Planning for Marsh Migration at the Blackwater National Wildlife Refuge

Landscapes are changing, and our actions today can have profound impacts on the fate of land and water resources in the future. The Conservation Fund has been working with partners in the Chesapeake Bay region for over a decade to acquire land and identify restoration opportunities for coastal wetlands and migratory habitat. Blackwater 2100 is a collaborative strategic conservation plan that aims to address salt marsh loss and migration in Maryland.

The Chesapeake’s tidal marshes are an ecological treasure. And nowhere are they more abundant and productive than in Maryland’s Dorchester County, the location of Blackwater National Wildlife Refuge. The Refuge provides essential habitat to a suite of specialized birds that evolved in this landscape, such as saltmarsh and seaside sparrows, clapper rail and black rail. Other birds and wildlife, including migratory waterfowl, American bald eagle, Delmarva fox squirrel and a myriad of fish and shellfish, spend at least part of their life in these marshes or adjacent forests. Humans also have shared this dynamic landscape with wildlife for generations, creating a unique economy, culture and history.

Today, people and wildlife are facing a new challenge in this iconic place: Bay waters that are rising at an accelerating pace. Although the level of the oceans has risen approximately six inches over the past century worldwide, the Chesapeake region’s increase is nearly double over the same period. Rising waters have claimed more than 5,000 acres of marshland in Blackwater National Wildlife Refuge since it was established in the 1930s. Multiple factors contribute but scientists forecast accelerating rates of sea level rise as a result of climate change. The best available, science-based models forecast the Chesapeake’s water level to be more than 3 feet higher by the end of this century. If sea level rises three feet, virtually all the refuge’s tidal marshland will be submerged, including thousands of acres of priority bird habitat.

Although data indicates that the Blackwater National Wildlife Refuge lost over 5,000 acres of marsh to open water between 1938 and 2006 – an average of 74 acres per year – during the same period the refuge gained 2,949 acres of new marsh at upland edges, presumably through upslope migration of tidal marsh as sea levels rose. These observations indicate that new tidal marsh is forming, although it is not currently keeping the pace with loses. The U.S. Fish and Wildlife Service, particularly the staff of the Chesapeake Marshlands Complex which includes Blackwater NWR, has been working collaboratively for more than three years with planners, scientists and policy specialists from The Conservation Fund, Audubon Maryland-DC, Maryland Department of Natural Resources and other public agencies and organizations, to assess the impact of sea level rise on the Refuge.

The project team used an enhanced analytic and forecasting tool, the Sea Level Affecting Marshes Model to study the effects of sea level rise on high marsh — essential nesting habitat for birds that breed only in salt (or tidal) marsh — and transitional marsh, the upper boundary of tidal marshes since rising sea levels are actively transforming it into high marsh.

This assessment concluded that the projected loss of high tidal marsh across the Dorchester County project area would greatly exceed the potential gains in new high marsh from upslope marsh migration. However, changing the status quo in marsh management should help existing tidal marsh to persist longer. Key conservation actions that can increase marsh resilience to sea level rise include: increasing surface elevation, reducing the amount of interior ponding and eliminating invasive plants.

Tidal marshes are home to a unique assemblage of birds that evolved in this habitat and are found nowhere else. These species include four birds on the American Bird Conservancy and Audubon Society’s Watch List: Black rail, saltmarsh sparrow, seaside sparrow and clapper rail, plus three other salt marsh specialists — American black duck, coastal plain swamp sparrow and willet. They were selected as focal species for the project since their presence is a prime indicator of tidal marsh health. The assessment produced maps showing the projected shift of high value tidal marsh over the Dorchester landscape in future decades as Bay waters continue to rise.

Considering cost and logistical challenges of marsh restoration, it is infeasible to attempt preserving all tidal marsh in the project area. Instead we identified a key area of existing marsh where management actions are likely to yield the greatest long-term conservation benefits. The proposed Blackwater NWR Fishing Bay Marsh Conservation Zone includes approximately 20,000 acres of high marsh in a continuous arc surrounding Fishing Bay. Selection criteria included:

• Greatest predicted longevity under sea level rise scenarios.

• Most intact current condition, defined by lack of interior of ponding.

• Highest abundance of seven focal salt marsh birds, measured by SHARP surveys.

• Extensive area of contiguous interior.

Partners selected primary and secondary tidal marsh migration “corridors,” to indicate those areas where the SLAMM model and factors such as land use and ownership patterns, future development plans and bird presence indicate the greatest potential for high quality tidal marsh to relocate. Summarized, the adaptation project team’s comprehensive strategy recommendations fall into three categories:

• Actions improving targeted, tidal marsh health and productivity.

• Actions helping targeted transitional areas convert into high quality tidal marsh.

• Strategic conservation in primary marsh migration corridors.

To date, three types of pilot projects are underway demonstrating elements of the strategy. Thanks to a grant award from the National Fish and Wildlife Foundation’s Hurricane Sandy Coastal Resiliency Competitive Grants Program, four additional adaptation projects will soon be added. Altogether, these projects will include the following:

Actions improving current tidal marsh health and productivity

• Sediment enhancement (thin layering) and re-vegetation of targeted tidal marsh.

• Improving tidal water exchange in coastal marshes.

• Controlling or eradicating invasive plants (Phragmites) and animals (nutria)

Actions helping targeted transitional areas convert into tidal marsh

• Eliminating dead and dying trees

• Planting transitional corps (switchgrass) on agricultural fields

• Controlling spread of invasive plants (Phragmities)