Natural resources play a special role in the life of the poor. More than 1.3 billion people depend on fisheries, forests, and agriculture for employment. According to the World Bank, in 2002, 90 percent of the world’s 1.1 billion poor-those living on less than $1 per day-depended on forests for at least some part of their income.
Humans have altered the ecosystems in order to meet growing demands for natural resources, with recent decades experiencing more rapid and large scale changes due to increasing population pressure than any other period in human history.
Misuse of natural resources contributed to degradation and loss of ecosystems and biological diversity. Land ecosystems is exploited at a much faster rates than ever before with negative implications for sustainable human livelihood.
Soil is under pressure with declining quality and it is recognized that soil degradation is a serious problem which is driven by human activities such as inappropriate agricultural practices, urban and industrial sprawl, industrial activities, construction, and tourism.
Alteration of soil characteristics by anthropogenic impact changes functional capacities of the soil.
Agricultural technologies and current practices like mono cropping, residue management, mineral fertilization, overuse of pesticides, heavy agricultural machinery, inadequate management practices of soil and irrigation, can significantly affect the soil quality by changing physical, chemical, and biological properties.
Long-term human impact (e.g. sealing), as well as short-term soil management (e.g. irrigation) modifies material and energy flows.
Erosion, a decline in organic matter content and biodiversity, contamination, sealing, compaction, salinization, and landslides are major soil threats. Intensive use of pesticides and fertilizers is the main activity leading to deterioration of soil physical, chemical and biological properties.
These modifications result in transformation of the soil processes to smaller or greater extent. It is important to be aware that soil is a finite and non- renewable resource, because regeneration of soil through chemical and biological weathering of underlying rock requires geological time.
Due to agricultural intensification over recent decades, vast amounts of fertilizers and agrochemicals have been applied to agricultural land in order to achieve maximum productivity.
Excessive nutrient concentrations not recovered by the crop plants end up being washed into adjacent aquatic systems where they may cause problems such as eutrophication.
Agriculturally induced water pollution may occur from point sources e.g. manure storage tanks, feedlots, overflows, tile drains) as well as through diffuse pollution from farmed land.
The nutrients and agrochemicals applied on the fields may reach adjacent water bodies via overland flows and subsurface flows during precipitation events or, at a slower rate, reach surface water bodies through groundwater discharge.
Main flow paths differ between nutrient species. For example, phosphorus transport occurs mainly bound to soil particles as overland flow whereas dissolved agrochemicals and nitrogen can enter aquatic systems via overland flow, subsurface flows and groundwater flows.
An increased supply of nutrients, especially phosphates and nitrates, can cause algal blooms and excessive growth of aquatic macrophytes in both freshwater and marine ecosystems.
The increased productivity due to substantial nutrient inputs leads to increased bacterial decomposition of dead organic matter, which in turn, is the cause of declining oxygen concentrations.
Apart from nutrients and sediments, water quality may also be burdened by heavy metals which originate from organic and inorganic fertilizers, pesticide applications and irrigation water.
Soil structure and chemistry determine heavy metal solubility and bioavailability. In general, plant uptake and leaching losses are small compared to the total heavy metal loads entering the soils.
In the long term there is a potential for slow accumulation of toxic elements in the soil, which may lead to negative effects on plant growth and the function of soil organisms.
Ultimately, heavy metal related changes to the quality of soils may lead to mobilization and leaching of the accumulated toxic elements to groundwater reservoirs and adjacent freshwater systems.
Mining provides a variety of socio-economic benefits but its environmental disruption is massive in terms of land conversion and degradation, habitat alteration, water and air pollution.
Mining activities generates high concentrations of waste and effluents. Mining impact can be direct through the value chain activities of prospecting, exploration, site development, ore extraction, mineral dressing, smelting, refining/metallurgy, transportation, post mining activities and indirectly through the impact of the degradation on the socio-cultural development of communities.
