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1.
Groundwater recharge and chemical evolution in the southern High Plains of Texas, USA 总被引：3，自引：1，他引：3
The unconfined High Plains (Ogallala) aquifer is the largest aquifer in the USA and the primary water supply for the semiarid
southern High Plains of Texas and New Mexico. Analyses of water and soils northeast of Amarillo, Texas, together with data
from other regional studies, indicate that processes during recharge control the composition of unconfined groundwater in
the northern half of the southern High Plains. Solute and isotopic data are consistent with a sequence of episodic precipitation,
concentration of solutes in upland soils by evapotranspiration, runoff, and infiltration beneath playas and ditches (modified
locally by return flow of wastewater and irrigation tailwater). Plausible reactions during recharge include oxidation of organic
matter, dissolution and exsolution of CO2, dissolution of CaCO3, silicate weathering, and cation exchange. Si and 14C data suggest leakage from perched aquifers to the High Plains aquifer. Plausible mass-balance models for the High Plains
aquifer include scenarios of flow with leakage but not reactions, flow with reactions but not leakage, and flow with neither
reactions nor leakage. Mechanisms of recharge and chemical evolution delineated in this study agree with those noted for other
aquifers in the south-central and southwestern USA.
Electronic Publication 相似文献
2.
《Applied Geochemistry》1997,12(4):347-366
The research site at Otis Air Base, Cape Cod, Massachusetts, has been developed for hydrogeological and geochemical studies of sewage-effluent contaminated ground water since 1982. Research of hydrologic properties, transport, and chemical and biological processes is ongoing, but the origin of background water chemistry has not been determined.The principal geochemical process giving rise to the observed background water chemistry is CO2-controlled hydrolysis of Na feldspar. Geochemical modeling demonstrated that CO2 sources could vary over the project area. Analyses of unsaturated zone gases showed variations in CO2 which were dependent on land use and vegetative cover in the area of groundwater recharge. Measurements of CO2 in unsaturated-zone gases showed that concentrations of total inorganic C in recharge water should range from about 0.035 to 1.0 mmoles/L in the vicinity of Otis Air Base. Flux of CO2 from the unsaturated zone varied for 4 principal land uses, ranging from 86 gC/m2/yr for low vegetated areas to 1630 gC/m2/yr for a golf course. Carbon dioxide flux from woodlands was 220 gC/m2/yr, lower than reported fluxes of 500 to 600 gC/m2/yr for woodlands in a similar climate. Carbon dioxide flux from grassy areas was 540 gC/m2/yr, higher than reported fluxes of 230 to 490 gC/m2/yr for grasslands in a similar climate. 相似文献
3.
Release of CO2 from surface ocean water owing to precipitation of CaCO3 and the imbalance between biological production of organic matter and its respiration, and their net removal from surface
water to sedimentary storage was studied by means of a quotient θ = (CO2 flux to the atmosphere)/(CaCO3 precipitated). θ depends not only on water temperature and atmospheric CO2 concentration but also on the CaCO3 and organic carbon masses formed. In CO2 generation by CaCO3 precipitation, θ varies from a fraction of 0.44 to 0.79, increasing with decreasing temperature (25 to 5°C), increasing atmospheric
CO2 concentration (195–375 ppmv), and increasing CaCO3 precipitated mass (up to 45% of the initial DIC concentration in surface water). Primary production and net storage of organic
carbon counteracts the CO2 production by carbonate precipitation and it results in lower CO2 emissions from the surface layer. When atmospheric CO2 increases due to the ocean-to-atmosphere flux rather than remaining constant, the amount of CO2 transferred is a non-linear function of the surface layer thickness because of the back-pressure of the rising atmospheric
CO2. For a surface ocean layer approximated by a 50-m-thick euphotic zone that receives input of inorganic and organic carbon
from land, the calculated CO2 flux to the atmosphere is a function of the CaCO3 and Corg net storage rates. In general, the carbonate storage rate has been greater than that of organic carbon. The CO2 flux near the Last Glacial Maximum is 17 to 7×1012 mol/yr (0.2–0.08 Gt C/yr), reflecting the range of organic carbon storage rates in sediments, and for pre-industrial time
it is 38–42×1012 mol/yr (0.46–0.50 Gt C/yr). Within the imbalanced global carbon cycle, our estimates indicate that prior to anthropogenic
emissions of CO2 to the atmosphere the land organic reservoir was gaining carbon and the surface ocean was losing carbon, calcium, and total
alkalinity owing to the CaCO3 storage and consequent emission of CO2. These results are in agreement with the conclusions of a number of other investigators. As the CO2 uptake in mineral weathering is a major flux in the global carbon cycle, the CO2 weathering pathway that originates in the CO2 produced by remineralization of soil humus rather than by direct uptake from the atmosphere may reduce the relatively large
imbalances of the atmosphere and land organic reservoir at 102–104-year time scales. 相似文献
4.
