Introduction
Beginning around 2000, abundance indices of four
pelagic fishes (delta smelt, striped bass, longfin smelt,
and threadfin shad) within the San Francisco Bay and
Sacramento–San Joaquin Delta began to decline sharply
(Sommer and others, 2007). These declines collectively
became known as the pelagic organism decline (POD).
No single cause has been linked to this decline, and current
theories suggest that combinations of multiple stressors are
likely to blame. Contaminants (including current-use pesticides)
are one potential stressor being investigated for its role
in the POD (Anderson, 2007). Pesticide concentration data
collected by the U.S. Geological Survey (USGS) at multiple
sites in the delta region over the past two decades are critical
to understanding the potential effects of current-use pesticides
on species of concern as well as the overall health of the delta
ecosystem.
In April 2010, a compilation of contaminant data for
the delta region was published by the State Water Resources
Control Board (Johnson and others, 2010). Pesticide occurrence
was the major focus of this report, which concluded that
“there was insufficient high quality data available to make
conclusions about the potential role of specific contaminants
in the POD.” The report cited multiple sources; however, data
collected by the USGS were not included in the publication
even though these data met all criteria listed for inclusion in
the report.
What follows is a summary of publicly available USGS
data for pesticide concentrations in surface water and sediments
within the Sacramento–San Joaquin Delta region from
the years 1990 through 2010. Data were retrieved though the
USGS National Water Information System (NWIS) database,
a publicly available online-data repository (U.S. Geological
Survey, 1998), and from published USGS reports (also available
online at http://pubs.er.usgs.gov/).
The majority of the data were collected in support of
two long term USGS monitoring programs—National Water
Quality Assessment Program (NAWQA; http://water.usgs.gov/
nawqa/) and National Stream Quality Accounting Network
(NASQAN; http://water.usgs.gov/nasqan/)—and through projects
associated with the USGS Toxics Substances Hydrology
Program (http://toxics.usgs.gov/). In addition, data were collected
during multiple research projects that were supported
by various federal, state, and local agencies.
Although these data have been previously published in
some form, it is hoped that by focusing on samples collected
within the delta region and presenting these data in a concise
format, they will be a valuable resource for scientists, resource
managers, and members of the public working to understand
the role of pesticides in the POD and their potential effects on
the overall health of the delta ecosystem.
