Abstract
Algal blooms have occurred in the Taehwa River estuary in South Korea despite the improvement of water quality since environmental renewal projects in the 1990s. In this study, we investigated the causes of algal blooms by measuring the water retention time using a floating buoy, water quality parameters, and phytoplankton distribution data from 2012. An algal bloom did not occur in February because of phosphate limitations in the Taehwa River estuary; however, the concentration of nutrients in the water inflow from the basin triggered a significant algal bloom in the upper estuary in the month of May. In this regard, the phytoplankton population was dominated by nano- and pico-sized flagellates. In August, the freshwater inflow into the estuary greatly increased due to heavy rainfall, resulting in a shorter retention time of the water bodies, which seemed to prevent an algal bloom. In November, a bloom of Cryptophyceae occurred at one of the sites (the U2 site) due to sufficient nutrients in the water and the long retention times of the water bodies. Our results indicate that a decrease in the nutrients (N and P) supplied from the basin is required for a reduction in algal blooms in the Taehwa River estuary. Additional studies are needed to further elucidate the effects of the land-based, nutrient-rich pollutants flowing into the Taehwa River estuary on algal bloom generation considering the fact that the streams have different environmental characteristics.
Highlights
Algal blooms are generally considered to be a major problem in estuaries and coastal areas worldwide [1,2,3]
We plotted the data of two buoys with tide level and wind velocity on trace graphs; tide level data were acquired from the Korean Hydrographic and Oceanographic Agency, and wind velocity data were acquired from the Korea Meteorological Administration
We did not detect an algal bloom in February, which was during the dry season, because the water level was higher and the flow rate was double compared to the results of the other study [24]; we found that other factors disrupt algal blooms
Summary
Algal blooms are generally considered to be a major problem in estuaries and coastal areas worldwide [1,2,3]. Nutrient-rich rivers have begun to flow into estuaries as the world becomes increasingly industrialized and urbanized [4]. Algal blooms enhance the deposition of organic matter [8], which can lead to hypoxia at the water and sediment interface of an estuary and in the sediments. Such an impact could negatively affect the entire dynamics of the aquatic and benthic ecosystem
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