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161.
Paleowaters in Silurian-Devonian carbonate aquifers: Geochemical evolution of groundwater in the Great Lakes region since the Late Pleistocene 总被引:2,自引:0,他引:2
Changes in the climatic conditions during the Late Quaternary and Holocene greatly impacted the hydrology and geochemical evolution of groundwaters in the Great Lakes region. Increased hydraulic gradients from melting of kilometer-thick Pleistocene ice sheets reorganized regional-scale groundwater flow in Paleozoic aquifers in underlying intracratonic basins. Here, we present new elemental and isotopic analyses of 134 groundwaters from Silurian-Devonian carbonate and overlying glacial drift aquifers, along the margins of the Illinois and Michigan basins, to evaluate the paleohydrology, age distribution, and geochemical evolution of confined aquifer systems. This study significantly extends the spatial coverage of previously published groundwaters in carbonate and drift aquifers across the Midcontinent region, and extends into deeper portions of the Illinois and Michigan basins, focused on the freshwater-saline water mixing zones. In addition, the hydrogeochemical data from Silurian-Devonian aquifers were integrated with deeper basinal fluids, and brines in Upper Devonian black shales and underlying Cambrian-Ordovician aquifers to reveal a regionally extensive recharge system of Pleistocene-age waters in glaciated sedimentary basins. Elemental and isotope geochemistry of confined groundwaters in Silurian-Devonian carbonate and glacial drift aquifers show that they have been extensively altered by incongruent dissolution of carbonate minerals, dissolution of halite and anhydrite, cation exchange, microbial processes, and mixing with basinal brines. Carbon isotope values of dissolved inorganic carbon (DIC) range from −10 to −2‰, 87Sr/86Sr ratios range from 0.7080 to 0.7090, and δ34S-SO4 values range from +10 to 30‰. A few waters have elevated δ13CDIC values (>15‰) from microbial methanogenesis in adjacent organic-rich Upper Devonian shales. Radiocarbon ages and δ18O and δD values of confined groundwaters indicate they originated as subglacial recharge beneath the Laurentide Ice Sheet (14-50 ka BP, −15 to −13‰ δ18O). These paleowaters are isolated from shallow flow systems in overlying glacial drift aquifers by lake-bed clays and/or shales. The presence of isotopically depleted waters in Paleozoic aquifers at relatively shallow depths illustrates the importance of continental glaciation on regional-scale groundwater flow. Modern groundwater flow in the Great Lakes region is primarily restricted to shallow unconfined glacial drift aquifers. Recharge waters in Silurian-Devonian and unconfined drift aquifers have δ18O values within the range of Holocene precipitation: −11 to −8‰ and −7 to −4.5‰ for northern Michigan and northern Indiana/Ohio, respectively. Carbon and Sr isotope systematics indicate shallow groundwaters evolved through congruent dissolution of carbonate minerals under open and closed system conditions (δ13CDIC = −14.7 to−11.1‰ and 87Sr/86Sr = 0.7080-0.7103). The distinct elemental and isotope geochemistry of Pleistocene- versus Holocene-age waters further confirms that surficial flow systems are out of contact with the deeper basinal-scale flow systems. These results provide improved understanding of the effects of past climate change on groundwater flow and geochemical processes, which are important for determining the sustainability of present-day water resources and stability of saline fluids in sedimentary basins. 相似文献
162.
The hydrogeochemical and carbon isotope characteristics of the Krka River, Slovenia, were investigated to estimate the carbon transfer from the land ecosystem in the watershed. During the 3-year sampling period (2008–2010), temperature, pH, electrical conductivity, major ion content, dissolved inorganic carbon (DIC) and dissolved organic carbon content, and the isotopic composition of DIC (δ13CDIC) were monitored in the main stream of the Krka River and its tributaries. The major solute composition of analysed waters is dominated by an input of HCO3 ?, Ca2+ and Mg2+ originating from carbonate dissolution. The Mg2+/Ca2+ and Mg2+/HCO3 ? molar ratio values ranging from 0.24 to 0.71 and 0.05 to 0.30, respectively, indicate a high degree of dolomite dissolution relative to calcite. Dissolved CO2 concentrations in the river were up to tenfold supersaturated relative to the atmosphere, resulting in supersaturation with respect to calcite and degassing of CO2 downstream. The δ13C values in river water range from ?15.6 to ?9.4 ‰ and are controlled by the input of tributaries, exchange with atmospheric CO2, degradation of organic matter, and dissolution of carbonates. The mass balance calculations for riverine DIC suggest that the contribution from carbonate dissolution and degradation of organic matter have major influence, whereas the exchange with atmospheric CO2 has minor influence on the inorganic carbon pool in the Krka River. 相似文献
163.
164.
