Effects of Varying Redox Potential on P Release from Stream Bank Sediments.

When eroded into stream water, stream bank sediment may function as an internal source of P to the overlying water column. This study investigated P release from stream bank sediments at varying redox potentials. Four sediments, representing major alluvial units in Walnut Creek, Iowa (Camp Creek, Roberts Creek, Gunder, and Pre-Illinoian till) were used. A reactor was specifically designed for this study. Sediment samples were enclosed in 3,500 MWCO dialysis tubing, inserted into simulated stream water, and rotated at a controlled velocity. Oxic and anoxic conditions in the reactor were created by flowing air or nitrogen gas into the reactor. We found that varying oxic and anoxic conditions governed Eh, pH, dissolved organic carbon, and release of P from sediment to the column water. The highest dissolved P concentrations in the column water were exhibited by Camp Creek and Roberts Creek sediments under anoxic conditions, indicating a higher potential for these sediments to function as P sources in anoxic environments.