Carbon dynamics in the Mekong Delta

Borges, Alberto; Abril, Gwénaël; Bouillon, Steven

doi:10.5194/bg-2017-444

Cited by 12 publications

(17 citation statements)

References 65 publications

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“…Lower GHG concentrations during the monsoon period (Figure 3) might have resulted from wastewater dilution by a monsoonal increase in discharge. However, higher concentrations of GHGs observed in several sites along the middle and lower reaches of the studied rivers (Figures 4, and ) are consistent with the patterns of pCO 2 observed in some sites of the lower Mekong (Borges, Abril, & Bouillon, 2018; Li et al., 2013) and the lower Yellow River (Ran et al., 2015). Monsoonal increases in CO 2 have been explained by the flushing of CO 2 and OM from the soil, floodplains, and other allochthonous sources and subsequent degradation of the allochthonous OM during riverine transport (Borges, Abril, & Bouillon, 2018; Li et al., 2013).…”

Section: Discussionsupporting

confidence: 86%

“…While δ 13 C has widely been measured to track downstream alterations of various DIC components in inland water systems, including CO 2 ,

{HCO}_{3}^{-}

, and

{CO}_{3}^{2 -}

(Borges, Abril, & Bouillon, 2018; Campeau et al., 2017; Jin et al., 2018), our approach is unique in linking the optical characterization of wastewater‐derived DOM to the isotopic signatures of CO 2 and CH 4 in the urbanized middle and lower reaches of the studied rivers. The measured values of δ 13 C‐CO 2 ranging from −6.0 to −24.5‰ (Table 2) span nearly the full range of reported values of δ 13 C‐CO 2 in streams, rivers, and estuaries (Campeau et al., 2017; Jin et al., 2018; Maher et al., 2013; McCallister & del Giorgio, 2008).…”

Section: Discussionmentioning

confidence: 99%

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Localized Pollution Impacts on Greenhouse Gas Dynamics in Three Anthropogenically Modified Asian River Systems

et al. 2021

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Despite growing research on greenhouse gas (GHG) emissions from inland waters, few systematic efforts have been made to assess the regional-scale GHG emissions from Asian rivers under increasing anthropogenic stress. We examined factors controlling longitudinal and seasonal variations in the partial pressure of CO 2 (pCO 2 ), and CH 4 and N 2 O concentrations in the Ganges, Mekong, and Yellow River by simultaneously measuring gas concentrations and stable C isotopes, and optical properties of dissolved organic matter (DOM) from 2016 to 2019. The levels of pCO 2 and CH 4 were distinctively higher in polluted tributaries and affected reaches of the Ganges and Mekong than in the Yellow River. The highest levels of N 2 O were found in the Ganges, followed by the Yellow River and Mekong. Across these basins, dry-season mean concentrations of CO 2 , CH 4 , and N 2 O were 1.6, 2, and 7 times higher than those measured in the monsoon season, respectively. This seasonality was consistent with that of δ 13 C-CO 2 , while δ 13 C-CH 4 showed an opposite pattern. GHG concentrations exhibited significant positive relationships with DOM concentrations and optical properties including fluorescence index and proteinlike fluorescence, implying the contribution of anthropogenic, labile DOM to production of GHGs in the polluted reaches. Graphical mixing models of δ 13 C-CO 2 and δ 13 C-CH 4 support the stronger impact of wastewater on the Ganges and Mekong than on the Yellow River. The overall results suggest that neglecting localized pollution impacts on GHG emissions from increasingly urbanized river basins can result in a substantial underestimation of global riverine GHG emissions.Plain Language Summary Rapid urbanization and poor wastewater infrastructure are turning many large rivers in Asia into significant sources of greenhouse gases (GHGs). We examined controlling factors for the concentrations of CO 2 , CH 4 , and N 2 O in the Ganges, Mekong, and Yellow River by simultaneously measuring gas concentrations and stable carbon isotopes, and optical properties of dissolved organic matter (DOM). The concentrations of CO 2 and CH 4 were distinctively higher in polluted tributaries and affected sections of the Ganges and Mekong than in the Yellow River. N 2 O concentration was highest in the Ganges, followed by the Yellow River and Mekong. Across these basins, the concentrations of the three gases were generally higher during dry periods than in the monsoon season. GHG concentrations were positively related to DOM optical properties indicating the contribution of easily degradable DOM from pollution sources. The stable carbon isotope ratios of CO 2 and CH 4 support the stronger impact of wastewater on the Ganges and Mekong than on the Yellow River. The overall results suggest that neglecting local pollution impacts on GHG emissions from increasingly urbanized river basins can result in a substantial underestimation of global riverine GHG emissions. BEGUM ET AL.

