Showing papers by "Denise J. Reed published in 2020"

Applications and utility of the surface elevation table-marker horizon method for measuring wetland elevation and shallow soil subsidence-expansion

Abstract: 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.

Elevation and accretion dynamics at historical plots in the Biloxi Marshes, Mississippi Delta

Abstract: The objectives of this study were to examine changes in accretion and elevation change over periods of up to 15 years for the Biloxi marsh complex (BMC) in southeastern Louisiana, part of the Mississippi Deltaic Plain, identify factors affecting accretionary dynamics, and put these findings in the context of ongoing restoration. We present elevation and accretion data from Surface Elevation Table (SET) and feldspar marker horizon sites first established in 2003. The sites were clustered in two areas (East and West) in the central BMC on the eastern edge of the Mississippi delta. Accretion markers were used in conjunction with elevation measurements to calculate shallow subsidence. These data were analyzed along with similar data from nearby Coastwide Reference Monitoring System (CRMS) sites located around the periphery of the BMC. Elevation decreased at the Western sites by −0.35 ± 0.13 cm/yr, and increased at the Eastern and CRMS sites by 0.40 ± 0.03 cm/yr and 0.72 ± 0.09 cm/yr, respectively. The rate of accretion was similar at the Western (0.49 ± 0.14 cm/yr) and Eastern (0.64 ± 0.07 cm/yr) sites, and over twice as much (1.30 ± 0.11 cm/yr) at the CRMS sites. Shallow subsidence, calculated as the difference between vertical accretion and surface elevation change, was 0.76 ± 0.49 cm/yr at the Western sites, 0.23 ± 0.06 cm/yr at the Eastern sites, and 0.58 ± 0.11 cm/yr at the CRMS sites. These trends are consistent with the observation that sediment is brought in from Chandeleur Sound to the east and is attenuated as deposition occurs across the landscape from east to west, and that levee flank depressions associated with Bayou La Loutre, an abandoned Mississippi River distributary ridge, are causing locally high subsidence in the Western region. Without intervention, these localized areas of the Western region will be submerged within the next several decades at current rates of elevation loss and eustatic sea-level rise, while the Eastern sites and the wetlands on the periphery of the BMC are likely to keep pace with sea level rise well into the second half of this century. These results demonstrate the importance of accurate knowledge of both subsidence and accretionary dynamics in determining coastal wetland sustainability and restoration approaches.

Tidal wetland resilience to increased rates of sea level rise in the Chesapeake Bay: Introduction to the special feature

Abstract: The papers in this Special Feature are the result of the first Marsh Resilience Summit in the Chesapeake Bay region, which occurred in February 2019. The Chesapeake Bay region has one of the highest rates of relative sea level rise in the U.S., jeopardizing over 1000 km2 of tidal wetlands along with other coastal lands. The goal of the Summit and this collection of articles is to analyze tidal wetland response to accelerating sea level rise and the effect their response will have on adaptation planning for surrounding communities. Ten Summit presenters share their research in this Special Feature. In this Introduction, we summarize their findings on evaluating restoration potential at the site-specific level, measuring and projecting marsh migration and erosions rates, describing impacts of wetland migration on a marsh dependent animal, effects on human communities, and finally the roles of property owners and government on future tidal wetland extent. These contributions demonstrate that tidal marsh distribution is dynamic in response to sea level rise, and that social, legal, and policy tools can be used and further developed to enable opportunities for restoring or conserving wetlands when stakeholders are engaged effectively. The papers here and feedback from Summit participants illuminate diverse priorities, research unknowns, and next steps for land use planning toward resilience of the Chesapeake Bay region that also can inform global communities.