Retention, Movement, and the Biotic Response To Large Woody Debris in the Channelized Missouri River

Authors

Michael W. Archer, University of Nebraska at LincolnFollow

Date of this Version

2010

Comments

A Thesis Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Natural Resource Sciences, Under the Supervision of Professor Mark A. Pegg. Lincoln, Nebraska: December 2009
Copyright (c) 2009 Michael W. Archer

Abstract

Large woody debris (LWD) is an important component of a healthy aquatic ecosystem. However, little is known about the dynamics of LWD in a large, channelized river such as the Missouri River. My objectives were to first, assess the abundance of LWD found along the channelized portion of the Missouri River. Second, I documented movement of LWD that entered the river. Lastly, using PRIMER software I analyzed what effect, if any, river segments, bend types, and LWD had on the community composition of the macroinvertebrate and fish that inhabit the river. Abundance of LWD was greater along bends that have flow diverted away from the bank compared to bends that had recent modifications to divert flow to the shore (major modification bends) and areas with little bank armoring, such as, side channel chutes (P<0.05). Recruitment of LWD into the river that could become available as aquatic habitat occurred mostly within 5 m of the bankfull width (BFW). Telemetry analysis of LWD showed that LWD located within the BFW of the river was often (63% of LWD) displaced downstream. Minimum distance of displaced LWD was 0.02 rkm, median distance was 146.50 rkm, and maximum distance was 1454.69 rkm. No differences were found in the community composition of macroinvertebrates between segments (P=0.43) or between bend types (0.074). Community composition did differ between LWD and non-LWD sites (P=0.016). Fish communities differed between the segments (P=0.043) therefore further analyses were split between the segments. Segment 8 fish communities did not differ between bend types (P=0.35) or between LWD and non-LWD sites (P=0.55). Results were similar in Segment 9 (bend types (P=0.20), LWD and non-LWD sites (P=0.19)). Combining the macroinvertebrate communities and fish communities to test for differences in the combined biota community composition showed that differences did not exist between the segments (P=0.59) or bend types (p=0.29). However, the composition of the composite community was different between LWD and non-LWD sites (P=0.011). My results suggest that while retention of LWD is low it still has an effect on the composition of the composite communities that inhabit the Missouri River.