3.1. Emergy Accounting
The results obtained for the emergy analysis for the alluvial and underground ASGM systems are presented in
Table 3.
Figure 4 compares the proportions of the total emergy budget that were used by the major resource inputs in the emergy structure of the alluvial and the underground production systems. Such detailed structuring is useful to ascertain the vital resource flows for the respective systems and for comparison purposes to perceive the contrasting nature of the studied systems.
The results reveal that the use of renewable resources in the alluvial system was considerably less than the underground system. Within the alluvial system, renewable resources account for 2.3% (5.73 × 1016 sej) of its total emergy budget, compared to the underground system where it accounts for 7.8% (1.26 × 1018 sej). The reason for this difference is the harvest and use of local renewable resources (wood energy) to build cages that are used as supports to prevent the collapse of mines in their underground mining activities. Whereas the alluvial system had a lower renewable resource demand, it demanded more resources in terms of the amount of non-renewable resources used compared to the underground system usage of rocks and ground water. Thus, the non-renewable resource component of the system accounted for 28.3% (6.97 × 1017 sej) of its emergy budget compared to the underground mine whose rock oxide and groundwater, as non-renewable resources, formed 16.3% (2.64 × 1018 sej) of its total emergy used. The alluvial system does not use rock oxide and pumps groundwater but instead excavates alluvial sediments for gold production purposes, which makes the soil loose and subject to soil erosion. Similarly, soil loss was not part of the total emergy budget of the underground system since it does not use these sediments.
The feedback from the economy (F) was the largest contributor for the two systems. Major contributors were machine maintenance, labour, and operational costs (
Table 3 and
Figure 4). A greater proportion (35.5%; 8.72 × 10
17 sej) of total emergy used by the alluvial system was due to the economic inputs, specifically the renting of machinery and their maintenance. This is critical because the former production system uses expensive excavators to scoop the less useful topsoil to make available the sub- and gold-rich sediments. Comparatively, the emergy in the economic inputs of the underground system were mostly due to the cost of commercial rock crushing, rock grinding machines, etc. (30.2%; 4.90 × 10
18 sej). Their costs depend on the number of bags of rock oxide being processed. A different trend was observed for the labour emergy. The alluvial system had a lower labour emergy (15.8%; 3.91 × 10
17 sej) relative to the underground system, whose labour emergy formed 20.0% (3.29 × 10
18 sej) of its total emergy budget. This may be attributed to the less expensive and easily available local-based and unskilled at the disposal of the underground system. The operation costs for the studied systems included economic flows such as monies for food, royalties, etc. The emergy in the operation costs of the underground system represented 20.0% (3.26 × 10
18 sej), which was significantly higher than the alluvial system (14.4%; 3.56 × 10
17 sej). This may be due to the food supply for the larger number of cheap local employees and the higher royalties paid to work in previously owned mine concessions.
3.2. Emergy-Based Indices
The ability of emergy analysis to categorize upstream inputs into renewable, non-renewable resources, and purchased inputs make it influential in revealing the environmental sustainability of a product system. A number of indicators were calculated to assess the environmental performance and the sustainability of the two production systems. They included Unit Emergy Value (UEV), per cent renewable (%R), emergy yield ratio (EYR), environmental loading ratio (ELR), emergy exchange ratio (EER), and emergy sustainability index (ESI). They are discussed as follows:
Unit Emergy Value (UEV) measures the efficiency of the production system. When two or more processes yielding the same output are being compared, the higher UEV can be seen as a measure of lower efficiency because more resources are needed to produce the same amount of product [
17,
30,
37]. For these systems, we found that the alluvial system had a higher emergy per year to produce a gram of gold, with a UEV value of 4.11 × 10
14 sej/g, compared to the underground system at 3.12 × 10
14 sej/g. Therefore, the alluvial system was less efficient compared to the underground system. Moreover, the results suggest that when the same amount of emergy is supplied to both production systems, the underground mine can produce more gold. Technologies that can improve the extraction efficiency is required to ensure that these migratory production systems exhaust mineable lands before they move to a new location. The UEVs obtained for the studied systems are both higher than the 1.50 × 10
13 sej/g that Ingwersen [
20] obtained for a Peruvian mining system. This is probably because of the incorporation of an additional higher energy level, water reuse, into the system during the assessment. Moreover, Lefroy and Rydberg [
38] also reported that specific emergies are sensitive to location, products, and technology and cannot be the only parameter upon which an assessment can be performed. Cohen et al. [
35] also found a UEV of 5.00 × 10
11 sej/g for crustal gold in an attempt to segregate and compute specific emergies for different crustal elements, based on the previous global sedimentary cycle of 1.68 × 10
9 sej/g.
In a given system, the per cent renewable (%R) explains the degree of sustainability to some extent. A higher %R of a system indicates a stronger ability to survive economic stress [
25]. The %R of the alluvial system was 18.8%, relatively lower than that of the underground mine, which was 28.4%, indicating a higher dependency on non-renewable resources during the extraction and processing of the alluvial gold than the underground gold. From this perspective, the underground mine is more sustainable. In the long run, it is more likely to survive economic competition. The result of lower renewable resource contribution and hence high non-renewable inputs from this study did not come as a surprise, since Ingwersen [
20] also found a significant renewable resource contribution, with a %R of 35%, for the Peruvian large-scale gold mine. To some extent, and judging by the renewability values, the Peruvian large-scale mining system is more sustainable and is more likely to survive economic stress than the studied systems.
Emergy Yield Ratio (EYR) provides evidence of a system’s ability to exploit available local resources using purchased resources [
39]. Systems with the lowest possible EYR value of one depend solely on purchased resources [
23]. In general, EYR is sensitive to environment resources inputs and economic resource inputs, regardless of their renewability [
38]. This suggests that the higher the EYR, the higher the relative contributions of the free sources of emergy to the process. The EYR value of 1.44 computed for the alluvial system is higher than that of underground system at 1.32. This implies that the former has better market competitiveness and may be interpreted as having a higher emergy used to produce the gold than the emergy in the raw resources. This may be the result of soil losses in the non-renewable resource category, an important environmental cost, which accounted for a large fraction of the emergy budget of the alluvial system. In addition, a major boost of the economic input of the underground mine was from the large and cheap indigenous labour force of the mining communities and beyond. The fact that the alluvial and underground systems used economic resource inputs, which accounted for 69.4% and 76.0% of their total emery budget, respectively, may explain the discrepancy between the EYR of the two systems.
The environmental loading ratio (ELR) is based on the concept of environmental service trade-offs [
40]. The intensity of the environment’s emergy dissipates when used by a product system, particularly during the transformation process. ELR is used to indicate the pressures on the environment from product systems. A higher ELR means higher environmental stress [
38] and less sustainability [
26] and vice versa. With an ELR of 4.31, the alluvial system places more stress on the environment compared to the underground system that recorded an ELR of 2.53. The finding of higher environmental load by the alluvial system may be attributed to the excavation of large stretches of land in the short term. This leaves the lands bare, which are then subject to large annual soil organic matter loss. The alluvial system is sometimes on-river and/or on river basins that may result in the deteriorated water bodies and the creation of diversion channels. The ELR reaffirms the extremely damaging effects of ASGM on the environment that have been suggested by Hentschel et al. [
4]. The relatively higher ELR associated with surface alluvial mining is inconsistent with the findings of Scheuler et al. [
41] who found that the economic growth of the mining sector is associated with more economic and social costs than had previously perceived. A thorough exploration of a proposed mine site should be completed before the main production activity is performed. This would minimize the environmental load and help mines stay within the limits of the environmental carrying capacity.
The emergy sustainability index (ESI) aggregates the yield ratio relative to the environmental loads. The concept of ESI is premised on minimizing the environmental load while encouraging long-term production. This agrees with the study of Ulgiati and Brown [
37] who found that to be sustainable, the load that a process exerts on the environment, measured by ELR, should be lower relative to a higher yield ratio. A gold production system may be termed as environmentally sustainable if it can concurrently provide gold, while reducing the overall environmental degradation. However, the ESI values calculated for the alluvial and underground systems, at 0.33 and 0.52, respectively, depict otherwise, though they do not differ markedly from each other. This implies that both systems provide a very low emergy return at the expense of a relatively high environmental load. However, the alluvial mine system had poorer sustainability performance than the underground system due to the greater dependence on non-renewable resources, such as the high emergy cost of surface soil loss.
The Emergy Exchange Ratio (EER) is used to describe the strength of the Ghanaian gold at the global trade interface. From a biophysical perspective, the EER indicates the emergy benefits or losses from the sale of Ghanaian gold. Generally, a fair and equitable trade at the global front is realized when the EER equals one [
38]. However, this is usually not the case and equitable trade of Ghanaian gold is not an exception to this situation. Both systems had an EER lower than one, which suggests that both companies supplied more emergy to the consumer, including trade partners and foreign regions, than they received. The calculated EER for the alluvial system was 0.23, whereas that of the underground mine was 0.33. Comparatively, the alluvial system losses slightly more than the underground mine. Ultimately, these trade partners undervalue the ecological impacts associated with these production systems, unlike the Peruvian large-scale mining, which received, in return for the supply of lower emergy, a higher emergy from trade partners (
Table 4). Given this empirical evidence, the prices of the Ghanaian gold should be made higher at the global front during international trade compared to those determined by the market prices. Based on the results of this study, we suggest a policy that is similar to the Forest Law Enforcement, Governance and Trade (FLEGT) and Voluntary Partnership Agreement (VPA) in Ghana that have shown success within the forestry sector. This trade agreement between Ghana and the E.U. aims to address illegal logging of timber, and forest governance and trade through the exportation of only FLEGT-licensed timber. Similarly, the gold that has been produced using environmentally friendly methods and/or has complied with agreed-upon standards should be bought at an EER of one by their trade partners to ensure equity. We see this as a new method of ecological compensation in the mining sector. However, further research work is needed to ascertain the environmental friendliness of the sector. Again, the standard by which the gold produce on small-scale basis must conform must be researched further.
This study has provided the basis for the Environmental Protection Agency (EPA) to plan sustainable land management. Because the miner’s choice of a production system does not depend on the ratio of economic inputs to outputs or the exacerbation of environmental loads and environmental sustainability, but rather the resource types, abundance, their location in the earth, and access to land. The rising popularity of ASGM in Ghana, therefore, would mean a higher load on the land, vegetation, and groundwater recharge, for alluvial and underground mines. This is because the amount of non-renewable emergy use, a critical environmental cost, revealed in our study, dominates the resource inputs in their production process.