Mine Restoration

Background, principles and context for risk-based completion criteria and monitoring (1 OF 7) , To view full report: Click here THE COMPLETION CRITERIA FRAMEWORK 2 A framework for developing mine-site completion criteria in Western Australia 2 3 CHAPTER 3 Background, principles and context for risk-based completion criteria and monitoring This section includes a review of current guidance, policy and scientific literature relating to completion criteria and associated monitoring. It focusses particularly on criteria and attributes relating directly, or indirectly, to biological elements in rehabilitation sites. It also considers methodologies for the selection of post-mined land uses (PMLUs), the consideration of offsets and application of risk assessment in identifying closure risk and in directing and prioritising rehabilitation effort. When discussing specific aspects and attributes, the study focusses on biophysical and environmental elements, but indicates to other elements where appropriate. This focus reflects the scope of the report, but also that most mine closure plans include environmental requirements. PMLUs that do not include environmental objectives will require consideration of other aspects and monitoring approaches (e.g. social or economic metrics). Nonetheless, the principals for completion criteria development, discussion of risk and approaches to selecting PMLUs should be relevant to all mines. The importance of completion criteria in the mining life-cycle are well recognised in numerous international and national handbooks and guidelines for mine closure planning. While there is no international or national standard for the development of completion criteria (Blommerde et al. 2015), more than 30 documents with guidance for the establishment of completion criteria -from jurisdictions across Australia (state and federal), Canada (provincial and federal), Peru, Chile, South Africa, Finland, Asia Pacific Economic Cooperation (APEC) and states within the United States of America -were identified. The most relevant of these are reviewed below. Documents from NSW (TIRE 2013) and Queensland (DEHP 2014) provide information specific to the mine rehabilitation and closure requirements of their jurisdictions, with the most detailed guidance on objectives and criteria for closure being provided by DEHP (2014). Rather than provide substantial detailed information on criteria development, the NSW guidance relies substantially on the Strategic Framework for Mine Closure (ANZMEC & MCA 2000) as a recommended source. The nationally focussed Australia and New Zealand Minerals and Energy Council/ Minerals Council of Australia Strategic Framework (ANZMEC & MCA 2000) is an industry document, which promotes establishment of completion criteria that are developed and agreed with stakeholders. It states that, where possible, completion criteria should be quantitative and capable of objective verification, and identifies the importance of developing performance indicators to measure progress in meeting the completion criteriawhich is distinct from, but supplementary to, monitoring to assess completion criteria. The Leading Practice Sustainable Development Program (LPSDP) for the mining industry handbook series includes handbooks devoted to mine closure (LPSDP 2016d), mine rehabilitation (LPSDP 2016e), biodiversity management (LPSDP 2016a) and evaluating performance: monitoring and auditing (LPSDP 2016b), among others. This excellent series, which aims to encourage best practice sustainable mining both in Australia and overseas, was developed by Australian Government

The growing global demand for minerals presents economic opportunities for countries such as the Philippines but also raises concerns about the impacts of mineral extraction on local communities and ecosystem services. This study explores an interdisciplinary community engagement process informing mine rehabilitation in the Philippines, framed through an ecosystem services lens. As part of the PROMT (Philippines Remediation of Mine Tailings) project, we conducted an initial participatory workshop at the Padcal Mine site, engaging Indigenous communities to assess local perspectives on ecosystem services and the impacts of mining activities. Through video presentations, a questionnaire, and focus groups, we found that 88% of participants understood the concept of ecosystem services after viewing an introductory video, while 62% believed mining negatively affected ecosystem services. Interestingly, 65% felt that rehabilitated mines could provide future ecosystem services, such as agriculture or ecotourism. Gender differences were evident, with women perceiving more significant mining impacts but being more optimistic about the rehabilitation potential. This underscores the importance of inclusive engagement approaches. The ecosystem services framework effectively bridges ecological knowledge with community priorities and tangible benefits, promoting social acceptance of mine rehabilitation. This interdisciplinary approach, particularly the integration of Indigenous perspectives, remains underused in mining contexts. Our community-based participatory methodology provides guidance for balancing diverse socioeconomic and environmental considerations.

