Catchment topography and wetland geomorphology drive macroinvertebrate community structure and juvenile salmonid distributions in south-central Alaska headwater streams

Abstract

Abstract. Conservation and management of headwater streams amid rapid global change require an understanding of the spatial and environmental factors that drive species distributions and associated ecosystem processes. We used a hierarchical analytical framework to model effects of catchment-scale topography and wetland geomorphic classes on stream physical habitat, chemistry, and macroinvertebrate and fish communities in 30 headwater streams across the Kenai Lowlands, southcentral Alaska, USA. We identified 135 macroinvertebrate taxa, 122 of which were aquatic insects, of which 79 were dipterans. We collected only 6 species of fish, but juvenile coho salmon and Dolly Varden were collected in 17 and 25 of the 30 streams and reached densities >500 and 1300/km, respectively. Flow-weighted slope, an indicator of water residence time and gradient, was the best catchment-scale correlate of macroinvertebrate and fish community structure, and its effect was mediated by wetland geomorphic classes and numerous wa...