Macroinvertebrate Monitoring of Redmond and Blakely Ridge Ephemeral Streams

Abstract

Since the early 1980’s biological monitoring has developed as a reliable tool for the assessment of stream and watershed health in an ecological context broader than traditional chemical and habitat assessment. In late May of 1991, macroinvertebrate samples were collected from 6 streams and 2 wetlands in the proposed Blakely and Redmond Ridge development projects (UPD) as a biological component of the project monitoring plan. The 1991 collections were intended to represent a pre-development, biological baseline upon which future monitoring efforts could be based. In an attempt to evaluate the streams using the benthic index of biological integrity (B-IBI), macroinvertebrates were again collected in late September 1997 from 5 streams sites and in late September 1998 from 1 stream in the development area. The researchers found the study streams were variably ephemeral and thus not appropriate for use in a standard Fall analysis using Puget Sound lowland B-IBI. To address the ephemeral streams dilemma, a project was undertaken to determine a period of time during which the UPD streams could be sampled and evaluated using macroinvertebrates. Following the methods outlined in Karr and Chu (1999), samples were to be taken at two week intervals beginning in late May on 7 small streams draining the development area. Sampling would be halted when stream dewatering inhibited sampling efforts. The set of samples taken two weeks prior to the early drying of streams would then be analyzed to represent the macroinvertebrate fauna present during the latest appropriate time for sampling the ephemeral streams and the response of that fauna to varying levels of human impact on the watershed. The spring and summer 1999 macroinvertebrate assessment effort and lessons from the study will be described in this report.Xerces Societ