Recreation of stable land forms and restoring soil productivity are the first tasks of ecological restoration in heavily degraded sites. In previous posts we covered the importance of functional land forms and the role of living organisms in soil formation. In this post we focus on the specifics of soil formation in post-mining sites, thanks to our guest blogger Prof. Jan Frouz.
Post mining substrates differ remarkably from ordinary soils. Assuming that the site is not severely contaminated by toxic or hydrophobic compounds (which may be the case in many post mining soils), the soil texture is the main factor affecting soil development in post-mining sites.
Post-mining soils lack structure due to the absence of roots and soil fauna. As vegetation develops on post-mining soils, and if suitable climatic conditions exist, this process can be rather fast, regardless of whether the plants were established naturally or were planted.
As roots penetrate the soil. litter accumulates on the surface and is processed by the soil biota. While microorganisms are chiefly responsible for the decomposition of litter, invertebrate organisms living in the soil fragment the litter and or mix it with the mineral soil (bioturbation). Earthworms play double role by supporting the formation of soil aggregates and by mixing the soil layers. [See a cool video on earthworms at work in a laboratory setting Video].
The degree of mixing depends on the properties of the litter: it is higher in grass communities and broad-leaved forests than in coniferous, where litter tends to accumulate. However the quality of the litter is just one factor. Equally important is the colonisation of the soils by macro-fauna and their soil mixing activity – bioturbation.
The development of vegetation is usually faster in reclaimed sites than in areas with natural regrowth. However, the difference in vegetation cover is most pronounced in the first 15-20 years of ecosystem development. Later, the differences diminish, and among older sites it is difficult to distinguish between reclaimed and spontaneously developed ones.
The same pattern applies to soil development, which is typically faster in reclaimed sites but in older sites, the differences fade out. Under suitable conditions, an approximately 10 cm deep A horizon can be well structured within 30-40 years, even in soils developing in situ by natural processes.
Post mining soils are typically less saturated with nutrients than the surrounding landscape, which is why plants grow less vigourously there. In the same time poor soils favour the occurrence of many rare and endangered plant species and stimulates the diversity of the plant community.
See cool video explaining why Poor often means Rich in ecology
This article was kindly written by Prof. Jan Frouz, Director of the Environment Center of Charles University, Prague
More about soil formation in post mining sites in his book Soil Biota and Ecosystem Development in Post Mining Sites (CRC Press 2013).