DISTRIBUTION AND SOURCES OF PHOSPHORUS IN TIDAL RIVER SEDIMENTS IN THE WASHINGTON, DC, AREA

Sediments in the rivers and basins around Washington, DC, have high co ncentrations of phosphorus, which, based on geographic distributions i s largely derived from urban runoff and municipal sewage. Dissolved-pa rticulate phosphate exchange reactions adn biological uptake of dissol ved phosphorus from the water column may be an added source of phospho rus to the sediments. Concentrations of total sedimentary phosphorus r anged form 24 to 56 mu m P/g-dw, and were highest in areas near combin ed sewer outfalls. As a part of this study, sedimentary phosphorus was fractionated into Fe-P, Ca-P, Al-P, and organic phases using a select ive-sequential leaching procedure. The distribution of the phases in a ll sediments analyzed follow the order, Fe-P > Ca-P > Al-P. Spatial va riations in the amounts of phosphorus in the different phases is relat ed to the sources of phosphorus to the area. The proportions of occlud ed Al-P and organic P are 10-20% of the total P, respectively. This su ggests that phosphorus from natural sources is small compared to anthr opogenic inputs in this area. The high leachable Fe-P and Ca-P in thes e sediments might contribute a substantial amount of P to the water co lumn under conditions of remobilization.