Fish and fisheries in the Upper Mekong: current assessment of the fish community, threats and conservation

The Mekong flows north to south, through six countries in south–east Asia. Many studies have concentrated on fish and fisheries in the Lower Mekong, which has been identified as one of the largest inland fisheries in the world with an incredibly rich diversity of species. In contrast, fish and fisheries in the Upper Mekong (Lancang River) have remained relatively undocumented. In this paper, we synthesized information on freshwater fish biodiversity and fisheries in the Upper Mekong and documented 173 species and subspecies (including 87 endemic species) among 7 orders, 23 families and 100 genera. We divided the Upper Mekong into 17 sub-basins based on Digital Elevation Model (DEM) and then used fish species data to cluster the sub-basins. Four parts (the headwater, the upper reach, the middle reach and the lower reach) and one lake have distinct fish species communities associated with them. There was a linear relationship between fish species (x) and endemic species (y) as y = 0.5464x − 3.2926. Relationship between species number or endemic species number (y) and mean altitude (x) can be described as y = −54.352 ln(x) + 460.79 or y = −30.381 ln(x) + 253.85, respectively. Fisheries kept as about 6,000 t from 1989 to 1998, and then steadily increased to 10,000 t in 2004. We reviewed the overall threats to the Upper Mekong fish and fisheries, and found that hydrological alteration is the largest threat in the basin, followed by over fishing and the introduction of exotic species. In terms of specific river sections, water pollution was the most serious threat to fishes in the upper reach of the Upper Mekong, whilst migratory fishes in the lower reach of the Upper Mekong are seriously threatened by the construction of cascade dams. The Buyuan River and the Nanla River were identified as important feeding and spawning habitats for upstream migrant species and should be considered as a priority for conservation.     

Development of new indicators to evaluate river fragmentation and flow regulation at large scales: A case study for the Mekong River Basin

Large hydropower schemes have recently gained renewed interest as a provider of efficient and renewable energy, particularly in developing countries. However, some dams may have widespread effects on hydrological and ecosystem integrity, which reach beyond the scales addressed by typical environmental impact assessments. In this paper we address two main ecological impacts—reduced river connectivity and changes in the natural flow regime—at the scale of the entire Mekong River Basin as an important component of dam evaluations. The goal is to improve our understanding of the effect of individual dams as well as clusters of dams at a very large scale. We introduce two new indices, the River Connectivity Index (RCI) as a tool to measure network connectivity, and the River Regulation Index (RRI) as a measure of flow alteration, and calculate the individual and cumulative impact of 81 proposed dams using HydroROUT, a graph-theory based river routing model. Furthermore, we demonstrate how quantitative weighting, e.g. based on river habitat characterizations or species distribution models, may be included in dam impact assessments.A global comparison of large rivers shows that the Mekong would experience strong deterioration in the fragmentation and flow regulation indices if all dams that are currently under consideration in the basin were built, placing it among other heavily impounded rivers in the world. The results illustrate the importance of considering the location of dams, both relative in the network and relative to other already existing dams. Our approach may be used as an index-based ranking system for individual dams, or to compare basin-wide development scenarios, with the goal of providing guidance for decision makers wishing to select locations for future dams with less environmental impacts and to identify and develop potential mitigation strategies.     

How to comprehensively evaluate river discharge under the influence of a dam

The dams in the upper reaches of the Yangtze River are highly concentrated. Dam construction can effectively solve water shortage problems; however, the natural hydrological regimes of rivers have changed to varying degrees under the influence of water conservancy projects. In this study, a comprehensive method is proposed to analyze the hydrological regime changes in a river impacted by a dam through the evaluation of hydrological periodicity, hydrological frequency and hydrological parameters. Hydrological periodicity is used to evaluate the time series from the vertical multiyear perspective, while hydrological frequency is used to evaluate the time series from the horizontal one-year perspective. The two parameters have complementary roles. The indicators of hydrologic alteration and environmental flow component parameters are used to analyze the changes in various hydrological factors affected by the dam. The results demonstrate that the construction of dams can change the multiyear periodicity of the flow and reduce the peak flow. As a result, downstream fish may be unable to sense the reduced floods and fail to spawn. The indicators of hydrologic alteration and environmental flow component parameters can complement each other and can be used to evaluate changes in a hydrological regime influenced by a dam. This comprehensive method can be used to analyze how the hydrological regime is affected by this dam.     

