Evaluating potential high marsh habitat following restoration of Delaware Refuges impounded wetlands
Dates
Start Date
2019-10-01
End Date
2020-09-30
Summary
High elevation portions of salt marsh ecosystems are of concern for FWS, as essential habitat for species such as Saltmarsh Sparrow, and Black Rail. Under increasing rates of sea-level rise, widespread transition of high marsh habitat to low marsh is occurring. Maintenance of impounded wetland as habitat for an array of migratory birds is another critical priority. Impoundments, and their associated flooded freshwater habitat, are also threatened by sea-level rise and associated intrusion of saline water, forcing decisions regarding enhancements of dikes and other structures vs. restoration to natural salt marsh. Broadly, evaluations are needed to support decisions regarding the timeframe over which each impoundment can be sustained, [...]
Summary
High elevation portions of salt marsh ecosystems are of concern for FWS, as essential habitat for species such as Saltmarsh Sparrow, and Black Rail. Under increasing rates of sea-level rise, widespread transition of high marsh habitat to low marsh is occurring. Maintenance of impounded wetland as habitat for an array of migratory birds is another critical priority. Impoundments, and their associated flooded freshwater habitat, are also threatened by sea-level rise and associated intrusion of saline water, forcing decisions regarding enhancements of dikes and other structures vs. restoration to natural salt marsh. Broadly, evaluations are needed to support decisions regarding the timeframe over which each impoundment can be sustained, and expected outcomes of restoration in terms of habitat provision, with particular concern for high marsh, and migration space for restored salt marsh habitat.
In FY19 our research team initiated dialogue with leadership for the U.S. Fish & Wildlife Service regarding National Wildlife Refuges in Delaware, and with the State of Delaware’s (DNREC) impoundment managers regarding status of impounded wetlands, and interactions with coastal resilience planning, habitat management, and wetland migration. Impounded wetlands within the FWS Refuge system were discussed as sites for potential restoration of critical high marsh habitat, as well as potential corridors for marsh transgression. To maximize high marsh habitat recovery, however, an analysis is needed to identify which impoundments are most suitable for restoration and the time frame over which restoration will be critical to maximizing habitat in the face of rising sea level. Further discussion occurred related to the need to predict behavior of groundwater and the water table, in response to rising sea level and the presence or removal of dikes. The fresh water table is a predictor of future occurrence of freshwater wetlands landward of existing wetlands, and indicates locations that are potential salt marsh migration corridors. The interaction between rising groundwater and soil elevation is likely to further predict expansion of invasive Phragmites australis. However, restoration activities have the potential to reduce aerial Phragmites coverage through reintroduction of saline water.
Recent feedback from Scott Covington, FWS NWRS Senior Ecologist, indicates strong interest, at both Headquarters and among Delaware NWR staff in the field, in developing an approach to determine fate of freshwater impoundments, coupled with information on how to increase expansion and upslope migration of high marsh habitat.
In this proposed study we will take the first steps toward a broader study of sea-level rise as a driver of groundwater rise in the coastal margin, wetland soil elevation response, and predicted changes in vegetation and high marsh habitat, under restored and non-restored future scenarios. The proposed research will be modeled on our ongoing research at the diked Herring River Estuary at the Cape Cod National Seashore. Existing wetland accretion and vegetation models are not designed for diked wetlands, and therefore in the Herring River project we are developing a new approach to predict change in response to sea-level rise. In FY20 our initial proposal is to 1) develop a mapped product that aggregates existing information on bathymetry of Delaware Refuge impoundments, adjacent land elevation, land cover, and land ownership; and 2) install a transect of shallow, instrumented groundwater wells across the upland/impoundment boundary in one of the impoundments. Prior to development of the full work plan, we will communicate with Refuge staff to identify existing data and data gaps, and to refine objectives. We are already in contact with Delaware Geological Survey and University of Delaware regarding relevant coastal groundwater monitoring and research, as well as the Delaware National Estuarine Research Reserve regarding salt marsh and freshwater habitat in Delaware.
Objectives:
The objectives identified here are the initial steps needed in a larger, multi-year effort to support FWS goals to maximize high salt marsh habitat. Coverage of high marsh habitat will be controlled by changes in relative elevation of soil, sea, and coastal groundwater. Future persistence and aerial coverage will be controlled to a large degree by land slope and sea level rise rate, as well as land cover. Predictions of coastal groundwater rise rate will support predictions of wetland salinity, as well as accretion rate.
