Assessment of the water quality factors influencing the primary production in Lake Kasumigaura

Abstract

 Fast Repetition Rate Fluorometry (FRRF) is one of the methods for quantifying primary production in aquatic environment, and it has the advantages in terms of quick measurement and being able to obtain the large amounts of data. In this study, FRRF has been applied to monitor the primary production from 2016 to 2019 in Lake Kasumigaura. Algal abundance and photosynthetic activity are assumed to be the factors affecting primary production. In Lake Kasumigaura, it was shown that primary production and the algal abundance had the causal relationship with the annual variation of strength. On the other hands, correlation analysis revealed that the extinction coefficient of light under the water (K_d) have much influenced on the photosynthetic activity in the lake. Furthermore, especially near the estuary, it was found that nitrate from the inflowing rivers during the rainfall events also affect the photosynthetic activity.