Next generation restoration metrics: Using soil eDNA bacterial community data to measure trajectories towards rehabilitation targets

Soil microbiota are fundamentally linked to the restoration of degraded ecosystems, as they are central to important ecological functions including the support of plant communities. High throughput sequencing of environmental DNA used to characterise soil microbiota offers promise to monitor ecological progress towards reference states. In post-mining rehabilitation, successful mine closure planning requires specific, measurable, achievable, relevant and time-bound (SMART) completion criteria, such as returning ecological communities to match a target level of similarity to reference sites. We analysed patterns of surface soil bacterial community similarity to reference ('rehabilitation trajectory') data from three long-term (> 25 year) post-mining rehabilitation chronosequence case studies from south-west Western Australia. We examined the influence of different ecological distance measures, sequence grouping approaches, and eliminating rare taxa on rehabilitation trajectories and predicted recovery times. We also explored the issue of spatial autocorrelation in our rehabilitation trajectory assessments and trialled a first-pass approach for correcting its undue influence. We found considerable variation in bacterial communities among reference sites within each case study minesite, providing valuable context for setting targets and evaluating recovery. Median Bray-Curtis similarities among references within each minesite ranged from 30-36%, based on amplicon sequence variant-level data. Median predicted times for rehabilitated sites to recover to these levels ranged from around 40 to over 100 years. We discuss strengths and limitations of the different approaches and offer recommendations to improve the robustness of this assessment method. Synthesis and applications. We demonstrate a proof-of-concept, complexity-reducing application of soil eDNA sequence-based surveys of bacterial communities in restoration chronosequence studies to quantitatively assess progress towards reference communities and corresponding rehabilitation targets. Our method provides a step towards developing microbiota-based SMART metrics for measuring rehabilitation success in post-mining, and potentially other, restoration contexts. Our approach enables prediction of recovery time, explicitly including uncertainty in assessments, and assists examination of potential barriers to ecological recovery, including biologically-associated variation in soil properties.

Study on the environmental state in Tan Rai bauxite mining area Bao Lam district, Lam Dong province

Planting trees in mining zones for post-mining rehabilitation is of great interest. Therefore, it is important and necessary to study the current state of the air, water, and soil environment in the mine exploited area. Therefore, this article studied and assessed the environmental state in Tan Rai bauxite mining area at Bao Lam district, Lam Dong province through the environmental components of air, water and soil, as a basis for selection of suitable crops for post-mining rehabilitation. The research result showed that the air quality in the bauxite mining area met the standard 3733/2002/QĐ-BYT. Almost monitoring parameters of surface water and wastewater is within the allowed threshold of Vietnam standards. However surface water had a sign of TSS and COD pollution (TSS and COD at the Danos stream after the received point of wastewater from No.6 tailing lake were 1.6 times and 1.07 times higher than those in standard). Ground water was polluted by Coliform (20-63,3 times over standard) and cation NH4+ (1.1-1.5 times over standard); Soil in exploiting region was strongly impacted, soil profile has changed, red-yellow soil dominated, soil fertility is pretty high, pHH20 and pHKC were from acid to neuter. This studied environment state is very suitable for planting pine and acacia. These results will be useful references, as a basis for orientation of post-mining rehabilitation. Việc trồng cây xanh để phục hồi các vùng mỏ sau khai thác hiện đang rất được quan tâm. Do vậy, việc nghiên cứu hiện trạng môi trường không khí, nước và đất ở vùng khai thác mỏ là rất quan trọng và cần thiết. Bài báo nghiên cứu đánh giá hiện trạng môi trường vùng khai thác mỏ Bauxite Tân Rai, huyện Bảo Lâm, tỉnh Lâm Đồng thông qua các thành phần môi trường không khí, nước, đất, làm cơ sở cho việc lựa chọn loại cây trồng phù hợp cho công tác phục hồi môi trường sau khai thác mỏ. Kết quả nghiên cứu cho thấy, chất lượng môi trường không khí tại vùng khai thác mỏ Bauxite đạt tiêu chuẩn 3733/2002/QĐ-BYT. Hầu hết các thông số quan trắc của nước mặt và nước thải đều nằm trong giới hạn cho phép theo tiêu chuẩn Việt Nam, tuy nhiên môi trường nước mặt cũng đang có dấu hiệu ô nhiễm TSS và COD (TSS và COD tại suối Danos phía dưới điểm tiếp nhận nước thải hồ quặng đuôi số 6 tương ứng gấp 1,6 lần và 1,07 lần so với tiêu chuẩn). Nước ngầm đang bị ô nhiễm Coliform (vượt quy chuẩn cho phép từ 20-63,3 lần) và NH4+ (vượt quy chuẩn cho phép từ 1,1-1,5 lần); Đất tại khu vực khai thác bị tác động mạnh mẽ, phẫu diện đất bị thay đổi, đất đỏ vàng chiếm ưu thế, đất có độ phì khá, pHH2O và pHKCl từ chua đến trung tính. Kết quả hiện trạng môi trường như vậy là phù hợp với trồng thông và keo. Những kết quả này là tài liệu tham khảo hữu ích, làm cơ sở cho việc định hướng phục hồi đất sau khai thác mỏ.

Microbial Biobanking Cyanobacteria-rich topsoil facilitates mine rehabilitation

Mining rehabilitation requires key solutions to complex issues relating to ecosystem function. In arid landscapes, the removal or disturbance of topsoil incorporating soil microbial communities can result in a shift in ecosystem function. Soil surfaces in arid regions are protected by biocrusts that regulate soil moisture, sequester carbon and fix significant quantities of atmospheric nitrogen. Cyanobacteria often dominate these bioactive surfaces and work as ecosystem engineers in that they are in sufficiently large quantities they initiate biocrust establishment and facilitate soil surface stabilisation. Cyanobacterial exopolymeric secretions form cohesive and protective layers at the soil surface that minimise wind erosion. This research encompassed soil microbial community profiling (using a polyphasic approach) with a focus on biobanking topsoil for rehabilitation purposes. The research was in collaboration with Iluka Resources at Jacinth–Ambrosia (J–A) mineral sand mine located in a semi-arid chenopod shrubland in southern Australia. At J–A diverse biocrusts included a significant representation of cyanobacteria, lichens and mosses that inhabited nearly half of all soil surfaces. Cyanobacterial community structure at J–A was comprised of a variety of species having a range of attributes that contributed to their resilience and survival in an arid environment. Stockpiling from shallow scrapings and storage at low profiles appeared beneficial in microbial biobanking cyanobacterial inoculum that would facilitate recovery over time. These studies have provided information for the establishment of a monitoring program that assesses the re-establishment of biocrusts following mining. Following soil stockpiling that occurred during the mining process, cyanobacterial taxa recovered at different rates. Cyanobacterial strategies central to survival include exopolymeric production, spectral adaptation, nitrogen fixation and motility. Biocrust re-establishment during mining rehabilitation relies on the role of cyanobacteria as a means of early soil stabilisation. Provided there is adequate cyanobacterial inoculum in the topsoil stockpiles their growth and the subsequent crust formation should take place largely unassisted. Ongoing monitoring of biocrust recovery is important as it provides an effective means of measuring important soil restoration processes.