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the use of a modified Hess circular sampler
<br />(Jacobi, 1978) or a D-ring kick net on riffle
<br />areas. Three samples were collected at each
<br />site and were preserved in 75% ethanol.
<br />Occasionally a small amount of
<br />formaldehyde was added to samples that
<br />contained large amounts of aquatic
<br />vegetation or organic detritus. Benthic
<br />macroinvertebrates were sorted in the
<br />laboratory and, identified.-using -taxonomic
<br />keys appropriate to the western United
<br />States (e.g., Baumann et al., 1977;
<br />Edmunds et al., 1978; Merritt and
<br />Cummins, 1984; Wiggins, 1979). Adult
<br />aquatic invertebrates were collected in a
<br />sweep net and a W light trap to
<br />complement the collection of immature
<br />benthic macroinvertebrates and chironomid
<br />pupal exuviae. The adult form was often
<br />useful in species level identification of the
<br />immature forms.
<br />Surveys for fish were conducted to obtain
<br />data on distribution and relative abundance.
<br />Where possible, fish were identified to
<br />species in the field, counted, and released
<br />upon completion of sampling. Specimens
<br />were identified using the taxonomic keys in
<br />Sublette et al. (1990); nomenclature
<br />followed Robins et al. (1991). On some
<br />sampling occasions, it was necessary to
<br />preserve specimens for subsequent
<br />examination. Most field collections were
<br />made by use of DC electrofishing
<br />equipment, including 24 volt, battery
<br />powered backpack shockers, and gas engine
<br />powered shore generators coupled with a
<br />DC pulsator. In some circumstances, a 16
<br />foot, 1/8 inch mesh seine was employed.
<br />On rare occasions gill nets of various mesh
<br />sizes were used. To assure representative
<br />collections, some of these collection
<br />techniques were employed in combination
<br />(e.g., electrofishing with block nets at the
<br />upper and lower ends of the-sample area).
<br />Sample areas were chosen to encompass the
<br />array of habitat types present at a site. The
<br />length of the area sampled varied depending
<br />on the size of the stream, but ranged
<br />generally from 100-200 meters.
<br />"Chemicat,'physical,-and climatic parameters
<br />were obtained for each collection site
<br />(Appendix 2). Chemical parameters were
<br />evaluated following contemporary standard
<br />laboratory methodology. Classification of
<br />stream substrate channel materials by
<br />particle size, and embeddedness, was made
<br />following the scheme of Platts et al. (1983)
<br />(Table 1). Land use designations followed
<br />the scheme of Dick-Peddie (unpublished).
<br />Four types of data were analyzed for sites in
<br />the upper Rio Grande drainage, i.e.,
<br />environmental variables representing
<br />physical, chemical, and climatic parameters,
<br />chironomid species distribution, benthic
<br />macroinvertebrate taxa distribution, and fish
<br />species distribution and abundance. The 22
<br />environmental variables analyzed herein
<br />(Appendix 2) were measured at 31 upper
<br />Rio Grande sites and were a combination of
<br />categorical and continuous variates. These
<br />environmental variables included alkalinity,
<br />ammonia, bicarbonate, calcium, chloride,
<br />embeddedness, growing season length,
<br />hardness, in-stream vegetation, Kjeldahl
<br />nitrogen', land use designation, magnesium,
<br />elevation, nitrate/nitrite, potassium, sodium,
<br />substrate composition, sulfate, total
<br />dissolved residue, total suspended solids,
<br />total phosphorus, and watershed area.
<br />Descriptions of the categorical variables for
<br />embeddedness, in-stream vegetation, land
<br />Kieldahl nitrogen,is a combination of organic nitrogen and ammonia.
<br />ao
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