Natural resources - uses and management practice questions.

Water draining from an abandoned metal mine is strongly acidic and stains the stream bed orange. The process responsible is that

• sulfide minerals in the waste rock oxidise in air and water
• the mine workings concentrate rainwater as it evaporates
• limestone in the surrounding rock dissolves into the draining water
• organic matter in the spoil decomposes without oxygen

Answer: sulfide minerals in the waste rock oxidise in air and water

Exposing sulfide minerals to air and water produces sulfuric acid and dissolves metals out of the rock, and the iron then precipitates as the orange coating. Because the reaction is self-sustaining once started, the discharge can continue for a century or more after the mine closes, which is why closure planning is a condition of consent.

A tropical timber concession replaces clear-felling with low-intensity selective logging on a long rotation. The main ecological advantage is that

• the total volume of timber removed each decade is greater
• canopy cover and forest structure are largely retained between harvests
• the concession no longer requires any access roads
• the soil is turned over regularly, which raises the fertility of the site

Answer: canopy cover and forest structure are largely retained between harvests

Keeping the canopy keeps the forest microclimate, the soil protection and most of the habitat, so the system continues functioning between harvests instead of restarting a succession. The yield per hectare is lower, which is the trade being made, and the access roads remain a serious secondary impact because they open the interior to settlement.

A tailings dam at a metal mine fails and releases the stored waste into the river below. The most immediate ecological harm is that

• the river warms because the fine suspended material absorbs more sunlight
• nutrients in the tailings cause an algal bloom downstream
• fine sediment and metals smother the bed and kill the invertebrates
• the increased flow erodes the banks along the whole valley

Answer: fine sediment and metals smother the bed and kill the invertebrates

Tailings are ground rock, so the release is a huge pulse of fine sediment carrying whatever metals the process did not recover. It buries the gravel where invertebrates and fish eggs live and poisons what survives, and because the material settles along the bed the effect persists long after the water has cleared.

One fuel returns about 30 units of energy for every unit of energy invested in obtaining it; another returns about 3. Compared with the first, the second is

• more sustainable, because it takes longer to deplete
• identical in usefulness, since both return more than they cost
• preferable, because a lower ratio indicates cleaner extraction
• far weaker as a net energy source, whatever its total volume

Answer: far weaker as a net energy source, whatever its total volume

What a society can actually use is the surplus after the energy spent getting it, so a falling return on investment means more of the economy must work simply to keep the energy flowing. Total reserves say how much is there; this ratio says how much is worth having.

Batteries, wind turbines and solar panels have sharply raised demand for lithium, cobalt, copper and rare earth elements. The implication for resource management is that

• these metals will be exhausted within the next ten years
• moving away from fossil fuels shifts pressure onto mining rather than removing it
• recycling can supply the whole of the additional demand immediately
• the deposits are evenly distributed worldwide, so no single country holds any advantage

Answer: moving away from fossil fuels shifts pressure onto mining rather than removing it

A low-carbon system substitutes a continuing fuel flow for a large one-off material stock, which is an improvement but not a release from material limits. The consequences show up as mining impacts, tailings, water use and concentrated supply chains rather than as combustion emissions.

A voluntary certification label on timber or seafood is intended to change producer behaviour. The mechanism it depends on is that

• consumer choice gives certified producers a market advantage
• national governments enforce the standard through inspection
• the label sets a legal maximum on the quantity harvested
• certification bodies take ownership of the certified resource

Answer: consumer choice gives certified producers a market advantage

Certification is a market instrument, not a regulation: it works only where enough buyers will pay for or prefer the labelled product, and where the audit behind the label is credible. Its weakness is that it reaches only the share of production that is exported to markets which care.