Increasing the Phosphorus Sorption Capacity of Southeastern Coastal Plain Soils Using Water Treatment Residuals

Long-term animal manure applications to many sandy Coastal Plain soils has resulted in the accumulation of excess soil phosphorus (P). When soils contain excessive P concentrations, dissolved phosphorus (DP) can be desorbed with water and transported into streams and rivers via runoff and leaching. The addition of DP into nutrient-sensitive Coastal aquatic ecosystems can then stimulate aquatic weed and algae growth and accelerate eutrophication. Augmenting a soil’s P sorption capacity using alum-based water treatment residuals (WTRs) may be a new chemical-based method for increasing the soil’s capacity to retain P. Laboratory experiments were conducted to determine if WTRs mixed into Autryville (Loamy, siliceous, subactive, thermic Arenic Paleudults) and Norfolk (Fine-loamy, kaolinitic, thermic Typic Kandiudults) soils could significantly increase their P sorption capacities. Water treatment residuals were obtained on two different occasions from a North Carolina municipal surface water treatment facility. Both WTRs (G1 and G2) were composed of fine-sized river sediments that were flocculated with liquid alum [Al2(SO4)3]. Phosphorus sorption isotherms were determined on the WTRs, the soils, and soil + WTR mixtures of 2.5, 5.0, 7.5, and 10.0% (w/w). The P sorption maximums (Pmax) were determined from the linear form of the Langmuir equation. The Pmax values for G1 and G2 (175 and 85 mg P g−1, respectively) were significantly higher than the Pmax values for the Autryville or Norfolk soils (<1.0 mg P g−1). Mixing WTRs into soils increased their Pmax values several-fold (between 1.7 to 8.5 mg P g−1) relative 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 has the potential to be a new chemical-based best management practice (BMP) for reducing off-site P transport.