Liming water and soil is a common way of reducing acidity level, which can be caused by many things, including Acid Rain. Liming agents contain large amounts limestone, a calcium rich mineral usually composed of calcium carbonate (chalk). The calcium acts as a base which counteracts with the acid and neutralizes it.
It is important to keep waterways alkaline (not acidic) to keep the inhabitants, particularly fish and aquatic plants, healthy. Studies show that fish are more likely to spawn in very alkaline water. It also reduces the toxicity of otherwise poisonous metals in the water.
Soil fertilizers contain a liming agent to keep the soil from poisoning plants and to add calcium to the soil for the plants to absorb.
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