Balancing Vertical and Lateral Carbon Fluxes of Agroecosystems

Reducing greenhouse gases (GHG) emissions is essential for limiting global warming and averting unprecedented climate-related risks and damages. Agroecosystem based GHG emissions reduction technologies are identified as important components of future sustainable emission pathways. Up to date, most terrestrial ecosystem carbon balance accounting efforts focus on monitoring and analyzing vertical carbon fluxes, with lateral carbon fluxes largely unaccounted for. Emerging evidence shows that the magnitude of lateral carbon fluxes from land to inland waters, as well as the emissions and stocks of carbon in aquatic ecosystems, is comparable to the estimated terrestrial carbon sink at the global scale. Therefore, there is an urgent need to include lateral carbon fluxes into carbon balance assessment of agricultural and other terrestrial ecosystems. In this study, we combine multi-year continuous field measurements, remote sensing data and process-based modeling to quantify and analyze the relevance of lateral carbon fluxes to the assessment of carbon balance of a continuous corn field located in the Tuckahoe Creek Watershed (TCW) in eastern Maryland, U.S. Specifically, we (1) calculate on-site vertical carbon dioxide (CO₂) fluxes or Net Ecosystem Exchange (NEE) using four years of flux tower measurements; (2) use measured riverine carbon fluxes and remote sensing observations of ecosystem variables to constrain the soil and water assessment tool-carbon (SWAT-C) model for simulating lateral flows of POC and DOC leaving the corn field; and (3) illustrate the relevance of lateral carbon fluxes for agroecosystem carbon balance assessment. The resulting modeling system is also applied to six agricultural fields in the US Midwest to highlight the importance of factoring in lateral carbon fluxes for sustainable agricultural carbon management.