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Phytoplankton absorb carbon dioxide from the atmosphere but emit carbon dioxide-equivalents (CO2-eq), making them net emitters, according to a new study in Nature Communications.
Thus, over the past four decades, severe phytoplankton blooms in eutrophic lakes may have had large cumulative impacts on the climate, stated the report released December 4, 2024.
In lakes, phytoplankton (microalgae) sequester atmospheric CO2 and store it in the form of biomass organic carbon. However, only a small fraction of this organic carbon emains buried, while the remaining part is recycled to the atmosphere as CO2 and methane (CH4), the report showed.
Moreover, global warming has stimulated phytoplankton growth in many lakes worldwide, creating a positive feedback loop.
This has the potential effect of adding CO2-equivalents (CO2-eq) to the atmosphere and producing a warming effect due to the higher radiative forcing of CH4 relative to CO2, the scientists explained.
During the course of the study, researchers used globally collected data to quantify the CO2-eq feedback capacity of phytoplankton in 1,649 lakes.
They analysed CO2-eq budget throughout the life cycle of phytoplankton, assessed the feedback at a global scale and predicted the extent of this reponse under future warming scenarios.
Over the past four decades, severe phytoplankton blooms in eutrophic lakes may have had large cumulative impacts on the climate.
Highly productive lakes have a particular strong CO2-eq feedback capacity. "In oligotrophic, mesotrophic and eutrophic lakes, the CO2-eq feedback is estimated to 166.5–999, 832.5–3,330, and > 3,330 g CO2-eq square metres per day over the 100-year horizon, respectively," the authors of the report noted.
The study found a 3.1-fold increase in CO2-eq emissions over a 100-year horizon, with the effect increasing with global warming intensity.
Wenqing Shi, Nanjing University of Information Science & Technology, China was the lead author of the study.
Phytoplankton blooms pose a worldwide water quality problem, and effective management requires comprehending their reactions to various interacting factors, such as nutrient influx and climate change.
Attempts to lessen the greenhouse effects by controlling carbon dioxide emissions could be compromised by the extensive growth of phytoplankton. It is crucial to implement strong nutrient management to address severe eutrophication in lakes worldwide.
Many studies in the past have called for water quality management efforts to better account for the interactions between climate change and local hydrological conditions. A 2019 Nature study, for instance, found that lakes with a decrease in phytoplankton bloom intensity warmed less compared to other lakes, suggesting that lake warming may be counteracting management efforts to ameliorate eutrophication.