Effects of hydraulic cues in barrier environments on fish navigation downstream of dams.

Understanding how hydraulic cues in the barrier environment affect fish navigation is critical to fish migration in dammed rivers. However, most of the current research on the effects of hydraulic cues on fish navigation focuses on the effects of a single hydraulic parameter on fish migration and usually ignores fish sensory perception and swimming ability. This study presents an effective approach that combines a computational fluid dynamics model of a river with a model of fish behaviour to elucidate the effects of hydraulic cues in the barrier environment on fish migration paths and strategies by simulating the fish's perception of flow direction and their regulation of multiple hydraulic parameters. Four release scenarios for the dam were reviewed and it was determined that the modelled fish movements realistically reflected actual observations. In various scenarios, the target fish (Schizothorax chongi) managed to move upstream to the tailrace downstream of the dam, despite the hydraulic barrier created by the mainstem area of the river; they overcame this obstacle by exploiting low-velocity zones on both sides of the mainstem and in the river's boundary layer. During upstream movement, the target fish preferred areas with flow velocities between 0.7 and 1.0 m/s and a turbulent kinetic energy of less than 0.3 m2/s2 to maintain aerobic activity. Additionally, the effects of alternative turbine release strategies on the fine-motor movement of target fish were reviewed and an optimised strategy was provided that could increase the proportion of target fish entering the fish passage facility from 0% to 53.8% in the original scenario to 82.6%. This study provides a feasible method for the simulation of fish fine motion in complex flow environments as well as a scientific basis for the management of fish resources in dammed rivers.

Differences in the Natural Swimming Behavior of Schizothorax prenanti Individual and Schooling in Spatially Heterogeneous Turbulent Flows.

Spatially heterogeneous turbulent flow refers to nonuniform flow with coexisting multiple flow velocities, which is widely distributed in fish natural or husbandry environments, and its hydraulic parameters affect fish swimming behavior. In this study, a complex hydrodynamic environment with three flow velocity regions (low, medium, and high) coexisting in an open-channel flume was designed to explore volitional swimming ability, the spatial-temporal distribution of fish swimming trajectories, and the range of preferred hydrodynamic parameters of Schizothorax prenanti individual and schooling (three fish). The results showed that the swimming speed of individual fish during upstream migration was significantly higher than that of fish schools (p < 0.05). The swimming trajectories of fish schooling showed that they spent more time synchronously exploring the flow environment during upstream migration compared with individual fish. By superimposing the fish swimming trajectories on the environmental flow field, the range of hydrodynamic environments preferred by fish in complex flow fields was quantified. This research provides a novel approach for investigating the natural swimming behavior of fish species, and a theoretical reference for the restoration of fish natural habitats or flow enrichment of husbandry environments.

Evaluating the impact of power station regulation on the suitability of drifting spawning fish habitat based on the fuzzy evaluation method.

Ecological regulation is an important means of reservoir adaptive management, but its effective evaluation faces two major difficulties: the response mechanism of fish spawning behavior is not completely clear, and how to establish a feedback regulation relationship of hydrological processes to improve the river environment is unknown. Based on a long-term series of early fish resources, hydrology, water temperature, and meteorology data, this research clarifies the fish spawning habitat requirements in the power station regulation environment, determines a habitat suitability evaluation index system and evaluation criteria, reveals the temporal and spatial variation characteristics of fish habitat suitability under power station regulation based on the fuzzy logic method, provides feedback to the existing regulation scheme, and proposes suggestions for sustainable adaptive management of the reservoir. The temporal and spatial variation characteristics of the spawning river sections habitat suitability are the comprehensive differences among multiple objectives and factors. The habitat suitability of each river section decreases after impoundment, especially in May, which is related to the delayed of water temperature changes under reservoir regulation. The reduced suitability of the Yibin(YB) river section is most affected by the impoundment regulation of the Xiluodu Reservoir (XLDR) and Xiangjiaba Reservoir (XJBR), while the Luzhou(LZ) river section is affected by the inflow of the Minjiang River (MJ) tributary, which reduces the suitability difference before and after impoundment. The Jiangjin(JJ) river section is less affected by the regulation of the XJBR and is greatly affected by tributaries and rainfall. How to adjust the regulation strategies under the new boundaries and new situations in the future, which are affected by the cumulative impact of the sustainable development of upstream cascades, is the focus of reservoir adaptive management. This research can provide technical support for the management of cascade reservoirs under future scenarios.

