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1.
Exploration of unconventional natural gas reservoirs such as impermeable shale basins through the use of horizontal drilling and hydraulic fracturing has changed the energy landscape in the USA providing a vast new energy source. The accelerated production of natural gas has triggered a debate concerning the safety and possible environmental impacts of these operations. This study investigates one of the critical aspects of the environmental effects; the possible degradation of water quality in shallow aquifers overlying producing shale formations. The geochemistry of domestic groundwater wells was investigated in aquifers overlying the Fayetteville Shale in north-central Arkansas, where approximately 4000 wells have been drilled since 2004 to extract unconventional natural gas. Monitoring was performed on 127 drinking water wells and the geochemistry of major ions, trace metals, CH4 gas content and its C isotopes (δ13CCH4), and select isotope tracers (δ11B, 87Sr/86Sr, δ2H, δ18O, δ13CDIC) compared to the composition of flowback-water samples directly from Fayetteville Shale gas wells. Dissolved CH4 was detected in 63% of the drinking-water wells (32 of 51 samples), but only six wells exceeded concentrations of 0.5 mg CH4/L. The δ13CCH4 of dissolved CH4 ranged from −42.3‰ to −74.7‰, with the most negative values characteristic of a biogenic source also associated with the highest observed CH4 concentrations, with a possible minor contribution of trace amounts of thermogenic CH4. The majority of these values are distinct from the reported thermogenic composition of the Fayetteville Shale gas (δ13CCH4 = −35.4‰ to −41.9‰). Based on major element chemistry, four shallow groundwater types were identified: (1) low (<100 mg/L) total dissolved solids (TDS), (2) TDS > 100 mg/L and Ca–HCO3 dominated, (3) TDS > 100 mg/L and Na–HCO3 dominated, and (4) slightly saline groundwater with TDS > 100 mg/L and Cl > 20 mg/L with elevated Br/Cl ratios (>0.001). The Sr (87Sr/86Sr = 0.7097–0.7166), C (δ13CDIC = −21.3‰ to −4.7‰), and B (δ11B = 3.9–32.9‰) isotopes clearly reflect water–rock interactions within the aquifer rocks, while the stable O and H isotopic composition mimics the local meteoric water composition. Overall, there was a geochemical gradient from low-mineralized recharge water to more evolved Ca–HCO3, and higher-mineralized Na–HCO3 composition generated by a combination of carbonate dissolution, silicate weathering, and reverse base-exchange reactions. The chemical and isotopic compositions of the bulk shallow groundwater samples were distinct from the Na–Cl type Fayetteville flowback/produced waters (TDS ∼10,000–20,000 mg/L). Yet, the high Br/Cl variations in a small subset of saline shallow groundwater suggest that they were derived from dilution of saline water similar to the brine in the Fayetteville Shale. Nonetheless, no spatial relationship was found between CH4 and salinity occurrences in shallow drinking water wells with proximity to shale-gas drilling sites. The integration of multiple geochemical and isotopic proxies shows no direct evidence of contamination in shallow drinking-water aquifers associated with natural gas extraction from the Fayetteville Shale. 相似文献
2.
《Applied Geochemistry》2005,20(5):961-972
The temperature dependence of the self-diffusion of HTO, 22Na+ and 36Cl− in Opalinus Clay (OPA) was studied using a through-diffusion technique, in which the temperature was gradually increased in the steady state phase of the diffusion. The measurements were done on samples from two different geological locations. The dependence of the effective diffusion coefficient on temperature was found to be of an Arrhenius type in the temperature range between 0 and 70 °C. A slight difference between the two locations could be observed. The average value of the activation energy of the self-diffusion of HTO in OPA was 21.1 ± 1.6 kJ mol−1, and 21.0 ± 3.5 and 19.4 ± 1.5 kJ mol−1 for 22Na+ and 36Cl−, respectively. The measured values for HTO are slightly higher than the values found for the bulk liquid water (HTO: 18.8 ± 0.4 kJ mol−1). This indicates that the structure of the confined water in OPA might be slightly different from that of bulk liquid water. Also for Na+ and Cl−, slightly higher values than in bulk liquid water (Na+: 18.4 kJ mol−1; Cl−: 17.4 kJ mol−1) were observed.The Stokes–Einstein relationship, based on the temperature dependency of the viscosity of bulk water, could not be used to describe the temperature dependence of the diffusion of HTO in OPA. This additionally indicates the slightly different structure of the pore water in OPA. 相似文献
3.
