b'14 Carnegie Science|Spring/Summer 2020Lakes Have More-Severe Algal Blooms WorldwideLago de Cahora Bassa in Mozambique was one of the lakes that Jeff Ho, Anna Michalak, and Nima Pahlevans study of the intensity of lake water algal blooms showed had sustained improvement over the 30-year period. Image courtesy NASA Earth Observatory, made by Jesse Allen using MODIS data from the Land Atmosphere Near-real-time Capability for EOS (LANCE) and Landsat data from the U.S. Geological SurveyNo long-term global studies of freshwater blooms had been undertaken until now.The intensity of summer algal blooms hasauthor Ho. Studies indicate that just in the increased over the past three decades,United States, freshwater blooms result in according to a first-ever global survey ofthe loss of $4 billion each year.dozens of large, freshwater lakes whichDespite this, studies on freshwater was conducted by Carnegies Jeff Ho andalgal blooms have either focused onCarnegies Jeff Ho (left) and Anna Michalak (right) were Anna Michalak and NASAs Nima Pahlevanindividual lakes or specific regions, or thecoauthors on the algal-bloom research published by NatureImages courtesy Carnegie Institution for Scienceand published by Nature period examined was comparatively short. Reports of harmful algal bloomslikeNo long-term global studies of freshwater the ones that shut down Toledos waterblooms had been undertaken until now.explained. This means that algal blooms supply in 2014 or led to states ofHo, Michalak, and Pahlevan used 30really are getting more widespread and emergency being declared in Florida inyears of data from NASA and the U.S.more intense, and its not just that we are 2016 and 2018are growing. These aquaticGeological Surveys Landsat 5 near-Earthpaying more attention to them now than phenomena are harmful because of thesatellite, which monitored the planetswe were decades ago. intensity of their growth or because theysurface between 1984 and 2013 at 30-meterAlthough the trend towards more-include populations of toxin-producingresolution, to reveal long-term trends inintense blooms was clear, the reasons for phytoplankton. But before this researchsummer algal blooms in 71 large lakes in 33this increase seemed to vary from lake to effort, it was unclear whether the problemcountries on six continents. To do so, theylake, with no consistent patterns among the was truly getting worse on a global scale.created a partnership with Google Earthlakes where blooms have gotten worse when Likewise, the degree to which humanEngine to process and analyze more thanconsidering factors such as fertilizer use, activityincluding agriculture, urban72 billion data points.rainfall, or temperature. One clear finding, development, and climate changewasWe found that the peak intensity ofhowever, is that among the lakes that contributing to this problem was uncertain.summertime algal blooms increased inimproved at any point over the 30-year Toxic algal blooms affect drinkingmore than two-thirds of lakes butperiod, only those that experienced the least water supplies, agriculture, fishing,decreased in a statistically significant waywarming were able to sustain improvements recreation, and tourism, explained leadin only six of the lakes, Michalakin bloom conditions. This suggests that climate change is likely already hampering lake recovery in some areas. This finding illustrates how important it is to identify the factors that make some lakes more susceptible to climate change, Michalak said. We need to develop water management strategies that better reflect the ways that local hydrological conditions are affected by a changing climate.SUPPORT:Lake Khanka (left) on the border between Russia and China and Lake St. Clair (right) between the United States andThe U.S. National Science Foundation, the Natural Sciences and Canada both showed improvement and then deteriorated in this study of algal blooms in large lakes.Engineering Research Council of Canada, a Google Earth Engine Khanka image made by Norman Kuring, NASAs OceanColor Web, and Lauren Dauphin. St. Clair image courtesy NASA Earth Observatory, madeResearch Award, a NASA ROSES grant, and by a U.S. Geological by Joshua Stevens using Landsat data from the U.S. Geological Survey Survey Landsat Science Team Award supported this research.'