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USGS2002

Environmental geochemistry of abandoned mercury mines in West-Central Nevada, USA

The Humboldt River is a closed basin and is the longest river in Nevada. Numerous abandoned Hg mines are located within the basin, and because Hg is a toxic heavy metal, the potential transport of Hg from these mines into surrounding ecosystems, including the Humboldt River, is of environmental concern Samples of ore, sediment, water, calcines (roasted ore), and leachates of the calcines were analyzed for Hg and other heavy metals to evaluate geochemical dispersion from the mines. Cinnabar-bearing ore samples collected from the mines contain highly elevated Hg concentrations, up to 6.9 %, whereas calcines collected from the mines contain up to 2000 mg Hg/kg. Stream-sediment samples collected within 1 km of the mines contain as much as 170 mg Hg/kg, but those collected distal from the mines (> 5 km) contain < 1 mg Hg/kg, indicating significant geochemical dispersion of Hg downstream from the mines. Sediment samples collected from the Humboldt River basin contain ??? 0.28 mg Hg/kg. Leachate samples of the calcines obtained by using a synthetic water leaching technique contain as much as 1500 ??g Hg/l, suggesting that some calcines contain soluble Hg compounds. However, much lower Hg concentrations were found in water samples collected from the Humboldt River system, and these were below the 0.012 ??g/l Hg standard used to protect against chronic effects to aquatic wildlife. Mercury transference from these mines to the Humboldt River basin is generally minor because the mines are typically > 8 km from the Humboldt River, and Hg is transported and diluted through a large volume of pediment before it reaches the Humboldt River. ?? 2002 Elsevier Science Ltd. All rights reserved.

Conference Paper↗

USGS2007

Landscape geochemistry near mineralized areas of eastern Alaska: Chapter H in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project

The Pogo lode gold deposit was discovered in eastern Alaska in the early 1990s and provided the opportunity to study elemental distribution and mobility in the natural environment prior to mine development. Studying mineralized systems prior to mining allows us to compare the natural biogeochemical signature in mineralized versus nonmineralized areas. The resultant data and interpretation also provide a baseline for evaluating what, if any, changes in elemental distribution result from development. This report investigates the chemistry of stream water, streambed sediment, and soil in the context of regional bedrock geology. The major-ion chemistry of the waters reflects a rock-dominated aqueous system, and the waters are classified as Ca 2+ and Mg 2+ - HCO 3 - to Ca 2+ and Mg 2+ - SO 4 -2 waters. Creeks draining the gneissic lithologies tend to be more sulfate dominated than those draining the intrusive units. Sulfate also dominated creeks draining mineralized areas; however, the underlying paragneiss unit could be contributing substantially to the sulfate concentration, and the sulfate concentration in these creeks may reflect a complex baltholith-paragneiss boundary rather than mineralization. Arsenic concentrations in bed sediments were elevated in mineralized areas relative to nonmineralized areas. Elevated concentrations of nickel, chromium, iron, manganese, and cobalt appear to reflect the presence of ultramafic rocks in the drainage. In general, aqueous metal concentrations were below the State of Alaska’s Aquatic Life Criteria and Drinking Water Standards, with the exception of arsenic in stream water, which ranged in concentration from less than 1 to 14 micrograms per liter (μg/L) and exceeded the drinking water standard at one site. The arsenic and antimony concentration in the A, B, and C soil horizons ranged from 3 to 410 milligrams per kilogram (mg/kg), 6.1 to 440 mg/kg, and 2 to 300 mg/kg, respectively, for arsenic and 0.4 to 24 mg/kg, 0.6 to 25 mg/kg, and 0.2 to 16 mg/kg, respectively, for antimony. The arsenic and antimony concentrations in stream waters correlate well with the concentrations in soils. However, significantly less arsenic and antimony was extracted from C horizon soils in water leaching experiments, indicating that the arsenic and antimony in the C horizon is present in a less available form than in the A or B horizons. Arsenic and antimony uptake by grayleaf willow (Salix glauca L.) appears minimal, with arsenic concentrations ranging from less than 0.01 to 0.14 mg/kg and antimony concentrations ranging from less than 0.003 to 0.23 mg/kg in willow leaves. In general, the highest concentrations of both arsenic and antimony in water and soils were found near mineralized areas. Elevated arsenic concentrations were also found in bed sediments from mineralized areas. In these sample matrices, the presence of arsenic and (or) antimony was a good indicator of contact with mineralized rock units.

