Abiotic and biotic impacts below impoundments within the context of the River Continuum (RCC) and the Serial Discontinuity Concepts (SDC) have been the focus of many lotic studies. Recovery gradients, however, are rarely examined in sufficient detail below dams. Further refinement and understanding are needed to inform science and river managers about regulated river ecology. In this study, we examine longitudinal patterns in abiotic and biotic characteristics in two regulated rivers in Northern Canada. We also examine spatial patterns on two natural rivers: a lake outlet river and a river with no lakes. Direct gradient analysis revealed that increases in periphyton, planktonic drift, primary production, substrate size, and changes in thermal regime at sites closest to the dam drive benthic invertebrate community characteristics. We test the Serial Discontinuity Concept by comparing predicted functional forms of each environmental variable with the empirically derived forms. Substrate size, periphyton biomass, and drift density increased below dams and recovered quickly within 5 km downstream, following closely with SDC predictions. The response of organic matter and water quality was variable, and benthic invertebrate richness recovered relatively quickly, contrary to SDC predictions. Thermal regime and flow took much longer to recover than most variables and represent a second longer gradient type below dams. Plecoptera, Gomphidae, and Simuliidae were strongly influenced by altered resource and habitat and may be good candidates for indicators and predictive modelling. Our results generally support predictions from the Serial Discontinuity Concept and highlight the need for the further testing and refinement of this concept.
Freshwater protected areas are rare even though freshwater ecosystems are among the most imperiled in the world. Conservation actions within terrestrial protected areas (TPAs) such as development or resource extraction regulations may spill over to benefit freshwater ecosystems within their boundaries. Using data from 175 lakes across Ontario, Canada, we compared common indicators of fish-assemblage status (i.e., species richness, Shannon diversity index, catch per unit effort, and normalized-length size spectrum slopes) to evaluate whether TPAs benefit lake fish assemblages. Nearest neighbor cluster analysis was used to generate pairs of lakes: inside versus outside, inside versus bordering, and bordering versus outside TPAs based on lake characteristics. The diversity and abundance indicators did not differ significantly across comparisons, but normalized-length size spectrum slopes (NLSS) were significantly steeper in lakes outside parks. The latter indicated assemblage differences (greater abundances of small-bodied species) and less-efficient energy transfer through the trophic levels of assemblages outside parks. Although not significantly different, pollution- and turbidity-tolerant species were more abundant outside parks, whereas 3 of the 4 pollution-intolerant species were more abundant within parks. Twenty-one percent of the difference in slopes was related to higher total dissolved solids concentrations and angling pressure. Our results support the hypothesis that TPAs benefit lake fish assemblages and suggest that NLSS slopes are informative indicators for aquatic protected area evaluations because they represent compositional and functional aspects of communities.
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