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51.
Aaron I. Packman Andrea Marion Mattia Zaramella Cheng Chen Jean-François Gaillard Denis T. Keane 《Water, Air, & Soil Pollution: Focus》2006,6(5-6):433-442
Hyporheic exchange is known to provide an important control on nutrient and contaminant fluxes across the stream-subsurface
interface. Similar processes also mediate interfacial transport in other permeable sediments. Recent research has focused
on understanding the mechanics of these exchange processes and improving estimation of exchange rates in natural systems.
While the structure of sediment beds obviously influences pore water flow rates and patterns, little is known about the interplay
of typical sedimentary structures, hyporheic exchange, and other transport processes in fluvial/alluvial sediments. Here we
discuss several processes that contribute to local-scale sediment heterogeneity and present results that illustrate the interaction
of overlying flow conditions, the development of sediment structure, pore water transport, and stream-subsurface exchange.
Layered structures are shown to develop at several scales within sediment beds. Surface sampling is used to analyze the development
of an armor layer in a sand-and-gravel bed, while innovative synchrotron-based X-ray microtomography is used to observe patterns
of grain sorting within sand bedforms. We show that layered bed structures involving coarsening of the bed surface increase
interfacial solute flux but produce an effective anisotropy that favors horizontal pore water transport while limiting vertical
penetration. 相似文献
52.
Aida Mendez Gary R. Sands Berangere Basin Chang‐Xing Jin Paul J. Wotzka 《Journal of the American Water Resources Association》2004,40(2):385-400
ABSTRACT: Surface and subsurface drainage make crop production economically viable in much of southern Minnesota because drainage allows timely field operations and protects field crops from extended periods of flooded soil conditions. However, subsurface drainage has been shown to increase nitrate/nitrogen losses to receiving waters. When engaging in drainage activities, farmers are increasingly being asked to consider, apart from the economic profit, the environmental impact of drainage. The Agricultural Drainage and Pesticide Transport model (ADAPT) was used in this study to evaluate the impact of subsurface drainage design on the soil water balance over a two‐year period during which observed drainage discharge data were available. Twelve modeling scenarios incorporated four drainage coefficients (DC), 0.64 cm/d, 0.95 cm/d, 1.27 cm/d, and 1.91 cm/d, and three drain depths, 0.84 m, 1.15 m, and 1.45 m. The baseline condition corresponded to the drainage system specifications at the field site: a drain depth and spacing of 1.45 m and 28 m, respectively (DC of 0.64 cm/d). The results of the two‐year simulation suggested that for a given drainage coefficient, soils with the shallower drains (but equal DC) generally have less subsurface drainage and can produce more runoff (but reduced total discharge) and evapotranspiration. The results also suggested that it may be possible to design for both water/nitrate/nitrogen reduction and crop water needs. 相似文献
53.
James F. Saunders Marylee Murphy Martyn Clark William M. Lewis 《Journal of the American Water Resources Association》2004,40(5):1339-1349
ABSTRACT: Historical flow records are used to estimate the regulatory low flows that serve a key function in setting discharge permit limits through the National Pollutant Discharge Elimination System, which provides a nationwide mechanism for protecting water quality. Use of historical records creates an implicit connection between water quality protection and climate variability. The longer the record, the more likely the low flow estimate will be based on a broad set of climate conditions, and thus provides adequate water quality protection in the future. Unfortunately, a long record often is not available at a specific location. This analysis examines the connection between climate variability and the variability of biologically based and hydrologically based low flow estimates at 176 sites from the Hydro‐Climatic Data Network, a collection of stream gages identified by the USGS as relatively free of anthropogenic influences. Results show that a record of 10 to 20 years is necessary for satisfactory estimates of regulatory low flows. Although it is possible to estimate a biologically based low flow from a record of less than 10 years, these estimates are highly uncertain and incorporate a bias that undermines water quality protection. 相似文献
54.
