How many gallons of water do you need to power a lightbulb?

Here's a measurement you probably haven't thought of before: it takes between 3,000 gallons and 6,000 gallons of water to power a 60-watt incandescent bulb for 12 hours a day over the course of a year.

The water equation comes to energy.

(Credit: Virginia Tech)

That statistic was published on Thursday by researchers at Virginia Polytechnic Institute and State University, who have studied how demand for a dwindling natural resource--fresh water--plays into energy.

The most water-efficient energy sources are natural gas and synthetic fuels produced by coal gasification. The least efficient are ethanol and biodiesel--two fuels booming in production because of supportive government policies, followed by rapid investment.

In terms of power generation, they found that geothermal and hydroelectric energy use the least amount of water, while nuclear plants use the most.

A United States-wide tally shows that power generation requires 655 billion gallons of water a year.

"There are several variables, such as geography and climate, technology type and efficiency, and accuracy of measurements that come into play. However, by standardizing the measurement unit (BTU, or British Thermal Unit), we have been able to obtain a unique snapshot of the water used to produce different kinds of energy," Virginia Tech professor Tamim Younos said.

Biofuels, in particular, are being increasingly scrutinized, as people start to measure the trade-offs of making liquid fuels from biomass.

Corn ethanol emits about 20 percent fewer greenhouse gases than gasoline, but it requires more water, and it has raised the price of grain and food.

Fresh-water supply is a serious concern among scientists studying climate change. Recent droughts in Europe and the southeast United States have been blamed for strains on production at nuclear and coal power generation facilities.

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Gibraltar to cull Barbary apes that terrorise tourists

Vets will track down the tearaways and kill them by lethal injection.

Gibraltar's iconic monkeys are facing a cull after terrorising tourists on the British colony.

A pack of 25 of the Barbary macaques have “run riot” on a beach, have broken into hotel rooms and have been caught scavenging in bins in the town centre.

The threat of attacks on humans and the possibility of the spread of disease has forced authorities to approve the cull “as a last resort”.

Ernest Britto, Gibraltar’s tourist minister, defended the plans for the cull, saying: “Children are frightened. People cannot leave their windows open for fear of the monkeys stealing. “Apes can bite, and contact with them runs the risk of salmonella or hepatitis.”

Vets are to track down the tearaways and put them down by lethal injection. Two have already been killed.

The Gibraltar population of the Barbary macaque – a monkey commonly referred to as the Barbary ape because of its stubby tail – numbers more than 200.

They attract hundreds of tourists every day to the areas around Apes Den and the Siege Tunnels at the top of the Rock.

Francis Cantos, the spokesman for the Government of Gibraltar, insisted: “This is being done as a last resort.

“The apes we are targeting are part of a breakaway group that are going into town and making a nuisance as well as posing health hazards.

“They’ve been spotted going through rubbish, vandalising property and stealing from people. They ran riot at the beach at Catalan Bay.”

The cull has the backing of many locals including staff at Gibraltar’s Caleta Hotel, where guests’ rooms were vandalised recently by apes looking for food.

However, the decision to destroy the rogue pack has been condemned by animal protection groups.

Helen Thirlway, the conservation and welfare director for the International Primate Protection League (IPPL) in the UK, said the monkeys were the colony’s most popular tourist attraction and the “needless slaughter has to stop”.

British soldiers are thought to have introduced the apes, natives of north Africa, into Gibraltar in the mid-18th century to use for shooting practice.

Local folklore has it that the colony would cease to be British if the monkeys were to leave.

Winston Churchill took it seriously enough to ship extra monkey from north Africa to Gibraltar during the Second World War.

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Plants 'thrive' on Moon rock diet

Growing plants in space will be far from easy

Scientists with the European Space Agency (Esa) say the day when flowers bloom on the Moon has come closer.

An Esa-linked team has shown that marigolds can grow in crushed rock very like the lunar surface, with no need for plant food.

Some see growing plants on the Moon as a step towards human habitation.

But the concept is not an official aim of Esa, and one of the agency's senior officials has dismissed the idea as "science fiction".

The new research was presented at the European Geosciences Union (EGU) meeting in Vienna, the largest annual European gathering of scientists studying the Earth, its climate and its neighbours in space.

Bernard Foing, a senior scientist with the European Space Research and Technology Centre (Estec) in the Netherlands, believes growing plants on the Moon would be a useful tool to learn how life adapts to lunar conditions, and as a practical aid to establishing manned bases.

"We would bring a system of water circulation and recovery, which is also the type of system that in any case you want to develop when you are going to manufacture a primitive sort of life support system," he told BBC News.

"So it is also a kind of `technological breadboard' for maintaining a simple life form in an extreme environment."

Microbe power

In principle, putting self-contained pieces of kit with seeds and nutrients on the Moon and giving them a supply of water and an artificial atmosphere would be little different from growing them on space stations, which has been done several times; although outside Earth's protective magnetic field they would be subject to higher levels of radiation.

Esa has made no firm plans yet to explore the lunar surface

The new step, taken in the experiments reported at the EGU, is to remove the need for bringing nutrients and soil from Earth.

A team led by Natasha Kozyrovska and Iryna Zaetz from the National Academy of Sciences in Kiev planted marigolds in crushed anorthosite, a type of rock found on Earth which is very similar to much of the lunar surface.

In neat anorthosite, the plants fared very badly. But adding different types of bacteria made them thrive; the bacteria appeared to draw elements from the rock that the plants needed, such as potassium.

Dr Foing, who presented the study at the EGU meeting, said there was no reason in principle why the same idea could not bear fruit on the Moon itself. Tools could crush lunar rock and add bacteria and seeds.

But, he added, scientists could look to go further, by selecting plants or bacteria that are especially well adapted to lunar conditions, or even by genetically engineering new strains.

Descent of man?

The last decade has seen a revival of interest in Moon exploration after years of neglect.

It is conceivable humans may one day live on the Moon

Europe's Smart 1 probe with its innovative ion engine ended its mission in 2006 with a deliberate crash onto the lunar surface.

China's Chang'e 1 and Japan's Kaguya (or Selene) orbiters both began operations last year, while India's Chandrayaan 1 is due for launch within months.

The US, meanwhile, is committed to putting human feet back on lunar soil by 2020.

But Esa is not yet sure about further Moon missions; a decision on whether to proceed with a concept called Moon Next, which would probably deploy a roving vehicle in about 2015, will be taken later this year.

Even if that gets the go-ahead, some Esa officials at the EGU meeting suggested that planting marigolds (or tulips or cabbages) would be unlikely to be part of the strategy: "it is science fiction," one observed.

But as director of the International Lunar Exploration Working Group (ILEWG), which looks for exciting and innovative ways to study our nearest cosmic neighbour, Bernard Foing believes that Europe or one of the other players will eventually decide to plant the seeds of Earth where previously humanity has merely planted flags.

"We are considering whether we could do this on some precursor robotic mission, even before we consider putting people on the Moon," he said.

"It is viable within the timeframe of Moon Next."

Richard.Black-INTERNET@bbc.co.uk

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