Buying Time with Runnels: a Climate Adaptation Tool for Salt Marshes

AbstractA prominent form of salt marsh loss is interior conversion to open water, driven by sea level rise in interaction with human activity and other stressors. Persistent inundation drowns vegetation and contributes to open water conversion in salt marsh interiors. Runnels are shallow channels originally developed in Australia to control mosquitoes by draining standing water, but recently used to restore marsh vegetation in the USA. Documentation on runnel efficacy is not widely available; yet over the past 10 years dozens of coastal adaptation projects in the northeastern USA have incorporated runnels. To better understand the efficacy of runnels used for restoration, we organized a workshop of 70 experts and stakeholders in coastal resource management. Through the workshop we developed a collective understanding of how runnels might be used to slow or reverse open water conversion, and identified unresolved questions. In this paper we present a synthesis of workshop discussions and results from a promising case study in which vegetation was restored at a degraded marsh within a few years of runnel construction. Despite case study outcomes, key questions remain on long-term runnel efficacy in marshes differing in elevation, tidal range, and management history. Runnel construction is unlikely to improve long-term marsh resilience alone, as it cannot address underlying causes of open water conversion. As a part of holistic climate planning that includes other management interventions, runnels may “buy time” for salt marshes to respond to management action, or adapt to sea level rise.

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Long-term invasion dynamics of Spartina increase vegetation diversity and geomorphological resistance of salt marshes against sea level rise

Biological Invasions ◽

10.1007/s10530-020-02408-0 ◽

2020 ◽

Author(s):

Dirk Granse ◽

Sigrid Suchrow ◽

Kai Jensen

Keyword(s):

Salt Marsh ◽

Species Diversity ◽

Sea Level Rise ◽

Sea Level ◽

Salt Marshes ◽

High Marsh ◽

Marsh Vegetation ◽

Vegetation Diversity ◽

The Impact

AbstractThe cordgrass Spartina anglica C.E. Hubbard (Poaceae) is an invasive transformer in many salt marsh ecosystems worldwide. Relatively little is known about the capacity of Spartina to accelerate salt marsh succession and to protect salt marshes against sea level rise. We analyzed long-term changes in vegetation and elevation in mainland salt marshes of the European Wadden Sea in Schleswig-Holstein, Germany, to estimate the impact of non-native Spartina on the geomorphological resistance of salt marshes to sea level rise and on changes in species diversity. From 1989 to 2019, the Spartina-zone shifted and expanded upwards to elevations of the high marsh zone and Spartina increased in frequency in several salt marsh vegetation communities. At sites where Spartina dominated the vegetation already three decades ago, elevation and species diversity increased with a higher rate compared to sites lacking Spartina. The median change rates reached for elevation MHT +8.6 versus +1.5 mm per year, for species richness +3 versus $$\pm$$ ± 0 species per three decades, and for evenness +0.04 versus −0.08 per three decades, regarding plots with versus without former Spartina dominance, respectively. Invasion of salt marshes by Spartina and its continued, long-term presence were associated with increased elevation and species diversity in the face of sea level rise.

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A Holistic Framework for Evaluating Adaptation Approaches to Coastal Hazards and Sea Level Rise: A Case Study from Imperial Beach, California

Water ◽

10.3390/w13091324 ◽

2021 ◽

Vol 13 (9) ◽

pp. 1324

Author(s):

David Revell ◽

Phil King ◽

Jeff Giliam ◽

Juliano Calil ◽

Sarah Jenkins ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Public Trust ◽

Adaptation Strategy ◽

Public Benefits ◽

Study Results ◽

Local Risk ◽

Over Time

Sea level rise increases community risks from erosion, wave flooding, and tides. Current management typically protects existing development and infrastructure with coastal armoring. These practices ignore long-term impacts to public trust coastal recreation and natural ecosystems. This adaptation framework models physical responses to the public beach and private upland for each adaptation strategy over time, linking physical changes in widths to damages, economic costs, and benefits from beach recreation and nature using low-lying Imperial Beach, California, as a case study. Available coastal hazard models identified community vulnerabilities, and local risk communication engagement prioritized five adaptation approaches—armoring, nourishment, living shorelines, groins, and managed retreat. This framework innovates using replacement cost as a proxy for ecosystem services normally not valued and examines a managed retreat policy approach using a public buyout and rent-back option. Specific methods and economic values used in the analysis need more research and innovation, but the framework provides a scalable methodology to guide coastal adaptation planning everywhere. Case study results suggest that coastal armoring provides the least public benefits over time. Living shoreline approaches show greater public benefits, while managed retreat, implemented sooner, provides the best long-term adaptation strategy to protect community identity and public trust resources.

