These ions are usually not free to migrate in the soil because they are bound to the negatively charged surface of immobile soil particles. These particles are negative because of the silicates on the surface of clays and the organic acids on particles of organic matter. The cation-exchange capacity is the ability of the soil to bind to the positively charged ions but acid rain depletes this capacity. Thus, in these two ways, acid rain can unlock the acidity, nutrients and toxic metals that are bound in the soil. The toxic metals leached from the soils are very important to the welfare of green plants and the aquatic ecosystem.
Acid rain can also increase the weathering of silicate minerals in soils.
This leads to a loss of mineral structure and possibly reduced fertility. Not all soils are subject to the effects of acid rain. In fact, lime is the best known buffer and consequently, is being used increasingly by farmers and foresters. The buffering capacity depends mainly on the underlying bedrock and the human use and management of the soil. The effects of acid rain on forests are devastating.