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Bioavailable concentrations of polycyclic aromatic hydrocarbons (PAHs) were investigated in water of Three Gorges Reservoir (TGR) using semipermeable membrane devices during the period of completely impounding water. ∑PAH concentrations in water of TGR in the period of completely impounding water were 15-381 ng L. ∑PAH concentrations increased from town or counties to big industrialized cities in TGR, indicating urbanization effects on PAH pollution in the water. Tributaries in TGR have a certain contribution of PAH pollution to the mainstream of Yangtze River and their pollution could not be neglected. An obvious decrease of PAH concentration was observed after 175-m water impounding in 2011 in TGR. Several factors may account for this decrease, including execution of comprehensive treatment and management measures in TGR, less rainfall in 2011, and sedimentation effect caused by the dam. Passive sampling method has been successfully applied in the investigation of trace PAH in water of TGR and proved to be a useful and efficient tool for the management and sustainable development of the big reservoir. The results of the study provide valuable information about PAH pollution in the whole reservoir including some tributaries, and the pollution status is dynamically related with human activities. Therefore, PAH could be used as a marker compound or indicator in the network monitoring system to surveil and trace the pollution status in TGR. [ABSTRACT FROM AUTHOR]

The impounding of the Three Gorges Reservoir (TGR) at the Yangtze River caused large flooding of urban, industrial, and agricultural areas, and profound land use changes took place. Consequently, substantial amounts of organic and inorganic pollutants were released into the reservoir. Additionally, contaminants and nutrients are entering the reservoir by drift, drainage, and runoff from adjacent agricultural areas as well as from sewage of industry, aquacultures, and households. The main aim of the presented research project is a deeper understanding of the processes that determines the bioaccumulation and biomagnification of organic pollutants, i.e., mainly pesticides, in aquatic food webs under the newly developing conditions of the TGR. The project is part of the Yangtze-Hydro environmental program, financed by the German Ministry of Education and Science. In order to test combinations of environmental factors like nutrients and pollution, we use an integrated modeling approach to study the potential accumulation and biomagnification. We describe the integrative modeling approach and the consecutive adaption of the AQUATOX model, used as modeling framework for ecological risk assessment. As a starting point, pre-calibrated simulations were adapted to Yangtze-specific conditions (regionalization). Two exemplary food webs were developed by a thorough review of the pertinent literature. The first typical for the flowing conditions of the original Yangtze River and the Daning River near the city of Wushan, and the second for the stagnant reservoir characteristics of the aforementioned region that is marked by an intermediate between lake and large river communities of aquatic organisms. In close cooperation with German and Chinese partners of the Yangtze-Hydro Research Association, other site-specific parameters were estimated. The MINIBAT project contributed to the calibration of physicochemical and bathymetric parameters, and the TRANSMIC project delivered hydrodynamic models for water volume and flow velocity conditions. The research questions were firstly focused on the definition of scenarios that could depict representative situations regarding food webs, pollution, and flow conditions in the TGR. The food webs and the abiotic site conditions in the main study area near the city of Wushan that determine the environmental preconditions for the organisms were defined. In our conceptual approach, we used the pesticide propanil as a model substance. [ABSTRACT FROM AUTHOR]

