Weighing up the damage against the green benefits

Published on Friday 4 September 2009 19:03

DESPITE its relatively small land mass, Scotland plays an important role in the UK in storing carbon on our land. We host 55 per cent of the UK's terrestrial carbon store.

The richest stores are our peat lands, poorly-drained soils where plant material decomposes sufficiently slowly that, since the last Ice Age approximately 12,000 years ago, carbon-rich stores have formed, sometimes more than five metres deep.

In fact, 88 per cent of carbon stored in UK peat lands is in Scotland. With carbon dioxide concentrations increasing in the atmosphere, wise land management acts to preserve this carbon store.

However, the landscapes that best accumulate carbon – our wild and windy moorlands – also offer the best sites for energy generation from wind power: Scotland has 25 per cent of Europe's wind energy source, according to the Scottish Government.

Onshore wind farms are often sited, or proposed to be sited, on peat lands and in upland areas that hold large stocks of soil carbon.

Scotland leads Europe in wind farm development: for example, we have Europe's largest onshore wind farm, Whitelee, south of Glasgow. Not far from there, the Clyde wind farm, which will be even bigger, is being built. But the Lewis wind farm has been refused, and currently causing controversy is the Shetland Viking wind farm.

Not since peat lands were drained to be reclaimed for agriculture or forestry have the needs of society placed as much pressure for development on our carbon landscapes.

The visual impact of turbines is much debated, but less consideration is given to how the landscape responds to hosting such infrastructure.

Payback time calculators, used by planners when considering a wind farm application, generally show that the carbon expended in wind farm construction is offset in the early years of energy generation, and after that the energy generated by a wind farm has no carbon footprint.

These payback time calculators, developed by a team led by colleagues at Aberdeen University, are thoughtfully designed, but based on our understanding of carbon losses from sites that have not hosted wind farms.

The Carbon Landscape research group at Glasgow University aims to better understand how the peat lands respond to the construction and operation of a wind farm.

We are doing this in two ways. Firstly, since planning was approved in 2006 we have monitored carbon losses in the rivers draining the Whitelee wind farm site. Although the data-set has yet to be fully analysed, at our sampling points outwith the wind farm boundary there is generally little increase in carbon lost to drainage systems.

This is good, as it suggests, at this site at least, the impact of disturbing the soils for construction is localised.

Secondly, starting in early 2010, we will carry out research at the smaller catchment scale, to assess how rotating turbines may change the way that carbon is trapped in soils or lost from the site.

The premise here is simple: rotating turbines remove energy from the wind. A resultant reduction in wind speed will reduce evaporation of water from the surface and transpiration from plants. Reduced evapotranspirative loss – the combined amount of evaporation from land and plants – could lead to a rise in the water table.

A higher water table will increase the zone low in dissolved oxygen, thus supporting peat accumulation by slower decomposition of dead plant carbon.

However, decomposition in a low oxygen region can generate gases such as methane that are more powerful greenhouse gases.

So, using Whitelee as our study site we will compare a site hosting wind turbines with a similar site nearby without turbines to discover if there is a trade-off between enhancing carbon storage and promoting losses.

Assessing the resilience and adaptation of our carbon landscapes to hosting wind farms offers exciting scientific investigation.

This research has been funded by the Scottish Government and the government-funded Natural Environment Research Council (NERC).

To ensure the knowledge we generate as scientists reaches the end-user, NERC have also provided me, and collaborators from Stirling University, funding to bring together those who manage carbon landscapes – regulatory and conservation bodies, landowners, developers – with academics who understand intimately how carbon is transferred from our rich terrestrial stores to catchment drainage systems.

Together we will pool our knowledge to produce guidelines on how to minimise carbon loss to catchment drainage systems, thereby informing the responsible development of facilities such as wind farms and ensuring Scotland's carbon stores remain as intact as possible.

&#149 Dr Susan Waldron is a senior lecturer in the Department of Geographical and Earth Sciences at Glasgow University