STUDY DESIGN AND DATA COLLECTION

Environmental Subareas Were Identified for Investigation

Secondary subareas were developed by subdividing the two primary subareas (headwater and basin areas) into land uses that represent more natural conditions (forest and range) or human activities (urban and agricultural land use; fig. 5). Water resources in the environmental subareas were then identified for study. Principal surface-water resources included in the investigation were Las Vegas Wash and Lake Mead, the Carson River, and the Truckee River (fig. 3). Principal aquifers (fig. 3) were defined as unconsolidated deposits beneath valleys with 100 ft or more of saturated thickness [60,61,62] and containing ground water with less than 1,000 mg/L of dissolved solids [63,64].

Headwater areas are primarily forest and basin areas are primarily range. The principal headwater urban area is Reno-Sparks and the principal headwater agricultural area is Carson Valley. The principal basin urban area is the Las Vegas urban area and the principal basin agricultural area is Carson Desert.

Effects of Urban and Agricultural Activities Were Focus of Investigations

Stream-chemistry data collection included a Bottom Sediment and Tissue Study, Basic and Intensive Fixed-Site networks, and a Surface-Water Synoptic Study (fig. 13). The Bottom Sediment and Tissue Study was done early in the Study Unit investigation and included sites being considered for selection as Basic and Intensive Fixed Sites. Basic Fixed Sites were located on streams downstream from forested headwater areas, urban and agricultural headwater areas, urban and agricultural basin areas, major sources of treated sewage effluent, and at downstream sites that integrate streamflow from throughout the study basins. An Intensive Fixed Site was operated to sample drainage from the Las Vegas urban area. The Surface-Water Synoptic Study increased the areal coverage of the Fixed-Site networks and provided additional data on pesticides and trace elements.  Stream-ecology activities included Fixed-Site Reach Assessments and Ecological Synoptic Studies (fig. 13). Fixed-Site Single-Reach Assessments were made at all Basic Fixed Sites in the Carson and Truckee River Basins. Fixed-Site Three-Reach Assessments were made at the farthest upstream Carson and Truckee River Basic Fixed Sites, to serve as reference sites, and at one downstream integrator site on each stream, to serve as trend sites. Ecological Synoptic Studies of benthic invertebrates and algae were completed in the Carson Valley agricultural area and the Reno-Sparks urban area to evaluate land-use effects.

(click for full-size figure; 74 K)  Figure 13. Study unit stream-chemistry, stream-ecology, and ground-water-chemistry sites, and areas of special studies were chosen to represent environmental subareas characterized by selected natural conditions and human activities.

Special studies of irrigation drainage and endocrine disruption were made with assistance from cooperating agencies (fig. 13). The Department of the Interior National Irrigation Water Quality Program provided financial resources for a joint investigation with the NVBR NAWQA to quantify loads of potentially toxic constituents and to document contributing source areas in irrigated lands of the Carson Desert [9]. The National Park Service provided financial assistance and participated with the U.S. Fish and Wildlife Service in a joint investigation with the NVBR NAWQA to identify synthetic organic compounds in Las Vegas Wash and Las Vegas Bay of Lake Mead and to evaluate carp endocrine systems with respect to estrogenic effects that could be caused by synthetic organic compounds [42].

 
Summary of data collection in the Nevada Basin and Range Study Unit, 1992-96
 

(a)

MBAS (methylene blue active substances), synthetic detergents or surfactants, occur in natural water almost exclusively as a result of pollution.

(b)

Additional data from a pilot NAWQA study of the Carson River Basin were used to help determine land-use effects on shallow ground water in Carson Valley and Carson Desert [19].

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