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481.
Laboratory column experiments run for up to 13 days compared air sparging of groundwater contaminated by dissolved petroleum hydrocarbons in sterile and non-sterile aquifer sediments as well as uncontaminated sediments and groundwater. Loss of dissolved BTEX compounds in the contaminated columns was very rapid, occurring through volatilisation. The majority of the dissolved total organic carbon (TOC) persisted for much longer periods however. A direct comparison between losses from sterile and non-sterile columns suggested a negligible contribution of biodegradation to the removal of TOC. This was difficult to confirm through examination of O2 utilisation because oxidation of a small amount of reduced sulphur in the aquifer materials was the dominant sink for O2. Despite this, it was possible to conclude that less than 22% of the removal of TOC was through biodegradation during the first three days of air sparging. 相似文献
482.
Subsidence is a primary factor governing marsh deterioration in Mississippi River deltaic plain coastal marshes. Marsh surface-water level relationships are maintained primarily through soil organic matter accumulation and inorganic sediment input. In this study we examined the role of soil organic matter accumulation in maintaining marsh elevation in a brackish Spartina patens marsh. Measured rates of soil organic accumulation were compared to plant biomass production and soil respiration (carbon dioxide and methane emission) at the study sites. The study demonstrated the importance of plant biomass production to soil organic carbon accumulation in maintaining viable Spartina patens marshes in sediment-deficient coastal environments. The role of Mississippi River freshwater reintroduction in maintaining conditions for organic accretion is discussed. 相似文献
483.
N. K. Woodfield J. W. S. Longhurst C. I. Beattie D. P. H. Laxen 《Journal of Environmental Planning and Management》2003,46(1):49-64
The UK National Air Quality Strategy has required local authorities to review and assess air quality in their area of jurisdiction and determine locations in their areas where concentrations of specific air quality pollutants are predicted to exceed national air quality objectives in the future. Statutory air quality management areas (AQMAs) are designated where air quality is predicted to be above specified objective concentrations by specific target dates, and statutory air quality action plans will be necessary to improve the local air quality within these areas. Over 124 local authorities in England (including London), Wales and Scotland anticipate declaring AQMAs following the conclusion of the statutory air quality review and assessment process. However, other influences are being exerted on the local air quality management process and AQMA decision-making processes. Such influences include regional and sub- regional collaborative working between local authorities and government agencies and wider political decision-making processes. Some regions of Great Britain (encompassing England (including London), Scotland and Wales) anticipate many AQMA designations, whilst other regions are not anticipating any such designations despite apparently similar air quality circumstances. Evidence for regional or sub-regional variations in the locations of anticipated AQMAs are examined through an evaluation of the outcomes of the scientific review and assessment process undertaken by local authorities declaring AQMAs, and through a local authority survey to identify influences on decision-making processes at a level above that of the local authority. Regional variation is reported in the type of pollutant causing AQMAs to be declared, in the numbers of AQMAs in regions and in the spatial distribution of AQMAs across Great Britain. 相似文献
484.
485.
Ian H. McBeth Katta J. Reddy Quentin D. Skinner 《Journal of the American Water Resources Association》2003,39(3):575-585
ABSTRACT: The Powder River Basin in Wyoming has become one of the most active areas of coalbed methane (CBM) development in the western United States. Extraction of methane from coalbeds requires pumping of aquifer water, which is called product water. Two to ten extraction wells are manifolded into one discharge point and product water is released into nearby unlined holding ponds. The objective of this study was to evaluate the chemistry, salinity, and sodicity of CBM product water at discharge points and associated holding ponds as a function of watershed. The product water samples from the discharge points and associated holding ponds were collected from the Cheyenne River (CHR), Belle Fourche River (BFR), and Little Powder River (LPR) watersheds during the summers of 1999 and 2000. These samples were analyzed for pH, electrical conductivity (EC), total dissolved solids (TDS), alkalinity, sodium (Na), calcium (Ca), magnesium (Mg), potassium (K), sulfate (SO42‐), and chloride (C1‐). From the chemical data, practical sodium adsorption ratio (SARp) and true sodium adsorption ratio (SARt) were calculated for the CBM discharge water and pond water. The pH, EC, TDS, alkalinity, Na, Ca, Mg, K, SARp, and SARt of CBM discharge water increased significantly moving north from the CHR watershed to the LPR watershed. CBM discharge water in associated holding ponds showed significant increases in EC, TDS, alkalinity, Na, K, SARp, and SARt moving north from the CHR to the LPR watershed. Within watersheds, the only significant change was an increase in pH from 7.21 to 8.26 between discharge points and holding ponds in the LPR watershed. However, the LPR and BFR exhibited larger changes in mean chemistry values in pH, salinity (EC, TDS), and sodicity (SAR) between CBM product water discharges and associated holding ponds than the CHR watershed. For instance, the mean EC and TDS of CBM product water in LPR increased from 1.93 to 2.09 dS/m, and froml,232 to 1,336 mg/L, respectively, between discharge and pond waters. The CHR exhibited no change in EC, TDS, Na, or SAR between discharge water and pond water. Also, while not statistically significant, mean alkalinity of CBM product water in BFR and LPR watersheds decreased from 9.81 to 8.01 meq/L and from 19.87 to 18.14 meq/L, respectively, between discharge and pond waters. The results of this study suggest that release of CBM product water onto the rangelands of BFR and LPR watersheds may precipitate calcium carbonate (CaCO3) in soils, which in turn may decrease infiltration and increase runoff and erosion. Thus, use of CBM product water for irrigation in LPR and BFR watersheds may require careful planning based on water pH, EC, alkalinity, Na, and SAR, as well as local soil physical and chemical properties. 相似文献
486.
