The instability of reservoir habitats and its impact on food webs

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The goal of this research is to assess the potential of the unstable physical environment of reservoirs to limit the productivity of their food webs. Reservoirs, although superficially similar to lakes, are engineered systems operated to maximize hydroelectric output or water storage. They tend to be situated in steep-sided basins, have high hydraulic throughput, and experience greater changes in water level than natural lakes. Productivity in natural lakes is driven by three major energy flow pathways, the pelagic, the littoral and the profundal; however in reservoirs the pelagic is generally dominant, and the littoral and the profundal zoobenthic pathways are generally of minor importance due to a combination of draw-down and the deep, steep-sided basins. In addition, water turnover can be sufficiently rapid to limit the development of zooplankton, which are usually absent from the riverine inputs to reservoirs, and lack the swimming ability to resist advective entrainment in the reservoir outflow. The proposal presents models that couple food webs to hydraulic stress, and predict that zooplankton and fish biomass will be lower in high throughput systems. A physical index of littoral stability that combines drawdown and factors that reduce photic zone depth is also presented. This index should be correlated to stable isotope measures of littoral energy flow. The proposed research will also examine the effect of habitat stability on mercury bioaccumulation in fish and invertebrates. In Canada, compliance of hydro-developments to the Canada Fisheries Act is critical to environmental assessment, and fisheries productivity of reservoirs is therefore an important environmental issue. The habitat indices proposed for modeling impacts on trophodynamics, may have useful analogues for modeling other types of ecosystem stresses.