In general, degradation arising from mining includes; air pollution, water pollution, land and forest degradation, noise pollution, solid and liquid waste disposal of toxic substances, as well as socio-cultural problems such as health complication and conflicts. The environmental impact of mining projects is summarized as follows:
Acid mine drainage and contaminant leaching
Acid mine drainage is considered one of mining’s most serious threats to water resources. A mine with acid mine drainage has the potential for long-term devastating impacts on rivers, streams and aquatic life.
Acid mine drainage is a concern at many metal mines, because metals such as gold, copper, silver and molybdenum, are often found in rock with sulfide minerals. When the sulfides in the rock are excavated and exposed to water and air during mining, they form sulfuric acid.
This acidic water can dissolve other harmful metals in the surrounding rock. If uncontrolled, the acid mine drainage may runoff into streams or rivers or leach into groundwater.
Acid mine drainage may be released from any part of the mine where sulfides are exposed to air and water, including waste rock piles, tailings, open pits, underground tunnels, and leach pads. If mine waste is acid-generating, the impacts to fish, animals and plants can be severe.
Many streams impacted by acid mine drainage have a pH value of 4 or lower-similar to battery acid. Plants, animals, and fish are unlikely to survive in streams such as this.
Acid mine drainage also dissolves toxic metals, such as copper, aluminum, cadmium, arsenic, lead and mercury, from the surrounding rock.
These metals, particularly the iron, may coat the stream bottom with an orange-red colored slime called yellow boy. Even in very small amounts, metals can be toxic to humans and wildlife.
Carried in water, the metals can travel far, contaminating streams and groundwater for great distances. The impacts to aquatic life may range from immediate fish kills to sub-lethal, impacts affecting growth, behavior or the ability to reproduce.
Metals are particularly problematic because they do not break down in the environment. They settle to the bottom and persist in the stream for long periods of time, providing a long-term source of contamination to the aquatic organisms that live there, and the fish that feed on them.
Acid mine drainage is particularly harmful because it can continue indefinitely causing damage long after mining has ended. Acid drainage and contaminant leaching is the most important source of water quality impacts related to metallic ore mining.
Due to the severity of water quality impacts from acid mine drainage, water treatment is required in perpetuity.
Acid mine drainageAcid mine drainage
Erosion of soils and mine wastes into surface waters
For most mining projects, the potential of soil and sediment eroding into and degrading surface water quality is a serious problem as a result of large area of land disturbed by mining operations and the large quantities of earthen materials exposed at sites.
Erosion causes significant loading of sediments (and any entrained chemical pollutants) to nearby water bodies especially during severe storm events.
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Sediment-laden surface runoff typically originates as sheet flow and collects in rills, natural channels or gullies, or artificial conveyances.
Major sources of erosion/sediment loading at mining sites include open pit areas, heap and dump leaches, waste rock and overburden piles, tailings piles, haul roads and access roads, ore stockpiles, vehicle and equipment maintenance areas, exploration areas, and reclamation areas.
A further concern is that exposed materials from mining operations (mine workings, wastes, contaminated soils, etc.) may contribute sediments with chemical pollutants, principally heavy metals.
The types of impacts associated with erosion and sedimentation are numerous, typically producing both short-term and long term impacts. In surface waters, elevated concentrations of particulate matter in the water column can produce both chronic and acute toxic effects in fish.
Sediments deposited in layers in flood plains or terrestrial ecosystems can produce many impacts associated with surface waters, ground water, and terrestrial ecosystems.
Minerals associated with deposited sediments may depress the pH of surface runoff thereby mobilizing heavy metals that can infiltrate into the surrounding subsoil or can be carried away to nearby surface waters.
The associated impacts could include substantial pH depression or metals loading to surface waters and/or persistent contamination of ground water sources. Contaminated sediments may also lower the pH of soils to the extent that vegetation and suitable habitat are lost.
Beyond the potential for pollutant impacts on human and aquatic life, there are potential physical impacts associated with the increased runoff velocities and volumes from new land disturbance activities.
