DISTRIBUTION OF PHOSPHORUS IN SEDIMENTS FROM TOMALES BAY, CALIFORNIA

The distribution of phosphorus among six sequentially extracted fracti ons was determined in suspended load and bottom sediments from Lagunit as Creek and Tomales Bay, California. The sequential extraction scheme was a modification of the sedex scheme of Ruttenberg (1992), using th e surfactant sodium dodecyl sulfate (SDS) to extract organic phosphoru s. SDS effectively removed organic phosphorus from sediments with litt le interference from inorganic phosphorus containing phases. The distr ibution of phosphorus in the sequentially extracted fractions was simi lar in suspended load and bottom sediments collected from Lagunitas Cr eek and the bay. The concentration of phosphorus in CDB-extractable ir on oxide phases was below detection in all samples. Most of the phosph orus (70-80%) contained in these sediments was found in the organic an d residual phases. Porewaters from sediment cores were analyzed for di ssolved inorganic carbon, ammonium, phosphate, sulfate, iron, calcium and fluoride. Within bay sediments, porewaters were depleted in phosph ate relative to dissolved inorganic carbon and ammonium, suggesting th at phosphate released from organic matter decomposition is being remov ed from the porewaters. Sequential extraction results suggest that app roximately 15% of the phosphate released from organic matter decomposi tion could be removed from the porewaters by adsorption into the excha ngeable phosphorus fraction and an additional 3% may be precipitated a s authigenic phosphate minerals. The remaining phosphate (82%) release d from organic matter decomposition must be either taken up within the sediment mixed layer (0-40 cm) or escapes to the overlying water colu mn. (C) Elsevier Science B.V. All rights reserved.