Open Cut » Environment
The use of reference sites for establishing closure criteria in areas disturbed by mining activities is accepted by regulators across Australia. However, this approach often creates impossible or unrealistic targets for miners seeking to close rehabilitated lands. In order to increase stakeholder certainty, transparency, and environmental performance in mine closure, this project looked at moving away from the use of reference sites towards an approach that considers the variability of the system under study. Using established multivariate statistical techniques, the model compares the biophysical criteria in rehabilitated sites to the overall spatial and temporal biophysical variability of the local environment (hereafter referred to as 'system variability'), rather than specific reference sites. The purpose of this project was to test the system variability approach as a potential closure technique ('proof-of-concept').
This project complements and extends existing project outcomes in C8030, C9068, C20017 and C23030 by combining river assessment techniques applied to diversions for the purposes of closure, which can also be applied to terrestrial ecosystems. This project was field-based, and also used artificial habitat to evaluate microbial colonisation. Site descriptions and descriptions of biophysical variables 'set the stage' for the difficulty of using reference sites in catchment and river restoration: sites within rivers were different, and seasonality drove differences in biophysical variables within sites over time.
River sites (32 total) on the Goulburn River and Bowman's Creek, New South Wales were sampled multiple times during an annual hydroperiod (2016-2017) for biophysical characteristics to test the system variability approach. Characteristics and potential management considerations for each individual study site over time are described.
As part of the system variability approach, the project also explored the use of pelagic and benthic microbes (Archaea, Bacteria) as indicators of river condition. While microbe assemblages at sites could demonstrate 'trajectory' towards the variability of the rest of the river, microbial function was not assessed.
In fulfilment of Objective 2 improvements to river monitoring protocols and sampling approaches have been provided throughout the report. A formal review of existing monitoring at both sites has not been undertaken as these are generally mandated by compliance requirements.
The system variability approach to closure allows companies to develop multiple lines of evidence that sites are being rehabilitated. This is an improvement on the reference site approach because it does not require pre-impact data and allows companies to track the progress of their sites over time. The approach also allows greater understanding of the overall system under study and is therefore more scientifically robust and transparent, providing a stronger case for closure to stakeholders.
The model clearly accounted for natural ecosystem temporal and spatial variability. However, in some cases visual portrayal was not useful because 'flattening' multidimensional ordinations for 2-dimensional viewing did not accurately portray differences among a priori groups. Nevertheless, the statistics are used in decision-making for closure and ordinations are for visual inspection only.
In Objective 4 artificial colonization media ('coupons') to two river sites (Ulan Creek, Goulburn River) was introduced and characterized microbial assemblages on coupons over time. Microbial assemblages on coupons at both sites were composed of 'core' taxa and 'peripheral taxa'. Microbial assemblages were different within the 50 m transect, indicating that microhabitat variables likely influenced assemblage composition. This result supports experimental design for the system variability approach, where homogenised sediments were within the 50 m transect to override (as much as possible) microhabitat differences.
In order to develop the most scientifically sound approach to the system variability model of closure, it is recommended stakeholders initially consult with a scientist who specialises in the system under study. The approach can be further refined to become more 'user friendly,' measuring only the most important indicators for ongoing monitoring. It is also recommended that ongoing data analysis occurs in conjunction with scientific consultation and all data is retained and methods documented to reduce bias.
The intensive nature of the data collection required for the systems variability approach revealed insights into the functioning of the rivers and potential challenges this may pose for companies, which have been detailed throughout the report.
In summary, this approach has merit as a closure technique, and can be further refined and extended to other taxa of interest. Due to the systematic study of the biophysical variables, combined with cutting-edge genomic techniques, this project has provided companies with a deeper understanding of processes occurring in diversions and mine-impacted catchments.