The Effectiveness of Forested and Hedgerow Riparian Buffers for Buffering Water Temperature and Improving Fish Habitat in…

Riparian restoration is a component of nearly every salmon recovery strategy. In the lowlands of the Nooksack River flood plain in Western Washington State, planted riparian buffers in agricultural landscapes must perform multiple functions to improve water quality and fish habitat while still allowing access to agricultural land use. Relatively narrow, 15 feet (4.6 meter) wide buffers, are a more palatable option for landowners than 35 feet (10.7 meters) which is required to be considered for cost incentive programs such as the Conservation Reserve Enhancement Program (CREP). We wanted to discover whether these two relatively narrow buffer widths would result in detectable differences in the effectiveness of water temperature maintenance (reduction from upstream to downstream warming via % effective shade) and differences in fish assemblage abundance. Results from this research conducted in 2014-2015 indicate that in 100-m long reaches, narrow, 15-ft-wide buffers provide similar amounts of shade as wider, 35-ft- wide buffers, but differences in upstream and downstream water temperature in terms of heat units were inconclusive. Heat units were expressed as the daily cumulative degrees above 17.5 degreesC relative to the number of temperature readings each day (Biologically Sensitive Heat Units). This excluded several sites from analysis that never reached temperatures above 17.5 degreesC and temperature maintenance at the remaining sites were highly variable. Differences in width was not a significant factor detecting differences in relative abundances of fish communities, but the 15' and 35' sites had greater species diversity and greater abundances of native coldwater species, such as coho salmon and cutthroat trout, than the sites without buffers.