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Effects of Urbanization on Stream Ecosystems

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Algae Communities and Biomass

• Benthic algae are plant communities that are found attached to or living in proximity to the bottom of streams and are the base of the foodweb. Algae are a critical part of the food chain in aquatic systems because they are the “primary producers” – organisms that can convert the energy of sunlight, together with certain chemicals, to an energy source for most other organisms. Different groups of algae produce energy sources of varying quality, so changes in the kinds and abundance of algae in a stream can affect many other organisms in the stream. Algae are useful indicators in water-quality assessments because they have rapid growth, are immobile, in direct contact with water, respond quickly to stressors (for example, sensitive species decrease and tolerant species increase), and integrate the effects of a stress over a relatively short period of time (day to month time scale). Algae are sensitive to changes in flow, chemistry (particularly nutrients), water temperature, light, and sediment. One group of algae, the diatoms, tends to decrease with degrading water quality as the amount of urban land increases. Blooms of another group, the green algae, may show up as long, thick green strands covering part of all of the rocks on stream bottoms. In addition, some species of blue-green algae (sometimes called “pond scum”) that bloom under high nutrient conditions can produce toxins of concern to fish, wildlife, and humans. Data on algal species, their abundances, their pollution tolerance and other environmental preferences, allow computation of metrics for water quality assessment in a manner similar to that used for invertebrates and fish. In this study, algal community composition and biomass were collected to compare sites along a gradient of urban intensity from low to high and in relation to other physical, chemical, and biological factors.

What we measured:
• Two quantitative samples were collected for algal community composition: one from hard substrates, mostly rocks or woody snags, located usually in a riffle or run, and another from soft sediment in a depositional area.
• A ‘multi-habitat’ qualitative sample for algal community was collected from various substrates present in the sampling reach only for studies that sampled in 2000.
• Chlorophyll content and ash-free dry mass samples were subsampled from the quantitative sample collected from hard substrates.

When we sampled:
• Algal community composition and biomass samples were collected once during low-flow conditions at each site.

Field collection protocols:
• Algae were sampled using protocols described in Porter and others, 1993 for samples collected in 2000-2001 and Moulton and others, 2002 for samples collected in 2002 to present.
• Each sample from rocks was a composite of five subsamples collected from each of five locations in the stream reach. Where rocks were unavailable, woody snags were used for algae samples. Ten woody snag sections were collected from the stream reach and composited for a sample.
• Each sample collected from soft sediments was a composite of subsamples taken at five locations in the stream reach.

Laboratory analyses:
• Algae samples were sent to The Academy of Natural Science, Patrick Center for Environmental Research in Philadelphia, Pennsylvania for taxonomic identification and enumeration using methods described in Charles and others, 2002.
• Algal biomass samples were analyzed at the USGS National Water-Quality Laboratory in Denver, Colorado using method described in Arar and Collins (1997) for chlorophyll and Britton and Greeson (1987) for ash-free dry mass.

What these samples represent:
• Quantitative samples are collected to provide actual abundances of species found in selected habitats at a site and allow computation of measures or metrics.
• The combination of qualitative and quantitative samples is intended to provide a comprehensive list of algae species at a site.
• Chlorophyll and ash-free dry mass represent the amount of algae found at site which can vary with physical and chemical characteristics of streams.

Arar, E. J., and Collins, G.B., 1997, U.S. Environmental Protection Agency method 445.0, in vitro determination of chlorophyll a and pheophytin a in marine and freshwater algae by fluorescence, revision 1.2: Cincinnati, Ohio, U.S. Environmental Protection Agency, National Exposure Research Laboratory, Office of Research and Development, 22 p.

Britton, L.J., and Greeson, P.W., eds, 1987, Methods for collection and analyses of aquatic biological and microbiological samples: U.S. Geological Survey Techniques of Water-Resources Investigations, book 5, chapter A4, p. 139-140.

Charles, D.F., Knowles, Canidia, and Davis, R.S., eds., 2002, Protocols for the analysis of algal samples collected as part of the U.S. Geological Survey National Water-Quality Assessment Program: Philadelphia, PA, The Academy of Natural Sciences, Patrick Center for Environmental Research Report No. 02-06, 124 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. []

Porter S. D., Cuffney, T.F., Gurtz, M.E. and Meador, M.R., 1993, Methods for collecting algal samples as part of the National Water-Quality Assessment Program: U.S. Geological Survey, Open-File Report 93-409, 39 p. []


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