Tjaša Kanduč Fausto Grassa Jennifer McIntosh Vekoslava Stibilj Marija Ulrich-Supovec Ivan Supovec Sergej Jamnikar 《Hydrogeology Journal》2014,22(4):971-984
The geochemical and isotopic composition of surface waters and groundwater in the Velenje Basin, Slovenia, was investigated seasonally to determine the relationship between major aquifers and surface waters, water–rock reactions, relative ages of groundwater, and biogeochemical processes. Groundwater in the Triassic aquifer is dominated by HCO3 –, Ca2+, Mg2+ and δ13CDIC indicating degradation of soil organic matter and dissolution of carbonate minerals, similar to surface waters. In addition, groundwater in the Triassic aquifer has δ18O and δD values that plot near surface waters on the local and global meteoric water lines, and detectable tritium, likely reflecting recent (<50 years) recharge. In contrast, groundwater in the Pliocene aquifers is enriched in Mg2+, Na+, Ca2+, K+, and Si, and has high alkalinity and δ13CDIC values, with low SO4 2– and NO3 – concentrations. These waters have likely been influenced by sulfate reduction and microbial methanogenesis associated with coal seams and dissolution of feldspars and Mg-rich clay minerals. Pliocene aquifer waters are also depleted in 18O and 2H, and have 3H concentrations near the detection limit, suggesting these waters are older, had a different recharge source, and have not mixed extensively with groundwater in the Triassic aquifer. 相似文献
165.
Stability of biomass-derived black carbon in soils 总被引:16,自引:0,他引:16
Biqing Liang Dawit Solomon Janice E. Thies Flavio J. Luizão Eduardo G. Neves 《Geochimica et cosmochimica acta》2008,72(24):6069-6078
Black carbon (BC) may play an important role in the global C budget, due to its potential to act as a significant sink of atmospheric CO2. In order to fully evaluate the influence of BC on the global C cycle, an understanding of the stability of BC is required. The biochemical stability of BC was assessed in a chronosequence of high-BC-containing Anthrosols from the central Amazon, Brazil, using a range of spectroscopic and biological methods. Results revealed that the Anthrosols had 61-80% lower (P < 0.05) CO2 evolution per unit C over 532 days compared to their respective adjacent soils with low BC contents. No significant (P > 0.05) difference in CO2 respiration per unit C was observed between Anthrosols with contrasting ages of BC (600-8700 years BP) and soil textures (0.3-36% clay). Similarly, the molecular composition of the core regions of micrometer-sized BC particles quantified by synchrotron-based Near-Edge X-ray Fine Structure (NEXAFS) spectroscopy coupled to Scanning Transmission X-ray Microscopy (STXM) remained similar regardless of their ages and closely resembled the spectral characteristics of fresh BC. BC decomposed extremely slowly to an extent that it was not possible to detect chemical changes between youngest and oldest samples, as also confirmed by X-ray Photoelectron Spectroscopy (XPS). Deconvolution of NEXAFS spectra revealed greater oxidation on the surfaces of BC particles with little penetration into the core of the particles. The similar C mineralization between different BC-rich soils regardless of soil texture underpins the importance of chemical recalcitrance for the stability of BC, in contrast to adjacent soils which showed the highest mineralization in the sandiest soil. However, the BC-rich Anthrosols had higher proportions (72-90%) of C in the more stable organo-mineral fraction than BC-poor adjacent soils (2-70%), suggesting some degree of physical stabilization. 相似文献
166.
Sea surface wind stress and drag coefficients: The hexos results 总被引:17,自引:1,他引:17
Stuart D. Smith Robert J. Anderson Wiebe A. Oost C. Kraan Nico Maat Janice De Cosmo Kristina B. Katsaros Kenneth L. Davidson Karl Bumke Lutz Hasse Helen M. Chadwick 《Boundary-Layer Meteorology》1992,60(1-2):109-142
Turbulent fluxes have been measured in the atmospheric surface layer from a boom extending upwind from the Dutch offshore research platform Meetpost Noordwijk (MPN) during HEXMAX (Humidity Exchange over the Sea Main Experiment) in October–November, 1986. We started out to study eddy flux of water vapour, but discrepancies among simultaneous measurements made with three different anemometers led us to develop methods to correct eddy correlation measurements of wind stress for flow distortion by nearby objects. We then found excellent agreement among the corrected wind stress data sets from the three anemometers on the MPN boom and with eddy correlation measurements from a mast on a tripod. Inertial-dissipation techniques gave reliable estimates of wind stress from turbulence spectra, both at MPN and at a nearby ship. The data cover a range of wave ages and the results yield new insights into the variation of sea surface wind stress with sea state; two alternative formulas are given for the nondimensional surface roughness as a function of wave age. 相似文献
167.
Mark J. Brooks Peter A. Stone Donald J. Colquhoun Janice G. Brown Kathy B. Steele 《Geoarchaeology》1986,1(3):293-307
Selected archaeological, stratigraphical, sedimentological, hydrological, sea level, and 14C data are considered in order to ascertain the times and rates of saltmarsh, floodplain, river swamp, and alluvial terrace development in the lower Savannah River valley. Archaeological data are emphasized in the elucidation of these developmental trends and their environmental correlates. It is concluded that the modern environments associated with the categories of archaeological sites examined (estuarine shell middens, river swamp point bar sites, raised terrace/point bar sites) are not representative of local conditions during occupation(s). Accordingly, a mid-Holocene development of lower energy depositional environments is documented, along with a corresponding shift in subsistence-settlement patterning that suggests more diffuse, or broad spectrum, socio-economic strategies. A base level (sea level) dominance on river sedimentation, even far inland from the coast, may also be indicated. 相似文献