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1.
A PCE groundwater plume discharging to a river: influence of the streambed and near-river zone on contaminant distributions 总被引:3,自引:0,他引:3
An investigation of a tetrachloroethene (PCE) groundwater plume originating at a dry cleaning facility on a sand aquifer and discharging to a river showed that the near-river zone strongly modified the distribution, concentration, and composition of the plume prior to discharging into the surface water. The plume, streambed concentration, and hydrogeology were extensively characterized using the Waterloo profiler, mini-profiler, conventional and driveable multilevel samplers (MLS), Ground Penetrating Radar (GPR) surveys, streambed temperature mapping (to identify discharge zones), drivepoint piezometers, and soil coring and testing. The plume observed in the shallow streambed deposits was significantly different from what would have been predicted based on the characteristics of the upgradient plume. Spatial and temporal variations in the plume entering the near-river zone contributed to the complex contaminant distribution observed in the streambed where concentrations varied by factors of 100 to 5000 over lateral distances of less than 1 to 3.5 m. Low hydraulic conductivity semi-confining deposits and geological heterogeneities at depth below the streambed controlled the pattern of groundwater discharge through the streambed and influenced where the plume discharged into the river (even causing the plume to spread out over the full width of the streambed at some locations). The most important effect of the near-river zone on the plume was the extensive anaerobic biodegradation that occurred in the top 2.5 m of the streambed, even though essentially no biodegradation of the PCE plume was observed in the upgradient aquifer. Approximately 54% of the area of the plume in the streambed consisted solely of PCE transformation products, primarily cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC). High concentrations in the interstitial water of the streambed did not correspond to high groundwater-discharge zones, but instead occurred in low discharge zones and are likely sorbed or retarded remnants of past high-concentration plume discharges. The high-concentration areas (up to 5529 microg/l of total volatile organics) in the streambed are of ecological concern and represent potential adverse exposure locations for benthic and hyporheic zone aquatic life, but the effect of these exposures on the overall health of the river has yet to be determined. Even if the upgradient source of PCE is remediated and additional PCE is prevented from reaching the streambed, the high-concentration deposits in the streambed will likely take decades to hundreds of years to flush completely clean under natural conditions because these areas have low vertical groundwater flow velocities and high retardation factors. Despite high concentrations of contaminants in the streambed, PCE was detected in the surface water only rarely due to rapid dilution in the river and no cDCE or VC was detected. Neither the sampling of surface water nor the sampling of the groundwater from the aquifer immediately adjacent to the river gave an accurate indication of the high concentrations of PCE biodegradation products present in the streambed. Sampling of the interstitial water of the shallow streambed deposits is necessary to accurately characterize the nature of plumes discharging to rivers. 相似文献
2.
Andrea Gori Sergio Rossi Cristina Linares Elisa Berganzo Covadonga Orejas Mark RT Dale Josep-Maria Gili 《Marine Biology》2011,158(8):1721-1732
In the Western Mediterranean Sea, the gorgonian Eunicella singularis (Esper, 1794) is found at high densities on sublittoral bottoms at depths from 10 to 70 m. Shallow colonies have symbiotic
zooxanthellae that deeper colonies lack. While knowledge of the ecology of the shallow populations has increased during the
last decades, there is almost no information on the ecology of the deep sublittoral populations. In October and November 2004
at Cap de Creus (42°19′12″ N; 03°19′34″ E), an analysis of video transects made by a remotely operated vehicle showed that
shallow populations (10–25 m depth) were dominated by small, non-reproductive colonies, while deep sublittoral populations
(50–67 m depth) were dominated by medium-sized colonies. Average and maximum colony heights were greater in the deeper populations,
with these deeper populations also forming larger patch sizes and more extensive regions of continuous substrate coverage.
These results suggest that shallow habitats are suitable for E. singularis, as shown by the high recruitment rate, but perturbations may limit or delay the development of these populations into a
mature stage. This contrasts with the deep sublittoral habitats where higher environmental stability may allow the development
of mature populations dominated by larger, sexually mature colonies. 相似文献
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4.
The potential to sequester atmospheric carbon in agricultural and forest soils to offset greenhouse gas emissions has generated interest in measuring changes in soil carbon resulting from changes in land management. However, inherent spatial variability of soil carbon limits the precision of measurement of changes in soil carbon and hence, the ability to detect changes. We analyzed variability of soil carbon by intensively sampling sites under different land management as a step toward developing efficient soil sampling designs. Sites were tilled cropland and a mixed deciduous forest in Tennessee, and old-growth and second-growth coniferous forest in western Washington, USA. Six soil cores within each of three microplots were taken as an initial sample and an additional six cores were taken to simulate resampling. Soil C variability was greater in Washington than in Tennessee, and greater in less disturbed than in more disturbed sites. Using this protocol, our data suggest that differences on the order of 2.0 Mg C ha(-1) could be detected by collection and analysis of cores from at least five (tilled) or two (forest) microplots in Tennessee. More spatial variability in the forested sites in Washington increased the minimum detectable difference, but these systems, consisting of low C content sandy soil with irregularly distributed pockets of organic C in buried logs, are likely to rank among the most spatially heterogeneous of systems. Our results clearly indicate that consistent intramicroplot differences at all sites will enable detection of much more modest changes if the same microplots are resampled. 相似文献
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6.
