Linlithgow Loch: Palaeolimnology fieldwork, sampling and analyses. Phase 2 report

Sediment coring of Linlithgow Loch took place over two field excursions in 2018 and 2019. In March 2018, two HON-Kajak cores (LLC1 and LLC2) were retrieved to assess the recent history of the lake; LLC1 (32 cm long, 10cm diameter) was retrieved from a deep part of the lake at >9 m depth and LLC2 (29 cm long, 10 cm diameter) from the shallower littoral area at 2 m water depth. The stratigraphy of these two cores was assessed prior to extrusion at 0.5 cm intervals on-site. In September 2019, parallel coring of two boreholes (LRC1 and LRC2) was undertaken using a Russian peat corer (100 cm chamber length, 10 cm diameter) to assess the longer-term history of the Loch. From the first borehole (LRC1), four consecutive core sections (of 1 m) were retrieved (from a water depth of 3.5 m) and from the second borehole, three continuous core sections (of 1 m) were retrieved (water depth 3.5 m). An additional HON-Kajak core (40 cm long) was also taken at this time, inspected on site for sedimentological changes and extruded at 0.5 cm intervals. On return to the laboratory at Loughborough University, the lithology of all Russian cores was assessed, and all sediment sequences (including the HON-Kajak cores) were sub-sampled for loss-on-ignition (LOI) analyses using standard methods. Briefly, ~1 cm3 aliquots of sediment (at 0.5 or 1 cm resolution were dried in an oven overnight, cooled and weighed before burning off the organic matter (OM) at 550�C, and calcium carbonate content (CaCO3) at 925�C (for 4 hours). The weight of the remaining residue (i.e., dry weight minus OM and CaCO3) made up the minerogenic content of the sediment. Parallel cores were subsequently cross-correlated using the physical LOI analyses to produce one continuous, depth-corrected sequence. The sediment cores were also sub-sampled for diatom analyses. To assess diatom preservation and recent anthropogenic change, diatom samples were prepared using standard methods where sediment aliquots were dissolved in 30% hydrogen peroxide (H2O2) solution for >4 hours at 80�C to remove organic material. Microspheres were added to determine diatom concentration prior to mounting on glass slides with Naphrax. Some diatom analyses were performed from the deep-water short core (LLC1) as part of a Loughborough University funded student bursary. Identification occurred at 1000x magnification under phase contrast, oil immersion, with at least 300 valves counted per sample. The preliminary diatom analyses of core LLC1 confirm that the lake is currently eutrophic and supports previous findings of dominance by centric, eutrophic diatoms and long-term nutrient enrichment (e.g., lasting at least 150 years according to Burgess et al. 2006). The lake has been monitored long-term (since the 1960s), and in this time has switched from mesotrophic classification to eutrophic/hyper-eutrophic due to nutrient loading from urban and agricultural sources, triggering various restoration initiatives. High productivity within the loch frequently results in toxic algal blooms during the summer when internal loading supplies a surplus of phosphorus, mixed throughout the lake on overturn. Furthermore, the loch is drained by only one outflow that is frequently blocked by silt, leading to low flushing and high retention rates as well as flood events. As a result of the algal blooms, habitat degradation and decreased levels of dissolved oxygen, the loch has experienced declining biodiversity and major fish kill events. Further detailed palaeoenvironmental analyses on the longer sediment Russian core sequences with sediment dating applied will extend our understanding of long-term human impacts on the lake beyond the last 150 years. This will enable assessment of the impacts of older industries on the lake system (e.g., tanneries, distilleries) evident in the archaeological record.