Factors influencing the organic carbon pools in tidal marsh soils of the Elbe estuary (Germany)

Hansen, K.; Butzeck, Christian; Eschenbach, Annette; Gröngröft, Alexander; Jensen, Kai; Pfeiffer, Eva‐Maria

doi:10.1007/s11368-016-1500-8

Cited by 32 publications

(33 citation statements)

References 48 publications

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“…Overall, soil OMD shows a significant decrease with elevation, which cannot be explained in terms of observed vegetation cover trends. These observations support the hypothesis that at lower locations, where inundation is more prolonged, a greater proportion of the fresh organic matter produced (or imported) may be buried as SOM and results in a greater OMD (Hansen et al, ). This hypothesis is further supported by the analysis of OMD as a function of flooding duration (Figure ).…”

Section: Discussionsupporting

confidence: 81%

The Spatial Variability of Organic Matter and Decomposition Processes at the Marsh Scale

et al. 2018

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Accretion rate in salt marshes is governed by inorganic soil deposition and soil organic matter (SOM) accumulation. Existing (limited) observations and modeling results suggest that SOM amounts, biomass production, and decomposition processes should vary widely and systematically at the marsh scale. However, we lack observations aimed at understanding how SOM production is modulated spatially within a marsh, and at elucidating the relative importance of the controlling processes. The little existing data suggest that competing effects between biomass production and decomposition processes determine an approximately spatially constant contribution of SOM to total accretion. Here we investigate this idea using concurrent observations of SOM and decomposition rates from marshes in North Carolina. Our results indicate that systematic spatial variations in SOM are small, possibly as a result of an at least partial compensation of opposing trends in biomass production and decomposed organic matter. Our analyses show that deeper soil layers are, on average, characterized by lower decomposition rates and higher stabilization factors than shallower layers, likely because of differences in the persistence of water-logged conditions. Overall, decomposition processes are sufficiently rapid that the labile material in the fresh biomass is completely decomposed before it can be sufficiently buried and stabilized. Our findings point to the importance of the fraction of initially refractory material and of stabilization processes in determining the final distribution of SOM within the soil column.

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Section: Discussionsupporting

confidence: 81%

The Spatial Variability of Organic Matter and Decomposition Processes at the Marsh Scale

et al. 2018

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“…Locally produced (autochthonous) biomass is generally considered to contribute significantly to the total OC pool in tidal marsh sediments (Ouyang, Lee, & Connolly, ), as tidal marshes are among the most productive ecosystems in the world (Rocha & Goulden, ). Along estuaries, biomass is generally larger on freshwater and brackish marshes than on saltmarshes (Dausse et al., ; Hansen et al., ; Wieski, Guo, Craft, & Pennings, ). This is a consequence of the generally larger nutrient availability and lower salinity levels in the former portions of estuaries, in addition to species differences (Whigham, ).…”

Section: Discussionmentioning

confidence: 99%

“…Along estuaries, biomass is generally larger on freshwater and brackish marshes than on saltmarshes (Dausse et al, 2012;Hansen et al, 2016;Wieski, Guo, Craft, & Pennings, 2010). This is a consequence of the generally larger nutrient availability and lower salinity levels in the former portions of estuaries, in addition to species differences (Whigham, 2009).…”

Section: Autochthonous Organic Carbon Inputs Along the Estuarymentioning

confidence: 99%

“…Although soil organic carbon (SOC) stocks are generally higher in freshwater tidal marshes as compared to saltmarshes (Craft, ; Loomis & Craft, ; Van de Broek, Temmerman, Merckx, & Govers, ), knowledge on OC sequestration mechanisms in brackish and freshwater tidal marshes is currently limited. Higher SOC stocks in freshwater tidal marsh sediments, compared to saltmarshes, have been attributed to multiple factors, such as higher rates of primary production of macrophytes (Hansen et al., ), higher OC concentrations and/or higher sedimentation rates associated with deposited terrestrial sediments (Hansen et al., ; Hayes et al., ; Van de Broek et al., ), lower extracellular enzyme activity and microbial activity (Morrissey, Gillespie, Morina, & Franklin, ), and lower overall decomposition rates of organic matter (Craft, ; Loomis & Craft, ). Systematic studies of the controls on SOC stocks in tidal marsh sediments along the full salinity gradient of estuaries, including differences in characteristics of OC inputs and preservation mechanisms of OC upon burial, are scarce (Hansen et al., ).…”

Section: Introductionmentioning

confidence: 99%

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Long‐term organic carbon sequestration in tidal marsh sediments is dominated by old‐aged allochthonous inputs in a macrotidal estuary

