San Juan Bay
Gamma Counting to Determine Sedimentation Rates
Type: Condition
of habitat and sources affecting habitat (i.e., the condition or
functionality of the habitat).
Category: Submerged
Cost: $150,000
Description: Estimation of sedimentation rates at selected
sites in the San Juan Bay Estuary system was determined from the
activity of Cs-137 in various sediment cores. The estimated rates
were used to define strata containing sediments and associated constituents
deposited during discrete time periods corresponding appoximately
to 1925-49, 1950-74, and 1975-95.
Outcome: A homogenized sample from each time interval was
analyzed for 17 organochlorine compounds including total PCB's and
PCN's, and seven trace elements (As, Ba, Cd, Cr, Pb, Hg, and Se).
The homogenized core sample representing the depositional period
1950-74 was also analyzed for four chlorophenoxy-acid herbicides
that were widely used during that time period. The surficial core
segment, that corresponding to the 1975-95 depositional period,
was analyzed for 52 semi-volatile organic compounds, and oil and
grease. All this data provided information about sediment quality
variations among different time periods. This study also analyzed
water quality samples for a wet and dry event.
Contact: Mr. Richard Webb, USGS-Colorado
Citation: Webb, R. M. T. and F. Gómez-Gómez, 1998. Synoptic
Survey of Water Quality and Bottom Sediments, San Juan Bay Estuary
System, Puerto Rico, December 1994-July 1995. US Geological Survey.
Water-Resources Investigations Report 97-4144.
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