Research Interests: Environmental Science, Oceanography, Ecology, Environmental Chemistry, Sea Level, and 15 moreMangrove, Biological Sciences, Environmental Sciences, Sea level rise, Brisbane, Ecosystems, Avicennia marina, Sedimentation, Intertidal Zone, Salt marsh, Coastal Wetlands, Marsh, Pace, Bay, and Mean Sea Level
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Accelerating relative sea-level rise (RSLR) is threatening coastal wetlands. However, rising CO 2 concentrations may also stimulate carbon sequestration and vertical accretion, counterbalancing RSLR. A coastal wetland dominated by a C 3... more
Accelerating relative sea-level rise (RSLR) is threatening coastal wetlands. However, rising CO 2 concentrations may also stimulate carbon sequestration and vertical accretion, counterbalancing RSLR. A coastal wetland dominated by a C 3 plant species was exposed to ambient and elevated levels of CO 2 in situ from 1987 to 2019 during which time ambient CO 2 concentration increased 18% and sea level rose 23 cm. Plant production did not increase in response to gradually rising ambient CO 2 concentration during this period. Elevated CO 2 increased shoot production relative to ambient CO 2 for the first two decades, but from 2005 to 2019, elevated CO 2 stimulation of production was diminished. The decline coincided with increases in relative sea level above a threshold that hindered root productivity. While elevated CO 2 stimulation of elevation gain has the potential to moderate the negative impacts of RSLR on tidal wetland productivity, benefits for coastal wetland resilience will diminish in the long term as rates of RSLR accelerate.
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We assessed the resilience of wetlands to sea-level rise along a transitional gradient from tidal freshwater forested wetland (TFFW) to oligohaline marsh by measuring processes controlling wetland elevation. We identified fundamental... more
We assessed the resilience of wetlands to sea-level rise along a transitional gradient from tidal freshwater forested wetland (TFFW) to oligohaline marsh by measuring processes controlling wetland elevation. We identified fundamental differences in how resilience is maintained across wetland community types, which have important implications for management activities that aim to restore or conserve resilient systems.
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Abstract The greatest climate-based threat to coastlines worldwide is sea-level rise. We tested the hypothesis that tropical coasts fringed by mangroves and receiving high inputs of terrigenous sediment are less vulnerable to sea-level... more
Abstract The greatest climate-based threat to coastlines worldwide is sea-level rise. We tested the hypothesis that tropical coasts fringed by mangroves and receiving high inputs of terrigenous sediment are less vulnerable to sea-level rise than biogenic systems dependent upon peat formation for vertical land development. An analysis of published data spanning a range of geomorphic settings showed that mineral accretion was a poor predictor of vulnerability to rising sea level. We additionally compared two oceanic island systems representing two extremes along this sediment gradient to further examine controls on elevation dynamics in minerogenic versus biogenic mangrove systems. Minerogenic systems characterized by intermediate to high rates of mineral sedimentation (Pacific high islands in Micronesia) were not better buffered against sea-level rise because of high subsidence rates. Peat-forming systems (Caribbean low islands in Belize) kept pace with relative sea-level rise (combined ocean and land movements) because of subsurface expansion driven by root matter accumulation. The data were not consistent with the paradigm that tropical coastlines characterized by peat-forming mangroves are generally more vulnerable to sea-level rise compared to minerogenic systems; however, they are not necessarily equally sensitive to the same external and internal forces controlling soil elevations. Our findings demonstrate that reliance on surface accretion data alone can lead to an inaccurate evaluation of coastal vulnerability and why all surface and subsurface land movements must be considered in relation to local sea-level trends to assess risk of submergence. Recognition of such differences is essential to proper management of tropical coastlines to ensure their resilience in the face of future sea-level rise.
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Research Interests: Earth Sciences, Geology, Mangrove, Biological Sciences, Pacific Islands, and 15 moreEnvironmental Sciences, Ecosystems, Soils, Sol, Accretion, Suspended Sediment, Sediment Traps, Mangrove forest, River Basin, Sedimentation, Micronesian Studies, Root System, Federated States Of Micronesia, Aerial root, and Bare Soil
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Page 1. Hurricane Mitch: A Regional Perspective on Mangrove Damage, Recovery, and Sustainability By Donald R. Cahoon and Philippe Hensel ... Page 3. USGS ACTIVITY B6 AND B7 Hurricane Mitch: A Regional Perspective on Mangrove Damage,... more
Page 1. Hurricane Mitch: A Regional Perspective on Mangrove Damage, Recovery, and Sustainability By Donald R. Cahoon and Philippe Hensel ... Page 3. USGS ACTIVITY B6 AND B7 Hurricane Mitch: A Regional Perspective on Mangrove Damage, Recovery and Sustainability ...
