“Chessie BIBI” Index for Streams

Interstate Commission on the Potomac River Basin

Measuring Stream Health

The Chesapeake basin-wide index of biotic integrity for stream macroinvertebrates, or “Chessie BIBI,” is a multi-metric index of biological health for freshwater streams and small, wadeable rivers in the Chesapeake Bay watershed. It is composed of family-level macroinvertebrate metrics (indicators) that discriminate strongly between high quality and degraded stream conditions.

The index was inspired by the Potomac BIBI and conceptualized in a 2008 Chesapeake pilot study. The index was developed in 2011 and updated and refined in 2016-2017 with Chesapeake Bay Program (CBP) support. Data from over 25,000 macroinvertebrate samples collected and counted by state, federal, and local agencies, and citizen groups were merged into a common database structure and used to develop the index. Crucial to the index’s success was the involvement of several technical advisory groups comprised of regional experts and resource managers.

Developing the Index

A map showing stream health within the Chesapeake Bay.

Chessie BIBI (family-level version of the bioregion index) ratings for streams and small rivers in the Chesapeake Bay watershed. When sufficient data (n > 3 catchments) are available, HUC12 watersheds are colored per the rating of their average index score. Otherwise, individual sampling locations are indicated and colored per their ratings.

A suite of metrics was calculated for each macroinvertebrate sample and samples were classified into one of five disturbance categories based on habitat and water quality conditions at the sampling site. Categories ranged from Reference (best quality) to Severely Degraded (poorest quality). Values of the macroinvertebrate metrics at Reference sites were then used as benchmarks against which other sites were scored.

Eight possible constructs for selecting and scoring metrics for the index were examined. The most discriminatory metrics representing key attributes of the community (composition, richness/diversity, pollution tolerance, habit, feeding group) were selected for the index. Bioregion and regional (Inland, Coast) spatial scales were investigated. Metrics keyed to order-, family-, or genus-level attributes were used to build versions of the index for different taxonomic resolutions of the raw counts. Order-level metrics are less sensitive, but they do not require laboratory enumeration and are suited for rapid screening in the field. Family-level metrics generally performed well, and bioregion indices built from scored family-level metrics had classification efficiencies between 70.4% and 90.0%. Bioregion indices built from genus-level metrics performed marginally better than family-level indices in some but not all bioregions.

A common scale of five narrative ratings was applied to the index scores of each taxonomic and spatial version of the Chessie BIBI index. The 50th, 25th, and 10th percentiles of each version’s index scores in Reference conditions were used to define Excellent, Good, Fair, and Poor macroinvertebrate status. A fifth rating, Very Poor, was defined by half the value of the 10th percentile. Ratings from the same taxonomic and spatial version of the index are directly comparable and can be used to estimate percentages of stream in healthy condition across the Chesapeake watershed.

Databases and Analysis Tools

In 2019 and 2020, ICPRB and CBP updated the 2017 dataset with additional data and produced a Chessie BIBI package containing the R-scripts, shape files, spreadsheets, and documentation needed to calculate a suite of metrics and the family-level, bioregion-specific Chessie BIBI from merged datasets of raw macroinvertebrate counts. The open source Rstudio program will be needed to run the R-scripts. The raw data, calculated metrics, and BIBI package are available in the online archive.

Database Versions: As demonstrated in the Chessie BIBI package, repeated runs of the program can produce slightly different index scores and ratings. This is due to the random selection of rare individuals in each program run as a sample is reduced to 100 individuals (rarefaction) in the data normalization step. Minor modifications made in 2019 to the habit assignments of a few macroinvertebrate taxa also changed the index scores and ratings at several stations. The scores and ratings used in the 2017 refinement version are called Version 2.0. Those calculated with the 2019 program from the same raw data are called Version 2.01. The updated database constructed in 2021 is Version 3.01.

Creating a Management Tool

Turning the Chessie BIBI index into an effective tool to track progress towards the CBP Stream Health management goal requires decisions on when and how to use it. At a 2018 workshop, scientists and managers agreed to measure stream health basin-wide with the Chessie BIBI and selected the 6-year period between 2006 and 2011 as the most practical “2008 baseline.”

The Chessie BIBI Timeline

Timeline: Chessie BIBI in Potomac and Chesapeake Assessments

Other ICPRB reports/projects

2017 Chessie BIBI

  • Maloney, K. O., D. M. Carlisle, C. Buchanan, J. L. Rapp, S. H. Austin, M. J. Cashman and J. A. Young. 2021. Linking Altered Flow Regimes to Biological Condition: an Example Using Benthic Macroinvertebrates in Small Streams of the Chesapeake Bay Watershed. https://doi.org/10.1007/s00267-021-01450-5.
  • Maloney, K. O., K. P. Krause, C. Buchanan, L. E. Hay, G. J. McCabe, Z. M. Smith, T. L. Sohl, and J. A. Young. 2020. Disentangling the potential effects of land‐use and climate change on stream conditions. https://doi.org/10.1111/gcb.14961.
  • Maloney, K. O., Z. M. Smith, C. Buchanan, A. Nagel and J. A. Young. 2019. Predicting biological conditions for small headwater streams in the Chesapeake Bay watershed. https://doi.org/10.1086/700701.

2011 Chessie BIBI

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