Thermal Structure-Induced Biochemical Parameters Stratification in a Subtropical Dam Reservoir.

Although stratification in deep lakes is well-discussed, few studies pay attention to thermal structure as well as its influences on stratification of biochemical parameters in subtropical lakes in mountainous cities. Here, we studied the depth profile of temperature and biochemical parameters in Longjing Lake, a subtropical reservoir in a mountainous city. Thermal stratification became strong during summer. Biochemical parameters were strongly associated with thermal structure. Stratification started at 2~6 m depth with a substantial decrease in dissolved oxygen, biochemical oxygen demand (BOD5), chlorophyll a, and pH, corresponding to an increase in total nitrogen, ammonium (<inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="02036-ilm01.gif"/>), nitrite (<inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="02036-ilm12.gif"/>), total inorganic nitrogen (TIN), total phosphorus, and soluble reactive phosphorus (SRP) with depth; the majority of biochemical parameters showed slight variations from 12 m downward. Our results indicated the stratification of Longjing Lake was stronger and more stable than the stratification of tropical and temperate lakes in lowland cities.