The thermal effects of cooling system of a thermal power plant on photosynthesis of marine phytoplankton

Abstract

The activity of photosynthesis and the contents of chlorophylla and pheo-pigments were compared in the samples of the intake and effluent seawater of Owase-Mita Thermal Power Plant and in the seawater samples in the Yoshimi Bay before and after heat treatment. At Owase-Mita Thermal Power Plant, after passage of sea water through the cooling system chlorophylla content reduced to about a half and pheo-pigment content doubled in August with high temperature (25–27‡C), but the contents of chlorophylla and pheo-pigments changed little in January with low temperature (16‡C); whereas the depression of photosynthetic activity after passing through the cooling system was 71–77 % in August and 31–46 % in January. In the laboratory experiments, the heat treatment at 34–43‡C for 7–8 sec., which resulted in temperature rise of 7–8‡C, gave the decrease of chlorophylla and an increase of pheo-pigments in August temperature (26.5‡C), but a slight decrease of chlorophylla and a slight increase of pheo-pigments in November at the initial temperature of 19.2‡C, while in January and December the samples with low initial temperature (11.6 and 10.8‡C) showed almost no change in the content of pigments; the decrease in photosynthetic activity was 32 % in August sample,ca. 11 % in November sample,ca. 15% in January and almost no change in December. It is concluded that the photosynthetic carbon assimilation of marine phytoplankton is suppressed by passing through the cooling system of a thermal power plant even at lower water temperature in winter, while the content of chlorophylla is affected very little at a temperature below 20‡C.