According to Ben Urbonas, president of the Urban Watersheds Research Institute, these nutrient contaminants tend to be more of a problem in closed water systems,like lakes, where concentrations can build up.

VOA: standard.2010.08.04

The number of moles stays the same a closed systems, gas doesn't come out.

摩尔数保持不变,因为是闭系，气体不会跑出去。

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