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I I I I I I I I 1 I I I I I I I I I I. are classified water quality limited due to violations of fecal coliform standards, however these are likely to be reclassified as effluent limited under new gUidelines from EPA. Eutrophication problems, characterized by nuisance algal growths, low dissolved oxygen levels and high nutrient con- centrations, have been observed in Elephant Butte and Cochiti Reservoirs, in the lower reaches of the Rio San Jose and the Santa Fe River, and in the Pecos River mainstem below Carlsbad. Violations of dissolved oxygen stan- dards have occurred. In the Rio Grande immediately downstream from El Paso in Texas, return flows from municipal and industrial sources and from agri- cultural irrigation have caused high levels of biochemical oxygen demand, fecal coliform bacteria, nutrients and total dissolved solids, and dissolved oxygen concentrations have been below the stream standard. Many of the streams in the Region are characterized by high turbidity levels and sediment loadings. It has been estimated that over 95 percent of sediment carried by New Mexico streams comes from such nonpoint sources as sheet, rill and gully erosion and from erosion of stream beds and banks. Erosion occurs naturally in the Region, and it also is accelerated or induced by many of man's activities such as over grazing of rangeland, road construc- tion, forest harvesting, farming, and mining. Major tributaries contributing sediment loads to the Rio Grande include the Rio Chama, Galisteo Creek, the Jemez River, the Rio Puerco and the Rio Salado, all of which are in WAU's 130201 and 130202. One of the major water quality problems in many parts of the Region is the occurrence of high salinity levels. Natural salt loadings occur in drainage areas comprised of soluable materials such as shale and gypsum. Although stormwater runoff accumulates salt as it flows over the land surface into channels and streams, the major source of dissolved minerals in surface waters is from saline ground water inflows and sprin9 discharges. Galisteo Creek, the Rio Puerco and the Rio Salado contribute significant salt loadings to the Rio Grande in New Mexico (WAU 13020). Average total dissolved solids (TDS) concentrations during 1974-1979 along the Rio Grande mainstem through New Mexico show a continual increase from 200 mg!l at the Colorado stateline to 600 mg!l just above El Paso, Texas. Irrigation return flows, high in salt content as a result of evapotranspiration, also contribute to the increase in 0067 47