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Section: Discussionsupporting

confidence: 86%

“…While δ 13 C has widely been measured to track downstream alterations of various DIC components in inland water systems, including CO 2 ,

{HCO}_{3}^{-}

, and

{CO}_{3}^{2 -}

Section: Discussionmentioning

confidence: 99%

Localized Pollution Impacts on Greenhouse Gas Dynamics in Three Anthropogenically Modified Asian River Systems

et al. 2021

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“…Alin et al (2011) measured similar values (~1200 atm) at eight mainstem locations in Laos and Cambodia. The seasonal trend in pCO2 opposes the alkalinity and DIC trends, peaking in the flood season and lowest in the dry season, similar to several previous studies in tropical river systems (Sarma et al, 2011;Borges et al, 2017). 420…”

Section: Effects Of Increasing Water Pollution In Asian River Systemssupporting

confidence: 70%

“…MoWRAM (2016) has recently reported that total nitrogen concentrations in the Mekong downstream the range of 703-1,597 atm observed in the upstream reach during the similar period (September-October, 2004 and2005) by Alin et al (2011). As suggested by Borges et al (2017), anthropogenic pollution sources in the densely populated and 435 cultivated areas of the Delta may release more CO2 and biodegradable OM compared to the upstream reach.…”

Section: Effects Of Increasing Water Pollution In Asian River Systemsmentioning

confidence: 97%

Reviews and syntheses: Anthropogenic perturbations to carbon fluxes in Asian river systems: Concepts, emerging trends, and research challenges

Park¹,

Nayna²,

Begum³

et al. 2018

Preprint

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Abstract. Human activities are drastically altering water and material flows in river systems across Asia. These anthropogenic perturbations have rarely been linked to the carbon (C) fluxes of Asian rivers that may account for up to 40-20 50% of the global fluxes. The primary object of this review was to provide a conceptual framework for assessing human impacts on Asian river C fluxes, along with a latest update on anthropogenic alterations of riverine C fluxes, focusing on the impacts of water pollution and river impoundments on CO2 outgassing from the rivers draining South, Southeast, and East Asian regions that account for the largest fraction of river discharge and C exports from Asia and Oceania. Recent booms in dam construction across Asia have created a host of environmental problems; yet only a small number of studies have 25 explicitly investigated altered rates of greenhouse gas (GHG) emissions and organic C transport. There have been contrasting reports on impoundment effects: decreases in GHG emissions in the reservoirs exhibiting enhanced primary production vs. increased emissions from the flooded vegetation and soils in the early years following dam construction or from the impounded river reaches and downstream estuaries during the monsoon period. These contrasting results suggest that the rates of metabolic processes in the impounded and downstream reaches can greatly vary longitudinally over time, as 30 a combined result of diel shifts in the balance between autotrophy and heterotrophy, seasonal fluctuations between the dry and monsoon periods, and a long-term change from a leaky post-construction phase to a gradual C sink. Rapid pace of urbanization across southern and eastern Asian regions has dramatically increased municipal water withdrawal, generating annually 120.2 km 3 of wastewater in 24 countries, which comprises 38.6% of the global municipal wastewater production disproportionately affect the receiving river water, particularly downstream of rapidly expanding metropolitan areas, including eutrophication, increases in the amount and lability of organic C, and pulse emissions of CO2 and other greenhouse gases (GHGs). As reviewed for three representative rivers (the Ganges, Mekong, and Yellow River), the lower reaches of these rivers and their polluted tributaries tend to exhibit higher levels of organic C and the partial pressure of CO2 (pCO2) than the eutrophic reservoirs and less impacted upstream reaches. More field measurements of pCO2, together with accurate 40 flux calculations based on river-specific model parameters, are urgently required to provide more accurate estimates of GHG emissions from the Asian rivers that are now underrepresented in the global C budgets. Researchers working on individual river systems need to be linked to collaborative research networks to facilitate global synthesis of local field data. These synthesis efforts, combined with conceptual and mathematical models, will contribute to a better understanding of how anthropogenic perturbations in rapidly urb...

