Crannogs, or artificial islands, were constructed during the Iron Age to Medieval period throughout Scotland and Ireland. At least 1500 crannogs are recognised, but little is known about their longevity and continuity of use, and they are difficult and expensive to excavate. An alternative, is to explore these questions through environmental analyses of the impacts of crannog construction and use on adjacent lake sediments.
We have begun to investigate crannog use and longevity using sediment cores from seven lakes and one excavation site. Multi-proxy analysis includes loss-on-ignition, and high-resolution x-ray fluorescence (XRF) to highlight input of clay, gravel, and stones from crannog construction. In addition, increased loading of heavy metals (Cu, Zn) might be related to metalworking on crannogs. The analysis of pollen, invertebrates, biomarkers (faecal sterols and n-alkanes), and sedimentary DNA (sedaDNA), will also provide insights into land use around the lakes and the conditions on the crannogs themselves. Changes in stable carbon and nitrogen isotopes, C:N ratios, diatoms, biogenic silica, and invertebrates will demonstrate how crannog construction and use are driving changes in lake environments.
Preliminary results indicate that XRF data (Cu, Ti, Zn) corroborate sediment stratigraphy and can be used to distinguish periods of crannog construction and use. One of the sites is a crannog in Lough Yoan (Co. Fermanagh, N Ireland), of which structural timber was 14C-dated to the 11th-13th century. Here, diatom assemblages indicate a substantial increase of nutrients during this period. Additional submerged substrates due to crannog construction also led to a more diverse cladoceran assemblage. At the early Iron Age lake-village at Black Loch of Myrton (SW-Scotland) we find increasing Ti and biogenic silica in the sediment record, which we interpret as an input of clay/silt and nutrients from the settlement. Evidence from sedimentary DNA of the vegetation at the site suggests that site development took place after the succession from a littoral to a terrestrial environment.