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.