By Paul Rincon
Science reporter, BBC News
In 1852, an engineer by the name of John Lawrence drove an iron post down through 22 feet of bog in Holme Fen, East Anglia, so that the top of the pillar was flush with the peat surface.
The Lewis peatlands are a rare and beautiful habitat
Mr Lawrence had recently finished draining the nearby lake of Whittlesey Mere. The landowner, a Mr William Wells, asked the engineer to sink the iron column so he could use it as a gauge to calculate peat shrinkage following drainage of the lake.
That cast iron pillar is very visible today - the top is now 15 feet above ground. Over 150 years, the peat vanished through a gradual, steady process of water loss and oxidation.
To Richard Lindsay, head of conservation at the University of East London (UEL), "Holme Fen Post" serves as a reminder of the delicate ecological balance in which peatland environments are held.
The fens of East Anglia were successively drained from the 17th Century onwards to make way for more profitable grazing and arable land, often against the will of local people.
Today, Britain's peatland habitats are at the centre of a different wrangle.
The drive towards cleaner energy alternatives to fossil fuels, backed by government, has jump-started the wind power industry. And many of the most suitable locations for wind farms in the British Isles happen to be on peat.
"There is this direct conflict," says Mr Lindsay. "The windiest areas tend to be on the west side of either Ireland or Britain.
"That means you are also going to be in areas with lots of rain, lots of mist and fog - exactly the environment you need for blanket bog development."
This week, the developers behind one of Britain's biggest onshore wind projects has submitted revised plans for scrutiny by the Scottish Executive.
Holme Fen Post now stands some 4m above ground
This wind farm on the island of Lewis has kicked up a storm of controversy because it would stand in protected conservation areas. The peatlands support breeding bird populations of national and international importance.
Those who back wind farms want the peatlands they build on to prosper despite the turbines. And the developer, Lewis Wind Power, is providing money for habitat conservation.
But opinions are sharply divided on the extent to which turbines and infrastructure will impact surrounding bog ecology - with some conservationists warning that this rare and beautiful habitat could be devastated.
"We regard the Lewis wind farm as the biggest conservation challenge in the UK at the moment," said Martin Scott, Western Isles conservation officer for RSPB Scotland.
The organisation commissioned Richard Lindsay to write a report on the project's environmental impact statement (EIS). The result, published last year, was a damning critique of the developer's assessment.
The central charge contained within Professor Lindsay's report was that the EIS underestimated by a factor of 30 the area of bog potentially affected by the wind farm.
The Lewis wind farm plan has stirred up controversy
One of the most important impacts on the blanket bog could be through the construction of drainage ditches, which could remove water from the peat, leading to erosion. Peat is 98% water held in an organic matrix of partially decayed vegetation, mainly sphagnum moss.
Richard Lindsay says that all access roads built as part of the project will need drainage ditches - despite the developer's statement that "floating roads", which can be laid down directly on top of the peat, would not need them.
"The developer's impact assessment has, at almost every turn, taken a minimalist view of the level of impact," he told BBC News.
Tom Dargie, the Lewis project ecologist counters: "I was very shocked when I read the report, then I thought: 'Okay, a 30-fold difference. That means one of us is wrong. And I know it's not me'."
"I've spent a year monitoring a wind farm as it is being built, looking at water levels away from roads, away from turbine bases, and everything fits the published literature - which is that you are not going to get an effect beyond 10m."
In his report, Richard Lindsay refers to a key scientific study from 1972, in which researchers measured the extent to which the water table was drawn down in peat around an open drainage ditch.
Birds like this red-throated diver may be at risk from turbines
The 1972 study might seem to suggest that the peatland water table is not drawn down very much beyond a few metres from the drainage ditch.
But over time, even a small fall in the water table can have a devastating effect if the ditch remains open; some of the peat becomes prone to the same slow, steady process of erosion that transformed Holme Fen, says Mr Lindsay.
This larger zone of influence was largely responsible for Mr Lindsay coming up with radically different figures from Tom Dargie for the impact of wind farms.
As the water table drops a little, Mr Lindsay says, fresh peat is exposed on the surface; this dries out and "oxidises", releasing carbon dioxide and water. The water table then drops a little more, and so the process continues.
"Over time, this will continue until the peat disappears and you are down to the mineral," the UEL researcher explains.
Tom Dargie, who runs Boreas Ecology argues that the 1972 study was based was a different type of peatland which is much wetter, and therefore inappropriate for calculating impacts on the Lewis peatlands.
"The Lewis peatlands are already eroded - the gully systems in them are natural drains and have already dried them out. So if you put another drying effect on top, you are not going to get the same effect as if it were pristine peat," he says.
But Mr Lindsay said the emphasis placed on erosion by the developer was unjustified, because some 67% of peat in the area surveyed is either stable or recovering: "The current general trend is... towards wetter more actively-growing bog," he said.
While the impact on peat remains a contentious area, it is bird deaths that have fuelled some of the most heated arguments over wind farms.
The vast Altamont Pass wind power site in California is an oft-cited example of the threat posed to birds by turbines. A study published in 2004 suggested the 4,000 turbines kill an estimated 880 to 1,300 eagles, hawks and falcons each year.
US trade publication Windpower Monthly has branded the report "a genuine black eye for the industry".
The California Wind Energy Association has now called the study's findings into question, publishing its own report pointing out what it says are flaws in the original study, including a claimed discrepancy in the figures for golden eagle deaths.
But there are many similar reports, from wind farms in Spain, Britain and Norway.
"You have a direct collision effect where birds fly into the turbine blades and get chopped up, says Martin Scott. "The other effect is disturbance; there is disturbance during the construction period, and then when they're up and running."
While some birds find it hard to avoid the turbines, others manage to dodge them all too well, giving the giant towers a wide berth. The net effect is to "sterilise" whole areas of birds.
"Wind turbines in Britain are probably killing birds in small numbers, due to care taken in siting individual wind farms," says Tom Dargie. "They are not killing birds in significant numbers.
"The opposition say [the industry is] covering up the data, but that is a major slur. There are very good ornithologists involved, they would not risk their reputations."
Lewis Wind Power says the level of threat to birds is being updated and revised all the time as new research becomes available.
It says the example of Altamont Pass cannot be applied to Lewis because it has taken steps such as mapping major areas of bird activity on the island and has used the data to inform the design and layout of the wind farm. This includes eliminating turbines from bird feeding corridors.
The Altamont report was a "black eye" for the wind farm industry
But Martin Scott is doubtful about these efforts: "It is totally untested," he says.
"It has never been done before because no one has ever thought it was possible. To be honest, we don't think it's possible either; it may be feasible with one or two turbines, but not with 181."
The attitudes of the island's inhabitants will also be crucial in any eventual decision on the wind farm.
And as the wind farm developers await the reaction to their revised application, the battle for hearts and minds on this Hebridean island looks set to continue.