Agricultural suitability assessment and rehabilitation of subsided coal mines: a case study of the Dawu coal mine in Jiangsu, Eastern China

Land-use suitability assessment crucial is for coal mine rehabilitation planning, especially for the coal mines that have undergone varying degrees of mining subsidence. In this study, we present an assessment on the suitability of crop cultivation in the Dawu coal mining district in NW Jiangsu province, Eastern China. Distribution of local land subsidence is delineated with topographic analysis, and the weight-of-evidence (WoE) suitability assessment has encompassed various factors including the conditions of soil (e.g., acidity and porosity), groundwater level, irrigation and drainage, terrain slope, and land pollution. Consequently, the Dawu district is divided into four categories (high, moderate, low, very-low) of agricultural suitability. Collaborating with the local government agencies (e.g., Land and Resources Bureau and Agriculture Bureau), a land-use plan is proposed. In the plan, the highly suitable areas for agriculture (and the surrounding moderately suitable areas) are allocated as farmlands, whilst the other moderately to lowly suitable areas are allocated as ecological zones for restoring the ecosystem and ecological diversity. The barely suitable areas with severe subsidence are allocated as artificial lakes, which also serve as reservoirs for farmland irrigation and drainage. To protect these new farmlands from soil erosion, infrastructure such as embankment and windbreak are also included in our rehabilitation plan. Our study highlights the necessity of forward planning in coal mine rehabilitation.

Soil bacterial communities and their associated functions for forest restoration on a limestone mine in northern Thailand

Opencast mining removes topsoil and associated bacterial communities that play crucial roles in soil ecosystem functioning. Understanding the community composition and functioning of these organisms may lead to improve mine-rehabilitation practices. We used a culture-dependent method, combined with Illumina sequencing, to compare the taxonomic richness and composition of living bacterial communities in opencast mine substrates and young mine-rehabilitation plots, with those of soil in adjacent remnant forest at a limestone mine in northern Thailand. We further investigated the effects of soil physico-chemical factors and ground-flora cover on the same. Although, loosened subsoil, brought in to initiate rehabilitation, improved water retention and facilitated plant re-establishment, it did not increase the population density of living microbes substantially within 9 months. Planted trees and sparse ground flora in young rehabilitation plots had not ameliorated the micro-habitat enough to change the taxonomic composition of the soil bacteria compared with non-rehabilitated mine sites. Viable microbes were significantly more abundant in forest soil than in mine substrates. The living bacterial community composition differed significantly, between the forest plots and both the mine and rehabilitation plots. Proteobacteria dominated in forest soil, whereas Firmicutes dominated in samples from both mine and rehabilitation plots. Although, several bacterial taxa could survive in the mine substrate, soil ecosystem functions were greatly reduced. Bacteria, capable of chitinolysis, aromatic compound degradation, ammonification and nitrate reduction were all absent or rare in the mine substrate. Functional redundancy of the bacterial communities in both mine substrate and young mine-rehabilitation soil was substantially reduced, compared with that of forest soil. Promoting the recovery of microbial biomass and functional diversity, early during mine rehabilitation, is recommended, to accelerate soil ecosystem restoration and support vegetation recovery. Moreover, if inoculation is included in mine rehabilitation programs, the genera: Bacillus, Streptomyces and Arthrobacter are likely to be of particular interest, since these genera can be cultivated easily and this study showed that they can survive under the extreme conditions that prevail on opencast mines.

Evaluation of Shrinkage and Desiccation Crack Propagation Patterns in Clays for the assessment of their suitability in landform rehabilitation

<p>The variation of water content has a significant effect on the engineering behaviour of clayey soils. This is in particular of high importance to infrastructure projects such as open pit mine rehabilitation. During the construction of open pit mines, the natural ground water level needs to be lowered for the feasibility of mining activities. This dewatering causes significant shrinkage and development of cracks amongst the deposits of cohesive soils. In order to design a rehabilitation plan, it is critical to investigate the shrinkage and desiccation cracks occurred within and around open pit mines as the result of dewatering. This study aims at identifying the shrinkage and crack development patterns using an experimental approach and utilizing image analysis. Three different types of clays were studied to this end. Physical properties including liquid limit, plastic limit and linear shrinkage of clays were determined. Soil samples were put in circular moulds of 150 mm diameter and 5 to 25 mm thickness. The variation of water content, while desiccating, was monitored. In addition, a digital camera was used to capture the initiation and propagation of desiccation cracks. Crack and shrinkage intensity factors were determined and analysed against various soil properties. The results obtained in this study could potentially lead to developing models to predict crack propagation patterns in various soils. This will ultimately result in more realistic and reliable future designs of infrastructures, such as mine rehabilitation.</p>

Field-Deployed Extruded Seed Pellets Show Promise for Perennial Grass Establishment in Arid Zone Mine Rehabilitation

Current methods of mine rehabilitation in the arid zone have a high failure rate at seedling emergence largely due to limited availability of topsoil and low water-holding capacity of alternative growth substrates such as mining overburden and tailings. Further, seedlings have consistently failed to emerge from seeds sown on the soil surface using traditional broadcasting methods. Seed pellets, formed by extruding soil mixtures and seeds into pellets, can potentially increase soil water uptake through enhanced soil-seed contact and thereby improve seedling emergence. We tested an extruded seed pelleting method in a three-factor field experiment (i.e., different pellet-soil mixtures, organic amendments, and simulated rainfall regimes) in north-western Australia. Given the observed lack of seedling emergence from broadcast seeds, the aims of the experiment were to assess: (i) the use of pellets to promote native seedling emergence and establishment and; (ii) the soil physico-chemical and microbiological changes that occur with this method of rehabilitation. The effects of pellet-soil mixtures, organic amendment, and rainfall regime on seedling emergence and survival of three native plant species suggest trade-offs among responses. Pellets made with a 1:1 blend of topsoil and a loamy-sand waste material had the highest seedling emergence, while 100% topsoil pellets had lower emergence probably because of hardsetting. Triodia pungens (a native grass) survived to the end of the experiment while Indigofera monophylla and Acacia inaequilatera (native shrubs) emerged but did not survive. Adding an organic amendment in the extruded pellet inhibited Triodia seedling emergence but increased soil microbial activity. Overall, extruded pellets made from a 1:1 blend showed promise for the establishment of Triodia seeds and beneficially, incorporates mine waste overburden and lesser amounts of topsoil. Further research is needed to improve pelleting production and to test the applicability of the method at scale, for different species and other ecosystem types.