Bibliometrics-based Research Hotspots and Development Trends in Eco-hydrology of Dammed Rivers

Water conservation initiatives satisfy the demand for water supply,electricity generation,irrigation,and flood control.While helping humanity,they have also altered the ecosystem of natural rivers,impacted river ecology,disrupted river continuity,and jeopardized the existence of aquatic creatures in rivers.Studying the impacts of dam construction on rivers can enhance our knowledge of river ecological and environmental concerns and help sustain the health of river ecosystems,thereby realizing the harmony between humans and water in both theoretical and practical aspects.This study used bibliometrics and constructed an author-keyword 2-mode matrix network using Co-Occurrence software to identify the hotspots and research trend in eco-hydrology of dammed rivers.We identified‘FLOW’‘SEDIMENT’‘QUALITY’and‘MODEL’as the research hotspots in the ecological impact of dammed rivers,and combined the related literatures,we highlight the research progress in the four directions.Then the research shortcomings and prospect were discussed,including strengthening the monitoring and analysis of critical ecological variables,enhancing the hydrological monitoring density for small rivers,strengthening the research of relationship between eutrophication and zooplankton,establishing multiscale approaches,and combining multi-sources information technologies to improve parameter accuracy in the model research.

Inducing Flow Velocities to Manage Fish Reproduction in Regulated Rivers

Conservation of endangered or economic fish and control of invasive fish is a great challenge of hydraulic engineering worldwide.Flow velocity has been recognized to affect the spawning of fishes delivering drifting eggs in rivers.However,solid scientific supports and associated mechanisms to establish quantitative relations between flow velocity and fish reproduction,taking into account spawning,fertilizing,hatching,as well as surviving,are lacking.In this paper,we quantified the relationship between flow velocity and reproduction of Chinese carps through both lab and field experiments.The results showed that a minimum velocity was required to trigger Hypophthalmichthys molitrix(H.molitrix)releasing eggs,and a velocity range was preferred to sustain spawning activity.However,the embryo incubation and larvae development of H.molitrix were found to be inhibited with the increase in flow velocity.Considering the requirements of spawning and hatching,as well as larvae surviving,an optimized flow velocity processes was identified for the reproduction of H.molitrix in rivers.These findings were of great significance to the adaptive operation of reservoirs to create reasonable and precise ecological flows for managing fish reproduction,as shown by the promising results in the engineering application to the Three Gorges Reservoir.

Damming effects on dissolved inorganic carbon in different kinds of reservoirs in Jialing River,Southwest China

To assess the effects of river damming on dissolved inorganic carbon in the Jialing River, a total of 40 water samples, including inflow, outflow, and stratified water in four cascade reservoirs(Tingzikou, Xinzheng,Dongxiguan, Caojie) were collected in January and July,2016. The major cations, anions, and δ^(13)C_(DIC) values were analyzed. It was found that the dissolved compositions are dominated by carbonate weathering, while sulfuric acids may play a relatively important role during carbonate weathering and increasing DIC concentration. Different reservoirs had variable characteristics of water physiochemical stratification. The DIC concentrations of reservoir water were lower in summer than those in winter due to the dilute effects and intensive aquatic photosynthesis, as well as imported tributaries. The δ^(13)C_(DIC) values in Tingzikou Reservoir were higher during summer than those in winter,which indicated that intensive photosynthesis increased the δ^(13)C_(DIC) values in residual water, but a similar trend was not obvious in other reservoirs. Except for in Xinzheng Reservoir, the δ^(13)C_(DIC) values in inflow and outflow reservoir water were lower than those in the surface water of stratified sampling in summer. For stratified sampling, it could be found that, in summer, the Tingzikou Reservoir δ^(13)C_(DIC) values significantly decreased with water depthdue to the anaerobic breakdown of organic matter. The significant correlation(p<0.01 or 0.05) between the DIC concentrations, the δ^(13)C_(DIC) values and anthropogenic species(Na^++K^+, Cl~–, SO_4^(2-) and NO_3^-) showed that the isotope composition of DIC can be a useful tracer of contaminants. In total, Tingzikou Reservoir showed lacustrine features, Xinzheng Reservoir and Dongxiguan Reservoir had "transitional'' features, and Caojie Reservoir had a total of "fluvial'' features. Generally, cascade reservoirs in the Jialing River exhibited natural river features rather than typical lake features due to characteristics of reservoir water in physiochemical stratification, spatiotemporal variations of DIC concentrations and isotopic compositions. It is evident that the dissolved inorganic carbon dynamics of natural rivers had been partly remolded by dam building.

