Puget Sound Stream Benthos

Vashon Project, King County - DNRP

King County Water and Land Resources Division collects annual benthic macroinvertebrate samples from three locations on Vashon Island. These sites (Shingle Mill, Judd, and Christensen Creeks) are strategically selected as representative streams for Vashon Island. Because of its island geography and unique hydrology, these indicator streams provide valuable data to track the overall health of Vashon Island’s major streams.

Sample collection methods are based on the recommended sampling protocols outlined by Karr and Chu (1999) with some minor modifications. At each location, a Surber sampler (500 micron mesh, 1 sq ft frame) is used to collect eight samples. With this method, two samples are taken from 4 different riffles starting downstream and working upstream to get a total sample size of 8 square feet. Prior to 2012, the protocol was to sample 1 square feet in 3 separate riffles for a total sample size of 3 square feet. Changing to the 8 square foot protocol provides a more representative sample of the overall benthic community, and also allows us to coordinate our methods with other agencies.

All large materials (e.g., large gravel and large wood) within the one square foot sampling area are washed clean of any invertebrates or detritus into the Surber net. A “weed tool” is used to vigorously agitate the substrate within the perimeter of the Surber frame to a depth of approximately 10 cm, for 60 seconds. The eight composited samples are then condensed and transferred to a sample container and preserved in the field with 90-95% ethanol (EtOH). Samples are then sent to a private lab for taxonomic identification. Chironomids are identified to family level; other taxa are identified to the lowest practical level. Sampling is conducted annually between early August and mid September, if possible. QC replicates are sampled at 10% of locations annually to address intra-site variability.

Contact Person: Jo Wilhelm, jo.wilhelm@kingcounty.gov; 206-477-4849 or Deb Lester, deborah.lester@kingcounty.gov, 206-477-4752

General macroinvertebrate information: http://www.kingcounty.gov/environment/data-and-trends/monitoring-data/stream-bugs.aspx

Reports and Sampling and Analysis plans: http://www.kingcounty.gov/environment/data-and-trends/monitoring-data/stream-bugs/stream-data.aspx