Alaska;Yukon↗

USGS2015

High-frequency, long-duration water sampling in acid mine drainage studies: a short review of current methods and recent advances in automated water samplers

Hand-collected grab samples are the most common water sampling method but using grab sampling to monitor temporally variable aquatic processes such as diel metal cycling or episodic events is rarely feasible or cost-effective. Currently available automated samplers are a proven, widely used technology and typically collect up to 24 samples during a deployment. However, these automated samplers are not well suited for long-term sampling in remote areas or in freezing conditions. There is a critical need for low-cost, long-duration, high-frequency water sampling technology to improve our understanding of the geochemical response to temporally variable processes. This review article will examine recent developments in automated water sampler technology and utilize selected field data from acid mine drainage studies to illustrate the utility of high-frequency, long-duration water sampling.

Applied Geochemistry↗

USGS1999

Carbon isotopic constraints on the contribution of plant material to the natural precursors of trihalomethanes

The δ 13 C values of individual trihalomethanes (THM) formed on reaction of chlorine with dissolved organic carbon (DOC) leached from maize (corn; Zea maize L. ) and Scirpus acutus (an aquatic bulrush), and with DOC extracted from agricultural drainage waters were determined using purge and trap introduction into a gas chromatograph-combustion-isotope ratio monitoring mass spectrometer. We observed a 16.8‰ difference between the δ 13 C values of THM produced from the maize and Scirpus leachates, similar to the isotopic difference between the whole plant materials. Both maize and Scirpus formed THM 12‰ lower in 13 C than whole plant material. We suggest that the low value of the THM relative to the whole plant material is evidence of distinct pools of THM-forming DOC, representing different biochemical types or chemical structures, and possessing different environmental reactivity.

Organic Geochemistry↗

USGS2021

Regional occurrence of aqueous tungsten and relations with antimony, arsenic and molybdenum concentrations (Sardinia, Italy)

T ungsten (W) is rarely found in natural waters, yet it can be introduced into the food chain and cause potentially toxic effects. Uptake of W by plants and vegetables, or trace presence of W in drinking water are possible vectors for ingestion of W by humans. The latter is recognized as a possible cause of lymphatic leukemia. Increased uses of W might result in a degradation of water resources, with attendant adverse effects on biota and human health. Therefore, this study was aimed at investigating regional occurrence and speciation of W in aquatic systems in Sardinia, Italy, factors affecting W mobility and possible relations with other oxyanion-forming trace elements such as Sb, As and Mo. Although our results are specifically from Sardinia, the implications are broader and should prompt future studies in other areas with known high W concentrations. A total of 350 sample sites are reported here, including surface waters, groundwaters, mine drainages, thermal waters and local seawater. The waters were analyzed for major and trace components, including W, Sb, As and Mo. The waters showed a variety of major chemical compositions and W concentrations. High concentrations of W were found in some mine waters and drainages from slag heaps, with W, Sb and As up to 140, 5000 and 800 μg L −1 , respectively. The highest concentrations of W occurred under slightly alkaline pH and oxygenated conditions, and were likely due to the dissolution of scheelite [CaWO 4 ] hosted in materials with which the water came into contact. High W concentrations also were observed in thermal waters, under alkaline pH and reducing conditions, and sometimes coincided with relatively high concentrations either of As or Mo. Previous studies of W geochemistry have focused on WO 4 2− as the major dissolved form of W. For this study, we have augmented the thermodynamic database in PHREEQC to include possible formation of many other W-bearing complexes gleaned from the literature. The results of the speciation calculations with the newly added complexation reactions shows that the neutral species CaWO 4 ° and MgWO 4 ° are particularly dominant in most W-bearing waters and lead to undersaturation with respect to scheelite and other W-bearing minerals. Assessing W contamination in water systems and establishing W limits in drinking water may prevent potential adverse effects of W on human and ecosystem health.