An analysis of the effects of topsoil handling and storage methods was undertaken to optimize the potential rehabilitation of southwest Western Australian Banksia woodland species present before site disturbance. An increase in the depth of topsoil stripped from the Banksia woodland, from 10 to 30 cm, correlated to decreasing seedling recruitment from the soil seedbank by a factor of three following in situ respreading in an area to be restored. There was no significant difference in total seedling recruitment in situ at two depths of spread, 10 cm and 30 cm. These results concur with an ex situ trial on the effects of depth of seed burial on seedling recruitment that showed most species failed to emerge from depths greater than 2 cm. In situ stockpiling of the woodland topsoil for 1 or 3 years demonstrated a substantial and significant decline in seedling recruitment to 54% and 34% of the recruitment achieved in fresh topsoil, respectively. Stripping and spreading during winter substantially depressed seedling recruitment, compared with autumn operations, as did in situ stockpiling followed by spreading in the wet season, or stockpiling in winter followed by spreading in spring. No loss in total seedling recruitment occurred when replaced topsoil and subsoil were ripped to 80 cm following spreading of topsoil in sites to be restored. Conclusions from this study are that (1) topsoil provides a useful source of seeds for rehabilitation of Banksia woodland communities in the southwest of Western Australia, (2) correct handling of the topsoil, stripped and replaced fresh and dry (autumn direct return) to the maximum depths of 10 cm, can be used to optimize revegetation of species-rich plant communities with this type of seedbank, and (3) ripping of topsoil and subsoil to ease compaction of newly restored soils does not diminish the recruitment potential of the soil seedbank in the replaced topsoil.

Lack of organic matter inputs into a pit lake inhibits ecological development. Connecting a river to a pit lake should add organic matter to the lake. Sedimentation traps and sediment sampling was undertaken in two co-occurring pit lakes: one with river flowthrough (Lake Kepwari) and one without (WO5H) in Collie, Western Australia. Carbon in the sediment did not vary between lakes or depths. Sedimentation rates did not vary between lakes during low/no river inflow periods. River inflow did increase sedimentation but without increasing allochthonous inputs of C. Even with river inflow C accumulation in the lakes remains very low.

The former BHP Beenup titanium minerals operation is in the biodiverse Scott River region in southwest Western Australia and was closed prematurely in 1999 after only two years of operation. Significant modifications to the landscape (including deep dredging to 55 m, lime sand blending with the natural soils to mitigate acid generation) combined with limited previous knowledge of the recruitment biology of many of the plant species, created significant uncertainty as to the feasibility of restoring the site to near-natural communities. This paper covers two aspects of the closure process: (1) a novel planning approach undertaken for setting the end use and target ecosystems using a designed based philosophy informed by risk assessment, and (2) the assessment of restoration success using ecological completion criteria. In terms of planning and design, the geomorphic and biodiversity features of the regional landform types (dunes, plains, sumplands, damplands etc.) formed the basis of design of closure sites. These regional ecosystems were surveyed in detail to characterise the soils, hydrology and vegetation of each major feature, with these ecological relationships then used to develop rehabilitation design criteria. Artificial landforms (deep pools created by dredging) were modified into lakes via void infilling and the creation of extensive shallow shorelines to generate a more naturalistic final shape. The focus on ecosystem design enabled revegetation to be tailored to the specific vegetation communities that best matched the reconstructed landforms; this significantly reduced seed wastage and increased the probability of success. As far as we are aware, it is the first project of this scale in Australia that has successfully created a functional range of wetland types similar to the surrounding natural wetlands. In terms of performance assessment, a detailed and prescriptive set of restoration and completion criteria were developed to enable a greater certainty of outcomes and enabled quantitative measurements of restoration success. The incorporation of sustainability and resilience, which are global indices of success used in ecological restoration projects outside of mining, were applied here to guide both the approach to restoration (so as to enable the site to adapt to changing climates and unpredictable events) and to the measurement of success (completion criteria). This was one of the first instances globally to embed these ecological concepts as key success categories for rehabilitation. Fifteen years after restoration, 15 ecological communities and more than 251 plant species have been successfully restored, including many conservation-listed species. The project achieved regulatory sign off against rehabilitation completion criteria in 2018 and is one of the few 'ecologically designed' post-mining landscapes globally.