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Middle and Late Holocene Sea-Level Changes in Eastern Maine Reconstructed from Foraminiferal Saltmarsh Stratigraphy and AMS 14C Dates on Basal Peat

Quaternary Research ◽

10.1006/qres.1999.2076 ◽

1999 ◽

Vol 52 (3) ◽

pp. 350-359 ◽

Cited By ~ 113

Author(s):

W.Roland Gehrels

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Tidal Range ◽

Sea Level Changes ◽

The Past ◽

Amplitude Fluctuations ◽

Vertical Distributions ◽

Low Amplitude ◽

Long Term Trend

A relative sea-level history is reconstructed for Machiasport, Maine, spanning the past 6000 calendar year and combining two different methods. The first method establishes the long-term (103 yr) trend of sea-level rise by dating the base of the Holocene saltmarsh peat overlying a Pleistocene substrate. The second method uses detailed analyses of the foraminiferal stratigraphy of two saltmarsh peat cores to quantify fluctuations superimposed on the long-term trend. The indicative meaning of the peat (the height at which the peat was deposited relative to mean tide level) is calculated by a transfer function based on vertical distributions of modern foraminiferal assemblages. The chronology is determined from AMS 14C dates on saltmarsh plant fragments embedded in the peat. The combination of the two different approaches produces a high-resolution, replicable sea-level record, which takes into account the autocompaction of the peat sequence. Long-term mean rates of sea-level rise, corrected for changes in tidal range, are 0.75 mm/yr between 6000 and 1500 cal yr B.P. and 0.43 mm/yr during the past 1500 year. The foraminiferal stratigraphy reveals several low-amplitude fluctuations during a relatively stable period between 1100 and 400 cal yr B.P., and a sea-level rise of 0.5 m during the past 300 year.

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Venice lagoon salt marsh vulnerability and halophytic vegetation vertical migration in response to sea level rise

10.5194/egusphere-egu2020-14404 ◽

2020 ◽

Author(s):

Zhicheng Yang ◽

Sonia Silvestri ◽

Marco Marani ◽

Andrea D’Alpaos

Keyword(s):

Salt Marsh ◽

Sea Level Rise ◽

Sea Level ◽

Salt Marshes ◽

Current Knowledge ◽

Venice Lagoon ◽

Sea Level Changes ◽

Human Pressure ◽

Sea Levels ◽

Vegetation Species

Salt marshes are biogeomorphic systems that provide important ecosystem services such as carbon sequestration and prevention of coastal erosion. These ecosystems are, however, threatened by increasing sea levels and human pressure. Improving current knowledge of salt-marsh response to changes in the environmental forcing is a key step to understand and predict salt-marsh evolution, especially under accelerated sea level rise scenarios and increasing human pressure. Towards this goal, we have analyzed field observations of marsh topographic changes and halophytic vegetation distribution with elevation collected over 20 years (between 2000 and 2019) in a representative marsh in the Venice lagoon (Italy).Our results suggest that: 1) on average, marsh elevation with respect to local mean sea level decreased , (i.e. the surface accretion rate was lower than the rate of sea level rise); 2) elevational frequency distributions are characteristic for different halophytic vegetation species, highlighting different ecological realized niches that change in time; 3) although the preferential elevations at which different species have changed in time, the sequence of vegetation species with increasing soil elevation was preserved and simply shifted upward; 4) we observed different vegetation migration rates for the different species, suggesting that the migration process is species-specific. In particular, vegetation species colonizing marsh edges (Juncus and Inula) migrated faster facing to changes in sea levels than Limonium and Spartina , while Sarcocornia was characterized by delayed migration in response to sea level changes. These results bear significant implications for long-term biogeomorphic evolution of tidal environments.

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IMMERSIVE EXPERIENCES IN CLIMATE ADAPTATION

Coastal Engineering Proceedings ◽

10.9753/icce.v36v.keynote.10 ◽

2020 ◽

pp. 10

Author(s):

Juliano Calil

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Coastal Erosion ◽

Climate Adaptation ◽

3D Models ◽

Coastal Communities ◽

Long Beach ◽

Coastal Risks ◽

Impacts Of Climate Change

As coastal communities worldwide contend with sea-level rise, coastal erosion, and other impacts of climate change, a critical piece of the puzzle has become educating stakeholders in highly creative, insightful, and practical ways. In this study, we will highlight the main findings from the use of immersive and interactive Virtual Reality (VR) experiences in climate adaptation. These tools are helping coastal communities better understand potential impacts as well as explore near- and long-term solutions to reduce coastal risks. We will describe the challenges and steps taken to develop these applications at four coastal locations in the U.S. (Turner Station, MD, and Santa Cruz, Long Beach, and Moss Landing in CA); from identifying key objectives of each experience, the critical messages, and target audiences, to flying drones over coastal areas and working with photogrammetry to create hyper-realistic 3D models that are inserted in the VR experience. These immersive and interactive experiences support planning, management and monitoring activities related to sea-level rise, storms, coastal erosion, king tides, and more. These tools are being developed by a multidisciplinary team with a range of expertise including climate and coastal scientists, city planners, communications experts, filmmakers, 3D animators, and VR developers.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/aDIkbn_FO1c

