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Red River Basin - human activities and climate change

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Thi Phuong Quynh Le, Nhu Da Le, Viet Nga Dao, Emma Rochelle-Newall, Cyril Marchand, Thi Mai Huong Nguyen, and Thi Thuy Duong. 2018. Change in carbon flux (1960 – 2015) of the Red River (Vietnam). Journal of Environmental Earth Science. Vol 77: 658. DOI: 10.1007/s12665-018-7851-2.  (SCI, ISSN: Print ISSN: 1866-6280 Online ISSN: 1866-6299; IF = 1.435.)
Global riverine carbon concentrations and fluxes have been impacted by climate and human-induced changes for many decades. This paper aims to reconstruct the longterm carbon concentrations and carbon fluxes of the Red River, a system under the coupled pressures of environmental change and human activity. Based on (1) the relationships between particulate and dissolved organic carbon (POC, DOC) or dissolved inorganic carbon (DIC), and suspended sediments (TSS) or river water discharge and on (2) the available detailed historical records of river discharge and TSS concentration, the variations of the Red River carbon concentration and flux were estimated for the period 1960–2015. The results show that total carbon flux of the Red River averaged 2555 ± 639 kton C year−1. DIC fluxes dominated total carbon fluxes, representing 64% of total, reflecting a strong weathering process from carbonate rocks in the upstream basin. Total carbon fluxes significantly decreased from 2816 kton C year−1 during the 1960s to 1372 kton C year−1 during the 2010s and showed clear seasonal
and spatial variations. Organic carbon flux decreased in both quantity and proportion of the total carbon flux from 40.9% in 1960s to 14.9% in 2010s, reflecting the important impact of dam impoundment. DIC flux was also reduced over this period potentially as a consequence of carbonate precipitation in the irrigated, agricultural land and the reduction of the Red River water discharge toward the sea. These decreases in TSS and carbon fluxes are probably partially responsible for different negatives impacts observed in the coastal zone.
Keywords Carbon fluxes · Dam impoundment · POC · Red river · Vietnam
Thi Phuong Quynh Le, Cyril Marchand, Cuong Tu Ho, Nhu Da Le, Thi Thuy Duong, XiXi Lu, Phuong Kieu Doan, Trung Kien Nguyen, Thi Mai Huong Nguyen and Duy An Vu. 2018. CO2 partial pressure and CO2 emissions from the lower Red River (Vietnam). Biogeosciences 15, 4799-4814, https://doi.org/10.5194/bg-15-4799-2018, 2018.  (SCIE; IF = 3.448;).  ISSN 1726-4170    eISSN 1726-4189.
The Red River (Vietnam) is representative of a south-east Asian river system, strongly affected by climate and human activities. This study aims to quantify the spatial and seasonal variability of CO2 partial pressure and CO2 emissions of the lower Red River system. Water quality monitoring and riverine pCO2 measurements were carried out for 24 h at five stations distributed along the lower Red River system during the dry and the wet seasons. The riverine pCO2 was supersaturated relative to the atmospheric equilibrium (400 ppm), averaging about 1589 ± 43 ppm and resulting in a water–air CO2 flux of 530.3 ± 16.9 mmol m−2 d−1 for the lower Red River. pCO2 and CO2 outgassing rates were characterized by significant spatial variation along this system, with the highest values measured at Hoa Binh station, located downstream of the Hoa Binh Dam, on the Da River. Seasonal pCO2 and CO2 outgassing rate variations were also observed, with higher values measured during the wet season at almost all sites. The higher river discharges, enhanced external inputs of organic matter from watersheds and direct inputs of CO2 from soils or wetland were responsible for higher pCO2 and CO2 outgassing rates. The difference in pCO2 between the daytime and the night-time was not significant, suggesting weak photosynthesis processes in the water column of the Red River due to its high sediment load.
Thi Mai Huong Nguyen, Gilles Billen, Josette Garnier, Thi Phuong Quynh Le, Quoc Long Pham, Sylvain Huon, Emma Rochelle-Newall. 2018. Organic carbon transfers in the subtropical Red River system (Vietnam): insights on CO2 sources and sinks.  Biogeochemistry. https://doi.org/10.1007/s10533-018-0446-x. (SCI, ISSN: 0168-2563
The Red River, draining a 169,000 km2 watershed, is the second largest river in Viet Nam and constitutes the main source of water for a large percentage of the population of North Viet Nam. Here we present the results of an investigation into the spatial distribution and temporal dynamics of particulate and dissolved organic carbon (POC and DOC, respectively) in the Red River Basin. POC concentrations ranged from 0.24 to 5.80 mg C L−1 and DOC concentrations ranged from 0.26 to 5.39 mg C L−1. The application of the Seneque/Riverstrahler model to monthly POC and DOC measurements showed that, in general, the model simulations of the temporal variations and spatial distribution of organic carbon (OC) concentration followed the observed trends. They also show the impact of high population densities (up to 994 inhab km−2 in the delta area) on OC inputs in surface runoff from the different land use classes and from urban point sources. A budget of the main fluxes of OC in the whole river network, including diffuse inputs from soil leaching and runoff and point sources from urban centers, as well as algal net primary production and heterotrophic respiration was established using the model results. It shows the predominantly heterotrophic character of the river system and provides an estimate of CO2 emissions from the river of 330 Gg C year−1. This value is in reasonable agreement with the few available direct measurements of CO2 fluxes in the downstream part of the river network.
Keywords Sub-tropical watershed modeling Organic carbon Point and diffuse sources C metabolism 
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