Carbon Isotope Analysis to Evaluate Nanoscale Fe(O) Treatment at a Chlorohydrocarbon Contaminated Site     

Martin Elsner  Georges Lacrampe Couloume  Silvia Mancini  Leanne Burns  Barbara Sherwood Lollar 《Ground Water Monitoring & Remediation》2010,30(3):79-95

Remediation of groundwater contaminated by chlorinated hydrocarbons via in situ technologies such as direct injection of nanoscale zero valent iron (ZVI, Fe(O)) particles is increasingly common. However, assessing target compound degradation by abiotic processes is difficult because (1) the injection may displace the contaminant plume so that concentration measurements alone are often inconclusive and (2) biodegradation may also occur, making it challenging to identify and evaluate the abiotic degradation component. In this study, trichloroethylene (TCE) and 1,1,1-trichloroethane (1,1,1-TCA) were treated in a highly heterogeneous hydrogeologic setting. The purpose of this study was to evaluate the potential for compound-specific stable isotope analysis (CSIA) to monitor the effectiveness of ZVI injection by assessing TCE and 1,1,1-TCA degradation. Prior to ZVI injection, carbon isotope measurements demonstrated biodegradation of TCE by native microorganisms. This in situ biodegradation was quantified by measuring the enrichment of ¹³C in TCE samples downstream of the suspected source. When ZVI was injected through only two injection wells, no changes in TCE and 1,1,1-TCA isotope signatures were detected compared to preinjection values. In contrast, when ZVI was injected through 11 wells covering a greater portion of the contaminated area, 5 out of 10 monitoring wells showed further enrichment of ¹³C in either TCE or 1,1,1-TCA, indicating additional target compound transformation. The abiotic nature of this TCE transformation was confirmed through temporal trends in carbon isotope values of the putative transformation products cis-dichloroethylene (cis-DCE), ethene and ethane. This demonstrates the usefulness of CSIA in distinguishing abiotic vs. biotic transformation in the field.  相似文献   

Impact of agriculture on groundwater in Ireland     

C. R. Aldwell  D. J. Burdon  M. Sherwood 《Environmental Geology》1983,5(1):39-48

Ireland has large water resources. Only 5.3% of developable waters are as yet developed, to supply some 650 I/day/per capita to the population of some 3.37 million people. State of development varies in each of the seven water resources regions. Precipitation is fairly evenly distributed over the year, but the percentage infiltrating to form groundwater varies quite sharply. Some 61% of infiltration occurs in the four winter months November to February, when agricultural activities are low. Only 10% infiltrates in the four summer months, May to August, when agricultural activities are high. In all, annual groundwater amounts to some 24.8 km³, of which 50% is considered to be recoverable. Capital groundwater reserves must be large, but are unquantified. Under these conditions, the impact of agriculture on groundwater quantities is negligible. Of the annual extraction of some 170 × 10⁶m³ of groundwater, some 66 × 10⁶m³/year are used in different agricultural activities. Drainage operations, however, have effects on Irish groundwater. Such lands may overlie impermeable strata or pans, or may receive concealed or visible groundwater discharge. Their drainage will affect the groundwater in various ways. There has been a considerable impact of agriculture on groundwater quality. The effects on the atmosphere and on precipitation are not identifiable. Effects of diffuse infiltration are treated with respect to: (a) application of ground limestone (lime); (b) application of K.N.P. inorganic fertilizer; (c) spreading of organic slurries; (d) development of organic nitrogen in soils, mainly after ploughing of grasslands; and (e) residues from herbicides, fungicides, and pesticides. The infiltration of these substances spread on the land is closely related to the interaction between times of ground-water recharge and times of fertilizer application. Effects of concentrated infiltration are treated under seven sub-heads: (a) infiltration of polluted surface waters; (b) localized farm infiltration; (c) concentrated waste disposal from feedlots; (d) concentrated waste disposal from silage; (e) concentrated waste disposal from agro-industries; (f) disposal through sinkholes and quarries; and (g) disposal by deep well injection. These operations are deliberate, and not related to times of groundwater recharge. They are often into the limestone aquifers, and so doubly dangerous.  相似文献   

Mineral magnetic record of paleoclimate variation in loess and paleosol from the Buenos Aires formation (Buenos Aires, Argentina)     

