Biosolids Monitoring Project, King County - DNRP

Biosolids, the nutrient-rich solid or semi-solid by-product of wastewater treatment, have been used as a soil amendment to promote tree growth in Hancock’s Snoqualmie Forest and the Marckworth Forest since 1987. A benthic macroinvertebrate monitoring program that included annual collection of macroinvertebrate samples was developed to evaluate biotic integrity of streams in these forest areas. Benthic macroinvertebrate sampling was conducted annually between the last week of August and the second week of October at up to ten sites on seven streams from 1996 to 2006.

Macroinvertebrates were collected following the recommended sampling protocols outlined by Karr and Chu (1999) and summarized here. At each location, a Surber sampler (500 micron mesh, 1 sq ft frame) was used to collect three replicate samples along the midline of a single riffle starting first with the downstream end, then the middle, and finally near the upstream end. All large materials (e.g., large gravel and large wood) within the sampling area were scrubbed by hand and examined before being placed downstream. A “weed tool” was used to vigorously agitate the substrate within the perimeter of the frame to a depth of approximately 10 cm, for 60 seconds. Each sample was condensed and transferred to a sample container and preserved in the field with 90-95% ethanol (EtOH). Samples were then sent to a private lab for taxonomic identification. Each sample was processed and taxonomically identified separately without compositing. Chironomids were identified to family level; other taxa were identified to the lowest practical level.

Contact: Jo Wilhelm, King County DNRP, jo.wilhelm@kingcounty.gov, 206.477.4849