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2014年春节期间,笔者班上的地理科代表兰宇来电话询问,乍得湖为什么是淡水湖?在他看来,乍得湖是一个内陆湖,只有河水注入,没有河水流出,加之这里属于热带草原气候,北部邻近世界面积最大的撒哈拉沙漠,气温高、蒸发量大,具有这样特征和位于这样环境里的湖泊,水应该是咸的,如里海、咸海等,或者像巴尔喀什湖一样,临近河口的湖区为淡水,远离河口的地方为咸水。而乍得湖却是地地道道的淡水湖,即使是没有河流注入的东北部,湖水也只是略带咸味,盐度非常低,与淡水相差不大。当时正值假期,笔者没有说出原因,只是要求他自己到网络上去找答案。
During Spring Festival 2014, Lan Yu, a geography representative in charge of the class, called and asked why Lake Chad is a freshwater lake. In his view, Lake Chad is an inland lake, with only river water injected and no river water flowing out. In addition, the climate here belongs to the savannah climate , The northern part of the Sahara, the largest of its kind in the world, with its high temperature and large amount of evaporation. It is characterized by the presence of lakes in such environments as the Caspian Sea, the Aral Sea, etc., or the Lake Balkhash, The lake area is freshwater, away from the mouth of the river is saltwater. Lake Chad, on the other hand, is an authentic freshwater lake. Even in the northeastern part of the country where there is no river inflow, the lake is only slightly salty with very low salinity and little difference from fresh water. At that time coincided with the holiday, I did not say the reason, just ask him to go to the network to find the answer.