Impact of water management on methane emission dynamics in Sri Lankan paddy ecosystems

Paddy ecosystems constitute a dominant source of greenhouse gases, particularly of methane (CH₄), due to the continuous flooding (CF) practiced under conventional paddy cultivation. A new management method, namely alternative wetting and draining (AWD) (i.e., flooding whenever surface water levels decline to 15 cm below the soil surface), is an emerging practice developed to mitigate CH₄ emissions while providing an optimal solution for freshwater scarcity. Despite extensive paddy cultivation in Sri Lanka, no systematic research study has been conducted to investigate CH₄ emissions under different water management practices. Thus, field experiments were conducted in Sri Lanka to investigate the feedback of controlled water management on seasonal and diel variation of CH₄ emission, water consumption, and crop productivity. Adopting the same rice variety, two water management methods, continuous flooding (CF) and alternative wetting and draining (AWD), were compared with plants (W/P) and without plants (N/P) present. The emission of CH₄ was measured using the static closed chamber method. The results show a 32% reduction in cumulative CH₄ emission, on average, under AWD when compared to CF. The yield under the AWD was slightly higher than that of CF. Although it was not statistically significant (p > 0.05) there was not any reduction in yield in AWD than in CF. The total water saving under AWD ranged between 27–35% when compared to CF. Thus, the results support (without considering the effect of nitrous oxide) AWD as a promising method for mitigating CH₄ emissions while preserving freshwater and maintaining grain yield in paddy systems

Transport of Colloids and Colloid-facilitated Cadmium in a Sri Lankan Agricultural Soil

Naturally occurring colloids, particles of diameter < 2 μm, are ubiquitous in geo environments and can potentially facilitate transport of numerous contaminants in soil via colloid-facilitated transport (CFT). Colloid mobilization, transport and CFT in various geo-media are highly sensitive to physico-chemical perturbations. This study investigated colloid, and colloid facilitated cadmium transport in saturated porous media with a series of column experiments. Soil colloids were extracted from soils belonging to two areas affected by chronic kidney disease of unknown etiology (CKDu) in Sri Lanka. Colloid breakthrough curves were obtained from the column studies under different flow rates (0.50, 1.60, and 4.00 ± 0.05 Em3/s) and ionic strengths (0.01, 0.05, and 0.10 E NaCl). The CFT was studied using Cd(II) as a model contaminant together with colloidal suspension under selected scenarios for high colloidal deposition. Elevated colloid concentrations were observed in highly CKDu affected area. The experimental results were numerically simulated on an advection-diffusion/dispersion modelling framework coupled with first-order attachment, detachment and straining parameters inversely estimated using Hydrus 1D software. Experimental and simulated colloid breakthrough curves showed a good agreement and recognized colloid attachment as the key retention mechanism. Both colloids and CFT of Cd(II) showed pronounced deposition under low flow rates and high ionic strengths

Effect of subsurface soil moisture variability and atmospheric conditions on methane gas migration in shallow subsurface

A major concern resulting from the increased use and production of natural gas has been how to mitigate fugitive greenhouse gas emissions (predominantly methane) from natural gas infrastructure (e.g., leaky shallow pipelines). Subsurface migration and atmospheric loading of methane from pipeline leakage is controlled by source configurations and subsurface soil conditions (e.g., soil heterogeneity and soil moisture) and are further affected by atmospheric conditions (e.g., wind and temperature). However, the transport and attenuation of methane under varying subsurface and atmospheric conditions are poorly understood, making it difficult to estimate leakage fluxes from methane concentration measurements at and above the soil surface. Based on a series of controlled bench-scale experiments using a large porous media tank interfaced with an open-return wind tunnel, this study investigated multiphase processes controlling migration of methane from a point source representing a buried pipeline leaking at fixed flow rate (kg/s) under various saturation and soil-texture conditions. In addition, potential effects of atmospheric boundary controls, wind (0.5 and 2.0 m s−1) and temperature (22 and 35 °C), were also examined. Results showed the distinct effects of soil heterogeneity and, to a varying degree, of soil moisture on surface methane concentrations. In addition, results also showed the pronounced effects of wind and, to a lesser degree, of temperature on surface methane concentrations in the presence of varying soil and moisture conditions. The observed subsurface methane profiles were simulated using the multiphase transport simulator TOUGH2-EOS7CA. Observed agreement between measured and simulated data demonstrates that for the conditions studied, multiphase migration of a multicomponent gas mixture (including methane) under density-dependent flow can be adequately represented with a Fickian advection-diffusion (or dispersion) model (ADM) framework. The dominant effect of saturation over the soil texture, could also be inferred from numerical characterization

Effect of subsurface soil moisture variability and atmospheric conditions on methane gas migration in shallow subsurface

A major concern resulting from the increased use and production of natural gas has been how to mitigate fugitive greenhouse gas emissions (predominantly methane) from natural gas infrastructure (e.g., leaky shallow pipelines). Subsurface migration and atmospheric loading of methane from pipeline leakage is controlled by source configurations and subsurface soil conditions (e.g., soil heterogeneity and soil moisture) and are further affected by atmospheric conditions (e.g., wind and temperature). However, the transport and attenuation of methane under varying subsurface and atmospheric conditions are poorly understood, making it difficult to estimate leakage fluxes from methane concentration measurements at and above the soil surface. Based on a series of controlled bench-scale experiments using a large porous media tank interfaced with an open-return wind tunnel, this study investigated multiphase processes controlling migration of methane from a point source representing a buried pipeline leaking at fixed flow rate (kg/s) under various saturation and soil-texture conditions. In addition, potential effects of atmospheric boundary controls, wind (0.5 and 2.0 m s−1) and temperature (22 and 35 °C), were also examined. Results showed the distinct effects of soil heterogeneity and, to a varying degree, of soil moisture on surface methane concentrations. In addition, results also showed the pronounced effects of wind and, to a lesser degree, of temperature on surface methane concentrations in the presence of varying soil and moisture conditions. The observed subsurface methane profiles were simulated using the multiphase transport simulator TOUGH2-EOS7CA. Observed agreement between measured and simulated data demonstrates that for the conditions studied, multiphase migration of a multicomponent gas mixture (including methane) under density-dependent flow can be adequately represented with a Fickian advection-diffusion (or dispersion) model (ADM) framework. The dominant effect of saturation over the soil texture, could also be inferred from numerical characterization