Hot spring drainage impact on fish communities around temperate estuaries in southwestern Japan

Study regionWe investigated in Beppu, Oita Prefecture, Japan. Hot spring drainage flows into a river and then flows into coastal areas in this area, a region in Japan with many hot springs.Study focusThe effects of that drainage on river and coastal area ecosystems remain unclear. We evaluated the impact of the hot spring drainage on fish communities near the estuary.New hydrological insightsFactor analysis results obtained using water quality data show that the scale of the hot spring drainage influence on rivers differs among rivers. The inflow of hot spring drainage into the rivers affects phytoplankton more than the inflow of domestic drainage, which increases the amount of phytoplankton. Furthermore, hot spring drainage creates a better habitat for Nile tilapia, a foreign species, by increasing food availability and water temperature.