Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Within and Upstream from the Amistad National Recreation Area, Texas, 2005-7: Usgs Scientific Investigations Report 2012-5038

To gain a better understanding of the water quality and status of fish and macroinvertebrate communities, the U.S. Geological Survey, in cooperation with the National Park Service and Amistad National Recreation Area, completed a reconnaissance-level survey of the water quality and fish and macroinvertebrate communities in the Devils and Pecos Rivers in and upstream from the Amistad National Recreation Area in southwest Texas during 2005-7. Water-quality conditions during the spring and summer months of 2005 in the Devils and Pecos Rivers were assessed at locations just upstream from the Amistad National Recreation Area, and the composition of fish and macroinvertebrate communities were assessed during 2006 and 2007 in and upstream from the Amistad National Recreation Area and Amistad Reservoir. Water-quality samples were collected at one site on both the Devils and Pecos Rivers. Fish and macroinvertebrates were collected at the water-quality sampling site on each river and at three additional sites on each river. The water-quality constituents of primary concern were total dissolved solids, chloride, sulfate, ammonia plus organic nitrogen, nitrate plus nitrite, orthophosphate, phosphorus, selenium, and selected pesticides. During the spring and summer of 2005, the concentrations of total dissolved solids ranged from 208 to 232 milligrams per liter (mg/L) in samples from the Devils River compared to 1,460 to 2,390 mg/L in samples from the Pecos River. Total dissolved solid concentrations measured in samples collected from the Devils River and Pecos River did not exceed the proposed State of Texas water-quality standard applicable for the segments of each river where samples were collected. During the spring and summer of 2005, chloride concentrations measured in samples collected in 2005 from the Devils River ranged from 11.6 to 12.9 mg/L, compared to chloride concentrations measured in samples collected from the Pecos River, which ranged from 519 to 879 mg/L. Chloride concentrations in samples collected from the Devils River in 2005 were less than the lower quartile (25th percentile) value of 14.0 mg/L reported for chloride concentrations in water-quality samples collected at the same sampling location during 1978-95 by the U.S. Geological Survey as part of the Hydrologic Benchmark Network program. The chloride concentrations measured in samples collected from the Pecos River during the spring and summer of 2005 represented a range of values similar to the interquartile range of 548 to 942 mg/L reported for samples collected during 1974-2007 at the same sampling location by the U.S. Geological Survey as part of the National Stream Quality Accounting Network program. None of the chloride concentrations measured in samples collected from the Devils or Pecos Rivers in 2005 exceeded applicable proposed State of Texas water-quality standards for chloride. Sulfate concentrations ranged from 7.55 to 8.20 mg/L in samples from the Devils River compared to 298 to 503 mg/L in samples from the Pecos River. Concentrations of sulfate did not exceed applicable proposed State of Texas water-quality standards. Ammonia plus organic nitrogen concentrations were reported as nitrogen ranged from 0.12 to 0.14 mg/L of nitrogen in samples collected from the Devils River compared to 0.15 to 0.32 mg/L of nitrogen in samples collected from the Pecos River. Ammonia plus organic nitrogen concentrations measured in samples collected from the Devils River in 2005 were less than the lower quartile (25th percentile) value of 0.23 mg/L of nitrogen for concentrations in water-quality samples collected at the same sampling location during 1978-95 by the U.S. Geological Survey as part of the Hydrologic Benchmark Network program. Ammonia plus nitrogen concentrations measured in samples collected from the Pecos River were similar to the range of historical concentrations measured in samples collected from the same Pecos River sampling location by the U.S. Geologic