红枫湖季节性热分层消亡期水体的理化特征

以云贵高原典型的人工河道型水库红枫湖为研究对象,对近2年来4个代表性湖区季节性热分层消亡期水体的理化特征进行了原位监测. 结果表明:红枫湖水体季节性热分层历经发生、发展和消亡的周期性演化过程,对湖泊水环境的变化起着重要的控制作用. 秋季初期,气温骤降易于引起季节性热分层的突发性消亡,表现为水体垂向混匀. 以2010年为例,分层消失使得上层水温由28.6 ℃降至23.0 ℃,ρ(DO)(溶解氧浓度)由9.6 mg/L降至4.0 mg/L,pH由8.8降至7.9,电导率由0.32 mS/cm升至0.36 mS/cm,局部湖区出现鱼类死亡现象；短时间内的剧烈垂直混合,致使沉积物营养盐扰动释放,上部水体ρ(TP)增加了约0.01 mg/L,ρ(TN)增加了0.1 mg/L. 红枫湖水体垂向混合可对湖泊水环境产生重要影响,其影响的水体深度和环境效应一方面与气温变幅等因素有关,另一方面还受湖泊温跃层位置和底层水体的绝对温度等因素控制,在预测该类突发性水质恶化事件及评估其环境影响时需予以考虑. 

Physical and Chemical Characteristics of Water in Lake Hongfeng during the Disappearance of Seasonal Stratification

The physical and chemical characteristics of water in the four lake areas of Lake Hongfeng in Guizhou Plateau were investigated during the period of disappearance of seasonal stratification over the last two years.The results showed that the seasonal water stratification in Lake Hongfeng evolved periodically,which significantly controlled the changes in water quality.The sudden decrease of temperature in the early fall caused the disappearance of water stratification,which appeared as a strong vertical convection leading to great deterioration of water quality.In 2010,for example,hierarchical disappearance resulted in a decrease of temperature in the surface water from 28.6 ℃ to 23.0 ℃,a reduction of the dissolved oxygen content from 9.6 mg/L to 4.0 mg/L,a decrease of pH from 8.8 to 7.9,and an increase in the conductivity from 0.32 mS/cm to 0.36 mS/cm.Release of sediment nutrients caused by the intense vertical mixing caused an increase in the total phosphorus concentration of about 0.01 mg/L,and an increase in the total nitrogen concentration of 0.1 mg/L in the upper water column.In Lake Hongfeng,the vertical mixing caused by sudden dramatic changes of temperature in the early autumn has a major impact on the water environment.Temperature amplitude,absolute temperature of the bottom water and depth of thermocline controlled the depth of water mixing and its environmental effects.Therefore,all these factors should be considered in predicting sudden deterioration of water quality and its environmental impacts.