Peter C. Van Metre & Edward
Callender
Abstract
Historical trends in selected water-quality
variables from 1912 to 1994 in White Rock Creek Basin
were identified by dated sediment cores from White Rock
Lake. White Rock Lake is a 4.4-km2 reservoir
filled in 1912 and located on the north side of Dallas,
Texas, with a drainage area of 259 km2. Agriculture
dominated land use in White Rock Creek Basin before
about 1950. By 1990, 72% of the basin was urban. Sediment
cores were dated using cesium-137 and core lithology.
Major element concentrations changed, and sedimentation
rates and percentage of clay-sized particles in sediments
decreased beginning in about 1952 in response to the
change in land use. Lead concentrations, normalized
with respect to aluminum, were six times larger in sediment
deposited in about 1978 than in pre-1952 sediment. Following
the introduction of unleaded gasoline in the 1970s,
normalized lead concentrations in sediment declined
and stabilized at about two and one-half times the pre-1952
level. Normalized zinc and arsenic concentrations increased
66 and 76%, respectively, from before 1952 to 1994.
No organochlorine compounds were detected in sediments
deposited prior to about 1940. Concentrations of polychlorinated
biphenyls (PCB) and DDE (a metabolite of DDT) increased
rapidly beginning in the 1940s and peaked in the 1940s
at 21 and 20 microgram kg-1, respectively,
which is coincident with their peak use in the United
States. Concentrations of both declined about an order
of magnitude from the 1960s to the 1990s to 3.0 and
2.0 microgram kg-1, respectively. Chlordane
and dieldrin concentrations increased during the 1970s
and 1980s. The largest chlordane concentration was 8.0
microgram kg-1 and occurred in a sediment
sample deposited in about 1990. The largest dieldrin
concentration was 0.7 microgram kg-1 and
occurred in the most recent sample deposited in the
early 1990s. Agricultural use of chlordane and dieldrin
was restricted in the 1970s; however, both were used
as termiticides, and urban use of chlordane continued
at least until 1990. Recent use of dieldrin and aldrin,
which degrades to dieldrin, has not been reported; however,
increasing trends in dieldrin since the 1970s suggest
recent urban use could have occurred.
Journal of Paleolimnology
17: 239-247, 1997.
Peter C. Van Metre
U.S. Geological Survey
8011 Cameron Road
Austin, TX 78754
Edward Callender
U.S. Geological Survey
12201 Sunrise Valley Drive
MS 432
Reston, VA 22092
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