Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2005
Publication Date: 9/8/2005
Citation: Novak, J.M., Watts, D.W. 2005. An alum-based water treatment residual can reduce extractable phosphorus concentrations in three phosphorus-enriched Coastal Plain soils. Journal of Environmental Quality. 34:1820-1827.
Interpretive Summary: Animal production in the southeastern Coastal Plain region of North Carolina is concentrated in small geographic areas. Because limited area for manure disposal is available, animal manure has been over-applied to some soils. This practice has resulted in the accumulation of high levels of soil phosphorus (P). Losses of P via runoff and leaching into streams and rivers can stimulate the growth of algae and aquatic weeds. This condition is undesirable because it lowers the quality of the water for swimming and fishing and increases clean up costs for manufacturers. Phosphorus transport into water systems can be reduced by using water treatment residuals (WTRs), which have the ability to bind with P. The WTRs are a byproduct produced after drinking water purification. A sample of WTRs was obtained from a water treatment plant along with three sandy soils high in P concentrations from eastern North Carolina. Our goal was to show the P binding effectiveness of the WTR. The WTR was mixed into the soils and incubated in the laboratory for 84 days. We compared soil P concentrations before and after the incubation and found that the amount of soil P was reduced by almost 40% compared to an untreated soil. A reduction in soil P concentrations means that less P may be available to move into stream and river systems, thereby potentially lowering the threat of poor water quality.
Technical Abstract: The accumulation of excess soil phosphorus (P) in watersheds under intensive animal production has been linked to increases in dissolved phosphorus (DP) concentrations in rivers and streams draining these watersheds. Reductions in water DP concentrations through forming insoluble soil P phases may be obtainable after land application of alum-based drinking water treatment residuals (WTR). Our objectives were: 1) to evaluate the ability of an alum-based WTR to reduce Mehlich 3 (M3P) and water soluble P (WSP) concentrations in three P-enriched Coastal Plain soils, 2) to model WTR application rates necessary to lower soil M3P levels to a target 150 mg/kg soil M3P concentration threshold level, and 3) to determine potential soil quality impacts. Three soils containing elevated M3P (145 to 371 mg/kg) and WSP (12.3 to 23.5 mg/kg) concentrations were laboratory incubated with between 0 and 6% WTR (w/w) for 84 days. Incorporation of WTR into the three soils caused a near linear and significant reduction in soil M3P and WSP concentrations. In two soils, 6% WTR application caused a soil M3P concentration decrease to below the soil P threshold level. An additional incubation on the third soil using higher WTR:soil treatments (10 to 15%) was required to reduce the mean soil M3P concentration to 178 mg/kg. After incubation, most treatments experienced less than a half pH unit decline and a slight increase in soil electrical conductivity (EC) values suggesting a minimal impact on soil quality properties. The results showed that WTR incorporated into soils with high P concentrations caused larger relative reductions in extractable WSP than M3P concentrations. The larger relative reductions in the extractable WSP fraction suggest that WTR can be more effective at reducing potential runoff P losses than usage as an amendment to lower M3P concentrations.