Effects of thermal stratification and mixing on the vertical distribution of dissolved oxygen in aquaculture ponds

Abstract

Thermal stratification and mixing in aquaculture ponds can seriously affect the vertical distribution of dissolved oxygen (DO) and result in a lack of DO in ponds. Therefore, revealing the vertical distribution of DO in aquaculture ponds influenced by thermal stratification and mixing can provide a theoretical basis for aquaculture water management. Here, we explore the impacts of thermal stratification and mixing on the vertical distribution of DO in two aquaculture ponds under different weather conditions. The results showed that thermal stratification mainly occurs during the daytime, and mixing occurs at nighttime. Water thermal stratification appears 4 h after sunrise, while mixing occurs 1 h after nightfall. When the Richardson index is less than 0.25, the mixing direction is unstable. In the daytime, the vertical distribution of DO, chlorophyll a (Chl-a), and phytoplankton abundance varied with thermal stratification and mixing. The concentration of DO gradually dropped with increasing water depth during the nighttime. The concentration of DO was lowest in the early morning and peaked in the afternoon. Multiple regression analysis demonstrated that water temperature (WT), Chl-a, and phytoplankton abundance provided the best model for the vertical distribution of DO. Based on our results, DO regulation can provide important insights for aquaculture pond management.