Microbially produced extracellular polymeric substances (EPS) have been linked with many important ecological functions in natural sediments; yet, most information has been derived from marine systems. The present paper is the first comprehensive study on EPS (i.e., carbohydrates and proteins) dynamics in riverine sediments addressing spatial (six reservoirs and four groyne fields across three European rivers), temporal (all seasons in 2003–2005), and vertical (over a 50-cm sediment depth transect) pattern. The variation in hydrodynamic regime found in the reservoirs and groyne fields was reflected in the biomass and composition of the benthic microorganisms that produce EPS. The microphytobenthic communities consisted mainly of diatoms and a higher algal biomass (up to 248 μg g−1 dry weight, DW) seemed to be indicative for higher amounts of secreted colloidal carbohydrates. Consequently, the model proposed by Underwood and Smith () for the relation chlorophyll–colloidal carbohydrates was also applicable for upper riverine sediment layers. The close relation between algal biomass and bacterial cell counts (108–109 cells g−1 DW) supports the idea of bacterial use of the secreted EPS. However, the data also suggest a contribution to the EPS pool through bacterial secretion of proteins/extracellular enzymes and possibly carbohydrates. Over depth, the relationships between microorganisms and EPS became increasingly decoupled along with increasing ratios of bound (refractory) to colloidal (labile) EPS. These data suggest fresh production of polymeric substances in upper sediment layers and mainly accumulation of refractory, biodegraded material in deeper layers. The high contents of EPS colloidal and bound carbohydrates (0.1–1.8 and 1.3–6.7 mg g−1 DW, respectively) and EPS proteins (0.4–12.9 mg g−1 DW) at the freshwater study sites might indicate an important role in sediment ecology. [ABSTRACT FROM AUTHOR]

Block ramps are a short length of a steep channel armored with rocks, which produce high dissipation of energy. This technical note presents the results of experiments performed on a ramp having a staggered arrangement of hemispherical boulders with base material on its bed. Compared to row and random arrangements of boulders, a staggered arrangement produces more dissipation of energy. Relative energy loss in the ramp depends not only on the discharge but also on boulder concentration and their sizes. A relationship is proposed that satisfactorily determines the dissipation of energy on the ramp with base material and boulders placed with a staggered arrangement. [ABSTRACT FROM AUTHOR]

Following the 2000 European Water Framework Directive and recent insights into sediment management on a river basin scale, we discuss in this paper an exposure model aiming to support a risk assessment for chemicals on a basin-wide scale. It establishes spatial relations between causes (pollution sources) and effects (ecological risk), taking into account the geometry, hydrology, and fine sediment dynamics of European river basins. The model, called EXPOBASIN, explicitly takes into account the interaction of chemicals with fine sediment particles, which is important for many policy-relevant chemicals, such as trace metals and polycyclic aromatic hydrocarbons, and it addresses the potential release of historically polluted sediments as a result of extreme floods, which is a major concern in different European river basins. Bioavailability and bioaccumulation are included in the assessment. As a result, the exposure can be quantified not only in terms of water concentrations, but also in terms of sediment concentrations and concentrations in biota. The primary question to be answered by EXPOBASIN is how chemicals, pollution sources, or both rank quantitatively and objectively on a basin-wide scale. Near the end of 2009, the tool will become available to all European water managers and their technical advisors, as a result of the European Union 6th Framework Programme project MODELKEY The calibration and validation of EXPOBASIN has only just started and will be completed in 2008/2009. Applications to 3 case study areas are planned in this respect. This paper presents the key building blocks of EXPOBASIN and shows some sample results illustrating the raking of pollution sources and chemicals. At the end of the paper, some perspectives for future developments are outlined. [ABSTRACT FROM AUTHOR]

Sediment stability is a critical component for the understanding of cohesive sediment dynamics. Traditionally, physico-chemical sediment conditions have been regarded as most important drivers of sediment stability. However, over the last decade, the stabilization of sediment by biological activity, particularly the influence of highly hydrated matrices of extracellular polymeric substances (EPS) has been given increasing attention. However, most studies have focused on the sediment/water interface and, usually, of marine systems. The present study exploits current knowledge of EPS dynamics from marine systems and applies it to freshwater habitats, also considering a wide range of biological and physico-chemical variables. Natural sediments were taken from a freshwater site with high levels of heavy metal pollution (Lauffen reservoir, River Neckar, Germany). Vertical profiles from the flocculent surface layer to depth of 50 cm within the sediment were investigated, monthly, over the course of year. Tubificidae and Chironomidae larvae constituted the majority of the macrofauna. Despite the turbidity of the water column, a highly diverse and abundant microphytobenthic community of diatoms (11–82 µg g−1 DW) was found at the sediment surface closely associated with high numbers of bacteria (109 cells g−1 DW). The concentrations of all EPS moieties were remarkably high (0.1–0.5, 1.7–3.8, 0.9–5.2 mg g−1 DW, for colloidal and bound carbohydrates and proteins, respectively) and levels were comparable to those determined in intertidal studies. The microalgal and bacterial biomass both showed strong correlations with the colloidal and bound EPS carbohydrate fractions. The data suggested that the present macrofauna as well as the metabolic activities of microalgae and bacteria interact with sedimentological factors to influence the properties of the sediment by binding fine-grained sediment, changing water content and enhancing the organic content through secretion products. The colloidal and bound EPS moieties showed strong correlation with the critical shear stress for erosion over sediment depth. It is suggested that the cohesive strength of the sediment was controlled by a high number of active adsorption sites and higher charge densities in fine grained sediments. The EPS network may significantly enhance this by embedding particles and permeating the void space but also in offering additional ionic binding sites and cross-linkages. [ABSTRACT FROM AUTHOR]

