Factors Controlling Storage, Sources, and Diagenetic State of Organic Carbon in a Prograding Subaerial Delta: Wax Lake Delta, Louisiana

Shields, Michael R.; Bianchi, Thomas S.; Kolker, Alexander S.; Kenney, William F.; Mohrig, David; Osborne, Todd Z.; Curtis, Jason H.

doi:10.1029/2018jg004683

Cited by 13 publications

(11 citation statements)

References 101 publications

(168 reference statements)

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“…Lignin‐phenols from the northern samples were extracted and analyzed, along with other cupric oxide (CuO) oxidation products, from freeze‐dried soil using the cupric oxide method of Hedges and Ertel (), modified by Louchouarn et al () and reported in detail in Shields et al (). Briefly, enough soil for 3–5 mg of OC was oxidized in a modified gas chromatograph oven for 3 hr at 150 °C using reaction vessels that contained soil, a stainless‐steel ball bearing, cupric oxide (CuO) powder, ferrous ammonium sulfate hexahydrate, and N 2 ‐sparged 2 N NaOH.…”

Section: Methodsmentioning

confidence: 99%

Increasing Rates of Carbon Burial in Southwest Florida Coastal Wetlands

et al. 2020

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Rates of organic carbon (OC) burial in some coastal wetlands appear to be greater in recent years than they were in the past. Possible explanations include ongoing mineralization of older OC or the influence of an unaccounted‐for artifact of the methods used to measure burial rates. Alternatively, the trend may represent real acceleration in OC burial. We quantified OC burial rates of mangrove and coastal freshwater marshes in southwest Florida through a comparison of rates derived from 210Pb, 137Cs, and surface marker horizons. Age/depth profiles of lignin: OC were used to assess whether down‐core remineralization had depleted the OC pool relative to lignin, and lignin phenols were used to quantify the variability of lignin degradation. Over the past 120 years, OC burial rates at seven sites increased by factors ranging from 1.4 to 6.2. We propose that these increases represent net acceleration. Change in relative sea‐level rise is the most likely large‐scale driver of acceleration, and sediment deposition from large storms can contribute to periodic increases. Mangrove sites had higher OC and lignin burial rates than marsh sites, indicating inherent differences in OC burial factors between the two habitat types. The higher OC burial rates in mangrove soils mean that their encroachment into coastal freshwater marshes has the potential to increase burial rates in those locations even more than might be expected from the acceleration trends. Regionally, these findings suggest that burial represents a substantially growing proportion of the coastal wetland carbon budget.

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Section: Methodsmentioning

confidence: 99%

Increasing Rates of Carbon Burial in Southwest Florida Coastal Wetlands

et al. 2020

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“…Most samples from the YRE region plot below the 0.4 mg C org m −2 line, which indicates a lower than normal C org content (0.4–1.0 mg C org m −2 ). The low C org /SA ratios (<0.4 mg C org m −2 ) observed in the YRE are comparable with those of C org sequestered in other river‐dominated margins that experience frequently remobilization and reoxygenation, such as the Amazon shelf, Pan‐Arctic shelf, and Bengal Fan (Bianchi et al, ; Goñi et al, ; Shields et al, ). Therefore, it is possible that the occurrence of low C org /SA ratios in sediments is a result of the insufficient sediment supply, a low SAR, the enhanced degradation associated with coarser deposits, and long oxygen exposure times in association with physical and/or biological reworking.…”

Section: Discussionmentioning

confidence: 53%

“…Relationships between sedimentary C org and (a) TN, and (b) modeled sedimentary particle surface area for all sediment samples collected from the YRE. Specific surface area (SA) for sediment samples was calculated using the method described in Mayer and Rossi () and Shields et al (). The ranges of C org –SA loading (0.4–1.0 mg C org m −2 ) commonly observed in river‐suspended material are shown (Blair & Aller, ).…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, the estimated TOM contributions present in the sediments, which range from 35.2% to 82.2% (52.3% on average), suggest that terrestrial inputs have an important role in the burial of C org within YRE sediments. Specific surface area (SA) for sediment samples was calculated using the method described in Mayer and Rossi (1982) and Shields et al (2019). The ranges of C org -SA loading (0.4-1.0 mg C org m −2 ) commonly observed in river-suspended material are shown (Blair & Aller, 2012).…”

