Surface Elevation Change and Susceptibility of Different Mangrove Zones to Sea-Level Rise on Pacific High Islands of Micronesia

A global standard for monitoring coastal wetland vulnerability to accelerated sea-level rise

“…The complete RSET-MH set-up (hereafter referred to as 'RSET') therefore provides net surface elevation change above the benchmark depth; moreover, as it has been repeatedly shown that vertical accretion is not a valid substitute for surface elevation change 20,32,39 , the complete set-up is necessary to identify the contribution of surface and shallow subsurface processes to surface elevation change at a specific site 39,40 . Repeated measurements allow chronicling of net surface elevation change, which can be integrated with region-specific relative SLR (tide-gauge data) to determine whether the surface elevation has kept pace with SLR over that time period [40][41][42][43] . Because the benchmark rod is immovable and permanently affixed into the wetland, data collection can be abandoned for significant periods of time (months to years), and resumed at any point in the future without compromising data quality.…”

“…The RSET method has been useful not only for documenting trends in surface elevation change in specific wetlands 40 , but also for comparing rates of elevation change among hydrogeomorphic zones within a site (for example, a delta 41 ), differentiating between sites dominated by surface processes 40 versus subsurface processes 14 , documenting high variability in sediment deposition from singular storm events 44 , capturing rapid peat collapse from small-scale (for example, lightning strikes) and large-scale (for example, hurricanes) disturbances 45,46 , measuring the effects of elevated atmospheric CO 2 concentrations on surface elevation change 47 , and disentangling complex interactions among herbivory, biomass production and surface elevation change 48 . RSET data have also contributed to more applied research assessing the impacts of management practices on site-specific vulnerability to SLR, such as prescribed burning 49 , sedimentation from point-source coastal management interventions 50 , water diversion 51 , fence construction to enhance sediment deposition 52 and thin-layer deposition of dredged sediment 53 .…”

“…Unlevelled RSET studies are therefore limited to assessing the relative local difference between wetland elevation change and sea-level change. Nevertheless, relative comparisons are useful for assessing differential vulnerability of specific wetlands to SLR 14,40 . Importantly, recent improvements to GPS are facilitating the development of geospatial frameworks; as vertical standards become available for specific regions in the future, previously collected local data can be calibrated, thereby making all time series linked to the same vertical datum comparable.…”

“…A third limitation is spatial in nature. RSETs provide point data, so when placed in different zones of a wetland (for example, open mudflat, shoreline or interior) they provide a broad indication of site vulnerability to SLR 60 , as well as within-site heterogeneity 40 . Such information would be crucial for making fundamental management decisions locally, such as whether a site requires intervention.…”

Ecosystem Services and Disservices of Mangrove Forests: Insights from Historical Colonial Observations

“…A key foundational concept in mangrove science is the role of minergenic mangroves in trapping and consolidating sediment, leading to long term surface elevation change [53,54]. Positive elevation change allows mangrove vegetation to remain in the same relative position in the tidal frame as sea levels rise over the long-term, and a reduction in sediment input is a key factor in mangrove vulnerability to sea level [55].…”