Endangered ecosystems: a review of the conservation status of tropical Asian rivers

Tropical Asian rivers are characterized by their flow seasonality. One (sometimes two) peaks in discharge cause temporary declines in phytoplankton, zooplankton and zoobenthos biomass, but lead to inundation of river floodplains and significant land-water interactions. Fishes undertake lateral or longitudinal breeding migrations within the river system during the flood season, which is marked also by intensive feeding upon allochthonous inputs.Among the diverse human influences upon tropical Asian rivers, three threats stand out. Firstly, degradation of drainage basins (particularly through deforestation and overgrazing) leads to increased suspended sediment loads and extensive flooding. Excessive floodplain siltation alters habitats causing species decline or disappearance. The second threat — river regulation and control — has been practised widely in the region for centuries but, with the planned development of massive projects on the Yangtze and Mekong Rivers, the potential for environmental damage has increased. Flow regulation reduces flood-season peaks, changing the magnitude and extent of floodplain inundation and land-water interactions. Fish breeding migrations may be disrupted, because dams block migration routes or changed flow regimes fail to stimulate reproduction. River pollution is pervasive throughout the region, and constitutes the third threat. Untreated sewage is a particular problem in densely-populated areas, and pollution by industrial effluents and mining wastes is becoming more important. The effects of pollution in tropical Asian rivers are essentially the same as those recorded in north-temperate regions. However, biological understanding has yet to be matched by an ability to halt or limit river degradation.Together, the three threats have led to declines and range constrictions of aquatic animals and those terrestrial species associated with riparian corridors and floodplains. River dolphins and certain crocodilians are particularly threatened, but declines in species of waterfowl, floodplain deer, a host of fishes, macrophytes, and invertebrates have been documented. Reversing the trend is difficult as pollution, flow regulation, and drainage-basin degradation have non-additive detrimental effects on river ecosystems, and enhance the success of exotic invasive species. Moreover, our ability to predict the outcome of man-made changes is hampered by a lack of knowledge of species' life histories and a paucity of data on the trophic basis of production. Despite a lack of detailed information, conservation of tropical Asian rivers will be effected only if limnologists move beyond the bailiwick of science. Ecologically viable management strategies for tropical Asian rivers will succeed only if the socioeconomic context of development plans is taken into account. A failure to rise this challenge will result in the further degradation of these endangered ecosystems.     

The effect of cascaded huge dams on the downstream movement of <Emphasis Type="Italic">Coreius guichenoti</Emphasis> (Sauvage &amp; Dabry de Thiersant, 1874) in the upper Yangtze River

Huge dams (installed capacity > 100 MKW) are generally built on large rivers that display high biodiversity and include major migration routes for many diadromous and potamodromous fish. As a result, these dams lead to severe ecological impacts and receive more attention than smaller dams. Most previous work on the impact of huge dams on fish downstream movement has focused on a single dam and reservoir, so little is known about the effect of cascaded huge dams and reservoirs on downstream movement. During the period 2012–2014, two huge dams (the Xiangjiaba and the Xiluodu) were constructed on the upper Yangtze River and the reservoir impoundments began, respectively in October 2012 and May 2013. These cascaded hydroelectric projects could have a large adverse effect on the downstream movement of an important potamodromous fish species, Coreius guichenoti. To study the effect of cascaded impact of sequential huge dams and reservoirs on passive and active downstream movement of C. guichenoti, eggs and larvae were collected in the Yibin section during 2012–2014 and fish were collected monthly at a site in the Hejiang section from June 2012 to July 2014. Our results showed that, compared to one huge reservoir and dam, cascaded dams exert a more serious effect and obstruct downstream movement of eggs, larvae and young fish (particularly the yearlings and two-year-olds) of C. guichenoti. Individual C. guichenoti were able to pass with relative ease through one reservoir and dam, but passing through both reservoirs and dams was very difficult. To allow access to the spawning grounds upstream, a fish passage should be built on the Xiluodu dam. However, due to the hydropower development in the whole upper basin, captive breeding and maintaining at least 60 km of riverine habitat upstream of a spawning ground could be a more cost-effective approach to maintaining C. guichenoti populations in the Upper Yangtze River.     