The assessment of the environmental impacts of CO2 geological storage requires the investigation of potential CO2 leakages into fresh groundwater, particularly with respect to protected groundwater resources. The geochemical processes and perturbations associated with a CO2 leak into fresh groundwater could alter groundwater quality: indeed, some of the reacting minerals may contain hazardous constituents, which might be released into groundwater. Since the geochemical reactions may occult direct evidence of intruding CO2, it is necessary to characterize these processes and identify possible indirect indicators for monitoring CO2 intrusion. The present study focuses on open questions: Can changes in water quality provide evidence of CO2 leakage? Which parameters can be used to assess impact on freshwater aquifers? What is the time scale of water chemistry degradation in the presence of CO2? The results of an experimental approach allow selecting pertinent isotope tracers as possible indirect indicators of CO2 presence, opening the way to devise an isotopic tracing tool.The study area is located in the Paris Basin (France), which contains deep saline formations identified as targets by French national programs for CO2 geological storage. The study focuses on the multi-layered Albian fresh water aquifer, confined in the central part of the Paris Basin a major strategic potable groundwater overlying the potential CO2 storage formations. An experimental approach (batch reactors) was carried out in order to better understand the rock–water–CO2 interactions with two main objectives. The first was to assess the evolution of the formation water chemistry and mineralogy of the solid phase over time during the interaction. The second concerned the design of an isotopic monitoring program for freshwater resources potentially affected by CO2 leakage. The main focus was to select suitable environmental isotope tracers to track water rock interaction associated with small quantities of CO2 leaking into freshwater aquifers.In order to improve knowledge on the Albian aquifer, and to provide representative samples for the experiments, solid and fluid sampling campaigns were performed throughout the Paris Basin. Albian groundwater is anoxic with high concentrations of Fe, a pH around 7 and a mineral content of 0.3 g L−1. Macroscopic and microscopic solid analyses showed a quartz-rich sand with the presence of illite/smectite, microcline, apatite and glauconite. A water–mineral–CO2 interaction batch experiment was used to investigate the geochemical evolution of the groundwater and the potential release of hazardous trace elements. It was complemented by a multi-isotope approach including δ13CDIC and 87Sr/86Sr. Here the evolution of the concentrations of major and trace elements and isotopic ratios over batch durations from 1 day to 1 month are discussed. Three types of ion behavior are observed: Type I features Ca, SiO2, HCO3, F, PO4, Na, Al, B, Co, K, Li, Mg, Mn, Ni, Pb, Sr, Zn which increased after initial CO2 influx. Type II comprises Be and Fe declining at the start of CO2 injection. Then, type III groups element with no variation during the experiments like Cl and SO4. The results of the multi-isotope approach show significant changes in isotopic ratios with time. The contribution of isotope and chemical data helps in understanding geochemical processes involved in the system. The isotopic systems used in this study are potential indirect indicators of CO2–water–rock interaction and could serve as monitoring tools of CO2 leakage into an aquifer overlying deep saline formations used for C sequestration and storage. 相似文献
5.
Playas are ephemeral, closed-basin wetlands that are hypothesized as an important source of recharge to the High Plains aquifer in central USA. The ephemeral nature of playas, low regional recharge rates, and a strong reliance on groundwater from the High Plains aquifer has prompted many questions regarding the contribution and quality of recharge from playas to the High Plains aquifer. As a result, there has been considerable scientific debate about the potential for water to infiltrate the relatively impermeable playa floors, travel through the unsaturated zone sediments that are tens of meters thick, and subsequently recharge the High Plains aquifer. This critical review examines previously published studies on the processes that control recharge rates and chemistry beneath playas. Reported recharge rates beneath playas range from less than 1.0 to more than 500 mm/yr and are generally 1–2 orders of magnitude higher than recharge rates beneath interplaya settings. Most studies support the conceptual model that playas are important zones of recharge to the High Plains aquifer and are not strictly evaporative pans. The major findings of this review provide science-based implications for management of playas and groundwater resources of the High Plains aquifer and directions for future research. 相似文献
6.
