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921.
When native grassland catchments are converted to pasture, the main effects on stream physicochemistry are usually related
to increased nutrient concentrations and fine-sediment input. We predicted that increasing nutrient concentrations would produce
a subsidy-stress response (where several ecological metrics first increase and then decrease at higher concentrations) and
that increasing sediment cover of the streambed would produce a linear decline in stream health. We predicted that the net
effect of agricultural development, estimated as percentage pastoral land cover, would have a nonlinear subsidy-stress or
threshold pattern. In our suite of 21 New Zealand streams, epilithic algal biomass and invertebrate density and biomass were
higher in catchments with a higher proportion of pastoral land cover, responding mainly to increased nutrient concentration.
Invertebrate species richness had a linear, negative relationship with fine-sediment cover but was unrelated to nutrients
or pastoral land cover. In accord with our predictions, several invertebrate stream health metrics (Ephemeroptera–Plecoptera–Trichoptera
density and richness, New Zealand Macroinvertebrate Community Index, and percent abundance of noninsect taxa) had nonlinear
relationships with pastoral land cover and nutrients. Most invertebrate health metrics usually had linear negative relationships
with fine-sediment cover. In this region, stream health, as indicated by macroinvertebrates, primarily followed a subsidy-stress
pattern with increasing pastoral development; management of these streams should focus on limiting development beyond the
point where negative effects are seen. 相似文献
922.
Agyin-Birikorang S O'Connor GA Jacobs LW Makris KC Brinton SR 《Journal of environmental quality》2007,36(1):316-323
Excessive soluble P in runoff is a common cause of eutrophication in fresh waters. Evidence indicates that drinking water treatment residuals (WTRs) can reduce soluble P concentrations in P-impacted soils in the short term (days to weeks). The long-term (years) stability of WTR-immobilized P has been inferred, but validating field data are scarce. This research was undertaken at two Michigan field sites with a history of heavy manure applications to study the longevity of alum-based WTR (Al-WTR) effects on P solubility over time (7.5 yr). At both sites, amendment with Al-WTR reduced water-soluble P (WSP) concentration by >or=60% as compared to the control plots, and the Al-WTR-immobilized P (WTR-P) remained stable 7.5 yr after Al-WTR application. Rainfall simulation techniques were utilized to investigate P losses in runoff and leachate from surface soils of the field sites at 7.5 yr after Al-WTR application. At both sites, amendment with Al-WTR reduced dissolved P and bioavailable P (BAP) by >50% as compared to the control plots, showing that WTR-immobilized P remained nonlabile even 7.5 yr after Al-WTR amendment. Thus, WTR-immobilized P would not be expected to dissolve into runoff and leachate to contaminate surface waters or groundwater. Even if WTR-P is lost via erosion to surface waters, the bioavailability of the immobilized P should be minimal and should have negligible effects on water quality. However, if the WTR particles are destroyed by extreme conditions, P loss to water could pose a eutrophication risk. 相似文献
923.
924.
Ground water input to coastal salt ponds of southern Rhode Island estimated using 226Ra as a tracer 总被引:2,自引:0,他引:2
The naturally occurring radionuclide 226Ra (t1/2 = 1600 years) was used as a tracer to determine ground water input to Point Judith, Potter, Green Hill and Ninigret ponds in southern Rhode Island. Measurements of 226Ra activity were made in samples collected from salt ponds, pore waters, sediments, and local ground water wells during June-August, 1997. These results were combined with a simple box model to derive ground water input fluxes of 0.1-0.3 cm3 cm-2 d-1 (2-5 x 10(7) L d-1), which are comparable to previous estimates of ground water input to these ponds. 相似文献
925.
Scale-dependence of land use effects on water quality of streams in agricultural catchments 总被引:4,自引:0,他引:4
The influence of land use on water quality in streams is scale-dependent and varies in time and space. In this study, land cover patterns and stocking rates were used as measures of agricultural development in two pasture and one native grassland catchment in New Zealand and were related to water quality in streams of various orders. The amount of pasture per subcatchment correlated well to total nitrogen and nitrate in one catchment and turbidity and total phosphorous in the other catchment. Stocking rates were only correlated to total phosphorous in one pasture catchment but showed stronger correlations to ammonium, total phosphorous and total nitrogen in the other pasture catchment. Winter and spring floods were significant sources of nutrients and faecal coliforms from one of the pasture catchments into a wetland complex. Nutrient and faecal coliform concentrations were better predicted by pastural land cover in fourth-order than in second-order streams. This suggests that upstream land use is more influential in larger streams, while local land use and other factors may be more important in smaller streams. These temporal and spatial scale effects indicate that water-monitoring schemes need to be scale-sensitive. 相似文献
926.
Groundwater Contamination in Karst Terranes 总被引:2,自引:0,他引:2
927.
