(Photo: Aerial Associates Photography, Inc. by Zachary Haslick)
Algae holds a valuable position in telling us about the health of a freshwater supply as well as the communities depending on it. For Lake Monroe, a reservoir just southeast of Bloomington, Indiana, and the city’s primary drinking water source, phytoplankton can serve as an early warning system for environmental and public health challenges. Using data from 2019 through 2023, I studied the phytoplankton community in Lake Monroe in an attempt to find how human activity, climate change, and ecological factors may be collectively altering the ecosystem’s balance. My findings highlighted growing risks, and offered potential action items for future researchers and lake managers.
A Reservoir at Risk
Phytoplankton are primary producers that serve as the foundation of the food web in aquatic ecosystems. In Lake Monroe, cyanobacteria, often incorrectly referred to as blue-green algae, dominate the phytoplankton community. This dominance raises major concerns for the ecosystem and the Bloomington community, as some cyanobacteria species can produce harmful algal blooms (or HABs) that threaten water quality and human health. HABs are known to contaminate drinking water with toxins, outcompete other phytoplankton species, deplete oxygen levels, and affect the public perception of water quality.
Lake Monroe is both the water source for the city of Bloomington and a popular recreation site in the area. In order to keep the communities that depend on Lake Monroe safe, it is essential to understand what drives these harmful algal blooms and work to prevent them.
Findings
I used data from 2019 to 2023 to analyze phytoplankton species and functional groups, nutrient levels, and climate data in order to find trends and look for interactions. A few factors stood out:
Cyanobacteria Dominance
Across all study years, cyanobacteria made up the majority of the phytoplankton community. In 2022, toxin-producing species were especially dominant. HABs-producing cyanobacteria typically thrive in nitrogen-limited conditions, where they can outcompete true phytoplankton by fixing their own nitrogen. In Lake Monroe, nitrogen-limitation is the typical state, causing concern for the future phytoplankton community structure there.
Low Biodiversity
Lake Monroe’s phytoplankton community showed consistently low levels of biodiversity, particularly in years with high cyanobacteria concentrations. Low biodiversity levels can weaken resilience in an ecosystem, making it harder for the lake to recover from environmental stressors.
Climate and Weather Impacts
Temperature and precipitation patterns had strong effects on the phytoplankton community. Warmer years with more rainfall saw higher cyanobacteria levels, while cooler and drier years saw more green algae dominance. However, long-term warming trends suggest that cyanobacteria will only become more prominent, and HABs may become more frequent in the future.
Taste and Odor
While the major concern surrounding cyanobacteria dominance is their production of toxins, some species also omit taste-and-odor-producing compounds. These compounds are responsible for the foul taste and smell of Bloomington’s tap water in the fall months. While these compounds are not harmful from a public health standpoint, they do have negative effects on public perception of water quality, and are often people’s only tangible insight on the quality of their tap water.
Why Should We Care?
Lake Monroe’s cyanobacterial dominance is as much a societal issue as it is an ecological one. Harmful algal blooms cause problems for the quality of drinking water, pose concerns for recreation safety, and can make water treatment significantly more expensive for the city. These risks are likely to continue to grow in severity with the ongoing rises in urbanization and climate change. While we can’t reduce the temperature of the globe in a day, there are some solutions to the cyanobacterial problem that are attainable now. These include:
- Promoting sustainable practices to reduce agricultural runoff into Lake Monroe
- Limiting new nutrient inputs through the strengthening of Lake Monroe’s watershed management
- Monitoring and studying phytoplankton community on a regular basis
Lake Monroe is not the only freshwater ecosystem facing these challenges. My research shows that understanding ecosystems on a fundamental level and studying their smallest parts can help solve environmental and social problems that are much larger in scale. Our approaches must be proactive in nature, and if we work to protect the strength of a phytoplankton community, we can in turn protect both the lake ecosystem and the community that relies on it. Reducing nutrient pollution and anticipating the effects of climate change are essential to preserving our freshwater sources and keeping them viable for generations to come.
Ella Jasnieski is a recent graduate of the O’Neill School of Public and Environmental Affairs, receiving her degree in Environmental Science. Her Honors thesis was titled Phytoplankton Community Structure in Lake Monroe and Its Environmental Drivers. She also was involved with the band department at the Jacobs School of Music throughout college. In the future, she plans to work in the nonprofit sector and attend a masters program at Indiana University.
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