[Distribution Characteristics of Water Temperature and Water Quality of Fuxian Lake During Thermal Stratification Period in Summer]

In order to explore the distribution characteristics and change rule in daytime of the water temperature and water quality of the deep plateau lake Fuxian Lake during the thermal stratification period in summer, a typical point location was selected respectively in the south, middle and north of Fuxian Lake in July 2014 to carry out investigation and observation after stratified sampling at each point location and continuous stratified sampling of the point location in the north during daytime. The result showed that ①The distribution of water temperature of Fuxian Lake in summer had the temperature distribution characteristics of deep lake during stratification period. The segment from the surface to a depth of 15 meters was epilimnion with a range of 25.51-22.81℃. The segment from the depth of 15m to 40m was thermocline with a range of 22.81-14.72℃. The segment below 40m was hypolimnion with a range of 14.72-13.70℃. The max temperature difference between the surface and the lakebed was 11.8℃, which was smaller than that of lakes in temperate zone during the same period. The temperature of the lakebed was about 14℃ which was higher than that of the lakes in temperate zone,which reflected the characteristics of water temperature stratification of the deep plateau lake Fuxian Lake; ②The water temperature stratification determined the characteristics of chemical stratification and the ecological stratification:the pH, DO and conductivity presented the same layered structure as the distribution of water temperature. What is noteworthy was that the DO concentration of the lakebed was as low as 2-3mg·L^-1. As an oligotrophic lake, the DO became lower and lower at the lakebed of Fuxian Lake, which indicated that it possibly faced ecological risks. Due to the separation of thermocline, the nutritive salt accumulative effect appeared in the hypolimnion. Chlorophyll a and permanganate index had a corresponding response relation with the water temperature stratification and showed the max value at the upper layer of the lake. ③During the thermal stratification period, the water temperature stratification of Fuxian Lake had a change during daytime. The increased thermal radiation in the noon caused the thermocline to dive, the strength to increase and the depth to narrow, which significantly influenced the dynamic distribution of pH, DO, conductivity and chlorophyll a of the epilimnion and the thermocline. The change rule of TP, TN and permanganate index during the daytime was not significant.