Damming of Large River by Debris Flow: Dynamic Process and Particle Composition

The frequency and extent of debris flows have increased tremendously due to the extreme weather and the Wenchuan earthquake on May 12, 2008. Previous studies focused on the debris flow from gullies damming the mountain streams. In this paper, an equation for the run-out distance of debris flow in the main river is proposed based on the dynamic equation of debris flow at different slopes given by Takahashi. By undertaking field investigations and flume experiments, a new calculation method of the volume of debris flow damming large river is obtained. Using the percolation theory and the renormalization group theory it was deduced that the large particles should comprise more than 50% for forming a stable debris flow dam. Hence, the criteria of damming large river by debris flow is presented in terms of run-out distance and grain composition which was then validated through the event of damming river by debris flow at Gaojia gully, the upper reaches of the Minjiang River, Sichuan, China, on July 3, 2011.

Effects of river damming on biogenic silica turnover:implications for biogeochemical carbon and nutrient cycles

Rivers link terrestrial ecosystems and marine ecosystems, and they transport large amounts of substances into oceans each year, including several forms of silicon(Si), carbon(C), and other nutrients. However, river damming affects the water flow and biogeochemical cycles of Si, C, and other nutrients through biogeochemical interacting processes. In this review, we first summarize the current understanding of the effects of river damming on the processes of biogeochemical Si cycle, especially the source, composition, and recycling process of biogenic silica(BSi). Then, we introduce dam impacts on the cycles of C and some other nutrients. Dissolved silicon in rivers is mainly released from phytolith dissolution and silicate weathering. BSi in suspended matter or sediments in most rivers mainly consists of phytoliths and mainly originates from soil erosion. However, diatom growth and deposition in many reservoirs formed by river interception may significantly increase the contribution of diatom Si to total BSi, and thus significantly influence the biogeochemical Si,C, and nutrient cycles. Yet the turnover of phytoliths and diatoms in different rivers formed by river damming is still poorly quantified. Thus, they should be further investigated to enhance our understanding about the effects of river damming on global biogeochemical Si, C and nutrient cycles.

水电梯级开发真的破坏下游河段营养盐情势吗?

River damming is believed to largely intercept nutrients,particularly retain more phosphorus(P)than nitrogen(N),and thus harm primary productivity,fishery catches,and food security downstream,which seriously constrain global hydropower development and poverty relief in undeveloped regions and can drive geo-political disputes between nations along trans-boundary rivers.In this study,we investigated whether reservoirs can instead improve nutrient regimes downstream.We measured different species of N and P as well as microbial functions in water and sediment of cascade reservoirs in the upper Mekong River over 5 years and modelled the influx and outflux of N and P species in each reservoir.Despite partially retaining total N and total P,reservoirs increased the downstream flux of ammonium and soluble reactive phosphorus(SRP).The increase in ammonium and SRP between outflux and influx showed positive linear relationships with the hydraulic residence time of the cascade reservoirs;and the ratio of SRP to dissolved inorganic nitrogen increased along the reservoir cascade.The lentic environment of reservoirs stimulated algae-mediated conversion of nitrate into ammonium in surface water;the hypoxic condition and the priming effect of algae-induced organic matter enhanced release of ammonium from sediment;the synergy of microbial phosphorylation,reductive condition and sediment geochemical properties increased release of SRP.This study is the first to provide solid evidence that hydropower reservoirs improve downstream nutrient bioavailability and N-P balance through a process of retention-transformation-transport,which may benefit primary productivity.These findings could advance our understanding of the eco-environmental impacts of river damming.

Impact of dam on inundation regime of flood plain wetland of punarbhaba river basin of barind tract of Indo-Bangladesh

Present study raises a serious issue of wetland loss and transformation due to damming and water di-version.At present study,it is noticed that overall rainfall trend(-0.006)of the study period(1978-2015)remains unchanged but riparian wetland area is attenuated after damming both pre monsoon(March to May)and post monsoon season(October to December).Total wetland area in pre-and post-monsoon seasons is respectively reduced from 42.2 km^(2) to 27.87 km^(2),and from 277.85 km^(2) to 220.90 km^(2) in post dam period.Transformation of frequently inundated wetland area into sparsely inundated wetland is mainly triggered by flow modification due to installation of Komardanga dam and Barrage over Punarbhaba and its major tributary Tangon river.Sparsely inundated seasonal wetland area is rapidly reclaimed for agricultural practice.This extreme issue will invite instability in socio-ecological setup of the neighbouring region.