It is challenging to predict the degree to which shallow groundwater might be affected by leaks from a CO2 sequestration reservoir, particularly over long time scales and large spatial scales. In this study observations at a CO2 enriched shallow aquifer natural analog were used to develop a predictive model which is then used to simulate leakage scenarios. This natural analog provides the opportunity to make direct field observations of groundwater chemistry in the presence of elevated CO2, to collect aquifer samples and expose them to CO2 under controlled conditions in the laboratory, and to test the ability of multi-phase reactive transport models to reproduce measured geochemical trends at the field-scale. The field observations suggest that brackish water entrained with the upwelling CO2 are a more significant source of trace metals than in situ mobilization of metals due to exposure to CO2. The study focuses on a single trace metal of concern at this site: U. Experimental results indicate that cation exchange/adsorption and dissolution/precipitation of calcite containing trace amounts of U are important reactions controlling U in groundwater at this site, and that the amount of U associated with calcite is fairly well constrained. Simulations incorporating these results into a 3-D multi-phase reactive transport model are able to reproduce the measured ranges and trends between pH, pCO2, Ca, total C, U and Cl− at the field site. Although the true fluxes at the natural analog site are unknown, the cumulative CO2 flux inferred from these simulations are approximately equivalent to 37.8E−3 MT, approximately corresponding to a .001% leak rate for injection at a large (750 MW) power plant. The leakage scenario simulations suggest that if the leak only persists for a short time the volume of aquifer contaminated by CO2-induced mobilization of U will be relatively small, yet persistent over 100 a. 相似文献
7.
《Applied Geochemistry》2001,16(7-8):745-758
The physical–chemical characteristics of the groundwater in the Baza–Caniles detrital aquifer system indicate that a wide diversity of hydrochemical conditions exists in this semiarid region, defining geochemical zones with distinct groundwater types. The least mineralized water is found closest to the main recharge zones, and the salinity of the water increases significantly with depth towards the center of the basin. Geochemical reaction models have been constructed using water chemistry data along flow paths that characterize the different sectors of the aquifer system, namely: Quaternary aquifer, unconfined sector and shallow and deep confined sectors of the Mio–Pliocene aquifer. Geochemical mass–balance calculations indicate that the dominant groundwater reaction throughout the detrital system is dedolomitisation (dolomite dissolution and calcite precipitation driven by gypsum dissolution); this process is highly developed in the central part of the basin due to the abundance of evaporites. Apart from this process, there are others which influence the geochemical zoning of the system. In the Quaternary aquifer, which behaves as a system open to gases and which receives inputs of CO2 gas derived from the intensive farming in the area, the interaction of the CO2 with the carbonate matrix of the aquifer produces an increase in the alkalinity of the water. In the shallow confined sector of the Mio–Pliocene aquifer, the process of dedolomitisation evolves in a system closed to CO2 gas. Ca2+/Na+ cation exchange and halite dissolution processes are locally important, which gives rise to a relatively saline water. Finally, in the deep confined sector, a strongly reducing environment exists, in which the presence of H2S and NH+4 in the highly mineralized groundwater can be detected. In this geochemical zone, the groundwater system is considered to be closed to CO2 gas proceeding from external sources, but open to CO2 from oxidation of organic matter. The geochemical modeling indicates that the chemical characteristics of this saline water are mainly due to SO4 dissolution, dedolomitisation and SO4 reduction, coupled with microbial degradation of lignite. 相似文献
8.
Hydrogeochemistry and isotope techniques to determine water interactions in groundwater-dependent shallow lakes,Wet Pampa Plain,Argentina 总被引：1，自引：0，他引：1
Asunción Romanelli Orlando Mauricio Quiroz Londoño Daniel Emilio Martínez Héctor Enrique Massone Alicia Haydée Escalante 《Environmental Earth Sciences》2014,71(4):1953-1966
This paper gives an account of the implementation of hydrochemical and isotopic techniques to identify and explain the processes that govern solute exchange in two groundwater-dependent shallow lakes in the Southeastern Pampa Plain of Argentina. Water samples (lakes, streams, spring water and groundwater) for hydrochemical and stable isotopic determination were collected and the main physical–chemical parameters were measured. The combination of stable isotope data with hydrogeochemical techniques was used for the identification of sources and preferential recharge areas to these aquatic ecosystems which allowed the explanation of the lake water origin. The hydrochemical processes which explain Los Padres Lake water chemistry are evaporation from groundwater, CO2 input, calcite dissolution, Na+ release by Ca2+ and Mg2+ exchange, and sulfate reduction. The model that best aligns with La Brava Lake hydrochemical constraints includes: mixing, CO2 and calcite dissolution, cationic exchange with Na+ release and Mg2+ adsorption, and to a lesser extent, Ca/Na exchange. This model suggests that the fractured aquifer contribution to this water body is greater than 50 %. An isotopic-specific fingerprint for each lake was identified, finding a higher evaporation rate for La Brava Lake compared to Los Padres Lake. Isotopic data demonstrate the importance of these shallow lakes as recharge areas to the regional aquifer, becoming areas of high groundwater vulnerability. The Tandilia Range System, considered in many hydrogeological studies as the impermeable bedrock of the Pampean aquifer, acts as a fissured aquifer in this area, contributing to low salinity waters and with a fingerprint similar to groundwater isotopic composition. 相似文献
9.
