Longitudinal patterns in riverine ecology within and among seven Pacific Northwest rivers: Implications for river research, monitoring and management

Abstract

AbstractRivers vary because of their different geographic settings and their differing levels of anthropogenic disturbances. Relative to wadeable streams, boatable or raftable rivers are much less studied because they require more expensive gear and are more dangerous to sample. Because of the importance of Pacific Northwest rivers for water supply, recreation, and endangered fish species, we selected seven rivers of interest to state, tribal, or federal agencies. Our objectives were to determine the degree to which fish and macroinvertebrate assemblages varied with water quality, habitat structure, and distance along each river, as well as the degree to which each river differed from the others. We sampled the rivers by inflatable rafts and assessed spatial patterns in fish and macroinvertebrate assemblages as well as water quality and physical habitat structure at 20 sites spread out longitudinally along each river. By analyzing site‐to‐site similarity matrices for fish, macroinvertebrates, chemistry, habitat, and river distance, we found that water quality‐river distance relationships were relatively strong, but habitat structure‐distance relationships were usually weak or absent. Also, site‐to‐site similarity in water quality was unrelated to the site‐to‐site similarity in habitat structure. Among‐river variability was much greater than within‐river variability for both fish and macroinvertebrate assemblages. We observed very different patterns among the seven rivers regarding the importance of distance, water quality, and physical habitat similarities relative to fish and macroinvertebrate assemblage similarities. The best set of environmental variables for distinguishing biotic assemblage similarities varied widely among rivers, and among the two assemblage types. We conclude that the riverscape concept is valuable for river monitoring, research, and management, as well as the value of rigorously sampling both water quality and physical habitat as well as both fish and macroinvertebrate assemblages.