negligible effects on water quality.