A Flow-Based Risk Characterization Model for HABs on the Ohio River
Citation:
Nietch, C., L. Gains-Germain, Jim Lazorchak, AND S. Keely. A Flow-Based Risk Characterization Model for HABs on the Ohio River. 10th U.S. Symposium on Harmful Algae, Orange Beach, AL, November 03 - 08, 2019.
Impact/Purpose:
Historical flow data for 27 Ohio River sites and an understanding of big river ecology were used to characterize the unique hydrologic conditions that coincided with a record-setting harmful algae bloom (HAB) in 2015. A risk characterization tool was developed to convey risk in terms of the similarity of flow conditions in the present to those that produced a CyanoHAB in the past. This tool is being made accessible to river stakeholders through our partner’s website, the Ohio River Valley Sanitation Commission (ORSANCO).
Description:
In August of 2015 an unprecedented harmful cyanobacteria bloom (CyanoHAB) occurred over 700 miles of the 981-mile Ohio River. The bloom threatened drinking water of 5 million people and caused five states to set advisories that lasted more than 2 months. To meet several assistance requests EPA Regions 3 and 5 funded a research effort to better understand the cause and consider what could be done to characterize the risk of Ohio River HABs in the future. First, preliminary analyses revealed unique flow trends during the time periods leading up the 2015 bloom. Next historical river flow data was obtained for 24 sites dating back to the beginning of 1996. A conceptual cause and effects model guided subsequent statistical modelling. Two lag terms were found to be highly explanatory, one indicating the degree the river was experiencing high flows 21 to 55 days prior to the observed bloom in 2015 and the other, the degree the river was under low flow conditions 19 days prior to the bloom. A Bayesian model was developed that uses the ratio of these two lag terms and the number of days the ratio itself was increasing as predictors. By pooling across sites, the model provides predictions and uncertainties in bloom probabilities, where a “bloom” is defined by the 2015 condition. Finally, a risk communication framework was developed to provide river stakeholders a visualization of the model results in real time along with other supporting information. Risk probability plots can be visualized for 20 sites along the river. These qualify the current conditions in terms of those that produced the bloom in 2015. The risk characterization tool for Ohio River HABs is currently being transferred to the Ohio River Valley Sanitation Commission, who will provide password-protected access through their website.