Strong sources of CO2 in upper estuaries become sinks of CO2 in large river plumes

Chen, Chen‐Tung Arthur; Huang, Ting-Hsuan; Fu, Yaw-Syan; Bai, Yan; He, Xianqiang

doi:10.1016/j.cosust.2012.02.003

Cited by 100 publications

(79 citation statements)

References 66 publications

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“…However, estuarine filtering prevents some of the carbon that reaches the estuaries from also entering the oceans Kemp et al, 1997;Middelburg and Herman, 2007;Chen et al, 2012;Dai et al, 2012). Further, the exact extent of speciation changes between the organic and inorganic or dissolved and particulate carbon in the estuaries, and how much of each of these forms of carbon actually enters the oceans are still unknown (Woodwell et al, 1973;Wiegner and Seitzinger, 2001;Cai, 2011;Maher and Eyre, 2011).…”

Section: C-t a Chen Et Al: Air-sea Exchanges Of Co 2 In The Worldmentioning

confidence: 99%

“…This phenomenon, however, may be more than counteracted by enhanced heterotrophic activity, supported by organic carbon input from rivers (Smith and Hollibaugh, 1993;Heip et al, 1995;Hedges and Keil, 1995;Hedges et al, 1997;Hansell and Carlson, 1998;Bouillon et al, 2006;Jiang et al, 2010). Additionally, direct inorganic carbon input from river water, submarine groundwater discharge and exchanges with tidal marshes and mangroves play an important role in increasing the pCO 2 of estuarine and shelf waters (Moran et al, 1991;Miller and Moran, 1997;Neal et al, 1998;Raymond and Bauer, 2001;Borges et al, , 2006Cai et al, 2003;Wang and Cai, 2004;Jahnke et al, 2005;Bouillon et al, 2008;Jiang et al, 2008aJiang et al, , 2010Chen et al, 2012).…”

Section: C-t a Chen Et Al: Air-sea Exchanges Of Co 2 In The Worldmentioning

confidence: 99%

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Air–sea exchanges of CO2 in the world's coastal seas

et al. 2013

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Abstract. The air-sea exchanges of CO 2 in the world's 165 estuaries and 87 continental shelves are evaluated. Generally and in all seasons, upper estuaries with salinities of less than two are strong sources of CO 2 (39 ± 56 mol C m −2 yr −1 , positive flux indicates that the water is losing CO 2 to the atmosphere); mid-estuaries with salinities of between 2 and 25 are moderate sources (17.5 ± 34 mol C m −2 yr −1 ) and lower estuaries with salinities of more than 25 are weak sources . Mixing with low-pCO 2 shelf waters, water temperature, residence time and the complexity of the biogeochemistry are major factors that govern the pCO 2 in estuaries, but wind speed, seldom discussed, is critical to controlling the air-water exchanges of CO 2 . The total annual release of CO 2 from the world's estuaries is now estimated to be 0.10 Pg C yr −1 , which is much lower than published values mainly because of the contribution of a considerable amount of heretofore unpublished or new data from Asia and the Arctic. The Asian data, although indicating high pCO 2 , are low in sea-to-air fluxes because of low wind speeds. Previously determined flux values rely heavily on data from Europe and North America, where pCO 2 is lower but wind speeds are much higher, such that the CO 2 fluxes are higher than in Asia. Newly emerged CO 2 flux data in the Arctic reveal that estuaries there mostly absorb rather than release CO 2 .Most continental shelves, and especially those at high latitude, are undersaturated in terms of CO 2 and absorb CO 2 from the atmosphere in all seasons. Shelves between 0 and 23.5 • S are on average a weak source and have a small flux per unit area of CO 2 to the atmosphere. Water temperature, the spreading of river plumes, upwelling, and biological production seem to be the main factors in determining pCO 2 in the shelves. Wind speed, again, is critical because at high latitudes, the winds tend to be strong. Since the surface water pCO 2 values are low, the air-to-sea fluxes are high in regions above 50 • N and below 50 • S. At low latitudes, the winds tend to be weak, so the sea-to-air CO 2 flux is small. Overall, the world's continental shelves absorb 0.4 Pg C yr −1 from the atmosphere.

