In recent years it has become increasingly common that on some of the hottest days of the summer, the freshwater lakes and ponds that we rely on to cool down are closed due to dangerous cyanobacterial blooms. Beyond this effect on recreation, blooms also have a significant, negative impact on freshwater ecosystems—they release toxins, block light needed by other organisms, and deplete oxygen.
Much research has been done and attention has been paid to better understanding conditions that promote cyanobacterial blooms, but most of the focus has been on warm and hot conditions. As global temperatures rise and all seasons in the northeastern U.S. get warmer due to climate change, this focus is understandable; but it doesn’t tell the whole story.
There is increasing evidence that cyanobacterial blooms can also occur in cold-water temperatures below 15 degrees Celsius (59 degrees Fahrenheit), including ice-covered conditions. A new study published in documents wide-ranging cold-water cyanobacterial blooms and identifies the multiple factors that influence their development.
The study was a collaborative effort of the Cyanobacteria Working Group and includes 28 authors from 9 countries. The authors reviewed the interacting environmental and physiological mechanisms that allow blooms to occur in cold water and documented observations in nearly 40 lakes. Dr. Mindy Morales-Williams, a University of Vermont (̽̽) scientist and ̽̽ PhD candidate Katelynn Warner co-authored the study.
“The impact of cyanobacterial blooms persisting in cold-water conditions is understudied because management efforts are focused on summer and early fall,” said Dr. Morales-Williams, Assistant Professor in the ̽̽ Rubenstein School of Environment and Natural Resources. “Without a greater understanding of the specific factors that impact bloom growth throughout the year, our ability to effectively create sustainable management plans for our freshwater systems is limited.”
Some possible consequences of cold-water cyanobacterial blooms on lake ecology include altered nutrient cycles and food webs, human and environmental health risks, and substantial shifts to sustainable lake management practices.
The study pulls together data from peer-reviewed research, news outlets, authors’ study systems, and citizen science programs operated by the U.S. Environmental Protection Agency. Results show cyanobacterial blooms do occur in cold-water conditions, they can occur in a wide range of lake types across the globe, and they can be dominated by a variety of species. Several of these species prefer cold conditions and have evolved to thrive in lower temperatures. For instance, low water temperatures can lead to changes in cell membranes, which slow physiological processes. Some cyanobacteria species have adapted to prevent this, developing more fluid biological membranes by accumulating fatty acids, evolving cold shock and antifreeze proteins, and modulating their biochemistry.
“The data we reviewed is likely a small sample of the true number of cold-water cyanobacterial blooms occurring globally but provides compelling evidence about the adaptive properties of cyanobacteria,” said Dr. Morales-Williams. “With this glimpse into the many factors impacting bloom occurrences, we have a better understanding of where our knowledge gaps are and where to focus future research as climate change alters lake seasonal processes.”
Climate change greatly influences the occurrence of cyanobacterial blooms. Shifts in light levels, nutrient availability, precipitation, shortened ice duration, and more will impact cyanobacteria production. And while all cyanobacteria will not thrive in all conditions, they are able to tolerate a wide range of environmental shifts, which will allow them to persist in the future. The study explores several potential implications of climate change on cold-water cyanobacterial blooms; and will help inform predictions of how climate change may exacerbate these types of blooms.
Many lakes throughout the world reach cold-water levels for at least half of the year, making it critical to establish a baseline for the occurrence and frequency of cold-water cyanobacterial blooms. This baseline will allow for more accurate tracking of bloom trends over time and impacts of climate change on freshwater ecosystems.
“We are at risk of missing early warning signs for future public and wildlife health risks,” said Dr. Morales-Williams. “By expanding cyanobacteria bloom observations year-round and coordinating across many geographic regions, we are able to collect comprehensive data that tells a more complete story and better prepares us to address the challenges faced by our lakes and ponds in Vermont and globally.”