Regional groundwater focusing of nitrogen and noble gases into the Hugoton-Panhandle giant gas field, USA     

Chris J. Ballentine  Barbara Sherwood Lollar 《Geochimica et cosmochimica acta》2002,66(14):2483-2497

The Hugoton-Panhandle giant gas field, located across SW Kansas and the Texas and Oklahoma panhandles in the USA, is the case type example of high nitrogen concentrations in a natural gas being linked with high helium concentrations. We collected 31 samples from producing wells in a north-south traverse of the 350-km-long field. The samples reflect the previously observed north-south change in ⁴He/N₂, with values changing from 0.020 to 0.049 respectively. ³He/⁴He, ²¹Ne/²²Ne, and ⁴⁰Ar/³⁶Ar vary between 0.14-0.25 Ra, 0.0373-0.0508, and 818-1156 respectively, and are caused by quantifiable contributions from mantle, crustal, and atmosphere-derived sources. The atmosphere-derived ²⁰Ne/³⁶Ar ratios are indistinguishable from groundwater values. The crustal ⁴He/²¹Ne* and ⁴He/⁴⁰Ar* ratios show a 60% excess of ⁴He compared to predicted production ratios in the crust and are typical of noble gases released from the shallow crust. The mantle ³He/N₂ and groundwater-recharge ³⁶Ar/N₂ ratios enable us to rule out significant magmatic or atmosphere contributions to the gas field N₂, which is dominantly crustal in origin.Correlated ²⁰Ne/N₂ and ⁴He/N₂ shows mixing between two distinct crustal N₂ components. One N₂ component (N₂*) is associated with the crustal ⁴He and groundwater-derived ²⁰Ne, and the other with no resolvable noble gas contribution. Measured δ¹⁵N_N2 values vary from +2.7‰ to +9.4‰. The N₂* and non-He-associated N₂ endmembers are inferred to have δ¹⁵N_N2 = −3‰ and +13‰ and contribute from between 25-60% and 75-40% of the nitrogen respectively. The non-He-associated nitrogen is probably derived from relatively mature organic matter in the sedimentary column. The δ¹⁵N_N2* value is not compatible with a crystalline or high-grade metamorphic source and, similar to the ⁴He, is inferred to be from a shallow or low metamorphic-grade source rock. ⁴He mass balance requires a regional crustal source, its association with significant magmatic ³He pointing to a tectonically active source to the west of the Hugoton system. The volume of groundwater required to source the ²⁰Ne in the gas field demonstrates the viability of the groundwater system in providing the collection, transport, and focusing mechanism for the ⁴He and N₂*. The N₂*/²⁰Ne ratio shows that the N₂* transport must be in the aqueous phase, and that the degassing mechanism is probably contact between the regional groundwater system and the preexisting reservoir hydrocarbon gas phase.  相似文献   

Impacts of hydrological changes on phytoplankton succession in the Swan River, Western Australia   总被引：2，自引：0，他引：2  

Terence U. Chan  David P. Hamilton  Barbara J. Robson  Ben R. Hodges  Chris Dallimore 《Estuaries and Coasts》2002,25(6):1406-1415

The Swan River estuary, Western Australia, has undergone substantial hydrological modifications since pre-European settlement. Land clearing has increased discharge from some major tributaries roughly 5-fold, while weirs and reservoirs for water supply have mitigated this increase and reduced the duration of discharge to the estuary. Nutrient loads have increased disproportionately with flow and are now approximately 20-times higher than pre-European levels. We explore the individual and collective impacts of these hydrological changes on the Swan River estuary using a coupled hydrodynamic-ecological numerical model. The simulation results indicate that despite increased hydraulic flushing and reduced residence times, increases in nutrient loads are the dominant perturbation producing increases in the incidence and peak biomass of blooms of both estuarine and freshwater phytoplankton. Changes in salinity associated with altered seasonal freshwater discharge have a limited impact on phytoplankton dynamics.  相似文献   

Detection of fluorescent compounds in the environment using granular activated charcoal detectors     

