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ABSTRACT Sea level rise and storm surges affect coastal forests along low‐lying shorelines. Salinization and flooding kill trees and favour the encroachment of salt‐tolerant marsh vegetation. The hydrology of this ecological transition is complex and requires a multidisciplinary approach. Sea level rise (press) and storms (pulses) act on different timescales, affecting the forest vegetation in different ways. Salinization can occur either by vertical infiltration during flooding or from the aquifer driven by tides and sea level rise. Here, we detail the ecohydrological processes acting in the critical zone of retreating coastal forests. An increase in sea level has a three‐pronged effect on flooding and salinization: It raises the maximum elevation of storm surges, shifts the freshwater‐saltwater interface inland, and elevates the water table, leading to surface flooding from below. Trees can modify their root systems and local soil hydrology to better withstand salinization. Hydrological stress from intermittent storm surges inhibits tree growth, as evidenced by tree ring analysis. Tree rings also reveal a lag between the time when tree growth significantly slows and when the tree ultimately dies. Tree dieback reduces transpiration, retaining more water in the soil and creating conditions more favourable for flooding. Sedimentation from storm waters combined to organic matter decomposition can change the landscape, affecting flooding and runoff. Our results indicate that only a multidisciplinary approach can fully capture the ecohydrology of retreating forests in a period of accelerated sea level rise.
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Carbon Dynamics of a Coastal Wetland Transitioning to Mangrove Forest
Abstract Coastal wetlands play a vital role in the global carbon cycle and are under pressure from multiple anthropogenic influences. Altered hydrology and land use change increase susceptibility of wetlands to sea‐level rise, saltwater intrusion, tidal flood events, and storm surges. Flooding from perigean spring tides and storm surges rapidly inundates coastal wetlands with saline waters, quickly surpassing vegetation tolerances, leading to shifts in soil microbial respiration, peat collapse, and plant mortality, followed by establishment of salt‐tolerant vegetation. The Southeast Saline Everglades (SESE) is facing many of these pressures, making it a model system to examine the impacts of ecosystem state transitions and their carbon dynamics. Saltwater flooding from Hurricane Irma (2017) initiated a transitional state, where less salt‐tolerant vegetation (e.g.,Cladium jamaicense) is declining, allowing halophytic species such asRhizophora mangleto colonize, altering the ecosystem's biogeochemistry. We utilized eddy covariance techniques in the SESE to measure ecosystem fluxes of CO2and CH4in an area that is transitioning to an alternative state. The landward expansion of mangroves is increasing leaf area, leading to greater physiological activity and higher biomass. Our site was presented initially as a small C source (47.0 g C m−2) in 2020, and by 2022 was a sink (−84.24 g C m−2), with annual greenhouse carbon balance ranging from −0.04 to 0.18. Net radiative forcing ranged from 2.04 to 2.27 W m−2 d−1. As the mangrove landward margin expands, this may lead the area to become a greater carbon sink and a potential offset to increasing atmospheric CO2concentrations.
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- Award ID(s):
- 2025954
- PAR ID:
- 10510058
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 129
- Issue:
- 4
- ISSN:
- 2169-8953
- Page Range / eLocation ID:
- e2023JG007991
- Subject(s) / Keyword(s):
- eddy covariance carbon dioxide methane state shift Everglades
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2023JG007991
