Saltmarsh pool and tidal creek morphodynamics: Dynamic equilibrium of northern latitude saltmarshes?

Wilson, Carol; Hughes, Zoë; FitzGerald, Duncan M.; Hopkinson, Charles S.; Valentine, Vinton; Kolker, Alexander S.

doi:10.1016/j.geomorph.2014.01.002

Cited by 96 publications

(152 citation statements)

References 58 publications

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“…Image comparison revealed instances of isolated ponds that were drained by channels in the period between 1954 and 1991 and subsequently revegetated (Figure ). This pond drainage and closure is analogous to that reported in marshes from northern New England [ Wilson et al , , ].…”

Section: Study Sites: Pond Recovery or Not Recovery?supporting

confidence: 80%

“…For simplicity, I neglect the detailed trajectory of the pond width and depth. Following previous observations [ Wilson et al , , ], I assume that ponds deepen and expand until eventually drained by a channel (Figure ). Once connected with the channel network, tidal flushing reestablishes a biochemistry conducive for marsh plant growth; mudflats can revegetate and recover the marsh platform elevation.…”

Section: Model For Pond Dynamicsmentioning

confidence: 95%

“…Pond deepening and expansion occurs even if the surrounding marsh keeps pace with relative RSLR [ Wilson et al , ]. In particular, it has been observed that marsh vegatation next to both isolated and connected ponds is as healthy as the vegetation far from ponds [ Nyman et al , ].…”

Section: Model For Pond Dynamicsmentioning

confidence: 99%

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

Mariotti

2016

JGR Earth Surface

119

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Ponds are unvegetated rounded depressions commonly present on marsh platforms. The role of ponds on the long‐term morphological evolution of tidal marshes is unclear—at times ponds expand but eventually recover the marsh platform, at other times ponds never recover and lead to permanent marsh loss. Existing field observations indicate that episodic disturbances of the marsh vegetation cause the formation of small (1–10 m) isolated ponds, even if the vegetated platform keeps pace with relative sea level rise (RSLR) and that isolated ponds tend to deepen and enlarge until they eventually connect to the channel network. Here I implement a simple model to study the vertical and planform evolution of a single connected pond. A newly connected pond recovers if its bed lies above the limit for marsh plant growth or if the inorganic deposition rate is larger than the RSLR rate. A pond that cannot accrete faster than RSLR will deepen and enlarge, eventually entering a runaway erosion by wave edge retreat. A large tidal range, a large sediment supply, and a low rate of RSLR favor pond recovery. The model suggests that inorganic sediment deposition alone controls pond recovery, even in marshes where organic matter dominates accretion of the vegetated platform. As such, halting permanent marsh loss by pond collapse requires to increase inorganic sediment deposition. Because pond collapse is possible even if the vegetated platform keeps pace with RSLR, I conclude that marsh resilience to RSLR is less than previously quantified.

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Section: Study Sites: Pond Recovery or Not Recovery?supporting

confidence: 80%

Section: Model For Pond Dynamicsmentioning

confidence: 95%

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

Mariotti

2016

JGR Earth Surface

119

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“…The reduced role of both organic and inorganic matter in the upper Bay marshes indicates that marsh swelling, or saturation of the sediments due to excess water retention, is important in controlling marsh surface elevation. The shifting marsh structure in combination with higher water levels may be linked to the documented 10 % loss of marsh vegetation observed in region since 1970 (Watson et al 2014), the widening channel creeks (Wilson et al 2014;Watson et al (submitted)), and the sudden marsh dieback events recently observed throughout Narragansett Bay (Bertness et al 2014;Raposa et al (submitted)). The link between such recent observations of marsh change deserves closer inspection.…”