Background, Aims, 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. 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, micro- algal 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 tiefenabhängigen 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 and Discussion. 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), TOC (Total Organic Carbon) and 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 between binding capacity as well as charge densities of the sediment particles and the biologically produced compounds constituting active surfaces. The combined influence of sedimentological and biological properties on sediment stability over depth was assessed by PCA (Principal Component Analysis). 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, CEC, TOC 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.… [ABSTRACT FROM AUTHOR]

A benthic in situ flume and a 1D biogeochemical sediment model to evaluate solute fluxes across the sediment–water interface have been developed. The flume was successfully used to determine oxygen and nutrient fluxes at various locations of the Neckar River in Germany. The experimental results were linked with vertical pore water concentration profiles and independently verified with the model. By combining experimental and model results we assessed the influence of dissolved oxygen concentrations in the water column and the availability of degradable organic matter on sediment oxygen demand. The results and the derived relations can be used to parameterize the sediment module of large scale water quality models, allowing one to assess the influence of sediment–water interactions on various aspects of river water quality. Moreover, the biogeochemical sediment model can help to improve the general understanding of the processes governing solute concentrations and fluxes in sediments and across their interfaces. [ABSTRACT FROM AUTHOR]

Sediments are an essential habitat compartment in rivers, which is a subject to dynamic transport processes. In many rivers, the fine deposited sediments are contaminated with heavy metals and organic compounds. Contaminated deposits are considered as potential hot spots because of the risk of the mobilization under erosive hydraulic conditions. Numerical models for particulate contaminant transport are then necessary and can be applied to estimate and predict the potential impact of mobilized contaminants as an important contribution to sediment management. This paper focuses on the quantification of the amount of contaminated sediments resuspended during the extreme flood event in 1999 and the prediction of deposition one year after the flood event. To assess such erosive flood event, a 2D numerical transport model was developed to analyse the dynamics of erosion and sedimentation processes in the headwater of a cross dam at the Upper Rhine River. The dam consists of a weir, a hydropower plant, and a navigation lock. As the weir is operating only for flood management, a huge amount of sediment highly contaminated with the hexachlorobenzene (HCB) was deposited in the weir zone. Therefore, numerical simulations were performed to determine the spatial and temporal distribution of deposited contaminated sediments as depending on the river discharge and its distribution to the hydraulic structures. The numerical investigation presented here is taken as a retrospective analysis of the contaminated sediment dynamics in the headwater to improve future sediment management. [ABSTRACT FROM AUTHOR]

Background and Scope. Apart from their function as indicator or memory for local pollutant inputs, sediments, and especially sediment cores, can be used as a tool for assessing emission-immission relationships of contaminants on a river-basin scale. Methods. In the framework of the SEDYMO program, source effects, i.e. intensity of sediment erosion under different shear stress, were investigated using a combination of core profile or sampling box studies in laboratory flumes and a mobile in-situ testing device for sediment stability. Results. Calculations of immission risks on downstream areas, e.g., from a three-step approach (substances of concern, areas of concern, areas of risk; Heise et al. 2004), may be directly confirmed from sediment core data, specifically from flood layers, at the target site. [ABSTRACT FROM AUTHOR]

