Renaturalised bodies of water can reduce greenhouse gas emissions | Umweltbundesamt

During biological and chemical decomposition processes of plant and other organic material, carbon and nitrogen are converted into carbon dioxide, methane and nitrous oxide in water bodies. The gases escape into the atmosphere or are stored in the sediment. Natural sediment redistribution processes, such as floods or turbulence, can release the stored gases into the atmosphere and contribute to the greenhouse gas (GHG) effect.

Anthropogenic greenhouse gas emissions from water bodies

Bodies of water naturally absorb carbon from the atmosphere, store it in sediments and transport it to the oceans via rivers. Plants and animals in water bodies also utilise carbon for their growth.

However, the removal of sediment is severely restricted by the damming of rivers by humans. The utilisation of water bodies for agriculture or energy production has led to them being increasingly straightened, deepened, dammed and provided with bank protection. This applies to 86 % of our water bodies (BMUV/⁠UBA, 2021).

As a result, organic material (leaves, dead plant parts, algae, etc.) accumulates in the backwater areas of transverse structures and dams, for example, which forms greenhouse gases when it decomposes. This reduces the savings potential of hydropower plants as a renewable energy source, even though this type of electricity production is significantly more climate-friendly than the combustion of fossil fuels. In addition, decomposition consumes oxygen, which can increase methane production. The negative impact of methane on the climate is almost 30 times greater than that of carbon dioxide (IPCC 2021).

Solutions

In order to avoid greenhouse gas emissions from water bodies, renaturalisation (near-natural design), the reduction of nutrient inputs and the avoidance of backwater areas at transverse structures are particularly effective. The comprehensive UBA study shows that renaturalisation can make a moderate to high contribution to reducing greenhouse gas emissions (an overview of renaturalisation measures can be found on our website). This includes the reconnection of floodplains as greenhouse gas sinks, in which greenhouse gases can be bound through the formation of floodplain soils and vegetation.

 Measures to completely or significantly improve water flow and avoid backwater areas are highly effective.

Conclusion

The evaluation of over 250 scientific studies has shown that emissions from water bodies are underestimated in previous greenhouse gas assessments (UBA 2023). It can therefore be assumed that the potential greenhouse gas emissions from surface waters are higher than previously assumed. In this context, the UBA is working on a valid recording of greenhouse gas emissions.

The protection and restoration of aquatic ecosystems is necessary to reduce greenhouse gas emissions and contributes to climate change adaptation, as well as to the objective of the European Water Framework Directive: a “good status” for all water bodies in Europe. According to the new Restoration Law, freshwater ecosystems must also be renaturalised by 2030.