Aquifer-based groundwater quality assessment offers critical insight into the major hydrochemical processes, and aids in making groundwater resources management decisions. The Texas Rolling Plains (TRP), spanning over 22 counties, is a major agro-ecological region in Texas from where highest groundwater nitrate (NO3 ?) levels in the state have been reported. In this study, we present a comparative assessment of major hydrochemical facies pertaining to NO3 ? contamination and a host of species such as sulfate (SO4 2?), chloride (Cl?), and total dissolved solids (TDS) in different water use classes in the Seymour and Blaine aquifers, underlying the TRP. Aquifer-stratified groundwater quality information from 1990 to 2010 was obtained from the Texas Water Development Board and aggregated over decadal scale. High groundwater salinization was found in the municipal water use class in the Blaine aquifer with about 100, 87 and 50 % of observations exceeding the secondary maximum contaminant level for TDS, SO4 2?, and Cl?, respectively in the 2000s (2000–2010). The NO3-contamination was more alarming in the Seymour aquifer with 82 and 61 % of observations, respectively, exceeding the maximum contaminant level (MCL) in the irrigation and municipal water use classes in the 2000s. Salinization was more influenced by SO4 2? and Cl? in the Blaine aquifer and by NO3 ? in the Seymour aquifer. High NO3 ? (>MCL) observations in the Seymour aquifer occurred in the Ca–HCO3 and Ca–Mg–HCO3 facies, the domains of fresh water recharge and anthropogenic influences (e.g., agricultural activities, waste disposal). High SO4 2?, Cl? and TDS observations in the Blaine aquifer dominated the Ca–Cl, Na–Cl, and mixed Ca(Mg)–SO4(Cl) facies indicating evaporite dissolution, mixing and solute exchange, and lack of fresh recharge. 相似文献
10.
Mengnjo Jude Wirmvem Takeshi Ohba Linus Anye Nche Brice Tchakam Kamtchueng Wiylahnyuy Edith Kongnso Mumbfu Ernestine Mimba Tasin Godlove Bafon Muga Yaguchi Gloria Eneke Takem Wilson Yetoh Fantong Ako Andrew Ako 《Environmental Earth Sciences》2017,76(9):354
High water demand for domestic use in Douala with over 3 million inhabitants is met mainly by shallow groundwater. Field measurements and water sampling in January 2015 were carried out to examine the major controls on the groundwater composition and spatial view of ions in the water, timing of recharge and link between the recharge process and quality of the water. Fifty-two water samples were analysed for major ions and stable hydrogen and oxygen isotopes. Low pH values (3.61–6.92) in the groundwater indicated an acidic aquifer; thus, prone to acidification. The dominant water type was Na–Cl. Nitrate, which exceeded the WHO guide value of 50 mg/l in 22% of the groundwater, poses a health problem. Mass ratios of Cl?/Br? in the water ranged from 54 to 3249 and scattered mostly along the mixing lines between dilute waters, septic-tank effluent and domestic sewage. A majority of the samples, especially the high NO3 ? shallow wells, clustered around the septic-tank effluent-end-member indicating high contamination by seepage from pit latrines; hence, vulnerable to pollution. Stable isotopes in the groundwater indicated its meteoric origin and rapid infiltration after rainfall. The δ18O values showed narrow ranges and overlaps in rivers, springs, open wells and boreholes. These observations depict hydraulic connectivity, good water mixing and a homogeneous aquifer system mainly receiving local direct uniform areal recharge from rainfall. The rapid and diffused recharge favours the leaching of effluent from the pit toilets into the aquifer; hence, the high NO3 ? and Cl? in shallow wells. Silicate weathering, ion exchange and leaching of waste from pit toilets are the dominant controls on the groundwater chemistry. Drilling of deep boreholes is highly recommended for good-quality water supply. However, due the hydraulic connection to the shallow aquifer, geochemical modelling of future effects of such an exploitation of the deeper aquifer should support groundwater management and be ahead of the field actions. 相似文献
11.