Chris Smart  Brad Simpson 《Environmental Geology》2002,42(5):538-545

Granular activated charcoal (GAC) acts as a general adsorptive medium for organic molecules, and is widely used to capture fluorescent tracer dyes. To investigate the capability of GAC in contaminant screening and tracer adsorption, a number of detectors were deployed for 2-6 days in a range of urban surface waters, and the adsorbed compounds eluted in an alkaline alcohol solution. Simultaneous water samples showed a diverse range of fluorescence environments, ranging from relatively clean, steady groundwater discharge, to highly concentrated and variable treated municipal sewage. A wide variety of organic compounds and dyes were found in the waters, as chronic and acute contaminants. The relationship between charcoal and water spectra depended on exposure time and loading. Short exposure times emphasized short wavelengths, longer exposure times emphasized longer wavelengths at the expense of shorter wavelengths. The magnitude of the effect depended on loading, being greater in enriched waters. In general, charcoal eluent shows a significant gain in fluorescence intensity over water. However, there may be an apparent loss at shorter wavelengths for samples with long exposure times and high loading. A similar bias was also discovered with the elution time of activated charcoal. Short wavelength fluorescence intensity peaked after a few minutes of elution; longer wavelength fluorescence increased over many days. These results show that charcoal is a reasonably effective material for adsorption of longer wavelength compounds. However, the ubiquity of many fluorescent dyes in the environment, and the complex relationship between the waters and the eluent spectrum, suggest that considerable care is required in the interpretation of eluent spectra.  相似文献   

First Palaeogene sedimentary rock palaeomagnetic pole from stable western Eurasia and tectonic implications   总被引：1，自引：0，他引：1  

Jason R. Ali  David J. Ward  Chris King  Alexandra Abrajevitch 《Geophysical Journal International》2003,154(2):463-470

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Genetic implications of pyrite chemistry from the Palaeoproterozoic Olary Domain and overlying Neoproterozoic Adelaidean sequences, northeastern South Australia   总被引：4，自引：0，他引：4  

Chris Clark  Ben Grguric  Andreas Schmidt Mumm 《Ore Geology Reviews》2004,25(3-4):237-257

Sulphide mineralisation associated with rocks from the Palaeoproterozoic Olary Domain (OD) and overlying Neoproterozoic Adelaidean sequences has undergone a complex history of metamorphism and remobilisation. In this study, new trace element and sulphur isotopic analyses of pyrites from a large number of deposits and paragenetic generations are combined with an existing data set to build up a sequence of mineralising events linked to the tectonometamorphic evolution of the region. The typically high Co/Ni ratios (>10) indicate that early strata-bound pyrite precipitated from a volcanic-related fluid, which had fluctuating activities of the two metals during the early stages of the evolution of the Willyama basin. This period of mineralisation was followed by a diagenetic concentration of sulphide mineralisation at the horizon known as the Bimba Formation, which occurred as a result of the differing redox conditions between the upper and lower sequences in the Willyama Supergroup. During the Mesoproterozoic (1600 to 1500 Ma) Olarian Orogeny, metamorphic remobilisation of strata-bound pyrite resulted in an epigenetic signature; the trace element concentrations of this generation were controlled primarily by the proximity of mineralisation to the mafic intrusive bodies found throughout the terrane. Further reworking of existing sulphides during the Delamerian Orogeny and associated granitoid-intrusive rocks led to the formation of a new generation of epigenetic pyrite that occurs in quartz veins in the Adelaidean sequences and veins that crosscut Olarian fabrics in the Olary Domain. δ³⁴S results range from 16‰ to 11‰, but most data fall between 2‰ and 4‰. This association is suggestive of an initial uniform deep-seated crustal reservoir of sulphur, which has been repeatedly tapped throughout the metallogenic history of the region. The isotopic outliers can be explained by the input of biogenic sulphur or sulphur derived from oxidised, possibly evaporitic, sediments, respectively. Previous workers have invoked the Kupferschiefer and the Zambian Copperbelt as analogues to mineralisation processes in the Olary Domain. This study shows that δ³⁴S and trace element data are suggestive of some affinities with the aforementioned analogues, but a more likely link can be made between epigenetic remobilisation in the Olary region and the iron oxide copper gold (IOCG) style of mineralisation found at the nearby Olympic Dam deposit.  相似文献   

Molecular and isotopic stratigraphy in an ombrotrophic mire for paleoclimate reconstruction     

Shucheng Xie  Chris J Nott  Darrel Maddy  Richard P Evershed 《Geochimica et cosmochimica acta》2004,68(13):2849-2862

