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61.
Calculation of ground water ages--a comparative analysis 总被引：1，自引：0，他引：1
Ground water age is a fundamental, yet complex, concept in ground water hydrology. Discrepancies between results obtained through different modeling approaches for ground water age calculation have been reported, in particular, between ground water ages modeled by advection and direct simulation of ground water ages (e.g., age-mass approach), which includes effects of advection and dispersion. Here, through a series of two-dimensional (2D) simulations, the impact of water mixing through advection and dispersion on modeled 14C and directly simulated ground water ages is assessed. Impact of dispersion on modeled ages is systematically stronger in areas where water velocities are smaller and far more pronounced on 14C ages. This effect is also observed in one-dimensional models. 2D simulations show that longitudinal dispersion generally acts as a "source" of 14C, while vertical dispersion acts as a "sink," leading to apparent younger or older modeled 14C ages as compared to advective and directly simulated ground water ages. The presence of permeable and impermeable faults provides an equally important source for discrepancies, leading to major differences in modeled ages among the three methods considered. Overall, our results show that a 14C modeling approach using a solute transport model for calculating ground water age appears to be more reliable in ground water systems without faults and where water velocities are relatively high than in systems that are relatively more heterogeneous and those where faults are present. Among the three modeling approaches considered here, direct simulation of ground water age seems to yield the most consistent results in complex, heterogeneous ground water flow systems, giving a vertical age structure consistent with ages expected from consideration of the flow system. 相似文献
62.
The threat of global climate change has caused concern among scientists because crop production could be severely affected by changes in key climatic variables that could compromise food security both globally and locally. Although it is true that extreme climatic events can severely impact small farmers, available data is just a gross approximation at understanding the heterogeneity of small scale agriculture ignoring the myriad of strategies that thousands of traditional farmers have used and still use to deal with climatic variability. Scientists have now realized that many small farmers cope with and even prepare for climate change, minimizing crop failure through a series of agroecological practices. Observations of agricultural performance after extreme climatic events in the last two decades have revealed that resiliency to climate disasters is closely linked to the high level of on-farm biodiversity, a typical feature of traditional farming systems.Based on this evidence, various experts have suggested that rescuing traditional management systems combined with the use of agroecologically based management strategies may represent the only viable and robust path to increase the productivity, sustainability and resilience of peasant-based agricultural production under predicted climate scenarios. In this paper we explore a number of ways in which three key traditional agroecological strategies (biodiversification, soil management and water harvesting) can be implemented in the design and management of agroecosystems allowing farmers to adopt a strategy that both increases resilience and provides economic benefits, including mitigation of global warming. 相似文献
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Methane Occurrences in Aquifers Overlying the Barnett Shale Play with a Focus on Parker County,Texas 
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下载免费PDF全文 Jean‐Philippe Nicot Patrick Mickler Toti Larson M. Clara Castro Roxana Darvari Kristine Uhlman Ruth Costley 《Ground water》2017,55(4):469-481
Clusters of elevated methane concentrations in aquifers overlying the Barnett Shale play have been the focus of recent national attention as they relate to impacts of hydraulic fracturing. The objective of this study was to assess the spatial extent of high dissolved methane previously observed on the western edge of the play (Parker County) and to evaluate its most likely source. A total of 509 well water samples from 12 counties (14,500 km2) were analyzed for methane, major ions, and carbon isotopes. Most samples were collected from the regional Trinity Aquifer and show only low levels of dissolved methane (85% of 457 unique locations <0.1 mg/L). Methane, when present is primarily thermogenic (δ13C 10th and 90th percentiles of ?57.54 and ?39.00‰ and C1/C2+C3 ratio 10th, 50th, and 90th percentiles of 5, 15, and 42). High methane concentrations (>20 mg/L) are limited to a few spatial clusters. The Parker County cluster area includes historical vertical oil and gas wells producing from relatively shallow formations and recent horizontal wells producing from the Barnett Shale (depth of ～1500 m). Lack of correlation with distance to Barnett Shale horizontal wells, with distance to conventional wells, and with well density suggests a natural origin of the dissolved methane. Known commercial very shallow gas accumulations (<200 m in places) and historical instances of water wells reaching gas pockets point to the underlying Strawn Group of Paleozoic age as the main natural source of the dissolved gas. 相似文献
64.
