Thierry Fonville

The main scientific interest that intrigues me is the impact that late prehistoric communities had on their environment. Since the discovery and implementation of agriculture, people have been able to drastically alter their landscapes. However, it is often not entirely known to what extent that took place. To understand the effects of current human impact, it is also important to understand how the climate has changed over time and how modern disturbances compare to human activity that took place is the past.

My PhD project revolves around the effect that early communities had their environment, by looking at distinct sites, named crannogs. Often all that remains of these sites is a conspicuous clump of trees surrounded by water (photo 1), which upon closer inspection often has submerged piles surrounding the edge of the island. Crannogs are in fact artificial islands in lakes built mainly during the late prehistoric and early medieval periods, in Scotland and Ireland (and one in Wales). Specifically I’m trying to determine if crannogs and their occupation had a profound effect on their direct environment (i.e. the lake in which they were built). This will be achieved by analysing lake sediments for specific components which are indicative of changes to the lake ecology and the surrounding landscape.

Derryhowlaght crannog in Co. Fermanagh, Northern Ireland. The trees in the middle of the photo are growing on the crannog

Derryhowlaght crannog in Co. Fermanagh, Northern Ireland. The trees in the middle of the photo are growing on the crannog

Hearth located in Cults Loch , indicated by the stone and timber construction

Hearth located in Cults Loch , indicated by the stone and timber construction

The sediments will be analysed for its geochemical composition by means of Loss-on-Ignition (LOI), X-Ray Fluorescence (XRF) and Magnetic Susceptibility (MS). This allows the determination of changes in the deposition environment, such as differences in erosion rates, heavy metal input and oxygenation of the lake. Next to that, both the aquatic and terrestrial realm will be analysed by means of a diatom and pollen analysis under the light microscope. Diatoms are photosynthetic algae that have glasslike cell walls, called frustules, which accumulate in lake sediments. These frustules can be identified to determine changes in the algal communities, which relate to nutrients, water level and acidity of the lake. The pollen grains accumulating in the lake sediments are a reflection of the vegetation surrounding the lake. The analysis of changes in the pollen assemblages allows the detection human impact to the landscape, such as woodland clearance and the creation of arable lands. The combination of the geochemical and biotic analyses of the lake sediments will give an indication of the effect that the construction of the crannog had on the lake ecology.

Over two seasons lake sediments were collected from two lakes in Northern Ireland (Derryhowlaght Lough and Ross Lough, District Fermanagh) and two in Scotland (Barhapple Loch and Cults Loch, Dumfries and Galloway). Each of these lakes contains at least one crannog to which the sediment record can be compared. Most of the lakes are shallow and small, increasing the likelihood that the crannog was able to disrupt the lake ecosystem.

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