Sustainable Shorescapes

CCRM-VIMS, W&M, ODU, UGA

The Chesapeake Bay by the numbers

~370,000 acres of salt and brackish marsh

~60% of our tidal shoreline has marsh

~8,700 miles of shoreline marshes

~2,100 miles of shoreline are armored

Shoreline Protection Approaches

Options for shoreline protection range from conserving natural features of marshes (which is always the preference), to hardened shores and in-between these options there are the newer innovations that combine natural and engineered features. These are called nature- based shoreline protection or living shorelines.

In practice, living shorelines should predominantly consist of organic techniques and materials that are characteristic of the local system. The connection between aquatic and terrestrial habitats should be maintained.

Shorescape Social-Ecological System (SES) conceptual framework 

We evaluated important feedbacks and interactions between coupled human-natural systems that are driving decisions on shoreline modification. 

We examined the relative importance of various interactions between the Bay system, shoreline resources (marshes and the ecosystem services they provide), law and policy (shoreline and marsh protection), resource users (property owners), influencing groups (scientists, neighbors, nonprofit organizations, and marine contractors), governance of resource usage (local and state policy makers and resource managers) to inform decision-making for sustainability and enhancement of ecosystem services.

Living Shoreline Benefits

Natural and Living shorelines study areas

Field studies

Approach: We evaluated the differences in ecosystem functions related to marsh ecosystem services for both natural marshes and a chronosequence of living shorelines (2 to 16 years from construction), within shorescapes representing the continuum of marsh connectivity conditions:

-Habitat provision (invertebrate, fish, bird, terrapin; abundance, biomass, diversity).

-Primary production (aboveground plant biomass), nutrient storage (aboveground plant and soil total N, P content).

-Carbon storage (aboveground plant and soil carbon content)

Summary of plant findings

Plant density in the low and high marsh was similar or higher in the living shorelines than the natural marshes

  • Living shoreline marsh plant characteristics look a lot like natural marshes within 2 years post construction
  • The first and primary benefit desired for a living shoreline is shore protection and erosion control. Marsh plant stem density, height, and aboveground biomass are good indicators of marsh productivity, viability, and performance because those features influence the ability of the marsh to trap sediments and attenuate wave energy.

Summary of fish findings

  • Living shorelines and natural fringing marshes were home to 43 different species of fish and crabs.

    • Living shorelines provide important habitat for both small-bodied and young fish and crabs, similar to natural marshes.

Collecting soil cores

Summary of soil findings

As the living shorelines ages, organic material (carbon) in the soils increases.

  • As living shoreline marshes age, nitrogen, phosphorus, and carbon storage become more similar to natural marshes. Average number of years to equivalence with natural marsh:
  • Carbon:      24 (±6) years
  • Nitrogen:    13 (±3) years
  • Phosphorus:  6 (±2) years 

Soil cores from living shoreline and natural fringing marshes were collected to 30 cm and analyzed for bulk sediment properties.

  • Owing to their predominantly sandy soils and recent planting, the younger living shoreline soils were characterized by lower water content, higher bulk density (indicator of soil compaction and drainage) and lower organic percentage than the older, natural fringing marsh soils.
  • The weight percent of total soil carbon, nitrogen and phosphorus all were lower in living shoreline soils.

Summary of bird findings

  • We compared shorebird use between living shorelines and natural fringe marshes using video and acoustic surveys.
  • Our research indicates that living shorelines function equivalently to natural fringe marshes for three of four heron species, but that marsh use varies depending on the time of day for two shorebird (Spotted Sandpiper and Killdeer) species. For these species, day sampling revealed more frequent use of living shorelines, whereas use was similar when evaluated with day-night data. 

    • Overall, our research shows that living shorelines provide additional habitat for herons and shorebirds and are indeed an ecologically valuable alternative to shoreline armoring.

