Geochemistry of phosphorus in sediments of rivers and estuaries

Phosphorus is an important limiting element in oceanic productivity. Rivers are the dominant mechanism for transferring phosphorus to the oceans from the continents and estuaries provide an important control on the exogenic cycle of phosphorus. The aim of this study is to understand the behavior and transport of solid forms of phosphorus in estuaries and to quantify the riverine P flux to the oceans. The major emphasis is placed on fluvial and estuarine sediments.;Both the modified extraction procedure and the microanalysis method have been applied to sediments from two world major rivers, the Amazon River and the Yellow River (Huang He). Results for the Amazon indicate that certain adsorbed phosphorus associated with hydrous ferric oxides and hydrous aluminum oxides and silicates, together with organic matter, could be the major forms for P delivery via rivers to the sea by suspended sediments. Results of the Huang He provides an example of a high-turbidity and low-bioactivity river. The phosphorus associated with CaCO;In order to identify and quantify the different forms of phosphorus in sediments, a modified selective extraction procedure has been developed which provides an optimized procedure with high precision. It distinguishes the following forms of phosphorus: organic P (Org-P), P associated with Fe oxyhydroxides (Fe-P), P extractable with pH 4 acetate buffer solution (Acet-P) and resistant P (Rest-P) that is normally assumed to represent detrital apatite. In addition, an independent standardized technique which avoids the problems of operational definitions that are inherent in any extraction method is developed in this study. This is a microanalysis method using the electron microprobe. This method provides a new approach toward a deeper understanding of the behavior of phosphorus in sediments; it is also a useful tool for checking the selective extraction method.