Marty D. Matlock Kevin Ray Kasprzak G. Scott Osborn 《Journal of the American Water Resources Association》2003,39(2):267-275
ABSTRACT: The lower reaches of the Arroyo Colorado have historically failed to meet their use under subsection 303(b) of the U.S. Clean Water Act due to fecal coliform bacteria and low dissolved oxygen (DO). Fish kills, especially at the tidal confluence at the Port of Harlingen, Texas, have been reported. Oxygen demand from sediment (SOD) for a river typically has two states‐diffusion limited SOD (SOD) and potential SOD (pSOD), expressed when sediment is resuspended through increased flow or other disturbances. The objective of this research was to measure SOD in the Arroyo Colorado River in situ, estimate pSOD ex situ, and evaluate the relationship between SOD and the depositional environment. We measured SOD and pSOD in the Arroyo Colorado River at up to eight sites over three sampling events. We identified the sample sites based on a modified Rosgen geomorphic index for streambed stabilization. Sites with high sediment deposition potential had high SOD. The average values of SOD between sites were 0.62 g/m2/day (standard deviation 0.38 g/m2/day) and ranged from 0.13 to 1.2 g/m2/day. Potential SOD values ranged from as low as 19.2 to as high as 2,779 g/m3 sediment/ day. Potential SOD can serve as an indicator of the possible impact of SOD from resuspended sediment in stream systems. 相似文献
487.
Joseph L. Ebersole William J. Liss Christopher A. Frissell 《Journal of the American Water Resources Association》2003,39(2):355-368
ABSTRACT: Discrete cold water patches within the surface waters of summer warm streams afford potential thermal refuge for cold water fishes during periods of heat stress. This analysis focused on reach scale heterogeneity in water temperatures as influenced by local influx of cooler subsurface waters. Using field thermal probes and recording thermistors, we identified and characterized cold water patches (at least 3°C colder than ambient streamflow temperatures) potentially serving as thermal refugia for cold water fishes. Among 37 study sites within alluvial valleys of the Grande Ronde basin in northeastern Oregon, we identified cold water patches associated with side channels, alcoves, lateral seeps, and floodplain spring brooks. These types differed with regard to within floodplain position, area, spatial thermal range, substrate, and availability of cover for fish. Experimental shading cooled daily maximum temperatures of surface waters within cold water patches 2 to 4°C, indicating a strong influence of riparian vegetation on the expression of cold water patch thermal characteristics. Strong vertical temperature gradients associated with heating of surface layers of cold water patches exposed to solar radiation, superimposed upon vertical gradients in dissolved oxygen, can partially restrict suitable refuge volumes for stream salmonids within cold water patches. 相似文献
488.
/ In this paper we develop a conceptual framework for selectingstressor data and analyzing their relationship to geographic patterns ofspecies richness at large spatial scales. Aspects of climate and topography,which are not stressors per se, have been most strongly linked withgeographic patterns of species richness at large spatial scales (e.g.,continental to global scales). The adverse impact of stressors (e.g., habitatloss, pollution) on species has been demonstrated primarily on much smallerspatial scales. To date, there has been a lack of conceptual developmenton how to use stressor data to study geographic patterns of speciesrichness at large spatial scales.The framework we developed includes four components: (1) clarification of theterms stress and stressor and categorization of factors affecting speciesrichness into three groups-anthropogenic stressors, natural stressors, andnatural covariates; (2) synthesis of the existing hypotheses for explaininggeographic patterns of species richness to identify the scales over whichstressors and natural covariates influence species richness and to providesupporting evidence for these relationships through review of previousstudies; (3) identification of three criteria for selection of stressor andcovariate data sets: (a) inclusion of data sets from each of the threecategories identified in item 1, (b) inclusion of data sets representingdifferent aspects of each category, and (c) to the extent possible, analysisof data quality; and (4) identification of two approaches for examiningscale-dependent relationships among stressors, covariates, and patterns ofspecies richness-scaling-up and regression-tree analyses.Based on this framework, we propose 10 data sets as a minimum data base forexamining the effects of stressors and covariates on species richness atlarge spatial scales. These data sets include land cover, roads, wetlands(numbers and loss), exotic species, livestock grazing, surface water pH,pesticide application, climate (and weather), topography, and streams.KEY WORDS: Anthropogenic impacts; Biodiversity; Environmental gradients;Geographic information systems; Hierarchy 相似文献
489.
Lee H. Macdonald Donald M. Anderson William E. Dietrich 《Environmental management》1997,21(6):851-863
2 /yr, respectively. Geomorphic evidence indicates that plantation agriculture during the 18th and 19th centuries did not cause
severe erosion. Since about 1950 there has been rapid growth in roads and development due to increasing tourism and second-home
development. Our field investigations identified the approximately 50 km of unpaved roads as the primary source of anthropogenic
sediment. Field measurements of the road network in two catchments led to the development of a vector-based GIS model to predict
road surface erosion and sediment delivery. We estimate that road erosion has caused at least a fourfold increase in island-wide
sediment yields and that current sedimentation rates are unprecedented. Paving the dirt roads and implementing standard sediment
control practices can greatly reduce current sediment yields and possible adverse effects on the marine ecosystems surrounding
St. John. 相似文献
490.
Agricultural economics has, until the 1990s, enjoyeda reputation for relevance and usefulness to theagri-food industry and policy-makers. Thatreputation has been jeopardized by a growinginfatuation with models and quantification, and aconcomitant underemphasis placed on many complexproblems and issues of society. An illustrativeexample is explored, using agriculturalactivity-related damage to the natural resourcebase, environment and ecology. Agriculturaleconomists are urged to respond by broadening theirterms of reference and joining forces with otherdisciplines. 相似文献