Towards improved accounting and mitigation of greenhouse gas emissions from ditches and canals

Abstract

First Paragraph Ditches and canals are important but largely unaccounted for components of global greenhouse gas(GHG) budgets. These human-made, linear water ways have a vast range of typologies and conditions (see Clifford et al 2025 for a detailed review). In general, ditches tend to be narrower, variably inundated, and primarily used for drainage of wet soils for agriculture or forestry, while canals tend to be wider, used for transportation or irrigation, more likely to be made of impermeable substrate and perennially inundated (but these two terms are sometimes used interchangeably) (table 1). The cumulative extent of ditches and canals is large; often rivaling stream and river length at regional scales (Brown et al 2006), but remains poorly quantified at the global scale. Recent global syntheses have shown that ditches and canals emit notable amounts of methane (CH4) (Peacock et al 2021, Gan et al 2024) as well as carbon dioxide (CO2) and nitrous oxide (N2O); often more per unit area than other inland waters (Silverthorn et al 2025), and in some land scapes, even exceeding emissions from adjacent terrestrial areas (van der Knaap et al 2025). These elevated emissions largely result from high nutrient and carbon inputs from the intensively managed agricultural and urban landscapes where these waterways are typically found(Peacocket al 2021).Although local-scale studies about GHG emissions from ditches and canals have increased(figure1(A)), these water bodies remain overlooked in global inland water GHG budgets and national inventory reporting, despite Intergovernmental Panel on Climate Change recommendations to include emission from ditches draining organic soils(IPCC2014)and subsequently from all ditches and canals(IPCC2019).