Annotated inventory of invertebrate populations of an alpine lake and stream chain in Colorado

Benthic macroin vertebrates were collected during the ice-free season (1 July-20 October) over a five-year period from a chain ot alpine lakes and intervening streams in the Green Lakes Valley (3,347-3,615 m) in Boulder County, Colorado. A list oftaxawas developed for 19S1 and 1982, with taxonomic additions for 19831985 and comments on community structure, seasonal and elevational changes in species abundance, and noteworthy occurrences. A total of 111 taxa was collected, of which 84% occurred in streams, 58% being exclusively lotic. Dipterans composed 73-81% of total abundance in streams. The littoral benthic zone of lakes was predominantly trichopterans and dipterans, 44-60% and 24-39%, respectively. Numerically important organisms in various lakes and streams were chironomids, simuliids (particularly Metacnephia), oligochaetes, and the bivalve Pisidiutn casertanum. An isolated lake and its outlet stream, with unique characteristics, were the sole locations ol Gamnmrus lacustris (Amphipoda) and Glossiphonia complanata (Hiriidinea). Manipulated lowering t)f a lake along the main drainage exposed abundant and luxuriant colonies of the bryozoan Fredehcella sultana. This organism was found on 43% of all rocks sampled, a preponderance heretofore unknown for this, or any, ectoproct in alpine or arctic lakes. There are few studies of lake chains and their intervening streams for mountainous subalpine regions of the world, and, to our knowledge, there are no such studies for true alpine environments. A general review of relevant published information for Colorado, temperate and subarctic North America, and other continents is given bv Bushnell et al. (1982). We obtained information during an extended study of the aquatic macroinvertebrates of an alpine drainage system in the Colorado Rocky Mountains. During the icefree season, macroinvertebrates were collected from five of six small lakes, and their intervening streams, in the Green Lakes Valley on the eastern slope of the Continental Divide, Boulder County, Colorado. This paper is a taxonomic inventory for 1981 and 1982, with additional new data for later years (Chironomidae excluded). Annotations are given on seasonal changes in species abundance, elevational aspects of community structure and abundance, and noteworthy occurrences. The only directly applicable information on the macroinvertebrates of the Green Lakes drainage is by Elgmork and Saether (1970) and Saether (1970), and it is solely for the streams. These publications discuss ta.xonomic identifications derived from stream collections made in July 1960. Other publications providing information on a variety of environmental topics are those of Halfpenny (1982), Caine (1984), Bushnell et al. (1984), Bushnell and Butler (1984), Caine et al. (1983), Hoffman et al. (1985), Short et al. (1983), Toetz (1985), and Toetz and Windell (1984). Site Description: Green Lakes Drainage The glacially carved Green Lakes Valley is about 40° N latitude and has been closed to the public since 1927 by the City of Boulder because the drainage is a municipal water source (Windell and Foster 1982). The entire study area (Fig. 1) lies above timberline in a 5.46-km" drainage basin, of which 0.42 km" is occupied by the five Green Lakes (GLs 1-5) and Lake Albion (Caine 1982). GL 5, fed by a stream from the Arikaree Glacier, is the highest lake (3,615 m) and is confluent with GL 4 (3,554 m; Fig. 2) via a connecting stream. The streams were named according to the lake from which they emanate; e.g.. Stream 5 leaves GL 5 and flows into GL 4; Stream 2 leaves GL 2 and flows into Lake Albion. Lake Albion (3,347 m) is the lowest lake in the study area, and the greatest elevaThis research was supported by National Science Foundation Grants BSR-8514.329 and BSR-S012()95 to the Institute of .Arctic and .\lpine Research. Department of Environmental, Population and Organismic Biolog\'. University of Colorado, Boulder, Colorado 80309.