《Applied Geochemistry》2004,19(8):1255-1293
In order to investigate the mechanism of As release to anoxic ground water in alluvial aquifers, the authors sampled ground waters from 3 piezometer nests, 79 shallow (<45 m) wells, and 6 deep (>80 m) wells, in an area 750 m by 450 m, just north of Barasat, near Kolkata (Calcutta), in southern West Bengal. High concentrations of As (200–1180 μg L−1) are accompanied by high concentrations of Fe (3–13.7 mg L−1) and PO4 (1–6.5 mg L−1). Ground water that is rich in Mn (1–5.3 mg L−1) contains <50 μg L−1 of As. The composition of shallow ground water varies at the 100-m scale laterally and the metre-scale vertically, with vertical gradients in As concentration reaching 200 μg L−1 m−1. The As is supplied by reductive dissolution of FeOOH and release of the sorbed As to solution. The process is driven by natural organic matter in peaty strata both within the aquifer sands and in the overlying confining unit. In well waters, thermo-tolerant coliforms, a proxy for faecal contamination, are not present in high numbers (<10 cfu/100 ml in 85% of wells) showing that faecally-derived organic matter does not enter the aquifer, does not drive reduction of FeOOH, and so does not release As to ground water.Arsenic concentrations are high (≫50 μg L−1) where reduction of FeOOH is complete and its entire load of sorbed As is released to solution, at which point the aquifer sediments become grey in colour as FeOOH vanishes. Where reduction is incomplete, the sediments are brown in colour and resorption of As to residual FeOOH keeps As concentrations below 10 μg L−1 in the presence of dissolved Fe. Sorbed As released by reduction of Mn oxides does not increase As in ground water because the As resorbs to FeOOH. High concentrations of As are common in alluvial aquifers of the Bengal Basin arise because Himalayan erosion supplies immature sediments, with low surface-loadings of FeOOH on mineral grains, to a depositional environment that is rich in organic mater so that complete reduction of FeOOH is common. 相似文献
4.
Large quantities of highly saline brine flow from gas wells in the Marcellus Formation after hydraulic stimulation (“fracking”). This study assesses the composition of these flowback waters from the Marcellus shale in Pennsylvania, USA. Concentrations of most inorganic components of flowback water (Cl, Br, Na, K, Ca, Mg, Sr, Ba, Ra, Fe, Mn, total dissolved solids, and others) increase with time from a well after hydraulic stimulation. Based on results in several datasets reported here, the greatest concentration of Cl− in flowback water is 151,000 mg/L. For total Ra (combined 226Ra and 228Ra) in flowback, the highest level reported is 6540 pCi/L. Flowback waters from hydraulic fracturing of Marcellus wells resemble brines produced from conventional gas wells that tap into other Paleozoic formations in the region. The Br/Cl ratio and other parameters indicate that both types of brine formed by the evaporation of seawater followed by dolomitization, sulfate reduction and subsurface mixing with seawater and/or freshwater. Trends and relationships in brine composition indicate that (1) increased salt concentration in flowback is not mainly caused by dissolution of salt or other minerals in rock units, (2) the flowback waters represent a mixture of injection waters with highly concentrated in situ brines similar to those in the other formations, and (3) these waters contain concentrations of Ra and Ba that are commonly hundreds of times the US drinking water standards. 相似文献
5.
Hyperfiltration is the ability of a membrane to retard the passage of a solute under a hydraulic head in excess of osmotic pressure. Disaggregated and recompacted shales, mudstones, clays and tuff have been shown to exhibit hyperfiltration-induced membrane effects in past experiments. However, limestone and dolomite have not previously been tested. Therefore, eight hyperfiltration experiments were performed on intact Burlington Limestone and Jefferson City Dolomite to assess the membrane properties of these lithologies. Four experiments were conducted on each lithology using 0.0050 and 0.0100 M Cl− solutions at heads of 0.50 and 1.00 m. Reflection coefficients, a measure of osmotic efficiency, ranged from 0.34 to 0.39 for the Burlington Limestone and 0.32 to 0.40 for the Jefferson City Dolomite. At the end of the hyperfiltration experiments, Cl− was concentrated within the cell above input concentrations by 85–95% for the Burlington Limestone and 79–105% for the Jefferson City Dolomite. An additional experiment passed 0.0020 M dissolved silica solution through the Burlington Limestone at a head of 0.965 bar (14 psi). The final concentration of silica within the cell was 0.0043 M dissolved silica at steady-state; a concentration 114% higher than the original input solution concentration. The reflection coefficient for this experiment was calculated to be 0.33. The results of these experiments suggest that membrane properties in these lithologies may be worthy of consideration in some geologic scenarios, including: (1) shallow or perched aquifers bounded by thin limestone or dolomite strata, (2) overpressured aquifers bounded by limestone or dolomite, (3) limestone or dolomite bounded aquifers with significant vertical components of flow, and (4) facies changes with significant lateral component of flow bounded by either lithology. Furthermore, the results suggest that silica cementation may be possible even under relatively low head conditions. Cementation due to hyperfiltration, even at shallow depths and low pressures should be further investigated. Similarly, other low permeability lithologies lacking a charged surface could potentially function as geologic membranes. 相似文献
6.
《Applied Geochemistry》2006,21(11):1955-1968
Elemental Hg–Au amalgamation mining practices are used widely in many developing countries resulting in significant Hg contamination of surrounding ecosystems. The authors examined for the first time Hg contamination in air, water, sediment, soil and crops in the Tongguan Au mining area, China, where elemental Hg has been used to extract Au for many years. Total gaseous Hg (TGM) concentrations in ambient air in the Tongguan area were significantly elevated compared to regional background concentrations. The average TGM concentrations in ambient air in a Au mill reached 18,000 ng m−3, which exceeds the maximum allowable occupational standard for TGM of 10,000 ng m−3 in China. Both total and methyl-Hg concentrations in stream water, stream sediment, and soil samples collected in the Tongguan area were elevated compared to methyl-Hg reported in artisanal Au mining areas in Suriname and the Amazon River basin. Total Hg concentrations in vegetable and wheat samples ranged from 42 to 640 μg kg−1, all of which significantly exceed the Chinese guidance limit for vegetables (10 μg kg−1) and foodstuffs other than fish (20 μg kg−1). Fortunately, methyl-Hg was not significantly accumulated in the crops sampled in this study, where concentrations varied from 0.2 to 7.7 μg kg−1. 相似文献
7.
《Chemie der Erde / Geochemistry》2014,74(4):641-651
Groundwaters in the crystalline aquifers are the major source of drinking water in Vaniyambadi area of Vellore district. Geochemical methods in collaboration with statistical methods were applied in this industrial area to understand the natural and anthropogenic influences on groundwater quality. To accomplish this objective, groundwater samples were collected and analyzed for physicochemical parameters and the results showed a dominance in the order of Na+ > Mg2+ > Ca2+ > K+ and HCO3− > Cl− > SO42− > NO3− for anions and cations, respectively. In contrast to this anion dominance were changed to Cl− > HCO3− > SO42− > NO3− in samples collected near the tannery industries. Groundwater quality evaluation using TDS and TH suggested that 57% of the total samples are hard-brackish type, indicating its unsuitability for drinking purpose. Generally the water type is Na+Cl− to Ca2+Mg2+HCO3− type with an intermediate Ca2+Mg2+Cl−, suggesting the mixing of fresh groundwater with tannery effluent and cation exchange. Factor analysis and bivariate plots of major ions suggests that both natural and anthropogenic inputs are equally influencing the groundwater quality. Further investigations proved that silicate weathering is the dominant geogenic source of groundwater solute content, whereas tannery effluent is the anthropogenic source. Saline water mixing index (SWMI) and Cl− vs NO3− bivariate plot were employed to differentiate the tannery contamination from the other anthropogenic inputs such as agricultural fertilizers, municipal sewages, etc. This analysis shows that samples 2, 4, 8 and 9 (located within the tannery cluster) have a SWMI value greater than 1, representing the groundwater–tannery effluent mixing. This study infers that groundwater in the Vaniyambadi area is under serious threat from both natural and anthropogenic contamination. However, the controlling discharge of untreated tannery effluents must be regulated to reduce the further deterioration of this vital resource in this part of the country. 相似文献
8.
《Applied Geochemistry》2005,20(1):55-68
In 49 samples of groundwater, sampled in Muzaffargarh District of south-western Punjab, central Pakistan, concentrations of As exceeded the World Health Organisation provisional guideline value, and United States Environmental Protection Agency (USEPA) Maximum Contaminant Level (MCL), of 10 μg L−1 in 58% of samples and reached up to 906 μg L−1. In this semi-arid region canal irrigation has lead to widespread water-logging, and evaporative concentration of salts has the potential to raise As concentrations in shallow groundwater well above 10 μg L−1. In fact, in rural areas, concentrations stay below 25 μg L−1 because As in the oxic shallow groundwater, and in recharging water, is sorbed to aquifer sediments. In some urban areas, however, shallow groundwater is found to contain elevated levels of As. The spatial distribution of As-rich shallow groundwater indicates either direct contamination with industrial or agricultural chemicals, or some other anthropogenic influence. Geochemical evidence suggests that pollutant organics from unconfined sewage and other sources drives reduction of hydrous ferric oxide (HFO) releasing sorbed As to shallow groundwater. The situation is slightly less clear for seven wells sampled which tap deeper groundwater, all of which were found with >50 μg L−1 As. Here As concentrations seem to increase with depth and differing geochemical signatures are seen, suggesting that As concentrations in older groundwater may be governed by different processes. Other data on parameters of potential concern in drinking water are discussed briefly at the end of the paper. 相似文献
9.
《Applied Geochemistry》2005,20(3):627-638
Concentrations of total Hg and methylmercury (MMHg) in riparian soil, mine-waste calcine, sediment, and moss samples collected from abandoned Hg mines in Wanshan district, Guizhou province, China, were measured to show regional dispersion of Hg-contamination. High total Hg and MMHg concentrations obtained in riparian soils from mined areas, ranged from 5.1 to 790 mg kg−1 and 0.13 to 15 ng g−1, respectively. However, total Hg and MMHg concentrations in the soils collected from control sites were significantly lower varying from 0.1 to 1.2 mg kg−1 and 0.10 to 1.6 ng g−1, respectively. Total Hg and MMHg concentrations in sediments varied from 90 to 930 mg kg−1 and 3.0 to 20 ng g−1, respectively. Total Hg concentrations in mine-waste calcines were highly elevated ranging from 5.7 to 4400 mg kg−1, but MMHg concentrations were generally low ranging from 0.17 to 1.1 ng g−1. Similar to the high Hg concentrations in soil and sediments, moss samples collected from rocks ranged from 1.0 to 95 mg kg−1 in total Hg and from 0.21 to 20 ng g−1 in MMHg. Elevated Hg concentrations in mosses suggest that atmospheric deposition might be an important pathway of Hg to the local terrestrial system. Moreover, the spatial distribution patterns of Hg contamination in the local environment suggest derivation from historic Hg mining sites in the Wanshan area. 相似文献
10.
《Applied Geochemistry》2005,20(3):639-659
The oxidation of sulfide minerals from mine wastes results in the release of oxidation products to groundwater and surface water. The abandoned high-sulfide Camp tailings impoundment at Sherridon, Manitoba, wherein the tailings have undergone oxidation for more than 70 a, was investigated by hydrogeological, geochemical, and mineralogical techniques. Mineralogical analysis indicates that the unoxidized tailings contain nearly equal proportions of pyrite and pyrrhotite, which make up to 60 wt% of the total tailings, and which are accompanied by minor amounts of chalcopyrite and sphalerite, and minute amounts of galena and arsenopyrite. Extensive oxidation in the upper 50 cm of the tailings has resulted in extremely high concentrations of dissolved SO4 and metals and As in the tailings pore water (pH < 1, 129,000 mg L−1 Fe, 280,000 mg L−1 SO4, 55,000 mg L−1 Zn, 7200 mg L−1 Al, 1600 mg L−1 Cu, 260 mg L−1 Mn, 110 mg L−1 Co, 97 mg L−1 Cd, 40 mg L−1 As, 15 mg L−1 Ni, 8 mg L−1 Pb, and 3 mg L−1 Cr). The acid released from sulfide oxidation has been extensive enough to deplete carbonate minerals to 6 m depth and to partly deplete Al-silicate minerals to a 1 m depth. Below 1 m, sulfide oxidation has resulted in the formation of a continuous hardpan layer that is >1 m thick. Geochemical modeling and mineralogical analysis indicate that the hardpan layer consists of secondary melanterite, rozenite, gypsum, jarosite, and goethite. The minerals indicated mainly control the dissolved concentrations of SO4, Fe, Ca and K. The highest concentrations of dissolved metals are observed directly above and within the massive hardpan layer. Near the water table at a depth of 4 m, most metals and SO4 sharply decline in concentration. Although dissolved concentrations of metals and SO4 decrease below the water table, these concentrations remain elevated throughout the tailings, with up to 60,600 mg L−1 Fe and 91,600 mg L−1 SO4 observed in the deeper groundwater. During precipitation events, surface seeps develop along the flanks of the impoundment and discharge pore water with a geochemical composition that is similar to the composition of water directly above the hardpan. These results suggest that shallow lateral flow of water from a transient perched water table is resulting in higher contaminant loadings than would be predicted if it were assumed that discharge is derived solely from the deeper primary water table. The abundance of residual sulfide minerals, the depletion of aluminosilicate minerals in the upper meter of the tailings and the presence of a significant mass of residual sulfide minerals in this zone after 70 a of oxidation suggest that sulfide oxidation will continue to release acid, metals, and SO4 to the environment for decades to centuries. 相似文献
11.