M. J. OrgeIra  A. M. Walther  C. A. Vsquez  I. Di Tommaso  S. Alonso  G. Sherwood  Hu Yuguan  J. F. A. Vilas 《Journal of South American Earth Sciences》1998,11(6):561-570

Environmental magnetic techniques were applied to a loess–paleosol sequence of the Chacopampean plain (Buenos Aires, Argentina). Mineral magnetic carriers and their grain size were identified in order to detect magnetic mineral fluctuations associated with climatic changes. Multidomain magnetite of detrital origin dominates the record. In paleosols, a high coercivity fraction was identified. Horizons with no visual evidence of pedogenesis, but showing magnetic behavior analogous to that of paleosols were observed and are thought to represent environmental conditions similar to those prevailing during paleosol formation.The results suggest that the magnetic signal yielded by paleosols in these South American loess deposits is different from that in the Chinese loess. This may be due to differences in parent materials, diagenetic processes and/or differences in paleoclimatic conditions in both regions.  相似文献   

Palaeointensity studies of a late Permian lava succession from Guizhou Province, South China: implications for post-Kiaman dipole field behaviour   总被引：1，自引：0，他引：1  

D. N. Thomas  T. C. Rolph  J. Shaw  S. Gonzalez de Sherwood  & Z. Zhuang 《Geophysical Journal International》1998,134(3):856-866

Palaeomagnetic results are presented from a volcanic sequence in Zhijin County, Guizhou Province, Southern China. The lavas and associated volcanic breccias comprising the sequence represent a southern extension of the Emeishan volcanic province. Biostratigraphic dating of interbedded limestone units and stratigraphic constraints indicate that the section formed during the late Permian (∼263–255  Ma), and is thus somewhat older than the Emei stratotype section in Sichuan Province, and close in age to reported estimates of the termination of the Permo-Carboniferous (Kiaman) reverse superchron. Rock magnetic analyses and reflected light microscopy indicate that the magnetic mineralogy of the lava units is dominated by fresh, primary magnetites containing a significant fraction of single-domain grains. Thermal demagnetization behaviour of the breccia units is poor, but most lava samples have one or two components of remanence above 250 °C. The normal polarity characteristic remanence held by the lavas implies a post-Kiaman age for this succession and suggests that the termination of the Kiaman occurred prior to 263  Ma, supporting recently published estimates. According to standard criteria, Thellier palaeointensity results from the lavas are of good quality and reveal that the dipole field strength was comparatively low shortly after the termination of the superchron. 80 per cent of samples record relative VDM values in the range 42–52 per cent of the present-day value, supporting recent studies of mid-Kiaman field intensity. This suggests that a low-energy dipole existed at least between 300 and 255  Ma and does not appear to have been confined to the stable reverse polarity interval.  相似文献   

Historical changes in the Columbia River Estuary     

Christopher R Sherwood  David A Jay  R Bradford Harvey  Peter Hamilton  Charles A Simenstad 《Progress in Oceanography》1990,25(1-4)

