Tuesday, May 27, 2008 - 11:30 AM
162

Macroinvertebrate Drift Distance during Summer Low Flow in Headwater Tributaries of the Calapooia River

Robert J. Danehy and Russell B. Langshaw. Environmental Forestry, Weyerhaeuser Company, 785 North 42nd St., Springfield, OR 97478

We examined the abundance, biomass, and composition of macroinvertebrate drift in headwater tributaries of the Calapooia watershed in Oregon during summer low flow. We tested how far macroinvertebrates were drifting by blocking drift in 3 of 8 headwaters. The treated sites had invertebrate drift blocked (250 micron mesh) 100 m upstream of our sample nets for 48 days. Samples were collected in three approximately two week intervals after the initial samples. Overall mean abundance and overall mean biomass of drift did not differ between treatments, p = 0.345 and p = 0.821 respectively. There was a temporal trend of declining abundance (p = 0.001) and biomass (p = <0.001), even with data standardized to amount per m3 of discharge. Tests among major insect orders, which accounted for 74% of the drift abundance and 66% of biomass, showed no treatment differences. The same was true for 16 common genera that comprised at least 1% of the total sample. Temporal changes of both individual orders and genera were variable. We conclude that during low flow conditions in headwater streams drift distance is less than 100 m and of local origin.


Web Page: macroinvertebrate drift, baseflow, distance

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