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Section: C-t a Chen Et Al: Air-sea Exchanges Of Co 2 In The Worldmentioning

confidence: 99%

Section: C-t a Chen Et Al: Air-sea Exchanges Of Co 2 In The Worldmentioning

confidence: 99%

Air–sea exchanges of CO2 in the world's coastal seas

et al. 2013

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“…Huge amounts of sediment would be deposited in the estuary and delta zones, and would not actually reach the Bohai Sea (H. J. . The deposited OC in these zones would further be oxidized due to strong flow turbidity (Chen et al, 2012). Consequently, both the sediment and OC amounts that actually enter the ocean should be smaller than the determined.…”

Section: Uncertainties From the Organic Carbon Termsmentioning

confidence: 99%

Erosion-induced massive organic carbon burial and carbon emission in the Yellow River basin, China

Ran

Xin

2014

Biogeosciences

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Abstract. Soil erosion and terrestrial deposition of soil organic carbon (SOC) can potentially play a significant role in global carbon cycling. Assessing the redistribution of SOC during erosion and subsequent transport and burial is of critical importance. Using hydrological records of soil erosion and sediment load, and compiled organic carbon (OC) data, estimates of the eroded soils and OC induced by water in the Yellow River basin during the period 1950-2010 were assembled. The Yellow River basin has experienced intense soil erosion due to combined impact of natural process and human activity. Over the period, 134.2 ± 24.7 Gt of soils and 1.07 ± 0.15 Gt of OC have been eroded from hillslopes based on a soil erosion rate of 1.7-2.5 Gt yr −1 . Approximately 63 % of the eroded soils were deposited in the river system, while only 37 % were discharged into the ocean. For the OC budget, approximately 0.53 ± 0.21 Gt (49.5 %) was buried in the river system, 0.25 ± 0.14 Gt (23.5 %) was delivered into the ocean, and the remaining 0.289 ± 0.294 Gt (27 %) was decomposed during the erosion and transport processes. This validates the commonly held assumption that 20-40 % of the eroded OC would be oxidized after erosion. Erosion-induced OC redistribution on the landscape likely represented a carbon source, although a large proportion of OC was buried. In addition, about half of the terrestrially redeposited OC (49.4 %) was buried behind dams, revealing the importance of dam trapping in sequestering the eroded OC. Although several uncertainties need to be better constrained, the obtained budgetary results provide a means of assessing the redistribution of the eroded OC within the Yellow River basin. Human activities have significantly altered its redistribution pattern over the past decades.

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“…With an estimated global efflux of 0.10-0.15 Pg C yr −1 (Chen et al, 2013;Laruelle et al, 2013), estuarine CO 2 degassing is thought to counterbalance CO 2 uptake on the continental shelves (Chen and Borges, 2009;Laruelle et al, 2010;Cai, 2011). Almost every estuary on Earth, for which data are available, is generally supersaturated with CO 2 with respect to the atmosphere (Cai and Wang, 1998;Frankignoulle et al, 1998;Borges, 2005;Borges et al, 2005Borges et al, , 2006Chen and Borges, 2009;Laruelle et al, 2010;Cai, 2011;Chen et al, 2012;Bauer et al, 2013;Chen et al, 2013;Regnier et al, 2013), with CO 2 partial pressures (pCO 2 ) ranging from 400 to 10 000 µatm (in contrast, the atmospheric pCO 2 in coastal zones was approximately 360-385 µatm in the year 2000) (Cai, 2011). Although estuaries are generally net sources of CO 2 , there is considerable variability and uncertainty in estimates of their CO 2 emissions, reflecting the limited spatial and temporal coverage of pCO 2 measurements in estuaries as well as their heterogeneous nature (hydrological and geomorphological differences, differences in magnitude and stoichiometry of 3222 A.…”

