Rivers across the world are undergoing alarming changes, with rising temperatures, declining oxygen levels and increasing greenhouse gas emissions, according to a new global study. Scientists warn that these shifts are not only damaging aquatic ecosystems but are also contributing significantly to climate change.
The research, led by Ricky Mwangada Mwanake at the Karlsruhe Institute of Technology, analysed river systems across 5,084 catchments between 2002 and 2022. The findings reveal a consistent global trend of rivers becoming warmer and more polluted, with increased levels of heat-trapping gases such as carbon dioxide, methane and nitrous oxide.
Experts say these changes are closely linked to rising global temperatures and human activities, which are accelerating chemical and biological processes in river ecosystems.
Declining Oxygen Levels Driving Emissions And Ecosystem Stress
One of the most critical findings of the study is the sharp decline in dissolved oxygen levels in rivers. Warmer water naturally holds less oxygen, while increased organic pollution from agriculture, cities and wastewater boosts microbial activity. These microbes consume oxygen as they break down waste, creating low-oxygen conditions that stress aquatic life.
At the same time, these processes generate greenhouse gases. Carbon dioxide is released from decomposing organic matter, methane forms in oxygen-poor sediments, and nitrogen pollution leads to nitrous oxide emissions. Over the past two decades, additional emissions from rivers have reached an estimated 1.5 billion metric tonnes of carbon dioxide equivalent.
Researchers used machine learning techniques to analyse data from more than 1,000 monitored sites and extend the findings globally. The results highlight that these changes are not isolated but part of a widespread environmental shift.
Human Activity Intensifying River Pollution And Climate Impact
The study found that areas with intensive agriculture and urban development are the most affected. Fertiliser runoff, soil erosion and wastewater discharge increase nutrient levels in rivers, fuelling microbial activity and gas production. Urban areas further contribute through heat from paved surfaces and polluted runoff.
In heavily impacted regions, methane levels were found to be dramatically higher than in less disturbed ecosystems. Scientists say this highlights the strong link between land use and river health, as well as the growing role of rivers in global greenhouse gas emissions.
Regional variations were also observed. Parts of Asia and South America showed significant declines in oxygen levels and increases in emissions, driven by rapid urbanisation and warming conditions. Similar trends were noted in Australia, where land-use changes and rising temperatures are reshaping river systems.
River Restoration Key To Climate Mitigation
Despite the concerning trends, researchers emphasise that the situation can still be improved. Reducing pollution from agriculture and urban areas can significantly lower nutrient inputs into rivers, slowing down the processes that generate greenhouse gases.
Measures such as better wastewater treatment, controlled fertiliser use and planting vegetation buffers along riverbanks can help restore water quality. According to experts like Ralf Kiese, protecting rivers could play an important role in climate mitigation if their emissions are properly accounted for in environmental policies.
The findings underline the need to include rivers in climate strategies, as they represent a critical link between land use, water systems and atmospheric emissions. Scientists warn that without stronger monitoring and policy action, rivers could become an increasingly significant and overlooked source of greenhouse gases in the future.