Water Chemistry

Overview:
. 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 communities.

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, 1997-Present).

Laboratory analyses:
. 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 (1995).

Quality control:
. 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 a watershed.
. 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.

Reference:
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. [http://pubs.usgs.gov/of/1997/223/]

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