A 40 cm deep Sphagnum-dominated peat monolith from Bolton Fell Moss in Northern England was systematically investigated by lipid molecular stratigraphy and compound-specific δ¹³C and δD analysis using gas chromatography (GC), GC-mass spectrometry (GC-MS), GC-combustion-isotope ratio-MS (GC-C-IRMS) and GC-thermal conversion-IRMS (GC-TC-IRMS) techniques. ²¹⁰Pb dating showed the monolith accumulated during the last ca. 220 yr, a period encompassing the second part of Little Ice Age. While the distributions of lipids, including n-alkan-1-ols, n-alkan-2-ones, wax esters, sterols, n-alkanoic acids, α,ω-alkandioic acids and ω-hydroxy acids, display relatively minor changes with depth, the cooler climate event was recorded in the concentrations of n-alkanes and organic carbon, CPI values of n-alkanes and n-alkanoic acids, and the ratio of 5-n-alkylresorcinols/sterols. Superimposed on the fossil fuel effect, the relatively cooler climate event was also recorded by δ¹³C values of individual hydrocarbons, especially the C₂₃n-alkane, a major compound in certain Sphagnum spp. The δD values of the C₂₉ and C₃₃n-alkanes correlated mainly with plant composition and were relatively insensitive to climatic change. In contrast the C₂₃n-alkane displayed variation that correlated strongly with recorded temperature for the period represented by the monolith, agreeing with previously reported deuterium records in tree ring cellulose spanning the same period in Scotland, Germany and the USA, with more negative values occurring during the second part of Little Ice Age. These biomarker characteristics, including the compound-specific δ¹³C and δD records, provide a new set of proxies of climatic change, potentially independent of preserved macrofossils which will be of value in deeper sections of the bog where the documentary records of climate are unavailable and humification is well advanced.  相似文献   

Evidence and Implications of Recent Climate Change in Northern Alaska and Other Arctic Regions   总被引：19，自引：0，他引：19  

Larry D. Hinzman  Neil D. Bettez  W. Robert Bolton  F. Stuart Chapin  Mark B. Dyurgerov  Chris L. Fastie  Brad Griffith  Robert D. Hollister  Allen Hope  Henry P. Huntington  Anne M. Jensen  Gensuo J. Jia  Torre Jorgenson  Douglas L. Kane  David R. Klein  Gary Kofinas  Amanda H. Lynch  Andrea H. Lloyd  A. David McGuire  Frederick E. Nelson  Walter C. Oechel  Thomas E. Osterkamp  Charles H. Racine  Vladimir E. Romanovsky  Robert S. Stone  Douglas A. Stow  Matthew Sturm  Craig E. Tweedie  George L. Vourlitis  Marilyn D. Walker  Donald A. Walker  Patrick J. Webber  Jeffrey M. Welker  Kevin S. Winker  Kenji Yoshikawa 《Climatic change》2005,72(3):251-298

The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates convincingly; the Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions are being experienced, a range of biophysical states and processes influenced by the threshold and phase change of freezing point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to isolate due to compounding factors. In almost every discipline represented, we show how the biocomplexity of the Arctic system has highlighted and challenged a paucity of integrated scientific knowledge, the lack of sustained observational and experimental time series, and the technical and logistic constraints of researching the Arctic environment. This study supports ongoing efforts to strengthen the interdisciplinarity of arctic system science and improve the coupling of large scale experimental manipulation with sustained time series observations by incorporating and integrating novel technologies, remote sensing and modeling.  相似文献   

The Climate Change Benefits of Reducing Methane Emissions     

Chris Hope 《Climatic change》2005,68(1-2):21-39

The PAGE95 integrated assessment model is used to calculate the marginal benefit of immediate cutbacks in methane emissions, and compare them with the benefits of carbon dioxide reductions and the costs of methane reduction measures. The main result is that immediate cutbacks of methane bring a marginal benefit of between $30 and $260 per tonne, with a mean value of $110 per tonne. This compares to a benefit of between $10 and $50 per tonne of carbon, with a mean value of $20, for immediate cutbacks of carbon dioxide (all values in 1990 dollars). A sectoral and regional breakdown finds that two-thirds of the benefit is non-economic and only about 5% of the benefit occurs in the European Union (EU) and 8% in the USA; the vast majority of the benefit is felt in other regions, particularly in the developing world. Analysis up to 2200 shows the benefit continuing throughout the next century, peaking after 2050, even though methane stays in the atmosphere for only about a decade. This is because the surface-troposphere system typically takes decades to regain equilibrium, owing principally to the thermal inertia of the oceans. Exploring a range of alternative assumptions shows that the benefit from methane reduction is most sensitive to the discount rate. Using a pure time preference rate of 2% per yr instead of 3% per yr, almost doubles the mean benefit to $190 per tonne; a rate of 1% per yr doubles the mean benefit again to $380 per tonne.  相似文献   

