SYSTEM FOR CONTINUOUS MEASUREMENT OF BIOLOGICAL ACTIVITY IN AQUATIC SYSTEMS

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At the center of Lake Kasumigaura, water temperature, DO, pH, and chlorophyll a were measured at 6 different depths at 24-minute intervals for four 1- week periods. Using the models for vertical mixing and air-water exchange, the vertical distribution of biological changes in the lake water was estimated quasi-continuously, although the estimation was difficult when the decay of stratification occurred. Simultaneous measurements of DO and pH demonstrated the accuracy of the estimated biological activities. This system shows potential for field measurements of biological activities, e.g., primary productivity and respiration in the columns of aquatic systems.Similar measurement has been done in the reservoir of Simajigawa-dam (Yamaguchi Prefecture) to monitor the vertical and temporal change in water quality. The higher biological activity at 2-4 m depth and gradual DO decrease near sediments were clearly observed ; then this system presents quite useful information in reservoir management.