Ditches and canals may cut greenhouse gas emissions with targeted management

A new study reports that ditches and canals are widespread hotspots of methane and nitrous oxide and describes management options — such as reduced nutrient inputs, vegetation buffers, dredging and floating plants — that can lower emissions.

A recent study reports that human-made ditches and canals are widespread freshwater systems and notable sources of greenhouse gases. These waterways often receive nutrients from fertiliser, manure and stormwater, creating low-oxygen conditions that favour methane and nitrous oxide production. The study brings together past measurements and field trials to outline ways of lowering those emissions through management. It also highlights gaps in knowledge about the global extent of ditch networks and regional emission data. Key points: - At least 5.3 million hectares of ditches and canals were estimated, equal to about 22% of the UK's land area, though global mapping is incomplete. - Previous calculations reported ditches emit about 333 teragrams of carbon dioxide equivalents, roughly comparable to the UK's total greenhouse gas emissions in 2023. - Low-oxygen, high-nutrient conditions from fertiliser, manure and urban runoff favour production of methane and nitrous oxide. - Management measures discussed include reducing fertiliser inputs, excluding livestock from ditch banks, and managing pollution sources such as wastewater treatment plants. - Field trials in the Netherlands found dredging reduced ditch emissions by about 35% after one year, while also noting dredging disturbs habitats and that emissions from removed sediments must be accounted for later. - Trials of floating vegetation, including Sphagnum moss in peatland ditches, reported initial methane reductions of roughly 40%; the study recommends continuous sensors to capture bubble-driven methane pulses and other "hot moments". Summary: The study indicates that managing ditches and canals offers potential to reduce potent greenhouse gas emissions, while noting trade-offs and limited geographic data. The study identifies priorities: improved global mapping, expanded measurements in underrepresented regions (notably South America and Africa), better monitoring of methane release patterns, and further field trials to assess practical benefits and scalability.