Estuaries of Southeast Asia are increasingly impacted by land-cover changes and pollution. Here, our research objectives were to (1) determine the origins of nutrient loads along the Can Gio estuary (Vietnam) and (2) identify the processes that affect the nutrient pools during the monsoon. We constructed four 24-h time-series along the salinity gradient measuring nutrient concentrations and stable isotopes values. In the upper estuary, urban effluents from Ho Chi Minh City were the main input of nutrients, leading to dissolved oxygen saturation <20%. In the lower estuary, ammonium and nitrite concentration peaks were explained by mangrove export. No contribution from aquaculture was detected, as it represents <0.01% of the total river discharge. Along the salinity gradient, nutrient inputs were rapidly consumed, potentially by phytoplankton while nitrate dual-stable isotopes indicated that nitrification occurred. Thus, even in a large and productive estuary, urban wastewater can affect nutrient dynamics with potentially important ecological risks.

东南亚的河口越来越受到土地覆盖变化和污染的影响。在这里，我们的研究目标是（1）确定Can Gio河口（越南）沿岸养分的来源，以及（2）确定影响季风期间养分池的过程。我们沿着盐度梯度构建了四个24小时时间序列，用于测量营养物浓度和稳定的同位素值。在河口上游，来自胡志明市的城市污水是养分的主要输入，导致溶解氧饱和度<20％。在较低的河口，红树林的出口解释了铵和亚硝酸盐的浓度峰值。未检测到水产养殖的贡献，因为它占总河流排放量的<0.01％。沿着盐度梯度，营养物质输入被迅速消耗，可能是由浮游植物引起的，而硝酸盐双稳态同位素表明发生了硝化作用。因此，即使在较大的生产性河口中，城市废水也可能影响营养动态，并可能带来重要的生态风险。