Sediment coring
A sediment core was collected from the deepest point of Esthwaite Water using a HTH 9 cm diameter gravity corer (Pylonex, Sweden) in August 2021. Coring equipment was thoroughly sterilised with ethanol and rinsed with deionised water three times before use. After collection, the 35 cm long sediment core remained intact within the sealed Perspex core tube and was kept upright on ice in a large cool box in the field and during transportation to UKCEH, Wallingford, where it was stored at 4 °C in the dark prior to sectioning.
The sediment core was sectioned in 1 cm intervals using the extruding device (Pylonex, Sweden), beginning with recent sediment at the top and working downwards. Each 1 cm sediment section was pushed out the top of the core tube directly into a sterile petri dish of the same diameter to minimise contact with the air. A broad stainless-steel blade was used to cut between the core tube and the petri dish containing the extruded sediment section, which was then sealed with a lid and secured with parafilm. The blade was sterilised with bleach and ethanol and rinsed with deionised water between each section. Clean lab coats, gloves and masks were worn when handling the sediment core to minimise contamination risk. Each sediment core section was then sub-sampled in a UV-sterilised laminar flow cabinet. Using a sterilised spatula, a small amount of undisturbed sediment from the centre of each section which did not come into contact with the blade or core tube was transferred to a sterile Eppendorf tube for storage at -20 °C prior to DNA extraction.