Diffusive CH4 Emissions From Agricultural Ditches Overshadow CH4 Sinks by Upland Fields

Wu, Wenxin; Yan, Zhifeng; Peacock, Mike; Ge, Zhengkui; Wei, Xinhai; Yao, Yuanzhi; Ayal, Desalegn Yayeh; Yu, Guirui; Smith, Pete

doi:10.1029/2025JG009175

Abstract

Ditches are potentially important sources of methane (CH4) in agricultural regions, but their CH4 emissions are largely unknown due to data scarcity. Here, we investigated CH4 concentrations and diffusive fluxes across different ditches in the North China Plain (NCP), an extensive upland agricultural region with maize-wheat rotations, and well-constructed ditch systems. Based on intensive monthly and extensive regional surveys, we found that (mean +/- SD) CH4 concentrations (11.42 +/- 37.69 mu mol L-1) and fluxes (344.7 +/- 1,198.1 mu mol m-2 h-1) in the agricultural ditches (ADs) showed high variability, primarily driven by spatial and temporal heterogeneity in nutrient and carbon inputs. On average, CH4 concentrations and fluxes were 3-12 times higher than those in the nearby agricultural-rural ditches (3.80 mu mol L-1, 99.8 mu mol m-2 h-1) and rivers (0.92 mu mol L-1, 47.1 mu mol m-2 h-1). Dissolved organic carbon (DOC) and ammonium (NH4 +-N) were primary drivers of CH4 emissions in the ADs, highlighting the key role of nutrient and carbon inputs from surrounding fields. The annual diffusive CH4 emission from ADs in the NCP was estimated to be 1,836.3 +/- 311.6 Gg CH4 yr-1 and 68.1 +/- 7.3 Gg CH4 yr-1 based on the mean and median CH4 fluxes, respectively, acting as a significant source of CH4 emissions, despite large uncertainty. This emission overwhelmingly offsets the CH4 uptake by soils (i.e., -9.2 Gg CH4 yr-1) in the NCP, highlighting the necessity of including CH4 emissions from ADs in estimating CH4 budget from upland agricultural regions.

Keywords

agricultural ditch; methane emission; cropland; soil methane uptake

Published in

Journal of Geophysical Research: Biogeosciences
2025, volume: 130, number: 11, article number: e2025JG009175
Publisher: AMER GEOPHYSICAL UNION

SLU Authors

Peacock, Michael
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
- University of Liverpool

UKÄ Subject classification

Environmental Sciences
Geosciences, Multidisciplinary

Publication identifier

DOI: https://doi.org/10.1029/2025JG009175

Permanent link to this page (URI)

https://res.slu.se/id/publ/144815