Historical changes in the hydrology, sedimentology, and physical oceanography of the Columbia River Estuary have been evaluated with a combination of statistical, cartographic, and numerical-modelling techniques. Comparison of data digitized from US Coast and Geodetic Survey bathymetric surveys conducted in the periods 1867–1875, 1926–1937, and 1949–1958 reveals that large changes in the morphology of the estuary have been caused by navigational improvements (jetties, dredged channels, and pile dikes) and by the diking and filling of much of the wetland area. Lesser changes are attributable to natural shoaling and erosion. There has been roughly a 15% decrease in tidal prism and a net accumulation of about 68 × 10⁶m³ of sediment in the estuary. Large volumes of sediment have been eroded from the entrance region and deposited on the continental shelf and in the balance of the estuary, contributing to formation of new land. The bathymetric data indicate that, ignoring erosion at the entrance, 370 to 485 × 10⁶m³ of sediment has been deposited in the estuary since 1868 at an average rate of about 0.5 cm y⁻¹, roughly 5 times the rate at which sea level has fallen locally since the turn of the century.Riverflow data indicate that the seasonal flow cycle of the Columbia River has been significantly altered by regulation and diversion of water for irrigation. The greatest changes have occurred in the last thirty years. Flow variability over periods greater than a month has been significantly damped and the net discharge has been slightly reduced. These changes in riverflow are too recent to be reflected in the available in the available bathymetric data.Results from a laterally averaged, multiple-channel, two-dimensional numerical flow model (described in Hamilton, 1990) suggest that the changes in morphology and riverflow have reduced mixing, increased stratification, altered the response to fortnightly (neap-spring) changes in tidal forcing, and decreased the salinity intrusion length and the transport of salt into the estuary.The overall effects of human intervention in the physical processes of the Columbia River Estuary (i.e. decrease in freshwater inflow, tidal prism, and mixing; increase in flushing time and fine sediment deposition, and net accumulation of sediment) are qualitatively similar to those observed in less energetic and more obviously altered estuarine systems. A concurrent reduction in wetland habitats has resulted in an estimated 82% reduction in emergent plant production and a 15% reduction in benthic macroalgae production, a combined production loss of 51,675 metric tons of organic carbon per year. This has been at least partially compensated by a large increase in the supply of riverine detritus derived from freshwater phytoplankton primary production. Comparison of modern and estimated preregulation organic carbon budgets for the estuary indicates a shift from a food web based on comparatively refractory macrodetritus derived from emergent vegetation to one involving more labile microdetritus derived from allochthonous phytoplankton. The shift has been driven by human-induced changes to the physical environment of the estuary.While this is a relatively comprehensive study of historical physical changes, it is incomplete in that the sediment budget is still uncertain. More precise quantification of the modern estuarine sediment budget will require both a better understanding of the fluvial input and dredging export terms and a sediment tranport model designed to explain historical changes in the sediment budget. Oceanographic studies to better determine the mechanisms leading to the formation of the turbidity maximum are also needed. The combination of cartography and modelling used in this study should be applicable in other systems where large changes in morphology have occurred in historical time.  相似文献   

Influence of diet on growth, condition and reproductive capacity in Newfoundland and Labrador cod (Gadus morhua): Insights from stable carbon isotopes (δC)     

Graham D. Sherwood  Rick M. Rideout  Susan B. Fudge  George A. Rose 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2794

Cod populations in Newfoundland and Labrador waters have shown differing growth, condition and recruitment since near-universal declines in these properties during the cold period of the late 1980s and early 1990s. To assess the influence of variable prey communities on these parameters, we compared cod energetics and diet in populations off Labrador and the northeast and south coasts of Newfoundland. Many properties were highest in the southern group(s) and lowest in the northern group(s), including growth, somatic condition, liver index and age-at-maturity. Most differences could be explained by variations in diet, as measured by stomach contents and stable carbon isotopes (δ¹³C). The diet of Labrador cod consisted almost entirely of northern shrimp (Pandalus borealis), and these cod displayed the most benthic δ¹³C signatures. Northeast cod had a more varied diet that included capelin and other fish, but still had mostly benthic δ¹³C signatures, suggesting the importance of benthic prey like shrimp in this population. South coast cod exhibited the most varied diet, including capelin (Mallotus villosus), zooplankton, crabs and other fish, and had the most pelagic δ¹³C signatures. Among and within populations, the benefits of a more pelagic diet in medium-sized (30–69 cm) cod included higher somatic condition, higher liver index (lipid stores) and greater spawning potential (decreased incidence of atresia). It is hypothesized that major rebuilding of Newfoundland and Labrador cod stocks will require a return to a system that supports mostly pelagic feeding (i.e. capelin) in cod.  相似文献   

Determination of orthophosphate in highly saline waters     

J. E. Sherwood  M. J. Kokkinn  W. D. Williams 《International Journal of Salt Lake Research》1994,3(2):159-173

Standard methods for the determination of phosphorus as phosphate ion are now well established for fresh and marine waters. In highly saline waters, however, salt effects due to ionic strength, or to particular ions present, may result in method interferences. Three methods of analysis of phosphate based on the formation of phosphomolybdenum blue complexes have been evaluated here for hypersaline waters. Stannous chloride reduction in aqueous media exhibits a substantial salt effect and its use is not recommended. Stannous chloride reduction following extraction into non aqueous solvents shows a significant salt effect (up to 30 per cent) in solutions of salinity >100 g L^–1. Dilution of hypersaline waters to below this salinity may overcome the salt effect but the method suffers from other disadvantages involving resource constraints and health and safety considerations. Ascorbic acid reduction, catalysed by antimony (III) ions, appears to offer the most promise for hypersaline waters. Turbidity in samples having high salinity (> 100 g L^–1) and high phosphorus concentrations (> 500 g P L^–1) changes the spectral characteristics of solutions but linear calibration curves still result for concentrations in the range 400 to 1,000 g P L^–1. The occurrence of turbidity is also affected by the ionic composition of hypersaline waters since solutions made from sea salt give different results to those made from sodium chloride. Dilution of samples, to give salinities less than 100 g L^–1 prior to reduction is recommended to avoid turbidity. The salt effect in these lower salinity waters is less than 3 per cent up to 100 g L^–1.  相似文献   

