Holocene development and anthropogenic disturbance of a shallow lake system in Central Ireland recorded by diatoms

Abstract

Three cores from two connected lakes in Central Ireland (Lough Kinale and Derragh Lough) were investigated using diatom analysis to establish the Holocene development of the lacustrine system, any local variations within the lakes and any anthropogenic influences. The study area was situated in a lowland location and the lakes were shallow, unstratified and interconnected. Litho-and bio-stratigraphical analyses of the lake cores and deposits beneath a mire separating the two lakes showed the changing spatial configuration of the lake system in the early Holocene and the separation of the initial lake into three basins (cf. lacustrine cells) and finally into two interlinked lakes. The evolution of the lake system is conceptualised as the development of distinct lacustrine cells, and its sediments have recorded changes in the physical (geography, depth and sedimentation) and chemical (water chemistry) properties of the lakes inferred through diatom analyses. The longest sequence, from the early Holocene, records fluctuating lake levels and these are correlated with geomorphological mapping and surveying of palaeoshorelines. The diatom assemblages of the upper 2 m of the three cores, covering approximately the last 2000-3000 radiocarbon years show considerable difference in trophic status and life-form categories. This is related to the location of the cores in the lake and also the distance from human settlement with particular reference to proximity to crannog (artificial island) construction and use. The most central core from the deepest part of Lough Kinale has the least representation of the human settlement and agricultural activity in the catchment and on the fringes of the lake, whereas the core taken from the edge of a crannog is able to identify when construction and use of the crannog occurred. The local nature of the palaeoecological response to human activity due to incomplete water mixing has the advantage of allowing the lake sediment cores to be used to determine spatially discrete settlement patterns.

Ancient DNA, lipid biomarkers and palaeoecological evidence reveals construction and life on early medieval lake settlements

“…6 ), indicating lake shallowing. Given that the lake outlet is on bedrock, this apparent ‘lake-shallowing’ can only be caused by the creation of a ‘shore-edge’ as the crannog is constructed 17 . Values of Ti, taken as an indicator for in-wash of mineral particles, show an increase, compared to background values, at the start of the crannog phase, concomitant with changes in other proxies.…”

6700 years of diatom changes related to land use and climatic fluctuations in the Lake Aydat catchment (Auvergne, France): Coupling with cyanobacteria akinetes, pollen and non-pollen palynomorphs data

“…4) were observed. Moreover, there is an increase in tychoplanktonic and periphytic diatom taxa, such as "Fragilaria" taxa like Ulnaria acus, that could suggest inwash of diatom species from other habitats (Selby and Brown, 2007) with the development of aquatic plants in the littoral zone or more turbid conditions (Selby and Brown, 2007;Baier et al, 2004). Miras et al (2015) confirmed the presence of aquatic plants by observing that algae (Pediastrum, Spirogyra) progress, parallel to a rise in the presence of rotifer resting eggs.…”

“…6dB) and, 2) the development of hemp cultivation and retting with an increase in detrital material into the lake (presence of NPPs associated to soil disturbance as Diporotheca rhizophila) (Miras et al, 2015). The different uses exercised by man on the catchment could explain the increase in tychoplanktonic "Fragilaria" diatoms that could be linked with possible inwash of surrounding soil-derived material (Baier et al, 2004;Selby and Brown, 2007). This increase could also be linked to the hemp cultivation.…”