. Nutrients, pesticides, minerals (major
ions), and suspended sediment are categories of chemicals found
in water. Nutrients are chemical elements essential to plant and
animal nutrition. The two most common nutrients, nitrogen and phosphorus,
are the major component of fertilizers for houseplants, lawns and
gardens, and agricultural crops. Pesticides are chemicals applied
to crops, rights-of-way, lawns, residences, golf courses, or other
settings to kill or control weeds, insects, fungi, nematodes, rodents,
or other unwanted organisms. Specific conductance, sulfate, and
chloride are measures of major ions. Major ions are those ions
that contribute significantly to the salinity of a stream. Suspended
sediment represents sediment that is transported in suspension
by a stream. Changes in water chemistry can occur in response to
increasing urbanization in a watershed. The objective of this study
was to compare nutrients, pesticides, major ions, and suspended
sediment at sites spatially and not over time. The scope of this
study was not large enough to fully characterize chemical conditions
during baseflow (periods of sustained low flow) and stormflow conditions,
so chemical samples were collected only during baseflow. In this
study, water chemistry data were collected to compare sites along
a gradient of urban intensity from low to high and to determine
the relation to other physical, chemical, and biological factors.
What we measured:
. Water samples were collected for nutrients,
pesticides, dissolved and particulate organic carbon, suspended
sediment, sulfate, and chloride.
. Field measurements of dissolved oxygen, pH, and specific conductance.
When we sampled:
. Baseflow water samples were collected a
minimum of two times at each site. One sample was collected near
the time of biological sampling.
. Field measurements were taken at time of collection of water samples and biological
Field collection protocols:
. Samples were collected using standardized
depth- and width-integrating techniques and were processed and
preserved onsite using standard methods (National Field Manual,
. Nutrients and pesticides samples were analyzed
at the USGS National Water-Quality Laboratory in Denver, Colorado
using methods described in Fishman (1993) and Zaugg and others
. Quality-control samples including field blanks, replicates, and laboratory
spikes were collected throughout the study (Mueller and others, 1997).
What these samples represent:
. Water chemistry results provide information
on the transport of chemical contaminants and suspended sediment
to streams in association with increasing urban intensity in
Nutrients are essential to life in small amounts; however,
in high concentrations nutrients are considered contaminants.
In excess quantities, nutrients can overnourish algae,
causing algal blooms. These blooms deprive deeper waters
of the sunlight and oxygen needed by aquatic organisms.
. Pesticides analyzed in this study represent a variety of pesticide classes
that are commonly applied in urban settings (including pyrethroid and organophosphate
insecticides, triazine and miscellaneous herbicides), plus selected pesticide
degradates. Degradates are compounds produced from the transformation of a parent
pesticide or another degradate through either abiotic processes (such as hydrolysis
and oxidation) or biologically mediated processes (such as microbial degradation).
Pesticides can have unintended harmful effects on the environment. Recent studies
suggest that some pesticides can disrupt endocrine systems and affect reproduction
and growth in aquatic organisms by interfering with natural hormones. Certain
pesticides with low solubility in water and high resistance to degradation can
accumulate in streambed sediments and fatty tissue in fish and can persist in
the environment for long periods of time. Often, contamination occurs as a mixture
of pesticides, and little is known about the toxicity of these mixtures.
. Specific conductance provides a measure of ion concentrations in a water sample
- as specific conductance increases, the concentration of major ions generally
increases. Major ions are those ions that contribute significantly to the salinity
of a water body. Sulfate and chloride are two of the major anions commonly found
in surface waters. During storm events, major ions contained in salts from streets,
fertilizers from lawns, and other material can be washed into streams and rivers.
. Suspended sediment can decrease water clarity and transport bound contaminants.
Suspended sediment can also damage stream habitat, reduce the amount of light
in the stream, clog fish gills, and interfere with visual and filter feeding
by aquatic organisms.
Fishman, M. J., 1993, Methods of analysis
by the U.S. Geological Survey National Water Quality Laboratory--Determination
of inorganic and organic constituents in water and fluvial sediments:
U.S. Geological Survey Open-File Report 93-125, 217 p.
Mueller, D.K., Martin, J.D., and Lopes, T.J.,
1997, Quality-control design for surface-water sampling in the
National Water-Quality Assessment Program: U.S. Geological Survey
Open-File Report 97-223, 17 p.
National Field Manual, 1997 to present, National
field manual for the collection of water-quality data: U.S. Geological
Survey Techniques of Water-Resources Investigations, book 9,
Chaps. A1-A9, 2 v., variously paged. [http://water.usgs.gov/owq/FieldManual/]
Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg,
K.M., 1995, Methods of analysis by the U.S. Geological Survey National
Water-Quality Laboratory-Determination of pesticides in water by
C-18 solid-phase extraction and capillary-column gas chromatography/mass
spectrometry with selected-ion monitoring: U.S. Geological Survey
Open-File Report 95-181, 49 p. [http://nwql.usgs.gov/Public/pubs/OFR95-181/OFR95-181.html]
Photos of water quality sampling in Raleigh, North
Carolina Study Area http://nc.water.usgs.gov/albe/Pics/pics_sw2/index.html
Video clips of water quality sampling in Raleigh,
North Carolina Study Area http://nc.water.usgs.gov/albe/video/video2_QW.html