River bacteria consume methane but fall short as global warming boosts emissions

River bacteria play a crucial role in mitigating methane emissions by consuming the greenhouse gas before it enters the atmosphere. However, new research indicates that this natural process is increasingly ineffective due to rising global temperatures and pollution, leaving rivers as a growing source of methane emissions. A study led by Alberto Borges, an oceanographer at the University of Liège, highlights how microbial oxidation of methane varies significantly between regions and is being undermined by environmental changes. The study, published in Science Advances, compares microbial methane oxidation in rivers across Belgium and Africa. It finds that while bacterial consumption of methane occurs in both regions, it is far more pronounced in African rivers. In contrast, Belgian rivers exhibit lower levels of microbial oxidation, attributed to human activities such as riverbank development and the proliferation of invasive species like the Asian corbicula, a bivalve known for filtering water and altering ecosystem dynamics. These factors disrupt the natural flow of microbial communities into river systems, reducing their ability to oxidize methane effectively. Methane, a potent greenhouse gas, contributes significantly to climate change, ranking second in impact after carbon dioxide. Rivers are a major source of atmospheric methane, accounting for approximately one-third of total emissions linked to agricultural activities, which remain the largest contributor to increased methane concentrations in the atmosphere. The balance of methane emissions in rivers depends on two primary processes: methanogenesis, where microorganisms generate methane as part of their metabolic functions, and microbial oxidation, where specific bacteria break down methane to obtain energy or biomass. In many cases, microbial oxidation serves as a critical buffer against excessive methane release. Yet, the study reveals that this natural filter is becoming less effective. Headwater rivers, which are responsible for the bulk of methane emissions from river systems, show particularly weak microbial oxidation rates. Despite their high emission potential, these smaller rivers lack the conditions necessary for efficient methane consumption, exacerbating the overall contribution of rivers to atmospheric methane buildup. Borges explains that the observed decline in microbial oxidation is partly due to the effects of global warming and eutrophication, excessive nutrient runoff leading to nitrate pollution. As temperatures rise and nutrient inputs increase, methane production in river ecosystems is expected to grow. However, the capacity of microbial communities to counteract this increase appears limited, especially in areas where human interventions have altered natural river dynamics. The presence of invasive species and modifications to riverbanks further complicate efforts to maintain healthy microbial populations capable of oxidizing methane. The implications of these findings suggest that current strategies aimed at reducing methane emissions must account for the changing roles of riverine ecosystems. While microbial oxidation offers a natural means of mitigation, its effectiveness is diminishing under present environmental pressures. Scientists warn that without targeted conservation and restoration efforts, rivers could become even greater contributors to global methane emissions, accelerating climate change impacts. Looking ahead, researchers emphasize the need for continued monitoring of microbial activity in different river environments and the implementation of policies that protect and restore natural river functions. Understanding the complex interactions between microbial communities, environmental stressors, and human influences will be essential in developing more effective approaches to mitigate methane emissions from aquatic systems.