# Soil Quality in Rehabilitated Coal Mining Areas
###### Abstract  
In arid and semiarid environments, the sustainability of rehabilitation actions in degraded areas is a matter of concern. It has not been extensively researched. In a Spanish coal mining area, new soils to support vegetation were created (Technosols) using mine spoils and different organic wastes. Eight years after the establishment of rehabilitation measures, the quality of the works was assessed. Soil properties (organic matter, microbial biomass, structural stability and porosity) were evaluated as quality indicators. thermogravimetric analysis differentiated between organic-C and other mineral-C sources. The degree of aggregation and the presence of interconnected pores and organic matter with different degrees of decomposition were identified by micromorphological techniques. Microbial biomass and water-stable aggregates satisfactorily traced the early pedogenesis of mine spoils, resulting in good indicators of the quality of new Technosols. Substrates prepared with sludges promoted soil development better than those created using pig slurries, primarily by favoring a higher porosity and organic matter content. Despite that, both treatments demonstrated, after 8 years, their ability to support the ecosystem services of biomass production, carbon sequestration, and organic matter recycling they were planned for, therefore ensuring their sustainability. aggregate stability; microbial biomass; micromorphology; organic matter; pig slurry; porosity; sewage sludge; soil erosion; thermogravimetry +
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parent materials, is of interest [6], also because the bioavailability of heavy metals they might contain will be reduced in basic pH soils. Furthermore, farmers in these areas can develop an important animal-rearing activity, as is the case in the NE of Spain, where waste management is a critical environmental issue [7]. Sewage sludge is widely available and linked to wastewater treatment plants [8]. Thus, mine rehabilitation arises as an additional alternative use for sludge in the context of the need for recirculating nutrients from these organic residues [9]. The pedagenesis process in Technosols requires the enhancement of soil fertility, vegetation establishment and biomass productivity [10]. Plant biomass production also contributes to an additional organic carbon increase in the soil [11; 12; 13]. The quality of created Technosols and the success of different rehabilitation techniques should be evaluated through indicators [14; 15]. Soil organic carbon (SOC) content is one of the best indicators of soil quality. However, in coal mining areas, SOC must be firstly differentiated from other carbon types that are also present, such as the one coming from the coal itself or as the inorganic carbon contained in carbonates [16]. In fact, environmental services provided by the soil depend on the high levels of quality descriptors related to soil organic matter (SOM), such as total porosity and aggregate stability [17]. Thus, soil structure properties can be used as some of the indicators of the success of the rehabilitation process. The micromorphology of undisturbed soil samples, in particular those assessing structure and porosity, is used for such studies. Microscopic techniques allow for the observation of soil organization [18] and the identification of its constituents, among which pores and aggregates stand out [19]. Pores have been defined by [PERSON] [20] as soil spaces (soil atmosphere) filled or partially filled with a water solution. Aggregates, from the point of view of micromorphology, have been defined as groups of different soil particles. Differences in structural stability between similar textured soils are also explained by their organic matter content [21]. As a result, soils offer a differential resistance to particle dispersion or implosion of aggregates, due to the impact of raindrops or slaking [22]. Runoff and erosion of dispersed materials cause soil degradation, so it is important to prevent them in the rehabilitation process [23].