Areal and seasonal variations in the quality of surface water in the Alameda Creek basin, California., from 1974 to 1979 were analyzed to determine the effects of wastewater discharges and imported water releases. Statistically significant differences were found among mean values of constituents in streamflow below the treated wastewater discharge points, imported water released from the South Bay Aqueduct, and the combined outflow at Alameda Creek near Niles. During periods before and after the drought of 1976-1977, concentrations of dissolved solids, dissolved chloride, and total nitrate varied inversely with water discharge. From 1974 to 1976, decreases in nutrient values coincided with increased in imported water releases. Values of physical properties and chemical constituents decreased during the spring and summer of 1976. During the second winter of the drought, imported water was decreased, and concentrations of dissolved solids, chloride, and total nitrate increased dramatically in the water at Alameda Creek near Niles. At the upstream tributary, Arroyo de la Laguna, increased chemical property and constituent values during 1976 and 1977 were attributed to decreased natural flow, hence the greater contribution of wastewater treatment plant effluent. Concentrations of several constituents exceeded limits set by the State water-quality objectives for the basin. With the return to normal flow levels in 1978-79, some concentrations returned to predrought levels. (USGS)
