Climatic Factors Affecting Water Quality under Natural Conditions: A Field Survey of a Local Reservoir

The global water cycle is closely related to climate change, and fresh water is a precious resource. Therefore, the effects of climate change on fresh water quality are of major importance. Worldwide, shallow lakes and ponds are the most abundant reservoir types. However, there have been few studies about ponds despite their large number. It is commonly accepted that wind-driven currents and thermal stratification mainly affect water circulation and oxygen diffusion in lakes. The presented research aims to verify whether this accepted view would be observed in a pond (⁓1 m depth and ⁓5,600 m2 area) under natural conditions accompanying changes in temperature and wind. A field survey performed over 7 months in Japan has demonstrated that (i) the temperature variations in the air and the pond water were negatively correlated with the dissolved oxygen concentration; and (ii) the wind variation shows weak negative correlation with the dissolved oxygen level in the bottom layer. A simple concept of the link between temperature and dissolved oxygen is established through these findings – the oxygen solubility dependent on temperature is important rather than thermal stratification and wind in terms of discussing the climate change effects on pond water quality.