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41.
Most nonpoint source pollution problems on forest lands can be controlled by careful planning and management of specific critical areas. Critical areas include sites with high mass and surface erosion hazards, overland flow areas, and the riparian zone. Some guides for identifying critical areas are presented along with examples of land-use constraints that might be applied. 相似文献
42.
Jonathan D. Phillips 《Journal of the American Water Resources Association》1984,20(6):847-850
In areas where there is little or no topographic relief and where soils, vegetation, geologic structure and other factors are essentially uniform, identification of drainage basin boundaries is difficult or impossible. In such a homogeneous landscape, however, assumptions may be made that the hydrologic and geomorphic controls over drainage basin development are constant within the area. If this is true, it is suggested, the drainage area of a stream is related solely to the stream length and factors governing the length-area relationship are also constant. A simple formula based on these assumptions and the gravity model is proposed which can be used to estimate drainage divides in a homogeneous landscape. 相似文献
43.
Sandra L Postel 《Natural resources forum》2003,27(2):89-98
A fundamentally new approach to water and human development will be needed during this new century if we are to secure sufficient freshwater to meet the needs of some 9 billion people while at the same time protecting the critical ecosystem services upon which the human economy depends. Signs of unsustainable water use — including falling water tables, shrinking lakes, and the drying up of rivers and streams — are widespread and spreading. In many regions, greater modification and appropriation of freshwater systems for human purposes will yield greater costs than benefits and create the risk of irreversible losses of species and ecosystem services. A new mindset is needed to guide water use and management in this new century, one that views the human water economy as a subset of nature's water economy. Living within nature's limits will require that societies satisfy the basic needs of people and ecosystems before non-essential water demands are met. It will require on the order of a doubling of water productivity. And it will require stronger institutions to encourage equitable sharing of water to alleviate tensions within and between countries. 相似文献
44.
Importance of Riparian Forests in Urban Catchments Contingent on Sediment and Hydrologic Regimes 总被引:1,自引:0,他引:1
Roy AH Freeman MC Freeman BJ Wenger SJ Ensign WE Meyer JL 《Environmental management》2006,37(4):523-539
Forested riparian corridors are thought to minimize impacts of landscape disturbance on stream ecosystems; yet, the effectiveness
of streamside forests in mitigating disturbance in urbanizing catchments is unknown. We expected that riparian forests would
provide minimal benefits for fish assemblages in streams that are highly impaired by sediment or hydrologic alteration. We
tested this hypothesis in 30 small streams along a gradient of urban disturbance (1–65% urban land cover). Species expected
to be sensitive to disturbance (i.e., fluvial specialists and “sensitive” species that respond negatively to urbanization)
were best predicted by models including percent forest cover in the riparian corridor and a principal components axis describing
sediment disturbance. Only sites with coarse bed sediment and low bed mobility (vs. sites with high amounts of fine sediment)
had increased richness and abundances of sensitive species with higher percent riparian forests, supporting our hypothesis
that response to riparian forests is contingent on the sediment regime. Abundances of Etheostoma scotti, the federally threatened Cherokee darter, were best predicted by models with single variables representing stormflow (r2 = 0.34) and sediment (r2 = 0.23) conditions. Lentic-tolerant species richness and abundance responded only to a variable representing prolonged duration
of low-flow conditions. For these species, hydrologic alteration overwhelmed any influence of riparian forests on stream biota.
These results suggest that, at a minimum, catchment management strategies must simultaneously address hydrologic, sediment,
and riparian disturbance in order to protect all aspects of fish assemblage integrity. 相似文献
45.
超稠油废水处理的实验研究 总被引:2,自引:0,他引:2
针对超稠油废水污染的问题 ,确定采用混凝沉降、砂滤、活性炭吸附处理超稠油废水 ,处理后的水达到国家排放标准。此方法工艺比较简单 ,处理效果好 相似文献
46.
This paper examines the underlying assumptions and consequences of applying a steady-state equation to sediment profiles of radioactive tracers in order to deconvolute sedimentation from bioturbation processes modelled as a diffusive type process.Several factors follow immediately from this investigation:
- (i)
- if the observed radioactive concentration increases with depth over any finite depth range then the proposed steady-state, constant flux equation is not applicable. Any increase in radioactive concentration with depth implies a negative mixing coefficient which is a physical impossibility;
- (ii)
- when the radioactive concentration systematically decreases with increasing sedimentary depth then solutions to the steady-state conservation equation exist only when either the constant solid state flux to the sediment surface is small enough so that a positive mixing coefficient results or when the mixing coefficient is small enough so that a positive flux results.
47.
Marloes H.N. Bakker 《Journal of the American Water Resources Association》2009,45(3):553-566
Abstract: While transboundary flood events have become more frequent on a global scale the past two decades, they appear to be overlooked in the international river basin (IRB) cooperation and management arena. The present study therefore combined geopolitical measures with biophysical and socioeconomic variables in an attempt to identify the IRBs with adequate institutional capacity for management of transboundary floods. It also classified basins that would possibly benefit from enlarging the institutional capacity related to transboundary floods. Of the 279 known IRBs, only 78 were represented by a transboundary rivers institution. A mere eight of the 153 identified institutions had transboundary flooding listed as an issue in their mandate. Overall, 43 basins, where transboundary floods were frequent during the period 1985‐2005, had no institutional capacity for IRBs. The average death and displacement tolls were found to be lower in the 37 basins with institutional capacity, even though these basins experienced twice as much transboundary floods with significant higher magnitudes than those in basins without institutional capacity. Overall, the results suggested that institutional capacity plays a role in the reduction of flood‐related casualties and affected individuals. River basins such as the Juba‐Shibeli, Han, Kura‐Araks, Ma, Maritsa, Po, Coco/Segovia, Grijalva, Artibonite, Changuinola, Coatan Achute, and Orinoco experienced more than one transboundary river flood, but have not yet set up any institutions for such events, or signed any appropriate treaties focused on floods. These basins were therefore recommended to consider focusing attention on this apparent lack of institutional capacity when it comes to managing transboundary flood events. 相似文献
48.