Natural gas reservoirs in organic-rich shales in the Appalachian and Michigan basins in the United States are currently being produced via hydraulic fracturing. Stratigraphically-equivalent shales occur in the Canadian portion of the basins in southwestern Ontario with anecdotal evidence of gas shows, yet there has been no commercial shale gas production to date. To provide baseline data in the case of future environmental issues related to hydraulic fracturing and shale gas production, such as leakage of natural gas, saline water, and/or hydraulic fracturing fluids, and to evaluate hydrogeochemical controls on natural gas accumulations in shallow groundwater in general, this study investigates the origin and distribution of natural gas and brine in shallow aquifers across southwestern Ontario. An extensive geochemical database of major ion and trace metal chemistry and methane concentrations of 1010 groundwater samples from shallow, domestic wells in bedrock and overburden aquifers throughout southwestern Ontario was utilized. In addition, select wells (n = 36) were resampled for detailed dissolved gas composition, δ13C of CH4, C2, C3, and CO2, and δD of CH4. Dissolved gases in groundwater from bedrock and overburden wells were composed primarily of CH4 (29.7–98.6 mol% of total gas volume), N2 (0.8–66.2 mol%), Ar + O2 (0.2–3.4 mol%), and CO2 (0–1.2 mol%). Ethane was detected, but only in low concentrations (<0.041 mol%), and no other higher chain hydrocarbons were present, except for one well in overburden overlying the Dundee Formation, which contained 0.81 mol% ethane and 0.21 mol% propane. The highest methane concentrations (30 to >100 in situ % saturation) were found in bedrock wells completed in the Upper Devonian Kettle Point Formation, Middle Devonian Hamilton Group and Dundee Formation, and in surficial aquifers overlying these organic-rich shale-bearing formations, indicating that bedrock geology is the primary control on methane occurrences. A few (n = 40) samples showed Na–Cl–Br evidence of brine mixing with dilute groundwater, however only one of these samples contained high (>60 in situ % saturation) CH4. The relatively low δ13C values of CH4 (−89.9‰ to −57.3‰), covariance of δD values of CH4 and H2O, positive correlation between δ13C values of CH4 and CO2, and lack of higher chain hydrocarbons (C3+) in all but one dissolved gas sample indicates that the methane in groundwater throughout the study area is primarily microbial in origin. The presence or absence of alternative electron acceptors (e.g. dissolved oxygen, Fe, NO3, SO4), in addition to organic substrates, controls the occurrence of microbial CH4 in shallow aquifers. Microbial methane has likely been accumulating in the study area, since at least the Late Pleistocene to the present, as indicated by the co-variance and range of δD values of CH4 (−314‰ to −263‰) and associated groundwater (−19‰ to −6‰ δD-H2O). 相似文献
12.
《Applied Geochemistry》2006,21(11):1986-1998
Elevated concentrations of Hg are present (averaging 36 μg/g), mainly as cinnabar, in the Murray Brook Au deposit, located in northern New Brunswick, Canada. After the mined ore was subjected to CN leaching, the tailings were deposited in an unsaturated pile, and 10 a after mine closure an estimated 4.7 × 103 kg of CN and 1.1 × 104 kg of Hg remain in the pile. Elevated Hg concentrations have been measured in the groundwater (up to 11,500 μg/L) and surface water (up to 32 μg/L) down-gradient of the tailings. To investigate the controls on Hg mobility and leaching persistence, laboratory experiments were conducted using unsaturated columns filled with tailings. Within the first 0.2 pore volumes (PV) eluted, the concentrations of Hg and CN increased to peak concentrations of 12,900 μg Hg/L and 16 mg CN/L, respectively. In the subsequent 0.9 PV, concentrations decreased to approximately 1300 μg Hg/L and 2.8 mg CN/L. Thermodynamic calculations demonstrate that >99.8% of the mobilized Hg in the tailings pore water is in the form of Hg–CN complexes, indicating that Hg mobility to the surrounding aquatic environment is directly dependent on the rate of CN leaching. One-dimensional transport simulations suggest that leached CN can be partitioned into conservative (24%) and non-conservative (76%) fractions. Extrapolation of simulation results to the field scale suggests that CN, and by extension Hg, will continue to elute from the tailings for at least an additional 130 a. 相似文献
13.