Evaluation of Volitional Swimming Behavior of Schizothorax prenanti Using an Open-Channel Flume with Spatially Heterogeneous Turbulent Flow.

Effective fishway design requires knowledge of fish swimming behavior in streams and channels. Appropriate tests with near-natural flow conditions are required to assess the interaction between fish behavior and turbulent flows. In this study, the volitional swimming behavior of S. prenanti was tested and quantified in an open-channel flume with three (low, moderate, and high) flow regimes. The results showed that, when confronted with alternative flow regimes, S. prenanti preferred to select regions with low flow velocities (0.25−0.50 m/s) and turbulent kinetic energy (<0.05 m2/s2) for swimming, while avoiding high-turbulence areas. Moreover, S. prenanti primarily employed steady swimming behavior to search for flow velocities lower than the average current to conserve energy in low- and moderate-flow regimes. It is hypothesized that in regions with higher flow velocities, fish may change their swimming strategy from energy conservation to time conservation. Additionally, the average and maximum burst speeds of S. prenanti were 2.63 ± 0.37 and 3.49 m/s, respectively, which were 2.21- and 2.28-fold higher than the average (1.19 m/s) and maximum (1.53 m/s) burst speeds estimated from the enclosed swim chamber for fish of similar length. This study contributes a novel research approach that provides more reliable information about fish volitional swimming behavior in natural habitats, as well as recommendations for hydraulic criteria for fishways and the identification of barriers to fish migrations.

Identifying three-dimensional swimming corridors for fish to match their swimming characteristics under different hydropower plant operations: Optimization of entrance location for fish-passing facilities.

Fish that require migration are often diverse in the dam-built river, and some of them are benthic. For fish to pass efficiently across the dams, it is necessary to identify the swimming corridors and possible cluster areas of the target fish. However, previous studies have only predicted the two-dimensional swimming corridors of a single species. In this study, the relationships between the swimming behaviours of different species of fish and the three-dimensional (3D) hydrodynamic field were determined, and a model of the 3D swimming corridors corresponding to the fish swimming characteristics was constructed. The model was verified by a fish acoustic telemetry experiment. By simulating the river 3D hydrodynamic field in different scenarios, the possible swimming corridors and clustering areas of the target fish were further evaluated. We showed that the swimming corridors of the target fish were different among different scenarios, and the swimming corridors were mainly concentrated on both sides of the mainstream. With increased flow due to power station operation, the proportion of potential swimming corridors of target fish throughout the basin gradually decreased, and the proportion of velocity barrier zones of target fish gradually increased. By analyzing the possible swimming corridors of the target fish, the slow-flowing areas near the suddenly narrowed swimming corridors were considered to be the areas of target fish clustering. The cluster areas of the target fish weres also the optimal choice of the fish passing facility entrances, so as to ensure the best fish-crossing effect. The reliable and quantitative 3D fish swimming corridors model proposed in this study can provide a scientific basis for the layout of fish-crossing facilities and facilitate the scientific operation and management of the reservoir in the fish spawning season.

Comparative study on the bioaccumulation of lead, cadmium and nickel and their toxic effects on the growth and enzyme defence strategies of a heavy metal accumulator, Hydrilla verticillata (L.f.) Royle.

The current hydroponic experiment investigated differences in the uptake, physiological response and defence mechanisms of Hydrilla verticillata (L.f.) Royle in response to three representative toxic heavy metals. The results revealed the following: as an excellent heavy metal accumulator, H. verticillata showed an accumulation pattern of Ni > Cd > Pb within experimental scope. Fourteen days (Ni and Cd) and 21 days (Pb) were the time thresholds under the same heavy metal concentration toxicity, while 33.06 µM (Ni) and 40 µM (Cd and Pb) were the concentration thresholds under the same 21-day duration treatment, to accumulate the most amount of metals. Hence, Pb might be accumulated more if it expands the experimental duration and concentration, for it continuously increases throughout the experimental period. Reasons for these uptake differences are that plant physiological response, tolerance and resistance vary under different heavy metal stress. First, the biomass and protein content of H. verticillata were both the highest under Pb stress, indicating the plant largest tolerance to Pb stress. Second, the tolerance thresholds of three antioxidant enzymes (SOD, CAT and POD) were the highest under Pb stress. Third, the three antioxidant enzymes and two other related resistance-causing enzymes (PPO and PAL) revealed that plant resistance was strongest at low Cd concentrations (0-20 µM) and at high Pb stress levels (40 µM). Furthermore, CAT is the most important antioxidant enzyme to combat three metal stresses (average relevance: CAT(0.89) > POD(0.48) > SOD(0.42)), while PAL is more important than PPO (average relevance: PAL (0.77) > PPO(0.72)). In conclusion, Pb-polluted water is best treated with H. verticillata because of the latter's high uptake potential and strong defence capacity. These results provide an accurate, efficient and economical reference for phytoremediation. Graphical abstract.

