Summary

Description

In 1996 and 1997, the U.S. Fish Wildlife Service investigated the biological, chemical, and physical characteristics of four intermittent streams on the Los Alamos National Laboratory in New Mexico. Width, depth, substrate, temperature, velocity, cover, and other physical parameters were measured. Water, sediment, sediment porewater, and biota were analyzed for various inorganic, organic, or radioactive chemicals. Habitat suitability models and rapid bioassessment protocols were used to identify suitable living space for fish and benthic macroinvertebrates. Toxicity tests of water and sediment powerwater and surveys for benthic macroinvertebrates were also conducted. Adult, female, fathead minnow Pimephales promelas were caged in these streams for two months to measure their survival, growth, and contaminant accumulation. Each measured characteristic was compared to the reference site or to applicable criteria, and these ratios were converted into indices of biological, chemical, and physical quality, which were summed into a Water Quality Index in order to identify any stream impairment. All stream segments were found to contain cold, flowing water and a community of aquatic life. Los Alamos Canyon contained a perennial stream above the Los Alamos Reservoir with a population of brook trout Salvelinus fontinalis, and was the reference site for all comparisons. Sandia Canyon, Pajarito Canyon, and Valle Canyon stream segments had no fish populations. The Sandia Canyon stream was composed of waste water effluents, although the proportion and contributions of these discharges and storm water runoff were not quantified. Elevated concentrations of aluminum, barium, chromium, molybdenum, explosives, or polychlorinated biphenyls were found either in water, sediment, sediment porewater, caddisflies Hesperophylax sp., or in the cagedfish. Surface water toxicity to laboratory invertebrates was identified in Valle Canyon, probably from a runoff event, and reproductive toxicity was found in laboratory invertebrates using sediment porewater from Sandia Canyon. However, the causes of toxicity were not conclusive in either event. No surface water toxicity to fathead minnows was found during laboratory testing. In the cagedfish study, factors other than contaminants, particularly flooding, accounted for most of the mortality observed. The benthic macroinvertebrate community was slightly impaired in Pajarito and Valle Canyons, and moderately impaired in Sandia Canyon; where taxa richness was onefourth of that from the reference site. Habitat suitability models for brook trout indicated aboveaverage to marginal quality habitat. The Valle Canyon stream segment lacked the flow volume necessary to fully support adult trout, while excess fines in riffles reduced the quality of potential habitat for trout eggs. Diminished stream velocity, cover, prey abundance and diversity, as well as excess nutrients in the Sandia Canyon reduced potential trout habitat. Scouring, erosion, and embedded substrates also reduced the quality of the habitat for benthic macroinvertebrates. The Pajarito Canyon had fair trout habitat, though the lower portion had reduced flow and fewer deep pools. The Water Quality Index suggested a 30 impairment of the water quality in Valle Canyon, a 22 impairment in Pajarito Canyon, and a 30 impairment in Sandia Canyon compared to the reference site. Physical impacts were greater in Pajarito and Valle Canyons, whereas chemical impacts were greatest in Sandia Canyon. However, the Cerro Grande Fire burned a large portion of these canyons watersheds and therefore, water quality impairments are expected to increase as are restoration efforts. Recommendations were provided to focus water quality management objectives on protection of aquatic life in these intermittent streams. The techniques and evaluation procedures used in this study may be applicable to the water quality assessments of other water bodies in New Mexico.