Sardinia↗

USGS2009

Metal contamination and post-remediation recovery in the Boulder River watershed, Jefferson County, Montana

The legacy of acid mine drainage and toxic trace metals left in streams by historical mining is being addressed by many important yet costly remediation efforts. Monitoring of environmental conditions frequently is not performed but is essential to evaluate remediation effectiveness, determine whether clean-up goals have been met, and assess which remediation strategies are most effective. Extensive pre- and post-remediation data for water and sediment quality for the Boulder River watershed in southwestern Montana provide an unusual opportunity to demonstrate the importance of monitoring. The most extensive restoration in the watershed occurred at the Comet mine on High Ore Creek and resulted in the most dramatic improvement in aquatic habitat. Removal of contaminated sediment and tailings, and stream-channel reconstruction reduced Cd and Zn concentrations in water such that fish are now present, and reduced metal concentrations in streambed sediment by a factor of c. 10, the largest improvement in the district. Waste removals at the Buckeye/Enterprise and Bullion mine sites produced limited or no improvement in water and sediment quality, and acidic drainage from mine adits continues to degrade stream aquatic habitat. Recontouring of hillslopes that had funnelled runoff into the workings of the Crystal mine substantially reduced metal concentrations in Uncle Sam Gulch, but did not eliminate all of the acidic adit drainage. Lead isotopic evidence suggests that the Crystal mine rather than the Comet mine is now the largest source of metals in streambed sediment of the Boulder River. The completed removal actions prevent additional contaminants from entering the stream, but it may take many years for erosional processes to diminish the effects of contaminated sediment already in streams. Although significant strides have been made, additional efforts to seal draining adits or treat the adit effluent at the Bullion and Crystal mines would need to be completed to achieve the desired restoration.

Montana↗

USGS1989

Organic geochemistry and brine composition in Great Salt, Mono, and Walker Lakes

Samples of Recent sediments, representing up to 1000 years of accumulation, were collected from three closed basin lakes (Mono Lake, CA, Walker Lake, NV, and Great Salt Lake, UT) to assess the effects of brine composition on the accumulation of total organic carbon, the concentration of dissolved organic carbon, humic acid structure and diagenesis, and trace metal complexation. The Great Salt Lake water column is a stratified Na-Mg-Cl-SO 4 brine with low alkalinity. Algal debris is entrained in the high density (1.132–1.190 g/cc) bottom brines, and in this region maximum organic matter decomposition occurs by anaerobic processes, with sulfate ion as the terminal electron acceptor. Organic matter, below 5 cm of the sediment-water interface, degrades at a very slow rate in spite of very high pore-fluid sulfate levels. The organic carbon concentration stabilizes at 1.1 wt%. Mono Lake is an alkaline (Na-CO 3 -Cl-SO 4 ) system. The water column is stratified, but the bottom brines are of lower density relative to the Great Salt Lake, and sedimentation of algal debris is rapid. Depletion of pore-fluid sulfate, near l m of core, results in a much higher accumulation of organic carbon, approximately 6 wt%. Walker Lake is also an alkaline system. The water column is not stratified, and decomposition of organic matter occurs by aerobic processes at the sediment-water interface and by anaerobic processes below. Total organic carbon and dissolved organic carbon concentrations in Walker Lake sediments vary with location and depth due to changes in input and pore-fluid sulfate concentrations. Nuclear magnetic resonance studies ( 13 C) of humic substances and dissolved organic carbon provide information on the source of the Recent sedimentary organic carbon (aquatic vs. terrestrial), its relative state of decomposition, and its chemical structure. The spectra suggest an algal origin with little terrestrial signature at all three lakes. This is indicated by the ratio of aliphatic to aromatic carbon and the absence of chemical structures indicative of the lignin of vascular plants. The dissolved organic carbon of the Mono Lake pore fluids is structurally related to humic acid and is also related to carbohydrate metabolism. The alkaline pore fluids, due to high pH, solubilize high molecular weight organic matter from the sediments. This hydrophilic material is a metal complexing agent. Despite very high algal productivities, organic carbon accumulation can be low in stratified lakes if the anoxic bottom waters are hypersaline with high concentrations of sulfate ion. Labile organic matter is recycled to the water column and the sedimentary organic matter is relatively nonsusceptible to bacterial metabolism. As a result, pore-fluid dissolved organic carbon and metal-organic complexation are low.