Surveying ribbed mussels

Summary of ribbed mussel findings

  • Ribbed mussels were similarly abundant in both living shorelines and natural fringing marshes, but only when the mussels on the stone sill of the living shoreline were also included in the count.
  • Increasing the number of ribbed mussels in the marshes of living shorelines would increase their ability to remove nitrogen from the water and make the marsh more resilient because they help maintain healthy marshes.

Diamondback terrapin using marshes and living shorelines

Summary of Terrapin findings

  • Diamondback terrapins are North America’s only turtle that lives exclusively in estuaries.
  • Terrapin life cycles depend on the connectivity among open water, intertidal marsh and adjacent upland.
  • On three different dates during the nesting season, we completed 30-minute visual surveys in the open water adjacent to each living shoreline and paired natural fringing marsh.
  • We found no difference in the detection and abundance of terrapins associated with the living shoreline and natural fringing marshes.

Barriers to use

We used multiple approaches to assess why people decide to modify their shoreline and the type of shoreline modification they choose.

Surveys- We surveyed current property owners to determine the factors that impacted their decisions. We also surveyed multiple groups to assess their level of influence and role in property owner decisions, including local Wetlands Boards (i.e., citizen permit review board), state Tidal Wetland Regulators (VMRC), local non-profit organizations, and marine contractors.

Econometric analysis- We examined historic patterns of shoreline modification decisions using wetlands permit data combined with cadastral and environmental data to assess the primary factors driving decisions on different shoreline modifications (i.e., armor, living shoreline, or do nothing).

Legal review- We evaluated shore and marsh protection laws from Florida to Delaware for commonalities and variation in the characteristics of the law that drive trends in shoreline modification.

Findings:

  • Property owner shoreline modification decisions are primarily influenced by marine contractors, neighbors, websites, and non-profit organizations.
  • Direct training and engagement of key influencing groups (contractors, non-profit organizations) could enhance living shoreline use and integration into local and social norms.
  • Armored shorelines are held to a lesser standard in the law than living shorelines, limiting living shoreline use.
  • To manage for sustained ecosystem services, regulations should be updated to have a shorescape perspective that accommodates shifting marsh boundaries with sea level rise and reflects current societal concerns and values.
  • Revised policies, in concert with enhanced communication by influencing groups like non-profit organizations to property owners on the effectiveness and benefits of living shorelines and marshes as nature-based coastal protection, will likely result in more sustainable shorelines and coastal communities under a changing climate.

In sum, if regulations and incentives resulted in increased and widespread use of living shorelines and land management policies preserved marsh migration opportunities, the near-term outcome for marsh ecosystem services and shoreline protection could be substantially improved.

What you can do

For more information

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Living Shorelines:Beaches and Dunes

Acknowledgements

Project Investigators

VIMS – Carl Hershner, Donna Marie Bilkovic, Molly Mitchell, Joseph Zhang, Karinna Nunez, Julie Herman, Jian Shen, Amanda Guthrie, Robert Isdell, David Stanhope, Kory Angstadt, Christine Tombleson, Madison Cannon, Emma Butler, Abbi Belvin, Riley Olekszyk, Jacob Smouse, Jes Watts, Erin Ferrare

W&M – Randy Chambers, Matthias Leu, Sarah Stafford, Bob Galvin, Sam Mason, Grace Williams, Will Hickman; Jes Watts, Elise Turrietta, Holly Funkhouser, Ansley Levine, Jesse Smyth, Sean Murphy, and Adrianna Gorsky  

ODU – Wie Yusuf, Michelle Covi, Pragati Rawat, Ogechukwu Agim, Taiwo Oguntuyo, Lenzie Ward

UGA – Shana Jones, Scott Markley, Julia Shelburne, Maria Ferrero, Hunt Revell, Kelsey Broich

Plant density in the low and high marsh was similar or higher in the living shorelines than the natural marshes

As the living shorelines ages, organic material (carbon) in the soils increases.