Ecogeomorphology of<i>Spartina Patens</i>-dominated tidal marshes: Soil organic matter accumulation, marsh elevation dynamics, and disturbance

Cahoon, Donald R.; Ford, Mark; Hensel, Philippe

doi:10.1029/ce059p0247

Cited by 18 publications

(16 citation statements)

References 31 publications

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“…Grazing by nutria in a brackish marsh can cause a reduction in below-ground production that leads to decreased elevation (Ford and Grace, 1998). Burning of a brackish marsh can cause an increase in the volume of root biomass that leads to increased elevation (Cahoon et al, 2004). Plant production by Spartina alterniflora increases as the elevation of the salt marsh becomes lower within its optimum growth range, and then decreases as elevations approach the minimum depth at which vegetation can grow (Morris et al, 2002).…”

Section: Implications For Wetland Sustainabilitymentioning

confidence: 98%

Sediment infilling and wetland formation dynamics in an active crevasse splay of the Mississippi River delta

2011

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Section: Implications For Wetland Sustainabilitymentioning

confidence: 98%

Sediment infilling and wetland formation dynamics in an active crevasse splay of the Mississippi River delta

2011

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“…However, the limited time span of the existing studies (Table ) make this unidirectional hypothesis difficult to validate, and at least one study (Cahoon et al. ) did document natural recolonization with a more flood‐tolerant species following the elevation drop, leading to the question of if this should be considered peat collapse.…”

Section: Working Definition Of Peat Collapsementioning

confidence: 99%

“…Furthermore, several studies measured elevation only at the start and end of the study (with no observations over the intervening months or years), making it difficult to identify the precise timescale when the elevation loss occurred. The most rapid rates of elevation loss published are~2.8 cm within 5 months in an excessively flooded Texas marsh (Cahoon et al 2004) and 6-8 cm within 6 months in intact freshwater marsh cores treated with seawater (Portnoy and Giblin 1997), while most other rates are on the order of approximately 1-3 cm/yr (Table 1). For context on how these rates compare to related ecological phenomena, even the lowest published annual rate of elevation loss (1.0 cm/yr) is still more than three times greater than the rate of eustatic sea level rise (Church et al 2013), but within the range (0-2.2 cm/yr) of globally documented coastal wetland accretion rates (Breithaupt et al 2018).…”

Section: Abrupt Eventmentioning

confidence: 99%

Toward a mechanistic understanding of “peat collapse” and its potential contribution to coastal wetland loss

Chambers

Steinmuller

Breithaupt

2019

Ecology

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Coastal wetlands are susceptible to loss in both health and extent via stressors associated with global climate change and anthropogenic disturbance. Peat collapse may represent an additional phenomenon contributing to coastal wetland loss in organic‐rich soils through rapid vertical elevation decline. However, the term “peat collapse” has been inconsistently used in the literature, leading to ambiguities regarding the mechanisms, timing, and spatial extent of its contribution to coastal wetland loss. For example, it is unclear whether peat collapse is distinct from general subsidence, or what biogeochemical changes or sequence of events may constitute peat collapse. A critical analysis of peer‐reviewed literature related to peat collapse was supplemented with fundamental principles of soil physics and biogeochemistry to develop a conceptual framework for coastal wetland peat collapse. We propose that coastal wetland peat collapse is a specific type of shallow subsidence unique to highly organic soils in which a loss of soil strength and structural integrity contributes to a decline in elevation, over the course of a few months to a few years, below the lower limit for emergent plant growth and natural recovery. We further posit that coastal wetland peat collapse is driven by severe stress or death of the vegetation, which compromises the supportive structure roots provide to low‐density organic soils and shifts the carbon balance of the ecosystem toward a net source, as mineralization is no longer offset by sequestration. Under these conditions, four mechanisms may contribute to peat collapse: (1) compression of gas‐filled pore spaces within the soil during dry‐down conditions; (2) deconsolidation of excessively waterlogged peat, followed by transport; (3) compaction of aerenchyma tissue in wetland plant roots, and possibly collapse of root channels; and (4) acceleration of soil mineralization due to the addition of labile carbon (dying roots), oxygen (decreased flooding), nutrients (eutrophication), or sulfate (saltwater intrusion). Scientists and land managers should focus efforts on monitoring vegetation health across the coastal landscape as an indicator for peat collapse vulnerability and move toward codifying the term “peat collapse” in the scientific literature. Once clarified, the contribution of peat collapse to coastal wetland loss can be evaluated.

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“…A negative value indicates shallow expansion; a positive value shallow subsidence. Processes in coastal wetlands driving shallow subsidence or expansion include root zone expansion from increased root volume (Cahoon et al 2004;Langley et al 2009;Cherry et al 2009;, root zone collapse from reduced root production, increased decomposition of plant roots, and loss of root volume (Ford and Grace 1998;Cahoon et al 2003Cahoon et al , 2004), shrink-swell related to changes in ground water level (Paquette et al 2004;Whelan et al 2005;Cahoon et al 2011a;Rogers and Saintilan 2008), and compaction (Cahoon et al 1995. Major storms can affect all these processes either directly or indirectly (Cahoon 2006).…”

Section: Subsurface Process Controls On Wetland Elevationmentioning

confidence: 99%

Estimating Relative Sea-Level Rise and Submergence Potential at a Coastal Wetland

Cahoon

2014

Estuaries and Coasts

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A tide gauge records a combined signal of the vertical change (positive or negative) in the level of both the sea and the land to which the gauge is affixed; or relative sealevel change, which is typically referred to as relative sea-level rise (RSLR). Complicating this situation, coastal wetlands exhibit dynamic surface elevation change (both positive and negative), as revealed by surface elevation table (SET) measurements, that is not recorded at tide gauges. Because the usefulness of RSLR is in the ability to tie the change in sea level to the local topography, it is important that RSLR be calculated at a wetland that reflects these local dynamic surface elevation changes in order to better estimate wetland submergence potential. A rationale is described for calculating wetland RSLR (RSLR wet ) by subtracting the SET wetland elevation change from the tide gauge RSLR. The calculation is possible because the SET and tide gauge independently measure vertical land motion in different portions of the substrate. For 89 wetlands where RSLR wet was evaluated, wetland elevation change differed significantly from zero for 80 % of them, indicating that RSLR wet at these wetlands differed from the local tide gauge RSLR. When compared to tide gauge RSLR, about 39 % of wetlands experienced an elevation rate surplus and 58 % an elevation rate deficit (i.e., sea level becoming lower and higher, respectively, relative to the wetland surface). These proportions were consistent across saltmarsh, mangrove, and freshwater wetland types. Comparison of wetland elevation change and RSLR is confounded by high levels of temporal and spatial variability, and would be improved by co-locating tide gauge and SET stations near each other and obtaining longterm records for both.

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Ecogeomorphology ofSpartina Patens-dominated tidal marshes: Soil organic matter accumulation, marsh elevation dynamics, and disturbance

Cited by 18 publications

References 31 publications

Sediment infilling and wetland formation dynamics in an active crevasse splay of the Mississippi River delta

Sediment infilling and wetland formation dynamics in an active crevasse splay of the Mississippi River delta

Toward a mechanistic understanding of “peat collapse” and its potential contribution to coastal wetland loss

Estimating Relative Sea-Level Rise and Submergence Potential at a Coastal Wetland

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