Research suggests that there are potentially millions of abandoned mines around the globe. As such, it is highly probable that these operations have the potential of resulting in a magnitude of social and environmental issues. However, there is limited literature on their social impacts specifically to a local community. To explore this issue, we investigated four case studies through a literature review using a wide range of white, grey and peer-reviewed literature. We examined case studies in Australia, China, Europe, and the USA. From this preliminary review, we determined that all have a significant number of abandoned mines. We examined these Case Studies as their respective economies rely heavily on the mining industry. The terminology ''abandoned mines'' is often ambiguous and potentially not well understood. Our research shines the spotlight on the problem and examines novel solutions to manage issues associated with abandoned mines. We also examine the closure requirements for abandoned mines in a broad setting, and how these operations can be successfully monitored using Unmanned Aerial Vehicles (UAVs). Accordingly, our aim was to explore a wide range of jurisdictions and determine how local communities are affected by abandoned mine, and where UAVs technologies are commonly utilised

Topsoil is a valuable resource for revegetation of mine sites as it contains seeds of plant species indigenous to the local environment. As mine site restoration is undertaken after the completion of mining, it is a common practice to stockpile topsoil in preparation for restoration activities. While many studies have found a decrease in seedling emergence with increasing stockpile age in temperate regions around the world, a few examine the effect of stockpile age on topsoil seed bank and seedling recruitment in arid environments. Seed longevity is promoted under dry conditions whereas viability loss is increased under warm and moist conditions. Here in a study in Australia's Great Sandy Desert, the effect of topsoil storage age and method of storing topsoil (under-cover and exposed) on seedling recruitment was examined for a major gold mining site. There was a trend for lower seedling emergence (68% lower) and species richness (30% lower) from topsoil stored for 2 years than from topsoil direct returned and topsoil stored for 1 year. Seedling emergence from topsoil stockpiled for 2 years was more than 3.5-fold higher from covered topsoil stockpiles than uncovered topsoil stockpiles. For two ecologically dominant species, after 2 years of storage, seedling emergence of the grass Triodia basedowii was 13% of direct returned topsoil and seedling emergence of the shrub Acacia stellaticeps was 68% of direct returned topsoil. The implication of the decline in seedling emergence from topsoil stockpiling on mine site revegetation in a biodiverse arid region is discussed.

Long term effects of heavy metal pollution caused by decennial sewage sludge disposal (12 t hayr-) from 980 to 1990 on soil biota of an experimental field in Northern Germany were investigated 16 years after the last sludge application. The plots still exist to date as permanent pas ture. The consequences of the soil treatment were shown by means of heavy metal concentrations of soil and earth worms. Additional effects on soil microorganisms by en zyme activities were investigated. The disposal of heavy metal enriched sewage sludge caused increased soil heavy metal concentrations com pared to mineral fertilised control plots. The increased soil heavy metal concentration was transferred to soil organ isms. The earthworm biomass from the sewage sludge treated plots bore increased heavy metal concentrations. Cadmium showed the highest transfer factor from soil to earthworms. The amount of transfer into biomass is spe cific for each element and depends on heavy metal soil concentration. Despite the higher heavy metal concentra tion of earthworm biomass, the number of earthworms was increased in soil of the sewage sludge treated plots which is attributed to the enhanced soil organic matter (SOM) concentration. The number of earthworms did not correlate significantly with SOM but the weight of earth worms did. The microbial activities of dehydrogenase and alkaline phosphatase enzymes were reduced in soil of the sewage sludge treated plots compared to the control plots. The enzyme activities of cellulase and protease however were enhanced by the application of heavy metal enriched sew age sludge compared to the control plots. One the one hand sewage sludge addition enhanced soil organic mat ter concentration; on the other hand its microbial decom position was retarded by toxic effects of heavy metals due to reduced enzyme activities.

