Carbon dynamics in agricultural soils: Insights into methane fluxes under changing hydrological conditions.

NEVERMANN S.; JOBBÁGY E.; NOSETTO, MARCELO; HOUSPANOSSIAN. J; DIEZ F.; NICK OSTLE; RUFINO M.

Viena

Congreso; EGU General Assembly 2025,; 2025

Soils serve as critical carbon sinks, playing a vital role in mitigating global warming and ensuringglobal food security. However, rapidly changing climatic and environmental conditions, such asextreme weather events, threaten the soil’s capacity to act as carbon sinks. Land use changes,particularly those driven by agricultural intensification, can alter hydrological regimes and carbondynamics in landscapes. Understanding these dynamics by measuring GHG fluxes andinvestigating soil properties is crucial for designing sustainable land management practices thatpromote both environmental stability and climate resilience, ensuring soils continue to play acritical role in combating climate change.Currently, little is known of how soil carbon responds to extreme events such as floods anddroughts and how their repeated impacts shape carbon storage and loss and ultimately affect thecarbon balance.This study examined the impact of altered hydrological conditions, driven by the conversion ofnative vegetation to cropland, on carbon dynamics and carbon loss pathways. The aim is toidentify patterns of methane and carbon dioxide emissions from naturally and recently inundatedsoils and their key driving factors.We conducted in situ gas measurements using mobile trace gas analysers and a mobile smartchamber in the heavily agricultural Argentinian Pampas and Espinal ecoregions. Additionally, wecollected soil samples from 0-30 cm depth for chemical analysis (including total and dissolvedorganic carbon) and measured soil temperature, electrical conductivity, soil moisture, and pH.The results show complex interactions and dependencies between methane emissions andenvironmental variables. Methane fluxes are more than 5 times higher in saturated areas (median= 49.98 μg/m²) compared to dry areas (median =-8.34 μg/m²), primarily influenced by water tabledepth and soil moisture. Contrary to expectations, soil salinity, measured as electrical conductivity,exhibited a positive effect on methane production, reaching a threshold around 55 mS/m,suggesting possible tolerance or adaptation mechanisms of methanogens. Carbon dioxideemissions showed a reduction of almost 50 % in drier areas, primarily driven by soil moisture,highlighting the strong impact of moisture on carbon dynamics.The findings highlight the critical role of hydrological conditions, particularly flooding, in drivingmethane fluxes from soils, emphasizing the need for targeted management practices to mitigatecarbon loss and adapt to changing climatic conditions. Additionally, the effect of soil salinity onmethane production underscores the importance of considering salinity in future research andmanagement strategies.