55.
Ramsis B. Salama 《Water, Air, & Soil Pollution: Focus》2005,5(1-2):27-44
Perth groundwater resources are obtained from three major aquifers that occur beneath the Perth metropolitan area: the Superficial
aquifer, Leederville aquifer and Yarragadee aquifer. Each aquifer has a unique seasonal water level pattern controlled by
soils, geomorphology and geology. Landuse is mainly responsible for variations in recharge; however, the hydraulic properties
control aquifer response and water level pattern to a greater degree. Groundwater in the three aquifers is generally of very
good quality except in localised areas. Salinity increases with depth and in direction of groundwater flow in the three aquifers.
The best water quality is in the Superficial aquifer in the Wanneroo well field area. The geochemistry and stable isotope
signatures from the three major aquifers revealed distinct water types that suggest very little hydraulic connection or mixing
of waters between these aquifers at the present abstraction and recharge regimes. The results also show that the Leederville
and Yarragadee aquifers were recharged during earlier cooler times while the Superficial aquifer is being recharged at present. 相似文献
56.
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58.
地下水水质评价的多元线性回归分析模型研究 总被引:4,自引:0,他引:4
运用回归分析理论和方法,建立了一个基于多元线性回归分析法的地下水水质评价模型,并将该模型用于遵义市海龙坝地下水水质评价.结果表明,建立的模型较符合本研究区的实际情况. 相似文献
59.
Alan M. Stueber Robert E. Criss 《Journal of the American Water Resources Association》2005,41(2):267-290
ABSTRACT: An extensive base of water quality information emphasizing the effects of land use and hydrology was obtained in the karstified Fountain Creek watershed of southwestern Illinois to help resolve local water quality issues. Agrichemicals dominate the loads of most water quality constituents in the streams and shallow karstic ground water. Only calcium (Ca), magnesium (Mg), Aluminum (A1), and sulfate (SO4) ions are predominantly derived from bedrock or soils, while agrichemicals contribute most of the sodium (Na), potassium (K), chlorine (Cl), nitrate (NO3), fluorine (F), phosphorus (P), and atrazine. Concentrations of individual ions correlate with discharge variations in karst springs and surface streams; highly soluble ions supplied by diffuse ground water are diluted by high flows, while less soluble ions increase with flow as they are mobilized from fields to karst conduits under storm conditions. Treated wastewater containing detergent residues dominates the boron load of streams and provides important subordinate loads of several other constituents, including atrazine derived from the Mississippi River via the public water supply. Average surface water concentrations at the watershed outlet closely approximate a 92:8 mixture of karst ground water and treated wastewater, demonstrating the dominance of ground water contributions to streams. Therefore the karst aquifer and watershed streams form a single water quality system that is also affected by wastewater effluent. 相似文献
60.
Douglas G. Boyer 《Journal of the American Water Resources Association》2005,41(2):291-300
ABSTRACT: Water quality indicators of two agriculturally impacted karst areas in southeastern West Virginia were studied to determine the water quality effects of grazing agriculture and water quality trends following initiation of water quality improvement programs. Both areas are tributaries of the Greenbrier River and received funding for best management practices under the President's Initiative for Water Quality and then under the Environmental Quality Incentives Program (EQIP). After 11 years of study there was little evidence to suggest that water quality improved in one area. Three and a half years of study in the other area showed little evidence of consistent water quality improvement under EQIP. Lack of consistent water quality improvement at the catchment scale does not imply that the voluntary programs were failures. Increased livestock numbers as a result of successful changes in forage management practices may have overridden water quality improvements achieved through best management practices. Practices that target well defined contributing areas significantly impacting aquifer water quality might be one way to improve water quality at catchment scales in karst basins. For example, a significant decrease in fecal coliform concentrations was observed in subterranean drainage from one targeted sinkhole after dairy cattle were permanently excluded from the sinkhole. 相似文献