ECOLOGY OF SWANPOOL, FALMOUTH .5. PHYTOPLANKTON AND NUTRIENTS

Nutrient levels, plant pigments, oxygen balance and phytoplankton populations have been studied over a period of 2 years in a brackish-water lagoon. In general the lagoon was found to be supplied with abundant nutrients for plant growth by its freshwater inflow stream. Being shallow, it was therefore frequently eutrophic in summer. The number of phytoplankton species found in the pool was low, but several species showed marked continuity over the study period. Phytoplankton diversity was low, as often found in eutrophic lakes, and on occasions extremely low owing to the dominance of Gyrodinium resplendens. This species formed dense blooms which showed uneven horizontal and vertical distributions. In early summer, G. resplendens accumulated in strongly stratified layers of water about 1·5 m below the surface and caused maxima of oxygen and oxygen production at this level. Over the period of study some marked changes of species composition occurred, but these did not conform to any clear seasonal pattern such as that typical of many temperate freshwater lakes. © 1979.