Geochimica et Cosmochimica Acta↗

USGS2013

Mercury and methylmercury dynamics in the hyporheic zone of an Oregon stream

The role of the hyporheic zone in mercury (Hg) cycling has received limited attention despite the biogeochemically active nature of this zone and, thus, its potential to influence Hg behavior in streams. An assessment of Hg geochemistry in the hyporheic zone of a coarse-grained island in the Coast Fork Willamette River in Oregon, USA, illustrates the spatially dynamic nature of this region of the stream channel for Hg mobilization and attenuation. Hyporheic flow through the island was evident from the water-table geometry and supported by hyporheic-zone chemistry distinct from that of the bounding groundwater system. Redox-indicator species changed abruptly along a transect through the hyporheic zone, indicating a biogeochemically reactive stream/hyporheic-zone continuum. Dissolved organic carbon (DOC), total Hg, and methylmercury (MeHg) concentrations increased in the upgradient portion of the hyporheic zone and decreased in the downgradient region. Total Hg (collected in 2002 and 2003) and MeHg (collected in 2003) were correlated with DOC in hyporheic-zone samples: r 2 =0.63 (total Hg-DOC, 2002), 0.73 (total Hg-DOC, 2003), and 0.94 (MeHg-DOC, 2003). Weaker Hg/DOC association in late summer 2002 than in early summer 2003 may reflect seasonal differences in DOC reactivity. Observed correlations between DOC and both total Hg and MeHg reflect the importance of DOC for Hg mobilization, transport, and fate in this hyporheic zone. Correlations with DOC provide a framework for conceptualizing and quantifying Hg and MeHg dynamics in this region of the stream channel, and provide a refined conceptual model of the role hyporheic zones may play in aquatic ecosystems.

Water, Air, & Soil Pollution↗

USGS2013

Long-distance transport of Hg, Sb, and As from a mined area, conversion of Hg to methyl-Hg, and uptake of Hg by fish on the Tiber River basin, west-central Italy

Stream sediment, stream water, and fish were collected from a broad region to evaluate downstream transport and dispersion of mercury (Hg) from inactive mines in the Monte Amiata Hg District (MAMD), Tuscany, Italy. Stream sediment samples ranged in Hg concentration from 20 to 1,900 ng/g, and only 5 of the 17 collected samples exceeded the probable effect concentration for Hg of 1,060 ng/g, above which harmful effects are likely to be observed in sediment-dwelling organisms. Concentrations of methyl-Hg in Tiber River sediment varied from 0.12 to 0.52 ng/g, and although there is no established guideline for sediment methyl-Hg, these concentrations exceeded methyl-Hg in a regional baseline site (<0.02 ng/g). Concentrations of Hg in stream water varied from 1.2 to 320 ng/L, all of which were below the 1,000 ng/L Italian drinking water Hg guideline and the 770 ng/L U.S. Environmental Protection Agency (USEPA) guideline recommended to protect against chronic effects to aquatic wildlife. Methyl-Hg concentrations in stream water varied from <0.02 to 0.53 ng/L and were generally elevated compared to the baseline site (<0.02 ng/L). All stream water samples contained concentrations of As (<1.0–6.2 μg/L) and Sb (<0.20–0.37 μg/L) below international drinking water guidelines to protect human health (10 μg/L for As and 20 μg/L for Sb) and for protection against chronic effects to aquatic wildlife (150 μg/L for As and 5.6 μg/L for Sb). Concentrations of Hg in freshwater fish muscle ranged from 0.052–0.56 μg/g (wet weight), mean of 0.17 μg/g, but only 17 % (9 of 54) exceeded the 0.30 μg/g (wet weight) USEPA fish muscle guideline recommended to protect human health. Concentrations of Hg in freshwater fish in this region generally decreased with increasing distance from the MAMD, where fish with the highest Hg concentrations were collected more proximal to the MAMD, whereas all fish collected most distal from Hg mines contained Hg below the 0.30 μg/g fish muscle guideline. Data in this study indicate some conversion of inorganic Hg to methyl-Hg and uptake of Hg in fish on the Paglia River, but less methylation of Hg and Hg uptake by freshwater fish in the larger Tiber River.

Tiber River Basin↗

USGS2014

Mercury concentrations and distribution in soil, water, mine waste leachates, and air in and around mercury mines in the Big Bend region, Texas, USA

