Overestimation of marsh vulnerability to sea level rise

Kirwan, Matthew L.; Temmerman, Stijn; Skeehan, Emily E.; Guntenspergen, Glenn R.; Fagherazzi, Sergio

doi:10.1038/nclimate2909

Cited by 628 publications

(628 citation statements)

References 85 publications

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“…For example, it is predicted that as air and sea temperatures increase, some herbaceous wetland vegetation will be replaced with tropical woody mangrove species (Comeaux et al 2012;Osland et al 2012;Doughty et al 2015) and that these community shifts may influence carbon production and accumulation rates in wetland soils. Sea-level rise is also predicted to produce more saline environmental conditions that could drive transitions of fresh marshes to more saline marsh types (Herbert et al 2015) or drive salt marsh transgression inland (Kirwan et al 2016). In addition, large-scale restoration projects could introduce more fresh water to some estuaries, resulting in fresher marsh types (Morris et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Relationships Between Salinity and Short-Term Soil Carbon Accumulation Rates from Marsh Types Across a Landscape in the Mississippi River Delta

et al. 2017

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Salinity alterations will likely change the plant and environmental characteristics in coastal marshes thereby influencing soil carbon accumulation rates. Coastal Louisiana marshes have been historically classified as fresh, intermediate, brackish, or saline based on resident plant community and position along a salinity gradient. Short-term total carbon accumulation rates were assessed by collecting 10-cm deep soil cores at 24 sites located in marshes spanning the salinity gradient. Bulk density, total carbon content, and the short-term accretion rates obtained with feldspar horizon markers were measured to determine total carbon accumulation rates. Despite some significant differences in soil properties among marsh types, the mean total carbon accumulation rates among marsh types were not significantly different (mean ± std. err. of 190 ± 27 g TC m −2 year −1 ). However, regression analysis indicated that mean annual surface salinity had a significant negative relationship with total carbon accumulation rates. Based on both analyses, the coastal Louisiana total marsh area (1,433,700 ha) accumulates about 2.7 to 3.3 Tg C year −1 .Changing salinities due to increasing relative sea level or resulting from restoration activities may alter carbon accumulation rates in the short term and significantly influence the global carbon cycle.

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Section: Introductionmentioning

confidence: 99%

Relationships Between Salinity and Short-Term Soil Carbon Accumulation Rates from Marsh Types Across a Landscape in the Mississippi River Delta

et al. 2017

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“…Sedimentation dynamics partially determine the survival of salt marshes under rising sea level (Baustian et al, 2012;Kirwan and Megonigal, 2013;Kirwan et al, 2016) and the delivery and storage of organic matter (OM; Duarte et al, 2013;Lovelock et al, 2013). Salt marsh soils may be minerogenic (dominated by mineral inputs) or organogenic (dominated by biomass and litter production and/or allochthonous OM inputs), although most comprise both mineral and organic fractions (Adam, 2002;Baustian et al, 2012).…”

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confidence: 99%

Sediment and carbon deposition vary among vegetation assemblages in a coastal salt marsh

