Principales logros

The threats to peat depend in part on the location of the deposits; in the UK,

commercial peat extraction has more or less ceased but it continues in Ireland, Finland and some other areas. For lowland and upland raised mires, this had been the biggest threat of the last century, though this is reducing as alternatives in horticulture and agriculture are perfected. It is still used as fuel in some places, and so these environments remain under threat, but they also provide us with ongoing

opportunities for new discoveries, as long as any extraction operations are done with cooperation between archaeologists and the companies involved, as it was during the Somerset Levels Project (Coles & Coles 1986, 190).

A more insidious problem, particularly in the lowlands, is the drainage of peatlands.

In many cases this was started in the middle ages, but as farming intensifies and practices change, it is increasingly a problem. Drainage causes rapid changes in the ecosystem of a bog, and has implications for any buried archaeological remains. As the range of the local water-table increases, the catotelm is reoxygentated and its preservation properties are rapidly lost (Hobbs 1986, 25). If this is accompanied by dry conditions, then peat may be lost from the top of the bog surface to wind erosion, particularly if it is under cultivation. For example, large areas of the East Anglian Fens have sunk some 4-5m since the mid 19th century, as evidenced by the Holme Fen Post (Godwin 1987, 27, 31). Drainage is not just for agriculture; development requires the consolidation and stabilisation of these environments to allow structures to be built. There is growing concern about the footprint of developments in peatland environments having effects far beyond the immediately affected area as changes to the hydraulic gradients within the peat occur.

This problem is compounded by the effects of climate change; increasingly dry summers are possibly contributing to erosion and drying in lowland environments.

There are real fears in the ecological community that climate change could well be accelerated by the release of methane and stored CO2 in these areas as the peat becomes oxygenated and starts to decay.

Threats are not restricted to the lowlands. As discussed above, the upland mires in the UK are distinctive environments, relatively common here but rare globally. They occur due to our unique oceanic climate. If significant shifts in rainfall patterns occur, it is possible that the conditions that sustain these ecosystems could cease to be maintained. Drier summers, combined with changes in agricultural policy (see below) also have a more immediately catastrophic affect in the form of fires. Dry peat is a fuel source, and if fire takes hold in a desiccated bog, the whole acrotelm, and

possibly the catotelm can be lost. Once the acrotelm is gone, the catotelm is subject to further drying and wind and water erosion, so problems can continue long after the

fires are extinguished. One example of this sort of threat is the large fire that occurred on Fylingdales Moor, North Yorkshire in September 2003 (English Heritage 2003).

This catastrophic fire exposed a whole landscape of features, from prehistoric field systems to Medieval alum mining. Whilst the fire allowed site prospection by aerial photography, fragile archaeological remains were at risk of damage and destruction until vegetation cover could be restored.

There are also threats from more direct human activity. Upland moors in the UK were artificially created and maintained landscapes; they rely, to some extent, on ongoing human exploitation in the form of hill farming to retain their character. As the nature of farming is changing, and incentives to manage these landscapes run dry in the light of the current economic climate, vegetational shifts are already being observed, and some of them are starting to affect the visibility of archaeological sites, for example on Dartmoor. Here, local landowners and community members have been trying to raise awareness of these problems (Dartmoor Preservation Association 2008; Paxman

& Turner 2008; Rendell 2009). If the situation continues, the need for a prospection tool in these environments becomes all the more pressing, as invasive damage from bracken and gorse, and the loss of visibility of sites under molinia, take their toll.

Chapter 4: Peat and geophysical prospection

4.1 Introduction

This chapter deals with peat and geophysical prospection. As already mentioned above, geophysical surveys have been undertaken in peatland environments, though not many by archaeologists, or with archaeological targets in mind. This chapter will examine briefly archaeological geophysics as sub-discipline of near-surface

geophysical prospection, and assumptions within that speciality about the utility of prospecting in peat. Then, archaeological surveys that have been carried out on peatland will be examined to see if any conclusions can be drawn about prospection guidelines Non archaeological applications of geophysical survey in these

environments will also be examined. A final section looks at some very recent developments in archaeological applications, and considers data processing and validation methods briefly. The specifics of the selected geophysical techniques and of data processing and validation are discussed in detail in Section 2, Chapters 5 and 6.