Broek

Vandendriessche

Poppelmonde

et al. 2018

Global Change Biology

114

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Tidal marshes are vegetated coastal ecosystems that are often considered as hotspots of atmospheric CO sequestration. Although large amounts of organic carbon (OC) are indeed being deposited on tidal marshes, there is no direct link between high OC deposition rates and high OC sequestration rates due to two main reasons. First, the deposited OC may become rapidly decomposed once it is buried and, second, a significant part of preserved OC may be allochthonous OC that has been sequestered elsewhere. In this study we aimed to identify the mechanisms controlling long-term OC sequestration in tidal marsh sediments along an estuarine salinity gradient (Scheldt estuary, Belgium and the Netherlands). Analyses of deposited sediments have shown that OC deposited during tidal inundations is up to millennia old. This allochthonous OC is the main component of OC that is effectively preserved in these sediments, as indicated by the low radiocarbon content of buried OC. Furthermore, OC fractionation showed that autochthonous OC is decomposed on a decadal timescale in saltmarsh sediments, while in freshwater marsh sediments locally produced biomass is more efficiently preserved after burial. Our results show that long-term OC sequestration is decoupled from local biomass production in the studied tidal marsh sediments. This implies that OC sequestration rates are greatly overestimated when they are calculated based on short-term OC deposition rates, which are controlled by labile autochthonous OC inputs. Moreover, as allochthonous OC is not sequestered in-situ, it does not contribute to active atmospheric CO sequestration in these ecosystems. A correct assessment of the contribution of allochthonous OC to the total sedimentary OC stock in tidal marsh sediments as well as a correct understanding of the long-term fate of locally produced OC are both necessary to avoid overestimations of the rate of in-situ atmospheric CO sequestration in tidal marsh sediments.

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“…Although the feedback of SOC concentrations to increased surface/pore water salinity and soil salinity has been studied for decades from different perspectives, there is no consensus regarding the effects of salinity on SOC concentrations. Some studies suggested that elevated salinities can decrease SOC concentrations (Hansen et al, ; Więski et al, ), some reported increases in SOC concentrations and inhibition of decomposition processes (Hu et al, ; Stagg et al, ), and others indicated no significant impact on SOC accumulation (Spalding & Hester, ). In this context, it is imperative to identify the relationship between soil salinities and SOC concentrations, especially under the accelerated sea‐level rises and aggravated saltwater intrusion scenarios.…”

Section: Introductionmentioning

confidence: 99%

Salinity Affects Topsoil Organic Carbon Concentrations Through Regulating Vegetation Structure and Productivity

Xue

Jiang

et al. 2020

JGR Biogeosciences

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Estuarine salt marshes have been recognized as one of the most efficient carbon sinks in the biosphere, with considerable potential for climate change mitigation. However, there are still uncertainties about the response of soil carbon stocks to enhanced soil salinization caused by accelerated sea-level rises and aggravated saltwater intrusion. We therefore conducted both field investigations in the Chongming Dongtan salt marsh of the Yangtze River Estuary, China, and manipulative experiments on marsh soils occupied, respectively, by the invasive Spartina alterniflora, and the native Phragmites australis and Scirpus mariqueter, to identify the effects of elevated soil salinity on top soil organic carbon (SOC) concentration. Our field data showed that SOC concentrations were significantly positively associated with soil salinity concentrations, annual net primary productivity, and marsh surface elevation but showed a significant negative relationship with median grain size. Compared with the two native species, S. alterniflora preferred more saline conditions and had a higher SOC concentration. Although raised flooding salinities (0-35 ppt) did not strongly affect SOC concentrations, elevated soil salinities significantly corresponded with low SOC concentrations and plant biomass in manipulative experiments. These findings indicated that soil salinity, plant species, and soil texture were key factors controlling SOC concentrations in the studied salt marsh. Moreover, soil salinity could affect SOC concentrations through regulating vegetation spatial structure and plant biomass production. The further invasion of the S. alterniflora community will exert a positive influence on SOC concentrations in the Chongming Dongtan salt marsh.Plain Language Summary Estuarine salt marshes are sedimentary environments that are among the most productive ecosystems on Earth and can continuously sequester carbon through plant production and sedimentary processes. Although sea-level rises and saltwater intrusion may cause widespread soil salinization in estuarine ecosystems, its impact on top soil organic carbon (SOC) concentrations is highly uncertain. We therefore conducted field investigations that revealed the variation in SOC concentrations along a natural salinity gradient and manipulative experiments that raised flooding salinities from freshwater (0 ppt) to seawater (35 ppt) to identify the independent impacts of soil salinity on SOC concentrations. Our findings indicated that soil salinity was an important factor controlling SOC concentrations through indirectly regulating vegetation spatial structure and plant biomass production.

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Factors influencing the organic carbon pools in tidal marsh soils of the Elbe estuary (Germany)

Cited by 32 publications

References 48 publications

The Spatial Variability of Organic Matter and Decomposition Processes at the Marsh Scale

The Spatial Variability of Organic Matter and Decomposition Processes at the Marsh Scale

Long‐term organic carbon sequestration in tidal marsh sediments is dominated by old‐aged allochthonous inputs in a macrotidal estuary

Salinity Affects Topsoil Organic Carbon Concentrations Through Regulating Vegetation Structure and Productivity

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