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Date Permissions Signed
Date of Award
Master of Science (MS)
Hooper, David U., 1961-
Peterson, Merrill A., 1965-
Matthews, Robin A., 1952-
Sofield, Ruth M.
Stream conservation and restoration strategies often focus on preserving extant riparian forest and restoring riparian habitat. In the Pacific Northwest, these efforts are often directed toward restoring and maintaining habitat that supports salmon populations. Riparian restoration, though beneficial to stream habitat, may not be sufficient to restore functioning stream ecosystems in watersheds heavily altered by intensive land use. To evaluate this hypothesis, I measured the biological condition of streams affected by human activity, and compared reaches with and without limited riparian corridors. I assessed 12 streams in watersheds dominated by different land use (cultivated, developed, forested, grassland) and sampled from reaches with and without riparian forests. This study integrated invertebrate data and abiotic stream parameters collected in 2006 and water nutrients and sediment toxicity collected in 2009-2010. I calculated the percent of individuals (relative abundance) from insect orders Ephemeroptera, Plecoptera, and Trichoptera (%EPT) and assessed specific conductance, dissolved oxygen (DO), temperature, and substrate, water nutrients and sediment toxicity. Relative abundance of intolerant invertebrates was highest in watersheds that most resembled historic forested habitat. Forested watersheds averaged the highest %EPT (23.8) followed by grassland (16.1), cultivated (1.96), and developed (0.31). Riparian forests were not associated with increased %EPT in forested, cultivated or developed watersheds. However, in grassland watersheds, %EPT was ~8-fold higher in forested than non-forested reaches. High values of %EPT were associated with ostensibly good abiotic conditions (i.e., large stream substrate, low specific conductance and temperature), common in forested watersheds. Developed and cultivated watersheds did not follow this pattern. In some cases, %EPT was low despite abiotic conditions similar to forested watersheds, where %EPT was high. While water nutrients were higher in cultivated watersheds, there were no discernable patterns in sediment toxicity, and neither nutrients nor toxicity were correlated with %EPT. These results confirm that intensive land use degrades stream biological communities, and suggest that patchy forested riparian corridors are insufficient to mitigate severe, large-scale biological degradation.
Western Washington University
Subject – LCSH
Stream ecology--Washington (State)--Puget Sound Watershed; Water quality biological assessment--Washington (State)--Puget Sound Watershed; Water quality--Washington (State)--Puget Sound Watershed; Land use--Environmental aspects--Washington (State)--Puget Sound Watershed; Riparian restoration--Washington (State)--Puget Sound Watershed
Puget Sound Watershed (Wash.)
Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Wahl, Colin, "Land use, riparian buffers, and biological stream conditions in the Puget lowlands of Washington" (2012). WWU Graduate School Collection. 213.