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European Rivers*

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... Due to the complex geomorphology of the delta and the inconsistent appellation of its river system, there is no conventional definition in the literature of the geographical boundaries of the RMS Delta. Different calculation methods evaluate its area between 20,000 km 2 (Meyer & Nijhuis 2014) and 25,000 km 2 (Tockner et al. 2009). In order to compare it with Taihu Basin, this research defines the RMS Delta region as the coastal zone with an altitude below 10 m above sea level (a.s.l.), and focuses exclusively on its Dutch part in order to reflect on national-level data and policies. ...
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This paper aims to compare the Rhine-Meuse-Scheldt Delta in Europe and the Taihu Basin part of the Yangtze River Delta in China from a long-term historical perspective. Urbanized deltas are among the most prosperous and populated regions in the world, but also the most vulnerable. To cope with growing uncertainty, their systematic comparison has become instrumental in building mutual learning on the theory and practice of spatial planning and water resource management in such vulnerable contexts. Based on a systematic comparative mapping approach of Delta Urbanism with critical review of policies, this research highlights important similarities between these two deltas in terms of physical characteristics, dense occupation, and management history evolving from a decentralized polder-based system to a centralized control model, and a recent adoption of integrated and adaptive water management strategies. On the other hand, the comparison reveals distinct management focuses in current delta plans, as well as contrasting approaches to public participation and historical hydraulic landscapes. It is found from this comparative study that, beyond the socio-cultural specificities that can explain the distinct management practice of each region, the systematic use of mapping as a visualization and communication tool would facilitate integrative and adaptive delta management.
... European rivers have been significantly modified by human actions (e.g. Piégay et al. 2009;Surian et al. 2009b;Tockner et al. 2009). For example, channel narrowing and incision have been widely observed following human disturbances such as changes in land use, dam construction and sediment mining of the river bed (e.g. ...
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Disturbances affecting flow and sediment transport regimes (e.g. dams, diversions, gravel mining, weirs, bank reinforcements, climate changes) can promote riverbed degradation and channel narrowing, and thus influence vegetation dynamics and composition. This study investigates the relationships and feedbacks between channel adjustments and riparian vegetation dynamics by combining an analysis of morphological channel changes with a wider phytosociology analysis of existing vegetation within the river corridor. These relationships were illustrated by using the case study of the Panaro River (located in the Northern Apennines, Italy), being a representative case of a deeply incised and narrowed river. More specifically we analyzed: (1) the relations between landforms and distributional patterns of vegetation types and characteristic plant species (index species): these provided information about the hydrogeomorphic condition of fluvial landforms and about channel adjustments; (2) the distance of riparian vegetation conditions from expected conditions as a consequence of human impact, based on the fact that each species and vegetation type has a given tolerance for specific disturbance regimes or stresses. Although some expected relations between landforms and vegetation types were found, we recorded significant deviations from the typical correlation pattern existing between morphology and vegetation, and this could be used to infer the intensity and the typology of human disturbances. In particular, the index species can indicate present ecological conditions and on past channel evolution. With this knowledge it might be possible to develop botanical recovery models in the future and, even more importantly, enable the recognition of the differences between temporal and spatial diversity.
... Most aquatic systems experience water level fluctuations, which temporarily expose the previously flooded sediments not only to air but also to desiccation. Such water level fluctuations occur seasonally or as single events in lakes and reservoirs (Wantzen et al. 2008b), and temporary streams are also a common phenomenon (Tockner et al. 2009). Sediment drying can range spatially from minor water level fluctuations affecting only the littoral zone, to large drawdown events which also affect the profundal zone of a lake. ...
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Sediment drying associated with large water level fluctuations is an increasingly common feature of temporary streams and lakes worldwide. Drying-induced sediment aeration and re-flooding periodically alter redox conditions, and therefore stimulate redox-sensitive processes influencing phosphorus (P) binding forms. We experimentally tested the effects of drying on P binding forms, and the P sorption potential, by drying and re-flooding lake sediments in the laboratory. Wet and dried fine sediments were re-flooded in columns, and the overlying water was continuously re-stocked to a constant P concentration. We measured changes in P forms, P uptake rates, and the pore water dynamics in each column over 36 weeks. Drying decreased the fraction of stable P, stimulated the mineralization of organic P, and increased the proportion of labile and reductant-soluble forms. Drying of sediment furthermore reduced its P sorption affinity and capacity by up to 32 % in batch equilibrium experiments, and led to a fourfold increase in sediment compaction which increased P uptake rates by a factor of 1.7 in sediment column experiments. Compaction due to drying also induced the development of a sharp gradient below which P was mobilized. These results indicate that in fine sediments, a single drying event can result in the transformation of P components into more labile forms which accumulate in the uppermost sediment layer, therefore raising the potential for a pulsed P release under reducing conditions.
... and more floods and droughts, are predicted by the end of the twenty first century (Giorgi et al. 2004). These changes are of particular consequence for temporary streams, which are found on every continent and climate, and which are the dominant freshwater type in Southern Europe (Tockner et al. 2009). Intermittent flow is expected to become more common in streams across the globe due to the effects of global change (Larned et al. 2010). ...
