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You are here:   Home → Natural Environment → Stream Health Based on Benthic Index of Biotic Integrity
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Indicator: Stream Health Based on Benthic Index of Biotic Integrity

Figure 2. Land Use in Sampled Sub-basins

Figure 1. Proportion of Sub-basins ranked as "good", "fair", "poor", or "very poor".

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Upstream Indicators
  •   Urbanization and Impervious Surface Changes --- The number of acres of urban land, clear-cut, and regenerating forest have increased in King County since 1986. Acres of grass and deciduous, mixed and coniferous forest have decreased. Acres of rural forests and privately owned working forests have declined in recent years  (view data graph)
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Downstream Indicators

There are currently no published Downstream Indicators.

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Sustainability Snapshot:

We tend to gravitate toward charismatic animals such as bears or wolves, or even slippery ones like salmon, in telling stories. But when it comes to measuring environmental impacts, it's the smaller, less visible creatures that often tell the best story. The Benthic Index of Biological Integrity, or B-IBI, is often used as a "report card" for measuring the health of the benthic bug community and for stream ecosystem as a whole. Bugs play a crucial role in the stream nutrient cycle. If bug populations are suffering it will affect the whole ecosystem. The presence or absence of pollution tolerant and intolerant bug types can also indicate the condition of the stream. As many bug life cycles are short (sometimes one season in length), their numbers are useful in detecting population fluctuations in a short period of time.

Sustainability Trend:

Baseline data collected in 2002 and 2003. Insufficient data is available for determining a sustainability trend at this time.

Data Discussion

The Indicator Defined

An B-IBI, or Benthic Index of Biotic Integrity, is composed of ten metrics, including the diversity of bug species, number of bugs, presence of bugs that are tolerant and intolerant to pollution, reproductive strategy, feeding ecology, and population structure.

Data Interpretation/Evaluation

Baseline studies on resident benthic macroinvertebrate communities in King County streams were conducted by the King County Water and Land Resources Division (WLRD) in 2002 and 2003 using the Benthic Index of Biotic Integrity (B-IBI).  King  County plans to use the results of these and anticipated future analyses to monitor change in regional aquatic ecosystem health.

Data were collected from a total of 130 sites in 20 sub-basins in the Green-Duwamish River and Greater Lake Washington watersheds during 2003.  Sites were ranked as "good" (B-IBI score 38 to 44), "fair" (B-IBI score 28 to 36), "poor" (B-IBI score 18 to 26) or "very poor" (B-IBI score 10 to 16).

Of the 20 sub-basins sampled, only four - Deep and Coal Creeks, Issaquah Creek, and Lower Cedar River Tributaries - contained stations which were ranked as "good" (Figure 1).  B-IBI scores for most or all of the stations sampled in the North and Swamp creeks, West Lake Washington Tributaries, and Duwamish River Tributary subbasins were ranked as “very poor”.  Most other sampled sub-basins contained a mixture of stations ranked as “fair”, “poor”, and “very poor”. B-IBI scores were significantly correlated with land use, in particular the degree of urbanization in sampled areas. B-IBI scores increased as the amount of forest and scrub/shrub in a watershed increased, and decreased with the amount of developed land (i.e., bare ground, asphalt, concrete) in the watershed (Figure 2).

No significant changes in biological conditions were found between the 2002 and 2003 monitoring in any measured parameter, except in the Evans and Jenkins Creek sub-basins, where biological conditions declined, and in the Mill Creek sub-basin, where biological conditions improved. These areas will continue to be monitored closely to determine if a trend exists. 

Data Source and Limitations

All data including figures from:
EVS Environmental Consultants.  2005.  Benthic Macroinvertebrate Study of the Greater Lake Washington and Green-Duwamish River Watersheds Year 2003 Data Analysis.  Prepared for King County Department of Natural Resources and Parks, Water and Land Resources Division. Available online at http://dnr.metrokc.gov/wlr/waterres/Bugs/data.htm.

Data are from the 2003 monitoring year and may be somewhat out-of-date. 


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