Geographical patterns of flow-regime alteration by flood-control dams in Japan

Natural variability in water flow is an inherent feature of river ecosystems, but many rivers in the world have been dammed, altering the flow regime and leading to ecosystem degradation. Dam reoperation to maintain environmental flows has been proposed for ecosystem and biodiversity improvement. Reoperation requires an understanding of flow alteration due to dam operations. However, knowledge of natural flow regimes and their degree of alteration remain poor in Japan. The Japanese islands extend from the sub-Arctic to the subtropics with four seasons and thus are considered to show high spatial and temporal variation in flow regime and alterations caused by those variations. We examined the spatial and temporal dependency of flow alteration by flood-control dams in Japan. We confirmed that flood-control dams reduced the rate of change in discharge and peak discharge and that such dams fulfilled their primary role of preventing flood disaster by reducing and delaying flooding. However, other flow characteristics, such as high- and low-flow frequency and duration, were also altered. We demonstrated that the magnitude, frequency, duration, and seasonality of high and low flows in undammed flow regimes differed with latitude and that discharge alteration was spatially and temporally dependent, presumably because dam operation responded to the inherent differences in seasonal flow variability at different latitudes.     

Freshwater fish biodiversity in the Yangtze River basin of China: patterns, threats and conservation

We synthesized information on freshwater fish biodiversity in the Yangtze River basin. We documented 361 species and subspecies that had been recorded and described from the basin. Of these, 177 species are endemic. The basin is usually divided into three parts, i.e. the upper reaches, the middle reaches and the lower reaches. This study indicated that the three reaches approach was not supported by fish distribution patterns. Hydrological alterations are perhaps the largest threat to fish biodiversity in the basin. Fishes in the upper reaches will be seriously affected by the construction of the Three Gorges Dam and other dams, and action should be taken for priority conservation. The most immediate restoration need is reconnection of the Yangtze River with its lakes. The cluster of lakes in the Central Yangtze should be protected to maintain habitats for spawning, feeding and migration of migratory fishes. Our study indicates a need to identify areas of high fish biodiversity and to select nature reserves to mitigate the loss of fish biodiversity in the Yangtze River basin.     

Hydropower and the future of Amazonian biodiversity

In an effort to ensure energy independence and exploit mineral resources, the governments of Amazonian countries are embarking on a major dam building drive on the basin’s rivers, with 191 dams finished and a further 246 planned or under construction. This rush to harvest the basin’s vast renewable energy capacity has come without proper consideration of the likely negative environmental externalities on the world’s most speciose freshwater and terrestrial biotas. Here we highlight the economic drivers for hydropower development and review the literature to summarise the impacts of dam building on Amazonian biodiversity. We identify both direct and indirect impacts through the anticipated loss, fragmentation and degradation of riparian habitats. We then propose a series of measures to assess, curb and mitigate the impacts of destructive dams on Amazonian biodiversity.     

Influence of damming on anuran species richness in riparian areas: A test of the serial discontinuity concept

Almost all large rivers worldwide are fragmented by dams, and their impacts have been modeled using the serial discontinuity concept (SDC), a series of predictions regarding responses of key biotic and abiotic variables. We evaluated the effects of damming on anuran communities along a 245‐km river corridor by conducting repeated, time‐constrained anuran calling surveys at 42 locations along the Broad and Pacolet Rivers in South Carolina, USA. Using a hierarchical Bayesian analysis, we test the biodiversity prediction of the SDC (modified for floodplain rivers) by evaluating anuran occupancy and species diversity relative to dams and degree of urbanized land use. The mean response of the anuran community indicated that occupancy and species richness were maximized when sites were farther downstream from dams. Sites at the farthest distances downstream of dams (47.5 km) had an estimated ~3 more species than those just below dams. Similarly, species‐specific occupancy estimates showed a trend of higher occupancy downstream from dams. Therefore, using empirical estimation within the context of a 245‐km river riparian landscape, our study supports SDC predictions for a meandering river. We demonstrate that with increasing distance downstream from dams, riparian anuran communities have higher species richness. Reduced species richness immediately downstream of dams is likely driven by alterations in flow regime that reduce or eliminate flows which sustain riparian wetlands that serve as anuran breeding habitat. Therefore, to maintain anuran biodiversity, we suggest that flow regulation should be managed to ensure water releases inundate riparian wetlands during amphibian breeding seasons and aseasonal releases, which can displace adults, larvae, and eggs, are avoided. These outcomes could be achieved by emulating pre‐dam seasonal discharge data, mirroring discharge of an undammed tributary within the focal watershed, or by basing real‐time flow releases on current environmental conditions.     

