Chemical properties of the upper tailings beneath biotic crusts

Abstract Four types of vascular plant communities were established on a wasteland of the copper mined tailings located in Tongling, East China. Biotic crusts, as an earlier stage of primary succession or a ground-layer within plant communities, became widely distributed on the surface of the tailings wasteland. The major aim of this study is to investigate the relationship between biotic crusts and the chemical properties of the upper tailings. According to the difference in vascular plant communities, authors divided the tailings wasteland into six types of areas, i.e., Hippochaete ramosissimum + Zoysia sinica community area (Type 1), Imperata cylindrica community area (Type 2), Z. sinica community area (Type 3), Cynodon dactylon community area (Type 4), biotic crust area (no vascular plants, Type 5), and bare tailings area (Type 6). Each of Types 1–4 was again divided into subtype with biotic crusts and subtype without biotic crusts. Eighty samples of the upper tailings (area: 20 cm × 20 cm, depth: 0–3 cm) were collected. Then, pH, electrical conductivity, organic matter, total nitrogen, available phosphorus, available potassium, and water content were determined. Results showed that the bare tailings were very deficient in nutrients. Plant communities growing on the tailings wasteland, especially plant communities with biotic crusts, could significantly improve the water content and chemical properties of the upper tailings. Organic matter, total nitrogen, extractable potassium, water-soluble potassium, electrical conductivity, and water content in the upper tailings with biotic crusts (Subtypes 1.1, 2.1, 3.1 and 4.1) were 1.9–3.6, 3.3–10.7, 2.0–4.4, 2.4–5.9, 2.3–10.9 and 3.7–10.5 times that of the bare tailings, respectively. Compared to the bare tailings, pH values of the upper tailings of Subtypes 1.1, 2.1, 3.1 and 4.1 depressed 0.27–0.74 units. Compared to the four subtypes with biotic crusts, the effect of four subtypes without biotic crusts from the same type of vascular plant communities on the water content and chemical properties of the upper tailings was less. A comparison between Type 5 and Type 6 also indicated that biotic crusts could significantly improve the water content and chemical properties of the upper tailings. The contents of organic matter, total nitrogen, extractable potassium, water-soluble potassium, and water in the upper tailings of the former were 1.5, 2.0, 2.1, 2.4 and 5.0 times that of the later, respectively. Among four types of vascular plant communities, H. ramosissimum + Z. sinica community was the best and the C. dactylon community was the least in improving water content and chemical properties of the upper tailings. This investigation also indicated that the influence of biotic crusts on available phosphorus of the upper tailings was not significant. Increase of water content in the upper tailings caused by biotic crusts played a very important role in improving chemical properties of the upper tailings.