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Simultaneous measurements of vertical accretion from marker horizons and marsh-elevation change from sedimentation-erosion tables (SET) were made in selected marshes along the East Anglian coast of the UK in order to address the following... more
Simultaneous measurements of vertical accretion from marker horizons and marsh-elevation change from sedimentation-erosion tables (SET) were made in selected marshes along the East Anglian coast of the UK in order to address the following objectives: (1)to ascertain the validity of treating accretion measurements obtained within tidally dominated, minerogenic saltmarshes as equivalent to surface elevation changes;(2)to explore the implications, in terms of physical and biological processes, of discrepancies between separately measured vertical accretion and elevation change within contrasting marsh types.Data were collected from several marsh environments at Scolt Head Island and Stiffkey on the North Norfolk coast and at an experimental managed realignment project near Tollesbury, Essex. Scolt Head Island was selected for its long-term datasets of marsh accretion, Stiffkey for its contrasting open coast-back barrier settings, and Tollesbury for its experimental management, in order to illustrate the potential application of the SET method and evaluate the relationship between vertical accretion and elevation change in a variety of marsh settings.The relationship between vertical accretion and elevation change varied widely among marsh settings of different age and height (within the tidal frame) at Scolt Head Island and Stiffkey. Rates of vertical accretion and elevation change were similar in the older and midheight settings on Scolt Head Island, indicating control of elevation change by surface accretionary processes (e.g. sediment deposition). However, subsurface processes controlled elevation at three of the marsh sites. Spartina Marsh, the youngest and lowest of the back barrier settings at Scolt Head Island, exhibited continuous shallow subsidence (vertical accretion greater than elevation change) over a 4-year period, implying that compaction controls elevation change. In the upper part of Hut Marsh and the interior of the Stiffkey marshes, elevation change exceeded vertical accretion suggesting that subsurface processes (e.g. organic accumulation) controlled elevation in these settings. Surface accretionary processes control elevation change in both the highly dynamic, outer marsh at Stiffkey and the low, restored marsh at Tollesbury. Despite the occurrence of shallow subsidence, all sites gained elevation at an annual rate comparable to that of sea-level rise. In summary, the SET provides the means to critically evaluate the influence of vertical accretion measures on elevation and represents an improved method by which to evaluate the vulnerability of a marsh to sea-level rise.
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Research Interests: Environmental Science, Oceanography, Wetlands, Ecology, Subsidence, and 14 moreSea Level, Mangrove, Biological Sciences, Environmental Sciences, Sea level rise, Wetland, Ecosystems, Anthropogenic Disturbance, Sediment, Mangrove forest, Ecosystem, Ecosystem service, Federated States Of Micronesia, and Perturbation
Research Interests: Earth Sciences, Environmental Science, Geology, Climate Change, Conservation Biology, and 15 moreConservation, Climatology, Energy, Adaptation, Environmental Management, Ecology, Climate, Carbon Cycle, Databases, Earth System Science, Global change, Environmental Resource Management, Environmental Assessment, Climate Science, and Coastal Areas
Research Interests: Geography, Earth Sciences, Environmental Science, Geology, Climate Change, and 15 moreSoil, Mangrove, Medicine, Biological Sciences, Sea level rise, Roots, Avicennia marina, New South Wales, Accretion, Ecosystem, Disturbance, NET PRIMARY PRODUCTIVITY, Rhizophoraceae, Oceans and Seas, and Environmental drivers
Research Interests: Earth Sciences, Environmental Science, Geology, Climate Change, Sea Level, and 15 moreMangrove, Medicine, Multidisciplinary, Nature, Indian Ocean, Forests, Social and Behavioral Sciences, Avicennia marina, Seawater, Pacific ocean, Salt marsh, Altitude, Medicine and Health Sciences, Rhizophoraceae, and Geologic Sediments
Much uncertainty exists about the vulnerability of valuable tidal marsh ecosystems to relative sea level rise. Previous assessments of resilience to sea level rise, to which marshes can adjust by sediment accretion and elevation gain,... more
Much uncertainty exists about the vulnerability of valuable tidal marsh ecosystems to relative sea level rise. Previous assessments of resilience to sea level rise, to which marshes can adjust by sediment accretion and elevation gain, revealed contrasting results, depending on contemporary or Holocene geological data. By analyzing globally distributed contemporary data, we found that marsh sediment accretion increases in parity with sea level rise, seemingly confirming previously claimed marsh resilience. However, subsidence of the substrate shows a nonlinear increase with accretion. As a result, marsh elevation gain is constrained in relation to sea level rise, and deficits emerge that are consistent with Holocene observations of tidal marsh vulnerability.