Samples of soil, water, mine waste leachates, soil gas, and air were collected from areas mined for mercury (Hg) and baseline sites in the Big Bend area, Texas, to evaluate potential Hg contamination in the region. Soil samples collected within 300 m of an inactive Hg mine contained elevated Hg concentrations (3.8–11 µg/g), which were considerably higher than Hg in soil collected from baseline sites (0.03–0.05 µg/g) distal (as much as 24 km) from mines. Only three soil samples collected within 300 m of the mine exceeded the probable effect concentration for Hg of 1.06 µg/g, above which harmful effects are likely to be observed in sediment-dwelling organisms. Concentrations of Hg in mine water runoff (7.9–14 ng/L) were generally higher than those found in springs and wells (0.05–3.1 ng/L), baseline streams (1.1–9.7 ng/L), and sources of drinking water (0.63–9.1 ng/L) collected in the Big Bend region. Concentrations of Hg in all water samples collected in this study were considerably below the 2,000 ng/L drinking water Hg guideline and the 770 ng/L guideline recommended by the U.S. Environmental Protection Agency (USEPA) to protect aquatic wildlife from chronic effects of Hg. Concentrations of Hg in water leachates obtained from leaching of mine wastes varied widely from <0.001 to 760 µg of Hg in leachate/g of sample leached, but only one leachate exceeded the USEPA Hg industrial soil screening level of 31 µg/g. Concentrations of Hg in soil gas collected at mined sites (690–82,000 ng/m 3 ) were highly elevated compared to soil gas collected from baseline sites (1.2–77 ng/m 3 ). However, air collected from mined areas at a height of 2 m above the ground surface contained concentrations of Hg (4.9–64 ng/m 3 ) that were considerably lower than Hg in soil gas from the mined areas. Although concentrations of Hg emitted from mine-contaminated soils and mine wastes were elevated, persistent wind in southwest Texas disperses Hg in the air within a few meters of the ground surface.

Texas↗

USGS2022

Water-quality trends for a stream draining the Southern Anthracite Field, Pennsylvania

Stream flow, chemical and biological data for the northern part of Swatara Creek, which drains a 112 km 2 area in the Southern Anthracite Field of eastern Pennsylvania, indicate progressive improvement in water quality since 1959, after which most mines in the watershed had been flooded. Drainage from the flooded mines contributes substantially to base flow in Swatara Creek. Beginning in 1995, a variety of treatment systems and surface reclamation were implemented at some of the abandoned mines. At Ravine, Pa., immediately downstream of the mined area, median SO 4 concentration declined from about 150 mg l −1 in 1959 to 75 mg l −1 in 1999 while pH increased from acidic to near-neutral values (medians: c. pH 4 before 1975; c. pH 6 after 1975). Fish populations rebounded from non-existent during 1959–1990 to 21 species identified in 1999. Nevertheless, recent monitoring indicates (1) episodic acidification and elevated concentrations and transport of Fe, Al, Mn, and trace metals during storm flow; (2) elevated concentrations of Fe, Mn, Co, Cu, Pb, Ni, and Zn in streambed sediments relative to unmined areas and to toxicity guidelines for aquatic invertebrates and fish; and (3) elevated concentrations of metals in fish tissue, notably Zn. The metals are ubiquitous in the fine fraction (<0.063 mm) of bed sediment in mining-affected tributaries and the main stem of Swatara Creek. As a result of scour and transport of streambed deposits, concentrations of suspended solids and total metals in the water column are correlated, and those for storm flow typically exceed base flow. Nevertheless, the metals concentrations are poorly correlated with stream flow because concentrations of suspended solids and total metals typically peak prior to peak stream stage. In contrast, SO 4 , specific conductance and pH are inversely correlated with stream flow as a result of dilution of poorly buffered stream water with weakly acidic storm runoff derived mainly from low-pH rainfall. Declines in pH to values approaching 5.0 during storm flow events or declines in redox potential during burial of sediment could result in the remobilization of metals associated with suspended solids and streambed deposits.

Pennsylvania↗

USGS2001

Geochemical and mineralogical controls on trace element release from the Penn Mine base-metal slag dump, California

