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Water Quality in the Las Vegas Valley Area and Carson and Truckee River Basins, Nevada and California, 1992-96

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WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

Stream Quality || Ground-water quality

Comparison of Stream Quality in the Nevada Basin and Range Study Unit with Nationwide NAWQA Findings

Seven Major Water-Quality Characteristics Were Evaluated for Stream Sites in Each NAWQA Study Unit.
National map Summary scores for each characteristic were computed for all sites that had adequate data. Scores for each site in the Nevada Basin and Range Study Unit were compared with scores for all sites sampled in the 20 NAWQA Study Units during 1992-95. Results are summarized by percentiles; higher percentile values generally indicate poorer quality compared with other NAWQA sites. Water-quality conditions at each site also are compared to established criteria for protection of aquatic life. Applicable criteria are limited to nutrients and pesticides in water, and semivolatile organic compounds, organochlorine pesticides and PCBs in sediment. (Methods used to compute rankings and evaluate aquatic-life criteria are described by Gilliom and others [58].)
Nutrients Were Higher Than the National Median in Las Vegas Wash but Were Lower in the Carson and Truckee Rivers

Nutrient concentrations in surface-water samples from two sites on Las Vegas Wash were greater than the national 75th percentile. The flow at the upstream site is primarily from urban drainage. The downstream site, which receives urban drainage and discharge of tertiary-treated sewage, had a nutrient concentration above the national 99th percentile. All NAWQA samples from this site exceeded the aquatic-life criterion for un-ionized ammonia [29]. However, more recent measurements by other agencies during 1996-97 (Steven W. Miller, City of Las Vegas, written commun., 1998) indicate that un-ionized ammonia concentrations are now below the aquatic-life criteria because of full implementation of tertiary treatment.

nutrient map explanation

Nutrient concentrations in surface-water samples from all sites in the Carson and Truckee River Basins were below the national median. Five of the eight sites had nutrient concentrations below the national 25th percentile. Two of those five, which are in forested headwater areas, had nutrient concentrations below the national 10th percentile. Two sites on the Carson River downstream from agricultural areas in Carson Valley and Carson Desert had nutrient concentrations between the national 25th percentile and median--- higher than the concentrations at sites in the forested headwater areas. Nutrient concentrations at one site on the Truckee River, several miles downstream from the discharge of tertiary-treated sewage effluent from the Reno-Sparks urban area, were the highest measured on the Truckee River, but were less than the national median.

pesticides map Pesticides in Las Vegas Wash Were Greater Than the National 75th Percentile 

Pesticides were commonly detected in water samples from Las Vegas Wash. The Las Vegas Wash site is downstream from most of the urban area, thus, most flow at the site is urban drainage. It is upstream from the discharge of tertiary-treated sewage. Pesticide concentrations at this site were greater than the national 75th percentile. Diazinon and malathion concentrations exceeded aquatic-life criteria [32,33] in 47 and 25 percent of the samples from this site, respectively. Las Vegas Wash transports these pesticides to Las Vegas Bay of Lake Mead, which is a National Recreation Area administered by the National Park Service. Although water samples for pesticide analyses were collected at additional sites in Las Vegas Valley and in the Carson and Truckee River Basins [31], the number of samples and duration of sampling were insufficient for national comparisons [58].

Trace Elements in Bottom Sediment Downstream From Mineral Deposits, Historical Mining Activities, and Urban Areas Were Greater Than the National Median 

Trace elements (arsenic, cadmium, chromium, copper, lead, mercury, nickel, selenium, and zinc) were greater than the national median in bottom sediment at some sites in the Study Unit. Trace-element concentrations in bottom sediment at two sites downstream from the Las Vegas urban area, Las Vegas Wash and Las Vegas Bay in Lake Mead, were between the national median and 75th percentile. These sites are affected by urban drainage and sewage effluent. 

