Palaeoenvironmental investigations of crannogs in south west Scotland and Co. Fermanagh, Northern Ireland

Crannogs are widely distributed archaeological sites in Scotland and Ireland and can be described as artificially constructed islands, dated mainly to the Iron Age and Medieval periods. However, little is known about the function and chronology of these sites. This study aims to show how palaeoecological and palaeoenvironmental analyses can support the interpretation of these sites. Two regions were chosen, as national archaeological databases indicated that they had a high concentration of dated crannogs: south west Scotland and Co. Fermanagh, Northern Ireland. Five lakes in total were selected: Cults Loch, Barhapple Loch and Black Loch of Myrton from south west Scotland, and Derryhowlaght Lough and Ross Lough in Co. Fermanagh. By analysing the lake sediments near the crannogs using palaeoecological/environmental techniques, a more detailed concept of the timing and use of these sites can be formalized. The approach employed in this study explores multiple lines of evidence, where the lake cores were analysed for their geochemical proxies (loss-on-ignition, magnetic susceptibility and X-ray fluorescence) as well as their fossil diatom and pollen assemblages. By examining those sediments dating from around the time of the crannog, disturbances in the lake ecology as a result of the crannog can be identified and explored. The geochemical and diatom records show varying responses, indicating that crannogs had a wide range of impact upon the lake ecology. Some sites indicate eutrophication and acidification, while other sites indicate increased erosion rates. The most common crannog related disturbance is a minor deforestation event around the time of the crannog construction, indicating that the large wooden component of the crannog would have impacted nearby woodlands. In some sites a secondary occupation period showed a stronger palaeoecological response than the estimated depth of the crannog construction. By comparing the long term lake records within these regions, it was also possible to identify large scale regional disturbances. The Scottish crannogs appear to have been built between major deforestation phases in the catchment, while the sites in Co. Fermanagh indicate a major deforestation phase taking place after the main construction phase of the crannogs. In Co. Fermanagh this deforestation phase was synchronous with catchment erosion and increases in planktonic and periphytic diatoms. These disturbances all took place around the end of the Early Medieval Period. There are some limitations to the study, as all of the palaeoecological sequences would benefit from an improved age-depth model and an improved understanding of the interactions between diatom taxa in shallow lakes. Overall this thesis identified the potential of applying palaeoecological analyses to lake cores in these highly disturbed sediments and contributed to an understanding of this common occupation type and place in the landscapes of the North-West of the British Isles