IN-SITU MEASUREMENT OF ALGAL GROWTH-POTENTIAL IN AQUATIC ECOSYSTEMS BY IMMOBILIZED ALGAE

Cells of the green alga Selenastrum capricomutum were immobilized in alginate beads. The alga was able to grow inside these beads without being grazed by zooplankton. For P-limited immobilized cells, however, a lower mu(m) and initial slope of the Monod growth curve mu(m)/K(s) were found than for free cells. To study the feasibility of immobilized algae to estimate algal growth potential in situ in aquatic ecosystems, a series of experiments were conducted in indoor model ecosystems (microcosms) and in a small stream. The use of immobilized algae allowed a continuous registration of algal growth potential integrated over periods with natural fluctuations in the environment. The method of encapsulation of the algae can, however, still be improved. The alginate matrix is exposed to marked degradation by microorganisms when incubated in polluted streams for a period longer than two weeks. The applicability of other types of matrices should be tested.