Virginia Coast Reserve Long Term Ecological Research VII

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The highly protected Virginia Coast Reserve (VCR) is the largest undeveloped region along the Atlantic seaboard.The VCR is managed by the Nature Conservancy, and was designated a Man and the Biosphere Reserve in 1979, providing a unique environment for which to study coastal impacts of climate change on a variety of coastal ecosystems from barrier islands across back barrier lagoons, mudflats, marshes and into upland forests.

The Challenge: 

Nonlinear seagrass dynamics: In 1933 the seagrass, already stressed by disease were locally extirpated by a hurricane. This loss resulted in severe decline in shellfish populations as the once seagrass stabilized sediment was exposed to wind wave resuspension and subsequent poor water column light conditions.  In the early 1990’s, small naturally occurring patches of seagrass prompted large scale restoration efforts which have resulted in the most successful restoration of seagrass worldwide. This long lag in seagrass recovery was posited to either lack of seagrass propagules or poor light conditions.  Modelling efforts suggested that decreases in sediment size and increases in water temperature and degree of eutrophication have the potential to shift the depth range in which seagrasses of the bay exhibit bistable behavior to shallower depths, with more of the bay bottom unable to sustain seagrass. The presence of nonlinear dynamics has direct repercussions on our understanding of the resilience of seagrass systems to changing drivers and climatic conditions; helping to identify dominant drivers and key thresholds leverageable by restoration efforts.

Marsh Migration into upland forests: The response of salt marshes to sea level rise (SLR) is important as they provide critical ecosystem services and habitat. Marshes can be lost both laterally and vertically and are affected by interacting drivers and feedbacks resulting in an  ecogeomorphic evolution which can exhibit non-linear behavior. For example, lateral salt marsh loss may provide inorganic sediment back to the marsh platform helping the marsh to maintain vertical elevation.  SLR can also lead to marsh expansion into upland regions. This is a spatially extensive process and is thought to be the primary control on the long-term survival of marshes.   The processes influencing the pace of ecosystem transgression remain poorly understood.

The Science: 

Nonlinear seagrass dynamics: The impact of numerous modeling efforts has led to ongoing field-based hypothesis testing exercises within the coastal lagoons of the VCR.  A pilot study in collaboration with Randolph Macon College with focus on undergraduate research outreach was initiated that examined biologic versus structural controls on benthic sediment and carbon.  This study involved designing and installing artificial seagrass meadows, leveraging information about seagrass morphology, the critical stem density to affect hydrodynamics and meadow size.  Grain size distribution changes and organic matter over the course of the year-long pilot project are being examined alongside hydrodynamic measurements. 

Marsh Migration into upland forests: The non-linear dynamics involved in the marsh to upland forest transition is being explored by a new experiment which establishes a long term disturbance experiment in which replicate forest plots along an elevation gradient from the marsh-forest transition to high forest stand are monitored for two years prior to a “disturbance event” (realized by girdling the trees in some of the plot).  The sites are monitored for inundation, salinity, light, temperature, vegetation characteristics, organic soil accretion and surface elevation changes among other key variables.  Already the USGS has provided expertise in installing Surface Elevation Tables in the experimental plots.  This experiment mimics an ongoing USGS marsh transgression experiment at Blackwater Wildlife.

The Future:

Nonlinear seagrass dynamics: Understanding physical and biological impacts of seagrass is important as subtidal meadows expand due to both natural propagation and restoration efforts.  This understanding is crucial as we seek to understand how those transitions, or state change, may propagate across the landscape via coupled and tele-coupled dynamics.   This plays a critical role in our ability to project projecting the long-term responses of coastal systems to climate drivers. 

Marsh Migration into upland forests: This is a long-term experiment which will provide valuable information to help inform models for forecasting the potential of marshes to migrate inland and inform our understanding of ecosystem transitions.  This understanding is crucial as we seek to understand how those transitions, or state change, may propagate across the landscape via coupled and tele-coupled dynamics.   This plays a critical role in our ability to project projecting the long-term responses of coastal systems to climate drivers.