Freshwater systems such as rivers and lakes play an important role in the climate because they can emit the greenhouse gases carbon dioxide, methane and nitrous oxide. These emissions increase when large amounts of nutrients enter the water, for example through agriculture or wastewater. This can lead to changes in the ecosystem, such as the development of oxygen depletion. Micro-organisms in water and soil have a significant influence on how much greenhouse gases are produced or broken down, but how these mechanisms are controlled by external factors is not yet fully understood. This thesis investigates how microorganisms respond to changes in nutrients, oxygen, acidity and seasons in freshwater systems in the Netherlands and Denmark and in bioreactors in the laboratory. We show that human influences control the activity of microorganisms and thus influence the cycles and emissions of greenhouse gases. Some systems even appear to be able to temporarily absorb greenhouse gases. These insights help to better understand and predict how microorganisms and freshwater contribute to greenhouse gas cycles.
In 2021, Ida Peterse (1996) completed her Master's degree in Microbiology at Radboud University with honours. She then began a PhD at Radboud University in 2021 under the supervision of Annelies Veraart and Sebastian Lücker. Her PhD research, which she completed in 2025, combined microbiology with ecological issues.