Base-metal slag deposits at the Penn Mine in Calaveras County, California, are a source of environmental contamination through leaching of potentially toxic elements. Historical Cu smelting at Penn Mine (1865-1919) generated approximately 200,000 m3 of slag. The slag deposits, which are flooded annually by a reservoir used for drinking water and irrigation, also may be in contact with acidic ground waters (pH < 4) from the adjacent mine area. Slags vary from grey to black, are glassy to crystalline, and range in size from coarse sand to large (0.6 ?? 0.7 ?? 1.5 m), tub-shaped casts. Metals are hosted by a variety of minerals and two glass phases. On the basis of mineralogy, slags are characterized by 4 main types: fayalite-rich, glassy, willemite-rich, and sulfide-rich. The ranges in metal and metalloid concentrations of 17 slag samples are: As, 0.0004-0.92; Ba, 0.13-2.9; Cd, 0.0014-1.4; Cu, 0.18-6.4; Pb, 0.02-11; and Zn, 3.2-28 wt.%. Leachates from Toxicity Characteristic Leaching Procedure tests (acetic acid buffered at pH 4.93) on two wiltemite-rich slags contained Cd and Pb concentrations (up to 2.5 and 30 mg/l, respectively) in excess of US Environmental Protection Agency (USEPA) regulatory limits. Analyses of filtered (0.45 ??m) water, collected within the flooded slag dump during reservoir drawdown, reveal concentrations of Cd (1.7 ??g/l), Cu (35 ??g/l), and Zn (250 ??g/l) that exceed USEPA chronic toxicity guidelines for the protection of aquatic life. Data from field and laboratory studies were used to develop geochemical models with the program EQ3/6 that simulate irreversible mass-transfer between slag deposits and reservoir waters. These models include kinetic rate laws for abiotic sulfide oxidation and surface-controlled dissolution of silicates, oxides, and glass. Calculations demonstrate that the main processes controlling dissolved metal concentrations are (1) dissolution of fayalite, willemite, and glass; (2) sulfide oxidation; and (3) secondary phase precipitation. Close agreement between model results and measured concentrations of Al, Ba, Cu, Fe, SiO2, and SO4 in the slag dump pore waters suggests that the dissolved concentrations of these elements are controlled by solubility equilibrium with secondary phases. Differences between predicted and measured Cd and Pb concentrations imply that field weathering rates of glass and sulfides are approximately two orders of magnitude lower than laboratory rates. Overprediction of Pb release may also reflect other attenuation processes in the natural system, such as sorption or coprecipitation. ?? 2001 Elsevier Science Ltd. All rights reserved.

Applied Geochemistry↗

USGS2015

The fate of cyanide in leach wastes at gold mines: an environmental perspective

This paper reviews the basic chemistry of cyanide, methods by which cyanide can be analyzed, and aspects of cyanide behavior that are most relevant to environmental considerations at mineral processing operations associated with gold mines. The emphasis is on research results reported since 1999 and on data gathered for a series of U.S. Geological Survey studies that began in the late 1990s. Cyanide is added to process solutions as the CN − anion, but ore leaching produces numerous other cyanide-containing and cyanide-related species in addition to the desired cyanocomplex of gold. These can include hydrogen cyanide (HCN); cyanometallic complexes of iron, copper, zinc, nickel, and many other metals; cyanate (CNO − ); and thiocyanate (SCN − ). The fate of these species in solid wastes and residual process solutions that remain once gold recovery activities are terminated and in any water that moves beyond the ore processing facility dictates the degree to which cyanide poses a risk to aquatic organisms and aquatic-dependent organisms in the local environment. Cyanide-containing and cyanide-related species are subject to attenuation mechanisms that lead to dispersal to the atmosphere, chemical transformation to other carbon and nitrogen species, or sequestration as cyanometallic precipitates or adsorbed species on mineral surfaces. Dispersal to the atmosphere and chemical transformation amount to permanent elimination of cyanide, whereas sequestration amounts to storage of cyanide in locations from which it can potentially be remobilized by infiltrating waters if conditions change. From an environmental perspective, the most significant cyanide releases from gold leach operations involve catastrophic spills of process solutions or leakage of effluent to the unsaturated or saturated zones. These release pathways are unfavorable for two important cyanide attenuation mechanisms that tend to occur naturally: dispersal of free cyanide to the atmosphere and sunlight-catalyzed dissociation of strong cyanometallic complexes, which produces free cyanide that can then disperse to the atmosphere. The widest margins of environmental safety will be achieved where mineral processing operations are designed so that time for offgassing, aeration, and sunlight exposure are maximized in the event that cyanide-bearing solutions are released inadvertently.