We made use of land cover maps, and land use change associated with urbanization, to provide estimates of the loss of natural
resource lands (forest, agriculture, and wetland areas) across the 168,000 km2 Chesapeake Bay watershed. We conducted extensive accuracy assessments of the satellite-derived maps, most of which were produced
by us using widely available multitemporal Landsat imagery. The change in urbanization was derived from impervious surface
area maps (the built environment) for 1990 and 2000, from which we estimated the loss of resource lands that occurred during
this decade. Within the watershed, we observed a 61% increase in developed land (from 5,177 to 8,363 km2). Most of this new development (64%) occurred on agricultural and grasslands, whereas 33% occurred on forested land. Some
smaller municipalities lost as much as 17% of their forest lands and 36% of their agricultural lands to development, although
in the outlying counties losses ranged from 0% to 1.4% for forests and 0% to 2.6% for agriculture. Fast-growing urban areas
surrounded by forested land experienced the most loss of forest to impervious surfaces. These estimates could be used for
the monitoring of the impacts of development across the Chesapeake Bay watershed, and the approach has utility for other regions
nationwide. In turn, the results and the approach can help jurisdictions set goals for resource land protection and acquisition
that are consistent with regional restoration goals. 相似文献
928.
In South Africa an intensive reform process to democratize policy, legislation and related institutions in the country commenced after the first democratic elections in 1994. While environmental law reform includes active public participation and equity principles, it is proposed in this paper that ecological modernization dominates current environmental assessment practice. This paper presents a Social Impact Assessment (SIA) of a proposed landfill on the periphery of Durban, where large informal settlements and peri-urban areas exist as a relic of apartheid planning. The methodology of the SIA was explicitly designed within a framework of social justice to include poor and marginalized people, who remain excluded from environmental decision making despite the promise of democratic equality. The study claims to deepen democratic practice by demonstrating that alternative methodologies can be designed to include the interests of ‘invisible stakeholders’ in environmental assessments despite the dominance of ecological modernization in the implementation of environmental law and policy. 相似文献
929.
Diamond DD True CD Gordon TM Sowa SP Foster WE Jones KB 《Environmental management》2005,35(2):130-137
We used an existing conservation opportunity area (OA) data layer for four contiguous ecological subsections within the Ozark Highlands to quantitatively evaluate the influence of conservation targets and assessment region size on conservation priorities. OAs are natural and seminatural land-cover patches that are away from roads and away from patch edges. To evaluate the influence of targets, we assigned a priority score to each OA polygon for each of five different conservation targets, including land-cover patch size, landform representation, target vertebrate richness, target breeding bird richness, and target land cover. The top-scoring OAs for each target were added to an OA selection set for that target until 50% of the study area was chosen. These five OA selection sets were overlain to quantify overlap in priorities. Only 1.6% of the study area, or 2.1% of all OA polygons, was selected by all five targets. To evaluate the influence of assessment region size, we compared results of priority ranking of OAs relative to the entire study area against a merged set of priority rankings established separately relative to each of the four subsections within the study area. When high-priority OAs were added until 25% of the region was within the selection set for each of the five targets, the sets based on the whole study area versus each subsection evaluated separately overlapped from 45.4% to 81.9%. Thus, perceived priorities of conservation assessments are strongly influenced both by the targets that are evaluated and by the size of the assessment region. 相似文献
930.
An experiment was performed to examine the phytoremediation potential of Rhodes grass (Chloris gayana Kunth cv. ‘Pioneer’). The study sought to determine substrate tolerance, biomass production, and plant uptake of antimony (Sb), arsenic (As), cadmium (Cd), lead (Pb), silver (Ag), and zinc (Zn). The plants were grown on weight percent mixtures (5 percent, 15 percent, 25 percent, 35 percent, 50 percent) of a vertisol soil and base‐metal mine tailings (7–2,040 μg/g As, ≥ 30 μg/g Cd, 30–12,000 μg/g Pb, and 72–4,120 μg/g Zn). The 5 percent and 15 percent amendment of mine tailings increased the biomass production of Rhodes grass (from 0.1 g/plant to ≈ 3.5 g/plant) without appreciably elevating plant concentrations of the elements. Plant growth decreased by greater than 50 percent for the substrate containing greater than 25 percent tailings (3,023 μg/g Pb and 1,084 μg/g Zn). Reduced biomass production coincided with maximal Zn uptake by Rhodes grass (249.8 μg/g), indicating tailings induced phytotoxicity. The total concentrations of metals and metalloids tolerated by Rhodes grass in the plant‐growth medium indicated hypertolerance to elevated As, Pb, and Zn concentrations. Partial extraction of the plant‐growth medium determined that plant‐available Pb was ten times higher than Ag, As, Cd, and Zn availability. However, Rhodes grass accumulated low levels of Pb, in addition to As and Cd, over the experimental range, indicating low fodder toxicity risk to browsing livestock. This study concludes that if there are no invasive species issues associated with conservation land uses, Rhodes grass is well suited to metalliferous mined land revegetation and would therefore be highly effective for such programs in subtropical and tropical Australia. © 2005 Wiley Periodicals, Inc. 相似文献