Aquaculture plays a crucial role in meeting the increasing demand for protein-rich food. However, aquaculture production also comes with a large carbon footprint, partly due to the substantial emission of greenhouse gases, particularly methane (CH₄), during the aquaculture production. Yet, our understanding on the magnitude, pathways, and drivers of CH4 emission from aquaculture ponds is limited, particularly in the Asian continent where more than 90% of global aquaculture production occurs. In this study, we quantified CH4 concentrations, air–water fluxes, production in anoxic sediments, and oxidation in the water column across multiple tropical aquaculture ponds where one of the most commonly cultivated shrimp species, Litopenaeus vannamei, is farmed. Field measurements showed that the diffusive CH4 emissions, with a mean value of 3.40 ± 1.76 mg m−2 day−1, varied greatly—ranging from 0.68 to 7.12 mg m−2 day−1—and were regulated by a suit of environmental variables. Salinity and total phosphorus (TP) concentration were the key determinants of diffusive CH4 flux: CH4 emission decreased with increasing salinity, while it increased with TP. Accordingly, our results suggest that shifting from freshwater to saline water aquaculture can decrease CH₄ emissions, thereby reducing the carbon footprint of aquaculture production. However, an increase in phosphorus concentration can offset this salinity-driven emission reduction. Therefore, management practices should prioritize reducing phosphorus loads to effectively mitigate CH₄ emissions and enhance the sustainability of aquaculture. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.

Rivers are globally significant sources of atmospheric carbon dioxide (CO2). However, the processes governing supersaturation of CO2 in large tropical fluvial networks are poorly understood. In particular, strikingly little is known about the role of land use in shaping CO2 variability in South Asian river basins, which are undergoing rapid urbanization. Here, we show that the wide variability in the partial pressure of CO2 (pCO2: 246.3-21271.2 μatm) in an agriculture-dominated river basin (Krishna River basin, India) is primarily shaped by the extent of urbanization. Specifically, a strong positive correlation between pCO2 and built-up area (%) was observed when the built-up area exceeded 2%. Furthermore, machine learning analysis showed that pCO2 variability was predicted by built-up area (%), Strahler order, and altitude, together explaining ∼77% of the spatial variability. Additionally, a strong negative correlation between excess CO2 and oxygen relative to atmospheric equilibrium indicates that in-stream metabolism, fueled by organic matter inputs from urbanized areas, is the primary cause of CO2 supersaturation, establishing a mechanistic link between pCO2 and the built-up area. Given that pCO2 increases with urbanization, limiting urban inputs is crucial for reducing fluvial CO2 emissions from South Asian river basins. © 2025 American Chemical Society.

Aquatic sediments represent a key component for understanding CH4 dynamics and emission to the atmosphere. Once produced in the sediments, CH4 is released either by diffusion at the sediment–water interface or by bubbling out to the atmosphere when total gas pressure in the sediment exceeds local ambient pressure due to high CH4 production. Although bubbling is one of the dominant CH4 emission pathways in lakes, direct measurements of this flux are hampered by its high spatiotemporal variability and methodological limitations. Here, we develop a conceptual approach to quantify CH4 production in lake sediments and particularly its release as bubbles based on simple measurements of bubble gas content and depth. Its main assumptions were empirically tested using > 200 long-term bubble trap deployments collected from 4 temperate lakes. We then applied the developed methodology to a suite of 408 Canadian lakes to produce the first standardized large-scale assessment of lakes CH4 ebullitive flux during summer. Our results show that lake sediments produced CH4 at a median rate of 3.3 mmol m−2 d−1 (ranged from 0.2 to 11.8 mmol m−2 d−1), releasing 33% via ebullition to the atmosphere. These rates are remarkably similar in magnitude to other regional estimates in the literature. Moreover, our approach revealed that catchment slope was an important determinant of both the lake-wide ebullitive fluxes and the fraction of sediment CH4 production released as bubbles. © 2024 The Author(s). Limnology and Oceanography published by Wiley Periodicals LLC on behalf of Association for the Sciences of Limnology and Oceanography.

Aerobic methane oxidation (MOX) significantly reduces methane (CH4) emissions from inland water bodies and is, therefore, an important determinant of global CH4 budget. Yet, the magnitude and controls of MOX rates in rivers – a quantitatively significant natural source of atmospheric CH4 – are poorly constrained. Here, we conducted a series of incubation experiments to understand the magnitude and environmental controls of MOX rates in tropical fluvial systems. We observed a large variability in MOX rate (0.03 - 3.45 μmol l-1d-1) shaped by a suit of environmental variables. Accordingly, we developed an empirical model for MOX that incorporate key environmental drivers, including temperature, CH4, total phosphorus, and dissolved oxygen (O2) concentrations, based on the results of our incubation experiments. We show that temperature dependency of MOX (activation energy: 0.66 ± 0.18 eV) is lower than that of sediment methanogenesis (0.71 ± 0.21 eV) in the studied tropical fluvial network. Furthermore, we observed a non-linear relationship between O2 concentration and MOX, with the highest MOX rate occuring ∼135 μmol O2l-1, above or below this “optimal O2” concentration, MOX rate shows a gradual decline. Together, our results suggest that the relatively lower temperature response of MOX compared to methanogenesis along with the projected decrease of O2 concentration due to organic pollution may cause elevated CH4 emission from tropical southeast Asian rivers. Since estimation of CH4 oxidation is often neglected in routine CH4 monitoring programs, the model developed here may help to integrate MOX rate into process-based models for fluvial CH4 budget. © 2024 Elsevier Ltd

Oxygenated surface layers of aquatic systems are ubiquitously oversaturated with methane (CH4). A growing number of studies suggest that CH4 oversaturation in surface waters can be sustained, at least partly, by methanogenesis occurring under oxic conditions. Although we are gaining a better understanding of the extent and drivers of oxic CH4 production (OMP) in oceanic and lake environments, the existence and variability of OMP in rivers and streams remain unknown. Here, we present experimental evidence for the occurrence and a large variability of OMP rates in a tropical river network. The positive correlation between chlorophyll a concentration and OMP rates and reduction of OMP during the experimental inhibition of photosynthesis establishes a clear link between OMP and photosynthesis. At the same time, a general decrease of the OMP rates with increasing total phosphorus (TP) concentration and the correlation between stable carbon isotopic (δ13C-CH4) values of the OMP-derived CH4 and TP suggest the likely involvement of P-availability as well in regulating the OMP rates. While our estimation suggested a minor contribution of the OMP in the CH4 cycling of the studied tropical system, we show that the OMP in the fluvial environment may be highly sensitive to the current and future changes in algal and nutrient dynamics. © 2024 American Chemical Society.