Last post of the series dedicated to soils of post mining sites. What are the most commonly used techniques for soil restoration at post mining sites and how do they work? Soils are a valuable resource and their protection in the course of mining and storage is extremely important to avoid irreversible damage. Soil management and replacement with exogenous soil is also very expensive. That is why the first priority should be to conserve the existing soil in the best possible condition.
The most common reclamation techniques include leveling of the surface by earth moving machinery, the application of soil or soil substitutes and the planting of seedlings or drilled seeds. The aim of leveling is to make the site more homogeneous in terms of physical and chemical properties, and to enable the use of machinery after reclamation (e.g. for arable farming).
In many cases, post-mining sites are heaped in such a way that results in a wavelike appearance. These rolling waves promote spatial variation in the physical and chemical properties that may be beneficial for spontaneous establishment of vegetation, especially trees and shrubs (for example, seeds of airborne species can be trapped on the leeward side of these waves). Variety and differentiation can also promote specific micro sites with faster soil development. On the other hand, leveling causes soil compaction, which tends to stimulate grasses and suppresses the growth of trees.
On the photo below one can see graded overburden covered by grasses in distance there is ungraded spoil covered by trees, both parts are unreclaimed and about the same age (10 years), nice example how grading and associated compaction promote grasses, while loose substrate promote trees.
The planting of seeds or seedlings is a basic restoration technique that speeds up succession and soil development. Planted vegetation and the quality of plant litter are of key importance to soil development, as explained in an earlier post.
The application of topsoil substitutes, or even more complex covers consisting of several layers, is a very complex reclamation approach. This operation instantly improves soil conditions and allows for rapid establishment of highly productive vegetation. It is irreplaceable in restoring agricultural land or in reclaiming extreme, specific toxic substrates. On the down side, topsoil spreading is a costly operation, and besides the clear advantages mentioned above, it may also bring some disadvantages; soil spreading may promote soil compaction and the release of nutrients.
Compaction may also negatively affect the rooting of plants, especially trees. The release of nutrients may support grasses and promote the competition of grasses over trees and decrease plant diversity, which can lead to many rare species being lost as they cannot compete with most fast-growing common species.
Furthermore, the stockpiling of topsoil causes the formation of anaerobic (low or lack of oxygen) conditions in the pile, which may lead to eradication of the existing seed bank, soil fauna and changes in the soil microbial community.
Most restoration techniques aim to restore the above-ground biota. Soil-related restoration practices mainly focus on improving the physical and chemical conditions of the initial soils. The interesting question from a practitioner’s point of view is how to modify the restoration techniques to support soil biota recovery, in order to promote faster restoration of soil biological functions and from there – the ecosystem.
his article was kindly written by Prof. Jan Frouz, Director of the Environment Center of Charles University, PragueMore about soil formation in post mining sites in his book Soil Biota and Ecosystem Development in Post Mining Sites (CRC Press 2013).