Applied Geochemistry↗

USGS2000

Mercury mine drainage and processes that control its environmental impact

Mine drainage from mercury mines in the California Coast Range mercury mineral belt is an environmental concern because of its acidity and high sulfate, mercury, and methylmercury concentrations. Two types of mercury deposits are present in the mineral belt, silica-carbonate and hot-spring type. Mine drainage is associated with both deposit types but more commonly with the silica-carbonate type because of the extensive underground workings present at these mines. Mercury ores consisting primarily of cinnabar were processed in rotary furnaces and retorts and elemental mercury recovered from condensing systems. During the roasting process mercury phases more soluble than cinnabar are formed and concentrated in the mine tailings, commonly termed calcines. Differences in mineralogy and trace metal geochemistry between the two deposit types are reflected in mine drainage composition. Silica-carbonate type deposits have higher iron sulfide content than hot- spring type deposits and mine drainage from these deposits may have extreme acidity and very high concentrations of iron and sulfate. Mercury and methylmercury concentrations in mine drainage are relatively low at the point of discharge from mine workings. The concentration of both mercury species increases significantly in mine drainage that flows through and reacts with calcines. The soluble mercury phases in the calcines are dissolved and sulfate is added such that methylation of mercury by sulfate reducing bacteria is enhanced in calcines that are saturated with mine drainage. Where mercury mine drainage enters and first mixes with stream water, the addition of high concentrations of mercury and sulfate generates a favorable environment for methylation of mercury. Mixing of oxygenated stream water with mine drainage causes oxidation of dissolved iron(II) and precipitation of iron oxyhydroxide that accumulates in the streambed. Both mercury and methylmercury are strongly adsorbed onto iron oxyhydroxide over the pH range of 3.2-7.1 in streams impacted by mine drainage. The dissolved fraction of both mercury species is depleted and concentrated in iron oxyhydroxide such that the amount of iron oxyhydroxide in the water column reflects the concentration of mercury species. In streams impacted by mine drainage, mercury and methylmercury are transported and adsorbed onto particulate phases. During periods of low stream flow, fine-grained iron hydroxide sediment accumulates in the bed load of the stream and adsorbs mercury and methylmercury such that both forms of mercury become highly enriched in the iron oxyhydroxide sediment. During high-flow events, mercury- and methylmercury-enriched iron hydroxide sediment is transported into larger aquatic systems producing a high flux of bioavailable mercury. (C) 2000 Elsevier Science B.V.

Science of the Total Environment↗

USGS2026

Evaluating drivers of environmental change in a lake sediment core: Insights from spectroscopic metrics of water-extractable organic matter and stable carbon isotopes

Freshwater lakes play a critical role in the global carbon cycle by storing and transforming organic matter (OM) from both terrestrial and aquatic sources. Small lakes in northern temperate regions, despite their limited surface area, disproportionately influence regional carbon budgets. Buried sediments integrate OM inputs over time and archive ecosystem responses to natural and anthropogenic disturbances. However, the direction and magnitude of recent environmental changes on sediment carbon (C) dynamics remain poorly understood. A 23-cm core was collected from a small temperate lake in northeastern USA to evaluate sediment OM content and composition over timescales relevant to historical land-use change, damming, and recovery from acid deposition. Patterns in OM burial and source contributions were revealed via elemental and isotopic analyses of bulk OM and ultraviolet-visible spectrophotometry of water-extractable organic matter (WEOM). The optical metrics expanded observations of likely OM sources beyond the information gained from bulk carbon metrics (total carbon, δ 13 C). The aromaticity of WEOM increased downcore, which is consistent with a shift from increased terrestrial inputs during early logging and damming activity (pre ∼1920) to more microbial-derived OM in recent surficial sediments. Future applications of WEOM optical properties as complements to traditional geochemical metrics can enhance interpretations of lake ecosystem responses recorded in lake sediments to environmental perturbations in temperate lakes.

New York↗

USGS2008

Dissolved and labile concentrations of Cd, Cu, Pb, and Zn in the South Fork Coeur d'Alene River, Idaho: Comparisons among chemical equilibrium models and implications for biotic ligand models

In order to evaluate thermodynamic speciation calculations inherent in biotic ligand models, the speciation of dissolved Cd, Cu, Pb, and Zn in aquatic systems influenced by historical mining activities is examined using equilibrium computer models and the diffusive gradients in thin films (DGT) technique. Several metal/organic-matter complexation models, including WHAM VI, NICA-Donnan, and Stockholm Humic model (SHM), are used in combination with inorganic speciation models to calculate the thermodynamic speciation of dissolved metals and concentrations of metal associated with biotic ligands (e.g., fish gills). Maximum dynamic metal concentrations, determined from total dissolved metal concentrations and thermodynamic speciation calculations, are compared with labile metal concentrations measured by DGT to assess which metal/organic-matter complexation model best describes metal speciation and, thereby, biotic ligand speciation, in the studied systems. Results indicate that the choice of model that defines metal/organic-matter interactions does not affect calculated concentrations of Cd and Zn associated with biotic ligands for geochemical conditions in the study area, whereas concentrations of Cu and Pb associated with biotic ligands depend on whether the speciation calculations use WHAM VI, NICA-Donnan, or SHM. Agreement between labile metal concentrations and dynamic metal concentrations occurs when WHAM VI is used to calculate Cu speciation and SHM is used to calculate Pb speciation. Additional work in systems that contain wide ranges in concentrations of multiple metals should incorporate analytical speciation methods, such as DGT, to constrain the speciation component of biotic ligand models.

