Relationships of Marsh Soil Strength to Belowground Vegetation Biomass in Louisiana Coastal Marshes

Sasser, Charles E.; Evers-Hebert, E.; Holm, Guerry O.; Milan, B.; Sasser, J. B.; Peterson, E. F.; DeLaune, Ronald D.

doi:10.1007/s13157-017-0977-2

Cited by 25 publications

(24 citation statements)

References 14 publications

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“…Significantly lower soil shear strength in deteriorating wetlands relative to reference wetlands has been observed, particularly in the root zone (Day et al 2011, Twohig and Stolt 2011, Wigand et al 2014). Further study indicates that measures of soil shear strength are strongly correlated with live belowground biomass (Sasser et al 2018). Because roots form the scaffolding that holds highly porous organic soils together, dead, dying, or stressed vegetation that is not allocating biomass belowground can weaken the soil structure within the root zone.…”

Section: Reduced Soil Strengthmentioning

confidence: 96%

“…Further study indicates that measures of soil shear strength are strongly correlated with live belowground biomass (Sasser et al. ). Because roots form the scaffolding that holds highly porous organic soils together, dead, dying, or stressed vegetation that is not allocating biomass belowground can weaken the soil structure within the root zone.…”

Section: Semantics Of “Peat Collapse”mentioning

confidence: 99%

“…Root biomass (both live and dead) can represent up to 22% of the total mass of soil solids in coastal peatlands (Sasser et al. ) and typically holds together the largest pool of SOM–plant‐litter, in various phases of decay. To contribute to a quantifiable elevation loss, SOM must compact (decrease in vertical volume) or transform (e.g., change state, such as through mineralization).…”

Section: Mechanisms Of Coastal Wetland Peat Collapsementioning

confidence: 99%

“…Soil organic matter comprises everything below the soil surface of biotic origin: fresh, degraded, and humified plant and animal matter, live and dead roots, and soil micro-and macro-organisms (Reddy and DeLaune 2008). Root biomass (both live and dead) can represent up to 22% of the total mass of soil solids in coastal peatlands (Sasser et al 2018) and typically holds together the largest pool of SOM-plant-litter, in various phases of decay. To contribute to a quantifiable elevation loss, SOM must compact (decrease in vertical volume) or transform (e.g., change state, such as through mineralization).…”

Section: Soil Organic Matter Compaction and Transformationmentioning

confidence: 99%

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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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Section: Reduced Soil Strengthmentioning

confidence: 96%

Section: Semantics Of “Peat Collapse”mentioning

confidence: 99%

Section: Mechanisms Of Coastal Wetland Peat Collapsementioning

confidence: 99%

Section: Soil Organic Matter Compaction and Transformationmentioning

confidence: 99%

See 2 more Smart Citations

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

Chambers

Steinmuller

Breithaupt

2019

Ecology

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“…The belowground biomass of fertilized plots in year 1 was 161% of the control value, but 75% of that in the control plot in year 2. The root mass and SSS were strongly correlated in the surface layer for a variety of coastal plants in Louisiana (Sasser et al 2018), and particularly for P. hemitomon live belowground biomass (y) which is wellcorrelated with SSS (x) in the upper 15 cm (y = 18.7x-183.8, R 2 = 0.81, n = 40; Sasser et al 2013). Fluctuations in SSS in the upper layer can be considered a surrogate for a changing root biomass, but perhaps only a partial correspondence.…”

Section: Discussionmentioning

confidence: 99%

Soil Shear Strength Losses in Two Fresh Marshes with Variable Increases in N and P Loading

2020

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We measured soil shear strength (SSS) from 2009 to 2018 in two hydrologically distinct freshwater marshes dominated by Panicum hemitomon after nitrogen (N) and phosphorous (P) were applied to the surface in spring. The SSS averaged over 100cm depth in the floating and anchored marshes declined up to 30% throughout the profiles and with no apparent differences in the effects of the low, medium, and high N + P dosing. Plots with only N or P additions exhibited significant changes in SSS at individual depths below 40 cm for the anchored marsh, but not the floating marsh. The average SSS for the anchored marsh over the entire 100 cm profile declined when N and P were added separately or together. At the floating marsh, however, the SSS decreased when N and P were added in combination, or P alone, but not for the N addition. Increasing nutrient availability to these freshwater marsh soils makes them weaker, and perhaps lost if eroded or uplifted by buoyant forces during storms. These results are consistent with results from multi-year experiments demonstrating higher decomposition rates, greenhouse gas emissions, and carbon losses in wetlands following increased nutrient availability.

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Resistance of salt marsh substrates to near‐instantaneous hydrodynamic forcing

Brooks

Möller

Carr

et al. 2020

Earth Surf Processes Landf

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Salt marshes deliver vital ecosystem services by providing habitats, storing pollutants and atmospheric carbon, and reducing flood and erosion risk in the coastal hinterland. Net losses in salt marsh areas, both modelled globally and measured regionally, are therefore of concern. Amongst other controls, the persistence of salt marshes in any one location depends on the ability of their substrates to resist hydrodynamic forcing at the marsh front, along creek margins and on the vegetated surface. Where relative sea level is rising, marsh elevation must keep pace with sea‐level rise and landward expansion may be required to compensate for areal loss at exposed margins. This paper reviews current understanding of marsh substrate resistance to the near‐instantaneous (seconds to hours) forcing induced by hydrodynamic processes. It outlines how variability in substrate properties may affect marsh substrate stability, explores current understanding of the interactions between substrate properties and erosion processes, and how the cumulative impact of these interactions may affect marsh stability over annual to decadal timescales. Whilst important advances have been made in understanding how specific soil properties affect near‐instantaneous marsh substrate stability, less is known about how these properties interact and alter bulk substrate resistance to hydrodynamic forcing. Future research requires a more systematic approach to quantifying biological and sedimentological marsh substrate properties. These properties must then be linked to specific observable erosion processes, particularly at the marsh front and along creek banks. A better understanding of the intrinsic dynamics and processes acting on, and within, salt marsh substrates will facilitate improved prediction of marsh evolution under future hydrodynamic forcing scenarios. Notwithstanding the additional complications that arise from morphodynamic feedbacks, this would allow us to more accurately model the future potential protection from flooding and erosion afforded by marshes, while also increasing the effectiveness of salt marsh restoration and recreation schemes. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

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Relationships of Marsh Soil Strength to Belowground Vegetation Biomass in Louisiana Coastal Marshes

Cited by 25 publications

References 14 publications

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

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

Soil Shear Strength Losses in Two Fresh Marshes with Variable Increases in N and P Loading

Resistance of salt marsh substrates to near‐instantaneous hydrodynamic forcing

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