DISTRIBUTION AND BIOMAGNIFICATION OF SELENIUM IN A RESTORED UPLAND GRASSLAND CONTAMINATED BY SELENIUM FROM AGRICULTURAL DRAIN WATER

Kesterson Reservoir was a wetland contaminated with selenium (Se)-enri ched agricultural drainage water. As part of the remediation of the se lenium contamination, evaporation ponds at gesterson were dried out an d the selenium-contaminated wetlands were transformed into an upland g rassland. The distribution of Se in both the soil and vegetation was m onitored in these upland grasslands for 5 years. From May 1989 to Sept ember 1993 the distribution of soil Se in the sediment did not change significantly, and the soil Se inventory was not remobilized. Biomagni fication 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 incr ease from the water-extractable soil Se concentration (source) to the plant (producer) tissue Se concentration and from the grasshopper (pri mary consumer) tissue Se concentration to praying mantis (secondary co nsumer) 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 relations hip indicates that the insects were not actively moving from their loc al habitat. This discovery suggests that, indeed, a Se biomagnificatio n 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 w ith respect to the elevated soil Se concentrations. However, some exis ting high soil Se concentration sites in the grassland may produce tox ic levels of Se in the food chain. Additional research is needed to re store this deteriorated habitat and ensure the safety of wildlife and humans.