Effects of Nakdong River Estuary Barrage discharge on mesozooplankton community structure: opening of weirs in Nakdong River

Abstract

We investigated the mesozooplankton community structure and environmental variables in the Nakdong River Estuary during three periods in 2017. The periods were before and after opening of the four weirs (Gangjeong-Goryeong, Dalsung, Hapcheon-Changnyeong, Changnyeong-Haman) in the lower Nakdong River. The mesozooplankton and environmental factors (temperature, salinity, chlorophyll-a) were sampled before (May) and after (5 and 42 days; June and July, respectively) opening of weirs. The average daily discharge of Nakdong River Estuary Barrage (NREB) was relatively lower in June (38.6 m3s-1) than May and July. The mesozooplankton abundance was relatively higher by 5 times in May than in June and July, in which Noctiluca scintillans were dominant. In June, cladocerans (Podon schmackeri) were dominant species in the brackish region, while cladocerans (Daphnia cuculata and D. hyalina) prevailed throughout freshwater region. In July, cladocerans (Penilia avirostris) were dominant in the brackish to seawater region. These results indicated that considerable spatiotemporal heterogeneity of mesozooplankton community among study area depends on the management of freshwater discharge of weirs and barrage opening. Consequently based on the findings of this research, we can understand better of zooplankton distribution in the regulated river estuary barrage system as basic information for managerial actions.