Trace-element concentrations, particularly arsenic and mercury, in the bottom sediment at all sites in the Carson River Basin were greater than the national median. Mercury was present in the upstream forested headwater site of the East Fork Carson River because of naturally occurring mercury ore (cinnabar) [53]. This area is within one of three regions, worldwide, with economically extractable deposits of mercury ore [57]. Arsenic and mercury were much higher at the downstream site on the East Fork Carson River and the three sites on the Carson River, all of which are downstream from historical mining areas. Concentrations at these four sites exceeded the national 75th percentile. 

trace element map
Bottom sediment from two sites in the forested headwater area of the Truckee River Basin had trace-element concentrations less than the national median. Trace elements, particularly lead, copper, and zinc, in the sediments at three of the six sites in the Truckee River Basin were greater than the national 75th percentile. Those three sites are downstream from the Reno-Sparks urban area. Cadmium, chromium, copper, lead, and zinc are common in water and bottom sediments affected by urban activities [36,37,38].
 
organochlorine pesticide map Organochlorine Pesticides and Polychlorinated Biphenyls (PCBs) Were Not Detected at 11 of 13 Sampled Sites 

Concentrations of organochlorine pesticides and PCBs were not detected at 11 of the 13 sites where those compounds were analyzed in bottom sediment and clam tissue. Three degradation products of DDT were detected in Las Vegas Bay of Lake Mead, which receives urban drainage and sewage effluent from the Las Vegas urban area. The concentrations at that site were between the national median and 75th percentile. A degradation product of DDT was detected at one site in the lower Carson River [31], downstream from agricultural activities in Carson Desert; the concentration was less than the national 25th percentile. 

 
 
Semivolatile Organic Compounds (SVOCs) in Bottom Sediment Downstream From Urban Areas Were Greater Than the National 75th Percentile 

In the three study basins, 8 of 13 sites had bottom-sediment concentrations of semivolatile organic compounds (SVOCs) that were greater than the national median. The concentrations of SVOCs at two sites downstream from the Las Vegas urban area were greater than the national 75th percentile. Streamflow at the upstream site is primarily urban drainage. The downstream site is affected by the discharge of treated sewage as well. 

Two sites in the Carson River Basin had concentrations of SVOCs between the national median and 75th percentile. Both sites are downstream from small cities and agricultural areas. Three sites in the Truckee River Basin had SVOC concentrations in bottom sediment that were greater than the national 75th percentile. These sites are downstream from the Reno-Sparks urban area. The upstream site is affected by urban drainage and the two downstream sites are affected by urban drainage and treated sewage effluent. Three of four sites in forested headwater areas of the Carson and Truckee River Basins had concentrations that were less than the national median. 

SVOC map
 
fish community map Fish Communities in Lower Reaches of the Carson and Truckee Rivers Were More Degraded Than the National Median 

The degradation indices for fish communities were based on the number of non-native and omnivorous fish, the number of fish tolerant to human disturbance, and the number of fish with external parasites or lesions. Fish communities were not evaluated in Las Vegas Wash because it was primarily a conduit for urban drainage and tertiary-treated sewage effluent. However, a study of endocrine systems of common carp by the NVBR NAWQA, National Park Service, and U.S. Fish and Wildlife Service in 1995 showed evidence of endocrine disruption in Las Vegas Wash and Las Vegas Bay of Lake Mead as compared to Callville Bay, an upstream background site in Lake Mead [42]. Evidence of endocrine disruption included high levels of a male sex hormone in female carp from Las Vegas Wash, low levels of a male sex hormone in male carp from Las Vegas Bay, and the presence of an egg protein, which should be found only in females, in high percentages of male carp from Las Vegas Wash and Bay. Synthetic organic compounds detected in the water column, bottom sediment, and carp tissue from Las Vegas Wash and Bay have been shown to cause these effects in previous investigations of other areas [42].

