Water Quality in the Central Arizona Basins, Arizona, 1995-98

Cordy, G.E., Gellenbeck, D.J., Gebler, J.B., Anning, D.W., Coes, A.L., Edmonds, R.J., Rees, J.A.H., and Sanger, H.W., 2000, Water Quality in the Central Arizona Basins, Arizona, 1995-98: U.S. Geological Survey Circular 1213, 38 p.; Stream and River Highlights Most of the perennial streams in the Central Arizona Basins (CAZB) Study Unit drain relatively undeveloped basins in the Central Highlands that are covered by forests and (or) rangeland. The water quality of these forest/rangeland streams is primarily determined by natural factors, such as chemical weathering of rocks and soils. About 24 percent of samples from forest/rangeland streams had concentrations of phosphorus that exceeded the U.S. Environmental Protection Agency's (USEPA) desired goal for prevention of nuisance plant growth (eutrophication), whereas nitrate concentrations were typically less than the background levels for streams nationally. More than 75 percent of samples from the Salt River (above reservoirs) exceeded the USEPA drinking-water guideline for dissolved solids; however, rainfall and snowmelt runoff helped dilute these concentrations in reservoirs and in streamflow leaving the reservoirs. In the Basin and Range Lowlands, streams typically flow only when it rains (ephemeral streams). Consequently, a small fraction of the nutrients and dissolved solids applied to the land surface by human, animal, and natural sources is transported to streams. The remaining dissolved solids and nutrients are accumulating in basins and can degrade ground-water quality. Urban streams with perennial flow are sustained by the discharge of treated wastewater (effluent-dependent). Agricultural/urban streams are a combination of wastewater and irrigation return flows. All samples from both the effluent-dependent urban and agricultural/urban streams exceeded the USEPA's desired phosphorus goal for prevention of nuisance plant growth, and dissolved-oxygen concentrations were minimal for fish survival. Organochlorine compounds in streambed sediment and fish tissue from urban and agricultural/urban streams exceeded guidelines for protection of aquatic health and fish-eating wildlife. "Effluent-dependent urban streams are valuable water resources; however, the water quality is poor. "Organochlorine insecticides from past agricultural use persist in streams, streambed sediment, and fish tissue and are a concern because they exceed guidelines for protection of aquatic life and fish-eating wildlife. "Insecticide concentrations in water from streams affected by agricultural and urban land uses were among the highest in the Nation. Trends in stream water quality Water quality of forest/rangeland streams generally is improving over time. From 1950-90, dissolved-solids concentrations decreased in outflow from reservoirs as a result of dilution from increased precipitation and physical and chemical processes in reservoirs. A decrease in nutrient concentrations in forest/rangeland streams in the early 1980s to 1999 could be attributed to decreased contributions from natural sources, better land-use management practices upstream, or increased nitrogen use by aquatic life.