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Autumnal input of leaf litter is a pivotal energy source in most headwater streams. In temporary streams, however, water stress may lead to a seasonal shift in leaf abscission. Leaves accumulate at the surface of the dry streambed or in residual pools and are subject to physicochemical preconditioning before decomposition starts after flow recovery. In this study, we experimentally tested the effect of photodegradation on sunlit streambeds and anaerobic fermentation in anoxic pools on leaf decomposition during the subsequent flowing phase. To mimic field preconditioning, we exposed Populus tremula leaves to UV–VIS irradiation and wet-anoxic conditions in the laboratory. Subsequently, we quantified leaf mass loss of preconditioned leaves and the associated decomposer community in five low-order temporary streams using coarse and fine mesh litter bags. On average, mass loss after approximately 45days was 4 and 7% lower when leaves were preconditioned by irradiation and anoxic conditions, respectively. We found a lower chemical quality and lower ergosterol content (a proxy for living fungal biomass) in leaves from the anoxic preconditioning, but no effects on macroinvertebrate assemblages were detected for any preconditioning treatment. Overall, results from this study suggest a reduced processing efficiency of organic matter in temporary streams due to preconditioning during intermittence of flow leading to reduced substrate quality and repressed decomposer activity. These preconditioning effects may become more relevant in the future given the expected worldwide increase in the geographical extent of intermittent flow as a consequence of global change. KeywordsAnoxic pond–Drought–Mediterranean–Organic carbon dynamics–Temporary stream–UV radiation
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The European Union (EU) is a single political and economic union composed of 27 European countries.
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1. Seasonal flow intermittence in streams often coincides with early leaf abscission of riparian vegetation due to water stress. When accumulated on dry stream beds or in remaining pools, leaves are exposed to solar radiation or fermentation processes, respectively. However, very little informa-tion exists on how these preconditioning processes could affect leaf decomposition when stream flow has recovered. 2. We simulated natural preconditioning of leaves by irradiation with UV-VIS fluorescent lamps and incubation under anoxic conditions. Mass loss rates of preconditioned leaf litter from deciduous trees (Alnus glutinosa, Fraxinus excelsior, Populus tremula and Quercus petreae) were quantified in a tempo-rary stream during base flow conditions. Coarse and fine mesh litter bags were used to study the effect of benthic macroinvertebrates and microorganisms on leaf mass loss. 3. Preconditioning reduced the concentration of macronutrients such as P, K and Mg and increased the relative cellulose content of the leaves. Preconditioning changed the fungal community structure (analysed by DGGE) depending on leaf species and sampling date. Preconditioning in anoxic condi-tions also suppressed fungal decomposer biomass (measured as ergosterol) by 42% resulting in 33% lower mass loss rates in fine mesh bags. In contrast, mass loss rates were not affected by precondi-tioning when macroinvertebrate decomposers had access to the leaf litter. 4. In streams exhibiting seasonal flow intermittence, preconditioning will influence organic carbon dynamics towards lower rates of microbially mediated turnover and towards poorer quality of downstream-transported material.
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In the present thesis, the state and distribution of the European freshwater fish fauna was studied. For 161 river (sub-)catchments presence / absence records were retrieved from various sources. Spatial patterns of the fish fauna were analysed using GIS. Further, suggestions on how to reduce the loss of biodiversity are provided. A total of 400 freshwater fish species, including 32 species nonnative to Europe, were recorded. The European fish fauna is the most depauperate compared to other continents. Species richness of native European freshwater fish increases from west to east and from north to south. Species richness peaks in the Danube basin. Species richness of native species is strongly correlated to area and this relationship is best described by a power function. Within large river basins, however, the relationship between richness and subbasin area is weak. In contrast to native species, richness of introduced and extinct species is not related to area. Species introductions and -extinctions occur all over Europe. The proportion of introduced and extinct species can be 50%, or even higher. A high proportion of endemic and irreplaceable species occurs in southern European catchments. They are absent in catchments at latitudes > 50°N. Two species endemic in European catchments, are recorded as globally extinct. The most threatened and locally extinct species are long-migrating species (anadromous and catadromous species, such as sturgeons) These species travel along the river corridor and are thus especially vulnerable to river fragmentation. The “hot spots” of European freshwater fish, defined as areas with the highest proportion of irreplaceable and threatened species, occur in southern Europe (Iberian Rivers, rivers of the Balkan, and several rivers in Anatolia). Future conservation activities need to focus on those regions to prevent the future loss of irreplaceable species. “Hot spots” are not resistant against species introductions; they may contain high numbers of nonnative species. Since introduced species may pose a threat to the native fish fauna, their composition and ecological behaviour should be further analysed within all rivers that have been identified as conservation hot spots, and their abundances need to be managed.