Fish communities in the Carson and Truckee River Basins were degraded in the lower parts of both rivers. The attributes common to sites with degraded fish communities were low-gradient stretches of river, warm water temperature, sand to gravel stream bottom, streamflow depleted by major water diversions, and large populations of algae and aquatic plants. At three of the seven sites in both basins, the degradation indices for fish communities were less than the national 25th percentile, indicating little or no degradation. Two of those sites were in forested headwater areas. The attributes common to these three sites that seemed to favor native fish communities were cool water temperatures, high-gradient stretches of river, gravel to cobble stream bottom, low nutrient concentrations, little or no aquatic plant growth, and no major water diversions. The degradation indices for fish communities at the remaining four sites were greater than the national median; three of the four were greater than the national 75th percentile. The degraded fish communities at these four sites were composed of a high proportion of non-native fish species. Native fish at these sites had external parasites and lesions.
 
Stream Habitat at All Sites on Carson and Truckee River Systems Was Better Than the National Median 

Stream-habitat degradation was evaluated at seven sites in the Study Unit. The indices of stream habitat for all seven sites were less than the national median, indicating they were less degraded. Habitat-degradation indices were based on riparian vegetation, stream modification, bank stability, and bank erosion. Stream habitat was not evaluated in Las Vegas Valley because most streams there have been channelized, leveed, or otherwise altered in some way and probably differ greatly from their pre-urban character. The indices for four sites, two each in the Carson and the Truckee River Basins, were less than the national 25th percentile, indicating little or no habitat degradation. Of those four sites, one site in each basin is in a forested headwater area. All four sites had the following attributes in common: located in the middle to upper parts of the basin, little or no streambank erosion, streambanks highly stable with either dense stands of vegetation or broad areas of embedded boulders and cobbles. Habitat indices for the remaining three sites (one on the Carson River and two on the Truckee River) were between the national 25th percentile and median. The stream habitats at these three sites had the following attributes in common: located in the lower parts of the basin, low to moderate streambank erosion, moderately stable streambanks with moderate vegetation density, and some areas of embedded boulders and cobbles. 

stream habitat map
 
 
CONCLUSIONS
Compared to other NAWQA Study Units: 
    • Nutrients and pesticides in Las Vegas Wash downstream from the Las Vegas urban area were greater than the national medians, probably because almost all of the streamflow is from the discharge of urban drainage and tertiary-treated sewage.
    • Nutrients in surface water in the Carson and Truckee River Basins were less than the national medians. This probably is because crops grown in the Carson River Basin do not require heavy applications of fertilizers, agriculture is minimal in the Truckee River Basin, no sewage and little urban drainage is discharged to the Carson River, and natural streamflow in the Truckee River dilutes the discharge of tertiary-treated sewage and urban drainage from the Reno-Sparks area.
    • Trace elements and semivolatile organic compounds in bottom sediment downstream from the Las Vegas and Reno-Sparks urban areas were greater than the national medians, probably as a result of urban activities.
    • Trace elements in bottom sediment downstream from natural mineral deposits and historical mining activities in the Carson River Basin were greater than the national median.
    • Organochlorine compounds in bottom sediment downstream from the Las Vegas urban area were greater than the national median, probably as a result of urban activities.
    • Fish communities in the lower parts of the Carson River, between Carson City and Lahontan Reservoir, and Truckee River, downstream from Reno-Sparks, were more degraded than the national median.
    • Stream habitat in the Carson and Truckee Rivers was less degraded than the national median.
 

Wetlands in Carson Valley, November 1993.
Photograph by Michael S. Lico, U.S. Geological Survey.


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Suggested citation:
Bevans, H.E., Lico, M.S., and Lawrence, S.J., 1998, Water Quality in the Las Vegas Valley Area and the Carson and Truckee River Basins, Nevada and California, 1992-96, on line at <URL: http://water.usgs.gov/pubs/circ1170>, updated 19 March 1998

This page is a subpage of <URL:http://water.usgs.gov/pubs/circ1170>
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Last modified: Tue Mar 17 17:53:42 1998