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Modeling long‐term salt marsh response to sea level rise in the sediment‐deficient Plum Island Estuary, MA

Limnology and Oceanography ◽

10.1002/lno.11444 ◽

2020 ◽

Vol 65 (9) ◽

pp. 2142-2157 ◽

Cited By ~ 2

Author(s):

Amy K. Langston ◽

Orencio Durán Vinent ◽

Ellen R. Herbert ◽

Matthew L. Kirwan

Keyword(s):

Salt Marsh ◽

Sea Level Rise ◽

Sea Level

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Salt marsh resilience to sea-level rise and increased storm intensity

10.5194/egusphere-egu21-1294 ◽

2021 ◽

Author(s):

Natascia Pannozzo ◽

Nicoletta Leonardi ◽

Iacopo Carnacina ◽

Rachel Smedley

Keyword(s):

Salt Marsh ◽

Sea Level Rise ◽

Sea Level ◽

Storm Surge ◽

Salt Marshes ◽

Sediment Budget ◽

Geophysical Research ◽

Storm Intensity ◽

Combined Impact ◽

And Sea Level

Salt marshes are widely recognised as ecosystems with high economic and environmental value. However, it is still unclear how salt marshes will respond to the combined impact of future sea-level rise and possible increases in storm intensity (Schuerch et al. 2013). This study investigates marsh resilience under the combined impact of various storm surge and sea-level scenarios by using a sediment budget approach. The current paradigm is that a positive sediment budget supports the accretion of salt marshes and, therefore, its survival, while a negative sediment budget causes marsh degradation (Ganju et al. 2015). The Ribble Estuary, North-West England, was used as test case, and the hydrodynamic model Delft3D was used to simulate the response of the salt marsh system to the above scenarios. We conclude that the resilience of salt marshes and estuarine systems is enhanced under the effect of storm surges, as they promote flood dominance and trigger a net import of sediment.&#160; Conversely, sea-level rise threatens marsh stability, by promoting ebb dominance and triggering a net export of sediment. Ultimately, when storm surge and sea-level scenarios are combined, results show that storms with the highest intensities have the potential to counteract the negative impact of sea-level rise by masking its effects on the sediment budget.AcknowledgementsWe acknowledge the support of the School of Environmental Sciences, University of Liverpool.ReferencesGanju, N.K., Kirwan, M.L., Dickhudt, P.J., Guntenspergen, G.R., Cahoon, D.R. and Kroeger, K.D. 2015. &#8220;Sediment transport-based metrics of wetland stability&#8221;. Geophysical Research Letters, 42(19), 7992-8000.Schuerch, M., Vafeidis, A., Slawig, T. and Temmerman, S. 2013. &#8220;Modeling the influence of changing storm patterns on the ability of a salt marsh to keep pace with sea level rise&#8221;.&#160;Journal of Geophysical Research-Earth Surface, 118(1),&#160;84-96.

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Insights from Testing a Modified Dynamic Adaptive Policy Pathways Approach for Spatial Planning at the Municipal Level

Sustainability ◽

10.3390/su11020433 ◽

2019 ◽

Vol 11 (2) ◽

pp. 433

Author(s):

Christoffer Carstens ◽

Karin Mossberg Sonnek ◽

Riitta Räty ◽

Per Wikman-Svahn ◽

Annika Carlsson-Kanyama ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Spatial Planning ◽

Adaptive Policy ◽

New Ideas ◽

Legal Constraints ◽

Mind Set ◽

Municipal Level

The Dynamic Adaptive Policy Pathways (DAPP) approach has successfully been used to manage uncertainties in large infrastructure projects. However, the viability of the DAPP approach for spatial planning in smaller municipal settings is not clear. This paper examines opportunities and constraints of using adaptive pathways approaches to help small municipalities plan for future sea-level rise. The methodology was based on developing a simplified DAPP-approach, which was tested in a multiple experimental case study of spatial planning projects in three municipalities in Sweden. The results show that the approach promoted vulnerability-based thinking among the end-users and generated new ideas on how to manage the uncertain long-term impacts of future sea-level rise. However, the increased understanding of uncertainties was used to justify static, rather than adaptive, solutions. This somewhat surprising outcome can be explained by perceived legal constraints, lack of experience of adaptive pathways, and unwillingness to prescribe actions that could prove difficult to enforce in the future. More research is needed to further understand at what planning phases dynamic policy pathway approaches work best and how current barriers in legislation, practices, mind-set, organization, and resources can be overcome.

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