The Responses of phytoplankton and bacterial communities along the salinity gradients in the Seomjin River estuary

Abstract

To assess changes in abiotic and biotic factors between ood and ebb tides we investigated the seasonal phytoplankton and bacterial dynamics and environmental conditions along a salinity gradient at 14 stations in the Seomjin River estuary(SRE), Korea. We performed bioassays to identify the effect of additional nutrients (+N, +P, and +NP) on phytoplankton growth and performed high-resolution 16S rRNA tag pyrosequencing to obtain snapshots of the bacterial diversity and community structure along the salinity gradients. Nitrate+nitrite and silicate loading increased as a result of freshwater input, and that phosphates loading may primarily have involved leaching from bottom sediments of the shallow inner bay. Bioassays con rmed that relative phytoplankton growth in the saltwater zone near Gwangyang Bay was higher for +N and +NP treatments than for +P treatments, whereas it was signi cantly higher in the freshwater zone for +P treatments than for +N treatments. Base on the algal bioassays and the eld surveys, we suggested that nitrate+nitrite and phosphates could be limiting factors in the saltwater and freshwater zones, respectively. The signi cant differences in abiotic factors between ood and ebb tides play important roles in controlling the biotic factors, including the occurrence of aquatic organisms including microalgae. In particular, bacterial diversity was signi cant at station 9, where freshwater and saltwatSRE), Korea. We performed bioassays to identify the effect of additional nutrients (+N, +P, and +NP) on phytoplankton growth and performed high-resolution 16S rRNA tag pyrosequencing to obtain snapshots of the bacterial diversity and community structure along the salinity gradients. Nitrate+nitrite and silicate loading increased as a result of freshwater input, and that phosphates loading may primarily have involved leaching from bottom sediments of the shallow inner bay. Bioassays con rmed that relative phytoplankton growth in the saltwater zone near Gwangyang Bay was higher for +N and +NP treatments than for +P treatments, whereas it was signi cantly higher in the freshwater zone for +P treatments than for +N treatments. Base on the algal bioassays and the eld surveys, we suggested that nitrate+nitrite and phosphates could be limiting factors in the saltwater and freshwater zones, respectively. The signi cant differences in abiotic factors between ood and ebb tides play important roles in controlling the biotic factors, including the occurrence of aquatic organisms including microalgae. In particular, bacterial diversity was signi cant at station 9, where freshwater and saltwat