IMPACT OF WINTER PROCESSES ON SALT MARSH ACCRETION: VARIATIONS IN WINTER TIDAL DEPOSITION AND ICE-RAFTED SEDIMENT

Increasing rates of rising sea level have already resulted in substantial annual loss of intertidal wetlands in the southern United States. New England marshes are also threatened, but are dominantly supratidal and may therefore respond differently to any acceleration in rates of sea-level rise. Climate is likely a major factor controlling the evolution of salt marshes, as northern marshes experience a larger temperature range as well as lower average temperatures than do southern marshes. Winter processes may therefore play a critical role in the ultimate fate of northern salt marshes.

Ice rafting contributes to the total volume of inorganic sediment delivered to the marsh surface, augmenting vertical accretion. Initial measurements at Wells, ME indicate that ice rafting contributes a volume of sediment equivalent to a 0.33 mm-thick layer to the marsh surface, with maximum deposition in the mid-back marsh and near smaller tidal creeks. The deposition of ice-rafted sediment varies with moderate changes in latitude; more southerly New England marshes exhibit decreasing volumes of ice-rafted sediment. Salt marsh surface elevation and surface roughness also appear to contribute to observed regional and local depositional trends by controlling the distribution of ice rafts.

Storm surges and spring tidal flooding are the dominant delivery mechanisms for inorganic sediment to the marsh, and this process continues throughout the winter months. Sediment pads were deployed in a 50 m grid across a ~1 km2 section of the high marsh in Wells, ME during the 2004 winter season to measure the volume and spatial variability of tidally deposited suspended sediment. Total suspended sediment deposited is comparable to ice-rafted sediment, and shows surprising variability. Data are currently being analyzed to determine the impact of marsh surface elevation and distance from tidal creeks on the winter distribution of tidal sediment.