Organic carbon (C) storage in peat soils is critical to maintaining wetland elevation and coastal wetland
stability. As sea level rises, coastal freshwater and brackish wetlands like the southern coastal
Everglades are being exposed to increased duration and spatial extent of inundation and salinity, which
can affect soil C balance through soil redox potential, microbial respiration, and the intensity of osmotic
stress to vegetation. The term “peat collapse” has been used to describe a relatively dramatic shift in soil
C balance, leading to a rapid loss of soil elevation, and culminating in a conversion of vegetated
freshwater marsh to open water. Evidence of freshwater peat collapse has been observed in lower Shark
River Slough, Everglades, Florida, suggesting that this process is ongoing and may be affected by factors
of reduction in freshwater discharge, recent storm surges (e.g., Hurricane Wilma), sea level rise, and
possibly fire. The process has been documented to varying degrees across the U.S., contributing to
instability of coastal marshes and degradation of important ecosystem services including fisheries habitat,
shoreline stabilization, and C sequestration provided. In field and mesocosm experiments, we are increasing
salinity in freshwater and brackish marshes of the southern coastal Everglades, to investigate auto- and
heterotrophic mechanisms hypothesized to contribute to peat collapse. Long-term research on primary
productivity illustrates interactions with water management and climate to influencing coastal wetland carbon cycling.
Results/Conclusions
Evidence from our previous experiments with mangrove peats showed
predicted shifts in soil redox and enhanced C loss from soils exposed to increased salinity.
Results from our marsh studies show reduction in phosphorus and increase in C acquisition by soil
microbes in brackish marshes, which become stronger C sources during the dry season than freshwater
marshes. Long-term field research illustrates the interaction of water management and soil carbon stability,
linking carbon and water management across the landscape. Our experimental studies will elucidate plant-soil
mechanistic responses to elevated salinity that are hypothesized to stimulate loss of soil C in the coastal Everglades.
Our long-term research provides the landscape context for how water management drives primary productivity,
vegetation change and ecosystem carbon cycling.