Salt marsh, © George Gentry/USFWS

A Whole New World: Sea Level Rise and the Changing Face of the Chesapeake

Marshes, ©David Curson, Audubon Maryland-DC

Salt marshes (©David Curson, Audubon Maryland-DC)

The coastal wetlands of Maryland’s Lower Eastern Shore are one of the most extensive tidal marsh landscapes along the entire Atlantic Coast. Not only do they provide essential habitat for unique plants and animals (including the saltmarsh sparrow, which lives only in this region), but they also perform economically valuable services such as storm surge protection, water filtration, and serve as a nursery grounds for the Chesapeake Bay’s commercial fisheries. But there may be trouble in paradise. Without proper conservation planning, these vast tidal marshes could be lost forever by the end of the century.

The eminent threat is sea level rise. The Chesapeake Bay, behind only Louisiana and southern Florida, is the third most vulnerable region in the nation when it comes to sea-level rise. In 2011, the Maryland Department of Natural Resourced used a tool called the Sea Level Rise Affecting Marsh Model (SLAMM) to look at the potential impacts of sea level rise on Maryland’s coastal wetlands and determined that a 3.4 foot rise (a conservative prediction for the end of the century) could inundate more than 95% of existing tidal marsh.

Saltmarsh sparrow,  © Neil Pearson

Saltmarsh sparrow (© Neil Pearson)

As physical conditions change over time due to sea-level rise, an area’s ability to support tidal marsh will be lost, maintained, or improved. In other words, tidal marsh on the landscape may disappear, persist, or re-locate (migrate) to newly available areas. The majority of the Chesapeake region is low-lying, so if properly managed, it’s possible a large percentage of currently dry land could convert to marsh as sea levels rise, thereby helping to preserve this valuable ecosystem. But then again, it might not.

Defenders of Wildlife has partnered with Audubon Maryland-DC and the Lower Shore Land Trust to establish priorities and strategies for the conservation of the region’s tidal marsh ecosystem. We used computer modeling to identify areas that may support tidal marsh in the future as sea level rises, and to prioritize these locations according to their likely ecological value as future tidal marshes. We focused especially on marsh “migration corridors,” or the regions that can serve as connectors between marsh habitat today and marsh habitat in the future. In order for these regions to function as migration corridors for these threatened habitats, they must remain free of barriers, such as development and hardened shoreline protection.

Chesapeake SLAMM Map, © Defenders of Wildlife

“Transitional” and “irregularly flooded” marshes (dark and medium green) are the marsh types most important to tidal marsh obligate bird species, and were the marsh types focused on in this study. The five modeled degrees of sea-level rise (0.0 ft, 0.6 ft, 1.4 ft, 2.4 ft, and 3.4 ft) are roughly correlated with benchmark years beginning with the present and ending with 2100. These estimates of sea-level rise have been surpassed by the most recent report from the Maryland Commission on Climate Change, which predicts a 3.7 foot rise in sea levels by the end of the century. (Click to enlarge)

By combining spatial models of marsh ecological value, priority marsh bird habitat, marsh migration corridors, and future development risk, we were able to produce a map for a two-county area of the Lower Eastern Shore which identifies the highest priority areas for tidal marsh conservation and facilitated adaptation in response to climate change.

Simple identification of these conservation priorities of course is not enough. There are limited resources for preserving these lands, and protection of the highest priority areas is by no means assured. So our team also developed a set of conservation tools and targeted outreach and communications strategies to reach the audience that must be engaged in order to successfully conserve, manage, and maintain viable tidal marsh habitat. Commitment from public agencies, landowners and other conservation partners will be critical to the successful conservation of this exceptional ecosystem.

The Chesapeake Bay is a unique and special place. It is home to amazing wetlands, diverse wildlife and vibrant local communities. The challenges that this region faces as a result of climate change and rising sea levels are extreme, but they are also shared by many other coastal areas. Our hope is that this study will provide a conceptual framework for modeling marsh migration across time, and that others confronting similar conservation problems will be able to adapt our methods, strategies, and tools and apply them elsewhere.

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Anderson Shepard is a Conservation Planning Analyst at Defenders of Wildlife

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