Methane (CH4) is a potent greenhouse gas contributing to the warming of Earth's atmosphere. Lakes are a natural source of CH4, where CH4 generally is produced in oxygen depleted sediments. Ebullitive CH4 is regulated naturally in the oxic-anoxic interface of lakes by methane oxidizing bacteria, methanotrophs uses CH4 as a substrate when O2 is present. Lakes in boreal regions are among the largest sources of CH4 emissions, CH4 oxidation can mitigate some of the CH4 emissions from lakes. Gaps in knowledge and data remain regarding net fluxes of CH4, indicating that there are processes unaccounted for. Previous research highlights the variability of CH4 emissions and oxidations rates in lakes, there is lacking knowledge on what drives the variability of oxidation rates and total emissions. It’s been suggested that availability of phosphorus (P) has a positive relationship with increased oxidation rates. Moreover, availability of trace elements has been suggested to affect aerobic CH4 oxidation, but there is a lack of knowledge on these factors in natural lake waters. In this study incubations with lake water from two different lakes, Gårasjön and Kisasjön, were prepared with different treatments of P and/or trace elements. We investigate how this can affect the rate of CH4 oxidation when incubated in specific conditions. Our results indicate that treatments with added P had a greater tendency to exhibit higher rates of methane oxidation in both lakes, while treatments with trace elements and P had varied oxidation rates depending on the lake. This suggests that when there are no limitations of the substrates CH4 and O2, the oxidations rates in lakes might be limited by the availability of P and the specific lake conditions can influence CH4 oxidation.

Methane (CH4) is guaranteed to affect climate change and is essential in rising temperatures. Scientists have known for over two decades that wetlands emit CH4 to such an extent that it affects our climate. Tropical trees that grow in wetlands tend to emit or act as a conduit of CH4, to the extent that it has a negative environmental impact. However, until this study, no one has examined whether wetland species growing in another environment have the same effects. Hence, this thesis aimed to collect data from wetland-adapted tropical trees in a non-wetland environment, namely the Botanical Garden in Rio de Janeiro. The results showed a difference in the sampling height of the stem, namely that a decrease in emission is seen with an increased height. All the species except one (Pseudobombax munguba) showed both assimilation and emission from the day-to-day measurements of CH4, which speaks for the trees acting both as a sink and a source of CH4. This suggests that the species are more robust than the environmental stressors in a non-wetland environment. Previous studies have found that increased CH4 emissions can be seen with different meteorological parameters. The results presented in this thesis show the opposite, that some species tend to emit less or assimilate more CH4 during days with increased rainfall, humidity, and temperature.