Isotopic signatures of CH₄ and higher hydrocarbon gases from Precambrian Shield sites: A model for abiogenic polymerization of hydrocarbons     

B. Sherwood Lollar  G. Lacrampe-Couloume  T.C. Onstott 《Geochimica et cosmochimica acta》2008,72(19):4778-4795

Previous studies of methane and higher hydrocarbon gases in Precambrian Shield rocks in Canada and the Witwatersrand Basin of South Africa identified two major gas types. Paleometeoric waters were dominated by hydrocarbon gases with compositional and isotopic characteristics consistent with production by methanogens utilizing the CO₂ reduction pathway. In contrast the deepest, most saline fracture waters contained gases that did not resemble the products of microbial methanogenesis and were dominated by both high concentrations of H₂ gas, and CH₄ and higher hydrocarbon gases with isotopic signatures attributed to abiogenic processes of water-rock reaction in these high rock/water ratio, hydrogeologically-isolated fracture waters. Based on new data obtained for the higher hydrocarbon gases in particular, a model is proposed to account for carbon isotope variation between CH₄ and the higher hydrocarbon gases (specifically ethane, propane, butane, and pentane) consistent with abiogenic polymerization. Values of δ¹³C for CH₄ and the higher hydrocarbon gases predicted by the model are shown to match proposed abiogenic hydrocarbon gas end-members identified at five field sites (two in Canada and three in South Africa) suggesting that the carbon isotope patterns between the hydrocarbon homologs reflect the reaction mechanism. In addition, the δ²H isotope data for these gases are shown to be out of isotopic equilibrium, suggesting the consistent apparent fractionation observed between the hydrocarbon homologs may also reflect reaction mechanisms involved in the formation of the gases. Recent experimental and field studies of proposed abiogenic hydrocarbons such as those found at mid-ocean spreading centers and off-axis hydrothermal fields such as Lost City have begun to focus not only on the origin of CH₄, but on the compositional and isotopic information contained in the higher hydrocarbon gases. The model explored in this paper suggests that while the extent of fractionation in the first step in the hydrocarbon synthesis reaction chain may vary as a function of different reaction parameters, δ¹³C values for the higher hydrocarbon gases may be predicted by a simple mass balance model from the δ¹³C values of the lower molecular weight precursors, consistent with abiogenic polymerization. Integration of isotopic data for the higher hydrocarbon gases in addition to CH₄ may be critical for delineation of the origin of the hydrocarbons and investigation of formation mechanisms.  相似文献   

Zonal winds and southeast Australian rainfall in global and regional climate models     

Acacia S. Pepler  Lisa V. Alexander  Jason P. Evans  Steven C. Sherwood 《Climate Dynamics》2016,46(1-2):123-133

Southeast Australia is a region of high rainfall variability related to major climate drivers, with a long-term declining trend in cool-season rainfall. Projections of future rainfall trends are uncertain in this region, despite projected southward shifts in the subtropical ridge and mid-latitude westerlies. This appears to be related to a poor representation of the spatial relationships between rainfall variability and zonal wind patterns across southeast Australia in the latest Coupled Model Intercomparison Project ensemble, particularly in the areas where weather systems embedded in the mid-latitude westerlies are the main source of cool-season rainfall. Downscaling with regional climate models offers improvements in the mean rainfall climatology, and shows some ability to correct for poor modelled relationships between rainfall and zonal winds along the east coast of Australia. However, it provides only minor improvements to these relationships in southeast Australia, despite the improved representation of topographic features. These results suggest that both global and regional climate models may fail to translate projected circulation changes into their likely rainfall impacts in southeast Australia.  相似文献   

Dirt: The Erosion of Civilizations. David R. Montgomery, 2007, University of California Press,Berkeley, CA, 295 pp., $24.95 (hardcover)     

W. Cullen Sherwood 《Geoarchaeology》2008,23(3):420-422

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