Section: Introductionmentioning

confidence: 99%

“…A recent synthesis by Regnier et al (2013) highlighted the meagre spatial coverage of estuarine pCO 2 measurements, particularly along the eastern Canadian seaboard. Ironically, the Estuary and Gulf of St. Lawrence (EGSL) in eastern Canada is the largest semi-enclosed estuarine system in the world and is among the world's most intensively studied estuaries (El-Sabh and , but was left unmentioned in recent global (Cai, 2011;Chen et al, 2012Chen et al, , 2013 and regional (Laruelle et al, 2015) data compilations. Furthermore, previous estuarine CO 2 studies have focused on riverdominated estuaries, whereas there has been limited research on CO 2 dynamics in large estuaries and bays (Joesoef et al, 2015), i.e., marine-dominated systems, including the areas of mixing at sea (outer estuaries or river plumes) .…”

Section: Introductionmentioning

confidence: 99%

Spatial variability in surface-water pCO2 and gas exchange in the world's largest semi-enclosed estuarine system: St. Lawrence Estuary (Canada)

Dinauer

Mucci

2017

Biogeosciences

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Abstract. The incomplete spatial coverage of CO 2 partial pressure (pCO 2 ) measurements across estuary types represents a significant knowledge gap in current regional-and global-scale estimates of estuarine CO 2 emissions. Given the limited research on CO 2 dynamics in large estuaries and bay systems, as well as the sources of error in the calculation of pCO 2 (carbonic acid dissociation constants, organic alkalinity), estimates of air-sea CO 2 fluxes in estuaries are subject to large uncertainties. The Estuary and Gulf of St. Lawrence (EGSL) at the lower limit of the subarctic region in eastern Canada is the world's largest estuarine system, and is characterized by an exceptional richness in environmental diversity. It is among the world's most intensively studied estuaries, yet there are no published data on its surface-water pCO 2 distribution. To fill this data gap, a comprehensive dataset was compiled from direct and indirect measurements of carbonate system parameters in the surface waters of the EGSL during the spring or summer of 2003-2016. The calculated surface-water pCO 2 ranged from 435 to 765 µatm in the shallow partially mixed upper estuary, 139-578 µatm in the deep stratified lower estuary, and 207-478 µatm along the Laurentian Channel in the Gulf of St. Lawrence. Overall, at the time of sampling, the St. Lawrence Estuary served as a very weak source of CO 2 to the atmosphere, with an area-averaged CO 2 degassing flux of 0.98 to 2.02 mmol C m −2 d −1 (0.36 to 0.74 mol C m −2 yr −1 ). A preliminary analysis revealed that respiration (upper estuary), photosynthesis (lower estuary), and temperature (Gulf of St. Lawrence) controlled the spatial variability in surface-water pCO 2 . Whereas we used the dissociation constants of Cai and Wang (1998)

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Strong sources of CO2 in upper estuaries become sinks of CO2 in large river plumes

Cited by 100 publications

References 66 publications

Air–sea exchanges of CO<sub>2</sub> in the world's coastal seas

Air–sea exchanges of CO<sub>2</sub> in the world's coastal seas

Erosion-induced massive organic carbon burial and carbon emission in the Yellow River basin, China

Spatial variability in surface-water <i>p</i>CO<sub>2</sub> and gas exchange in the world's largest semi-enclosed estuarine system: St. Lawrence Estuary (Canada)

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Strong sources of CO2 in upper estuaries become sinks of CO2 in large river plumes

Cited by 100 publications

References 66 publications

Air–sea exchanges of CO&lt;sub&gt;2&lt;/sub&gt; in the world's coastal seas

Air–sea exchanges of CO&lt;sub&gt;2&lt;/sub&gt; in the world's coastal seas

Erosion-induced massive organic carbon burial and carbon emission in the Yellow River basin, China

Spatial variability in surface-water &lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt; and gas exchange in the world's largest semi-enclosed estuarine system: St. Lawrence Estuary (Canada)

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Air–sea exchanges of CO<sub>2</sub> in the world's coastal seas

Air–sea exchanges of CO<sub>2</sub> in the world's coastal seas

Spatial variability in surface-water <i>p</i>CO<sub>2</sub> and gas exchange in the world's largest semi-enclosed estuarine system: St. Lawrence Estuary (Canada)