Description

The West Grassland area consists of 26,690 hectares of federal, state, and private native pasture and seasonal wetlands representing the largest tract of waterfowl habitat in the San Joaquin Valley of California. Subsurface tile drains, designed to remove saline water from the root zone of agricultural crops, have been installed in irrigated farmland of the western San Joaquin Valley since 1960. Although subsurface drainage water contains elevated concentrations of selenium as well as other naturally occurring trace elements and salts, it was used for wetland management for several decades. In the early 1980s it was discovered that selenium in the drainwater caused malformations and reproductive failure in waterfowl at the Kesterson National Wildlife Refuge. Selenium levels in waterfowl tissue where also high enough to warrant the issuance of human health advisories. Beginning in 1985, Agricultural drainwater was no longer applied directly to wetlands, but wetland water supply channels continued to be used periodically to convey agricultural drainwater through wetland areas to the San Joaquin River. Since September of 1996 a new drainwater management program the Grassland Bypass Project GBP, has been diverting the agricultural drainwater through the San Luis Drain, thus removing drainwater from Grassland area channels that are used to supply wetlands. The purpose of this project is to provide a timely assessment of the degree to which drainwater management initiatives have indeed reduced toxicological risk to wildlife in the area. Selenium levels in most bird eggs 93.5 were below the 6.0 ugg level of concern. Somewhat elevated selenium concentrations in fish, tadpole, and invertebrate samples collected mainly from ditches and canals indicate that the selenium problem in the South Grassland area has improved but remains unresolved. Full recovery of the Grassland area wetland ecosystems may not yet be fully realized for two potential reasons: A recycling of a persistent reservoir of residual selenium, and B continuing input of additional selenium into the ecosystems.

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