Science Serving Maryland's Coasts

Jill Stevenson, Columbia University

Class Year: 

Project Title: 

Phosphorus Speciation in Brackish Water Marsh Soils of Chesapeake Bay


Tidal wetlands are highly productive ecosystems, which lie between open waters and the upland area surrounding Chesapeake Bay. The nutrient cycling within these marshes is strongly affected by the presence of phosphorus sorbing mineral phases in sediments. The objectives of this study were to identify the primary forms of phosphorus in sediments of varying salinity tidal marshes of Chesapeake Bay by observing phosphorus profiles and to assess the importance of iron to phosphorus retention in these marshes. Phosphate flux is thought to be controlled by the presence of surface iron oxides (Scudlark and Church, 1989.) Because of their high productivity, brackish marsh sediments contain more total phosphorus and a greater fraction of organic phosphorus: total phosphorus than subtidal sediments from Chesapeake Bay. Marsh sediments act as a nutrient burial zone, although they comprise less than 4% of the total estuarine area of the Choptank River Drainage Basin, brackish marshes are capable of absorbing up to 10% of the total phosphorus loaded into the basin. Nine cores were collected from three main locations on the Eastern Shore of Maryland using a 50 cm McCauley corer. The ability of marsh sediments to retain organic phosphorus and iron- bound phosphorus in varying redox potentials was determined by IN HC1 extraction for 18 hours and further spectrophotometric analyses. Total iron content was measured with an atomic absorption spectrometer.