¹Larson, G. L., C. D. McIntire, R. E. Truitt, W. J. Liss, R. Hoffman, E. Deimling, and G. Lomnicky. 1998. Phytoplankton assemblages in high-elevation lakes in the Northern Cascades Mountain Range, Washington State USA. Archives fur Hydrobiologie 142:71-93.

ABSTRACT

Phytoplankton assemblages in high-elevation lakes of North Cascades National Park Service Complex were studied during the open-water period in 1989. Collectively, 93 taxa were identified in 55 samples from 51 lakes. Based on cell densities, cyanobacteria had the highest relative abundance (36.7%), followed by chlorophytes (29.8%), and chrysophytes (19.6%). Aphanocapsa delicatissima had the highest proportional abundance (14.0%). Only 15.1% of the taxa occurred in more than 20 samples. Phytoplankton cell densities increased following a gradient of increasing lake-water temperature, alkalinity, and concentration of total Kjeldahl-N associated with decreasing lake elevation. Chrysophytes and cyanobacteria were the most important taxa (relative abundance) in alpine and subalpine lakes, whereas cyanobacteria had the highest relative abundances in high-forest and low-forest lakes. Chlorophytes had their highest relative abundance in high-forest lakes. Although low in relative abundance, diatoms and dinoflagellates were most abundant in alpine lakes. An ordination by correspondence analysis indicated that most alpine, subalpine, and high-forest lakes had similar floras. Although a few subalpine lakes exhibited deviations from this pattern, the main differences in phytoplankton composition were found in a group of low-forest and high-forest lakes. Canonical correspondence analysis (CCA) provided evidence that the distribution of samples and taxa in ordination space was correlated with a gradient of decreasing lake elevation and increasing water temperature, alkalinity, and concentration of nitrogen. When CCA was used to examine relationships among phytoplankton taxa and vegetation zones, a continuous distribution of taxa was found from the low-forest zone to the subalpine zone, with a large number of taxa occurring primarily in the subalpine and high-forest zones. Three phytoplankton taxa occurred primarily in alpine lakes, whereas five taxa co-occurred in alpine, subalpine, and high-forest zones. In NOCA lakes, elevation and associated changes in water quality and concentrations of nutrients, especially nitrogen, appeared to be the primary physical and chemical factors influencing the taxonomic structures of phytoplankton assemblages.

ACKNOWLEDGMENTS

This study was funded by the National Park Service and the USGS - Forest and Rangeland Ecosystem Science Center. Park staff assisted with logistical aspects in the field. Stanford Loeb, Stanley Dodson, John O'Brien, and William Neill provided constructive comments and suggestions of the project. Stanford Loeb, Stanley Dodson and James Petranka reviewed the manuscript. Ruth Jacobs edited and Rebecca Berkey typed the manuscript.