The impact of thermal energy and materials derived from the hot spring drainage on the fish community near the estuary

Abstract:

Beppu is a region with many hot springs in Japan. Some of environmental studies of the rivers in this region (e.g. Kawano et al., 1998, Ohsawa et al., 2008) show that hot spring drainage flows into a river and then flow into the coastal are, and it strongly affects the river water quality. On the other hands, several kinds of tropical fish lives in those rivers (Hiramatu et al., 1995). We can easily have watched those fish there. Although the relationship between hot spring drainage and the fish community had not been investigated in the past in this area, it is easily assumed that thermal energy and materials derived from the hot spring drainage strongly affect the ecosystem. However, the impact of the hot spring drainage on the ecosystem in river and coastal area is not clear. We investigated the river water quality and physical property of six rivers in this region. Additionally, we investigated the fish community near the estuary at two rivers which are strongly affected by the hot spring drainage and not the influence of the hot spring at all. We tried an evaluation about the influence of thermal energy and materials derived from the hot spring drainage on the fish community near the estuary.
The results of chemical and physical data in these rivers are as follows. The size of influence of hot spring drainage on river is different every river. In this region, Hirata River is most strongly affected by the hot spring drainage. The water temperature of Hirata River maintains 25 degrees Celsius or more through the year and the concentrations of dissolved component is very high. On the other hand, the water temperature and the concentrations of dissolved component of Hiya Rive is low. These data are similar to data of the upper side of Hirata River. The results of investigating the fish community indicate that Oreochromis niloticus and Rhinogobius giurinus is the dominant species at Hirata River and Hiya River respectively. In addition, there is more the number of species of Hiya River than that of Hirata River. In this presentation, we will report and discuss the impact of the hot spring drainage on the fish community near the estuary.