Pit lakes are similar to natural lakes formed by faulting, glacial action, volcanic action and asteroid collisions. These natural lakes have, after thousands of years, developed into environmentally significant ecosystems. As artificial constructs, pit lakes can be modified prior to filling to enhance lake attributes, such as modification of catchment size, creation of littoral zones and addition of organic matter. Significant advances could be made in successful closure and relinquishment of pit lakes, by 1) choosing appropriate model lakes, 2) understanding successional processes, 3) designing pit lakes to enhance ecological values, and 4) recognizing that it will take time to develop desired characteristics.

The use of reference sites for establishing closure criteria in areas disturbed by mining activities is common practice. 'Reference' sites are those considered to be largely unimpacted by anthropogenic activity (retaining desirable natural characteristics), and occurring near disturbed sites. Sites are considered rehabilitated when their biophysical condition approximates that of the reference site. However, this approach often creates impossible or unrealistic targets for miners seeking to close rehabilitated lands. For example, reference sites are often limited in availability (or non-existent) due to impacts by other land uses. Further, any available reference sites might not be realistic matches for the rehabilitated sites-in many rivers (for example) it is questionable whether sites which superficially appear similar are actually ecologically similar. We propose a more achievable approach to mine closure by comparing the bio-physical characteristics of rehabilitated sites to overall ecosystem variability, rather than specific target reference sites. Using multivariate ordination-a classic data clustering technique in ecology-as an applied management tool allows managers to measure how different their rehabilitated sites are from co-occurring sites, and how the rehabilitated sites are tracking over time. Our approach also identifies the key biological, physical, and chemical parameters that potentially differentiate a rehabilitated site and, therefore, the necessary actions to bring a rehabilitation site within range of normal river variability. Further, this conceptual paper introduces two unique case studies used to develop the model, involving microbes as indicators of rehabilitation progress and mine water impact in Australian rivers. The challenges and benefits associated with implementation of this approach from the practitioners' perspectives are discussed. The outcome of this new approach to closure will allow miners to create realistic and definable targets for relinquishing rehabilitation land in already modified landscapes, potentially simplifying closure and project approvals.

Gold is a highly valued and volatile commodity which is subject to many external forces, such as price and availability. Global gold stocks are increasing but the supply is dwindling. Gold mining companies are always looking for novel methods to optimise extraction and processing thereby reducing operating costs and maximising profit. The extraction and processing of gold involves complex chemical processing which results in large volumes of waste, including toxic tailings, and damage to aquatic and terrestrial ecosystems. Our research indicates that gold mines in Western Australia regularly enter an operational phase known as 'care and maintenance' where active mining is not occurring but the site is not yet formally closed. It is a mode generally used to reduce operating costs and overheads, whilst maintaining the option to recommence mining in the future. Sites in care and maintenance are often neglected and minimal rehabilitation is undertaken resulting in massive environmental liabilities and social issues. In worst case scenarios, companies simply mothball the site and they become abandoned or legacy sites. We recently quantified the disturbance footprint and environmental legacies around a representative sample of gold mines in the West Australian Goldfields region. Our results suggest that sites in care and maintenance are a potential emerging problem for regulators left carrying the can for the costs of rehabilitation.

The broad objective of this research was to determine the environmental drivers of macroinvertebrate and microbial assemblages in acidic pit lakes. This is important because pit lake ecosystem development is influenced by prevailing environmental characteristics. Three lakes (Stockton, Kepwari, WO5H) within a larger pit-lake district in Collie, Western Australia were surveyed for spatial variability of benthic macroinvertebrate and microbe (Archaea, Bacteria) assemblage composition as well as potential environmental drivers (riparian condition, aquatic habitat, sediments, and aquatic chemistry) of assemblages. With the exception of sediment chemistry, biophysical variables were significantly different across lakes and reflected riparian condition and groundwater chemistry. Microbial assemblages in pit lakes were significantly different across lakes and correlated with water chemistry, particularly metals in Lake WO5H. However, the most abundant microbes were not readily identified beyond class, making it difficult to speculate on their ecological function. Macroinvertebrate assemblage composition and species richness were also significantly different across all lakes, and in Lake WO5H (a lake with low pH and high metal concentrations), taxa were correlated with benthic organic matter as well as water chemistry. Results indicated that despite poor water quality, input of nutrients from terrestrial leaf litter can support or augment pit lake ecosystems. This is a demonstration of the concept that connection of pit lakes to catchments can positively affect aquatic ecosystems, which can inform management actions for remediation.

This study evaluated the influence of planting sites on the establishment and ectomycorrhizal (ECM) colonization of American chestnut (Castanea denetata(Marsh.) Borkh.) on an abandoned coal mine in an Appalachian region of the United States. Root morphotyping and sequencing of the fungal internal transcribed spacer (ITS) region were used to identify the ECM species associated with the chestnut seedlings. Germination, survival, ECM root colonization, and growth were assessed in three habitats: forest edge, center (plots without vegetation), and pine plots (a 10-year-old planting ofPinus virginiana). Seedlings in pine plots had higher survival (38%) than the other plot types (center 9% and forest edge 5%;P=0.007). Chestnuts found colonized by ECM within the pine plots were larger (P=0.02), contributed by a larger root system (P=0.03). Forest edge and pine plots had more ECM roots than seedlings in center plots (P=0.04). ITS fungal sequences and morphotypes found among chestnut and pin...

This study evaluated the influence of planting sites on the establishment and ectomycorrhizal (ECM) colonization of American chestnut (Castanea denetata(Marsh.) Borkh.) on an abandoned coal mine in an Appalachian region of the United States. Root morphotyping and sequencing of the fungal internal transcribed spacer (ITS) region were used to identify the ECM species associated with the chestnut seedlings. Germination, survival, ECM root colonization, and growth were assessed in three habitats: forest edge, center (plots without vegetation), and pine plots (a 10-year-old planting ofPinus virginiana). Seedlings in pine plots had higher survival (38%) than the other plot types (center 9% and forest edge 5%;P=0.007). Chestnuts found colonized by ECM within the pine plots were larger (P=0.02), contributed by a larger root system (P=0.03). Forest edge and pine plots had more ECM roots than seedlings in center plots (P=0.04). ITS fungal sequences and morphotypes found among chestnut and pin...

Restoration is becoming an increasing global priority. Particularly in high impact developments like open cut mining, restoring ecosystems to pre-disturbance states is difficult but essential. Successful restoration of vegetation communities requires complex achievements of cover, density, community composition, species richness and structural elements. This study synthesizes 10 years of monitoring surveys to measure restoration success in six mining operations in the semi-arid Pilbara of Western Australia, with the goal of quantifying current and past restoration performance. We assessed composition, structure, cover, density, and richness. We found that each metric resulted in slightly different performance measures within mining operations. For example, native perennial grasses in restored sites fell short of reference density and cover, while woody species density and cover were regularly within the reference range. Richness was often much higher in restored than in reference sites. Finally, to explore the potential drivers of performance, we analyzed the influence of restoration characteristics on each of the vegetation metrics. We found that older restoration had increased cover and density of all vegetation types compared to more recent restoration, while other variables had impacts on restoration results that shifted between metrics and monitoring periods. Compositional similarity with reference sites was higher when restoration occurred on low impact mining activities, when first year rainfall was higher, and when seeding treatments were not applied. Overall, this assessment of long-term monitoring data highlighted where each performance measure was important to understanding overall restoration patterns in semi-arid systems and paves the way for improving future restoration practice.

