McKnight, D. M., Miller, C., Smith, R. L. , Baron, J. A., & Spaulding, S. A. (1988)

Phytoplankton population in lakes in Loch Vale, Rocky Mountain National Park, Colorado: Sensitivity to acidic conditions and nitrate enrichment

U.S. Geological Survey Water-Resources Investigations Report, 88–4115. 102 pp.

Three distinct periods in the succession of phytoplankton populations occur during the open-water period in lakes in Loch Vale, Rocky Mountain National Park, Colorado: (1) A spring bloom of the planktonic diatom Asterionella formosa, (2) a midsummer period of low algal abundance, and (3) an autumnal bloom of the blue-green alga Oscillatoria limnetica. Onsite measurements indicated that, although the zooplankton are sparse in these lakes on most occasions, the peak in zooplankton abundance coincides with the decrease in diatom abundance. Measurement of photosynthetic rates at different depths during the three periods confirmed the rapid growth of Asterionella formosa during the spring. Depth profiles for photosynthetic rates indicated photoinhibition at the surface that is comparable to that measured in temperate lakes at lower elevations. Measurements of changes in photosynthetic rate on exposure to acid conditions indicated that the Asterionella formosa population, which comprises the spring bloom, is much less sensitive to acid conditions than the Oscillatoria limnetica population, which comprises the autumnal bloom. For both populations, growth stimulation resulted from 8- and 16-micromolar amendments with calcium nitrate and sulfuric acid, but the reason for this stimulation cannot be determined from these data.