Injury and mortality of fish during downstream passage through hydropower turbines is among the leading direct impacts of hydropower. Understanding the relationships among various strike variables and injury and mortality rates are necessary for improvements in turbine design. We subjected three species of fish to simulated blade strike in laboratory studies with different blade thicknesses, impact velocities, and body orientations to develop relationships between these variables and probability of injury and mortality. Midbody strikes resulted in higher mortality than head strikes, and tail strikes produced the least mortality. Lateral strikes caused more mortality than dorsal and ventral strikes, and higher strike velocities and thinner blades contributed to increased mortality. Several injury types were significantly associated with increased mortality, including injuries to the operculum, gills, viscera, heart, liver, swim bladder, muscle, and bone fractures. Results from this study will be used to define biologically based design criteria that can be used by turbine designers to improve designs (e.g., increased leading-edge thickness and slower turbine speeds) to minimize the probability and impact of blade strike.

An important environmental issue facing the marine and hydrokinetic energy industry is whether fish that encounter underwater energy devices are likely to be struck and injured by moving components, primarily rotating turbine blades. The automated analysis of nearly 3 weeks of multibeam hydroacoustics data identified about 35,000 tracks of fish passing a tidal turbine in the East River, New York. These tracks included both individual fish and schools during periods with the turbine absent, the turbine present and operating, and the turbine present but not operating. The density of fish in the sampled area when the turbine was absent was roughly twice the density observed when the turbine was in place, particularly when the turbine was operating. This suggests that some avoidance occurred before fish were close enough to the turbine to be observed by the hydroacoustics system. Various measures of swimming behavior (direction, velocity, and linearity) were calculated for each track and evaluated for indication of behavioral responses to turbine presence and operation. Fish tracks were grouped based on tidal cycle, current velocity, and swimming direction and were evaluated with respect to turbine presence and operation and with respect to distance from the turbine. Nonparametric tests (Kolmogorov–Smirnov test) and multivariate analysis (canonical discriminant analysis) found significant differences among groups with respect to turbine presence and operation, suggesting that some fish responded to the turbine by adjusting swimming behavior, such as making small adjustments to swimming direction and velocity as they passed near the turbine. We found no evidence that fish were being struck by rotating blades, but there did appear to be large‐scale avoidance initiated out of the range of the hydroacoustics detection system. More study is needed to determine whether such avoidance behavior has significant ramifications for normal fish movement patterns, bioenergetics, seasonal migrations, and predator exposure.Received October 28, 2016; accepted May 29, 2017 Published online August 2, 2017

Emissions of CO₂ and CH₄ from freshwater reservoirs constitute a globally significant source of atmospheric greenhouse gases (GHGs), but knowledge gaps remain with regard to spatiotemporal drivers of emissions. We document the spatial and seasonal variation in surface diffusion of CO₂ and CH₄ from Douglas Lake, a hydropower reservoir in Tennessee, USA. Monthly estimates across 13 reservoir sites from January to November 2010 indicated that surface diffusions ranged from 236 to 18,806 mg·m⁻²·day⁻¹ for CO₂ and 0 to 0.95 mg·m⁻²·day⁻¹ for CH₄. Next, we developed statistical models using spatial and physicochemical variables to predict surface diffusions of CO₂ and CH₄. Models explained 22.7% and 20.9% of the variation in CO₂ and CH₄ diffusions respectively, and identified pH, temperature, dissolved oxygen, and Julian day as the most informative predictors. These findings provide baseline estimates of GHG emissions from a reservoir in eastern temperate North America, a region for which estimates of reservoir GHGs emissions are limited. Our statistical models effectively characterized non-linear and threshold relationships between physicochemical predictors and GHG emissions. Further refinement of such modeling approaches will aid in predicting current GHG emissions from unsampled reservoirs and forecasting future GHG emissions.

During August–September 2012, we sampled six hydropower reservoirs in southeastern United States for CO₂ and CH₄ emissions via three pathways: diffusive emissions from water surface; ebullition in the water column; and losses from dam tailwaters during power generation. Estimates of average areal emission rates of CO₂ attributable to the six reservoirs (i.e., reservoir plus tailwater emissions) ranged from 994 to 2760 mg·m⁻²·day⁻¹, which is low to moderate compared to CO₂ emissions rates reported for tropical hydropower reservoirs and boreal ponds and lakes, and similar to rates reported for other temperate reservoirs. Similar average rates for CH₄ were also relatively low, ranging from 6 to 187 mg·m⁻²·day⁻¹. On a whole-reservoir basis, estimates of total emissions of CO₂ ranged 10-fold, from 42,740 kg per day for Fontana to 501,151 kg per day for Guntersville, and total emissions of CH₄ ranged over 30-fold, from 251 kg per day for Fontana to 9153 kg per day for Allatoona. Emissions through the tailwater pathway varied among reservoirs, comprising from 19% to 65% of total CO₂ emissions and 0% to 84% of CH₄ emissions, depending on the reservoir. Emission rates were significantly correlated with several reservoir morphological and water quality characteristics, including metrics related to vertical stratification (e.g., minimum water column temperature and maximum dissolved oxygen) and reservoir productivity (e.g., water transparency and chlorophyll a concentration).

Hydrokinetic energy is proposed as an environmentally preferred means of generating electricity from river and tidal currents. To resolve environmental concerns, it is important to investigate potential effects on aquatic organisms from the electromagnetic fields (EMFs) that are created by underwater generators and transmission cables. We evaluated the behavioral responses of some representative freshwater fishes to static and variable EMFs in a series of laboratory experiments. Fish were exposed for 46 h to a static (DC) EMF with a permanent bar magnet or to a variable (AC) EMF with an electromagnet. Fish locations were recorded with a digital imaging system, and changes in activity level and distribution relative to the magnet position were quantified at 5‐min intervals. Experiments with Fathead Minnow Pimephales promelas, Redear Sunfish Lepomis microlophus, Striped Bass Morone saxatilis, Lake Sturgeon Acipenser fulvescens, and Channel Catfish Ictalurus punctatus produced mixed results. Except for Fathead Minnow, there was no effect on fish activity level. Only Redear Sunfish and Channel Catfish exhibited a change in distribution relative to the position of the magnet, with both species showing an apparent attraction to the EMF source. In a separate experiment, rapid behavioral responses of Paddlefish Polyodon spathula and Lake Sturgeon to the onset of an AC field were recorded with high‐speed video. Paddlefish did not react to a variable, 60‐Hz magnetic field (i.e., like that emitted by an AC generator or cable), but Lake Sturgeon consistently responded with a variety of altered swimming behaviors. These results will be useful for positioning cables or generators to minimize interactions with EMF‐sensitive species.