Thermal Stratification in Saline Shallow Water Bodies

Abstract

Thermal stratification occurs in water bodies because of the heat that is absorbed during daytime and the heat that is released during nighttime. Understanding the behavior of water temperature in shallow waters is important for practical applications in aquaculture. In this study, thermal stratification in the closed saline water bodies of three aquaculture ponds has been investigated with different initial salinities of 0, 15, and 30 psu at the Klongwan Fisheries Research Station, Kasetsart University in the Prachuap Khirikhan province, Thailand. Further, the weather and the vertical profiles of water temperature were measured at 10-min intervals from June 1 to October 31, 2017. During the observation period, the solar radiation at noon time was approximately 400-700 W/m², the air pressure was higher than 100 kPa, and the air temperature was approximately 25 °C-35 °C. Further, rainfall occurred only for a short duration, and only a low amount of rainfall was received during the observation period. Over the whole observation period, 90% of the observed wind speeds was less than 4 knot, while the remaining 10% of the recorded speeds was high and ranged from 5 to 10 knot. A high wind speed was observed during nighttime. After sunrise, short-term stratification was observed during daytime, and stratification disappeared gradually as the water surface started cooling. The disappearance of stratification was caused by the thermal exchange between the air and the water surface. In case of saline water, the amount of heat exchanged during daytime and nighttime was higher than that observed in case of fresh water because the heat capacity of saline water was lower than that of fresh water.