[AHW32-P05] Estimation of lake water circulation mechanism in Lake Tazawa based on Physico-chemical characteristics
Keywords:Lake Tazawa, Water quality, Circulation, Turnover, Thermocline, Wind
The water samples of Lake Tazawa were collected at five locations in the lake and at some depths at each point. The samplings were carried out between June and October in 2019. Water temperature, pH, EC, Eh, density, specific gravity, quantity of suspended solids, and major dissolved ions were analyzed.
Water temperature was different between shallower and deeper layers and the water temperature in deep layer was almost constant around 4℃ from June to October. So, the thermocline existed through this period. On the other hand, values of pH and concentrations of major dissolved elements of the lake water were similar between all the sampling points and the depths. This result showed the water quality as the whole lake was almost uniform. In addition, the specific gravity and the quantity of suspended solids of lake water and river water of Tama-River were similar. The existence of thermocline and the results of specific gravity and suspended solids of lake water and river water showed that the difference of water density based on the water temperature is much larger than that based on the water quality. Thus, the first possibility was denied. On the other hand, if the shallower water is sufficiently cooled and the water temperature from bottom to surface becomes around 4℃ in winter, the difference of the density of lake water between the shallower and deeper layer will become small. Then, strong winds in this season are considered to cause the turnover of the lake water. The results of this study suggest that the future environment change such as the global warming and climate change may affect the circulation of lake water and the ecosystem of the lake.