Virginia Coast Reserve LTER

How will Coastal Marsh Systems Keep up with Rising Sea Levels?

Investigators at the Virginia Coast Reserve LTER site are examining how elevations of coastal barrier fluctuate over time, and how biotic communities respond to these fluctuations. Coastal salt marshes are home to nesting birds, as well as many species of plants. The marshes shelter nurseries for economically important fish, as well as vacation and permanent homes for people. At the Virginia Coast Reserve LTER the rate of relative sea level rise has been 3.5 mm/yr. over the 20th century, 1.0 mm/yr. of which is due to the eustatic sea-level rise and 2.5 mm/yr to land-level changes. Coastal salt marshes either increase in elevation to keep pace with rising sea level or are submerged and eroded away. The critical question is: what is the process by which the marshes capture enough sediments to keep up with sea level?

For marshes connected to barrier islands there is ample sand in circulation to supply the needed materials for staying ahead of sea level rise. However, marshes located in the lagoon are a different story.

Detailed sediment transport studies have revealed that sediments are deposited on the marsh surface during the tidal flooding, whereas sediment is transported off the marshes during the ebbing of the tide at a rate too low to be detected. Deposition rates on the marsh surface during tidal flooding exceeded the rate of relative sea level rise, which begs the question, why don't the marshes increase in elevation faster than the sea level rise? Observations over time under a wide range of conditions revealed that export of sediments from the marsh surface occurred not during the ebb tide, but during heavy rains at low tide. Rainstorms erode sediments from the marsh surface and were observed to wash sediments off the Spartina alterniflora stems. Thus, the climate controls on upward growth of marshes are due both to sea level rise and the local rainfall regime.

Examining Landscape Change 1693-Present

The LTER sites such as Virginia Coast Reserve combine long-term data with current research to closely examine ecosystem change over time. At VCR we have historic shoreline maps to compare recent changes detected through our studies.
One example, the “Jenifer map,” is especially interesting to VCR scientists as it will tells us much of the landscape changes of the last 400 years.

Virginia Coast’s Jenifer Map

St. Thomas Jenifer, surveyor of Accomack and Northampton Counties, died in 1693. Jenifer was at various times clerk of the Provincial Court, militia officer, and alderman as well as surveyor, sheriff, and justice of the peace. Jenifer's son Daniel, seeking his fathers postion as surveyor drew and conveyed this map of the Eastern Shore of Virginia and southern Maryland "For his Excellency Sir Edmund Andros their Majesties Leiutennand (sic) Governor Generall of Virginia." The original map, dated 1693, is in the Virginia Historical Society, in Richmond, VA.

The map is displayed overlaid by a modern, satellite image of the Eastern Shore of Virginia (blue). The shape and overall configuration of the peninsula on the 1693 map compared to a space photo is remarkable. In addition, island shapes and tidal creeks are remarkable in their detail and similarity to modern renderings. Other maps of this quality did not exist until the 1850s

Daniel Jenifer did not get the job of surveyor of Accomack and Northampton Counties despite the strong Royalist support St. Thomas Jenifer had lent the Governor.

Tracking Changes in Storm Regimes

The dominant agents of ecological disturbance at the Virginia Coast Reserve are winter storms. They generate storm tides, high waves and longshore currents that result in the redistribution of sediments that both erodes and builds the islands. For example 90% of the upland land surface of Hog Island is new since 1871.
Around 1900 there were fewer than 10 storms per year on average. Today there are in excess of 25 storms per year, showing a systematic increase storminess at this LTER site over the past century (Hayden 2000). This pattern of storm climate change is evident along the Atlantic Coast but the magnitude of the change increases with latitude. This trend in storminess is not consistent with General Circulation Models of global warming due to a doubling of carbon dioxide (Hayden 2000).