Factors controlling phyto plankton production and succession in a highly eutrophic lake kinnego bay lough neagh part 2 phyto plankton production and its chief determinants
Journal of Ecology 65(2): 561-578
ISSN/ISBN: 0022-0477 Accession: 005441198
Photosynthesis and respiration of phytoplankton in Kinnego Bay [N Ireland] were studied over a 2-yr period using the oxygen light-and-dark-bottle technique. Hourly areal photosynthesis was high and was largely independent of irradiance, being closely related to biomass and photosynthetic capacity. However, daily areal photosynthesis was shown to be strongly dependent on a function of radiation which incorporated day length. Since daily radiation is also a determinant of water temperature it exerted a further influence through the photosynthetic capacity, which was strongly correlated with temperature. Blue-green algal growth could produce considerable self-shading, to the extent that a further increase in algal density could not increase the areal photosynthesis. Self-shading was not so severe during diatom growth, although chlorophyll a concentrations could be higher than for blue-green algal growth, because of the lower incremental light extinction values exhibited during diatom growth. The chlorophyll a content of the euphotic zone would consequently be expected to be highest during diatom growth, but the large background contribution to light extinction prevented the theoretical maximum content being attained. Annual gross photosynthesis was high, the result of a high photosynthetic capacity and large algal crops subjected to little nutrient stress, but phytoplankton respiration was considerable and annual net production was probably only some 40% of gross.