Enhanced Understanding of Sediment Phosphorus Dynamics in River Systems with a Simple Supplemental Mass Balance Tool

Abstract

In this study, a mass balance model is developed to improve the understanding of phosphorus fluxes (P fluxes) between sediment and water in a river that is strongly influenced by low-head dams and discharges from wastewater-treatment plants (WWTPs). Before this study, recommendations had been made for dredging the river without a complete understanding of the causes and effects of sediment phosphorus flux. This study changed the way the river dynamics are understood and will provide a basis for watershed management and permitting decisions into the future. The analysis presented focuses on sorption processes at the sediment-water interface as a function of the diagenesis flux rate into the sediment, reactions within the sediments with partitioning between dissolved and particulate forms, and the inorganic phosphorus concentration in the overlying waters. The sediment is modeled as two layers with a thin (0.8 mm) surface aerobic layer and an underlying, thicker (10 cm) anaerobic layer. The phosphorus settling and diagenesis flux and the initial phosphorus concentrations in the sediment and water column are varied to simulate seasonal fluctuations and evaluate the effectiveness of different river management scenarios aimed at reducing phosphorus concentrations. This study shows the importance of including such a microanalysis within water-quality studies to enhance overall system understanding when making water management decisions.