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1.
Background, Aims and Scope Sediment management in rivers basins has tended to deal with local issues associated with either excessive amounts of sediment
(clean and contaminated) or sediment deficit. With sediment management increasingly needing to address both sediment quantity
and sediment quality issues, it is becoming increasingly apparent that for sediment management to be effective the river basin
represents the most appropriate scale for consideration. Although local and site-specific sediment issues are still likely
to be the main scales at which interventions are made they need to be placed within a broader context and with full appreciation
and consideration of their impacts within the river basin. This paper describes some of the reasons why the river basin scale
represents the most appropriate scale for sediment management, while recognizing the needs for site-specific interventions.
It also describes the development of conceptual river basin models (CRBM) for sediment.
Main Features A CRBM should identify, in a conceptual framework, the relevant key environments (subsystems) within a river basin and the
interrelationships between the environments. From a sediment perspective, key information includes the identification of sources
of sediment (and associated contaminants and nutrients), the pathways of sediment and contaminants within and between the
various environments, and the role of storage elements. Additional information that informs the CRBM includes, the assessment
of sediment fluxes (including storage), the residence time of sediment storage, and information on exchanges between sediment
and contaminants, although such information is often not available at the scale of the river basin. An example of a CRBM for
sediment for a hypothetical river basin and examples of several sediment budgets (for basins in USA and Zambia, and for Europe)
are presented which are based on data and information on sediment sources, sediment fluxes and storage. These are discussed
and some of the advantages and disadvantages for decision-making for sediment management are described.
Conclusion and Recommendation Conceptual frameworks and models for sediment offer considerable potential for certain stages of the management process.
They are, however, only part of a much larger decision-making process, which involves, amongst other things, stakeholder participation,
evaluation of the appropriate legislation and guidelines, and the use of risk assessment and societal cost-benefit analysis. 相似文献
2.
Michiel J. van der Meulen Marc Rijnveld Lasse M. Gerrits Jan Joziasse Max W.I.M. van Heijst 《Journal of Soils and Sediments》2006,6(3):163-172
Background, Aim and Scope
Faced with higher peak discharges in the foreseeable future, the Dutch government has decided to increase the discharge capacities
of the Dutch Rhine and Meuse rivers. Instead of raising the dikes, river widening measures are to be undertaken, in and along
the riverbed. Such measures include surface level lowering along the rivers, channel deepening, the addition of high-discharge
channels and the removal of hydraulic obstacles. To cover or reduce the costs of river widening, a coupling with aggregates
(sand and/or gravel) extraction has been considered. Although the rationale of this concept is basically sound, it has met
with considerable resistance, especially along the southernmost stretch of the Dutch Meuse River, in the Maaswerken project
area.
Main Features:
The Dutch river widening projects are quite unique in size and occurrence, and the number of publicly documented case histories
available for the planning of such works is inevitably few. We review the planning and decision-making process for the Maaswerken
project, which is in a more advanced stage than that of the corresponding project for the Rhine. Sediment handling and aggregates
extraction are focused on, which are key issues to this case.
Results:
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Discussion:
In the study area, there is a conflict of interests between the extractive industry and the local communities. The industry
faces a policy of phasing out mineral extraction; river widening presents the last significant prospects in the area. The
general public, however, has come to resent mineral extraction because of its historical impacts. Aiming at a manageable process,
the Maaswerken project management kept most stakeholders in a basically reactive position: the general public was kept informed
and enabled to submit formal reactions to draft planning decisions. Aggregate extraction plans and extraction volumes were
only discussed with the industry. Despite not being represented, the public influenced this negotiation process by expressing
dissatisfaction with interim outcomes through the media and political channels. Plans had to be reconsidered, and this closed
process turned out to be only seemingly efficient.
Conclusions:
The level of public concern regarding the Maaswerken project suggests that the overall level of stakeholder involvement may
have been insufficient, even though it complied with pertinent environmental and planning legislation. A participation deficit
seems to have mainly occurred when defining the project's preconditions: a predefined, controversial role for the extractive
industry was implicit in self-financed river widening. As planning and decision making in large projects such as the Maaswerken
are prone to be affected by a negative public opinion, it is recommended that social feasibility is assessed and addressed
at the very outset.
Perspectives:
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3.
Sabine U. Gerbersdorf Thomas Jancke Bernhard Westrich 《Journal of Soils and Sediments》2007,7(1):25-35
Background, Aim and Scope
Riverine sediments store large quantities of hazardous contaminants, remaining a 'legacy of the past' world-wide. Natural
events such as floods may cause the resuspension of polluted sediments and accordingly, the former immobilized contaminants
might become bioavailable and toxic again. Hence, a comprehensive erosion risk assessment of contaminated sites is of crucial
importance. The present study aimed to implement 'master-variables' for a reliable, easy-to-manage and economically more viable
determination of stability in cohesive sediments.
