Abstract Tropical estuaries may release large amounts of carbon dioxide to the atmosphere, but remain understudied relative to temperate systems. Here, we investigate hydrological drivers of pCO2 along ~22 km of an aquatic continuum from the mountain river to the coastal ocean, including highly modified aquaculture and urban zones (Perancak Estuary, Ijo Gading River, Bali, Indonesia). We report seasonal spatial surveys (n = 8) and stationary time series observations (n = 4 days) during a rain event. Overall, pCO2 ranged from 330 μatm to 12,126 μatm, with the lowest values observed near the estuary mouth and in the river upstream of the urban zone, and the highest values in the upper estuary where radon (222Rn, a natural groundwater tracer) revealed elevated groundwater discharge. Average atmospheric CO2 fluxes in the upper estuary (107.3 mmol m−2 d−1) were ~5-fold greater than in the lower estuary (19.1 mmol m−2 d−1), while the river was a minor atmospheric CO2 sink (−0.2 mmol m−2 d−1). Overall, the estuary was a source of CO2 to the atmosphere with area-weighted emissions of ~67 mmol m−2 d−1. Seasonal spatial surveys revealed strong correlations between antecedent rainfall and pCO2 and 222Rn in the estuary, implying pCO2 responds to delayed groundwater discharge. A detailed 4-day time series covering an episodic flooding event revealed sharp transitions in CO2 drivers, including dilution by rainfall followed by inputs of CO2-enriched groundwater. Groundwater discharge, as traced by radon, explained most of pCO2 variability in dry and wet conditions. Overall, we highlight the importance of seasonal and episodic rainfall and how delayed groundwater seepage may drive CO2 distribution in a highly modified tropical estuary.

中文翻译：

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季节性和降雨事件时间尺度上热带河口的二氧化碳动态

摘要 热带河口可能会向大气释放大量二氧化碳，但相对于温带系统，研究仍然不足。在这里，我们沿着从山区河流到沿海海洋的约 22 公里的水生连续体调查 pCO2 的水文驱动因素，包括高度改造的水产养殖和城市地区（Perancak Estuary、Ijo Gading 河、印度尼西亚巴厘岛）。我们报告了降雨事件期间的季节性空间调查 (n = 8) 和平稳时间序列观测 (n = 4 天)。总体而言，pCO2 范围从 330 μatm 到 12,126 μatm，在河口附近和市区上游河流中观察到的值最低，而在河口上游的氡（222Rn，一种天然地下水示踪剂）显示升高的值最高地下水排放。河口上游的平均大气 CO2 通量 (107. 3 mmol m-2 d-1) 是河口下游 (19.1 mmol m-2 d-1) 的约 5 倍，而河流是一个较小的大气 CO2 汇 (-0.2 mmol m-2 d-1 ）。总体而言，河口是大气 CO2 的来源，面积加权排放量约为 67 mmol m-2 d-1。季节性空间调查显示，河口前期降雨量与 pCO2 和 222Rn 之间存在很强的相关性，这意味着 pCO2 对延迟的地下水排放有反应。涵盖偶发性洪水事件的详细 4 天时间序列揭示了 CO2 驱动因素的急剧转变，包括被降雨稀释，然后是富含 CO2 的地下水的输入。由氡追踪的地下水排放解释了大部分干燥和潮湿条件下 pCO2 的变化。全面的，