Anthropedogenesis in coal mine overburden; the need for a comprehensive, fundamental biogeochemical approach.

The primary solid waste product of surface coal mining is overburden (also known as spoil), the material that is moved to access the underlying coal seams. Once removed, this material is generally stored in large (>100 m in height) piles until it is re-contoured in preparation for post-mining rehabilitation, often remaining there for decades. Under ideal conditions, these new landforms would have at least 30 cm veneer of topsoil applied as a growth medium for plants. However, topsoil deficit conditions are common in coal mines, so the forced use of overburden that possess poor chemical, biological, and physical properties as the growth medium hinders plant establishment. To reach the characteristics of a functional soil that can support plants, it is necessary to dramatically improve spoil quality, i.e., accelerate pedogenesis, as an integral part of the rehabilitation process. For decades, overburden rehabilitation has often taken the traditional approach of using the agricultural practice of fertilizer application or focusing primarily on the types of plants used to stabilize these young landforms. In contrast, success improved when the rehabilitation procedures employed a more holistic approach to establishing self-sustaining plant-soil ecosystems. Here we identify constraints that impede spoil-to-soil transformation, discuss the global treatment options practiced post-mining for coal spoils, and describe how a comprehensive biogeochemical approach can be implemented in spoil reclamation processes going forward. Integrating the revitalization of soil organisms, reclamation of soil chemistry, soil structure, and landform into rehabilitation procedures can accelerate the transformation of coal spoils to functional soils. We believe that a shift in the nature of the question from "what chemicals and seeds should we add to coal spoil during site rehabilitation?" to something fundamentally more specific: "How do we induce pedogenic functions in coal spoils to develop fertile soils?" is needed.