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Green Bulkheads: Giving Life to Our Hardened Shorelines - September 24, 2017

The 7,000 miles of shoreline in Maryland provide an irreplaceable habitat—both to humans and animals. Natural shorelines of the Coastal Bays region are home to a multitude of native biodiversity including crustaceans, amphibians, insects, fish, and shorebirds. Vegetation is arguably the most critical piece of a shoreline—it provides habitat for the aforementioned wildlife, stabilizes the land by anchoring sediment, and acts as a buffer for nutrients and pollutants running off from the land to the water. The vegetation filters out many human-caused pollutants including chemicals from lawns and roadways, fertilizer containing harmful nitrogen and phosphorous, gasoline overflow, domestic animal waste, lawn trimmings, and litter. Shorelines are famously dynamic environments, ever-changing from the natural processes of erosion and accretion due to wind and wave energy.

However, as the Eastern Shore becomes increasingly developed and populated by humans, the shorelines are hardened to protect valuable property from erosion. This disrupts the natural fluctuation of shorelines, ultimately leaving them depleted and stripped of much of their ecosystem value. 

There are two main methods of shoreline hardening in the Coastal Bays watershed: riprap and bulkhead. Riprap consists of a series of large rocks situated along the intertidal zone of the shore at a gradual incline, providing a barrier that dissipates wave energy. The arrangement of rock typically allows some growth of vegetation and can still be hospitable for some wildlife such as crabs, oysters, and birds. Bulkhead, the more detrimental option, is unfortunately the more popular choice in our region. A bulkhead is a completely vertical wall made of either wood or vinyl that completely removes any area of transition between the land and the water. Wooden bulkheads are often treated with harmful chemicals such as creosote and arsenic that leech out into the water and sediment years after their construction. Due to the vertical nature of the wall, it reflects wave energy instead of dissipating or absorbing it, causing residual waves that often increase erosion in neighboring areas. The reverberated wave energy also tends to scour the sub-tidal zone, taking a toll on submerged aquatic grasses that are crucial for juvenile crabs, fish, and other aquatic organisms. Additionally, bulkheads offer no opportunity for vegetation or wildlife, leaving an ultimately sterile habitat. Lack of vegetation also means there is no filtering of pollution and runoff from the land, causing a significant detriment to water quality.

In an effort to offset the harmful effects of bulkheads in the Coastal Bays ecosystem, MCBP has implemented Green Bulkhead projects in two Ocean City locations in collaboration with University of Maryland Center for Environmental Science and the Town of Ocean City. Located on Bayshore Drive and Old Landing Road, installation was completed in 2013. The design resembles a Peruvian flute, constructed with three tiers of 10-inch diameter PVC pipes. Engineered with nature in mind, each tier corresponds to a different level of marsh vegetation: high marsh, intertidal marsh, and submerged aquatic vegetation, all of which contain exclusively native species.

This summer, MCBP staff conducted the first monitoring project since the Green Bulkheads’ installation, finding that biodiversity increased drastically compared to nearby bare bulkheads. Both overall biomass and species richness of fish and crustaceans were greater, including commercially important species such as menhaden and blue crabs. Sessile organism abundance, namely barnacles and rib mussels, was also greater at the Green Bulkheads compared to the bare bulkheads. The spaces between the PVC tubes provides a habitat that receives sufficient flushing of water, yet is more sheltered from wave action than bare bulkhead. The Green Bulkheads are relatively cheap to construct, making it realistic to recreate in several areas of the Coastal Bays watershed. By promoting native vegetation and providing a more hospitable habitat for native flora and fauna, the Green Bulkheads are an opportunity to give life to the hardened shorelines of the Coastal Bays.

Waite is a Seasonal Scientist with the Maryland Coastal Bays Program.

 



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