The former BHP Beenup titanium minerals operation is in the biodiverse Scott River region in southwest Western Australia and was closed prematurely in 1999 after only two years of operation. Significant modifications to the landscape (including deep dredging to 55 m, lime sand blending with the natural soils to mitigate acid generation) combined with limited previous knowledge of the recruitment biology of many of the plant species, created significant uncertainty as to the feasibility of restoring the site to near-natural communities. This paper covers two aspects of the closure process: (1) a novel planning approach undertaken for setting the end use and target ecosystems using a designed based philosophy informed by risk assessment, and (2) the assessment of restoration success using ecological completion criteria. In terms of planning and design, the geomorphic and biodiversity features of the regional landform types (dunes, plains, sumplands, damplands etc.) formed the basis of...

Surface mining for coal has contributed to widespread deforestation and soil loss in coal mining regions around the world, and particularly in Appalachia, USA. Mined land reforestation is of interest in this and other regions where forests are the dominant pre-mining land use. This study evaluated mine soil development on surface-mined sites reforested according to the Forestry Reclamation Approach, representing a chronosequence of time ranging from 0 to 19 years after reclamation. Soils were sampled in depth increments to 50 cm and analyzed for a suite of soil physical and chemical characteristics. Overall, soil fines (silt + clay) tended to increase over time since reclamation (17% silt at year 0 increasing to 35% at year 11; 3.2% clay at year 0 increasing to 5.7% at year 14) while concentrations of metals (e.g., Al, Mg, Mn, Na) demonstrated varied relationships with time since reclamation. Concentrations of organic carbon (OC) tended to increase with time (0.9% OC at year 0 incre...

Earthworms are known to bio-degrade various types of organic materials added or already present in soil. Two soils were collected from different land use patterns viz. an agricultural land (AL) and an undisturbed land (UL) of a mountain ecosystem of State of Himachal Pradesh in India for the present investigation. A laboratory microcosm study was carried out to elucidate effects of various agriculturalsoil amendments, viz. wood ash (WA), rice husk (RH), cow dung (CW) and their mixture (MA) applied @25 t ha À1 , on selective biological and chemical properties of earthworm (Eisenia fetida) casts and growth in the collected soils. Subsequently, earthworms were reared in soils from both AL & UL, treated with the amendments; and the resultant earthworm cast (E w C) properties were found to be largely determined by the nature of amendments rather than land use types. Soils treated with MA produced casts displayed higher nutrient content, microbial biomass C with higher activities of dehydrogenase and urease. Earthworm growth and cast formation were greater in the soil from UL over soil from AL for all treatments except WA, implying better acclimatization and earthworm activity in the former. Further, casts produced under UL had higher nutrient mobilization and enzyme activity in comparison to AL. Results suggested that agricultural intervention in an undisturbed land might weaken its ability to support growth, development in conjunction with the activities of earthworms and associated enzymes.

Gold is a highly valued and volatile commodity which is subject to many external forces, such as price and availability. Global gold stocks are increasing but the supply is dwindling. Gold mining companies are always looking for novel methods to optimise extraction and processing thereby reducing operating costs and maximising profit. The extraction and processing of gold involves complex chemical processing which results in large volumes of waste, including toxic tailings, and damage to aquatic and terrestrial ecosystems. Our research indicates that gold mines in Western Australia regularly enter an operational phase known as 'care and maintenance' where active mining is not occurring but the site is not yet formally closed. It is a mode generally used to reduce operating costs and overheads, whilst maintaining the option to recommence mining in the future. Sites in care and maintenance are often neglected and minimal rehabilitation is undertaken resulting in massive environmental liabilities and social issues. In worst case scenarios, companies simply mothball the site and they become abandoned or legacy sites. We recently quantified the disturbance footprint and environmental legacies around a representative sample of gold mines in the West Australian Goldfields region. Our results suggest that sites in care and maintenance are a potential emerging problem for regulators left carrying the can for the costs of rehabilitation.

