Phosphorus sorption-desorption of soils and sediments in the Rathbun Lake watershed

Abstract

Livestock grazing in pastures has been identified as a possible factor controlling sediment and phosphorus (P) delivery to Rathbun Lake and associated water bodies in the watershed. The risk of P loss from soils in this watershed was estimated by Mehlich-3 (M3) extractable P, P sorption indices (Smax and k), degree of P saturation (DPS) and P desorption indices (equilibrium phosphorus concentration (EPC) and phosphorus equilibrium buffering capacity (PEBC)) for seven representative soil samples. Most of selected soils had low risk of P loss as indicated by PM3 and DPS. However, EPC values indicated that some soils could potentially behave as sources by releasing P to the water once they become suspended sediments. Selected soil physicochemical properties, including pH, particle size, total C, total N, total P, FeM3, AlM3, CaM3, MgM3, oxalate-Fe and Al (Feox and Alox), dithionite-Fe and Al (Fed and Ald), were correlated with k, EPC, and PEBC to better understand P sorptiondesorption of selected soils. We found that k was positively correlated with Fed (r 2 = 0.96, p < 0.001). PEBC was not correlated with any selected soil physicochemical properties. EPC was positively correlated to FeM3 (r 2 = 0.72, p < 0.05) and Feox (r 2 = 0.62, p < 0.05) suggesting that P desorption was controlled by Fe.