《Journal of Asian Earth Sciences》2003,21(4):423-429
In Saudi Arabia, coastal sabkhas cover extensive areas along the coasts of the Red Sea and Arabian Gulf in addition to the continental sabkhas scattered in many places inland. Al-Lith sabkha is one of the typical coastal sabkhas located along the Red Sea coast. Sabkhas, in general, pose a number of geotechnical problems and need to be carefully investigated before being urbanized.A generalized geologic section in Al-Lith sabkha indicates a salty crust at the surface followed by yellowish brown silt and silty sand, olive gray silt and sandy silt and bottomed by coralline reefal limestone. Within this succession, there are several isolated lenticular bodies of sandy silt, silty sand and shelly silty sand. The clay minerals constituting the fine-grained portion of the soil are, in decreasing order, kaolinite, illite and montmorillonite in addition to minor chlorite.The depth to groundwater in 17 observation wells ranged from 0.18 to 1.81 m with a maximum fluctuation of 0.60 m between summer and winter. The permeability of the top silt layer was found to be very low with an average of 5.4×10−4 m/day. A pumping test was performed in a deep well penetrating the coralline limestone. The measured permeability is 1.1×102 m/day and the estimated storage coefficient is 4×10−5.Soil water evaporation was measured using a lysimeter constructed with undisturbed soil samples having different depths to the water level. The rate of evaporation ranges from 2.8 to 27.8 ml/day decreasing with an increase in depth to the water level.Groundwater samples were analyzed for their major anions and cations. Salt concentrations show a general increase toward the sea except for the calcium and carbonates that show a landward increase. The groundwater could be classified as a Cl+SO4 brine. The salinity of the groundwater was determined at different depths in the pumping well and was found to be low in the top 4 m. It sharply increases until it reaches a value approximately 10 times the salinity of the top layer indicating groundwater intermixing with freshwater and salt-water intrusion. The change in the salinity during pumping was erratic but within a range of 2%. 相似文献
14.
Dissolved and particulate Zn and Ni concentrations were determined at 76 locations along the Yangtze River basin from the headwaters to the estuary during flood and dry seasons. Spatial and temporal variations of Zn and Ni were investigated and six major source zones were identified. The Three Gorges Dam (TGD) blocked most of the suspended loads and extremely low concentration of Zn and Ni were observed downstream of the dam. Dissolved (ranging from 0.062 to 8.0 μg L−1) and particulate (ranging from 12 to 110 mg kg−1) Ni showed similar levels of concentrations during flood and dry seasons, whereas dissolved (ranging from 0.43 to 49 μg L−1) and particulate (ranging from 54 to 1100 mg kg−1) Zn were slightly and much lower in the flood season than dry season, respectively. This was attributed to the increased water discharge during the flood season causing a dilution effect and sediment resuspension. In the flood season, average concentrations of Zn and Ni were higher in the main channel than in tributaries, due to soil erosion and mining activities providing the dominant inputs. The situation was opposite in the dry season, attributed to the contribution of municipal sewage, industrial activities, and waste disposal. During the flood season, dissolved Zn and Ni concentrations were negatively correlated with pH. Water and suspended particulate matter (SPM) from the upper reaches, middle reaches, and lower reaches of the Yangtze River were characterized by their Zn and Ni concentrations. The Panzhihua, Nanling and Tongling mining areas were considered as the most important source zones of particulate Zn and Ni. The Chongqing region, Wuhan region and the Yangtze River Delta provided most of the dissolved Zn and Ni inputs into the river. Annual net flux of Zn (10–72 × 105 kg a−1) and Ni (5.0–19 × 105 kg a−1) in each source zone were estimated according to their respective influent and effluent fluxes. Contributions of the source zones to Zn and Ni transport decreased from the upper reaches to the lower reaches. 相似文献
15.
《Applied Geochemistry》2006,21(11):1868-1879
Ultra-clean sampling methods and approaches typically used in pristine environments were applied to quantify concentrations of Hg species in water and microbial biomass from hot springs of Yellowstone National Park, features that are geologically enriched with Hg. Microbial populations of chemically-diverse hot springs were also characterized using modern methods in molecular biology as the initial step toward ongoing work linking Hg speciation with microbial processes. Molecular methods (amplification of environmental DNA using 16S rDNA primers, cloning, denatured gradient gel electrophoresis (DGGE) screening of clone libraries, and sequencing of representative clones) were used to examine the dominant members of microbial communities in hot springs. Total Hg (THg), monomethylated Hg (MeHg), pH, temperature, and other parameters influential to Hg speciation and microbial ecology are reported for hot springs water and associated microbial mats.Several hot springs indicate the presence of MeHg in microbial mats with concentrations ranging from 1 to 10 ng g−1 (dry weight). Concentrations of THg in mats ranged from 4.9 to 120,000 ng g−1 (dry weight). Combined data from surveys of geothermal water, lakes, and streams show that aqueous THg concentrations range from l to 600 ng L−1. Species and concentrations of THg in mats and water vary significantly between hot springs, as do the microorganisms found at each site. 相似文献
16.