The use of reference sites for establishing closure criteria in areas disturbed by mining activities is common practice. ‘Reference’ sites are those considered to be largely unimpacted by anthropogenic activity (retaining desirable natural characteristics), and occurring near disturbed sites. Sites are considered rehabilitated when their biophysical condition approximates that of the reference site. However, this approach often creates impossible or unrealistic targets for miners seeking to close rehabilitated lands. For example, reference sites are often limited in availability (or non-existent) due to impacts by other land uses. Further, any available reference sites might not be realistic matches for the rehabilitated sites – in many rivers (for example) it is questionable whether sites which superficially appear similar are actually ecologically similar. We propose a more achievable approach to mine closure by comparing the bio-physical characteristics of rehabilitated sites to ...

Despite the large body of riparian literature for rivers and lakes, there are few studies on the catchments of mine pit lakes. Therefore, the broad objective of this research was to determine if catchment characteristics were related to pit lake nutrient concentrations. We hypothesised that: (1) catchment characteristics would vary among pit lakes, (2) pit lake catchments would differ from co-occurring naturally-forested catchments, and (3) connecting a pit lake (Kepwari) to a naturally-forested catchment via a river flow-through would increase C accumulation in the lake. The research was conducted in pit lakes of the Collie lake district in Western Australia and examined catchment characteristics (soil nutrients, litter biomass, vegetation, and biomass), carbon and sedimentation rates in pelagic and benthic materials, and establishment of a simple nutrient budget for Lake Kepwari. Broadly, results indicated that catchment vegetation differed significantly among pit lakes (although ...

The broad objective of this research was to determine the environmental drivers of macroinvertebrate and microbial assemblages in acidic pit lakes. This is important because pit lake ecosystem development is influenced by prevailing environmental characteristics. Three lakes (Stockton, Kepwari, WO5H) within a larger pit-lake district in Collie, Western Australia were surveyed for spatial variability of benthic macroinvertebrate and microbe (Archaea, Bacteria) assemblage composition as well as potential environmental drivers (riparian condition, aquatic habitat, sediments, and aquatic chemistry) of assemblages. With the exception of sediment chemistry, biophysical variables were significantly different across lakes and reflected riparian condition and groundwater chemistry. Microbial assemblages in pit lakes were significantly different across lakes and correlated with water chemistry, particularly metals in Lake WO5H. However, the most abundant microbes were not readily identified beyond class, making it difficult to speculate on their ecological function. Macroinvertebrate assemblage composition and species richness were also significantly different across all lakes, and in Lake WO5H (a lake with low pH and high metal concentrations), taxa were correlated with benthic organic matter as well as water chemistry. Results indicated that despite poor water quality, input of nutrients from terrestrial leaf litter can support or augment pit lake ecosystems. This is a demonstration of the concept that connection of pit lakes to catchments can positively affect aquatic ecosystems, which can inform management actions for remediation.

Lack of organic matter inputs into a pit lake inhibits ecological development. Connecting a river to a pit lake should add organic matter to the lake. Sedimentation traps and sediment sampling was undertaken in two co-occurring pit lakes: one with river flowthrough (Lake Kepwari) and one without (WO5H) in Collie, Western Australia. Carbon in the sediment did not vary between lakes or depths. Sedimentation rates did not vary between lakes during low/no river inflow periods. River inflow did increase sedimentation but without increasing allochthonous inputs of C. Even with river inflow C accumulation in the lakes remains very low.