Geology topics

Research about Lahontan Reservoir

Source-linked reports with geographic coverage including Lahontan Reservoir.

3 recordsLinked to original sources

USGS2023

Long-term mercury loading and trapping dynamics in a Western North America reservoir

Study Region The Carson River including Lahontan Reservoir in Northwestern Nevada, USA Study Focus The discovery, mining, and processing of silver and gold from the Comstock Lode in northwestern Nevada heavily contaminated the Carson River system with mercury (Hg). The river now contains some of the highest recorded water column and bed sediment Hg concentrations reported in peer-reviewed literature. Acute Hg contamination in river and reservoir bed sediment has led to elevated methylmercury (MeHg) concentrations across all trophic levels of Lahontan Reservoir, culminating in significant health risks to humans. Lahontan Reservoir, located downstream from the mills that processed Comstock ore, has served as a Hg trap since the completion of the dam in 1915. Starting in 1997 and extending through 2021, the U.S. Geological Survey has collected and analyzed hundreds of discrete water samples entering and exiting Lahontan Reservoir for unfiltered total Hg (uf.THg), thereby providing a first-of-its-kind opportunity for studying long-term Hg trapping efficiencies within a western North American reservoir. Continuous time series of uf.THg concentration and flux above and below the reservoir were estimated using the weighted regressions on time, discharge, and season with the Kalman filtering (WRTDS-K) method employed with newly developed methods to account for non-natural (i.e., managed) hydrographs below a reservoir. New hydrological insights for the region An estimated 31,650 kg (34.89 US tons) of uf.THg entered Lahontan Reservoir during the 25 year period of analysis, accounting for approximately 0.5% of the total uf.THg estimated to have been released to the Carson River system [6.8 million kg (7500 US tons)] over a multi-decade mining boom. Moreover, approximately 92% of the estimated uf.THg entering Lahontan Reservoir was trapped. On an annual basis, however, trapping efficiencies range between 34% and 98%, and are closely related to the total annual discharge. Results also indicate that flow-normalized uf.THg concentrations and loads above and below the reservoir are trending down.

Nevada↗

USGS2009

Mercury and drought along the Lower Carson River, Nevada: III. effects on blood and organ biochemistry and histopathology of snowy egrets and black-crowned night-herons on Lahontan Reservoir, 2002-2006

A 10-year study (1997-2006) was conducted to evaluate reproduction and health of aquatic birds in the Carson River Basin of northwestern Nevada (on the U.S. Environmental Protection Agency Natural Priorities List) due to high mercury (Hg) concentrations from past mining activities. This part of the study evaluated physiological associations with blood Hg in young snowy egrets (Egretta thula) and black-crowned night-herons (Nycticorax nycticorax), and organ biochemistry and histopathological effects in snowy egrets on Lahontan Reservoir (LR) from the period 2002-2006. LR snowy egret geometric mean total Hg concentrations (μg/g ww) ranged from 1.5 to 4.8 for blood, 2.4 to 3.1 liver, 1.8 to 2.5 kidneys, 1.7 to 2.4 brain, and 20.5 to 36.4 feathers over these years. For night-herons, mean Hg for blood ranged from 1.6 to 7.4. Significant positive correlations were found between total Hg in blood and five plasma enzyme activities of snowy egrets suggesting hepatic stress. Histopathological findings revealed vacuolar changes in hepatocytes in LR snowy egrets as well as correlation of increased liver inflammation with increasing blood and tissue Hg. Hepatic oxidative effects were manifested by decreased hepatic total thiol concentration and glutathione reductase activity and elevated hepatic thiobarbituric acid-reactive substances (TBARS), a measure of lipid peroxidation. However, other hepatic changes indicated compensatory mechanisms in response to oxidative stress, including decreased oxidized glutathione (GSSG) concentration and decreased ratio of GSSG to reduced glutathione. In young black-crowned night-herons, fewer correlations were apparent. In both species, positive correlations between blood total Hg and plasma uric acid and inorganic phosphorus were suggestive of renal stress, which was supported by histopathological findings. Both oxidative effects and adaptive responses to oxidative stress were apparent in kidneys and brain. Vacuolar change and inflammation in peripheral nerves were found to correlate with blood and tissue Hg. Hg-associated effects related to the immune system included alterations in specific white blood cells and lymphoid depletion in the bursa that were correlated with blood and tissue Hg. When the number of plasma variables that differed between young snowy egrets from the LR site and the reference site were compared between wet and drought years, over twice as many variables were affected during drought years. This resulted in many more variables correlating with blood total Hg during dry than during wet years, suggesting the combination of drought and Hg was more stressful than Hg alone. Drought may have exacerbated Hg-related effects as reported previously for overall productivity. This relationship was not evident in black-crowned night-herons, although data were more limited.

Nevada↗

USGS2007

Development of a mercury speciation, fate, and biotic uptake (BIOTRANSPEC) model: Application to Lahontan Reservoir (Nevada, USA)

A mathematically linked mercury transport, speciation, kinetic, and simple biotic uptake (BIOTRANSPEC) model has been developed. An extension of the metal transport and speciation (TRANSPEC) model, BIOTRANSPEC estimates the fate and biotic uptake of inorganic (Hg(II)), elemental (Hg(0)) and organic (MeHg) forms of mercury and their species in the dissolved, colloidal (e.g., dissolved organic matter [DOM]), and particulate phases of surface aquatic systems. A pseudo-steady state version of the model was used to describe mercury dynamics in Lahontan Reservoir (near Carson City, NV, USA), where internal loading of the historically deposited mercury is remobilized, thereby maintaining elevated water concentrations. The Carson River is the main source of total mercury (THg), of which more than 90% is tightly bound in a gold-silver-mercury amalgam, to the system through loadings in the spring, with negligible input from the atmospheric deposition. The speciation results suggest that aqueous species are dominated by Hg-DOM, Hg(OH)2, and HgClOH. Sediment-to-water diffusion of MeHg and Hg-DOM accounts for approximately 10% of total loadings to the water column. The water column acts as a net sink for MeHg by reducing its levels through two competitive processes: Uptake by fish, and net MeHg demethylation. Although reservoir sediments produce significant amounts of MeHg (4 g/d), its transport from sediment to water is limited (1.6 g/d), possibly because of its adsorption on metal oxides of iron and manganese at the sediment-water interface. Fish accumulate approximately 45% of the total MeHg mass in the water column, and 9% of total MeHg uptake by fish leaves the system because of fishing. Results from this new model reiterate the previous conclusion that more than 90% of THg input is retained in sediment, which perpetuates elevated water concentrations.

Nevada↗