Waters, S., McKnight, D., Wolfe, A., Vinebrooke, R., Sundermann, S., O'Brien, M., Williams, M., Roche, A. (0)

Algal and Biochemical Responses to Environmental Change in an Alpine Lake

to be submitted

We studied diatom species distribution in a 26 cm sediment core sample from Green Lake 4, an alpine lake in the Rocky Mountains. Over the past 20 years, the lake ice-cover has become thinner and nitrogen deposition has increased in Green Lakes Valley . Above the 9 cm depth in the core (corresponding to about 1940), the organic carbon content and the concentrations of chlorophyll a and fucoxanthin increased, and the fluorescence index changed in a manner indicating increases in microbially-derived fulvic acids. Small benthic diatom species, including Fragilaria pinnata Ehrenberg, Fragilaria construens var. venter (Ehrenberg) Grunow, and Fragilaria brevistriata Grunow, were most abundant above 9-10 cm in the core. Deeper sediments (10-26 cm) were characterized by larger contributions by species of the genus Aulacoseira. Analysis of the complete data set using Principal Components Analysis showed that the first axis explained 78.6 % of the variation. These results suggested that changes in Green Lake 4 associated with climatic change and nitrogen enrichment have caused increased growth of benthic diatoms, greater accumulation of sediment organic matter, and shifts in planktonic diatom species.