Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 13, 2003
Publication Date: March 1, 2004
Citation: Novak, J.M., Watts, D.W. 2004. Increasing the phosphorus sorption capacity of southeastern coastal plain soils using water treatment residuals. Soil Science 169(3):206-214. Interpretive Summary: Off-site transport of the nutrient phosphorus (P) from manure-treated fields can be an important source of water quality issues for aquatic ecosystems along the Carolina coast. For many years, over-application of animal manure to some sandy Coastal Plain soils has contributed to an accumulation of excess soil P. Soils that contain excess P can lose P through runoff and leaching and eventually enrich concentrations in streams and rivers. Transport of P into coastal wetlands and estuaries can cause excess weed and algae growth, which can degrade water quality and the aquatic habitat for fish and shellfish. It would be beneficial if the retention ability of soils that contain excess P was increased using P-sorbing material like chemical amendments. Water treatment residuals (WTRs) are a by-product produced from chemical treatment of river or ground water by municipal drinking water treatment facilities. Aluminum (Al) or iron (Fe) salts are used to settle out sediments in the raw water sources, so the WTRs contain Al or Fe compounds. We determined that WTRs, by themselves, were very effective at sorbing P because they contain a high amount of Al compounds. Mixing the WTRs into sandy, Coastal Plain soils also substantially increased their P sorbing capacity compared to untreated soils. We propose that off-site transport of P from fields receiving animal manure may be reduced after applying WTRs because the soil's ability to sorb P has been increased.
Technical Abstract: Long-term animal manure applications to many sandy Coastal Plain soils have resulted in the accumulation of excess soil phosphorus (P). When soil contain excess P concentrations, dissolved phosphorus (DP) can be desorbed with water and transported off-site by runoff and leaching. Enrichment of DP into nutrient-sensitive coastal aquatic ecosystems can stimulate aquatic weed and algae growth and accelerate eutrophication. Augmenting the soil's P sorption capacity, using alum-based water treatment residuals (WTRs), may be a new chemical-based method for soils to retain P. Laboratory experiments were conducted to determine if WTRs mixed into an Autryville and Norfolk soil could significantly increase their P sorption capacities. Water treatment residuals were obtained on two different occasions from a NC municipal surface water treatment facility. Both WTRs were composed of fine-sized river sediments that were flocculated with liquid alum. Phosphorus sorption isotherms were determined on both WTRs, soils alone, and for WTR + soil mixtures of 2.5, 5.0, 7.5, and 10.0% (w/w). The P sorption maximums were determined from the linear form of the Langmuir equation. The P sorption maximum values for both WTRs were significantly higher than the P sorption maximum values for the Autryville and Norfolk soils (<1.0 mg P/g). Mixing WTRs into soils increased their P sorption maximum values several-fold (from 1.7 to 8.5 mg P/g) when compared to soils with no WTR addition. This experiment demonstrates the feasibility of using alum-based WTRs to increase a sandy soil's ability to sorb more P. Our results suggest that WTR incorporation into sandy soils can potentially be a new chemical-based best management practice to reduce off-site P transport.