Respective contribution of urban wastewater and mangroves on nutrient dynamics in a tropical estuary during the monsoon season

• Published in: Marine pollution bulletin Vol. 160; p. 111652
• Main Authors: Taillardat, Pierre, Marchand, Cyril, Friess, Daniel A., Widory, David, David, Frank, Ohte, Nobuhito, Nakamura, Takashi, Van Vinh, Truong, Thanh-Nho, Nguyen, Ziegler, Alan D.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.11.2020; Elsevier BV
• Subjects: Ammonium; Ammonium compounds; Aquaculture; Dissolved oxygen; Dynamics; Effluents; Environmental risk; Estuaries; Estuarine dynamics; Isotopes; Land cover; Land pollution; Land use; Mangroves; Mineral nutrients; Monsoons; Nitrate stable isotopes; Nitrification; Nutrient concentrations; Nutrient dynamics; Nutrient loading; Nutrients; Oxygen content; Phosphate; Phytoplankton; River discharge; River flow; Salinity; Salinity effects; Salinity gradients; Saturation; Stable isotopes; Tropical climate; Urban effluents; Vegetated coastal ecosystems; Wastewater; Wind; Urban effluents; Vegetated coastal ecosystems; Ammonium; Phosphate; Nitrate stable isotopes; Aquaculture
• ISSN: 0025-326X; 1879-3363
• DOI: 10.1016/j.marpolbul.2020.111652

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. •Nutrient dynamics during the wet season were studied along the Can Gio Estuary.•Nutrients in the upper estuary originated from urban wastewater•Mangrove-derived nutrients dominated the lower estuary•Nutrients from aquaculture seemed to be rapidly diluted.•Nitrification, phytoplankton and heterotrophic activity are key elements of nutrient cycling.