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Research and decision tools support management of harmful algal blooms


An algal bloom in western Lake Erie, September 26, 2017, captured by the USGS/NASA Landsat 8 satellite. Brighter shades of green indicate a higher concentration of algae. Source: USGS/NASA.

Harmful algal blooms, or HABs, occur when colonies of cyanobacteria grow to a much greater size and density than normal, resulting in negative effects on water quality, ecosystem health, and the health of humans and animals. Climate-related factors contribute to HABs, including water temperatures and the frequency and intensity of extreme events such as intense storms, both of which are affected by climate change. The impacts of climate change are expected to further increase risks from HABs in recreational and drinking water sources in the coming decades.1

While researchers have identified many factors that contribute to HABs, how these factors come together to create a bloom of algae is not well understood. Interagency research efforts seek to advance understanding of how and why HABs form to improve detection and forecasting of these seasonal events. Other efforts are using currently available data to provide communities with advance warning of events so they can prepare for the adverse environmental, economic, and health impacts of HABs.

Nutrient runoff from fertilizer applied to agricultural fields is one source of risk for HABs. USDA’s Agricultural Research Service (ARS) is conducting a series of pond-scale experiments to evaluate how excess nitrogen and phosphorous affects the development of algal blooms at the ecosystem scale. ARS is also conducting field work to understand seasonal variability in environmental factors that influence algal blooms in agricultural water bodies. These efforts are critical to closing research gaps between understanding of the biological factors and the environmental conditions that influence algal growth rates, and will help resource managers predict and manage risk within agricultural water bodies. This research is conducted jointly with EPA and the USGS.

In a separate project, a regional network of agricultural fields and small watersheds is serving as an outdoor laboratory for ARS units in West Lafayette, Indiana and Columbus, Ohio, allowing researchers to quantify the impacts of human-caused and natural climate changes on nutrient runoff that fuels HAB formation in Lake Erie.2,3,4  Assessment of long-term trends in precipitation, discharge, and water quality identified associated changes in rainfall patterns and land management practices that influence algal blooms. Research evaluating the uptake of nutrients by crops and the transport of water through the system, coupled with field-scale testing of novel conservation practices, has resulted in new strategies and recommendations for decreasing nutrient loss under current and future climatic conditions.5 This research is conducted jointly with EPA and the USGS.

Like a weather forecast, an HAB forecast provides advance warning of conditions that could lead to potentially harmful algal blooms. EPA’s Cyanobacteria Assessment Network Mobile Application (CyAN app) alerts officials and members of the public when an HAB may be forming, based on satellite observations of changes in water color. The app provides access to satellite algal bloom data for over 2,000 of the largest lakes and reservoirs across the United States.

The CyAN app is a product of the multi-agency Cyanobacteria Assessment Network, a collaboration among EPA, NASA, NOAA, and the USGS to develop an early warning indicator system using historical and current satellite data to detect algal blooms in U.S. freshwater systems.


1 Ebi, K.L., J.M. Balbus, G. Luber, A. Bole, A. Crimmins, G. Glass, S. Saha, M.M. Shimamoto, J. Trtanj, and J.L. White-Newsome, 2018: Human Health. In: Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 539–571. https://doi.org/10.7930/NCA4.2018.CH14

2 Smith, D.R., Jarvie, H.P. 2018. Carbon, nitrogen, and phosphorus stoichiometric response to hydrologic extremes in a tributary to Lake Erie, USA. Agricultural and Environmental Letters. 3:180043. https://doi.org/10.2134/ael2018.08.0043

3 Mehan, S., Gitau, M.W., Flanagan, D.C. 2019. Reliable future climate projections for sustainable hydro-meteorological assessments in the Western Lake Erie Basin. Water. 11(3):581. https://doi.org/10.3390/w11030581

4 Wilson, R., Beetstra, M., Reutter, J., Hesse, G., Fussell, K., Johnson, L., King, K.W., Labarge, G., Martin, J., Winslow, C. 2019. Commentary: Achieving phosphorus reduction targets for Lake Erie. Journal of Great Lakes Research. 45(1):4-11. https://doi.org/10.1016/j.jglr.2018.11.004

5 Ibid.