Chemical Fractionation of Sediment Phosphorus in Residential Urban Stormwater Ponds in Florida, USA

Abstract

Stormwater ponds collect and transform pollutants (including nutrients, such as nitrogen and phosphorus) in urban runoff and are often hydrologically connected to downstream waters, making it important to maximize their pollutant retention efficiency. A key mechanism for phosphorus (P) removal in stormwater ponds is sedimentation. However, sediment P in stormwater ponds may be present in several chemical forms with varying bioavailability and potential to move from sediments into the overlying water column. The purpose of this study was to characterize the chemical fractions of sediment P in residential urban stormwater ponds, with the goal of better understanding expected movement of P from sediments to water. We used a chemical fractionation scheme to separate sediment P into the following pools: loosely adsorbed and readily available P, Fe- and Al-bound P, Ca- and Mg-bound P, NaOH-exchangeable organic P, and refractory P. From six stormwater ponds in the Tampa Bay, Florida urban area, we found the pool of readily available P was less than 3% of total sediment P, and the refractory P pool was 28–40% of Total P. However, both Fe/Al-bound and Ca/Mg-bound P each accounted for about 18% of total sediment P. These latter pools may become available under anoxic or low pH (<6) conditions, respectively, demonstrating that a change in environmental conditions could cause internal P loading from sediments to pond water.