The Salton Sea. Physical and Chemical Characteristics1

The Salton Sea of California lying below sea level in a desert basin, serves as a sump for irrigation water diverted from the Colorado River. The present Sea reached its maximum size and highest surface elevation at the time of its formation in 1907. Due to evaporation at the rate of six feet per year the surface elevation fell from −195 feet to its minimum of −240 feet in 1948, the surface area decreased from about 500 square miles to about 320, and the salt content (salinity) increased from 3.6‰ to about 40‰. Since 1948 increased "wastage" of water into the Sea has raised the surface to −235 feet (1956) and diluted the waters to a salinity of about 33‰. Although the total salinity is approximately the same as that of the oceans the waters of the Sea contain a different proportion of ions, and the pH is slightly higher.The annual range of water temperature is from 10° to 36°C. In spring the surface may become as much as 5° warmer than the bottom, but since the maximum depth of the Sea is about 12 meters, mixing by winds rapidly removes differences between surface and bottom; during most of the year (August to May) there is less than 1°C difference between surface and bottom. Concentrations of dissolved oxygen ranged up to 11.8 mg/L at the surface and 9.3 mg/L at the bottom during winter. During calm periods in summer, however, the water at depths below 8-9 meters became anoxic for periods as long as 1-3 days; the surface waters, too, became depleted of oxygen, but for only an hour or so at about dawn. Concentrations of sulfide as high as 85 µg-at./L, and of ammonia as high as 50 µg-at./L were found during the anoxic periods in summer.