SOIL REDOX CHEMISTRY LIMITATION OF SELENIUM CONCENTRATION IN CAREX SPECIES SEDGES

Abstract

Soil samples from normally wet and normally dry locations on an alpine study site were analyzed for total selenium, available selenium, pH, and oxidation-reduction potential (ORP). The selenium concentration of Carex species sedges from the same sample locations were also analyzed. Total selenium concentrations in soil were variable, and not correlated with Carex selenium concentration. However, soil available selenium and Carex selenium concentrations were found to be related to soil ORP. Similarly, soil samples maintained in a saturated condition in the laboratory showed rapid decreases in ORP and in available selenium. The conditions that favor the thermodynamic transition between available and nonavailable Se occur within the range of pH and ORP found naturally in soil at this location. Water-saturated soil conditions and the resulting low ORP appear to limit the Se concentration in Carex, a forage plant used by wildlife at the study area.