Carbon dioxide (CO₂) super-saturation in estuaries and the associated efflux to the atmosphere is an important part of the global carbon cycle. However, the net global estuarine emission of CO₂ is based on limited spatial data. In this study, alkalinity, pH, salinity and temperature data were used to quantify the CO₂ dynamics in the Devi estuary formed by the main distributary of the Mahanadi river on the east coast of India. The samples were collected during summer, monsoon and winter of 2018–19 in order to understand the seasonal and spatial variability of pCO₂ and CO₂ efflux from the estuary. High pCO₂ (1565 ± 782 μatm) in comparison to the atmosphere (389 μatm) was found in the estuary throughout the study period. The highest pCO₂ was observed during winter season (2071 ± 828 μatm) and the lowest one during monsoon (951 ± 316 μatm). A decreasing trend in pCO₂ from the upper estuary to lower estuary was observed. The mean dissolved oxygen saturation (DO%) was 137% throughout the study period indicating well-oxygenated waters. A decrease in DO% with increased pCO₂ accompanied by a decrease in pH suggests that organic matter degradation is a major controlling factor of pCO₂ in the estuary. Thus, heterotrophic environmental condition is prevalent in the estuary. Net annual CO₂ efflux from the Devi river estuary was estimated to be 40.1 ± 7.5 mol C m⁻² yr⁻¹, and the highest efflux was observed during summer season (126 ± 69 mmol C m⁻² d⁻¹) due to higher temperature and wind speed. The net efflux from the Devi river estuary is about 0.003–0.006% of the total global CO₂ emission from estuaries. This study highlights the importance of small-scale estuaries in emitting large flux of CO₂ to the atmosphere. The results contribute to the increasing dataset of pCO₂ and CO₂ effluxes from estuaries worldwide in order to accurately estimate the role of estuaries in the global carbon budget.

河口二氧化碳 (CO ₂ ) 超饱和以及相关的排放到大气中是全球碳循环的重要组成部分。然而，CO _{2 的}全球净河口排放基于有限的空间数据。在这项研究中，碱度、pH 值、盐度和温度数据用于量化由印度东海岸马哈纳迪河的主要支流形成的德维河口的 CO ₂动态。样本是在 2018-19 年夏季、季风和冬季收集的，以了解河口pCO ₂和 CO ₂流出的季节和空间变化。高 pCO ₂(1565 ± 782 μatm) 与大气 (389 μatm) 相比，在整个研究期间在河口发现。在冬季 (2071 ± 828 μatm) 期间观察到最高的 pCO ₂，在季风期间观察到最低的 pCO ₂ (951 ± 316 μatm)。观察到pCO ₂从上河口到下河口呈下降趋势。整个研究期间的平均溶解氧饱和度 (DO%) 为 137%，表明水体充氧良好。DO% 随 pCO ₂增加而降低，同时 pH 值降低表明有机物降解是河口pCO ₂的主要控制因素。因此，异养环境条件在河口普遍存在。净年度 CO ₂德维河口的流出量估计为 40.1 ± 7.5 mol C m ^-2 yr ^-1，由于较高的温度和风，在夏季观察到最高流出量（126 ± 69 mmol C m ^-2 d ^-1）速度。德维河河口的净流出量约占全球河口CO ₂排放总量的 0.003-0.006% 。这项研究强调了小规模河口在向大气排放大量 CO _{2 方面}的重要性。结果有助于增加全球河口pCO ₂和 CO ₂流出的数据集，以准确估计河口在全球碳预算中的作用。