Background and Scope. Characteristic dynamic features of sediment-related processes in rivers include (i) dramatic effects of stormwater events on particle transport, (ii) rapid and far-reaching effects of sulfide oxidation during resuspension, and (iii) biological accumulation and potential release of toxic chemicals. Pollutant mobility is the net result from stabilizing and mobilizing effects in both hydraulic and chemical fields. In practice, emphasis has to be given to fine-grained sediments and suspended matter, since these materials exhibit large surface areas and high sorption capacities. Discussion. Organic materials are highly reactive. Degradation of organic matter will induce depletion of oxygen and may enhance formation of flocs and biofilms. Study of variations of sediment and water chemistry should predominantly include changes of pH and redox conditions, competition of dissolved ions and processes such as complexation by organic substances. All these processes will influence solution/solid equilibrium conditions and have to be studied prior to modeling the overall effects of pollutants on the water body and aquatic ecosystems. Conclusion. The cooperative program SEDYMO (‘Fine Sediment Dynamics on Pollutant Mobility in Rivers’) is funded by the German Federal Ministry of Education and Research (BMBF) since May 2002. It comprises 13 research projects and its interdisciplinary approach focuses on the release of DOC, nutrients and pollutants into the open water due to hydrodynamic processes in rivers and estuaries. Three themes are studied: ‘experimental techniques’, ‘processes and properties’, ‘development/validation of models’. [ABSTRACT FROM AUTHOR]

The article reports on the findings of a research work done on assessing and forecasting of the impact of environmental key pollutants on freshwater and marine ecosystems and biodiversity. A model called "MODELKEY," was designed which comprised a multidiciplinary approach aiming at developing interlinked tools for an enhanced understanding of cause-effect-relationships between insufficient ecological status and environmental pollution. An end-user-directed decision support system will be provided for cost-effective tool selection and appropriate risk and site prioritisation.

Data from the Elbe River and its tributaries indicate, despite extensive improvement in water quality during the last 15 years, that the respective sediment situation of many priority pollutants has not reached an acceptable level. For the coming decades, risks for downstream sites and stakeholders will persist, mainly due to secondary sources originating from historical pollution of soils and sediments in the catchment area. In practice, a catchment-wide assessment of historical contaminated soil and sediment should apply a three-step approach: (i) Identification of substances of concern (s.o.c.) and their classification into ’hazard classes of compounds’; (ii) identification of areas of concern (a.o.c.) and their classification into ‘hazard classes of sites’; (iii) identification of areas of risk (a.o.r.) and their assessment relative to each other with regard to the probability of polluting the sediments in the downstream reaches. The conversion of this concept has to consider the underlying philosophy of the EU Water Framework Directive, particularly with respect to the analysis and monitoring of priority substances in solid matrices. However, major deficiencies are still in the assessment and prognosis of resuspension processes, and potential approaches to fill this gap are described both in theory and from examples of the Elbe River. The sediment stability testing facilities consist of a unique triple set developed by innovative experimental laboratory and field research. The instrumental facilities consisting of a tube corer and a pressurized channel allow one to measure not only the onset of erosion (critical bed shear stress), but also the erosion rate for different sediment layers. Undisturbed sediment samples were taken from contaminated sites, e.g. in near-bank groyne fields and floodplains, using (i) core sampler (diameter 14 cm, length 150 cm) for sediment erodibility depth profiling and (ii) box sampler (30*70 cm2 top view area, 28 cm depth) for comparing and upscaling the results from the laboratory to the field. Sediment properties such as grain size spectrum (laser beam attenuation), water and gas content were analyzed by a non-intrusive, high frequency, capacity measurement method and bulk density by γ-ray. Sediment core samples from flooded areas in the Middle Elbe indicate, that, except from the uppermost 5 cm and at a depth of from 47 to 48 cm, where the critical shear stress is very low (0.5 Pa), the critical bottom shear stress is between 1.2 Pa and 3.4 Pa, i.e. at a moderate level. Major reasons for the distinct heterogeneity of the erosion stability are differences in consolidation processes, grain size distribution and in the composition of stabilizing exudates in the individual sediment layers. Similar to the erosion stability depth profile, the metal data exhibit short-range heterogeneities; the variations in the individual layers can be explained by different proportions of fine grained components and by an improvement of suspended matter quality in the course of time. A comparison of the metal contents of embanked alluvial soils and unembanked alluvial areas suggests the following causal chain: Recent floodplain areas at low mean water levels exhibiting high concentrations of organic carbon represent the most highly contaminated sites. On the other hand, insignificant pollution has occurred on alluvial areas, which were embanked already at pre-industrial times. In the case of flood events, due to the combination of flooding probability and flow conditions, the most favorable conditions for the deposition of nutrient- and contaminant-rich suspended particulate matter are found in the low level depressions with low current... [ABSTRACT FROM AUTHOR]

