Coastal landscapes are among the most vulnerable to changing climate conditions. Periodic, extreme storm events, superimposed over background conditions of gradual sea-level rise, can force dramatic changes in these geographically marginal, unprotected systems.
The redistribution of sediment by waves and currents is typically the driving force behind these changes. For instance, storm waves that overwash a barrier island can push sand from the beach and dunes into the backbarrier tidal marsh, effectively rolling the island landward. Waves and currents may erode sediment from one part of a barrier island or marsh and deposit it elsewhere, or wash it away completely, depending on constantly evolving interactions between climate, sea level, sediment supply, and shoreline position. Over time, these processes alter the location, distribution, and areal coverage of coastal ecosystems. Because of the dynamic nature of these landscapes, understanding natural patterns of coastal change is crucial for management and conservation.
The Virginia Coast Reserve (VCR) LTER site is a pristine coastal landscape consisting of barrier islands, marshes, and lagoons fed by mainland watersheds. The VCR is essentially free of human development, providing a unique opportunity for researchers to monitor natural, long-term changes in ecosystem distribution. VCR scientists have found that between 1973 and 2001, while there have been high rates of localized change, there has been very little net change in the total area occupied by major land cover types (e.g., lagoon, marsh, barrier island) at the landscape level. At any given point on the landscape, there is a 43% chance of change (e.g., marsh becoming lagoon, island becoming marsh, etc.), yet on the landscape scale, there has been only a 7% loss in total coverage by marshes, and only a 6% loss by barrier islands.
These results indicate that under current conditions, ecosystems in this dynamic coastal landscape are remaining relatively stable in terms of aerial extent, even as they are reshuffled in response to sea-level rise and storm events. However, if sea-level rise accelerates or storminess increases past a critical threshold, or if the coastal barrier system becomes developed or engineered, the dynamic stability of ecosystem reshuffling may give way to greater rates of habitat loss. This research highlights the necessity of long-term monitoring for developing comprehensive, landscape-level models of ecosystem change.