Vegetation impacts soil water content patterns by shaping canopy water fluxes and soil properties 下载免费PDF全文
下载免费PDF全文 Johanna Clara Metzger Thomas Wutzler Nicolas Dalla Valle Janett Filipzik Christoph Grauer Robert Lehmann Martin Roggenbuck Danny Schelhorn Josef Weckmüller Kirsten Küsel Kai Uwe Totsche Susan Trumbore Anke Hildebrandt 《水文研究》2017,31(22):3783-3795
Soil water content is a key variable for biogeochemical and atmospheric coupled processes. Its small‐scale heterogeneity impacts the partitioning of precipitation (e.g., deep percolation or transpiration) by triggering threshold processes and connecting flow paths. Forest hydrologists frequently hypothesized that throughfall and stemflow patterns induce soil water content heterogeneity, yet experimental validation is limited. Here, we pursued a pattern‐oriented approach to explore the relationship between net precipitation and soil water content. Both were measured in independent high‐resolution stratified random designs on a 1‐ha temperate mixed beech forest plot in Germany. We recorded throughfall (350 locations) and stemflow (65 trees) for 16 precipitation events in 2015. Soil water content was measured continuously in topsoil and subsoil (210 profiles). Soil wetting was only weakly related to net precipitation patterns. The precipitation‐induced pattern quickly dissipates and returns to a basic pattern, which is temporally stable. Instead, soil hydraulic properties (by the proxy of field capacity) were significantly correlated with this stable soil water content pattern, indicating that soil structure more than net precipitation drives soil water content heterogeneity. Also, both field capacity and soil water content were lower in the immediate vicinity of tree stems compared to further away at all times, including winter, despite stemflow occurrence. Thus, soil structure varies systematically according to vegetation in our site. We conclude that enhanced macroporosity increases gravity‐driven flow in stem proximal areas. Therefore, although soil water content patterns are little affected by net precipitation, the resulting soil water fluxes may strongly be affected. Specifically, this may further enhance the channelling of stemflow to greater depth and beyond the rooting zone. 相似文献
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Juan Reynerio Fagundo-Castillo Joel José Carrillo-Rivera Iñaki Antigüedad-Auzmendi Patricia González-Hernández Roberto Peláez-Díaz Rebeca Hernández-Díaz Dámaso Cáceres-Govea José Ramón Hernández-Santana Margaret Suárez-Muñoz Clara Melián-Rodríguez Mónica Rodríguez-Piña 《Environmental Geology》2008,55(2):247-267
Flows of different hierarchy, which travel through limestone, schist, sandstone and ultra-basic rocks, with ages from the
Paleocene to the Jurassic, at Sierra del Rosario, Pinar del Río, Cuba, were characterized. The waters were sampled from 1984
until 2004 and the data were statistically processed by means of chemical equilibrium and physico-chemical models, under a
flow system view of interpretation. Results demonstrate that the physico-chemical properties of the water are controlled by
water–rock interaction resulting from residence time since rainwater infiltrate and the path it follows to the discharge zone
and the type of aquifer material the different groundwater flows are in contact with. Geochemical indices allow the definition
of the different types of flow (local, intermediate, regional) to be characterized, permitting a further definition of the
different flow systems and rock type involved, as well as its use for water supply and medical use. The main geochemical processes
which control the chemical composition acquisitions mode are: congruent dissolution of calcite, dolomite, and halite; incongruent
dissolution of plagioclase and microcline minerals; pyrite oxidation, sulphate reduction, and silica dissolution at the surface
or silica precipitation at deep saturation and circulation zones. 相似文献
66.
Transpiration in Quercus suber trees under shallow water table conditions: the role of soil and groundwater 下载免费PDF全文
下载免费PDF全文 Clara A. Pinto Nadezhda Nadezhdina Jorge S. David Cathy Kurz‐Besson Maria C. Caldeira Manuel O. Henriques Fernando G. Monteiro João S. Pereira Teresa S. David 《水文研究》2014,28(25):6067-6079
Water is one of the major environmental factors limiting plant growth and survival in the Mediterranean region. Quercus suber L. woodlands occupy vast areas in the Iberian Peninsula, frequently under shallow water table conditions. The relative magnitude of soil and groundwater uptake to supply transpiration is not easy to evaluate under these circumstances. We recently developed a conceptual framework for the functioning of the root system in Q. suber that simulates well tree transpiration, based on two types of root behaviour: shallow connected and deep connected. Although this significantly improved knowledge on the functional traits of Mediterranean Q. suber, the approach has the limitation of requiring root sap flow data, which are seldom available. In this work, we present alternative methodologies to assess if trees are connected to groundwater and to estimate the soil and groundwater contributions to tree transpiration. We provide evidence on the tree unrestricted access to groundwater solely based on meteorological, stem sap flow and leaf water potential data. Using a soil mass balance approach, we estimated the yearly soil and groundwater contributions to tree transpiration: 69.7% and 30.3%, respectively. Groundwater uptake became dominant in the dry summer: 73.2% of tree transpiration. Results reproduce extremely well those derived from root modelling. Because of its simplicity both in formulation and data requirements, our approach is potentially liable to be adapted to other groundwater‐dependent Mediterranean oak sites, where interactions between land use and water resources may be relevant. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
67.
Mnica Susana Hoffmeyer Menndez María Clara Biancalana Florencia Nizovoy Alicia Mabel Torres Eduardo Ramn 《Estuarine, Coastal and Shelf Science》2009,84(3):181-392
This study focuses on the composition, abundance and distribution of ichthyoplankton in the inner shelf area off Bahía Blanca Estuary on the SW Atlantic Ocean during late spring. Eggs and larvae of Brevoortia aurea, Engraulis anchoita, Parona signata, Sciaenidae spp. – such as Cynoscion guatucupa and Micropogonias furnieri –, and Odontesthes argentinensis were found. Species richness was low probably as a result of season and shallow depths. Ichthyoplankton abundance reached values close to 10 000 per 10 m−3 (eggs) and 4000 per 10 m−3 (larvae) and displayed a spatial distribution pattern with maximum abundance values restricted to a band parallel to the coast. Differences between egg and larval patterns, probably derived from a different displacement and hydrodynamic behavior, were observed. Egg and larvae distribution patterns were found related with spawning areas and to directly depend on salinity and mesozooplankton. The larvae distribution pattern, in particular, was found to inversely depend on particulate organic carbon. In addition, the geographic location of egg and larvae maxima strongly coincided with a saline front reported for this area in springtime, thus suggesting a direct relationship with it. 相似文献
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