Tidal wetland ecosystems supply essential habitat for fish, shellfish, birds and other fauna and flora, many of which have great economic importance. At the same time, tidal wetlands provide critical services to society by serving as a physical barrier between our cities, roads and homes and the rising sea. If healthy and properly managed, those barriers have an increased potential to respond to sea-level rise through ongoing elevation gain and landward migration, maintaining important services to society into the future.
Tidal wetlands are geological structures that are built and sustained, or degraded and lost, due to a complex interplay between mineral sediment dynamics and ongoing productivity and preservation of below ground plant material and the biogeochemical processes that lead to preservation or degradation of soil organic matter. Over a period of years to millennia, root material and sediment are transformed into peat or mineral soil. Their future persistence relies on critical processes that drive vertical growth and landward migration, such as plant photosynthesis and growth, plant trapping of sediment suspended in tidal water, growth of plant roots, and preservation and retention of soil organic matter and mineral sediment.
Research in the Environmental Geochemistry group strives to understand current and future persistence of marshes through studies that measure, model, and map the biogeochemical, geological, and hydrological factors that affect these ecosystems. These include distributions and vitality of plant communities across gradients of environmental conditions, including hydrology and hydrodynamics, salinity, long-term weather, latitude, and sea-level rise.
Tidal wetlands are undergoing rapid change on a national and global scale in response to a host of environmental changes and challenges. Where observations have been made, elevation reconstructions over the past several millennia suggest that tidal wetlands have generally maintained a nearly constant position with tidal frames, while transgressing in response to ~1mm/year of sea level rise and eroding on their seaward edges. In the 20th century, and particularly in the 21st century, the global rate of sea-level rise has increased several-fold, while local rates in some areas are now greater than 5 mm/year. The enhanced rate of sea-level rise is an unprecedented challenge for tidal wetlands, and their continued persistence will be determined by their capacity to gain elevation through storage of organic and inorganic soil components, while migrating landward. One important consequence of the marsh elevation recovery has been the coincident intensification of carbon storage, largely driven by an expanding accommodation space favorable for organic matter preservation, made possible by sea-level rise. Therefore, coastal wetlands provide a negative feedback on climate, through enhanced carbon storage that is stimulated by the climate warming that drives accelerating sea-level rise.
Extensive deployment of structures that manage coastal hydrology, including dikes, berms, levees, ditches, and seawalls caused widespread tidal restriction in coastal wetlands, with drained, impounded and tidally restricted wetlands comprising 30 to 40% of total, mapped tidal wetland area. Consequences of these changes in hydrology for carbon cycle processes and for coastal hazards include changes in soil carbon processes and greenhouse gas cycling. Research by the Environmental Geochemistry group informs how these processes are impacted by wetland management decisions, including restoration.