Brack W Klamer HJ López de Alda M Barceló D 《Environmental science and pollution research international》2007,14(1):30-38
Background, Aim and Scope
Extensive monitoring programs on chemical contamination are run in many European river basins. With respect to the implementation
of the European Union (EU) Water Framework Directive (WFD), these programs are increasingly accompanied by monitoring the
ecological status of the river basins. Assuming an impact of chemical contamination on the ecological status, the assignment
of effects in aquatic ecosystems to those stressors that cause the effects is a prerequisite for taking political or technical
measures to achieve the goals of the WFD. Thus, one focus of present European research is on toxicant identification in European
river basins in order to allow for a reduction of toxic pressure on aquatic ecosystems according to the WFD.
Main Features:
An overview is presented on studies that were performed to link chemical pollution in European river basins to measurable
ecotoxic effects. This includes correlation-based approaches as well as investigations that apply effect-directed analysis
(EDA) integrating toxicity testing, fractionation and non-target chemical analysis. Effect-based key toxicants that were identified
in European surface waters are compiled and compared to EU priority pollutants. Further needs for research are identified.
Results:
Studies on the identification of effect-based key toxicants focused on mutagenicity, aryl hydrocarbon receptor-mediated effects,
endocrine disruption, green algae, and invertebrates. The identified pollutants include priority pollutants and other well-known
environmental pollutants such as polycyclic aromatic hydrocarbons, polychlorinated dibenzo-p-dioxins, furans, and biphenyls,
nonylphenol, some pesticides and tributyltin, but also other compounds that were neither considered as environmental pollutants
before nor regulated such as substituted phenols, natural or synthetic estrogens and androgens, dinaphthofurans, 2-(2-naphthalenyl)benzothiophene,
and N-phenyl-2-naphthylamine.
Discussion:
Individual studies at specific sites in a European river basin demonstrated the power of combined biological and chemical
analytical approaches and, particularly, of effect-directed analysis. However, the available information on effect-based key
toxicants is very limited with respect to the entirety of rivers possibly at risk due to chemical contamination and with respect
to toxicological endpoints considered at a specific site. A relatively broad basis of information exists only for estrogenicity
and aryl hydrocarbon, receptor-mediated effects.
Conclusions:
The development of tools and strategies for an identification of key toxicants on a broader scale are a challenging task for
the next years. Since investigations dealing with toxicant identification are too labor and cost-intensive for monitoring
purposes, they have to be focused on the key sites in a river basin. These should include hot spots of contamination, particularly
if there is evidence that they might pose a risk for downstream areas, but may also involve accumulation zones in the lower
reach of a river in order to get an integrated picture on the contamination of the basin.
Perspectives:
While EDA is almost exclusively based on measurable effects in in vitro and in vivo biotests to date, an increasing focus
in the future should be on the integration of EDA into Ecological Risk Assessment and on the development of tools to confirm
EDA-determined key toxicants as stressors in populations, communities and ecosystems. Considering these requirements and applied
in a focused way, toxicant identification may significantly help to implement the Water Framework Directive by providing evidence
on the main stressors and possible mitigation measures in order to improve the ecological status of a river ecosystem. 相似文献
49.
Exploratory study of suspended sediment concentrations downstream of harvested peat bogs 总被引:1,自引:0,他引:1
Pavey B Saint-Hilaire A Courtenay S Ouarda T Bobée B 《Environmental monitoring and assessment》2007,135(1-3):369-382
Peat bog harvesting is an important industry in many countries, including Canada. To harvest peat, bogs are drained and drainage
water is evacuated towards neighboring rivers, estuaries or coastal waters. High suspended sediment concentrations (SSC) were
found in the drainage water at one particular site during the 2001–2002 spring seasons in New Brunswick (Canada). The main
objective of this study was to verify this observation at other sites, compare SSC levels leaving harvested peat bogs with
those leaving an unharvested bog, and to determine if high SSC events happen only in Spring or all year round. Suspended sediment
concentrations were monitored downstream of three harvested peat bogs and an unharvested reference bog located in New Brunswick
during the ice free seasons of 2003–2004. On average, SSC at the harvested sites exceeded 25 mg/l, which is the recommended
daily maximum concentration, 72% of the time, while the same concentration was exceeded 30% of the time at the unharvested
sites. SSC were found to be significantly higher at harvested sites than at the reference sites for all seasons. The highest
SSC medians were recorded in the Fall but SSC was elevated in all seasons. High SSC levels in receiving waters may be caused
by field ditching activities and insufficient sediment controls. Findings suggest the NB Peat Harvesting 25 mg/l SSC guideline
should be reviewed. 相似文献
50.