Groundwater surveys were performed by detailed(around 300 sites) grid-analysis of water temperature, pH, redox potential, electrical conductivity, 222Rn, alkalinity and by calculating the pCO2, throughout the Ciampino and Marino towns in the Alban Hills quiescent volcano (Central Italy). Following several episodes of dangerous CO2 exhalation from soils during the last 20 years and earlier ashistorically recorded, the work aimed at assessing the Natural Gas Hazard (NGH) including the indoor-Rn hazard. The NGH was defined as the probability of an area to become a site of poisonous peri-volcanic gas exhalations from soils to the lower atmosphere (comprising buildings). CO2 was found to be a ``carrier' for the other poisonous minor and in trace components (HsS, CH4, 222Rn, etc.). This assessment was performed by extrapolating in the aquifer CO2 and 222Rn conditions, and discriminating sectors where future CO2 flux in soils as well as indoor-Rn measurements have to be noted. A preliminary indoor-Rn survey was performed at about 200 sites. The highest values were found in the highest pCO2 and high 222Rn values in groundwater. This indicates convection and enhanced permeability in certain sectors of the main aquifer, i.e., along the bordering faults and inside the gas-trap of the Ciampino Horst., where ``continuous gas-phase micro-macro seepage mechanism' is invoked to explain the high peri-volcanic gases flux. 相似文献
12.
Groundwater samples from boreholes and springs in the unconfined Chalk aquifer of Cambridgeshire were analysed for N2O and other N species on a monthly basis between March 1995 and February 1996. Land use in the study area is devoted to intensive arable farming supported by the application of N-based fertilisers. All groundwater samples were strongly oversaturated with N2O, with concentrations ranging from 13 to 320 times the saturation concentration with respect to air-equilibrated water.A very good positive correlation between N2O and NO3 concentrations was obtained (r2=0.80), but no relationship was established between N2O and NO2 or NH4 concentrations. Concentrations of N2O and NO3 increased continuously in the direction of groundwater flow, with molar net gain ratios of NO3 to N2O varying between 204 and 410. These ratios are within the range reported in previous studies of nitrification. Corresponding dissolved O2 levels in groundwater samples were moderately undersaturated, further indicating that the main source of N2O in Chalk groundwater in Cambridgeshire is probably nitrification. No consumption of N2O seems to take place within the unconfined aquifer with degassing to the atmosphere apparently being the sole mechanism for N2O removal from groundwater.An estimated N2O flux of around 0.05 kg N2O ha−1 a−1 from the sampled groundwater discharge points to the atmosphere was calculated for the study area. This figure is likely to be much higher, since it does not account for diffuse N2O emissions from groundwater seepage areas or any degassing from the unconfined aquifer through the unsaturated zone. Both these processes will contribute substantially to the total aerial flux, thus suggesting that groundwater may be a significant contributor to the global N2O budget. 相似文献
13.
Saed Khayat Peter Möller Stefan Geyer Amer Marei Christian Siebert Fayez Abu Hilo 《Environmental Geology》2009,57(8):1739-1751
The spatial and temporal changes of the composition of the groundwater from the springs along the Wadi Qilt stream running
from the Jerusalem–Ramallah Mountains towards the Jericho Plain is studied during the hydrological year 2006/2007. The residence
time and the intensity of recharge play an important role in controlling the chemical composition of spring water which mainly
depends on distance from the main recharge area. A very important factor is the oxidation of organics derived from sewage
and garbage resulting in variable dissolved CO2 and associated HCO3
− concentration. High CO2 yields lower pH values and thus under-saturation with respect to calcite and dolomite. Low CO2 concentrations result in over-saturation. Only at the beginning and at the end of the rainy season calcite saturation is
achieved. The degradation of dissolved organic matter is a major source for increasing water hardness. Besides dissolution
of carbonates dissolved species such as nitrate, chloride, and sulfate are leached from soil and aquifer rocks together with
only small amounts of Mg. Mg not only originates from carbonates but also from Mg–Cl waters are leached from aquifer rocks.
Leaching of Mg–Cl brines is particularly high at the beginning of the winter season and lowest at its end. Two zones of recharge
are distinguishable. Zone 1 represented by Ein Fara and Ein Qilt is fed directly through the infiltration of meteoric water
and surface runoff from the mountains along the eastern mountain slopes with little groundwater residence time and high flow
rate. The second zone is near the western border of Jericho at the foothills, which is mainly fed by the under-groundwater
flow from the eastern slopes with low surface infiltration rate. This zone shows higher groundwater residence time and slower
flow rate than zone 1. Groundwater residence time and the flow rate within the aquifer systems are controlled by the geological
structure of the aquifer, the amount of active recharge to the aquifer, and the recharge mechanism. The results of this study
may be useful in increasing the efficiency of freshwater exploitation in the region. Some precautions, however, should be
taken in future plans of artificial recharge of the aquifers or surface-water harvesting in the Wadi. Because of evaporation
and associated groundwater deterioration, the runoff water should be artificially infiltrated in zones of Wadis with high
storage capacity of aquifers. Natural infiltration along the Wadis lead to evaporation losses and less quality of groundwater. 相似文献
14.
