Stream Biomonitoring


Caddis flies emerging from casings

Two Year Experimental Stream Macroinvertebrate Monitoring

In 1999, the City completed an experimental stream monitoring pilot program to collect and analyze information on the condition of streams in the watershed. The pilot study design involved three main areas of data collection: hydrology, water quality, and benthic macroinvertebrate communities (biomonitoring). The results of the pilot study were used as baseline stream conditions for long-term monitoring and HCP aquatic project monitoring. They also provided an overview of and help in identifying and prioritizing sites for restoration.

The use of benthic macroinvertebrate data as a monitoring tool was evaluated through the development of a calibrated Benthic Index of Biological Integrity (BIBI). The BIBI shows indicators and reflectors of natural and anthropogenic disturbances in the environment, and has been used successfully as a measure of stream health throughout much of the developed Puget Sound region.

The pilot study attempted for the first time to use the BIBI in a low impacted forested environment in the Pacific Northwest from 45 sites in 1995 and 39 sites in 1996. The study was able to develop a BIBI score for small (1-3 order), high elevation (greater than 3,000 ft) streams. The study was not able to develop a BIBI score for small, low elevation (less than 3,000 ft.) and larger streams and rivers (4-6 order). The Cedar River at the Landsburg facility is a sixth order river. One of the most interesting results of the study was the significantly different BIBI scores between 1995 and 2005 without any anthropogenic disturbances.

Assessment of Stream Biomonitoring Approaches

In an effort to understand the differences in the BIBI scores from the Two-Year Experimental Stream Monitoring Study and to provide the City of Seattle and other biomonitoring efforts in the region with a potentially more sensitive monitoring tool, a second study was conducted in 2005.

The objectives of this study were to examine the yearly trends in 1) BIBI scores across this relatively undisturbed watershed, 2) the observed to expected ratio for the River Invertebrate Prediction and Classification (RIVPAC) biomonitoring system, and 3) the mean taxonomic-distinctness value, which evaluates average invertebrate community complexity within the river. The study also included a recommendation for the most appropriate biomonitoring methods for a low impact watershed.

As expected, BIBI, RIVPAC, and the taxonomic-distinctness values for sites in the Cedar River watershed were higher than those of the urban sites for all three biomonitoring scores. The results of the study also shows that traditional BIBI biomonitoring in low impact streams may be misleading because of large fluctuations in annual factors such as rainfall and storm flows and not because of human factors. The use of other monitoring techniques like RIVPACS or mean taxonomic-distinctness may provide additional evidence in addition to BIBI scores to the overall condition of low impacted streams.

Results of this study will be used to design future biomonitoring. One possibility recommended by the study is to sample at 20 sites using BIBI and RIVPACS techniques roughly every five years for the life of the HCP. Other biomonitoring tools may be used in the future when more appropriate techniques are developed for low anthropogenic impacted forested watersheds.