Kettle (landform)
If water in a kettle becomes acidic due to decomposing organic plant matter, it becomes a kettle bog. Otherwise, if underlying soils are lime-based, which has the effect of neutralizing the acidic conditions somewhat, it becomes a kettle peatland. Kettle bogs are closed ecosystems because they have no water source other than precipitation (rainfall and snowfall). Both acidic kettle bogs and fresh water kettles are important ecological niches for some symbiotic (mutually dependent) species of flora and fauna.