Phosphorus accumulation in bottom sediments of retention/detention ponds

Laboratory and field studies were conducted to characterize phosphorus in bottom sediments for retention/detention ponds. The laboratory studies, including batch and column experiments, were conducted to assess possible removal processes. Sediment core samples were collected from detention ponds receiving urban runoff. These cores were analyzed for phosphorus at different layers including accumulated top sediments and the lower parent soil beneath it at a depth of 1, 3, 5, 10 and greater than 10 cm. The phosphorus accumulation rate was found to decline with calculated overflow rates from an average storm. Also attenuation of phosphorus with sediment depth followed an exponential decline. Batch experiments showed a higher adsorption capacity to remove phosphorus for top accumulated sediments than the lower parent soil, which is consistent with data from field studies showing greater phosphorus in the sediments. Phosphorus adsorption can be described by the Freundlich and Linear isotherms. Mass transfer rates varied with phosphorus concentration and contact time. A generalized model was developed to predict phosphorus removal in column studies