The nettle caterpillar, Darna pallivitta (Moore) (Lepidoptera: Limacodidae), is an invasive pest with established populations on three Hawai’ian islands. Indigenous
to Southeast Asia, D. pallivitta caterpillars cause defoliation of ornamental nursery stock and pose a human health hazard due to their urticating hairs that
can cause painful skin reactions. Identification of the pheromone component n-butyl (E)-7,9-decadienoate (E7,9-10:COOnBu) from D. pallivitta has made it possible to investigate the phenology and population dynamics using baited traps. Male captures in Jackson traps
baited with E7,9-10:COOnBu showed a vegetation preference for tall-grass fields and forest/grass interfaces over forest areas. Microlocation
preferences were also found for trap height, with over 65% of males being caught in traps suspended at 1 m, compared with
the traps at 3 and 5 m. Captures of male moths in traps baited with live females, and direct observations of female calling
behavior, showed peak activities 6–7 h after the onset of scotophase. This is a much later communication period than for D. bradleyi and D. trima and may provide a mechanism by which D. pallivitta maintains reproductive isolation in areas where all three species are present. Coastal and inland transects established in
eastern Hawai’i measured aspects of population fluctuations and radiation into new areas with relation to elevation and microclimate.
Population expansion was measured by comparing moth population means and 80% population boundaries over time. Both population
measures showed a higher expansion for the coastal transect. Differences in population expansion may be attributed in part
to temperature and elevation, while precipitation does not seem to have a strong effect. Both the behavioral and ecological
data collected can be used to optimize deployment of detection/control strategies and to predict population expansion/risk
assessment for establishing quarantine protocols for the nettle caterpillar. 相似文献
7.
Sedinger JS Ward DH Schamber JL Butler WI Eldridge WD Conant B Voelzer JE Chelgren ND Herzog MP 《Ecology》2006,87(1):151-159
Climate in low-latitude wintering areas may influence temperate and high-latitude breeding populations of birds, but demonstrations of such relationships have been rare because of difficulties in linking wintering with breeding populations. We used long-term aerial surveys in Mexican wintering areas and breeding areas in Alaska, USA, to assess numbers of Black Brant (Branta bernicla nigricans; hereafter brant) on their principal wintering and breeding area in El Ni?o and non-El Ni?o years. We used Pollock's robust design to directly estimate probability of breeding and apparent annual survival of individually marked brant at the Tutakoke River (TR) colony, Alaska, in each year between 1988 and 2001. Fewer brant wintered in Mexico during every El Ni?o event since 1965. Fewer brant were observed on the principal breeding area following each El Ni?o since surveys began in 1985. Probability of breeding was negatively related to January sea surface temperature along the subtropical coast of North America during the preceding winter. Between 23% (five-year-olds or older) and 30% (three-year-olds) fewer brant nested in 1998 following the strong El Ni?o event in the winter of 1997-1998 than in non-El Ni?o years. This finding is consistent with life history theory, which predicts that longer-lived species preserve adult survival at the expense of reproduction. Oceanographic conditions off Baja California, apparently by their effect on Zostera marina (eelgrass), strongly influence winter distribution of brant geese and their reproduction (but not survival), which in turn affects ecosystem dynamics in Alaska. 相似文献
8.
Grassland management affects soil organic carbon (SOC) storage and can be used to mitigate greenhouse gas emissions. However, for a country to assess emission reductions due to grassland management, there must be an inventory method for estimating the change in SOC storage. The Intergovernmental Panel on Climate Change (IPCC) has developed a simple carbon accounting approach for this purpose, and here we derive new grassland management factors that represent the effect of changing management on carbon storage for this method. Our literature search identified 49 studies dealing with effects of management practices that either degraded or improved conditions relative to nominally managed grasslands. On average, degradation reduced SOC storage to 95% ± 0.06 and 97% ± 0.05 of carbon stored under nominal conditions in temperate and tropical regions, respectively. In contrast, improving grasslands with a single management activity enhanced SOC storage by 14% ± 0.06 and 17% ± 0.05 in temperate and tropical regions, respectively, and with an additional improvement(s), storage increased by another 11% ± 0.04. We applied the newly derived factor coefficients to analyze C sequestration potential for managed grasslands in the U.S., and found that over a 20-year period changing management could sequester from 5 to 142 Tg C yr–1 or 0.1 to 0.9 Mg C ha–1 yr–1, depending on the level of change. This analysis provides revised factor coefficients for the IPCC method that can be used to estimate impacts of management; it also provides a methodological framework for countries to derive factor coefficients specific to conditions in their region. 相似文献
9.
Alex H.S. Chik Melissa B. Glier Mark Servos Chand S. Mangat Xiao-Li Pang Yuanyuan Qiu Patrick M. DAoust Jean-Baptiste Burnet Robert Delatoll Sarah Dorner Qiudi Geng John P. Giesy Robert Mike McKay Michael R. Mulvey Natalie Prystajecky Nivetha Srikanthan Yuwei Xie Bernadette Conant Steve E. Hrudey 《环境科学学报(英文版)》2021,33(9):218-229
10.
Experimental warming shows that decomposition temperature sensitivity increases with soil organic matter recalcitrance 总被引:3,自引:0,他引:3
Soil C decomposition is sensitive to changes in temperature, and even small increases in temperature may prompt large releases of C from soils. But much of what we know about soil C responses to global change is based on short-term incubation data and model output that implicitly assumes soil C pools are composed of organic matter fractions with uniform temperature sensitivities. In contrast, kinetic theory based on chemical reactions suggests that older, more-resistant C fractions may be more temperature sensitive. Recent research on the subject is inconclusive, indicating that the temperature sensitivity of labile soil organic matter (OM) decomposition could either be greater than, less than, or equivalent to that of resistant soil OM. We incubated soils at constant temperature to deplete them of labile soil OM and then successively assessed the CO2-C efflux in response to warming. We found that the decomposition response to experimental warming early during soil incubation (when more labile C remained) was less than that later when labile C was depleted. These results suggest that the temperature sensitivity of resistant soil OM pools is greater than that for labile soil OM and that global change-driven soil C losses may be greater than previously estimated. 相似文献