Increased velocities and volumes can lead to downstream flooding, scouring of stream channels, and structural damage to bridge footings and culvert entries.
In areas where air emissions have deposited acidic particles and the native vegetation has been destroyed, runoff has the potential to increase the rate of erosion and lead to removal of soil from the affected area.
Impacts of tailing impoundments, waste rock, heap leach, and dump leach facilities
The impacts of wet tailings impoundments, waste rock, heap leach, and dump leach facilities on water quality can be severe. These impacts include contamination of groundwater beneath these facilities and surface waters.
Toxic substances can leach from these facilities, percolate through the ground, and contaminate groundwater, especially if the bottoms of these facilities are not fitted with an impermeable liner.
Tailings (a by-product of metallic ore processing) is a high-volume waste that contain harmful quantities of toxic substances, including arsenic, lead, cadmium, chromium, nickel, and cyanide (if cyanide leaching is used).
Most mining companies dispose of tailings by mixing them with water (to form slurry) and disposing of the slurry behind a tall dam in a large wet tailings impoundment.
Because the ore is usually extracted as slurry, the resulting waste contains large amounts of water, and generally forms ponds at the top of the tailings dams that can be a threat to wildlife.
Cyanide tailings in precious metals mines are particularly dangerous. Ultimately, tailing ponds will either dry, in arid climates, or may release contaminated water, in wet climates. In both cases, specific management techniques are required to close these waste repositories and reduce environmental threats.
During periods of heavy rain, more water may enter a tailings impoundment than it has the capacity to contain, necessitating the release of tailings impoundment effluent.
Since this effluent can contain toxic substances, the release of this effluent can seriously degrade water quality of surrounding rivers and streams, especially if the effluent is not treated prior to discharge.
Dozens of dam breaks at wet tailings impoundments have created some of the worst environmental consequences of all industrial accidents.
When wet tailings impoundments fail, they release large quantities of toxic waters that can kill aquatic life and poison drinking water supplies for many miles downstream of the impoundment.
Impacts of mining projects on air quality
Airborne emissions occur during each stage of the mine cycle, but especially during exploration, development, construction, and operational activities.
Mining operations mobilize large amounts of material, and waste piles containing small size particles that are easily dispersed by the wind.
The largest sources of air pollution in mining operations are particulate matter transported by the wind as a result of excavations, blasting and transportation of materials.
Exhaust emissions from mobile sources (cars, trucks, heavy equipment) raise these particulate levels.
Large-scale mining has the potential to contribute significantly to air pollution, especially in the operation phase.
All activities during ore extraction, processing, handling, and transport depend on equipment, generators, processes, and materials that generate hazardous air pollutants such as particulate matter, heavy metals, carbon monoxide, sulfur dioxide, and nitrogen oxides.
Mercury is commonly present in gold ore. Although concentrations vary substantially, even within a specific ore deposit.
If the content of mercury in a gold ore is 10 mg/ kg, and one million tons of ore is processed at a particular mine (not unusual concentrations), 10 tons of mercury are potentially released to the environment.
In some gold mining projects, gold-containing ore is crushed and then, if necessary, heated and oxidized in roasters or autoclaves to remove sulfur and carbonaceous material that affects gold recovery.
Mercury that is present in the ore is vaporized, particularly in roasters, which are some of the largest sources of mercury emitted to the atmosphere.
Noise pollution associated with mining may include noise from vehicle engines, loading and unloading of rock into steel dumpers, chutes, power generation, and other sources.
Cumulative impacts of shoveling, ripping, drilling, blasting, transport, crushing, grinding, and stock-piling can significantly affect wildlife and nearby residents.
Vibrations are associated with many types of equipment used in mining operations, but blasting is considered the major source.
Vibration has affected the stability of infrastructures, buildings, and homes of people living near large-scale open-pit mining operations. The animal life, on which the local population may depend, might also be disturbed.