ENVIRONMENT Effects of geothermal effluents on eco systems Several environmental concems have the potential to impede development of geothermal energy sources. Among them are hydrogen sulfide emissions (from geothermal steam) and mineral emissions from the cooling towers of geothermal power plants. Under the auspicesof the Assistant Secretaryfor the Environment(U.S. Department of Energy), we are evaluating the effects of hydrogen sulfide and mineral emissions on surrounding ecosystems. Our goal is to determine to what extent these geothermal emissions are actually harmful. For further information contact Joseph H. Shinn (422-6806). Several potential pollutants are associated with the developmentof geothermal energy. Hydrogen sulfide gas separates from geothermal steam in a mixture consisting mostly of carbon dioxide but including traces of ammonia, methane, boric acid, mercury vapor, and other trace gases. Minerals in the hot water associated with geothermal energy production are of concern as they escape from cooling towers, in- filtrate the leaves of nearby trees and plants, and enter streams and lakes. LLNL researchers are involved in studies of the effects of these materials on ecosystems in the vicinity of geothermal power plants. me ee ed we ee The physiological response of vegetation to hydrogen sulfide Very little was known, about the effect of hydrogen sulfide on ecosystems before geothermal development began. Ourexperience told us that the organisms most affected by it would be plants. Woodyplants will respond to sulfur qa 2s dioxide when exposed to concentrations of under 0.10 ppm for a few hours. (Hydrogen sulfide begins to affect human health—by irritating nasal passages in a minor way—only at concentrations an or- der of magnitude above those at which harmful effects on plants are first observed.) We also knew that the uptake of gases by leaf ceils is strongly controlled by the solubility of the gases in water and thatall inorganic forms of sulfur gases are metabolized in the same manner. We hypothesized that foliar injury due to hydrogen sulfide, although significant, would be less than that due to sulfur dioxide and that the long-term effects could include damage to habitat and food sources in forests and damage to crops in agricultural areas. In 1976 we first measured the physiological response of plants to various combinations of geothermal emissions. We placed opentopped chambers around rows of