Reservoir Construction Has Reduced Organic Carbon Deposition in the East China Sea by Half Since 2006

Wang, Chenglong; Hao, Zhe; Gao, Jianhua; Feng, Ziyue; Ding, Yongcheng; Zhang, Chuchu

doi:10.1029/2020gl087357

Cited by 12 publications

(9 citation statements)

References 55 publications

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“…It is worth noting that rapid decrease of sediment load from the Changjiang and Yellow Rivers has been considered as an important factor influencing present and future OC burial (Li et al., 2015; Sun et al., 2020; Wang et al., 2020). In particular, after impoundments of the Three Gorges Reservoir (TGR) in 2003 and Xiaolangdi Reservoir in 1999, sediment loads in the Changjiang and Yellow Rivers sharply decreased and kept at very low values relative to pre‐dam building period (Figure S9).…”

Section: Discussionmentioning

confidence: 99%

Controls on Organic Carbon Burial in the Eastern China Marginal Seas: A Regional Synthesis

Zhao

Yao

Bianchi

et al. 2021

Global Biogeochemical Cycles

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Marginal seas are important burial centers of both marine and terrestrial organic carbon (OC), accounting for the burial of more than 90% of sedimentary OC in marine environments Burdige, 2005;Hedges & Keil, 1995). These marginal seas receive vast amounts of sediments, freshwater, and nutrients from their adjacent rivers and coastal erosion, especially in those large delta-front estuaries (Bianchi & Allison, 2009;Kuehl et al., 2020). Large seasonal shifts of terrigenous inputs impact sedimentation rates, sources/age of OC, and primary productivity -all critical in controlling burial and decomposition of OC in marginal seas (Bauer et al., 2013;Bianchi et al., 2014;Liu et al., 2010). Recent work on differentiation of rock-derived or petrogenic OC (OC petro ) from physical erosion of bedrock in river drainage basins Abstract A regional synthesis of organic carbon (OC) burial was conducted using a comprehensive data set to reveal some of the key drivers and human multi-stressors controlling OC burial and transport in the Eastern China Marginal Seas (ECMS). Both OC and Δ 14 C values of suspended particulate matter (SPM) in the Changjiang River, were significantly higher than estuarine mobile-muds, suggesting selective decay of more labile younger OC from both marine and terrestrial sources and the accumulation of more recalcitrant older OC. Some of this decay is likely to be associated with iron-redox cycling in mobile-muds. In contrast, OC, δ 13 C, and Δ 14 C values increased along the Yellow River sediment dispersal pathway, indicating adding of young marine OC and less decay of terrestrial OC. OC burial efficiency in mud areas in the Bohai Sea (∼43%) was significantly higher than those in the Yellow (∼11%) and East China Seas (∼16%), owing to rapid deposition. Burial flux of biospheric OC in mud areas of the ECMS is 7.00 ± 0.79 Mt yr −1 , corresponding to atmospheric CO 2 drawdown by silicate weathering in major river drainage basins of mainland China. The burial flux of petrogenic OC was estimated to be 0.81 ± 0.25 Mt yr −1 , accounting for >1.9% of total burial in the global ocean. While the ECMS is an important OC sink, river damming has greatly reduced OC burial. Thus, the overall impact on anthropogenically altered riverdominated marginal seas remains an important and rapidly changing component of the coastal ocean carbon budget.Plain Language Summary A comprehensive regional synthesis of organic carbon (OC) burial and its drivers, were investigated across the Eastern China Marginal Seas (ECMS). Variation of OC content and carbon isotopic composition from suspended particulate matter to mobile muds, in Changjiang sediment dispersal pathways, indicated selective decomposition of younger more labile marine and terrestrial OC, which resulted in the accumulation of older more recalcitrant OC. However, continuous adding of young marine OC, with little loss of terrestrial OC, in Yellow River sediment dispersal pathway, resulted in more recalcitrant terrestrial OC buried in this relatively more quiescent sedimentary ...

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Section: Discussionmentioning

confidence: 99%

Controls on Organic Carbon Burial in the Eastern China Marginal Seas: A Regional Synthesis

Zhao

Yao

Bianchi

et al. 2021

Global Biogeochemical Cycles

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“…As human activities intensify, the preservation of OC in river-influenced inner shelf mud areas will be severely affected. Prior studies have found that watershed engineering (e.g., dam construction) can significantly change the sedimentary dynamic environment (Wang et al, 2020). In 2018, the OC deposition flux in the ECS shelf area decreased by ∼45% compared with that before the operation ( 2006) of the Three Gorges Dam (Wang et al, 2020).…”

Section: Implications For the Burial Of Oc In Marginal Seasmentioning

confidence: 99%

“…Prior studies have found that watershed engineering (e.g., dam construction) can significantly change the sedimentary dynamic environment (Wang et al, 2020). In 2018, the OC deposition flux in the ECS shelf area decreased by ∼45% compared with that before the operation ( 2006) of the Three Gorges Dam (Wang et al, 2020). The reduction in terrestrial particle inputs exacerbates seabed erosion and sediment mobilization.…”