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The rates of production, leaf grazing, and stem decomposition associated with Hibiscus moscheutos were quantified to contrast the ecology of this brackish herbaceous perennial with fresh and salt marsh species. Average net aerial primary... more
The rates of production, leaf grazing, and stem decomposition associated with Hibiscus moscheutos were quantified to contrast the ecology of this brackish herbaceous perennial with fresh and salt marsh species. Average net aerial primary production (NAPP) during 1978 and 1979 was estimated to be slightly over 1200 gm~2yr_1, which was calculated by summing: peak standing crop (49%); leaf mortality and litter production (36%); and losses to herbivores (15%). Three species of herbivorous insects were found to be important grazers: Atomacera decepta, Chionodes hibiscella, and Althaeus hibisci. Herbivore consumption was far greater than previously reported in salt marsh systems and rivals that of terrestrial communities. The root: shoot ratio (2.3) is comparable to many fresh marsh species but lower than most high-salinity species. The decomposition rate of Hibiscus stem material was estimated to be on the order of 7-8 yr, or up to five times slower than stems and leaves of other typical...
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One of the key questions to be addressed by the U.S. Climate Change Science Program’s (CCSP) sea level rise synthesis and assessment is “To what extent can wetlands vertically accrete and
Research Interests: Geology and Geophysical
Transgression into adjacent uplands is an important global response of coastal wetlands to accelerated rates of sea level rise. “Ghost forests” mark a signature characteristic of marsh transgression on the landscape, as changes in tidal... more
Transgression into adjacent uplands is an important global response of coastal wetlands to accelerated rates of sea level rise. “Ghost forests” mark a signature characteristic of marsh transgression on the landscape, as changes in tidal inundation and salinity cause bordering upland tree mortality, increase light availability, and the emergence of tidal marsh species due to reduced competition. To investigate these mechanisms of the marsh migration process, we conducted a field experiment to simulate a natural disturbance event (e.g., storm-induced flooding) by inducing the death of established trees (coastal loblolly pine, Pinus taeda) at the marsh-upland forest ecotone. After this simulated disturbance in 2014, we monitored changes in vegetation along an elevation gradient in control and treatment areas to determine if disturbance can lead to an ecosystem shift from forested upland to wetland vegetation. Light availability initially increased in the disturbed area, leading to an i...
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The Mississippi River delta and chenier plains in Louisiana are experiencing catastrophic coastal land loss rates exceeding 100 km2/yr. Louisiana's coastal zone contains 40 percent of the U. S. wetlands and 80 percent of the... more
The Mississippi River delta and chenier plains in Louisiana are experiencing catastrophic coastal land loss rates exceeding 100 km2/yr. Louisiana's coastal zone contains 40 percent of the U. S. wetlands and 80 percent of the Nation's loss occurs here. The origin and stability of these coastal environments is tied to the sediments discharged by the Mississippi River throught the delta cycle process. Sediments accumulate in well-defined delta complexes at approximately 800-1000 year intervals followed by abandonment and barrier island formation. The delta-cycle process, that bulds new delta complexes, barrier islands, and cheniers is curently stopped by flood and navigation control structures. These structures harness the flow of the Mississippi River within a massive levee system, channeling most of the sediments off the continental shelf. Deprived of sediments and subsiding rapidly, Louisiana's wetlands are vanishing. Researchers have long recognized the catastrophic coa...