Section: Org Sources To the Yre Sedimentmentioning

confidence: 99%

“…It is essential to constrain the fate of C org buried in estuarine modern sediments to better understand the present and future role of estuaries in global carbon cycling. However, doing so is difficult, mainly with respect to the inherent complex biogeochemical processes (Bauer et al, 2013;Hedges et al, 1997;Keil et al, 1994;Shields et al, 2019) such as changes in oxygen levels and exposure times, the redox condition, the C org -clay association, C org sources, sediment accumulation rates (SARs), and hydrodynamic conditions (Arndt et al, 2013;Bianchi et al, 2016;Canfield, 1994;Galy et al, 2007;Gordon & Goñi, 2003;Hedges & Keil, 1995;Keil et al, 1994;Mayer, 1994;Shields et al, 2019;Tesi et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Fate of Organic Carbon Burial in Modern Sediment Within Yangtze River Estuary

et al. 2020

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Large river‐dominated margins play a potential key role in regulating global carbon cycle and budget due to high terrestrial organic carbon (Corg) inputs and sediment accumulation rates. Here bulk elements (Corg and TN), isotopic compositions (δ13Corg and δ15N), radioisotope 210Pb, sedimentary grain size, pH, Eh, and physicochemical properties were analyzed on samples from the Yangtze River Estuary to determine the mechanism involved in transporting sedimentary Corg offshore. In addition, nine box‐cores were analyzed to further reveal the potential effects of the declining sediment load on the modern depositional pattern of Corg. The statistical analyses indicate that the hydrodynamically driven sediment composition exerts a significant control on the transport, mobilization, and accumulation of sedimentary Corg from the river to the estuary, with respect to the redistribution of fine‐grained sediments. Furthermore, X‐radiographs and 210Pb indicate that reworked environment dominates carbon burial in the Yangtze proximal deposit, while a stable sedimentary environment of Corg (3.50–5.58 g cm−2 year−1) is observed in the Yangtze distal mud. Notably, the enhanced erosional inputs that contain terrestrial plant debris (mainly the coarse fractions) have tended to become important sources for Corg. Although reworked sediments in the Yangtze River Estuary are frequently exposed to oxygen during physical and biological processes, there appears to be a high potential for long‐term sedimentary Corg storage, due to its association with sediment particles (mainly the clay fractions) that provide physical protection against its degradation.

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Mud‐associated organic matter and its direct and indirect role in marsh organic matter accumulation and vertical accretion

Mariotti

Elsey‐Quirk

Bruno

et al. 2020

Limnology & Oceanography

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In situ plant production is often assumed to be the major contributor to organic matter (OM) accumulation and vertical accretion in tidal marshes. Here, we evaluate the contribution of mud-associated OM in salt and brackish marshes in Louisiana. Based on 14 soil cores, the OM content of the mud fraction-i.e., any material smaller than 64 μm-was 17% AE 7% for the salt marshes and 28% AE 14% for the brackish marshes. This remains nearly uniform over the top 35 cm depth, suggesting that this material is deposited contemporaneously with the mud. The dry bulk density of the mud (300-450 kg m −3) is also much lower than what was estimated using a previously proposed two-constituent mixing model (1990 kg m −3). To reconcile this discrepancy, we developed a modified mixing model that includes mud OM and differentiates sand as a separate constituent with its high dry bulk density. The model estimates that mud contributes to~60% of the total marsh vertical accretion in Louisiana, considerably higher than the~14% estimated with the two-constituent mixing model. The result, which is a direct consequence of the relatively high porosity of mud, highlights that mud deposition is crucial for the accretion of microtidal marshes. Further, the model estimates that the mud OM constitutes~60% of the total soil OM, emphasizing that in situ plant production is not the only-and, in minerogenic marshes, not the major-contributor to OM accumulation.

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Factors Controlling Storage, Sources, and Diagenetic State of Organic Carbon in a Prograding Subaerial Delta: Wax Lake Delta, Louisiana

Cited by 13 publications

References 101 publications

Increasing Rates of Carbon Burial in Southwest Florida Coastal Wetlands

Increasing Rates of Carbon Burial in Southwest Florida Coastal Wetlands

Fate of Organic Carbon Burial in Modern Sediment Within Yangtze River Estuary

Mud‐associated organic matter and its direct and indirect role in marsh organic matter accumulation and vertical accretion

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