Habitat Fragmentation and Species Extirpation in Freshwater Ecosystems; Causes of Range Decline of the Indus River Dolphin (Platanista gangetica minor)

Habitat fragmentation of freshwater ecosystems is increasing rapidly, however the understanding of extinction debt and species decline in riverine habitat fragments lags behind that in other ecosystems. The mighty rivers that drain the Himalaya - the Ganges, Brahmaputra, Indus, Mekong and Yangtze - are amongst the world’s most biodiverse freshwater ecosystems. Many hundreds of dams have been constructed, are under construction, or are planned on these rivers and large hydrological changes and losses of biodiversity have occurred and are expected to continue. This study examines the causes of range decline of the Indus dolphin, which inhabits one of the world’s most modified rivers, to demonstrate how we may expect other vertebrate populations to respond as planned dams and water developments come into operation. The historical range of the Indus dolphin has been fragmented into 17 river sections by diversion dams; dolphin sighting and interview surveys show that river dolphins have been extirpated from ten river sections, they persist in 6, and are of unknown status in one section. Seven potential factors influencing the temporal and spatial pattern of decline were considered in three regression model sets. Low dry-season river discharge, due to water abstraction at irrigation barrages, was the principal factor that explained the dolphin’s range decline, influencing 1) the spatial pattern of persistence, 2) the temporal pattern of subpopulation extirpation, and 3) the speed of extirpation after habitat fragmentation. Dolphins were more likely to persist in the core of the former range because water diversions are concentrated near the range periphery. Habitat fragmentation and degradation of the habitat were inextricably intertwined and in combination caused the catastrophic decline of the Indus dolphin.     

Detrimental effects of a novel flow regime on the functional trajectory of an aquatic invertebrate metacommunity

Novel flow regimes resulting from dam operations and overallocation of freshwater resources are an emerging consequence of global change. Yet, anticipating how freshwater biodiversity will respond to surging flow regime alteration requires overcoming two challenges in environmental flow science: shifting from local to riverscape‐level understanding of biodiversity dynamics, and from static to time‐varying characterizations of the flow regime. Here, we used time‐series methods (wavelets and multivariate autoregressive models) to quantify flow‐regime alteration and to link time‐varying flow regimes to the dynamics of multiple local communities potentially connected by dispersal (i.e., a metacommunity). We studied the Chattahoochee River below Buford dam (Georgia, U.S.A.), and asked how flow regime alteration by a large hydropower dam may control the long‐term functional trajectory of the downstream invertebrate metacommunity. We found that seasonal variation in hydropeaking synchronized temporal fluctuations in trait abundance among the flow‐altered sites. Three biological trait states describing adaptation to fast flows benefitted from flow management for hydropower, but did not compensate for declines in 16 “loser” traits. Accordingly, metacommunity‐wide functional diversity responded negatively to hydropeaking intensity, and stochastic simulations showed that the risk of functional diversity collapse within the next 4 years would decrease by 17% if hydropeaking was ameliorated, or by 9% if it was applied every other season. Finally, an analysis of 97 reference and 23 dam‐affected river sites across the U.S. Southeast suggested that flow variation at extraneous, human‐relevant scales (12‐hr, 24‐hr, 1‐week) is relatively common in rivers affected by hydropower dams. This study advances the notion that novel flow regimes are widespread, and simplify the functional structure of riverine communities by filtering out taxa with nonadaptive traits and by spatially synchronizing their dynamics. This is relevant in the light of ongoing and future hydrologic alteration due to climate non‐stationarity and the new wave of dams planned globally.     

