Total organic carbon fluxes of the Red River system (Vietnam)

Abstract

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.

Riverine carbon fluxes to the South China Sea

“…Our estimation is similar to the measured result. Another example, the reported annual POC fluxes in the Hong River (Red R.) and Brantas River are 0.15 and 0.015 Mt C, respectively [ Le et al ., ; Jennerjahn et al ., ], but the estimated values are 0.92 ± 0.98 and 0.07 ± 0.07 Mt C, respectively. These significant differences resulted from differences in the sediment loads.…”

Sediment Fingerprinting Suggests Differential Suspended Particulate Matter Formation and Transport Processes Across Hydrologic Regimes

“…Previous studies examining POM dynamics across discharge regimes have identified phytoplankton and degraded terrestrial detritus as important POM sources during low flows (including nonevent baseflows; Bukaveckas et al, 2011;Coynel et al, 2005;Dodds et al, 2004;Hatten et al, 2012;Le et al, 2017;Pettine et al, 1998;Relexans et al, 1988). These materials are typically characterized by elevated C and N contents and low C:N values (Meybeck, 1982).…”

A Modeling Approach to Diagnose the Impacts of Global Changes on Discharge and Suspended Sediment Concentration within the Red River Basin

“…Therefore, high erosion plus the character of soil types colour the water of the Thao River and the Da River into "red" [50]. In Vietnam, the same Acrisols dominate on the slopes, and grey or alluvial soils dominate in the valleys [41]. Land use in China is mainly forest, accounting for 62% of the area, followed by grassland and cultivated land, accounting for 19% and 18%, respectively [1] .…”

“…The Red River is a typical Asian river system, combining different land uses, affected by human activities such as intensive dam implementations and agriculture [36,37]. Recent studies of hydrology and suspended sediment in this basin mainly used data from gauge stations or sampling to do statistical analysis [38][39][40][41], or use modeling to perform simulations at a local scale [42] or in the delta part [43] at a monthly scale; few studies analyzed fluxes at daily scale, but only on a short period [37], in the delta [44] or only for discharge or suspended sediment [45]. Both Q and SSC can vary greatly from day to day; therefore, it would be more favourable to calculate flux at a daily scale.…”