SHIFTING SANDS: QUANTIFYING LANDSCAPE EFFECTS ON THE CONTRIBUTION OF AEOLIAN SAND TO BACK-BARRIER ACCRETION

Transgressive barrier islands are characterized by low elevations and extensive washover fans that can extend across islands and into the back barrier intertidal where colonization by saltmarsh plants occurs. Inorganic sedimentation is a critical component of saltmarsh accretion and washover fans are commonly isolated from fluvial sediment sources. After the formation of the washover fan we hypothesize that aeolian-transported sand is an important inorganic sediment source promoting back-barrier marsh accretion. Aeolian sand flux across Onslow Island was examined at two sites. The first site is an extensive washover fan platform deposited recently in 1996, which is dominated by grasses and fringed with saltmarsh. The second site is characterized by a high-elevation (11 m maximum), 50-m wide dune ridge backed by maritime forest that borders a paleo-washover fan that is entirely colonized by salt marsh. A transect of continuously monitored sediment traps (CoMSeTs) was deployed across the island at each site. Anemometers were positioned at trap height to monitor wind speed and direction across the island and were paired with soil moisture sensors. Transects of omni-directional sand traps were also placed at each site for weekly observations. Preliminary data from one southerly wind event (maximum sustained winds of 24 km/hr), which was associated with precipitation, show a decrease in sand flux from the foredune to the back-barrier with greater transport, both quantity and distance, occurring at the first site (low elevation, washover fan). Traps closest to the marshes at both sites collected minimal (<5 g) sand. This is a continuing study and many additional wind events will be examined for thorough hypothesis testing.