Noble gas tracing of groundwater/coalbed methane interaction in the San Juan Basin, USA   总被引：1，自引：0，他引：1  

Zheng Zhou  Chris J. Ballentine  Martin Schoell 《Geochimica et cosmochimica acta》2005,69(23):5413-5428

The San Juan Basin natural gas field, located in northwestern New Mexico and southwestern Colorado in the USA, is a case-type coalbed methane system. Groundwater is thought to play a key role in both biogenic methane generation and the CO₂ sequestration potential of coalbed systems. We show here how noble gases can be used to construct a physical model that describes the interaction between the groundwater system and the produced gas. We collected 28 gas samples from producing wells in the artesian overpressured high production region of the basin together with 8 gas samples from the underpressured low production zone as a control. Stable isotope and major species determination clearly characterize the gas in the high production region as dominantly biogenic in origin, and the underpressured low producing region as having a significant admix of thermogenic coal gas. ³He/⁴He ratios increase from 0.0836R_a at the basin margin to 0.318R_a towards the center, indicating a clear but small mantle He signature in all gases. Coherent fractionation of water-derived ²⁰Ne/³⁶Ar and crustal ⁴He/⁴⁰Ar* are explained by a simple Rayleigh fractionation model of open system groundwater degassing. Low ²⁰Ne concentrations compared to the model predicted values are accounted for by dilution of the groundwater-associated gas by desorbed coalbed methane. This Rayleigh fractionation and dilution model together with the gas production history allows us to quantify the amount of water involved in gas production at each well. The quantified water volumes in both underpressured and overpressured zones range from 1.7 × 10³ m³ to 4.2 × 10⁵ m³, with no clear distinction between over- and underpressured production zones. These results conclusively show that the volume of groundwater seen by coal does not play a role in determining the volume of methane produced by secondary biodegradation of these coalbeds. There is no requirement of continuous groundwater flow for renewing the microbes or nutrient components. We furthermore observe strong mass related isotopic fractionation of ²⁰Ne/²²Ne and ³⁸Ar/³⁶Ar isotopic ratios. This can be explained by a noble gas concentration gradient in the groundwater during gas production, which causes diffusive partial re-equilibration of the noble gas isotopes. It is important for the study of other systems in which extensive groundwater degassing may have occurred to recognize that severe isotopic fractionation of air-derived noble gases can occur when such concentration gradients are established during gas production. Excess air-derived Xe and Kr in our samples are shown to be related to the diluting coalbed methane and can only be accounted for if Xe and Kr are preferentially and volumetrically trapped within the coal matrix and released during biodegradation to form CH₄.  相似文献   

Resident Attitudes to Farmland Protection Measures in the Northern Rivers Region,New South Wales     

Chris Gibson  Rae Dufty  Danielle Drozdzewski 《The Australian geographer》2005,36(3):369-383

In-migration to popular ‘sea change’ and ‘tree change’ regions has produced conflicts between rural land users. In the Northern Rivers region of New South Wales, new residential developments have been built on much of what was previously prime agricultural land, while farmers (in particular, those negatively affected by the deregulation of the dairy industry) have sought to secure retirement incomes by subdividing land for sale. Although developers, local councils and individual farmers sometimes see eye to eye on the mutual benefits of in-migration and population growth, land use has none the less become the subject of a hotly contested local political battle. Conflicts occur at the interface of growing urban developments and surrounding farmland, with new residents finding the sights, sounds and smells of rural production intrusive. More generally, there is considerable concern that the best farmland in the region may be lost to urbanisation and rural residential subdivision. This paper discusses the results of a survey that collected opinions from local residents about the pressures on the region's land uses by in-migration, the future role of farmland as both an economic and cultural landscape, and views on proposed measures to protect prime farmland in the region. Results highlighted a strong and consistent ‘pro-farmland’ and ‘pro-protection’ attitude throughout the region, and across social groups. Yet, variations emerged when respondents were asked about why they attribute value to agricultural landscapes. For some, ‘economic’ values dominated, while for others, value was attributed in ways that reflected an emerging ethos of ‘localism’ and village lifestyle. Although values differed, a clear message from this study is that the population of Australia's pre-eminent ‘sea change’ region strongly support measures to curb urban development and the more destructive consequences of a dynamic property market.  相似文献