How Do Fine Sediments and Hangman Creek Discharge Affect Benthic Macroinvertebrates in the Spokane River?
Date
2019-06-27
Authors
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Eastern Washington University
Abstract
One of the most common causes of stream degradation globally is fine sediment
deposition. Most fine sediment deposition in stream beds is generated by land use
practices such as timber harvest, agriculture and urbanization. Hangman Creek is a major
tributary and source of fine sediment to the Spokane River. Benthic macroinvertebrates
play a crucial function in food webs as an important source of food for many stream
predators, including fish. Also, benthic invertebrates are effective indicators of the
ecological condition of rivers, including those that are adversely affected by fine
sediments. This study investigated the effects of fine sediments on Spokane River
macroinvertebrates. I sampled macroinvertebrate communities from 3 substrate types
with different levels of fine sediment (sand, 0 - 25% embedded cobbles, and 75-100 %
embedded cobbles) in the Spokane River upstream and downstream of its confluence and
in Hangman Creek. Water temperature, flow velocity, and depth were also measured.
Hangman Creek tended to be warmer and shallower than the Spokane River. The three
most common invertebrates in the Spokane River were Chironomidae, Baetis, and
Hydropsyche. The three most common invertebrates in Hangman Creek were
Chironomidae, Leptohyphidae and Hydropsyche. In early summer 2018, the substrates significantly affected the density of
macroinvertebrates; family richness for Ephemeroptera, Plecoptera, and Trichoptera
(EPT); proportion EPT; proportion clinger functional group; and the proportion of the
dominant taxon. Family richness for all taxa; Evenness; Shannon-Weaver diversity;
Hilsenhoff Family Biotic Index (HFBI); and Biological Sediment Tolerance Index
(BSTI) were not affected. In late summer 2018, substrate significantly affected only the
density of macroinvertebrates. Overall, the results suggest that areas with fine sediment
were ecologically impaired compared to unembedded cobbles. However, not all
indicators responded as expected. There was no evidence for the effects of fine sediment
to increase through the summer, or of significant ecological degradation in the Spokane
River directly below the confluence with Hangman Creek. This work will contribute to
our understanding of the biotic effects of fine sediment in the Spokane River.
Description
Keywords
Sedimentation, Macroinvertebrates, Spokane River