USGS Study Identifies Factors Related to Cyanobacterial Harmful Algal Blooms

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U.S. Geological Survey (USGS) scientists identified water-quality and environmental factors related to cyanobacterial harmful algal blooms at beaches in Ohio. This information was collected as part of a long-term plan to develop site-specific predictive models for microcystin concentrations.

Lake Erie green waters at the Beach with Buoy marking swim area

An algal bloom on a Lake Erie beach located in Maumee Bay State Park, Ohio. This beach was one of the sites that the scientists studied for water-quality and environmental factors related to cyanobacterial harmful algal blooms. Photo Credit: Pamela Struffolino, University of Toledo.

Harmful cyanobacterial "algal" blooms (cyanoHABs) and associated toxins, such as microcystin, are water quality issues for Lake Erie and inland lakes in Ohio. Prediction of algal toxin levels resulting from cyanoHABs in recreational waters is important to advise swimmers and boaters about potentially dangerous conditions. Although, models have been used successfully at Lake Erie beaches for predicting E. coli concentrations as part of the Ohio Nowcast, there are no nowcasts (estimates of current conditions) for predicting cyanoHAB toxin levels.

Scientists identified the most relevant chemical and environmental factors that were related to microcystin concentrations. Water-quality and environmental factors were measured at seven recreational areas in Ohio during 2013‒2014. Water samples were collected weekly to monthly and analyzed for microcystin, nutrients, cyanobacterial genes, and phytoplankton community structure.

Factors were identified that best explained microsystin concentrations in two types of models:

  1. Models that include easily or continuously measured factors and available environmental data that require no sample collection (real-time based models), and
  2. models that that include sample collection and analyses along with real-time measurements (comprehensive models).
A map of Ohio showing the locations of recreational areas sampled in the 2013-14 study

A map of Ohio showing the locations of recreational areas sampled in the 201314 study. Modified from figure 1, Francy and others, 2016.

(Public domain.)

Measurements of phycocyanin (a pigment produced by cyanobacteria), water clarity, pH of the water, streamflow from a nearby river, and lake level changes over 24 hours were among the factors for real-time models that best explained observed variations in microcystin concentrations. For comprehensive models, dissolved and total nitrogen or phosphorus, cyanobacterial genes (by molecular methods), and measures of the cyanobacterial community were among the best factors to estimate microcystin concentrations.

Environmental Health Considerations

Predicting when and where a cyanoHAB may occur is important to protect the public that uses and consumes a water resource. The significant factors identified in this study and ongoing studies are part of a long-term strategy to understand the factors related to cyanoHABs. The information and models generated as part of this long-term approach can provide real-time warning of cyanoHAB events needed for management of recreational use and drinking water quality.

The study was done in cooperation with the Ohio Water Development AuthorityUniversity of ToledoClermont County Soil and Water Conservation DistrictErie County Health DepartmentOhio Department of Natural ResourcesOhio Environmental Protection Agency, and the U.S. Environmental Protection Agency.

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