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This paper presents a multiple linear regression model developed for describing global river export of sediments (suspended solids, TSS) to coastal seas, and approaches for estimating organic carbon, nitrogen, and phosphorous transported as particulate matter (POC, PN, and PP) associated with sediments. The model, with river-basin spatial scale and a 1-year temporal scale, is based on five factors with a significant influence on TSS yields (the extent of marginal grassland and wetland rice, Fournier precipitation, Fournier slope, and lithology), and accounts for sediment trapping in reservoirs. The model generates predictions within a factor of 4 for 80% of the 124 rivers in the data set. It is a robust model which was cross-validated by using training and validation sets of data, and validated against independent data. In addition, Monte Carlo simulations were used to deal with uncertainties in the model coefficients for the five model factors. The global river export of TSS calculated thus is 19 Pg yr−1 with a 95% confidence interval of 11–27 Pg yr−1 when accounting for sediment trapping in regulated rivers. Associated POC, PN, and PP export is 197 Tg yr−1 (as C), 30 Tg yr−1 (N), and 9 Tg yr−1 (P), respectively. The global sediment trapping included in these estimates is 13%. Most particulate nutrients are transported by rivers to the Pacific (∼37% of global particulate nutrient export), Atlantic (28–29%), and Indian (∼20%) oceans, and the major source regions are Asia (∼50% of global particulate nutrient export), South America (∼20%), and Africa (12%).
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Natural flood plains are among the most biologically productive and diverse ecosystems on earth. Globally, riverine flood plains cover > 2 × 106 km2, however, they are among the most threatened ecosystems. Floodplain degradation is closely linked to the rapid decline in freshwater biodiversity; the main reasons for the latter being habitat alteration, flow and flood control, species invasion and pollution. In Europe and North America, up to 90% of flood plains are already ‘cultivated’ and therefore functionally extinct. In the developing world, the remaining natural flood plains are disappearing at an accelerating rate, primarily as a result of changing hydrology. Up to the 2025 time horizon, the future increase of human population will lead to further degradation of riparian areas, intensification of the hydrological cycle, increase in the discharge of pollutants, and further proliferation of species invasions. In the near future, the most threatened flood plains will be those in south-east Asia, Sahelian Africa and North America. There is an urgent need to preserve existing, intact flood plain rivers as strategic global resources and to begin to restore hydrologic dynamics, sediment transport and riparian vegetation to those rivers that retain some level of ecological integrity. Otherwise, dramatic extinctions of aquatic and riparian species and of ecosystem services are faced within the next few decades.
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Here we describe, test, and apply a spatially explicit, global model for predicting dissolved inorganic nitrogen (DIN) export by rivers to coastal waters (NEWS-DIN). NEWS-DIN was developed as part of an internally consistent suite of global nutrient export models. Modeled and measured DIN export values agree well (calibration R2 = 0.79), and NEWS-DIN is relatively free of bias. NEWS-DIN predicts: DIN yields ranging from 0.0004 to 5217 kg N km-2 yr-1 with the highest DIN yields occurring in Europe and South East Asia; global DIN export to coastal waters of 25 Tg N yr-1, with 16 Tg N yr-1 from anthropogenic sources; biological N2 fixation is the dominant source of exported DIN; and globally, and on every continent except Africa, N fertilizer is the largest anthropogenic source of DIN export to coastal waters.
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During the Last Glacial Maximum, the sea-level lowstand combined with the large extent of the Fennoscandian and British ice sheets led to the funneling of European continental runoff, resulting in the largest river system that ever drained the European continent. Here, we show an abrupt and early reactivation of the European hydrological cycle at the onset of the last deglaciation, leading to intense discharge of the Channel River into the Bay of Biscay. This freshwater influx, probably combined with inputs from proglacial or ice-dammed lakes, dramatically affected the hydrology of the region, both on land and in the ocean.
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A global overview of dam-based impacts on large river systems shows that over half (172 out of 292) are affected by dams, including the eight most biogeographically diverse. Dam-impacted catchments experience higher irrigation pressure and about 25 times more economic activity per unit of water than do unaffected catchments. In view of projected changes in climate and water resource use, these findings can be used to identify ecological risks associated with further impacts on large river systems.
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Hydrological changes in rivers are best expressed in the middle reaches where each substantial change in discharge and sediment load is reflected in the channel pattern, sediment facies and deposition rates. In general they have changed from braided rivers dominated by bedload to meandering suspended load rivers as the climate has ameliorated within the Holocene. Periods of instability and stability have followed each other, partly in response to second-order climatic variations. The chapter presents a model of changes to the fluvial system based upon field examples and notes the important role of anthropogenic disturbance as agriculture has expanded. -K.Clayton
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This study presents an overview of the present state of the water quality of European rivers. Water quality has been classified according to organic pollution (expressed in oxygen concentration and biological oxygen demand), eutrophication (nitrogen and phosphorus levels) and cadmium concentration. European rivers show various states of pollution. Although most European rivers are well aerated, organic pollution is still a problem and at regional level severe oxygen problems remain. Eutrophication is a serious problem in most rivers and has apparent detrimental effects on the riverine ecosystem. Cadmium pollution is poorly documented, but extremely high cadmium concentrations have been observed in some eastern European and Greek rivers. The availability of appropriate data on river-water quality, especially in eastern European countries, is limited. Substantially improved monitoring is a prerequisite to increasing essential knowledge of riverine ecosystems and to establishing a basis for river basin management on a European scale.