Mechanism Underlying Flow Velocity and Its Corresponding Influence on the Growth of Euglena gracilis, a Dominant Bloom Species in Reservoirs.

The effects of hydrodynamics on algae growth have received considerable attention, and flow velocity is one of the most frequently discussed factors. For Euglena gracilis, which aggregates resources and is highly resistant to environmental changes, the mechanism underlying the impact of flow velocity on its growth is poorly understood. Experiments were conducted to examine the response of algae growth to different velocities, and several enzymes were tested to determine their physiological mechanisms. Significant differences in the growth of E. gracilis were found at different flow velocities, and this phenomenon is unique compared to the growth of other algal species. With increasing flow velocity and time, the growth of E. gracilis is gradually inhibited. In particular, we found that the pioneer enzyme is peroxidase (POD) and that the main antioxidant enzyme is catalase (CAT) when E. gracilis experiences flow velocity stress. Hysteresis between total phosphorus (TP) consumption and alkaline phosphatase (AKP) synthesis was observed. Under experimental control conditions, the results indicate that flow velocities above 0.1 m/s may inhibit growth and that E. gracilis prefers a relatively slow or even static flow velocity, and this finding could be beneficial for the control of E. gracilis blooms.

An Approach Based on the Protected Object for Dam-Break Flood Risk Management Exemplified at the Zipingpu Reservoir.

Dam-break flooding is a potential hazard for reservoirs that poses a considerable threat to human lives and property in downstream areas. Assessing the dam-break flood risk of the Zipingpu Reservoir in Chengdu, Sichuan Province, China, is critically important because this reservoir is located on the Longmen Shan fault, which experiences high seismic activity. In this paper, we develop an approach based on the protected object for dam-break flood risk management. First, we perform a numerical simulation of dam-break flooding in four possible dam break scenarios. Next, the flood areas are divided into 71 analysis units based on the administrative division. Based on the numerical simulation results and the socio-economic demographic data affected by a flood, the importance and risk level of each analysis unit is confirmed, and the flood risk map is established according to the classification results. Finally, multi-level flood risk management countermeasures are proposed according to the results of the unit classification shown in the map.

The Ecological Water Demand of Schizothorax in Tibet Based on Habitat Area and Connectivity.

Water resource regulation is convenient for humans, but also changes river hydrology and affects aquatic ecosystems. This study combined a field investigation and two-dimensional hydrodynamic model (MIKE21) to simulate the hydrodynamic distribution from 1 March to 30 April of 2008-2013 and establish the HDI (habitat depth suitability index) and HVI (habitat velocity suitability index) based on static hydraulic conditions at typical points. Additionally, by using MIKE21 to simulate the hydraulic state in the study area under 20 flow conditions from 530-1060 m3/s, and combining these states with the HCI (habitat cover type suitability index), HDI, and HVI, we simulated the WUA (weighted usable area) and habitat connectivity under different runoff regulation scenarios to study the water requirements of Schizothorax during the spawning period in the Yanni wetland. The results showed the following: (1) the suitable cover type was cobble and rock substrate, with nearby sandy land; furthermore, the suitable water depth was 0.5-1.5 m, and the suitable velocity was 0.1-0.9 m/s. (2) Using the proximity index to analyse the connectivity of suitable habitats, the range of ecological discharge determined by the WUA and connectivity was 424-1060 m/s. (3) Habitat quality was divided into three levels to detail the flow demand further. When the flow was 424-530 m3/s or 848-1060 m3/s, the WUA and connectivity generally met the requirements under natural conditions. When the flow was 530-636 m3/s or 742-848 m3/s, the WUA and connectivity were in a good state. When the flow was 636-742 m3/s, the WUA and connectivity were in the best state. This study complements existing research on the suitability of Schizothorax habitat in Tibet, and introduces the connectivity index to enrich the method for calculating ecological water demand, providing a reference for resource regulation and the protection of aquatic organisms.

