CBP Stream Health Outcome
Interstate Commission on the Potomac River Basin
What is the Baseline?
The Chesapeake Bay Program (CBP) aims to use the Chessie BIBI as a management tool to track progress in restoring stream health across the Chesapeake Bay watershed. The Program’s goal for a Stream Health Outcome:
“Continually improve stream health and function throughout the watershed. Improve health and function of ten percent of stream miles above the 2008 baseline for the watershed.”
Turning the Chessie BIBI index into an effective tool to track progress towards this management goal requires decisions on when and how to use it. Scientists and managers addressed these issues at an April 2018 workshop. They 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.”
Model results could be used to fill in the gaps where observed data were not available. Other needs were identified, including building consensus on what qualifies as 10% improvement, developing indicators of stream function to complement the Chessie BIBI, and using the CBP data protocols and Chesapeake Environmental Data Repository to merge stream datasets in the future.
Establishing a Baseline
In 2019, ICPRB tested several approaches for establishing the 2008 baseline. Stream health was measured with the bioregion, family-level version of the Chessie BIBI. Ratings derived from observed (monitoring) data were merged with ratings predicted by a random forest model.
The ratings were area-weighted to reduce bias caused by uneven sample densities and aggregated to the Chesapeake basin scale, with monitoring results given preference. Streams in about 73% of the basin’s 64,020 mi2 drainage area were evaluated with monitoring results and the remaining 27% with modeled results. The combined results suggest approximately 60% of the basin’s area had acceptable stream ratings (Excellent, Good, or Fair) during the 2006 – 2011 baseline period.
ICPRB is currently working with USGS to improve the predictive random forest model and run it with more recent data. When completed, the model results will be merged with observed data. Together, they will provide a refined estimate of acceptable stream ratings for the 2006 – 2011 baseline period and the following 2012 – 2017, or “first interval,” period.
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