et al. 2017

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Abstract. Coastal salt marshes are dynamic, intertidal ecosystems that are increasingly being recognised for their contributions to ecosystem services, including carbon (C) accumulation and storage. The survival of salt marshes and their capacity to store C under rising sea levels, however, is partially reliant upon sedimentation rates and influenced by a combination of physical and biological factors. In this study, we use several complementary methods to assess short-term (days) deposition and medium-term (months) accretion dynamics within a single marsh that contains three salt marsh vegetation types common throughout southeastern (SE) Australia.We found that surface accretion varies among vegetation assemblages, with medium-term (19 months) bulk accretion rates in the upper marsh rush (Juncus) assemblage (1.74 ± 0.13 mm yr −1 ) consistently in excess of estimated local sea-level rise (1.15 mm yr −1 ). Accretion rates were lower and less consistent in both the succulent (Sarcocornia, 0.78 ± 0.18 mm yr −1 ) and grass (Sporobolus, 0.88 ± 0.22 mm yr −1 ) assemblages located lower in the tidal frame. Short-term (6 days) experiments showed deposition within Juncus plots to be dominated by autochthonous organic inputs with C deposition rates ranging from 1.14 ± 0.41 mg C cm −2 d −1 (neap tidal period) to 2.37 ± 0.44 mg C cm −2 d −1 (spring tidal period), while minerogenic inputs and lower C deposition dominated Sarcocornia (0.10 ± 0.02 to 0.62 ± 0.08 mg C cm −2 d −1 ) and Sporobolus (0.17 ± 0.04 to 0.40 ± 0.07 mg C cm −2 d −1 ) assemblages. Elemental (C : N), isotopic (δ 13 C), mid-infrared (MIR) and 13 C nuclear magnetic resonance (NMR) analyses revealed little difference in either the source or character of materials being deposited among neap versus spring tidal periods. Instead, these analyses point to substantial redistribution of materials within the Sarcocornia and Sporobolus assemblages, compared to high retention and preservation of organic inputs in the Juncus assemblage. By combining medium-term accretion quantification with short-term deposition measurements and chemical analyses, we have gained novel insights into above-ground biophysical processes that may explain previously observed regional differences in surface dynamics among key salt marsh vegetation assemblages. Our results suggest that Sarcocornia and Sporobolus assemblages may be particularly susceptible to changes in sea level, though quantification of below-ground processes (e.g. root production, compaction) is needed to confirm this.

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“…While awareness about potential global-warming impacts on OM preservation and their resulting threat to future tidal wetland stability has been raised (Kirwan & Mudd, 2012), concepts on the vulnerability of tidal wetlands to accelerated SLR mainly focus on plant-productivity responses and their biophysical feedbacks (Kirwan et al, 2016). Potentially negative effects of accelerated SLR on…”

Section: Discussionmentioning

confidence: 99%

Global change effects on decomposition processes in tidal wetlands: implications from a global survey using standardized litter

Müeller¹,

Schile-Beers²,

Mozdzer³

et al. 2017

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Tidal wetlands, such as tidal marshes and mangroves, are hotspots for carbon sequestration. The preservation of organic matter (OM) is a critical process by which tidal wetlands exert influence over the global carbon cycle and at the same time gain elevation to keep pace with sea-level rise (SLR). The present study provides the first global-scale field-based experimental evidence of 50 temperature and relative sea level effects on the decomposition rate and stabilization of OM in tidal wetlands. The study was conducted in 26 marsh and mangrove sites across four continents, utilizing commercially available standardized OM. While effects on decomposition rate per se were minor, we show unanticipated and combined negative effects of temperature and relative sea level on OM stabilization. Across study sites, OM stabilization was 29% lower in low, more frequently flooded 55 vs. high, less frequently flooded zones. OM stabilization declined by ~90% over the studied temperature gradient from 10.9 to 28.5°C, corresponding to a decline of ~5% over a 1°C-temperature increase. Additionally, data from the long-term ecological research site in Massachusetts, US show a pronounced reduction in OM stabilization by >70% in response to simulated coastal eutrophication, confirming the high sensitivity of OM stabilization to global 60 change. We therefore provide evidence that rising temperature, accelerated SLR, and coastal eutrophication may decrease the future capacity of tidal wetlands to sequester carbon by affecting the initial transformations of recent OM inputs to soil organic matter.

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Overestimation of marsh vulnerability to sea level rise

Cited by 628 publications

References 85 publications

Relationships Between Salinity and Short-Term Soil Carbon Accumulation Rates from Marsh Types Across a Landscape in the Mississippi River Delta

Relationships Between Salinity and Short-Term Soil Carbon Accumulation Rates from Marsh Types Across a Landscape in the Mississippi River Delta

Sediment and carbon deposition vary among vegetation assemblages in a coastal salt marsh

Global change effects on decomposition processes in tidal wetlands: implications from a global survey using standardized litter

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