Revisiting salt marsh resilience to sea level rise: Are ponds responsible for permanent land loss?

Mariotti, G.

doi:10.1002/2016jf003900

Cited by 93 publications

(148 citation statements)

References 56 publications

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“…The loss of vegetated marsh, both on the plain and fringes, reduces the long-term net trapping potential of a marsh complex by exposing the substrate and decreasing the momentum extraction and wave attenuation by stems26. In microtidal, sediment-starved settings, increased open water ultimately favours marsh erosion, which in turn increases the unvegetated area, in a positive feedback that deteriorates the entire marsh27. In certain cases, ponding on the marsh plain can result in permanent marsh loss through slumping and soil creep, with runaway erosion preventing recovery27.…”

Section: Resultsmentioning

confidence: 99%

“…In microtidal, sediment-starved settings, increased open water ultimately favours marsh erosion, which in turn increases the unvegetated area, in a positive feedback that deteriorates the entire marsh27. In certain cases, ponding on the marsh plain can result in permanent marsh loss through slumping and soil creep, with runaway erosion preventing recovery27. Sediment deposition is mostly controlled by vegetative influence on settling and direct capture, and therefore scales with the area of the vegetated surface.…”

Section: Resultsmentioning

confidence: 99%

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Spatially integrative metrics reveal hidden vulnerability of microtidal salt marshes

et al. 2017

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Salt marshes are valued for their ecosystem services, and their vulnerability is typically assessed through biotic and abiotic measurements at individual points on the landscape. However, lateral erosion can lead to rapid marsh loss as marshes build vertically. Marsh sediment budgets represent a spatially integrated measure of competing constructive and destructive forces: a sediment surplus may result in vertical growth and/or lateral expansion, while a sediment deficit may result in drowning and/or lateral contraction. Here we show that sediment budgets of eight microtidal marsh complexes consistently scale with areal unvegetated/vegetated marsh ratios (UVVR) suggesting these metrics are broadly applicable indicators of microtidal marsh vulnerability. All sites are exhibiting a sediment deficit, with half the sites having projected lifespans of less than 350 years at current rates of sea-level rise and sediment availability. These results demonstrate that open-water conversion and sediment deficits are holistic and sensitive indicators of salt marsh vulnerability.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Spatially integrative metrics reveal hidden vulnerability of microtidal salt marshes

et al. 2017

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“…Once elevation loss has been initiated and interior ponds form, hydrologic forces can expand the size of the pond through “bank slumping” (Stevenson et al. ) or “soil creep” (Mariotti ). These mass wasting processes begin when interior ponds reach a critical width (which varies according to the local tidal range), causing edge soils to move downslope by gravity, slowly expanding the pond (Mariotti , Mariotti et al.…”

Section: Future Research Directions and Management Implicationsmentioning

confidence: 99%

“…) or “soil creep” (Mariotti ). These mass wasting processes begin when interior ponds reach a critical width (which varies according to the local tidal range), causing edge soils to move downslope by gravity, slowly expanding the pond (Mariotti , Mariotti et al. ).…”

Section: Future Research Directions and Management Implicationsmentioning

confidence: 99%

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

Chambers

Steinmuller

Breithaupt

2019

Ecology

101

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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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“…Permanently inundated ponds are natural features of salt marshes and have been called pools, potholes, and rotten spots in the literature [ Harshberger , , ; Mariotti , ; Miller and Egler , ; Redfield , ]. They can occupy 1–60% of salt marsh platforms [ Adamowicz and Roman , ; Millette et al , ; Schepers et al , ; Wilson et al , ] but are rarely characterized or integrated into whole‐ecosystem assessments.…”

Section: Introductionmentioning

confidence: 99%

Shallow ponds are heterogeneous habitats within a temperate salt marsh ecosystem

et al. 2017

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Integrating spatial heterogeneity into assessments of salt marsh biogeochemistry is becoming increasingly important because disturbances that reduce plant productivity and soil drainage may contribute to an expansion of shallow ponds. These permanently inundated and sometimes prominent landscape features can exist for decades, yet little is known about pond biogeochemistry or their role in marsh ecosystem functioning. We characterized three ponds in a temperate salt marsh (MA, USA) over alternating periods of tidal isolation and flushing, during summer and fall, by evaluating the composition of plant communities and organic matter pools and measuring surface water oxygen, temperature, and conductivity. The ponds were located in the high marsh and had similar depths, temperatures, and salinities. Despite this, they had different levels of suspended particulate, dissolved, and sediment organic matter and abundances of phytoplankton, macroalgae, and Ruppia maritima. Differences in plant communities were reflected in pond metabolism rates, which ranged from autotrophic to heterotrophic. Integrating ponds into landcover‐based estimates of marsh metabolism resulted in slower rates of net production (−8.1 ± 0.3 to −15.7 ± 0.9%) and respiration (−2.9 ± 0.5 to −10.0 ± 0.4%), compared to rates based on emergent grasses alone. Seasonality had a greater effect on pond water chemistry, organic matter pools, and algal abundances than tidal connectivity. Alternating stretches of tidal isolation and flushing did not affect pond salinities or algal communities, suggesting that exchange between ponds and nearby creeks was limited. Overall, we found that ponds are heterogeneous habitats and future expansion could reduce landscape connectivity and the ability of marshes to capture and store carbon.

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Revisiting salt marsh resilience to sea level rise: Are ponds responsible for permanent land loss?

Cited by 93 publications

References 56 publications

Spatially integrative metrics reveal hidden vulnerability of microtidal salt marshes

Spatially integrative metrics reveal hidden vulnerability of microtidal salt marshes

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

Shallow ponds are heterogeneous habitats within a temperate salt marsh ecosystem

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