Avoiding timescale bias in assessments of coastal wetland vertical change

Abstract

There is concern that accelerating sea‐level rise will exceed the vertical growth capacity of coastal‐wetland substrates in many regions by the end of this century. Vertical vulnerability estimates rely on measurements of accretion and/or surface‐elevation‐change derived from soil cores and/or surface elevation tables (SETs). To date there has not been a broad examination of whether the multiple timescales represented by the processes of accretion and elevation change are equally well‐suited for quantifying the trajectories of wetland vertical change in coming decades and centuries. To examine the potential for timescale bias in assessments of vertical change, we compared rates of accretion and surface elevation change using data derived from a review of the literature. In the first approach, average rates of elevation change were compared with timescale‐averaged accretion rates from six regions around the world where sub‐decadal, decadal, centennial, and millennial timescales were represented. Second, to isolate spatial variability, temporal comparisons were made for regionally unique environmental categories within each region. Last, comparisons were made of records from sites where SET‐MH stations and radiometric measurements were co‐located in close proximity. We find that rates vary significantly as a function of measurement timescale and that the pattern and magnitude of variation between timescales are location‐specific. Failure to identify and account for temporal variability in rates will produce biased assessments of the vertical change capacity of coastal wetlands. Robust vulnerability assessments should combine accretion rates from multiple timescales with the longest available SET record to provide long‐term context for ongoing monitoring observations and projections.

Toward a mechanistic understanding of “peat collapse” and its potential contribution to coastal wetland loss

“…), but within the range (0–2.2 cm/yr) of globally documented coastal wetland accretion rates (Breithaupt et al. ). Therefore, whether these annual rates of elevation decline are significant enough to create a deficit in elevation capital that shifts the ecosystem toward conversion to open water depends on local rates of sea level rise, the persistence of the elevation loss, and the response of vegetation (Reed , Cahoon and Guntenspergen , Lovelock et al.…”

“…, Breithaupt et al. ). In order to classify a loss of surface elevation as something unusual, possibly even as a collapse event, it is necessary to have a record of previous elevation trends and fluctuations for comparison.…”

Increasing Rates of Carbon Burial in Southwest Florida Coastal Wetlands

“…Marsh vegetation at this site is sawgrass and has been subjected to prescribed and natural wildfire events (Smith et al, ). The mangrove site is otherwise known as SH4 (U.S. Geological Survey; Smith et al, ; Smoak et al, ; Anderson et al, ) and WSC‐8 (Breithaupt et al, ; Breithaupt et al, ). The marsh site is otherwise known as SH5 (U.S. Geological Survey; Jiang et al, ; Anderson et al, ).…”

The Role of the Upper Tidal Estuary in Wetland Blue Carbon Storage and Flux

“…Furthermore, organic matter fraction was still relatively high, averaging 27.3% (or 12.6% C). For comparison, bulk density in mangrove soils is generally lower; typically less than 0.3 g/cm 3 except for specific mineral sites along rivers or creeks (Breithaupt et al, ; Marchio et al, , etc.). Those sites would be in similarly positioned locations to our riverine sites.…”

“…Deposition rates changed considerably on these sites over time, especially over the last few hundred years (Noe et al, ). It is not surprising that vertical accretion and C‐14‐based accumulation rates are so different given the age disparity of assessment (Breithaupt et al, ). Spatial patterns of aboveground C growth also corresponded roughly with C in from surface sediment accumulation along the Waccamaw and Savannah rivers (Figures c and d).…”