在二十世纪六七十年代，铅沉积就在土壤和雪中不断累积，这主要是美国的含铅汽油排放的后果。
Lead deposits, which accumulated in soil and snow during the 1960s and '70s, were primarily the result of leaded gasoline emissions originating in the United States.
一旦完成了这个，河流带来的淤泥会沉积在此处，回报是丰厚的：产量是被雨水滋养的土壤的四到五倍。
Once this was done and the silt carried down by the rivers was planted, the rewards were rich: four to five times what rain-fed earth would produce.
该小组正在调查碳酸钙矿物中的元素，这些碳酸钙矿物沉积于距今2至170万年的湖内部及周边的淤泥和土壤中。
The team is investigating elements in the mineral calcium carbonate, which were deposited in the mud and soil in and around a lake between two and 1.7 million years ago.
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