1966 Volume 79 Issue 942 Pages 815-829
Seasonal changes of the chlorophyll quantity and photosynthetic nature of microphytobentic community were pursed at one fixed station in a mountain section of the River Arakawa during 1961 to 1963. Then the process of the dry matter production of microphytobentic community was discussed on the basis of the data obtained.
The chlorophyll amount at the study site was 300mg/m2 to 500mg/m2 in winter and 100mg/m2 to 200mg/m2 during the other seasons. As the maximum chlorophyll quantity in the photosynthetic layer of community 200mg/m2 was obtained experimentally and the light condition in phytobentic community can roughly be given by I=I0exp (-0.02M), where M is the amount of chlorophyll per square meter. The pattern of photosynthesis-light curve showed a remarkable seasonal change.
The typical sun form was found in summer and the shade one in winter. The seasonal differentiation of photosynthetic pattern was ascribed to the changes in the water temperature at the habitat of algae. The course of seasonal change in photosynthetic rate was almost the same as that of phytoplankton in lakes, and the rate showed the range of 2mg O2/chl.mg/hr. in winter to 12mg O2/chl.mg/hr. in summer. The Q10 of photosynthesis was approximately 2.3 within the range of water temperature in situ.
The dry matter production in microphytobentic community was computed by the chlorophyll method. The daily gross production was 11.3g O2/m2 in July and the lowest one was 2.5g O2/m2 in winter. The estimated annual gross production in situ was 2.3kg O2/m2 or 2.2kg glucose/m2.
In conclusion, the rate of primary production in the stream ecosystem is higher than that in other aquatic communities. However, the community P/R ratios were less than 1, thus the river ecosystem metabolism is heterotrophic.