Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2002
Publication Date: 7/20/2002
Citation: Maguire, R.O., Edwards, A.C., Sims, J.T., Kleinman, P.J., Sharpley, A.N. 2002. Effects of Mixing Soil Aggregates on the Phosphorus Concentration in Surface Waters. Journal of Environmental Quality. 31:1294-1299. Interpretive Summary: Concern over the contribution of phosphorus from eroded agricultural soil to eutrophication is currently widespread. Predicting the effect of erosion on phosphorus concentrations in surface waters, particularly dissolved phosphorus concentrations, has been particularly problematic. In a series of experiments designed to simulate the effect of erosion from multiple soils on phosphorus concentrations in surface water, this study clearly demonstrates how phosphorus released by one eroded soil aggregate may be adsorbed by another, which may result in a lower than expected solution phosphorus concentration in some surface waters. The strength with which an eroded aggregate can release or readsorb phosphorus to and from solution is in part determined by that aggregate's phosphorus buffer capacity.
Technical Abstract: Elevated concentrations of phosphorus (P) in surface waters have been linked to decreased water quality. At any time, the solution P concentration is determined by a complex interaction of inputs of soluble P and sorption/desorption reactions of P with sediments, which often originate from eroded soils. This study investigates what factors control P in solution when soil aggregates with differing P contents are mixed. The experimental mixing was seen as being analogous to what might be expected to occur naturally due to selective erosion events and transport within river systems. Fifteen soils with widely differing properties, but all considered to be overfertilized with P, were each separated into three aggregate size fractions (2 - 52 um, 53 - 150 um, and 151 - 2000 um). Resin-P, water soluble P (WSP), and the P buffer capacity (PBC = resin- P/WSP) were measured for each aggregate size fraction. Water soluble P was smeasured for 11 mixes of the aggregate fractions. The smallest aggregates tended to be enriched with resin-P relative to the larger aggregates and the whole soils, while the opposite was true for WSP. When two aggregate size fractions were mixed, the measured WSP was always lower than the predicted WSP (i.e. the average of the WSP in the two individual aggregates), indicating that WSP released by one aggregate fraction could be resorbed by another aggregate fraction. The magnitude of under prediction, was a function of the proportional difference between the PBCs of the two aggregates being mixed. This work clearly demonstrates how P released by one eroded soil aggregate may be resorbed by another, which may result in a lower than expected solution P concentration in some surface waters.