National Water-Quality Assessment (NAWQA) Program

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Effects of Urbanization on Stream Ecosystems

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Invertebrate Communities

• Benthic invertebrates are insects, mollusks, crustaceans, and worms found attached to or living in proximity to the bottom streams. Invertebrate communities are useful indicators in water-quality assessments because they live in, on, or near streambed sediments. With the exception of mollusks, most invertebrates have life cycles (months to a few years) that are intermediate to fish (years to decades) and algae (days to weeks), and are relatively immobile. Benthic invertebrates are sensitive to changes in streambed sediments (sedimentation or chemical contaminants), flow, habitat, and water chemistry. Benthic invertebrates are particularly useful for monitoring cumulative effects associated with landscape changes in the upstream basin. In this study, invertebrates were collected to compare sites along a gradient of urban intensity from low to high and to determine the relations between invertebrate responses and physical, chemical, and biological changes associated with increasing urbanization.

What we measured:
• A quantitative sample of invertebrates was taken from hard substrates, mostly rocks or wood, located usually in a riffle or run.
• A ‘multi-habitat’ qualitative sample of invertebrates was collected from all habitats and substrates present in the sampling reach.

When we sampled:
• Invertebrate samples were collected once during low-flow conditions at each site.

Field collection protocols:
• Benthic invertebrates were sampled using protocols described in Cuffney and others, 1993 for samples collected in 2000-2001 and Moulton and others, 2002 for samples collected in 2002 to present.
• Quantitative samples are taken from multiple representatives of the stream habitat thought to contain the richest assemblage of invertebrates:

o Riffle samples: Slack samples (0.25 square meters, 425-micron mesh net in 2000 or 500-micron mesh net in 2002 to present) collected from five separate riffle areas in the sampling reach are combined to form a single composite sample, or

o Snag samples: Woody snags were sampled at each of five locations along the stream reach and invertebrates were washed onto a 425-micron mesh sieve in 2000 or 500-micron mesh sieve in 2002 to present and combined to form a single composite sample.

• Qualitative multi-habitat samples of invertebrates are collected from as many habitats in the stream reach as were accessible using a 212-µm mesh dip net in 2000 or a 500-µm mesh dip net in 2002 to present supplemented with hand-picking of substrates.

Laboratory analyses:
• Invertebrate samples were sent to the USGS National Water Quality Laboratory in Denver, Colorado for taxonomic identification (identification of different types of organisms) and enumeration (counting) using method described in Moulton and others, 2000.

What this information represents:
• Quantitative samples were intended to provide a representation of invertebrate taxa richness (number of different types of organisms), abundance (number of invertebrates), and density (number of organisms per square meter) that could be used to compare responses to urbanization within a consistent substrate type (either riffles or snags) in each study. Quantitative samples are used to evaluate the effectiveness of measures of richness and density in detecting responses to urbanization.
• Qualitative and quantitative samples combined were intended to provide a comprehensive list of invertebrates in each sampling reach that incorporates the breadth of different habitat types present in the sampling reach and changes in habitat types that might occur in response to urbanization. Qualitative samples are used to evaluate the effectiveness of richness (number of different types of organisms) measures derived for the entire sampling reach in detecting responses to urbanization.

Cuffney, T.F., Gurtz, M.E., and Meador, M.R., 1993, Methods for collecting benthic invertebrate samples as part of the National Water-Quality Assessment Program: U.S. Geological Survey Open-File Report 93-406, 66 p. []

Moulton, S.R., Carter, J.L., Grotheer, S.A., Cuffney, T.F., and Short, T.M., 2000, Methods for analysis by the U.S. Geological Survey National Water Quality Laboratory – processing, taxonomy, and quality control of benthic macroinvertebrate samples: U.S. Geological Survey Open-File Report 00-212, 49 p. []

Moulton, S.R. II, Kennen, J.G., Goldstein, R.M., and Hambrook, J.A., 2002, Revised protocols for sampling algae, invertebrate, and fish communities as part of the National Water-Quality Assessment Program: U.S. Geological Survey Open-File Report 02-150, 75 p. []

Video clips of invertebrate sampling in Raleigh, North Carolina Study Area


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