Identifying operation scenarios to optimize attraction flow near fishway entrances for endemic fishes on the Tibetan Plateau of China to match their swimming characteristics: A case study.

Attracting fish at fishway entrances is vital for ensuring fish passage efficiency, which requires consideration of the swimming characteristics of fish. The objective of this case study was to propose optimized flow conditions downstream of a dam on the Tibetan Plateau to attract fish into fishways. Six local endemic species of Cyprinidae: Schizothoracinae were considered as protection targets. However, the swimming abilities of most endemic fishes on the plateau remain unclear, and no previous projects in this area could serve as a reference. Thus, the swimming performances of the target species were first tested based on three indexes, induction velocity, critical swimming speed and bursting swimming speed, and six behavior zones were classified by different flow velocity thresholds based on the test results. A verified 3D hydrodynamic model was then adopted to simulate the flow field downstream of the dam under four typical reservoir operation scenarios. By matching the simulated flow fields to the different behavior zones, all scenarios were assessed for the passability of the target fishes, and the results showed that there would be different potential migration routes under each scenario. For the most common scenario during the fish passage season, symmetrical use of turbines T1 and T6 was recommended so that the flow would be lower velocity and the turbulence would be less intense near the fishway entrances than the current regime. Moreover, the addition of a new entrance was suggested on the migration routes with high potential use to increase the chance that fish would enter. Beyond providing a solution for this specific case, this study enriches knowledge about the swimming features of endemic fishes on the Tibetan Plateau. Furthermore, this research provides a possible technical methodology that combines fish behavioral characteristics and hydraulic indexes when determining attraction flows in similar fish passage projects.

Effects of water depth on GBD associated with total dissolved gas supersaturation in Chinese sucker (Myxocyprinus asiaticus) in upper Yangtze River.

Spillway water falling from hydroelectric power plant dams in the upper Yangtze River creates a high pressure in plunge pools below the dams allowing gasses to be dissolved at high rates. The resulting supersaturation persists many miles downstream the dam which may elicit mortality in river fishes associated with gas bubble disease (GBD). We have in a two-year study (2014-15) evaluated the effect of water depth on development of GBD in an endemic and endangered fish species, the Chinese sucker Myxocyprinus asiaticus, 24 km downstream of Xiangjaiba dam. Mortality and incidence of GBD were recorded and it was seen that water depth and survival time/GBD development was positively correlated. The physiological mechanisms explaining increased resistance to GBD with increased water depths (and thereby higher hydrostatic pressure) are discussed. The results may be applied in future management of fish resources in order to protect endangered endemic fishes in rivers affected by dam constructions.

Hydraulic characteristics of stepped spillway dropshafts for urban deep tunnel drainage systems: the case study of Chengdu city.

Cities in southwestern China experience urban drainage and overflow pollution after extreme rainfall events, which are major problems. In this study, a type of stepped spillway dropshaft suitable for drainage by deep tunnels in Chengdu was proposed and the hydraulic characteristics were investigated experimentally. The results showed that the nappe flow and strong turbulent deflected jet flow in the stepped spillway allowed the dropshaft to greatly dissipate energy. According to the distribution of the time-averaged pressure on the steps, the flow on the steps could be divided into a recirculating region, a wall-impinging region and a mixing region. The time-averaged pressure on the outside of the step was higher than that on the inside due to the centrifugal force effect of the water. The fluctuating pressure distribution of the step approximated the normal distribution. It was acceptable to calculate the minimum pressure with 3 times the root mean square (RMS). The vibration of the flow on the stepped spillway did not resonate with the step. When the outflow tunnel was under submerged outflow conditions, the aeration in the stepped spillway was exhausted through air holes and only a small amount of air entered the outflow tunnel, thereby avoiding an air explosion.