The unadjusted 72-h gross alpha activities in water from two wells completed in marine and alluvial deposits in a coastal southern California aquifer 40 km north of San Diego were 15 and 25 picoCuries per liter (pCi/L). Although activities were below the Maximum Contaminant Level (MCL) of 15 pCi/L, when adjusted for uranium activity; there is concern that new wells in the area may exceed MCLs, or that future regulations may limit water use from the wells. Coupled well-bore flow and depth-dependent water-quality data collected from the wells in 2011 (with analyses for isotopes within the uranium, actinium, and thorium decay-chains) show gross alpha activity in marine deposits is associated with decay of naturally-occurring 238U and its daughter 234U. Radon activities in marine deposits were as high as 2230 pCi/L. In contrast, gross alpha activities in overlying alluvium within the Piedra de Lumbre watershed, eroded from the nearby San Onofre Hills, were associated with decay of 232Th, including its daughter 224Ra. Radon activities in alluvium from Piedra de Lumbre of 450 pCi/L were lower than in marine deposits. Chromium VI concentrations in marine deposits were less than the California MCL of 10 μg/L (effective July 1, 2014) but δ53Cr compositions were near zero and within reported ranges for anthropogenic chromium. Alluvial deposits from the nearby Las Flores watershed, which drains a larger area having diverse geology, has low alpha activities and chromium as a result of geologic and geochemical conditions and may be more promising for future water-supply development. 相似文献
17.
《Chemie der Erde / Geochemistry》2015,75(3):323-334
The current study was designed to investigate the extent and severity of contamination as well as the fractionation of potentially toxic elements (As, Cd, Cr, Cu, Pb, Zn, Ni) in minesoils and agricultural soils around a Pb–Zn mine in central Iran. For this purpose, 20 agricultural soils and eight minesoils were geochemically characterized. Results showed that minesoils contained elevated concentrations of As (12.9–254 mg kg−1), Cd (1.2–55.1 mg kg−1), Pb (137–6239 mg kg−1) and Zn (516–48,889 mg kg−1). The agricultural soils were also polluted by As (5.5–57.1 mg kg−1), Cd (0.2–8.5 mg kg−1), Pb (22–3451 mg kg−1) and Zn (94–9907 mg kg−1). The highest recorded concentrations for these elements were in soils influenced directly by tailing ponds. Chromium, Cu and Ni content in agricultural soils (with average value of 74.1, 34.6 and 50.7 mg kg−1, respectively) were slightly higher than the minesoils (with average value of 54.5, 33.1 and 43.4 mg kg−1, respectively). Sequential extraction data indicated that there were some differences between the speciation of PTEs in soil samples. In the agricultural soils, Zn and Cd were mainly associated with carbonate bound fraction, As and Pb with reducible fraction, Cu with oxidisable fraction and Cr and Ni with residual phase. With respect to mobility factor values, Zn and Cd in the agricultural soils have been found to be the most mobile while As mobility is negligible. Also, the mobility factor of As, Cd and Pb in agricultural soils adjoining tailing ponds was high. In minesoil sample Cd was most abundant in the carbonate form, whereas other studied elements were mainly present in the reducible and residual fractions; therefore, despite the high total concentrations of As, Pb and Zn in the minesoils, the environmental risk of these elements was low. Based on the obtained data, a portion of Cu, Cr and Ni input was from agricultural activities. 相似文献
18.
《Applied Geochemistry》2006,21(6):1016-1029
Nitrate concentrations approaching and greater than the maximum contaminant level are impairing the viability of many groundwater basins as drinking water sources. Nitrate isotope data are effective in determining contaminant sources, especially when combined with other isotopic tracers such as stable isotopes of water and 3H–He ages to give insight into the routes and timing of NO3 inputs to the flow system. This combination of techniques is demonstrated in Livermore, CA, where it is determined that low NO3 reclaimed wastewater predominates in the NW, while two flowpaths with distinct NO3 sources originate in the SE. Along the eastern flowpath, δ15N values greater than 10‰ indicate that animal waste is the primary source. Diminishing concentrations over time suggest that contamination results from historical land use practices. The other flowpath begins in an area where rapid recharge, primarily of low-NO3 imported water (identified by stable isotopes of water and a 3H–He residence time of <1 year), mobilizes a significant local NO3 source, bringing groundwater concentrations up to 53 mg NO3 L−1. In this area, artificial recharge of imported water via local arroyos increases the flux of NO3 to the regional aquifer. The low δ15N value (3.1‰) in this location implicates synthetic fertilizer. In addition to these anthropogenic sources, natural NO3 background levels between 15 and 20 mg NO3 L−1 are found in deep wells with residence times greater than 50 a. 相似文献
19.
