HR: 1400h
AN: OS23B-04    [Abstracts]
TI: Natural and Anthropogenic Influences on Coastal Evolution Rates: St. John, USVI
AU: * Wallace, L E
EM: wallacle@eckerd.edu
AF: Eckerd College, 4200 54th Avenue South, Saint Petersburg, FL 33711, United States
AU: Brooks, G R
EM: brooksgr@eckerd.edu
AF: Eckerd College, 4200 54th Avenue South, Saint Petersburg, FL 33711, United States
AU: Larson, R A
EM: larsonra@eckerd.edu
AF: Eckerd College, 4200 54th Avenue South, Saint Petersburg, FL 33711, United States
AU: Devine, B
EM: bdevine@uvi.edu
AF: University of the Virgin Islands, #2 John Brewers Bay, Saint Thomas, VI 00802, Virgin Islands (U.S.)
AU: Holmes, C
EM: cholmes@usgs.gov
AF: U.S. Geological Survey, 601 4th Street South, Saint Petersburg, FL 33701, United States
AU: Schwing, P T
EM: schwinpt@eckerd.edu
AF: Eckerd College, 4200 54th Avenue South, Saint Petersburg, FL 33711, United States
AB: Sediment cores collected in salt ponds along the coast of St. John, USVI, show that anthropogenic activities have accelerated the rate of coastal evolution. Previous phases of this research indicate that at least some salt ponds form by coral reef growth cutting off open embayments. Over time, ponds fill with island-derived sediments. Rates of sediment accumulation have been shown to increase where anthropogenic activities are present. The objective of this study is to quantify the time required to infill salt ponds in natural and anthropogenically influenced settings. Sediment cores were collected from five salt ponds, chosen primarily on the basis of degree of anthropogenic development within the watershed. Based on detailed geochronological analyses (²¹⁰Pb, ¹³⁷Cs, and ⁷Be for the last 100 years, and ¹⁴C for long-term accumulation) we determined accumulation rates using two methods. Linear accumulation rates were calculated to determine sediment accumulation over time. Compacted linear accumulation rates take into consideration compaction of sediments over time. Results show that ponds naturally infill at a rate of 3 - 7 cm/100 yrs. Ponds in pristine watersheds (Newfound Bay) have maintained their natural accumulation rate of 3 - 7 cm/100 yrs. Ponds in areas of low anthropogenic activities (Long Bay/Southgate) infill at 4 - 9 cm/100 yrs, reflecting a slight increase in accumulation due to anthropogenic activity. Ponds moderately impacted by anthropogenic activity (Fish Bay) show a substantial increase of 15 - 20 cm/100 yrs accumulation rate. This compares to heavily impacted areas, such as Coral Bay which has been shown to exhibit a 10-fold increase in sediment accumulation rate over the last 25-50 years. Thus, results show a progressive increase in sediment accumulation rate linked to increasing levels of anthropogenic activities within the associated watershed. Given these rates, ponds naturally become completely infilled in 4,000-6,000 years. Anthropogenic activities cause premature infilling of salt ponds 500-1,000 years sooner than under natural conditions. Once ponds are completely filled, sediments will empty directly into the marine environment, increasing the potential for degradation of nearby marine ecosystems (see companion poster by Larson, et. al).
DE: 1600 GLOBAL CHANGE
DE: 1724 Ocean sciences
DE: 3036 Ocean drilling
DE: 3050 Ocean observatories and experiments
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly