Microcosm testing of municipal sewage and green waste for full-scale remediation of an acid coal pit lake, in semi-arid tropical Australia

Pit lakes (abandoned flooded mine pits) represent a potentially valuable water resource to mining companies, the environment and regional communities across arid inland Australia. However, the water is often of low pH with high dissolved metal concentrations. The addition of organic matter to the pit lakes to enhance microbial sulfate reduction is potentially a cost effective and sustainable remediation strategy for these acid waters. However, the cost and availability of sufficient quantities of suitable organic substrates is typically limiting in these remote regions. Nevertheless, small quantities of sewage and green waste (organic garden waste) are often available in these areas from the regional towns which support the mines. This paper reports on preliminary microcosm laboratory experiments in preparation for the treatment of an acid (pH 2.2) coal mine pit lake in semi-arid tropical, inland north Queensland, Australia with municipal treated sewage and green waste. A laboratory experiment using microcosms (acrylic tubes) containing acid pit lake water and sediment were treated as follows; controls (untreated), sewage, green waste and sewage and green waste. The pH increased to a maximum of 5.5 in 145 days in the green waste and sewage treatment, with notable decreases of iron, aluminium and toxic heavy metals. Our results indicated that the green waste was a key component in alkalinity production and heavy metal removal

More Than Water Quality: Environmental Limitations to a Fishery in Acid Pit Lakes of Collie, South-West Australia

Marron (Cherax cainii Austin) are a freshwater crayfish native to permanent waterbodies in the south-west of Western Australia. A popular aquaculture and sports species, marron are considered a potential end-use fishery species for and have been deliberately released into several historic pit lakes of the Collie coal mining region. This study investigated what environmental factors in these acid mine drainage (AMD) contaminated pit lakes might be affecting the health and success of existing marron fisheries. Although pit lake water quality was often low (pH concentrations) this did not appear to lead to lower marron health indices. Rather, lack of burrow habitat, low biomass and quality of food with further competition for these resources from related non-fishery crayfish species may be the most important factors limiting marron health. Decreased marron health is likely to result in decreased individual growth rate and final fishery biomass. Such ecological considerations are not common to the mine water literature but offer a more holistic perspective to much mine water research and may provide more tangible environmental goals for achieving environmental and social sustainability of mine waters

Setting goals and choosing appropriate reference sites for restoring mine pit lakes as aquatic ecosystems: Case study from south west Australia

Pit lakes may form when open cut mining leaves a pit void behind that fills with ground and surface water. Often replacing terrestrial ecosystems that existed prior to mining, the pit lake may offer an alternative ecosystem with aquatic biodiversity values that can be realised through planned restoration. Restoration theory and mine closure regulatory requirements guides us toward restoring disturbed systems towards landscapes that are of regional value and relevance. However, how do we identify a restoration target for a novel aquatic habitat that did not exist prior to the new post-mining landscape? This paper presents a process of first identifying and then surveying local analogue aquatic systems to provide a direction for pit lake restoration efforts and achievement criteria for pit lake relinquishment. We illustrate this process using a case study from a sand mining operation located amongst wetlands in south western Australia. The company mines silica sands following mechanical removal of topsoil and then extraction of the ore from below the water table by dredging. Assessment of wetland and riparian vegetation in the surrounding area was completed through the establishment and measurement of temporary monitoring transects across five natural wetlands in the Kemerton area with several more visited and observations made. Distinct zonation of vegetation was found across each wetland, although typically wetland basins were unvegetated or filled with younger woody plants with patchy distributions. Fringing riparian vegetation consisted of few species (commonly Melaleuca rhaphiophylla and Lepidosperma longitudinale) but community composition and structure were variable between wetlands. The pattern of vegetation seen across natural wetlands was best explained by topography and soil chemistry with low lying areas more likely to experience regular flooding and accumulate organic matter and nutrients. We consider that, with good planning, rehabilitation, monitoring and management interventions to achieve a restoration trajectory, these new mining pit lakes can positively contribute to regional ecological values

Mine closure of pit lakes as terminal sinks: best available practice when options are limited?

In an arid climate, pit lake evaporation rates can exceed influx rates, causing the lake to function as a hydraulic terminal sink, with water levels in the pit remaining below surrounding groundwater levels. We present case studies from Western Australia for two mines nearing closure. At the first site, modelling indicates that waste dump covers for the potentially acid forming (PAF) material would not be successful over the long term (1,000 years or more). The second site is a case study where PAF management is limited by the current waste rock dump location and suitable cover materials. Pit lake water balance modelling using Goldsim software indicated that both pit lakes would function as hydraulic terminal sinks if not backfilled above long-term equilibrium water levels. Poor water quality will likely develop as evapoconcentration increases contaminant concentrations, providing a potential threat to local wildlife. Even so, the best current opportunity to limit the risk of contaminant migration and protect regional groundwater environments may be to limit backfill and intentionally produce a terminal sink pit lake

The seeds of divergence: the economy of French North America, 1688 to 1760

Generally, Canada has been ignored in the literature on the colonial origins of divergence with most of the attention going to the United States. Late nineteenth century estimates of income per capita show that Canada was relatively poorer than the United States and that within Canada, the French and Catholic population of Quebec was considerably poorer. Was this gap long standing? Some evidence has been advanced for earlier periods, but it is quite limited and not well-suited for comparison with other societies. This thesis aims to contribute both to Canadian economic history and to comparative work on inequality across nations during the early modern period. With the use of novel prices and wages from Quebec—which was then the largest settlement in Canada and under French rule—a price index, a series of real wages and a measurement of Gross Domestic Product (GDP) are constructed. They are used to shed light both on the course of economic development until the French were defeated by the British in 1760 and on standards of living in that colony relative to the mother country, France, as well as the American colonies. The work is divided into three components. The first component relates to the construction of a price index. The absence of such an index has been a thorn in the side of Canadian historians as it has limited the ability of historians to obtain real values of wages, output and living standards. This index shows that prices did not follow any trend and remained at a stable level. However, there were episodes of wide swings—mostly due to wars and the monetary experiment of playing card money. The creation of this index lays the foundation of the next component. The second component constructs a standardized real wage series in the form of welfare ratios (a consumption basket divided by nominal wage rate multiplied by length of work year) to compare Canada with France, England and Colonial America. Two measures are derived. The first relies on a “bare bones” definition of consumption with a large share of land-intensive goods. This measure indicates that Canada was poorer than England and Colonial America and not appreciably richer than France. However, this measure overestimates the relative position of Canada to the Old World because of the strong presence of land-intensive goods. A second measure is created using a “respectable” definition of consumption in which the basket includes a larger share of manufactured goods and capital-intensive goods. This second basket better reflects differences in living standards since the abundance of land in Canada (and Colonial America) made it easy to achieve bare subsistence, but the scarcity of capital and skilled labor made the consumption of luxuries and manufactured goods (clothing, lighting, imported goods) highly expensive. With this measure, the advantage of New France over France evaporates and turns slightly negative. In comparison with Britain and Colonial America, the gap widens appreciably. This element is the most important for future research. By showing a reversal because of a shift to a different type of basket, it shows that Old World and New World comparisons are very sensitive to how we measure the cost of living. Furthermore, there are no sustained improvements in living standards over the period regardless of the measure used. Gaps in living standards observed later in the nineteenth century existed as far back as the seventeenth century. In a wider American perspective that includes the Spanish colonies, Canada fares better. The third component computes a new series for Gross Domestic Product (GDP). This is to avoid problems associated with using real wages in the form of welfare ratios which assume a constant labor supply. This assumption is hard to defend in the case of Colonial Canada as there were many signs of increasing industriousness during the eighteenth and nineteenth centuries. The GDP series suggest no long-run trend in living standards (from 1688 to circa 1765). The long peace era of 1713 to 1740 was marked by modest economic growth which offset a steady decline that had started in 1688, but by 1760 (as a result of constant warfare) living standards had sunk below their 1688 levels. These developments are accompanied by observations that suggest that other indicators of living standard declined. The flat-lining of incomes is accompanied by substantial increases in the amount of time worked, rising mortality and rising infant mortality. In addition, comparisons of incomes with the American colonies confirm the results obtained with wages— Canada was considerably poorer. At the end, a long conclusion is provides an exploratory discussion of why Canada would have diverged early on. In structural terms, it is argued that the French colony was plagued by the problem of a small population which prohibited the existence of scale effects. In combination with the fact that it was dispersed throughout the territory, the small population of New France limited the scope for specialization and economies of scale. However, this problem was in part created, and in part aggravated, by institutional factors like seigneurial tenure. The colonial origins of French America’s divergence from the rest of North America are thus partly institutional

Biological Remediation of Low Sulphate Acidic Pit Lake Waters With Limestone PH Neutralisation and Nutrients

Pit lake water in Collie is typically acidic due to Acid Mine Drainage (AMD) caused by pyrite oxidation and ferrolysis coupled with a low natural buffering capacity in surrounding geologies. These pit waters have typically low sulphate, Fe and heavy metal concentrations. Nevertheless, Collie pit lakes have low biological productivity probably due to Al toxicity and low nutrient concentrations. Lake Kepwari (24 GL, max depth 65 m) is an acidic former coal open cut mine in Collie (Western Australia) that has been extensively revegetated and contoured for a water-ski park to facilitate its relinquishment back to the State. The main water treatment approach was rapid fill by river diversion but this has failed to prevent ingress of Fe2+ rich groundwater which has reduced pH to 4.8. In a manipulative mesocosm experiment using 1,200 L enclosures containing Lake Kepwari sediment and water, a control and three treatments were replicated three times. Treatment one, acidity was neutralised to pH 7 with powdered limestone, two had P concentrations maintained at eutrophic levels of approximately 20 μg L-1 (using K2HPO4), and three combined these same liming and P additions. Mesocosms were monitored for water quality (physico-chemical, nutrient and metal parameters) at 0, 77, 140, 191 and 255 days after establishment. Rainfall dilution resulted in the pH of the control increasing slowly from 4.8 to 6.5. Neutralised treatments remained circum-neutral, whilst P addition alone produced a higher final pH of \u3e7. Sulphate concentrations fell slightly in all mesocosms by about 10 mg L-1, presumably due to SO4 2- reduction or secondary mineralisation. In the treatments with P additions, stimulation of NO3 2- reduction appeared to be the principal mechanism for increasing pH above those of the control. Addition of P had the additional benefit of reducing toxic mono-valent Al concentrations; probably by coprecipitation. This study demonstrated that P additions alone might be a useful remediation approach for the Collie pit lakes, although remediation effectiveness is enhanced with concurrent limestone neutralisation. This combined approach, in addition to ongoing alkalinity production by nitrate reduction and primary production, may facilitate these lakes remaining circumneutral over longer periods of time than single acidity neutralisation treatments alone

Addition of bulk organic matter to acidic pit lakes may facilitate closure

Macro nutrients (C, N, P) are essential for sustaining freshwater ecosystems. However, acidic pit lakes are often nutrient-poor a low pH levels and metal complexation (by A1, Fe and Mn) reduces dissolved P and C concentrations. In contrast, N is often not limiting as it is readily available from groundwater and blasting residues. The Collie basin in Western Australia has a lake district of eleven acidic coal mine pit lakes (pH 3-7, low metals/metalloids and sulfate concentrations). Our previous researches at – microcosm, mesocosm and field scale demonstrated low C and P concentrations limit algal productivity. Addition of organic matter (in the form of terrestrial leaf litter) offered potential bioremediation benefits including habitat creation, sediment formation, the potential for sulfate reduction, and slow release of macronutrients to promote algal growth. We tested the effect of organic matter additions of straw, lawn clippings and eucalypt leaves on acidic pit lake water and sediment in 1,200 L replicated mescosms. We regularly measured water quality in each mesocosm over a year and concluded by measuring the development of macroinvertebrate communities. The highly labile C found in lawn clippings stimulated algal biomass, macroinvertebrate diversity and abundance, and improved water quality. Straw and eucalypt leaves did not alter water quality substantially but did increase abundance of macroinvertebrates. Additions of nutrients, particularly as bulk organic matter increased macroinvertebrate abundance but also altered species composition from carnivorous highly mobile opportunists found in the controls to a range of herbivores/omnivores, while not necessarily altering water quality substantially. The presence of labile C (particularly in the grass) was able to increase algal biomass and improve pH. If conservation values are important for closure of pit lakes and eutrophication is not a risk, then addition of bulk organic matter (particularly labile forms) should be considered in closure plans. Organic matter could be actively added or passively through the catchment. As environmental improvements were seen in all treatments, adding many readily available organic matter types to pit lakes, may be helpful to achieving closure objectives associated with biodiversity