Filtering, buffering and transformation

These soil functions have only been properly recognised in recent decades. They enable the soil to deal with harmful substances, preventing them from reaching groundwater or the food chain.

Substances can be mechanically filtered, absorbed or precipitated. Some organic substances could be decomposed or transformed. This soil function is crucial for groundwater protection, as about 65 percent of the European population depends on it as a main drinking water resource.

The soil buffers groundwater against chemical substances and temperature. Acid compounds react with and neutralise the basic cations of sodium, calcium, potassium and magnesium. The soil accumulates pollutants until the buffer capacity is reached.

In optimal conditions more than 99 percent of pesticides are transformed into non-toxic compounds. The remainder, however, is sufficient to threaten drinking water in areas with high inputs of pesticides. When the buffer capacity is exceeded, soil can become a source of chemicals that leaches pollutants into the groundwater.

Soil microorganisms are responsible for the decomposition of organic matter as well as the transformation of other substances, such as sulphates and nitrates.

Environmental changes may substantially reduce the capacity of the soil to withhold pollutants. Consequently, soil is a central factor in determining critical loads for natural ecosystems.