Defense Mechanisms of Two Pioneer Submerged Plants during Their Optimal Performance Period in the Bioaccumulation of Lead: A Comparative Study.

Ceratophyllum demersum L. and Hydrilla verticillata (L.f.) Royle, two pioneer, submerged plants, effectively remove heavy metals from contaminated water. The present work evaluates the bioaccumulation and defense mechanisms of these plants in the accumulation of lead from contaminated water during their optimal performance period. C. demersum and H. verticillata were investigated after 14 days of exposure to various lead concentrations (5⁻80 µM). The lead accumulation in both C. demersum and H. verticillata increased with an increasing lead concentration, reaching maximum values of 2462.7 and 1792 mg kg-1 dw, respectively, at 80 µM. The biomass and protein content decreased significantly in C. demersum when exposed to lead. The biomass of H. verticillata exposed to lead had no significant difference from that of the controls, and the protein content increased for the 5⁻10 µM exposure groups. The malondialdehyde (MDA) content and superoxide dismutase (SOD), peroxidase (POD), and polyphenol oxidase (PPO) activities were much higher in C. demersum, suggesting considerable damage from lipid peroxidation and sensitivity to lead stress. Enzyme inhibition and inactivation were also observed in C. demersum at high lead concentrations (40⁻80 µM). The excellent growth status, low damage from lipid peroxidation, and high activity of catalase (CAT) and phenylalanine ammonia-lyase (PAL) observed in H. verticillata illustrate its better tolerance under the same lead stress.

Ecohydraulogical Characteristic Index System of Schizopygopsis younghusbandi during Spawning Periods in the Yarlung Tsangpo River.

To address the species decline in aboriginal fish in the Yarlung Tsangpo River Basin and the lack of research on the habitat characteristics of fish spawning grounds, this paper studied the changing trends in runoff in spawning grounds and the habitat conditions characteristics of Schizopygopsis younghusbandi during the spawning period. In conventional approaches, inaccurate statistical results are obtained when a full river section is taken as the region to be assessed, so a new method for determining the statistical boundaries of characteristic indexes was proposed. By combining hydrological analyses, mathematical statistics, and numerical simulations, the statistical boundary of the index was determined, and a suitable range for the habitat characteristic indexes for the spawning field was finally obtained. The results showed that (1) the maximum percentage of the statistical boundary for the spawning grounds was 39% near the banks on both sides of the river; (2) the flow during the spawning period exhibited small variations, a short duration and a fluctuation cycle and was dominated by water rising events, and the interannual growth trend in the daily flow was obvious; and (3) during the spawning period, the flow velocity of the fish habitat was small, the turbulence level of the fluid was low, and the flow regime was stable. A suitable range for the habitat characteristic index of the target fish provided the basic data for the protection of aboriginal fish and was beneficial to maintain the balance of aquatic ecological system in the Yarlung Tsangpo River. The results of this study contribute to the rational development of water resources in the basin and the protection of species diversity and water environment.

Effects of Total Dissolved Gas Supersaturation on the Swimming Performance of Two Endemic Fish Species in the Upper Yangtze River.

Total dissolved gas (TDG) supersaturation has been identified as one of the possible negative environmental effects of the construction of dams in the upper Yangtze River. Juvenile Chinese sucker and Prenant's schizothoracin fish were selected to evaluate the impact of TDG supersaturation on the swimming performance of fish in the Upper Yangtze River. The critical swimming speeds (Ucrit) of Chinese sucker were 4.06, 2.83, 2.87, 2.68, and 2.29 BLs-1 at the TDG supersaturation levels of 100, 117, 122, 125 and 130%, respectively. The Ucrit of Prenant's schizothoracin were 7.38, 4.32, 3.98, and 3.74 BLs-1 at the TDG supersaturation levels of 100, 117, 125 and 130%, respectively. The burst swimming speed (Uburst) of the two species also significantly declined with increases in the TDG supersaturation level. The present results demonstrate that the swimming speeds of Prenant's schizothoracin that were exposed to 130% TDG supersaturation for 2 h exhibited significant recovery after 2 days, whereas the swimming speeds of Chinese sucker did not. The swimming speeds of Chinese sucker after 2 days of recovery were significantly reduced compared with those of control fish, whereas the speeds of Prenant's schizothoracin returned to normal levels.