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Riverine transport of organic carbon from terrestrial ecosystems to the oceans plays an important role in the global carbon cycle. The Red River is located in Southeast Asia where river discharge, sediment loads and fluxes of elements (carbon, nitrogen and phosphorus) associated with suspended solids have been dramatically altered over past decades as a result of reservoir impoundment and land use, population, and climate change. Dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations were measured monthly at four stations of the Red River system from January 2008 to December 2010. The results reveal that POC changed synchronically with total suspended solids (TSS) concentration and with the river discharge, whereas no clear trend was observed for DOC concentration. The mean value of total organic carbon (TOC = DOC + POC) flux in the delta of the Red River was 31.5 × 1013 ± 4.0 × 1013 MgC.yr−1 (range 27.9–35.8 × 1013 MgC.yr−1 which leads to a specific TOC flux of 2012 ± 255 kgC.km−2.yr−1 during this 2008–2010 period. About 80% of the TOC flux was transferred to the estuary during the rainy season as a consequence of the higher river water discharge. The high mean value of the POC:Chl‐a ratio (1585 ± 870 mgC.mgChl‐a−1) and the moderate C:N ratio (7.3 ± 0.1) in the water column system suggest that organic carbon in the Red River system is mainly derived from erosion and soil leaching in the basin. The effect of two new dam impoundments in the Red River was also observable with lower TOC fluxes in 2010 compared with 2008. Copyright © 2017 John Wiley & Sons, Ltd.

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Arsenic contamination in groundwater and its effect on human health has been a growing concern over recent decades. Some of the most severe incidents occurred in South and Southeast Asia, including the Red river delta, Vietnam. The highest concentration of arsenic found in the Red river delta was 810 μg/L, 16 times higher than the standard guidelines given by WHO for levels of arsenic concentration in groundwater (50 μg/L). However, the contamination levels were not uniform in the whole area. The arsenic levels might be affected by natural factors such as the characteristics of the aquifer, the chemical composition of groundwater and by human activities such as the exploitation of groundwater in the urban and industrial areas or irrigation in rural areas. Due to the complex mobilisation of arsenic in sediment and groundwater, questions remain about arsenic distribution, which are yet to be answered and are in need of further study.