HR: 1400h
AN: OS23B-08    [Abstracts]
TI: Terrestrial Sediment Delivery to Coastal and Marine Environments: US Virgin Islands
AU: * Larson, R A
EM: larsonra@eckerd.edu
AF: Eckerd College, 4200 54th Ave S, St. Petersburg, FL 33711, United States
AU: Brooks, G R
EM: brooksgr@eckerd.edu
AF: Eckerd College, 4200 54th Ave S, St. Petersburg, FL 33711, United States
AU: Devine, B
EM: bdevine@uvi.edu
AF: University of the Virgin Islands, #2 John Brewer's Bay, St. Thomas, VI 00802, Virgin Islands (U.S.)
AU: Wallace, L E
EM: wallacle@eckerd.edu
AF: Eckerd College, 4200 54th Ave S, St. Petersburg, FL 33711, United States
AU: Holmes, C W
EM: cholmes@usgs.gov
AF: US Geological Survey, 600 4th St S, St. Petersburg, FL 33702, United States
AU: Schwing, P T
EM: schwinpt@eckerd.edu
AF: Eckerd College, 4200 54th Ave S, St. Petersburg, FL 33711, United States
AB: Understanding terrestrial sediment dynamics in high-relief, tropical island settings, such as St. Thomas and St. John, USVI, has become a critical issue, as sediments are a potential threat to the health of down-slope environments. The primary depositional sinks of terrestrial sediments are 1) coastal buffer zones such as salt ponds, which trap sediments and keep them from being input into the marine environment, and 2) near-shore marine environments (coral reefs, seagrasses, algal flats etc.), many of which are adversely affected by terrestrial sedimentation. Land use change by anthropogenic activities has been shown to alter terrestrial sediment dynamics and greatly increase sediment delivery and accumulation rates in coastal and marine environments. Sediment cores collected in salt ponds and the near-shore marine environment were used to determine the sedimentology (texture and composition) and geochronology (using ¹⁴C, and ²¹⁰Pb) prior to anthropogenic activities to define the "natural signal", or "baseline", as well as recent deviations from the "natural signal", which may be attributed to anthropogenic activities. Salt pond and marine sediments in watersheds without anthropogenic activities exhibit no deviations from the "natural signal" in sedimentology or accumulation rate. Salt pond and marine sediments in watersheds with anthropogenic activities contain a deviation from the "natural signal" manifested as an increase in accumulation rate within the last 100 yrs (most likely within the last 25-50 yrs) ranging from 3 -10 times greater than the "natural" accumulation rate. Sedimentologically, salt ponds reflect no recent change, where as marine sediments do show a recent deviation in sedimentology. This marine deviation is represented by an increase in organic content, a decrease in grain size, and a decrease in carbonate content (marine-derived) compared to the "natural signal". This change reflects an increase in terrestrial (non- carbonate, finer-grained) sediment input to the marine environment. Anthropogenic activities result in major impacts on sediment dynamics and sediment delivery to coastal and marine environments. Increased terrestrial sediment input may cause premature infilling of coastal buffer zones such as salt ponds (see companion poster, Wallace et al). Once buffer zones are completely filled, terrestrial sediments are input directly to the near-shore marine environment, increasing the threat to sensitive environments such as coral reefs and seagrasses.
DE: 1115 Radioisotope geochronology
DE: 1834 Human impacts
DE: 1862 Sediment transport (4558)
DE: 1879 Watershed
DE: 4251 Marine pollution (0345, 0478)
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly