Soil and vegetation development along a 10-year restoration chronosequence in tailing dams in the Xiaoqinling gold region of Central China

Highlights

• Soil organic carbon and total nitrogen increased during the restoration period.

• Carbon sequestration was restricted by nitrogen in long-term natural restoration.

• Main species of plant community changed from annual into perennial over time.

• Plant productivity was positively related with soil nutrient content.

Abstract

Gold mining has increased sharply in response to global demand. Gold extraction usually causes the formation of tailing dams, in which organic matter and microbial activity decrease, and this consequently constrains plant growth. However, a full understanding of plant-soil interaction and plant community development in terms of natural restoration of gold mine tailing dam has not yet been developed. Three tailing dams, which had been naturally restored for 2 (R2), 5 (R5), and 10 (R10) years in the Xiaoqinlin gold region of Central China, were chosen to explore soil and plant community development in August, 2015. This study showed that soil bulk density and pH value were the lowest, whereas soil organic carbon, total nitrogen, microbial biomass carbon and nitrogen were the highest in the R10 tailing dam across two soil depths (0–10 cm and 10–20 cm). Soil organic carbon, total nitrogen, microbial biomass carbon and nitrogen decreased with soil depth across the restoration periods. The highest ratio of soil organic carbon to total nitrogen in the R10 tailing dam suggests that the rate of soil organic carbon accumulation may be restricted by the total nitrogen content in the long-term. Restoration stimulated plant community diversity and productivity, due to increment in soil nutrient content and microbial biomass carbon and nitrogen. The various ratios of root biomass to aboveground plant biomass among three tailing dams were caused by the shifting of the plant community composition from annual to perennial varietals. The mechanism by which plant-soil interaction and plant community composition change over time can be used to guide restoration programs in tailing dams in Central China.

Introduction

Gold mining has been expanding in recent years in response to increasing gold prices and worldwide demand (Alvarezberríos and Aide, 2015; Chainani, 2016). Gold ore is changed from a stone-like consistency into a slurry with the addition of vast amounts water using a ball mill instrument, or it is disaggregated under high pressure by water. Then, gold-bearing slurry is divided into gold particles and mine tailings in a sluice box (Román-Dañobeytia et al., 2015). Gold mining often renders land incapable of certain ecological functions, such as having enough nutrient supply for plant growth, and leaves a tailing dam with poor soil-forming materials and no vegetation (Herath et al., 2009; Keskin and Makineci, 2009; Alday et al., 2012; Albert, 2015; Kumar et al., 2015). Ecological restoration of degraded, bare tailing dams has become a major environmental issue, as mining and environmental enterprises seek to reduce the impact of mining on the degradation of soil and on biodiversity loss (Šourková et al., 2005a; Ilunga et al., 2015).

Gold mining affects soil quality, including the soil's physical structure (bulk density, particle size distribution), nutrient availability (soil organic carbon, total nitrogen), microbial activity (soil microbial biomass), and pH (Albert, 2015; Masto et al., 2015). After mining, the organic carbon pool in the soil can decrease by 70–81% due to increased sand proportion and deficiency in cation exchange capacity (Akala and Lal, 2001; Román-Dañobeytia et al., 2015). A larger proportion of sand in tailing soils may intensify water erosion during a rainy season, and strengthen wind erosion during a dry season (Ilunga et al., 2015; Pourret et al., 2015). The disproportionate sandiness of the soil texture causes low soil fertility, which is rendered insufficient to support normal plant growth. In addition, soil microbial biomass was found to decrease in tailing dams in Peru (Román-Dañobeytia et al., 2015) and French Guiana (Schimann et al., 2012) due to lower soil nutrient conditions and lower plant productivity. Therefore, understanding how soil's physical, chemical, and microbial properties change during restoration is critical for guiding the restoration of mined land (Abreu et al., 2009; Ronan et al., 2010; Alday et al., 2012).

Plant primary succession is a significant source of ideas for planning restoration programs, and identifying appropriate species suitable for revegetating tailing dams is a main goal of restoration management (Porqueddu et al., 2016). Natural recovery provides valuable lessons for understanding the temporal dynamics of soil and plants through long-term observation of severely disturbed habitats (Walker and del Moral, 2009). Soil quality and vegetation compositional changes depend on restoration duration time, and the response of vegetation can induce soil development. Increasing plant community diversity in mined areas has been found to be beneficial to restoring soil (Isermann, 2005; Alday et al., 2012). However, other study shows that plant diversity has no relationship with soil properties in a sequence of restoration projects along embankments (Li et al., 2016). More attention should be paid to the process of plant and soil development over the course of the restoration of bare soils to identify plant-soil interactions (Kardol and Wardle, 2010; Ilunga et al., 2015). The significant relationship between soil properties and plant functional traits suggests that overall plant–soil feedback effects should be studied to determine their suitability for enhancing ecological restoration (De Deyn et al., 2008; Putten et al., 2013; Ilunga et al., 2015). Natural restorations have been studied in clay wastes (Roberts et al., 1980), abandoned fields (Knops and Tilman, 2000), coal wastes (Alday et al., 2012; Kumar et al., 2015), forests (Matlack, 2009), inland drift sand dumps (De Kovel et al., 2000), and urban sites (Schadek et al., 2009). However, few attempts have been made to study the primary succession of natural restorations in gold mined tailing dams.

China has been the largest gold producing country since 2007, accounting for about 15% of global gold production (Chainani, 2016). The Xiaoqinling region, as the second largest gold mining area in China, has experienced a rapid expansion and an increased number of tailing dams since the early 1990s (Zhang et al., 2014). The ‘space-for-time’ method often offers valuable insights into soil and vegetation changes during restoration (Brantley, 2008; Chaudhuri et al., 2013; Kumar et al., 2015). The aims of this research were to examine the changes in the soil's physical, chemical, and microbial properties, and in the plant community structure in three gold mine tailing dams with an age sequence of 2-(R2), 5-(R5), and 10-(R10)-year primary succession, and discussed potential relationships between soil and plant properties.