Anthropogenic sources of contaminants in the Humboldt River and its terminal wetlands at the Humboldt Wildlife Management Area (WMA), Nevada, include irrigation drainage, livestock grazing, abandoned mines, mine dewatering, and municipal wastewater effluent.  A better understanding of the relative sources of contaminants in the Humboldt River is needed.  Several mining operations in Nevada have dewatered mine pits to facilitate mining below the water table.  Three of these mines (i.e., Lone Tree and Gold Quarry, parent company Newmont Gold Company; Goldstrike, parent company Barrick Goldstrike Mines Inc.) have discharged water to the Humboldt River.  Collectively, these mines are permitted to discharge 313,000 acre-feet per year, which exceeds the average annual flow of the main-stem Humboldt River; however, discharges have been lower than the maximum allowed. Additional mines could begin discharges within a few years, which could increase the magnitude and potential importance of future impacts. Sewage effluent from Lovelock is discharged to an agricultural drain which flows to the Toulon Drain, eventually reaching Toulon Lake in the Humboldt WMA. The Humboldt River, the largest watershed in Nevada, terminates in the Humboldt Sink in Pershing and Churchill Counties, except in years when the Humboldt Sink floods and discharges into the Carson Sink, such as in 1998. Wetlands in and near the Humboldt Sink provide important nesting, foraging, and resting habitat to large numbers of migratory birds. These wetlands, now contained within the Humboldt WMA, have been identified as one of the most important wildlife habitats in Nevada (Hallock et al. 1981).  In unusual years, such as 1977, the Humboldt WMA may be the most important wetland in Nevada as determined by waterfowl-use days (Hallock et al. 1981).  Shorebird use of the area is also important.

There are three objectives to this study.  First, the study was designed to obtain sufficient data to begin to assess trends in surface water quality and trace elements in aquatic vegetation, invertebrates, fish, and bird eggs and livers in the mid to lower Humboldt River basin.  Second, the study will assess the adequacy of current State and Federal water quality standards for dissolved solids and trace elements to protect fish and wildlife resources in the lower Humboldt River basin, and the possible need for the establishment of total maximum daily loads.  Early detection of potential biological effects is critical because of the terminal nature of the Humboldt River system, the persistence of trace elements in the environment, and the previous identification of adverse biological effects caused by inorganic contaminants in wetlands at the terminus of the river. Third, the study will attempt to determine the relative proportions of total dissolved solids and trace elements entering the Humboldt WMA that originate from mine dewatering and from agricultural drainwater in the Lovelock area.  An ecosystem approach will be used to determine impacts to biotic communities both in the Humboldt River and terminal wetlands at the Humboldt WMA.  This includes information on interactions between trace element concentrations in water, aquatic vegetation and invertebrates, fish, and aquatic birds. Impacts to avian reproduction will also be assessed. The study involved the collection of a full set of field data during the first 2 years (i.e., 1998 and 1999), followed by collection of a limited set of field data from four sites on the Humboldt River in the third year (i.e., 2000; using left over analytical funds).

Even though the concentration of trace elements in water in the river may not increase with increased flows, the total loads will increase.  Increased dissolved solids and trace element loading from mine dewatering discharges and other possible sources may exacerbate inorganic contamination existing in terminal wetlands at the Humboldt WMA, in part in relation to evapo-concentration of trace elements in the terminal wetlands. Problems may be further worsened if the period of increased loading is followed by an extended period of decreased flows in the Humboldt River, such as that which may occur with the cessation of mine dewatering.

Learn More by Reading the Full Report:Wiemeyer, S.N., Humboldt River and Humboldt Wildlife Management Area Contaminant Monitoring, USFWS. Reno FWO. 2001.

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