Simulating Carbon Emission Dynamics in Agricultural Drainage Ditches: Development and Evaluation of the PCDitch‐Carbon Model

Abstract

With their high abundance in agricultural landscapes, drainage ditches are important components of the global water cycle and potential carbon (CO ₂ and CH ₄ ) emission hotspots. However, explicit process‐based estimates of carbon emissions from these systems are lacking, with ditch biogeochemical complexity being a major constraining factor. To fill this gap, we developed PCDitch‐Carbon, a carbon emission model, from the well‐established process‐based ditch ecosystem model PCDitch. Our research goals were to (a) identify key parameters that affect carbon emissions using sensitivity analysis, (b) determine the responses in carbon emissions to external nutrient loading using bifurcation analysis and (c) validate the predicted carbon emissions with empirical observations. Sensitivity analysis highlighted hydromorphology, external nutrient and carbon loadings, and ecological states (submerged macrophyte vs. Lemnid dominated vegetation) as key drivers of carbon emissions. Bifurcation analysis showed decreased CO ₂ and increased CH ₄ emissions with external nutrient loading. Additionally, hysteresis related to ecological state was observed underlying the presence of ecological feedback loops in governing carbon emissions. Modeled emissions reflected empirical observations from 10 ditch systems reasonably well, with higher CH ₄ in summer–autumn and lower in winter–spring, as well as lower CO ₂ emissions during spring‐summer due to primary production. PCDitch‐Carbon demonstrates the potential of process‐based ecosystem models in understanding and predicting carbon emissions from drainage ditches. Furthermore, this study offers valuable insights into the carbon emission responses in ditch ecosystems over a nutrient loading and depth gradient, thus paving the way for assessing the effectivity of management scenarios in controlling carbon emissions from ditches.