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Abstract:
Rock
Creek Park is within the National Capital Region
in Washington, D.C., and is maintained by the
National Park Service. Part of Montgomery County,
Maryland, and part of the District of Columbia
drain into Rock Creek, which is a tributary
of the Potomac River. Water quality in Rock
Creek is important to biotic life in and near
the creek, and in the Potomac River Basin and
the Chesapeake Bay. The water quality of the
Rock Creek Basin has been affected by continued
urban and agricultural growth and development.
The U.S. Geological Survey, in cooperation with
the National Park Service, investigated water
quality and sediment quality in Rock Creek over
a 2-year period (1998–2000), and performed
a stream-channel classification to determine
the distribution of bottom sediment in Rock
Creek.
This
report presents and evaluates water quality
and bottom sediment in Rock Creek for water
years 1999 (October 1, 1998 to September 30,
1999) and 2000 (October 1, 1999 to September
30, 2000). A synoptic surface-water assessment
was conducted at five stations from June 23
to June 25, 1999, a temporal surface-water assessment
was conducted at one station from February 18,
1999 to September 26, 2000, and bed-sediment
samples were collected and assessed from three
stations from August 17 to August 19, 1999.
The synoptic surface-water assessment included
pesticides (parent compounds and selected transformation
products), field parameters, nutrients, and
major ions. The temporal surface-water assessment
included pesticides (parent compounds and selected
transformation products) and field parameters.
The bed-sediment assessment included trace elements
and organic compounds (including low- and high-molecular
weight polycyclic aromatic hydrocarbons, poly-chlorinated
biphenyls, pesticides, and phthalates). Some,
but not all, of the pesticides known to be used
in the area were included in the synoptic water-quality
assessment, the temporal water-quality assessment,
and the bed-sediment assessment. In addition
to the water-quality and sediment-quality assessments,
a Rosgen stream-channel classification was performed
on a 900-foot-long segment of Rock Creek.
In
the synoptic water-quality assessment, two pesticides
were found to be above published criteria for
the protection of aquatic life. In the temporal
water-quality assessment, four pesticides were
found to be above published criteria for the
protection of aquatic life. In the bed-sediment
assessment, 8 trace elements, 14 polycyclic
aromatic hydrocarbons, 6 pesticides, and 1 phthalate
compound were found to be above published criteria
for the protection of aquatic life. In the Rosgen
classification, a comparison to a previous classification
for this segment showed an increase in sands
and other fine-grained sediments in the creek
bed.
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