Long‐Term Phosphorus Immobilization by a Drinking Water Treatment Residual

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Abstract
Excessive soluble P in runoff is a common cause of eutrophication in fresh waters. 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 research was undertaken at two Michigan field sites with a history of heavy manure applications to study the longevity of alum‐based WTR (Al‐WTR) effects on P solubility over time (7.5 yr). At both sites, amendment with Al‐WTR reduced water‐soluble P (WSP) concentration by ≥60% as compared to the control plots, and the Al‐WTR‐immobilized P (WTR‐P) remained stable 7.5 yr after Al‐WTR application. Rainfall simulation techniques were utilized to investigate P losses in runoff and leachate from surface soils of the field sites at 7.5 yr after Al‐WTR application. At both sites, amendment with Al‐WTR reduced dissolved P and bioavailable P (BAP) by >50% as compared to the control plots, showing that WTR‐immobilized P remained nonlabile even 7.5 yr after Al‐WTR amendment. Thus, WTR‐immobilized P would not be expected to dissolve into runoff and leachate to contaminate surface waters or groundwater. Even if WTR‐P is lost via erosion to surface waters, the bioavailability of the immobilized P should be minimal and should have negligible effects on water quality. However, if the WTR particles are destroyed by extreme conditions, P loss to water could pose a eutrophication risk.
Funding Information
  • USEPA (CP-82963801)