Studies of the production ecology of the phytoplankton of Kinnego Bay, Lough Neagh

Abstract

The production ecology of the phytoplankton of Kinnego Day, Lough Neagh, is discussed in relation to environmental factors. Algal crops varied between 33 and 240 mg chlorophyll am -3. Spring and autumn growth was mostly of diatoms, Stephanodiscus hantzschii being the predominant species. Summer growth was dominated by two species of blue-green algae, Oscillatoria redekei and o. agardhii. Few species contributed significantly to the total algal biomass. Rates of photosynthesis, measured as changes in the concentration of oxygen in light and dark bottles, gave a maximum recorded rate of gross photosynthesis of 725 mg cm -3 hr -1 and daily integrals of up to 5.4 g Cm -2 day -1. Such figures show Kinnego Day to be day among the most productive of temperate lakes although high rates of respiration associated with the rates of gross photosynthesis substantially reduced the annual net production by phytoplankton in the bay. Temperature is shown to affect the respiration of Kinnego Day diatoms and blue-green algae differently and hence may also be significant in determining their relative seasonal dominance. Concentrations of inorganic ions both within the bay and in the inflow river provided no evidence that the growth of phytoplankton in the bay was seriously limited by a lack of nutrients. Rather, growth is considered to be chiefly a function of the interaction between algal physiology and temperature and light. The importance of the under- water light climate to phytoplankton is considered, in particular the ratio of illuminated to dark zones in the water column. Light attenuation was mainly due to the phytoplankton itself and to dissolved organic matter. Variation in the depth of the euphotic zone was largely governed by changes in phytoplankton biomass and although the variation throughout the year was limited to approximately 1.5 meters, this had a considerable influence on the light to dark ratio because of the shallow nature of the bay.

Date of Award	1976
Original language	English