Basics
Healthy Water Quality
Freshwater Quality
Indicator
Benthic Index of Biotic Integrity
Vital Sign Indicator
Each Unit (number)
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1. Protect: 100 percent of Puget Sound lowland stream drainage areas ranked as excellent retain excellent scores for the Benthic Index of Biotic Integrity for biological condition.

2. Restore: Improve and restore at least 30 streams ranked fair so their scores become good. 

Kate Macneale
Contributing Partners
Last Updated
12/31/2020 9:30:12 AM
Map
Biological condition of stream sites throughout Puget Sound as measured by the B-IBI. The map reflects data from the most recent sample collected at each stream site since 2006.
Description
The Benthic Index of Biotic Integrity (B-IBI) describes the biological condition of stream sites and their surrounding habitat based on the diversity and relative abundance of the benthic (bottom dwelling) macroinvertebrates found at the site. Ten measures of biological condition are scored and summarized as the B-IBI, which ranges from a score of 0, indicating very poor stream condition, to 100, indicating excellent condition.
Vital Sign Indicator Chart
Benthic Index of Biotic Integrity
By: Change in Biological Condition
Change in the biological condition of Puget Sound streams, based on the B-IBI, that were classified as "excellent" and "fair" in 2006-2009 and resampled in 2016-2019. Source: Puget Sound Stream Benthos.

Stream-dwelling organisms are a useful indicator of water quality and can help describe the biological condition of stream sites and the surrounding habitat. Macroinvertebrates vary in their tolerance to environmental stressors; some are quite sensitive and cannot thrive outside pristine environments, while others are tolerant of change. Thus, the abundance and types of macroinvertebrates found in a stream reflects the overall stream condition.

Key Vital Sign Indicator Results
  • The condition of stream sites throughout Puget Sound is fairly evenly distributed over the five B-IBI biological condition categories based on the most recent sample collected since 2006. Most sites were in good (26%) or fair (25%) condition, and an additional 16% of sites were in excellent condition. Unfortunately, the remaining one-third of sites were in either poor (16%) or very poor (17%) condition.
  • Progress toward the 2020 recovery targets was mixed based on the comparison of B-IBI scores for sites that were sampled in both 2006-2009 and 2016-2019. Overall, biological condition at some sites is declining, improving at others, and not changing at most.
  • Since the 2006-2009 time period, the B-IBI scores of some streams have dropped from “excellent” to “good”, indicating that not all of the “excellent” sites have remained in excellent condition. In contrast, there has been net improvement in the biological condition of streams previously ranked “fair” by the B-IBI.
  • The B-IBI is correlated with land use conversion and urbanization and scores tend to be lower in areas with greater urban development.
Methods
Monitoring Program

King County Benthic Index of Biotic Integrity for King County Streams

Washington State Department of Ecology Stream Biological Monitoring

Data Source

Puget Sound Stream Benthos

The Benthic Index of Biotic Integrity (B-IBI) monitors the diversity and relative abundance of the benthic (bottom dwelling) macroinvertebrates found in Puget Sound streams. These macroinvertebrates include aquatic insect larvae, including mayflies, stoneflies, caddisflies, beetles, flies, dragonflies, as well as other invertebrates such as worms, snails, and many others. The B-IBI combines ten measures of stream biology, such as taxa diversity and the presence of invertebrates that are tolerant and intolerant to pollution. The ten measures are scored and summarized as the B-IBI, which ranges from a value of 0, indicating very poor stream condition, to 100, indicating excellent condition. See the Puget Sound Stream Benthos B-IBI page for a description of the five biological condition categories used to describe ranges of B-IBI scores.

B-IBI data are routinely collected and reported by more than 20 local jurisdictions, tribes, and other state and federal organizations in Puget Sound for a variety of reasons. For instance, the Washington Department of Ecology samples 50 randomly selected stream and river sites every four years to get an unbiased estimate of regional conditions. Counties, cities, tribes and citizen groups also sample stream sites throughout Puget Sound to characterize the status and trends in stream condition.

Change over time for this update is calculated as the difference in scores at a subset of sites that were sampled at least once during 2006-2009 and then at least once again between 2016-2019. There were 219 sites across Puget Sound that were sampled at least once during both of these time periods. If a site was sampled more than once during each time period, the average score is calculated for that period.

Critical Definitions

Benthic refers to organisms found on, among, or within the bottom of a body of water. 

Interpretation of Results

Of the 83 Puget Sound stream sites that scored “excellent” between 2006 and 2009, 17 were sampled again between 2016 and 2019. Of these, 82% (14 sites) maintained their excellent ranking. However, 9 streams that had previously been ranked as good have improved to excellent. Therefore, while this indicator is not meeting the protection target to retain 100% of excellent scores, there are other sites where conditions have improved and are now classified as excellent. This has resulted in a net increase in the number of excellent sites between the two time periods.

Of the 172 stream sites that scored “fair” between 2006 and 2009, 50 were sampled again between 2016 and 2019. Over half of these sites remained fair over this period, but for the sites that did change, more stream sites improved (14 sites) than declined (7 sites).

Overall, when considering sites sampled in the two time periods, more sites improved than declined. The number of sites that scored fair, good, or excellent, improved over time, whereas the number of sites that scored very poor or poor declined (figure below).

The positive trends in site condition seen between these two time periods are consistent with trends observed at 125 sites that have been sampled more than 10 times since 2002. Recent analysis of trendlines from these sites indicates 37 sites are improving significantly, while no sites are declining significantly.

Comparison between two time periods (2006-2009 and 2016-2019) of the biological condition of streams in Puget Sound, based on the B-IBI. Source: Puget Sound Stream Benthos

Macroinvertebrate communities are impacted by a variety of stressors that are associated with land use conversion and urbanization, including but not limited to excessive fine sediment, contaminants in stormwater runoff, loss of riparian vegetation and scouring high flows. Thus, improvements in B-IBI scores are presumably due to reductions in these environmental stressors, however, it is difficult to point to specific actions. Since 2006, land use conversion has continued and urbanization has intensified, and yet macroinvertebrate communities appear to be recovering in many streams across the region. Studies are underway to fully understand how conditions have been improved over time, and whether credit can be given to changes in stormwater best management practices and stream and riparian restoration.

The Stormwater Strategic Initiative recently released the Freshwater Quality B-IBI Implementation Strategy which aims to improve water quality through integrated watershed planning and capacity building. The report outlines a series of actions, approaches, and interim results that are meant to reverse some of the impacts changes in land use have had on rivers and streams throughout the Puget Sound.

The "Restoration and Protection of Select Puget Lowland Stream Basins” project is a phased effort aiming to restore and protect streams throughout Puget Sound. The Stressor Identification and Recommended Actions for Restoring and Protecting Select Puget Lowland Stream Basins report is the second of five phases. The goal of this phase is to identify human activities that are impacting a select group of streams and recommend actions to facilitate restoration and protection within the stream basins.

Datasets

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Reporting Guidance
Reporting Instructions
Subcategories
Name
Change in Biological Condition
Improved, No Change, Declined