《Applied Geochemistry》2006,21(11):1855-1867
Methylmercury (MeHg) and total Hg (THg) concentrations in soil profiles were monitored in the Thur River basin (Alsace, France), where a chlor-alkali plant has been located in the city of Vieux-Thann since the 1930s. Three soil types were studied according to their characteristics and location in the catchment: industrial soil, grassland soil and alluvial soil. Contamination of MeHg and THg in soil was important in the vicinity of the plant, especially in industrial and alluvial soil. Concentrations of MeHg reached 27 ng g−1 and 29,000 ng g−1 for THg, exceeding the predictable no effect concentration. Significant ecotoxicological risk exists in this area and remedial actions on several soil types are suggested. In each type of soil, MeHg concentrations were highest in topsoil, which decreased with depth. Concentrations of MeHg were negatively correlated with soil organic matter and total S, particularly when MeHg concentrations exceeded 8 ng g−1. Under these conditions, MeHg concentrations in soil seemed to be influenced by THg, soil organic matter and total S concentrations. It was found that high MeHg/THg ratios (near 2%) in soil were mainly related to the combined soil environmental conditions such as low THg concentrations, low organic C/N ratios (<11) and relatively low pH (5–5.5). Nevertheless, even when the MeHg/THg ratio was low (∼0.04%), MeHg and THg concentrations were elevated, up to 13 ng g−1 and to 29,000 ng g−1, respectively. Thus, both THg and MeHg concentrations should be taken into account to assess potential environmental risks of Hg. 相似文献
20.
The relatively stable concentrations of calcium (42.2–122.3 mg/l) and magnesium (48.9–88.1 mg/l) between 2012 and 2013 and their possible weathering paths identified by mass balance models for both soil solutions and stream water from a small salted (regular applications of winter road deicing salt) watershed in New Jersey, USA indicate that the weathering of feldspars and dissolution of carbonates are the primary sources for these cations. However, the relatively stable and lower concentrations of sodium and chloride in soil solutions (19.6–46.1 mg/l for Na and 12.7–88.3 mg/l for Cl) and their fluctuating and higher concentrations in stream water (14.6–103.1 mg/l for Na and 15.2–260.4 mg/l)) from the same watershed during the same period also indicate that road deicing salt is the primary source for sodium and chloride in stream water. Furthermore, positive correlations between calcium and sulfur concentrations (correlation coefficient r = 0.77) and magnesium and sulfur concentrations (r = 0.73) in stream water between 2009 and 2013, as well as positive correlations between sulfur and iron concentrations in soil compositions (r = 0.27), indicate that both the dissolution of gypsum and the oxidation of pyrite into hematite might be the primary sources of sulfate in the watershed. Analyses of water chemistry from the related and much larger Delaware River Watershed (DRW) show that sodium and chloride concentrations have increased steadily (2.7 times for Na and 4.56 times for Cl for 10-year average) due to the regular application of winter deicing salt from 1944 to 2011 for which data are available. The greater increase of stream water chloride concentrations compared with sodium concentrations also results in the steady decline of Na+/Cl− molar ratios from 1.51 to 0.92 for the 10-year average during that time in the DRW and approximately 78% of the chloride in the DRW now being anthropogenic. In addition, the decline of sulfate concentration from 22.08 to 14.59 mg/l (∼34%) for the 10-year average from 1980 to 2011 in the DRW stream water may be attributed to the decline of sulfate levels in atmospheric deposition resulting from enhanced national and state environmental regulations and a shift in local economic activities. There also are more periods of low silica stream water concentrations in the DRW than in the past, perhaps as a result of recent increases in summer stream temperatures combined with an increase of impervious surface area in the region. Warmer stream water might cause the temporary bloom of biota requiring silica, particularly plankton, increasing its uptake from stream water, while an expanded impervious surface area increases the contribution of low-silica runoff water to total stream discharge, thereby lowering the silica concentration in stream water. The combined results of this study illustrate the possible changing anthropogenic factors that can control stream water chemistry in salted watersheds and that these factors need to be taken into account when future water quality regulations and policy are considered. 相似文献