Distribution and biomagnification of selenium in a restored upland grassland contaminated by selenium from agricultural drain water

Abstract

AbstractKesterson Reservoir was a wetland contaminated with selenium (Se)‐enriched agricultural drainage water. As part of the remediation of the selenium contamination, evaporation ponds at Kesterson were dried out and the selenium‐contaminated wetlands were transformed into an upland grassland. The distribution of Se in both the soil and vegetation was monitored in these upland grasslands for 5 years. From May 1989 to September 1993 the distribution of soil Se in the sediment did not change significantly, and the soil Se inventory was not remobilized. Biomagnification of selenium in seven sites representing a gradient of soil Se concentrations was examined for three food‐chain trophic levels. The pattern of Se bioaccumulation shows that there was a considerable increase from the water‐extractable soil Se concentration (source) to the plant (producer) tissue Se concentration and from the grasshopper (primary consumer) tissue Se concentration to praying mantis (secondary consumer) tissue Se concentration. No consistent pattern of increase in Se concentration from the plant to the grasshopper level was apparent. The absolute values of Se bioaccumulation in the insects reflect the available Se concentrations in the soil of the habitat. This relationship indicates that the insects were not actively moving from their local habitat. This discovery suggests that, indeed, a Se biomagnification process did occur in this upland grassland ecosystem. In comparison with the previous state of Kesterson wetland, the upland grassland had Se bioaccumulations less than 10% of those found in the wetland. The upland grassland appears to provide a safer habitat than the wetland with respect to the elevated soil Se concentrations. However, some existing high soil Se concentration sites in the grassland may produce toxic levels of Se in the food chain. Additional research is needed to restore this deteriorated habitat and ensure the safety of wildlife and humans.