Fish assemblages respond to altered flow regimes via ecological filtering of life history strategies

1. In riverine ecosystems, streamflow determines the physical template upon which the life history strategies of biota are forged. Human freshwater needs and activities have resulted in widespread alteration of the variability, predictability and timing of streamflow, and anticipating the biotic consequences of anthropogenic streamflow alteration is critical for successful environmental flow management. In this study, we examined relationships between dam characteristics, metrics of flow alteration and fish functional community composition according to life history strategies by coupling stream flow records and fish survey data in paired flow‐regulated and free‐flowing rivers across the conterminous United States. 2. Dam operations have generally reduced flow variability and increased flow constancy based on a comparison of pre‐ and post‐dam flow records (respective mean record lengths 26.2 and 43.1 years). In agreement with ecological theory, fish assemblages downstream of dams were characterised by a lower proportion of opportunistic species (a strategy favoured in environmental settings dominated by unpredictable environmental change) and a higher proportion of equilibrium species (a strategy favoured in more stable, predictable environments) compared to free‐flowing, neighbouring locations. 3. Multiple linear regression models provided modest support for links between alteration of specific flow attributes and differential life history representation below dams, and they provided strong support for life history associations with dam attributes (age and release type). We also found support for a relationship of both reduced flow variability and dam age with higher representation of non‐native species below dams. 4. Our study demonstrated that river regulation by large dams has significant hydrological and biological consequences across the United States. We showed that on ecological time scales (i.e. the order of years to decades), dams are effectively changing the functional composition of communities that have established over millennia. Furthermore, the changes are directional and indicate a filtering by dams for some life histories (equilibrium strategists) and against other life histories (opportunists). Finally, our study highlights that dependence upon long‐term flow records and availability of biotic surveys extracted from national survey efforts limit our ability to guide environmental flow standards particularly in data‐poor regions.     

Evidence for population genetic structure in two exploited Mekong River fishes across a natural riverine barrier

Impacts of urban development on aquatic populations are often complex and difficult to ascertain, but population genetic analysis has allowed researchers to monitor and estimate gene flow in the context of existing and future hydroelectric projects. The Lower Mekong Basin is undergoing rapid hydroelectric development with around 50 completed and under-construction dams and 95 planned dams. The authors investigated the baseline genetic diversity of two exploited migratory fishes, the mud carp Henicorhynchus lobatus (five locations), and the rat-faced pangasiid catfish, Helicophagus leptorhynchus (two locations), in the Lower Mekong Basin using the genomic double digest restriction site-associated DNA (ddRAD) sequencing method. In both species, fish sampled upstream of Khone Falls were differentiated from those collected at other sites, and N_e estimates at the site above the falls were lower than those at other sites. This was the first study to utilize thousands of RAD-generated single nucleotide polymorphisms to indicate that the Mekong's Khone Falls are a potential barrier to gene flow for these two moderately migratory species. The recent completion of the Don Sahong dam across one of the only channels for migratory fishes through Khone Falls may further exacerbate signatures of isolation and continue to disrupt the migration patterns of regionally vital food fishes. In addition, H. lobatus populations downstream of Khone Falls, including the 3S Basin and Tonle Sap system, displayed robust connectivity. Potential obstruction of migration pathways between these river systems resulting from future dam construction may limit dispersal, which has led to elevated inbreeding rates and even local extirpation in other fragmented riverine species.     

Identifying indicators and quantifying large-scale effects of dams on fishes

Although localized effects of individual dams on stream fish assemblages have been relatively well-studied, less is known about the effects of multiple dams within a stream network on fishes and the patterns that emerge when the combined effects of individual and multiple dams are viewed across entire river basins, ecoregions, and states. This study evaluated multiple stream network fragmentation metrics representing localized (e.g., distance-to-dams) and cumulative (e.g., total upstream reservoir storage) dam influences on streams in Michigan, Wisconsin, and Minnesota, developing an approach for identifying suitable fish indicators of dam effects. We used change point and correlation analyses to determine associations of stream fish catch per unit effort and various stream network fragmentation metrics with data from more than 2000 fish survey sites stratified by stream size, thermal regime, and ecoregion. Of the identified indicator species, predominantly warmwater, large river, and/or lentic species were positively associated with stream network fragmentation, whereas cold and coolwater lotic species were negatively associated with fragmentation. These results suggest a combination of downstream thermal effects and upstream influences from impoundments generated by dams. Variance partitioning analyses based on identified indicator species revealed greater upstream-dominated dam influences in headwaters than mid-sized streams, and a greater relative influence of dams vs. other non-dam anthropogenic influences in cold streams than warm streams. Overall, a combination of localized and cumulative fragmentation metrics, as well as upstream and downstream-oriented measures, were influential in indicator species responses, emphasizing the importance of selecting a diversity of fragmentation metrics when assessing effects of dams on stream fishes. Understanding multiple dam influences on stream fishes, including localized effects from individual dams and cumulative effects from all dams within a river basin, would provide useful information for a variety of management activities, including dam operation and dam removal prioritization. Dams significantly affect conservation and management options for stream fishes, with identification of multi-scale dam influences on fishes being critical to restoration and maintenance of aquatic biodiversity throughout the world.     