The Louisiana Department of Natural Resources, Coastal Management Division (CMD) implemented the Joint Public Notice System (JPNS), a cooperative agreement with the United States Army, Corps of Engineers, New Orleans District (COE) to... more
The Louisiana Department of Natural Resources, Coastal Management Division (CMD) implemented the Joint Public Notice System (JPNS), a cooperative agreement with the United States Army, Corps of Engineers, New Orleans District (COE) to issue joint public notices of permit applications for activities within the coincident jurisdiction of each agency. The 'one-window' system saves repeat applicants such as major corporations considerable effort and expense while making it simpler for the one time applicant who is unfamiliar with the permit process to obtain a permit.
Byrnes et al. (Geo-Marine Letters 39:265–278, Byrnes et al. 2019 ) present subsidence data for Barataria Basin located south and west of New Orleans in coastal Louisiana to better inform wetland protection and restoration planning by the... more
Byrnes et al. (Geo-Marine Letters 39:265–278, Byrnes et al. 2019 ) present subsidence data for Barataria Basin located south and west of New Orleans in coastal Louisiana to better inform wetland protection and restoration planning by the Louisiana Coastal Protection and Restoration Authority. They measured subsidence using geodetic GPS elevation surveys of rod benchmarks, similar to the rod benchmarks of the surface elevation table–marker horizon (SET-MH) method used to measure surface biophysical processes influencing elevation dynamics and shallow subsidence (i.e., subsidence occurring above the base of the rod) in coastal wetlands. Byrnes et al. (Geo-Marine Letters 39:265–278, Byrnes et al. 2019 ) argue that (1) SET-MH measures should not be included in subsidence measures because subsidence is a purely geologic process, separate from biophysical processes occurring in the active marsh zone, (2) shallow subsidence measured by the SET-MH method in deep Holocene sediments are not valid because of downdrag on the rod, and (3) high spatial variability of wetland surface processes precludes the ability to make meaningful estimates of subsidence using the SET-MH method. This reply paper presents an extensive summary of the peer-reviewed literature that refutes all three of these claims and demonstrates that it is not only reasonable but also essential to apply the SET-MH method to obtain a complete as possible assessment of surface elevation dynamics to inform coastal wetland restoration and management planning in Barataria Basin and other coastal wetlands worldwide.
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This review evaluates the importance of plants and associated biological processes in determining the vulnerability of coastal wetlands to sea-level rise. Coastal wetlands occur across a broad sedimentary continuum from minerogenic to... more
This review evaluates the importance of plants and associated biological processes in determining the vulnerability of coastal wetlands to sea-level rise. Coastal wetlands occur across a broad sedimentary continuum from minerogenic to biogenic, providing an opportunity to examine the relative importance of biological processes in wetland resilience to sea-level rise. We explore how plants influence sediment accretion, elevation capital (vertical position in the tidal frame), and compaction or erosion of deposited material. We focus on salt marsh and mangrove wetlands, which occupy a similar physiographic niche and display similar physical and biological controls on resilience to sea-level rise. In both habitats, plants stabilize emergent mudflats and help sustain the wetland position in the tidal frame relative to ocean height through both surface and subsurface process controls on soil elevation. Plants influence soil elevations by modifying (1) mineral sediment deposition and retention, (2) organic matter contributions to soil volume, and (3) resistance to compaction and erosion. Recognition of the importance of plants in coastal wetland resilience to sea-level rise is key to accurate predictions about the future fate of salt marshes and mangrove forests and for development of effective management and restoration plans.
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Climate change-mediated impacts originating from terrestrial and marine sources interact at the coast to influence coastal habitats (Nicholls et al., 2007; Rosenzweig et al., 2007; Figure 3-1; Table 3-1). On the landward side, increased... more
Climate change-mediated impacts originating from terrestrial and marine sources interact at the coast to influence coastal habitats (Nicholls et al., 2007; Rosenzweig et al., 2007; Figure 3-1; Table 3-1). On the landward side, increased temperatures and altered precipitation patterns interact with changing land-use and land-cover practices to affect soil moisture, ground water levels, hydrology, sediment supply, salinity, and pollution in watersheds. On the marine side, sea-level rise, changing ocean currents, increased wave heights, and intensification of coastal storms interact with changes in land use and land cover to exacerbate coastal erosion, flooding, and saltwater intrusion. As a result of these interactions, complex changes in coastal freshwater availability and water quality are also occurring.