In order to model the transport of cohesive sediments and associated contaminants accurately, knowledge of erosion rates is indispensable; at present, these are mostly obtained from the literature and usually extended by field data. In contrast to these theoretical approaches we have developed a method to determine erosion rates directly from experiments conducted with undisturbed sediment cores in a laboratory flume. Regularly spaced laser lines are projected onto the sediment surface during the erosion process. To compute the volume loss over a certain period of time, snapshots of the projected lines are taken and the relation between the deformed projected lines and the sediment surface is derived. With this relation and bilinear interpolation, the sediment surface is reconstructed. The volume difference between the reconstructed sediment surfaces corresponding to the snapshots is then calculated. Consequently, volume loss can be determined in mm3 per time with a maximum error of 7.2%. The average error is less than 1%. Combination with the bulk density results in erosion rates in kg m-1 s-1. The high sensitivity of the laser lines to sediment surface changes allows the determination of even small erosion rates. Thus, it is possible to determine erosion rates directly as a function of shear stress. Since it is possible to vary the area of calculated sediment-volume loss, scaling effects can be investigated as well. [ABSTRACT FROM AUTHOR]

The results of an experimental investigation of the time variation of scour hole and the flow characteristics of the quasiequilibrium state of scour of a cohesive bed downstream of an apron due to a submerged horizontal jet issuing from a sluice opening are presented. Experiments were carried out with natural cohesive sediment for various sluice openings, jet velocities, and lengths of apron. Attempts are made to explain the similarity existing either in the process of scour or in the scour profiles that the scour holes follow downstream of an apron. The scour profiles at different times follow a particular geometrical similarity and can be expressed by a polynomial using relevant parameters. The characteristic parameters affecting the time variation of scour depth are identified based on the physical reasoning and dimensional analysis. An equation for time variation of maximum scour depth is obtained empirically. The diffusion characteristics of the submerged jet, growth of boundary layer thickness, velocity distribution within the boundary layer, and shear stress at the quasi-equilibrium state of scour are also investigated. The expression of shear stress is obtained from the solution of the von Kármán momentum integral equation. [ABSTRACT FROM AUTHOR]

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The article presents information on the investigation of sediment management at the river basin scale. The author stresses that sustainable sediment management is a future challenge for interdisciplinary research in natural and engineering sciences. He cites that the risk of contaminated sediment mobilization for the aquatic environment, water and soil quality is an important issue in river engineering. Further, the author stresses that the impact of climate change on discharge and transport processes has to be considered in a site specific risk assessment. Meanwhile, the author describes the main subjects of the research.

An abstract of the article "Sediment Dynamics and Pollutant Mobility in Rivers (SEDYMO): Assessing Catchment-Wide Emission-Immission Relationships from Sediment Studies" is presented. Sediments are used for evaluating the emission-immission relations of contaminants on a river-basin scale. The intensity of sediment erosion was examined through using a combination of sampling box studies and a mobile testing device. Immission risks on downstream areas can be calculated from sediment core data.