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Effects of single and terraced beaver ponds on benthic macroinvertebrate communities

Authors: Stone, N. R.
Mentors: Bobbi Peckarsky, Angus McIntosh, Matt Fuller
Year: 2007
Publisher: UNKNOWN
Keywords: BENTHIC MACROINVERTEBRATES, INVERTEBRATES, BEAVER POND, IMPOUNDMENT, POND MORPHOLOGY

Abstract

Beavers are an important aspect of the landscape and have been increasing in abundance in montane regions of the western U.S. While beaver impoundments have been shown to affect downstream habitats, their influence is variable and may be attributed in part to variation in the morphology of impoundments. The purpose of this study was to estimate the effects of terraced and single beaver ponds on benthic macroinvertebrate functional feeding group composition and to test some potential mechanisms explaining differences between the two types of ponds. I took 30-s traveling kick samples of invertebrates and measured water chemistry, periphyton chlorophyll, seston AFDM, seston chlorophyll, and substrate particle size composition and installed Hobo continuous temperature and light recorders upstream and downstream of 6 beaver pond complexes (3 single and 3 terraced) in 2 montane catchments of the upper Gunnison River basin in western Colorado during summer 2007. Grazing invertebrates decreased in abundance downstream of single ponds, but increased downstream of terraced ponds, while suspension feeding invertebrates increased downstream of terraced ponds. There were too few shredders in these systems to test the effects of pond morphology on their abundance. Potential mechanisms for effects included increased ambient conductivity associated with higher grazer abundances, which could have caused higher primary productivity. Neither ammonium levels nor AFDM of seston explained abundance differences of grazers or suspension feeders upstream or downstream of impoundments. Water temperatures, phosphorus levels and chlorophyll in the periphyton and seston remain as viable hypotheses that will be tested when the data are completely analyzed. This study shows that beaver pond morphology should be taken into account when studying effects on stream ecosystems.

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