Modelling the effects of dams on freshwater fish distributions in Hokkaido, Japan

1. We examined the effects of habitat fragmentation caused by dams on freshwater fish species using a database of 7848 fish presence/absence surveys, conducted between 1953–2003 in Hokkaido, Japan. 2. A series of generalised linear models showed that for 11 of 41 taxa examined, the probability of occurrence had been influenced either negatively (eight taxa) or positively (three taxa) by the presence of a dam downstream from their habitat. 3. Maps of modelled predictions revealed that dams had had widespread negative impacts on certain taxa, while for other taxa the impact was limited to specific basins. Two of the three taxa whose probability of occurrence was increased in areas above dams have long been transplanted into reservoirs in Japan. 4. For four of the eight taxa whose probability of occurrence was reduced above dams and all three taxa whose probability of occurrence increased above dams, the temporal length of habitat isolation (i.e. the number of years between dam construction and sampling) was also a significant predictor of the probability of occurrence. This pattern indicates that these taxa experienced a gradual rather than an instantaneous population impact as a result of dam construction. 5. The eight taxa whose probability of occurrence was reduced as a consequence of dams all exhibit migratory life cycles. Although migratory taxa are probably more susceptible to the negative effect of dams, we could not detect significant relationships between migration life histories and the effect of fragmentation by dams. 6. These analyses enable stream and fisheries managers to quantify the impacts of habitat fragmentation because of dams for individual species. The spatially explicit nature of our analyses also enables identification of the areas of the impact at broad geographical scales. Using our results, managers can take effective conservation and restoration measures to predict, mitigate or remove the impact of dams. For example, our results can be used to prioritise dams for removal or to predict losses of biodiversity and ecosystem services in advance of dam construction.     

Biology, fisheries, and conservation of sturgeons and paddlefish in China

This paper reviews five of the eight species of acipenseriforms that occur in China, chiefly those of the Amur and Yangtze rivers. Kaluga Huso dauricus and Amur sturgeon Acipenser schrenckii are endemic to the Amur River. Both species still support fisheries, but stocks are declining due to overfishing. Acipenseriformes of the Yangtze River are primarily threatened by hydroelectric dams that block free passage to spawning and feeding areas. The Chinese paddlefish Psephurus gladius now is rare in the Yangtze River system, and its spawning activities were severely limited by completion of the Gezhouba Dam in 1981. Since 1988, only 3–10 adult paddlefishes per year have been found below the dam. Limited spawning still exists above the dam, but when the new Three Gorges Dam is complete, it will further threaten the paddlefish. Artificial propagation appears to be the only hope for preventing extinction of P. gladius, but it has yet to be successfully bred in captivity. Dabry's sturgeon A. dabryanus is a small, exclusively freshwater sturgeon found only in the Yangtze River system. It is concentrated today in reaches of the main stream above Gezhouba Dam. The fishery has been closed since 1983, but populations continue to decline. Acipenser dabryanus has been cultured since the 1970s, and holds promise for commercial aquaculture; availability of aquacultural methods offers hope for enhancing natural populations. The Chinese sturgeon A. sinensis occurs in the Yangtze and Pearl rivers and seas of east Asia. There is still disagreement about the taxonomy of the Pearl and Yangtze River populations. The Yangtze River population is anadromous. Adults begin spawning at about age 14 years (males) and 21 years (females), and adults spend over 15 months in the river for reproduction. Spawning sites of A. sinensis were found every year since 1982 below the Gezhouba Dam, but it seems that insufficient suitable ground is available for spawning. Since 1983, commercial fishing has been prohibited but more measures need to be taken such as establishing protected areas and characterizing critical spawning, summering and wintering habitats.     