Section: Resultsmentioning

confidence: 95%

“…Recent evidence suggests that marshes located in areas of low sediment loads (<20 mg L −1 ) will drown once a threshold of 0.5 cm year −1 of RSLR is attained . Specifically in the Northeast USA, shifting vegetation patterns indicative of wetter marsh platform (Warren and Niering 1993;Donnelly and Bertness 2001;Raposa et al (submitted)) and widening channel networks (Hartig et al 2002;Smith 2009;Watson et al (submitted)) coupled with cycles in marsh pool formation (Wilson et al 2014) and shifting marsh sediment structure (Wigand et al 2014) provide evidence that marsh elevation may be lagging behind rates of RSLR. Predicting how RSLR will impact marsh accretion is made even more complex by the non-linear feedbacks between sediment deposition, inundation, and primary production (Morris et al 2002;Kirwan et al 2010;D'Alpaos et al 2011).…”

Section: Introductionmentioning

confidence: 99%

The Declining Role of Organic Matter in New England Salt Marshes

Carey

Moran

Kelly

et al. 2015

Estuaries and Coasts

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The Northeast USA is experiencing severe impacts of a changing climate, including increased winter temperatures and accelerated relative sea level rise (RSLR). The sediment-poor, organic-rich nature of many Southern New England salt marshes makes them particularly vulnerable to these changes. In order to assess how marsh accretion has changed over time, we returned to Narragansett Bay, RI where salt marsh vertical accretion rates were documented almost 30 years ago. Using radionuclide tracers ( 210 Pb and 137 Cs), we observe no significant change in overall accretion rates (0.27-0.69 cm year −1 ) compared to historical averages (0.24-0.60 cm year −1 ), but we document a shift in how these marshes maintain elevation. Organic matter now plays a smaller role in contributing to vertical accretion across all study sites, declining by 22 % on average. We attribute this reduction to potentially higher decomposition rates fueled by higher water temperature. Inorganic matter also contributes less to accretion (declining by 44 % on average at marshes located more internal to the estuary), likely due to diminishing sediment supply in this region. With organic and inorganic solids accounting for less of the total accretion, several of the marshes are experiencing symptoms of swelling, with water and porespace contributing more towards accretion compared to historical values. Accretion rates (0.27-0.45 cm year −1 ) at these organic-rich (>40 % sediment organic matter) marshes are predominantly lower than the current (30 years) rate of RSLR (0.41±0.07 cm year −1 ). These results, combined with the increased rate of RSLR and the hardened shorelines inhibiting landward migration, call into question the longterm survivability of these marshes.

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Contributions of organic and inorganic matter to sediment volume and accretion in tidal wetlands at steady state

et al. 2016

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A mixing model derived from first principles describes the bulk density (BD) of intertidal wetland sediments as a function of loss on ignition (LOI). The model assumes that the bulk volume of sediment equates to the sum of self‐packing volumes of organic and mineral components or BD = 1/[LOI/k1 + (1‐LOI)/k2], where k1 and k2 are the self‐packing densities of the pure organic and inorganic components, respectively. The model explained 78% of the variability in total BD when fitted to 5075 measurements drawn from 33 wetlands distributed around the conterminous United States. The values of k1 and k2 were estimated to be 0.085 ± 0.0007 g cm−3 and 1.99 ± 0.028 g cm−3, respectively. Based on the fitted organic density (k1) and constrained by primary production, the model suggests that the maximum steady state accretion arising from the sequestration of refractory organic matter is ≤ 0.3 cm yr−1. Thus, tidal peatlands are unlikely to indefinitely survive a higher rate of sea‐level rise in the absence of a significant source of mineral sediment. Application of k2 to a mineral sediment load typical of East and eastern Gulf Coast estuaries gives a vertical accretion rate from inorganic sediment of 0.2 cm yr−1. Total steady state accretion is the sum of the parts and therefore should not be greater than 0.5 cm yr−1 under the assumptions of the model. Accretion rates could deviate from this value depending on variation in plant productivity, root:shoot ratio, suspended sediment concentration, sediment‐capture efficiency, and episodic events.

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Saltmarsh pool and tidal creek morphodynamics: Dynamic equilibrium of northern latitude saltmarshes?

Cited by 96 publications

References 58 publications

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

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

The Declining Role of Organic Matter in New England Salt Marshes

Contributions of organic and inorganic matter to sediment volume and accretion in tidal wetlands at steady state

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