Section: Implications For the Burial Of Oc In Marginal Seasmentioning

confidence: 99%

“…However, these complicated hydrodynamic processes prevent the sediments from leaving the continental shelf and restrict them to the inner shelf area (isobaths less than 75 m), forming a long and narrow mobile mud zone in the north-south direction (Gao & Collins, 2014;Liu et al, 2006). In addition to dynamic physical oceanographic processes, enhanced human activities (e.g., dam construction, dredging and sewage discharge) and the resulting algal blooms and hypoxia, coupled with the impact of climate change, contribute to discrete sedimentary dispersal and complex element cycles (Bauer et al, 2013;Gao et al, 2019;Hu et al, 2012;Wang et al, 2018Wang et al, , 2020…”

Section: Study Areamentioning

confidence: 99%

“…Although external disturbances have increased the BIT values, a strong relationship between BIT and δ 13 C values still exists (r = −0.54, p < 0.01). The three-end-member mixing model incorporating BIT and δ 13 C values has been applied in many studies to quantify the relative contribution of OC from marine, soil, and plant sources (Liao et al, 2018;Wang et al, 2020;Weijers et al, 2009). Considering that the reported end-member values of BIT were not suitable for this study and the contribution of plant-derived OC was not prominent, as revealed by the significant correlation between BIT and δ 13 C values, the simple two-end-member model based on δ 13 C was used to evaluate the proportion of marine and terrestrial OC.…”

Section: Sources and Reactivity Of Sedimentary Oc In The Ecmsmentioning

confidence: 99%

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Evaluation of Sedimentary Organic Carbon Reactivity and Burial in the Eastern China Marginal Seas

et al. 2021

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As the largest carbon pool in the global ecosystem, the ocean carbon pool is ∼20 times that of the terrestrial carbon pool and ∼50 times that of the atmospheric carbon pool (Holmén, 2000). Among the many constituents of the ocean carbon pool, shelf marginal seas are the focus of research. The continental margins cover less than 8% of the ocean area but account for more than 80% of the global organic carbon (OC) burial, and they play a pivotal role in the global carbon cycle (

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Terrestrial and marine POC export fluxes estimated by 234Th–238U disequilibrium and δ13C measurements in the East China Sea shelf

Zhong,

Huang,

Wang

et al. 2024

Biogeochemistry

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The use of 234Th–238U disequilibrium has been widely employed to estimate the sinking flux of particulate organic carbon (POC) from the upper sea and ocean. Here, the deficits of 234Th relative to 238U in the water column and the carbon isotope signature (δ13C) of POC in the East China Sea (ECS) Shelf were measured, which was used to distinguish the fraction of marine and terrestrial POC export fluxes. In the ECS Shelf, very strong deficits of 234Th relative to 238U were observed throughout the water column, with 234Th/238U activity ratios ranging from 0.158 ± 0.045 to 0.904 ± 0.068 (averaging 0.426 ± 0.159). The residence times of particle reactive radionuclide 234Th (τTh–T) in the ECS shelf water varied between 9 and 44 days, which is significantly shorter than that in the continental slope area or the basin area. This phenomenon indicates that there is a more rapid particle scavenging process in the ECS shelf water compared to the continental slope and basin upper water. By applying a two-end-member mixing model based on the δ13C, the fraction of terrestrial POC was estimated to be 0 to 74% (mean: 30 ± 22%) and the fraction of marine POC was in the range of 25% to 100% (mean: 70 ± 22%). Fluxes of marine and terrestrial POC settling to the seafloor exhibited significant spatial differences among different stations, ranging from 11 to 129 mmol C/m2/day and from 2.6 to 38 mmol C/m2/day, respectively. The averaged terrestrial POC fluxes in the southern and northern ECS Shelf were similar (~ 21 to 24 mmol C/m2/day), while the marine POC fluxes in the north (86 ± 37 mmol C/m2/day) were approximately four times higher than those in the south (26 ± 20 mmol C/m2/day). Interestingly, the estimated export flux of both marine and terrestrial POC were approximately one order of magnitude higher than the previously reported burial fluxes of POC (ranging from 1.1 ± 0.1 to 11.4 ± 1.1 mmol C/m2/day) in the underlying bottom sediments, indicating that the majority (> 90%) of both terrestrial and marine POC exported from the upper water column are degraded in the sediments of the ECS Shelf. This “carbon missing” phenomenon can greatly be attributed to rapid decomposition by other processes (including microbial reworking, cross-shelf transport, and possible consumption by benthic organisms). Our findings highlight the dynamic nature of carbon cycling in the continental shelf and the need for further research to understand these processes and improve carbon budget assessments.

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Reservoir Construction Has Reduced Organic Carbon Deposition in the East China Sea by Half Since 2006

Cited by 12 publications

References 55 publications

Controls on Organic Carbon Burial in the Eastern China Marginal Seas: A Regional Synthesis

Controls on Organic Carbon Burial in the Eastern China Marginal Seas: A Regional Synthesis

Evaluation of Sedimentary Organic Carbon Reactivity and Burial in the Eastern China Marginal Seas

Terrestrial and marine POC export fluxes estimated by 234Th–238U disequilibrium and δ13C measurements in the East China Sea shelf

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