Abstract
Evaporation pond as drainage system, and irrigation-induced selenium contamination problem in San Joaquin Valley, California were introduced. In south San Joaquin Valley, irrigated agriculture has performed for about 100 years without perfect drainage system. From 1971 to 1982, drainage water from this area was introduced into the reserviors in Kesterson National Wildlife Refuge. In 1982 scientists discovered that irrigation drainage water had contaminated the reservior with toxic level of selenium, and wildlife suffering by selenium toxicity. Now in this area, evaporation ponds are using instead of agricultural drainage system. Since the area of evaporation pond occupy 10% of irrigation land and the pond water contains toxic materials, management of the evaporation pond and purification of pond water are very important for sustaining the agriculture in this area. One of three ponds analyzed in this study contained 8 times of selenium in water compared to US-EPA standard (10ng/ml). Selenium species detected in pond water were selenite, selenate and organic selenium. It was assumed that the dominant inorganic selenium species expected in pond water was selenate. But the results of the present study indicated that the dominant inorganic selenium species in pond water is selenite, and the organic selenium showed a significant amount, suggesting that selenite and organic selenium are important as well as selenate on considering of selenium elimination from water system.
