Long-term biogeochemical functioning of the Red River (Vietnam): past and present situations

Abstract

International audienceThe Red River (North Vietnam) is a typical example of a subtropical Asian river system undergoing high human pressure. During the last 50 years, major changes have occurred in its watershed, extending over an area of 156,450 km(2) in Vietnam and China. We provide a detailed account of these changes, related to intensification of agriculture, deforestation, increase in population and urbanization, impoundment of reservoirs, etc. This information is used in a modeling approach of the nutrient transfers and transformations along the river system, in order to evaluate the changes in water quality of the Red River and its potential for coastal eutrophication. We conclude that the combination of increased nitrogen release from agriculture and retention of phosphorus in the reservoirs has considerably changed the balance of nutrients delivered at the outlet of the river, bringing the system close to a turning point in its nutrient biogeochemistry and its potential for coastal eutrophication. The upcoming impoundment of four new major dams in the watershed makes this conclusion particularly relevant

Carbon Dynamics Along the Seine River Network: Insight From a Coupled Estuarine/River Modeling Approach

“…The genericity of the Riverstrahler model has been demonstrated throughout successful applications to contrasted fluvial basins, from temperate climate including (among other) the Moselle (Garnier et al, 2000), the Danube (Garnier et al, 2002), the Scheldt (Thieu et al, 2009) among other, sub-tropical climate as the Red River (Le et al, 2014) or the Nam Kan river (Causse et al, 2015) and or under nordic climate, such as the Kalix and Lule rivers (Sferratore et al, 2008) and the Seine river (Raimonet et al, 2018). The Riverstrahler model has also been chained with the coastal marine model (ECO-MARS3D, Cugier et al, 2005), extended to the estuarine part in terms of hydrosedimentary representation (Passy et al, 2016), and with nutrient description (Romero et al, 2018).…”

CO<sub>2</sub> partial pressure and CO<sub>2</sub> emission along the lower Red River (Vietnam)

“…Average values (and standard deviation) of river water discharge at five studied sites of the Red River in 2014 (MONRE, 2014; regime characterized by large run-off during the wet season and low run-off during the dry season (Table 1). A series of dams and reservoirs was impounded in both Chinese and Vietnamese territories of the upstream part of Red River (Le et al, 2017). In the Da River, two large dams, Hoa Binh and Son La, were constructed in the river main stem, whereas in the Lo River, two large dams, Thác Bà and Tuyên Quang, were constructed in its tributaries.…”

“…The upstream part of the Red River in the Chinese part is dominated by mountainous areas, which are tectonically active and unstable, and this, combined with intense rainfall, causes high erosion rates (Fullen et al, 1998), whereas in the Vietnamese part, soils are mostly (70 %) grey and alluvial (Le et al, 2017). The delta is located in a very flat and low land, with an elevation ranging from 0.4 to 12 m above sea level (Nguyen Ngoc Sinh et al, 1995).…”

“…Previous studies reported the hydrology and suspended sediment load associated with some element loads (N, P, C) of the Red River (Dang et al, 2010;Le et al, 2015;Lu et al, 2015). Recently, the transfer of organic carbon of the Red River to the ocean has been studied (Dang et al, 2010;Le et al, 2017). However, there is a lack of data concerning CO 2 outgassing and the carbon budget of the lower Red River (Trinh et al, 2012;Nguyen et al, 2018).…”

The role of water nitrogen retention in integrated nutrient management: assessment in a large basin using different modelling approaches

“…The three models compared in this study are widely used in Europe and in the world to analyse nitrogen fluxes in large river basins, linking sources, pathways and impacts (Bouraoui et al 2014, Gassman et al 2014, Lee et al 2015. The RiverStrahler model is at the core of the operational tool SENEQUE-River-Strahler used by the Seine river basin's water agency (Agence de l'Eau Seine-Normandie).…”