Encyclopedia of Global Resources part 116 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the . Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 1078 Selenium Global Resources evaporation basin for the drainage waters of the western San Joaquin Valley. Originally this was surface water but by 1981 almost all the water entering the reser voir was subsurface agricultural drainage water from irrigated agricultural fields. Because of interest in saving some of Northern California s disappearing wetlands water that entered the reser voir was diverted and used to preserve wetlands in the adjacent Kesterson National Wildlife Refuge in Merced County California. By 1983 the incidence of embryo deformity and mortality among aquatic birds nesting in the Kesterson Reservoir was alarmingly high. No one immediately suspected when the drainage water was used in the wetlands that it contained almost milligrams of selenium per liter a selenium concentration one thousand times greater than in naturally occurring drainage in the region. As a consequence phytoplankton in the reservoir accumulated selenium to levels 100 to 2 600 times greater than normal. Since these plankton formed the base of the food chain in the reser voir the levels of selenium in the fish frogs snakes birds and mammals also increased to levels 12 to 120 times greater than normal 20 to 170 milligrams of selenium per kilogram . Migratory birds that fed on plants invertebrates and fish in the reser voir contained up to 24 times the normal level of selenium in their tissue. Between 1983 and 1985 an estimated one thousand migratory birds died as a consequence of selenium toxicity. To protect the migratory birds from future selenium exposure the reservoir was drained in 1988 and filled with dirt effectively bur ying and isolating the excess selenium. Selenium is a good demonstration of the adage the dose is the poison. Trace quantities of selenium are nutritionally essential and blood concentrations of milligram of selenium per liter are nutritionally sound. The minimum lethal concentration of selenium in tissue however is only to milligrams of
