Type N Experimental Buffer Treatment Study
Type N describes perennial and seasonal non fish-bearing streams under Washington State’s current stream-typing system. Although physical barriers, higher gradients, and seasonal low flows make Type N streams inaccessible to fish, exports from these relatively small basins are important to downstream fish-bearing waters. In contrast to larger, fish-bearing streams, Type N are more influenced by hill-slope processes. Land use practices in Type N basins streams may have consequences for fish populations downstream, and for stream biota and water quality in the Type N stream itself.
The Forests and Fish Law established forest practice rules that would contribute to the recovery of protected salmonids and other species as well as the enhancement of water quality in streams (FFR 1999, ESHB 2091). Under the rules, Type N streams receive a 50-foot buffer along 50 percent of the perennial stream length, a 50-foot buffer around perennial sensitive areas, and a 30-foot equipment limitation zone along the entire perennial and seasonal stream length. The effectiveness of the buffer prescriptions in protecting aquatic and riparian species and in maintaining water quality, however, has not been tested. The purpose of the Type N Experimental Buffer Treatment Study (Type N study) is to assess the influence of different buffer prescriptions on riparian inputs, stream-associated amphibians, water quality, exports to downstream fish-bearing waters, and fish.
Objective and Purpose
At the time of negotiations determining harvest regulations, almost no published studies existed on the efficacy of buffers for headwater streams or on clear guidance addressing buffer design (Hayes et al. 2005). This study should allow clear conclusions to be drawn in evaluating how logging practices impact resource targets such as amphibians.
Comparison of individual treatments to reference treatments (unharvested basins with comparable type and age of stands) will help determine whether observed changes are attributable to environmental variation or harvest treatment effect.
The critical questions for the Department of Ecology are What are the effects of different buffer treatments on:
Ehinger, W. and S. Estrella. 2007. Quality Assurance Project Plan: Type N Experimental Buffer Treatment Study: Addressing Buffer Effectiveness on Riparian Inputs, Water Quality, and Exports to Fish-Bearing Waters in Basaltic Lithologies. Washington State Department of Ecology, Environmental Assessment Program, Lacey, WA. 28 pp. + appendices. Publication No. 07-03-103. https://fortress.wa.gov/ecy/publications/summarypages/0703103.html
Hayes, M. P., W. J. Ehinger, R. E. Bilby, J. G. MacCracken, R. Palmquist, T. Quinn, D. Schuett-Hames, and A. Storfer. 2005. Study Plan for the Type N Experimental Buffer Treatment Study: Addressing Buffer Effectiveness on Stream-Associated Amphibians, Riparian Inputs and Water Quality, and Exports to and Fish in Downstream (Type F) Waters in Basaltic Lithologies of the Coastal Areas and the South Cascades of Washington State. Report submitted for the State of Washington Forest Practices Board Adaptive Management Program. 68 pp. [15 July].
Lewis, J. 1996. Turbidity-Controlled Suspended Sediment Sampling for Runoff-Event Load Estimation. Water Resources Research 32: 2299-2310
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