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Poplar Island: A story of successful restoration


When you first catch a glimpse of Poplar Island, you see mountains of sand and bright yellow construction equipment, but if you focus your perspective you begin to see the flourishing results of the Poplar Island Ecosystem Restoration Project. Marsh grasses thrive in individual plots of marshland, pairs of osprey nest on posts and the ground, and flocks of water birds bob in the waves.

Poplar Island has seen a vast change in its landscape over the last century. An island that in 1847 spanned more than 1,100 acres and was home to a population of 100 people was reduced to just about four acres of land in the 1990s. The cause? Erosion and sea-level rise in the Chesapeake Bay. The remnants of the island were bought and sold until it was finally retained by the State of Maryland as part of a Federal-State beneficial use of dredged material ecosystem restoration project.

But what exactly does restoring an entire island entail?

A collaboration between the U.S. Army Corps of Engineers, Baltimore District and the Maryland Department of Transportation Maryland Port Administration is what makes the largest engineering project of its kind in the nation possible. The engineering project set out to achieve three main goals: restoring remote island habitat, optimizing placement capacity of dredge material, and protecting the local environment over its 50-year timeline.

Poplar Island provides a placement site for dredged material, the sediment that builds up at the bottom of shipping channels, that needs to be removed in order to keep the Port of Baltimore navigable. By adding the substrate to the eroded island and reconstructing the habitat, the restored land becomes a thriving home for native wildlife.

The reconstruction of the island is also a collaborative scientific effort to effectively and successfully restore the habitat.  University of Maryland Center for Environmental Science researchers, Professor Emeritus Court Stevenson, Professor Jeff Cornwell, and Associate Research Scientist Lorie Staver are all part of the Poplar Island Working Group, a task force of experts who monitor and advise the restoration project while it is underway.

“Over 500 islands have eroded away in the Chesapeake Bay since settlement, and Poplar Island now provides habitat for ground and colonial nesting birds. These island’s tendency to be free of predators, or at least have low populations of predators, provides critical habitat for some of these species,” said Lorie Staver, a plant ecologist who studies the establishment of marsh grasses on the island.

Restoring and rebuilding an island

Barges use clamshell dredges to collect sediment that accumulates in the navigation channels leading to the Port of Baltimore. The contents are then transported to Poplar Island where they are mixed with water and pumped into individual containment cells, sections of the island that are filled incrementally to the appropriate elevation. The soupy material is then left to dry, and once the cell resembles a cracked and arid landscape, it is graded to create marsh contours before individual marsh plants are planted by hand.

The dredged sediments used to reconstruct Poplar Island have a unique quality when compared to more typical wetland restoration projects. Poplar Island dredged sediments have considerably higher concentrations of nitrogen and phosphorus—up to 100 times that found in the sandy sediments typically used. UMCES scientists Lorie Staver and Court Stevenson have been studying the dynamics between these high nutrient levels and plant growth in the Poplar Island system and monitoring plant characteristics such as height, diversity, and density for over 15 years. By monitoring the progress of Poplar Island, scientists are able to assess what works and what doesn’t throughout this long-term project. They can then reassess restoration approaches for Poplar Island and future marsh restorations, a process referred to as adaptive management.

University of Maryland Center for Environmental Science researchers Court Stevenson, Jeff Cornwell, and Lorie Staver are part of the Poplar Island Working Group, a task force of experts who monitor and advise the restoration project while it is underway.

Once a marsh cell is planted, the monitoring of its evolution and growth begins. Wetlands are dynamic systems that require low wave energy, salt water, and tides to grow and flourish. Through natural processes, marshes grow through the build-up of sediment brought by tides and organic matter (plant material). This is one aspect that is closely monitored by researchers. By measuring soil accretion on the island, scientists are able to compare the growth of Poplar Island wetlands to that of natural marshes. 

The health of plant life on Poplar Island is linked to its resilience to sea-level rise and erosion. “Plants that are not healthy are not producing as much organic material, and organic material is what helps marshes raise their own elevation so they can keep up with sea level rise,” said Staver.

Two main types of marsh grasses are planted on this island habitat: Spartina alterniflora, a low marsh species that is tolerant of standing water, and Spartina patens, a high marsh species. Poplar Island’s tidal range is only about half a meter, meaning the elevations at which these species are planted differ by centimeters, but they each have their purpose in maintaining the marsh ecosystem.

“What we’ve observed in the past 15+ years of monitoring is that in many cases species planted in the low marsh are now migrating into the high marsh, so the high marsh area is diminishing and the low marsh area is expanding,” said Staver.

This migration of species is partially due to sea-level rise, but the engineering and calculations related to grading and planting Poplar Island also play a role. While initial elevations were set at a lower elevation, the feedback provided from monitoring early cells provided the designers with critical information related to marsh development, and through adaptive management they were able to reassess and improve their approach to the ecosystem’s design. 

While the physical growth of the island is important to monitor, Jeff Cornwell from Horn Point Laboratory is studying another important aspect of the marsh. Cornwell’s research has been key to understanding the biogeochemical aspects, such as pH, iron and nitrogen of the soil on Poplar Island as it transforms from dredged material to marsh soil and how it compares to natural marshes, as well as more typical marsh restoration projects.

 

A sanctuary for wildlife in need of conservation

As you’re driven across Poplar Island with you guide, you’ll notice a diversity of habitats with changing habitat features built to suit specific groups of birds. A sandy hill with sparse vegetation invites ground nesting birds while water logged flatland welcomes small shorebirds. In 2017, the U.S. Geological Survey found that Poplar Island had the most successful Common Tern colony (state listed endangered species) in Maryland. The island also offers a safe overwintering ground for migrating waterfowl and birds such as the Snowy Owl.

Even though Poplar Island is not projected to be completed until 2044, the ecological benefits of restoring the island habitat are already being reaped. The Poplar Island Ecosystem Restoration Project, begun in 1994, initially focused on becoming a great sanctuary for birds, but the growing number of Diamondback Terrapins nesting onsite, with as many as 1,600 terrapin hatchlings documented in a single year, shows the project is offering a whole lot more than just bird habitat.  

Through the work of multiple State and Federal agencies and research institutions, the restoration project’s successes continue to be monitored and documented as the island’s habitats continue to expand and evolve. Once the habitat restoration is completed, the property rights will be handed back to the State and Poplar Island will become a passive recreation facility, where the public can enjoy the wildlife and take in the beauty of this flourishing restoration project in the middle of the Chesapeake Bay.

 

 

By: Emily Ramirez