Bernd Wiese Martin Zimmer Martin Nowak Linda Pellizzari Peter Pilz 《Environmental Earth Sciences》2013,70(8):3709-3726
In order to detect hydraulic and geochemical impact on the groundwater directly above the CO2 storage reservoir at the Ketzin pilot site continuous monitoring using an observation well is carried out. The target depth (446 m below ground level, bgl.) of the well is the Exter formation (Upper Triassic, Rhaetian) which is the closest permeable stratigraphic overlying formation to the CO2 storage reservoir (630–636 m bgl. at well location). The monitoring concept comprises evaluation of hydraulic conditions, temperature, water chemistry, gas geochemistry and δ13C values. This is achieved by a tubing inserted inside the well with installed pressure sensors and a U-tube sampling system so that pumping tests or additional wireline logging can be carried out simultaneously with monitoring. The aquifer was examined using a pump test. The observation well is hydraulically connected to the regional aquifer system and the permeability of about 1.8 D is comparatively high. Between Sept. 2011 and Oct. 2012, a pressure increase of 7.4 kPa is observed during monitoring under environmental conditions. Drilling was carried out with drilling mud on carbonate basis. The concentration of residual drilling mud decreases during the pump test, but all samples show a residual concentration of drilling mud. The formation fluid composition is recalculated with PHREEQC and is comparable to the literature values for the Exter formation. The gas partial pressure is below saturation at standard conditions and the composition is dominated by N2 similar to the underlying storage reservoir prior to CO2 injection. The impact of residual drilling mud on dissolved inorganic carbon and the respective δ13C values decreases during the monitoring period. The pristine isotopic composition cannot be determined due to calcite precipitation. No conclusive results indicate a leakage from the underlying CO2 storage reservoir. 相似文献
15.
An investigation was conducted to assess the hydrogeochemical processes of an alluvial channel aquifer located in a typical Karoo Basin of Southern Africa. The investigation was aimed at identifying and describing the groundwater chemistry evolution and its contribution to the overall groundwater quality. X-ray fluorescent spectrometry (XRF) and X-ray diffractometry (XRD) analyses were performed on geological samples to identify and quantify the major element oxides and minerals. The study utilises the conventional Piper diagram, bivariate plots and PHREEQC hydrogeochemical model to analyse groundwater chemistry data obtained during the wet (February and May) and dry seasons (August and December) of 2011. The XRF and XRD results show that the channel deposits are dominated by SiO2 element oxides and quartz minerals, thus elevated concentrations of silicon (Si4+) were found in the groundwater. Dolomite and calcite minerals were also detected in the unconsolidated aquifer sediments. The detailed study of the alluvial aquifer system has shown that dissolution of dolomite and calcite minerals and ion exchange are the dominant hydrogeochemical processes influencing the groundwater quality. The groundwater evolves from Ca2+–Mg2+–HCO3 ? recharge water that goes through ion exchange with Na+ in the clay-silt sediment to give a Na+–HCO3 ? water type. The groundwater is supersaturated with respect to quartz, dolomite and calcite minerals. The study shows the potential usefulness of simple bivariate plots as a complimentary tool to the conventional methods for analyzing groundwater hydrogeochemical processes. 相似文献
16.
The major ionic and dissolved inorganic carbon (DIC) concentrations and the stable carbon isotope composition of DIC (δ13CDIC) were measured in a freshwater aquifer contaminated by produced water brine with petroleum hydrocarbons. Our aim was to determine the effects of produced water brine contamination on the carbonate evolution of groundwater. The groundwater was characterized by three distinct anion facies: HCO3−-rich, SO42−-rich and Cl−-rich. The HCO3−-rich groundwater is undergoing closed system carbonate evolution from soil CO2(g) and weathering of aquifer carbonates. The SO42−-rich groundwater evolves from gypsum induced dedolomitization and pyrite oxidation. The Cl−-rich groundwater is contaminated by produced water brine and undergoes common ion induced carbonate precipitation. The δ13CDIC of the HCO3−-rich groundwater was controlled by nearly equal contribution of carbon from soil CO2(g) and the aquifer carbonates, such that the δ13C of carbon added to the groundwater was −11.6‰. In the SO42−-rich groundwater, gypsum induced dedolomitization increased the 13C such that the δ13C of carbon added to the groundwater was −9.4‰. In the produced water brine contaminated Cl−-rich groundwater, common ion induced precipitation of calcite depleted the 13C such that the δ13C of carbon added to the groundwater was −12.7‰. The results of this study demonstrate that produced water brine contamination of fresh groundwater in carbonate aquifers alters the carbonate and carbon isotopic evolution. 相似文献
17.
