抚仙湖夏季热分层时期水温及水质分布特征

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

为探究高原深水湖泊抚仙湖夏季热分层时期水温水质空间特征及昼间变化规律,于2014年7月在抚仙湖南部、中部及北部各选取一个代表点位,开展了各点分层采样及北部点位昼间连续分层采样调查观测.结果表明:(1)抚仙湖夏季水温分布具有明显的深水湖泊成层期温度分布特征,表面至水深15 m为变温层,水温变幅25.51~22.81℃,15~40 m为温跃层,水温变幅22.81~14.72℃,40 m以下为等温层,水温变幅14.72~13.70℃.湖体表层与湖底层的最大温差为11.8℃,与温带湖泊同期相比温差较小,而湖底等温层水温为14℃左右,较温带湖泊为高,体现了抚仙湖高原深水湖泊自身的水温成层特征.(2)水温成层决定了湖体的化学成层与生态成层特征:pH、溶解氧(DO)及电导率均呈现出与水温分布相同的分层结构,值得关注的是湖底层DO浓度低至2~3 mg·L^(-1),作为贫营养湖泊,抚仙湖底层开始出现溶解氧偏低的现象昭示着其可能面临潜在的生态风险;总磷(TP)及总氮(TN)由于温跃层的阻隔,等温层呈现一定程度的营养盐累积效应;叶绿素a与高锰酸盐指数也均与水温分层存在对应的响应关系,在湖体上层出现最大值.(3)抚仙湖热分层时期,水温分层存在昼间变化,中午光照辐射增强导致温跃层下潜,强度变大,厚度变窄,显著影响变温层和温跃层的pH、DO、电导率及叶绿素a等动态分布,TP、TN及高锰酸盐指数的昼间变化规律不显著.

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（1） The 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 15 m to 40 m was thermocline with a range of 22.81-14.72℃.The segment below 40 m 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;（2） The 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 2-3 mg·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.（3） During 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.