18-23. Predicting responses to sea level rise and restoration in diked salt marshes

Tidal wetlands are key coastal ecosystems that provide a wealth of services to society, including recreation, bird and fish habitat, protection from coastal storms, and rapid storage of atmospheric carbon in soil. Under natural conditions, tidal exchange between wetlands and the coastal ocean sustains these important ecosystem services since dynamic biogeochemical responses result in wetlands that are responsive to rising seas through elevation gain (Gonneea et al. 2019) and transgression. A substantial portion of coastal wetlands, however, have managed hydrology, and their management conditions and histories have important consequences for the carbon cycle processes that build elevation through soil formation, and thus for resilience to accelerating sea-level rise. Tidal restrictions and other managed coastal hydrology, including dikes, tide gates, road and railroad berms or culverts, water control structures, and ditches, alter both sea and aquifer elevations and disrupt the dynamic elevation response of fresh and saline coastal wetlands. In the U.S., we and our colleagues have estimated that there are ~0.48 million hectares of restricted/impounded wetlands, and ~0.24 million hectares of drained former wetlands (Kroeger et al. 2017; Crooks et al. 2018; Fargione et al. 2018). 

Related research indicates that alterations of wetland hydrology result in changes in water level, period and frequency of soil inundation, water salinity and chemistry, vegetation cover and productivity, habitat quality, soil carbon storage and elevation trajectory. When coastal wetlands are impounded, biogeochemical conditions favor the production of methane, a potent greenhouse gas, while the rate of elevation gain is diminished (Kroeger, et al. 2017, Gonneea et al. in prep.). Where wetlands are drained, enhanced aerobic respiration drives massive loss of soil carbon, as emitted carbon dioxide (IPCC 2013), driving rapid loss of soil elevation. As a result, under a range of widespread conditions, managed coastal landscapes have both impaired resilience to sea-level rise and diminished habitat value, while they emit substantial anthropogenic greenhouse gas. Finally, the same barriers that impound or drain the wetlands also serve as barriers to migration, preventing transgression.

Primary hypotheses are that restoration of saline, tidal flows in these managed wetlands will reduce greenhouse gas emissions, while restoring natural soil accretion, hazard protection, carbon storage, and ecosystem conditions. However, data and knowledge on responses to management and to environmental change remain limited, hampering our ability to predict the future condition of managed wetlands. Yet, federal agencies, including the Fish & Wildlife Service and National Park Service, as well as state and local governments, and other entities that manage impounded or drained wetlands, are increasingly facing decisions and requesting guidance related to elevation and habitat change under accelerating relative sea-level rise, as well as information on greenhouse management potential in coastal ecosystems. Research at the USGS Woods Hole Science Center has focused on broadly characterizing the consequences of a range of management actions in coastal wetlands, and on developing data and tools to guide and inform decisions based on consideration of habitat, elevation resilience, change in coastal hazards, and greenhouse gas management potential.

We seek a postdoctoral fellow to conduct basic and applied research that addresses the consequences of management actions in coastal wetlands, in the context of accelerating sea level rise. Following are examples of relevant questions that the project might address, though other topics may be within the scope of interest:

• How do managed wetlands respond to sea-level rise? 

• How does the interaction of sea-level rise with groundwater drive changes in vegetation, elevation, biogeochemistry, and resilience?

• How does altered tidal hydrology associated with diking and impoundment or drainage alter biogeochemical processes that drive soil accretion and greenhouse gas emissions? 

• What are the key drivers of soil carbon and gas flux rates, and can responses of those drivers to hydrological management predict feedbacks on climate? 

• How do interactions of sea level rise and hydrological management predict wetland persistence, change in coastal hazards, or habitat change?

• What are the trajectories of change in response to restoration, and can they be predicted? 

• What are the key drivers that must be considered in new predictive models for a range of sea-level and management change scenarios?

Interested applicants are strongly encouraged to contact the Research Advisors early in the application process to discuss project ideas.

References: 

Crooks, S., Sutton-Grier, A.E., Troxler, T. G., Herold, N., Bernal, B., Schile-Beres, L., Wirth, T., 2018, Coastal wetland management as a contribution to the US National Greenhouse Gas Inventory. Nature Climate Change, v. 8, p. 1109-1112.

Fargione, JE, Bassett, S, Boucher, T, Bridgham, S, et al. (Kroeger, KD), 2018. Natural Climate Solutions for the United States. Science Advances, 4 (11), eaat1869. DOI: 10.1126/sciadv.aat1869

Gonneea, M.E., C.M. Maio, K.D. Kroeger, A.D. Hawkes, J. Mora, R. Sullivan, S. Madsen, R.M. Buzard, N. Cahill, J.P. Donnelly. 2019. Salt marsh ecosystem restructuring enhances elevation resilience and carbon storage during accelerating sea-level rise. Estuarine and Coastal Shelf Science. 217, 56-68, https://doi.org/10.1016/j.ecss.2018.11.003.

Hiraishi, T. et al. 2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands. Intergovernmental Panel on Climate Change, Switzerland (2014).

Kroeger, KD, Crooks, S, Moseman-Valtierra, S, Tang, J. 2017. Restoring tides to reduce methane emissions as a new and potent Blue Carbon intervention. Scientific Reports 7, Article number: 11914, doi:10.1038/s41598-017-12138-4, https://www.nature.com/articles/s41598-017-12138-4

Proposed Duty Station: Woods Hole, MA

Areas of Ph.D.: Chemistry, hydrology, environmental science, oceanography, geology, ecology, biology, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet the qualifications for: Research Chemist, Research Hydrologist, Research Geologist, Research Physical Scientist, Research Ecologist, Research Oceanographer 

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Human Resources Office Contact: Audrey Tsujita, 916-278-9395, atsujita@usgs.gov