Stuart M.V. Gilfillan Chris J. Ballentine Dave Blagburn Scott Stevens Martin Cassidy 《Geochimica et cosmochimica acta》2008,72(4):1174-1198
Identification of the source of CO2 in natural reservoirs and development of physical models to account for the migration and interaction of this CO2 with the groundwater is essential for developing a quantitative understanding of the long term storage potential of CO2 in the subsurface. We present the results of 57 noble gas determinations in CO2 rich fields (>82%) from three natural reservoirs to the east of the Colorado Plateau uplift province, USA (Bravo Dome, NM., Sheep Mountain, CO. and McCallum Dome, CO.), and from two reservoirs from within the uplift area (St. John’s Dome, AZ., and McElmo Dome, CO.). We demonstrate that all fields have CO2/3He ratios consistent with a dominantly magmatic source. The most recent volcanics in the province date from 8 to 10 ka and are associated with the Bravo Dome field. The oldest magmatic activity dates from 42 to 70 Ma and is associated with the McElmo Dome field, located in the tectonically stable centre of the Colorado Plateau: CO2 can be stored within the subsurface on a millennia timescale.The manner and extent of contact of the CO2 phase with the groundwater system is a critical parameter in using these systems as natural analogues for geological storage of anthropogenic CO2. We show that coherent fractionation of groundwater 20Ne/36Ar with crustal radiogenic noble gases (4He, 21Ne, 40Ar) is explained by a two stage re-dissolution model: Stage 1: Magmatic CO2 injection into the groundwater system strips dissolved air-derived noble gases (ASW) and accumulated crustal/radiogenic noble gas by CO2/water phase partitioning. The CO2 containing the groundwater stripped gases provides the first reservoir fluid charge. Subsequent charges of CO2 provide no more ASW or crustal noble gases, and serve only to dilute the original ASW and crustal noble gas rich CO2. Reservoir scale preservation of concentration gradients in ASW-derived noble gases thus provide CO2 filling direction. This is seen in the Bravo Dome and St. John’s Dome fields. Stage 2: The noble gases re-dissolve into any available gas stripped groundwater. This is modeled as a Rayleigh distillation process and enables us to quantify for each sample: (1) the volume of groundwater originally ‘stripped’ on reservoir filling; and (2) the volume of groundwater involved in subsequent interaction. The original water volume that is gas stripped varies from as low as 0.0005 cm3 groundwater/cm3 gas (STP) in one Bravo Dome sample, to 2.56 cm3 groundwater/cm3 gas (STP) in a St. John’s Dome sample. Subsequent gas/groundwater equilibration varies within all fields, each showing a similar range, from zero to ∼100 cm3 water/cm3 gas (at reservoir pressure and temperature). 相似文献
18.
Grasslands of north-central Kansas are underlain by carbonate aquifers and shale aquitards. Chemical weathering rates in carbonates are poorly known, and, because large areas are underlain by these rocks, solute fluxes are important to estimating global weathering rates. Grasslands exist where the amount of precipitation is extremely variable, both within and between years, so studies in grasslands must account for changes in weathering that accompany changes in precipitation. This study: (1) identifies phases that dominate chemical fluxes at Konza Prairie Biological Station (KPBS) and Long-Term Ecological Research Site, and (2) addresses the impact of variable precipitation on mineral weathering. The study site is a remnant tallgrass prairie in the central USA, representing baseline weathering in a mid-temperate climate grassland.Groundwater chemistry and hydrology in the 1.2 km2 watershed used for this study suggest close connections between groundwater and surface water. Water levels fluctuate seasonally. High water levels coincide with periods of precipitation plus low evapotranspiration rather than during precipitation peaks during the growing season. Precipitation is concentrated before recharging aquifers, suggesting an as yet unquantified residence time in the thin soils.Groundwater and surface water are oversaturated with respect to calcite within limitations of available data. Water is more dilute in more permeable aquifers, and water from one aquifer (Morrill) is indistinguishable from surface water. Cations other than Ca co-vary with each other, especially Sr and Mg. Potassium and Si co-vary in all aquifers and surface water, and increases in concentrations of these elements are the best indicators of silicate weathering at this study site. Silicate-weathering indices correlate inversely to aquifer hydraulic conductivity.87Sr/86Sr in water ranges from 0.70838 to 0.70901, and it decreases with increasing Sr concentration and with increasing silicate-weathering index. Carbonate extracted from aquifer materials, shales, soil, and tufa has Sr ranging from about 240 (soil) to 880 ppm (Paleozoic limestone). 87Sr/86Sr ranges from 0.70834 ± 0.00006 (limestone) to 0.70904 ± 0.00019 (soil). In all cases, 87Sr/86Sr of aquifer limestone is lower than 87Sr/86Sr of groundwater, indicating a phase in addition to aquifer carbonate is contributing solutes to water.Aquifer recharge controls weathering: during periods of reduced recharge, increased residence time increases the total amount of all phases dissolved. Mixing analysis using 87Sr/86Sr shows that two end members are sufficient to explain sources of dissolved Sr. It is proposed that the less radiogenic end member is a solution derived from dissolving aquifer material; longer residence time increases its contribution. The more radiogenic end member solution probably results from reaction with soil carbonate or eolian dust. This solution dominates solute flux in all but the least permeable aquifer and demonstrates the importance that land-surface and soil-zone reactions have on groundwater chemistry in a carbonate terrain. 相似文献
19.
