Assessment of Avian Selenium Exposure at Agroforestry Sites in California : Final Report
Dr Joseph P. Skorupa Tom C. Maurer Steven Detwiler
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The west-side and southern end of the San Joaquin Valley in California is often poorly drained and infiltration of saline water into the root zone of crops affects a significant portion of the area. One option available to growers is installing subsurface tile drains to remove the saline groundwater and discharging it into large evaporation basins; however, this water often contains high concentrations of elements along with the salts. A chief element of concern, shown to have ecotoxicological significance, is selenium (Se). Alternatives to evaporation basins reused subsurface drainwater to grow salt tolerant crops leading to smaller evaporation basins. In early systems eucalyptus trees were commonly utilized and thus the practice was termed “agroforestry”. More elaborate management configurations incorporate salt tolerant traditional crops (cotton), non-traditional halophyte crops (pickleweed), eucalyptus trees, and small terminal solar evaporators with sequential recovery and re-use of drainage waste water. These systems are referred to as Integrated On-Farm Drainage Management (IFDM) or drainage “reuse facilities.” In 1996, U.S. Fish and Wildlife Service staff collected a small set of waterbird eggs from two agroforestry sites. These samples yielded the highest rates of selenium-induced teratogenesis (embryo deformities) ever reported. These findings highlighted the urgent need for a broad scale assessment of wildlife use of agroforestry sites prior to any further substantial expansion of agroforestry acreage. A range of agroforestry sites was monitored for avian reproductive activity over three seasons. Fifteen species of migratory birds were documented to nest at agroforestry study sites. Avian nests were located in every habitat component of IFDM plots—proving that these sites are capable of attracting both foraging and nesting birds. Selenium-typical, embryonic deformities were documented among nesting shorebirds along with instances of highly elevated egg selenium concentrations. This investigation has confirmed that agroforestry or IFDM sites are not without attendant risks; however, the question regarding the relative utility of this particular drainwater management option is more a function of realized risk to wildlife in light of the available alternatives. IFDM sites have reduced wildlife risks by about 80 percent compared to the alternative of operating a traditional evaporation basin to dispose of drainage water. Short of management alternatives that preclude the generation of seleniferous drainwater in the first place (e.g. land retirement), some form of disposal becomes necessary. In this context, IFDM becomes an attractive option. Management actions at IFDM sites that avoid or minimize avian exposure to selenium are discussed. During this study, as a direct result of preliminary best management practices recommendations provided to site operators, the documented rates of embryo deformity decreased by an order-of-magnitude.
U.S. Fish and Wildlife Service
http://www.fws.gov/Sacramento/EC/Investigations-And_Prevention/Agroforestry/Documents/Agroforestry%20Final.pdf, 4 MB
Sacramento Fish and Wildlife Office