Assessing the vegetation restoration potential on coal mine waste (Case study: Karmozd Savadkoh mines, Mazandaran province)

Mining is traditionally regarded as the world’s oldest and the most important activity after agriculture. Despite being an important economic activity, mining causes substantial damage to the environment worldwide. The environmental impact of mining includes erosion, formation of sinkholes, dust, noise and water pollution, vegetation degradation, loss of local biodiversity, and contamination of soil, groundwater, and surface water by chemicals from mining processes. Mine reclamation is the process of restoring land that has been mined to a natural or economically usable state. Establishment of a vegetation cover is essential to stabilize the bare area and to minimize the pollution problem. Mine restoration can aid in maintaining native wildlife populations while providing other valuable ecosystem services, such as erosion control, carbon sequestration, wood production, water-quality improvement, and watershed protection. Area under mining are often characterized by high bulk density, low pH, low nutrient availability, poor structure, low water holding capacity, and low biomass productivity. Basically, there are two approaches to reclamation or restoration of a disturbed site: (1) allowing spontaneous succession or (2) using technical reclamation with sowing or planting target species, accompanied by restoration or improvement of site conditions. There is also a third approach when spontaneous (natural) succession is reasonably directed with the aim to reach a target community. However, until now most restoration projects have relied on technical measures more than on spontaneous natural processes. Main technical methods include the use of mycorrhiza, remediation, fly ash, hydroseeding, top soil, and compost.
The main aim of mine restoration is the permanent establishment of vegetation and soil quality improvement in order to increase the ecosystem function. In the first step it is very important to identify the early successional species which can colonize on coal wastes. Spoil heaps after coal mining are an important component of the landscape in several parts of Alborz mountains, where lignite coal is mined deeply or in open-cast mining. Therefore, we studied the potential of plant establishment on spoil heaps and compared the natural vegetation recovery on these heaps with nearby rangelands.
This study was carried out in Karmozd area in Savadkoh county, Mazandaran provice (52º57'38" to 52º58'12" E and 36º05'57" to 36º06'53" N). This area has been one of the most important mining areas in central Alborz mountains. The climate of the area is cold humid (536.5 mm annual rainfall, 10.9 ◦C annual average temperature). Three spoil heaps were selected regarding age and the amount of spoil. Spoil heap 1 was the oldest and biggest one while spoil heap 3 was the youngest. Vegetation was samples in all three heaps and the rangeland nearby. Sampling was done along transects using 138 plots of 1 m2. The cover (%) of each species was estimated in each plot. Data were transformed using ASIN(SQRT(x/100)) and then a combination of analysis of variance and t-test were performed for individual species response. Also, we compared the species diversity and richness indices among these sites.
A total of 43 species from 20 families were identified in study area. Gramineae, Asteraceae and Lamiaceae were the most common plants. About 60% of species were perennials. In spoil heap 1 there were 35 species of which 22 species were unique (Table 1). Greater number of annuals and prennials were found in spoil heap 1. It seems that the seeds of 22 unique species were dispersed from surrounding area to spoil heap 1. The germination and establishment of new arrived seeds in spoil heap 1 is possible as this spoil heap is in the vicinity of river and also it had been longer existed than other heaps. The pioneer species in spoil heap 1 are those reported in other studies worldwide. There were 10 species common between spoil heaps and nearby rangelands. Alyssum linifolium, Artemisia scoparia, Bromus briziformis, Colutea persica, ¡Hordeum vulgare and Rumex acetosella were found only in spoil heap 1 and spoil heap 2. Artemisia scoparia was the dominant species in rangeland. In spoil heap 1 the dominant species were Hordeum vulgare¡Glaucium fimbrilligerum and Artemisia scoparia. The common species in spoil heap 2 were Glaucium fimbrilligerum, Melica persica and Artemisia scoparia while Kochia prostrata was the main dominant species in spoil heap 3. Greater EC was found in soil heap 3 and this is the main reason for the establishment of K. prostrata.
Spoil heap 3 significantly had the least species richness and diversity (Fig. 1). There was no significant differences among spoil heap 1, spoil heap 2 and rangeland regarding species diversity while species richness was significantly greater in rangeland than that in spoil heap 1 and spoil heap 2. The greater values of species richness and diversity indices were expected for rangeland as it has a thin layer of developed soil. The soil heap 3 is the youngest coal waste, so this can be the main reason for having less species richness and diversity indices.
The harsh environmental situation made this heap only suitable for K. prostrata establishment. Artemisia scoparia, Bromus briziformis and Stachys laxa significantly showed greater cover values in rangeland than that in spoil heaps. In contrast, greater cover (%) of Melica persica and Hordeum vulgare were found significantly in spoil heaps than that in rangeland. The greatest cover (%) of annuals was found in soil heap 1 and 2 while spoil heap 3 had the least cover (%) of annuals. The maximum and minimum cover (%) of perennials was found in rangeland and spoil heap 3, respectively.
Native species are recommended for long-term restoration of mine wastes as they have more potential for establishment. The establishment of early successional species is related to their seed dispersal from surrounding area. Thereafter, their potential for producing persistent seed bank is very important. The results of this study showed that there is a potential of early successional species to establish on coal wastes. The amount of natural colonization was different among spoil heaps and we found this was related to spoil heap area and age after abandonment.