Idaho↗

USGS2008

The 2005 catastrophic acid crater lake drainage, lahar, and acidic aerosol formation at Mount Chiginagak volcano, Alaska, USA: Field observations and preliminary water and vegetation chemistry results

A mass of snow and ice 400-m-wide and 105-m-thick began melting in the summit crater of Mount Chiginagak volcano sometime between November 2004 and early May 2005, presumably owing to increased heat flux from the hydrothermal system, or possibly from magma intrusion and degassing. In early May 2005, an estimated 3.8??10 6 m 3 of sulfurous, clay-rich debris and acidic water, with an accompanying acidic aerosol component, exited the crater through a tunnel at the base of a glacier that breaches the south crater rim. Over 27 km downstream, the acidic waters of the flood inundated an important salmon spawning drainage, acidifying Mother Goose Lake from surface to depth (approximately 0.5 km 3 in volume at a pH of 2.9 to 3.1), killing all aquatic life, and preventing the annual salmon run. Over 2 months later, crater lake water sampled 8 km downstream of the outlet after considerable dilution from glacial meltwater was a weak sulfuric acid solution (pH = 3.2, SO 4 = 504 mg/L, Cl = 53.6 mg/L, and F = 7.92 mg/L). The acid flood waters caused severe vegetation damage, including plant death and leaf kill along the flood path. The crater lake drainage was accompanied by an ambioructic flow of acidic aerosols that followed the flood path, contributing to defoliation and necrotic leaf damage to vegetation in a 29 km 2 area along and above affected streams, in areas to heights of over 150 m above stream level. Moss species killed in the event contained high levels of sulfur, indicating extremely elevated atmospheric sulfurcontent. The most abundant airborne phytotoxic constituent was likely sulfuric acid aerosols that were generated during the catastrophic partial crater lake drainage event. Two mechanisms of acidic aerosol formation are proposed: (1) generation of aerosol mist through turbulent flow of acidic water and (2) catastrophic gas exsolution. This previously undocumented phenomenon of simultaneous vegetationdamaging acidic aerosols accompanying drainage of an acidic crater lake has important implications for the study of hazards associated with active volcanic crater lakes. Copyright 2008 by the American Geophysical Union.

Geochemistry, Geophysics, Geosystems↗

USGS2026

Using sediment chemical fractions and multivariate statistics on water to identify sources, mobility, and bioavailability of aluminum in the Florida River near Durango, Colorado

The Florida River in southwestern Colorado, USA, flows through the Southern Ute Reservation and is a cultural and water resource to Tribal and non-Tribal communities. High concentrations of total Al, up to 16 400 µg l –1 , have been detected in the Florida River. Elevated Al concentrations in water may affect aquatic organisms’ ability to regulate ions and inhibit respiratory functions. Water chemistry collected during three sampling events in 2022 from the Florida River and two of its tributaries are used here to better understand the spatial distribution, seasonality, and sources of Al concentrations in the Florida River. Streambed sediment and rock chemistry is also used to infer geologic sources of Al in the watershed. A five-stage sequential extraction was performed on streambed sediment and rock samples to help determine Al transport processes. We assessed relations between major and trace elements in water using a principal component analysis, finding that high Al concentrations in the Florida River (>3500 µg l –1 total Al) are caused by the erosion of Al-laden sediments. We used a stepwise multiple linear regression to investigate the relationship between land use and Al concentrations. Land use did not reliably predict Al concentration, though increased streamflow connected to reservoir releases – particularly in the Salt Creek tributary – were found to contribute Al to the Florida River during the irrigation season. In this study, we demonstrate that successful metal source appropriation may be achieved through limited field sampling when performed with sufficient water chemistry analysis, sequential chemical extraction of stream sediments, and statistical and land-use analysis.

Colorado↗