Author(s): Donavan Maude

Presentation: poster

Wildfires are increasing in occurrence and severity throughout much of the intermountain west. Wildfire disturbances influence aquatic macroinvertebrate population dynamics by introducing large amounts of sediments and woody-debris into river systems, increasing channel complexity. This complexity contributes to habitat diversity and allows pioneer species to recolonize an area they may have been previously out competed. Therefore, we expect macroinvertebrate populations to differ in streams with different fire histories. Within sites, we expect macroinvertebrate populations to differ upstream and downstream of debris inputs. To test this we investigated the connection between stream complexity, aquatic macroinvertebrate abundance, and time since fire in three sub-basins (Rapid River, Pistol, Mayfield Creeks) of the Middle Fork of the Salmon River, Idaho. These tributaries provide spawning area for Chinook salmon (Oncorhyncus tshawytscha) and steelhead (Oncorhyncus mykiss). Organisms were sampled in triplicate at riffles, every 100 meters of our reaches. Channel geometry metrics (width, depth, slope) were surveyed with a Leica TS09 total-station and substrate size determined by using a Wolman pebble-count. Initial results showed macroinvertebrate abundance and stream complexity differing between sites (p<0.01;ANOVA). Current investigation focuses on variability as it relates to debris flows within each reach; comparing the macroinvertebrate abundance above and below the debris flow inputs.

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