CURRENT STATUS AND CONSERVATION PLANNING OF FISH BIODIVERSITY IN THE UPPER YANGTZE RIVER BASIN IN THE CONTEXT OF HYDROPOWER DEVELOPMENT北大核心CSCD

Nearly 90% of the hydropower resources in the Yangtze River basin are concentrated in the upper reaches of the Yangtze River. The cascaded hydropower dams and river channelization have caused habitat fragmentation and loss of fish diversity, which has aggravated the contradictions between hydropower development and environmental protection. This paper collected data on aquatic reserves (i.e. natural reserves and aquatic germplasm resources conservation zones) and cascade dams in the upper reaches of the Yangtze River, and vectorized the data in ArcGIS. Taking into account the diversity, richness and distribution of fish, we analyzed the changes in fish resources and the problems in the construction and management of the upper reaches of the Yangtze River. Therefore, several strategies have been proposed to reduce the conflicts between hydropower development and aquatic ecosystem protection, including conducting reserve census, evaluating management effectiveness of the protected areas for spatial optimization of the reserve networks, implementing the ecological restoration of essential fish habitats, implementing the rescue action plan for the upper Yangtze endangered endemic fish, establishing an efficient ecological compensation mechanism, and strengthening scientific monitoring and related research. These recommendations will provide a scientific basis for the coordinated development of hydropower exploitation and river ecological protection in the upper Yangtze River. © 2019, Institute of Hydrobiology, Chinese Academy of Sciences. All rights reserved.     

Dams in South Europe: socio-environmental approach and eDNA-metabarcoding to study dam acceptance and ecosystem health

Under current climate warming, dams and reservoirs are main options to ensure water supply in dry regions. However, the presence of these infrastructures encompasses impacts on ecosystem due to the alteration of connectivity and river habitat. We expect that as a result of the relation between water supply as a resource and the population will depend on their use or demand, so the benefits of dams compensate their negative impacts in regions with droughts while not having the same perception in zones where water supply is not a problem, so the public acceptance of dams is expected to change depending on the area. Here, we have employed a multidisciplinary approach to study dam acceptance and also measure ecosystem health in two dammed areas, Guadalhorce and Nalón rivers, Mediterranean dry south and Atlantic humid north of Spain, respectively. The methodology employed has included the use of Environmental DNA for phytoplankton inventory and surveys to stakeholders and ordinary citizens to measure dam’s acceptance. Worse bioindicators of water quality associated to dams were found in Guadalhorce than in Nalon River. However, stakeholders valued more the ecosystem services provided by Guadalhorce dams, especially of cultural nature, than those provided by Nalón dams. Most citizens consulted (N?=?319 and 300 in Guadalhorce and Nalón regions) were favourable to the presence of dams and reservoirs. They would also increase their annual taxes to restore river connectivity, especially in Guadalhorce River, while dam demolition was the least supported. The generally positive views would help to identify actions for improvement of dammed rivers highlighting the importance of restoring river connectivity without dam demolition for local river users.

     

Riparian vegetation diversity along regulated rivers: contribution of novel and relict habitats

1. The creation and maintenance of spatial and temporal heterogeneity by rivers flowing through floodplain landscapes has been disrupted worldwide by dams and water diversions. Large reservoirs ( novel ecosystems ) now separate and isolate remnant floodplains ( relict ecosystems ). From above, these appear as a string of beads, with beads of different sizes and string connections of varying lengths.
2. Numerous studies have documented or forecast sharp declines in riparian biodiversity in relict ecosystems downstream from dams. Concurrently, novel ecosystems containing species and communities of the former predam ecosystems have arisen along all regulated rivers. These result from the creation of new environments caused by upper reservoir sedimentation, tributary sedimentation and the formation of reservoir shorelines.
3. The contribution of novel habitats to the overall biodiversity of regulated rivers has been poorly studied. Novel ecosystems may become relatively more important in supporting riverine biodiversity if relict ecosystems are not restored to predam levels. The Missouri River of the north-central U.S.A. is used to illustrate existing conditions on a large, regulated river system with a mixture of relict and novel ecosystems.     

Damming interacts with the flood pulse to alter zooplankton communities in an Amazonian river

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