Natural resources practice questions.

A mining company's annual report lists 320 Mt of copper as 'resources' but only 45 Mt of the same deposit as 'reserves'. The reserves figure refers to

• the part of the deposit that has been located by drilling but not yet tested for grade
• the mass of metal the company is licensed to sell during the current year
• the part of the deposit that can be extracted profitably with current technology
• the part of the deposit that will be left in the ground when the mine closes

Answer: the part of the deposit that can be extracted profitably with current technology

Reserves are the economically workable fraction of a known deposit, so the figure moves with the metal price, the ore grade and the extraction technology rather than with geology alone. A price rise can convert resources into reserves without a single new tonne of rock being found.

An ecologist estimates the sustainable yield of a bamboo stand by measuring the standing biomass at the start of two successive years, during which nothing was cut. The sustainable yield is best estimated as

• the standing biomass measured at the start of the second year
• the mean of the two standing biomass measurements
• the standing biomass at the start of the first year, less the losses to decay over the year
• the increase in standing biomass between the two measurements

Answer: the increase in standing biomass between the two measurements

Sustainable yield is a rate, not a quantity in store: it is the increment the stock adds in a period, which can be removed while the store itself stays the same size. Measuring the growth of an unharvested stand is therefore the standard field method for setting a cutting rate.

A belt of mangrove forest reduces the height of storm waves reaching a coastal village. This benefit is best classified as which type of ecosystem service?

• Provisioning service
• Cultural service
• Supporting service
• Regulating service

Answer: Regulating service

Regulating services are benefits gained from the control of natural processes such as flooding, erosion and climate. Provisioning services are the goods extracted, while supporting services are the underlying processes such as soil formation that make the others possible.

Deposits of lithium-rich brine attracted almost no commercial interest until battery manufacture created large-scale demand for them. This shows that

• what counts as a resource shifts with technology and demand
• the brine deposits were chemically transformed into a new resource stock
• the deposits changed from a non-renewable to a replenishable resource
• resource value is fixed by natural abundance rather than by human use

Answer: what counts as a resource shifts with technology and demand

Resources are defined culturally and technologically: rock or brine becomes a resource only when a society has both a use for it and a means of extraction. The deposit itself did not change, the human system around it did.

An island generates 60 % of its electricity from wind, but demand still has to be met on calm evenings. Which measure addresses this problem most directly?

• Building additional wind turbines along the same ridge
• Installing grid-scale battery storage
• Improving the efficiency of household lighting and appliances
• Replacing the turbines with larger and more efficient models

Answer: Installing grid-scale battery storage

Intermittency is a timing problem rather than a capacity problem: more or larger turbines still produce nothing when the wind drops, whereas storage transfers energy from windy periods into calm ones.

A country is comparing a proposed nuclear power station with a proposed coal-fired station. Which environmental cost belongs to the nuclear option only?

• Release of carbon dioxide during electricity generation
• Emission of sulfur dioxide leading to acid deposition
• Reliance on a fuel that cannot be naturally replaced
• Storage of high-level waste for thousands of years

Answer: Storage of high-level waste for thousands of years

Fission releases neither carbon dioxide nor sulfur dioxide at the point of generation, and both fuels are non-renewable. What is distinctive is the long-lived radioactive waste and the cost of decommissioning the plant.