Materials and Methods:
A wide range of physico-chemical (bulk density, water content, particle size, mineral composition, cation exchange capacity
/ CEC, total organic matter / TOC, liquid and plastic limits of a soil) and biological (macrofauna abundances, microalgal
biomass and species composition, bacterial cell numbers, EPS fractions such as carbohydrates and proteins) properties were
determined simultaneously over depth spanning the zone between 0-35 cm. The data were related to sediment stability, determined
as the 'critical shear stress for mass erosion' in the SETEG (Stroemungskanal zur Ermittlung der tiefenabhaengigen Erosionsstabilitaet
von Gewaessersedimenten) - flume. The investigations were done on natural sediments, thereby covering vertical (over depth),
spatial (different study sites) and temporal (different seasons) aspects to ensure the transferability of the data. Here,
first data originating from three contaminated reservoirs in the lock-regulated River Neckar / Germany are presented.
Results:
Comparison of the rather low critical shear stress values (resisting force of sediment, determined in SETEG) with the possibly
occurring natural bottom shear stresses (attacking force, calculated for different hydraulic scenarios) at the three reservoirs
indicated a severe risk of sediment erosion even under moderate hydraulic conditions and was not restricted to the surface.
Critical shear stress was characterised by the following sediment properties of depth, grain size, CEC (Cation Exchange Capacity)
and concentrations of TOC (Total Organic Carbon), proteins as well as carbohydrates (water- and resin-extractable). Firstly,
biological stabilisation by extracellular polymeric substances (EPS) could be shown for riverine sediments, even over depth.
Secondly, erosion resistance was determined by the inter-particles forces, an interplay of the biologically produced compounds
constituting active surfaces and the binding capacity as well as charge densities of the sediments. The combined influence
of sedimentological and biological properties on sediment stability over depth was assessed by PCA (Principal Component Analysis).
Discussion:
Hence, a better correlation coefficient between sediment stability and the master variables could be achieved (Main component
II: Polymeric substances, R = 0.7, Main component III: Grain size, TOC, CEC, R = 0.9) compared to single correlations.
Conclusions:
The present paper revealed the combined influence of physico-chemical and biological properties on sediment stability over
depth by simultaneous investigation and statistical evaluation. It can be shown, that inter-particle forces, determined by
particles size classes, CEC, TOC and polymeric substances such as proteins and carbohydrates, affected sediment stability
most. Thereby, the impact of biogenic sediment mediation on riverine sediment stabilisation became evident, even over depth,
where mostly sedimentological parameters were considered as important before.
Recommendations and Perspectives:
The importance of a comprehensive risk assessment of contaminated riverine sites was again highlighted in the present study
by the comparison of natural occurring bottom shear stresses with the determined sediment erosion resistance. If a realistic
risk assessment is to be derived, the stabilizing potential of micro-organisms needs to be taken into account and the covariance
patterns of biological and physico-chemical sediment properties have to be addressed. 相似文献
4.
Goal, Scope and Background In a preliminary ecological risk assessment, potential adverse effects of contaminants are often evaluated by measuring chemical residues and comparing these with regulatory guidelines. However limitations with this approach with regards to establishing actual effects have resulted in the increasing usage of sublethal effects-based assays, including biomarkers, to evaluate the hazard posed by contaminants in the environment. In this study a number of effects-based endpoints in the earthworm Aporrectodea caliginosa were evaluated to determine their comparative sensitivity for assessment of adverse effects of soil contaminated with petroleum hydrocarbons. Methods Adult and juvenile earthworms were exposed for 4 weeks to sublethal concentrations of soil collected before and after remediation of a petroleum-contaminated site. A suite of endpoints were measured in these earthworms, including mortality, fecundity, growth, and juvenile maturation, and two less traditional endpoints, the biomarker, the neutral red retention assay (NRRA) and an avoidance behaviour test. Results and Discussion Cocoon viability in this species is not a reliable parameter to measure, due to low viability in controls and a high coefficient of variation. Growth in adult earthworms was a more sensitive parameter than cocoon production. Maturation and growth of juveniles have been proposed as more sensitive endpoints than adult cocoon production and growth respectively. This was not apparent in the growth parameters, but maturation of juveniles did appear to be more sensitive than cocoon production by adults. The NRRA was a more sensitive parameter than cocoon production, and the NRRA and growth were both affected at the lowest concentration tested. The NRRA response appeared to be more sensitive than growth, but NRRT was only evaluated in one soil only, while the other parameters were assessed in two soils. However, the NRRA has previously been found to be more sensitive than growth after exposure to a number of contaminants. The avoidance behaviour assay exhibited similar sensitivity to growth and fecundity and could therefore be useful as a simple pre-screening test. Conclusion The chronic endpoints, growth, cocoon production, and juvenile maturation parameters, were all sensitive endpoints for detecting exposure to the petroleum-hydrocarbon-contaminated soil. The NRRA was the most sensitive of the endpoints assessed and could be used as an early-warning indicator to predict adverse impacts. Avoidance behaviour could be used as a simple pre-screening test to evaluate contaminated soils prior to more extensive and invasive testing. Recommendations and Perspective Measuring chemical concentrations in environmental samples is not always useful, as the toxicological impacts of exposure to these concentrations are not always discernible. However, the use of effects-based endpoints, either in situ or in the laboratory using laboratory-reared earthworms, can account for the bioavailability of chemicals in the soil, and can therefore provide information on the toxicological impacts of exposure. The assays tested in this research were sensitive indicators of exposure, and therefore can be used to determine potential ecological risks at contaminated sites and to monitor the progress of remediation at these sites. 相似文献