Luke C. Jeffrey Damien T. Maher Isaac R. Santos Ashly McMahon Douglas R. Tait 《Estuaries and Coasts》2016,39(5):1325-1344
Coastal wetlands are hotspots for biodiversity and biological productivity, yet the hydrology and carbon cycling within these systems remains poorly understood due to their complex nature. By using a novel spatiotemporal approach, this study quantified groundwater discharge and the related inputs of acidity and CO2 along a continuum of a modified coastal acid sulphate soil (CASS) wetland, a coastal lake and an estuary under highly contrasting hydrological conditions. To increase the resolution of spatiotemporal data and advance upon previous methodologies, we relied on automated observations from four simultaneous time-series stations to develop multiple radon mass balance models to estimate groundwater discharge and related groundwater inputs of acidity and dissolved inorganic carbon (DIC), along with surface water to atmosphere CO2 fluxes. Spatial surveys indicated distinct acid hotspots with minimum surface water pH of 2.91 (dry conditions) and 2.67 (flood conditions) near a non-remediated (drained) CASS area. Under flood conditions, groundwater discharge accounted for ～14.5 % of surface water entering the lake. During the same period, acid discharge from the acid sulphate soil section of the continuum produced ～4.8 kg H2SO4?ha?1 day?1, a rate much higher than previous studies in similar systems. During baseflow conditions, the low pH water was rapidly buffered within the estuarine lake, with the pH increasing from 4.22 to 6.07 over a distance of ～250 m. The CO2 evasion rates within the CASS were extremely high, averaging 2163?±?125 mmol m?2 day?1 in the dry period and 4061?±?259 mmol m?2 day?1 under flood conditions. Groundwater input of DIC could only account for 0.4 % of this evasion in the dry conditions and ～5 % during the flood conditions. We demonstrated that by utilising a spatiotemporal (multiple time-series stations) approach, the study was able to isolate distinct zones of differing hydrology and biogeochemistry, whilst providing more reasonable groundwater acid input estimates and air–water CO2 flux estimates than some traditional sampling designs. This study highlights the notion that modified CASS wetlands can release large amounts of CO2 to the atmosphere because of high groundwater acid inputs and extremely low surface water pH. 相似文献
20.
Declining water levels in arid and semi-arid regions increase an aquifer’s vulnerability to natural and anthropogenic influences. A multi-isotope (δD, δ18O, 87Sr/86Sr, and δ11B) approach was used to resolve the geochemical evolution of groundwater in a declining aquifer in a semi-arid region of the southwestern USA as groundwater composition reacts to source-water mixing, cross-formational flow including saltwater intrusion, water–rock interaction, and likely agricultural recharge. Sub-aquifers or local flow systems are present in the Southern High Plains aquifer along the Western Caprock Escarpment in New Mexico, and the study site’s local flow system contains a Na–Cl, high dissolved-solids groundwater that flows from the escarpment until it mixes with a high quality regional aquifer or regional flow system. The local flow system contains water that is similar in composition to the underlying, upper Dockum Group aquifer. Saltwater found in the upper Dockum Group aquifer likely originates in the adjacent Pecos River Basin and crosses beneath or possibly through the hydrologic divide of the Western Caprock Escarpment. Strontium concentrations of 0.9–31 mg/L and a 87Sr/86Sr range of 0.70845–0.70906 were sufficient to estimate source-water fractions, mixing patterns, and contributions from chemical weathering through mass balance inverse calculations. Boron concentrations (59–1740 mg/L) and δ11B values (+6.0–+46.0‰) were used to confirm source-water mixing, further evaluate water–rock interaction, and examine the influence of possible agricultural recharge. Alteration of B concentrations and δ11B values in an area of likely agricultural recharge indicated the loss of B and decrease in δ11B values likely from plant uptake, adsorption, and weathering contributions in the soil/vadose zone prior to recharge. The effectiveness of 87Sr/86Sr and δ11B for resolving the geochemical influences in groundwater in the Southern High Plains along the Western Caprock Escarpment allowed for the reinterpretation of the isotopic composition of water that has been shown to be highly variable in the Southern High Plains. This study shows the utility of a multi-isotope approach for resolving the geochemical evolution of groundwater in an aquifer that has a complex relationship with underlying aquifers and the applicability of these isotopes as indicators of the alteration of source waters from natural or anthropogenic influences. 相似文献