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“…Rainfall and downstream dilution likely caused the exponential decline of DIC and TAlk with increasing river discharge (Figure ). Similar dilution effects of DIC and TAlk from rainfall or snowmelt have been found in the Chena (Amiotte Suchet, Probst, & Ludwig, ), the Mississippi (Cai, ; Raymond & Cole, ), the Changjiang (Cai et al, ; Zhai, Dai, & Guo, ), the Congo (Probst et al, ), the Pearl (Guo et al, ), and the Mekong rivers (Borges, Abril, & Bouillon, ). The lower slope of the power regression in the North and South Johnstone suggests that river flushing was more steadily and dilution more significant here compared to the other Great Barrier Reef rivers (Figure ).…”

Section: Discussionmentioning

confidence: 98%

Alkalinity and dissolved inorganic carbon exports from tropical and subtropical river catchments discharging to the Great Barrier Reef, Australia

Rosentreter

Eyre

2019

Hydrological Processes

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Dissolved inorganic carbon (DIC) transport by rivers is an important control on the pH and carbonate chemistry of the coastal ocean. Here, we combine DIC and total alkalinity (TAlk) concentrations from four tropical rivers of the Great Barrier Reef region in Australia with daily river discharge to quantify annual river loads and export rates. DIC in the four rivers ranged from 284 to 2,639 μmol kg−1 and TAlk ranged from 220 to 2,612 μmol kg−1. DIC:TAlk ratios were mostly greater than one suggesting elevated exports of free [CO2*]. This was pronounced in the Johnstone and Herbert rivers of the tropical wet north. The largest annual loads were transported in the two large river catchments of the southern Great Barrier Reef region, the Fitzroy and Burdekin rivers. The carbon stable isotopic composition of DIC suggests that carbonate weathering was the dominant source of DIC in the southern rivers, and silicate weathering was likely a source of DIC in the northern Wet Tropics rivers. Annual loads and export rates were strongly driven by precipitation and discharge patterns, the occurrence of tropical cyclones, and associated flooding events, as well as distinct seasonal dry and wet periods. As such, short‐lived hydrological events and long‐term (seasonal and inter‐annual) variation of DIC and TAlk that are pronounced in rivers of the tropical and subtropical wet and dry climate zone should be accounted for when assessing inorganic carbon loads to the coastal ocean and the potential to buffer against or accelerate ocean acidification.

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Carbon dynamics in the Mekong Delta

Cited by 12 publications

References 65 publications

Localized Pollution Impacts on Greenhouse Gas Dynamics in Three Anthropogenically Modified Asian River Systems

Localized Pollution Impacts on Greenhouse Gas Dynamics in Three Anthropogenically Modified Asian River Systems

Reviews and syntheses: Anthropogenic perturbations to carbon fluxes in Asian river systems: Concepts, emerging trends, and research challenges

Alkalinity and dissolved inorganic carbon exports from tropical and subtropical river catchments discharging to the Great Barrier Reef, Australia

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