Phytoplankton

Abstract

The base of the food pyramid consists of photosynthetic organisms that carry out the synthesis of organic carbon from inorganic carbon using solar radiation as the energy source. One of the main aspects of the present work on Lake Mendota has been a quantitative assessment of phytoplankton changes over the annual cycle and from year to year. A knowledge of phytoplankton dynamics is of interest from both a basic and applied standpoint:

• 1. Organic carbon derived from phytoplankton drives the biogeochemical cycles of the lake.

• 2. Phytoplankton provide the main food for the higher trophic levels.

• 3. The phytoplankton constitute the most numerous readily assessable microbial populations, and as such provide excellent populations for studies on the physiological ecology of microorganisms.

• 4. Many times of the year, there is more biomass present in phytoplankton than in any other group of organisms.

• 5. Lake Mendota has long been recognized as a lake with extensive phytoplankton blooms (Trelease, 1889), which have been considered an esthetic nuisance.

• 6. One group of phytoplankton, the cyanobacteria (blue-green algae), has members which produce animal and human toxins.

• 7. The cyanobacteria tend to float, contributing to the unsightly state of the lake at certain times of the year.

• 8. Some cyanobacteria are capable of nitrogen fixation, and may thus be responsible for some nutrient enrichment of the lake. Phytoplankton ecology has been reviewed many times (Fogg, 1975; Morris, 1980; Reynolds, 1984) and it is not the purpose of the present chapter to cover this same material. Rather, it is intended to place the studies of the dynamics of Lake Mendota phytoplankton within the existing broad theoretical framework. The rest of this introduction is intended merely to set the stage for the material in this chapter.