High-resolution chironomid counts for a Holocene record from Hatch Mere, Cheshire (UK)

This dataset provides palaeoecological data for the Holocene sediment sequence retrieved from Hatch Mere (UK) in 2023. Chironomid counts are presented against depth (cm) and age (year CE, year BP). The data provides information on the changes in the lake ecosystem, and has been used to identify the effects of external drivers, primarily eutrophication and attempted restoration, on biodiversity parameters (alpha and beta diversity). The cores were retrieved from the lake using a gravity corer (0-41.5 cm) and a Russian chamber corer (56.5-805.5 cm) deployed from a boat and a fixed platform, respectively, during field work in April 2023. The gravity core (HAT23-2-GC) was sampled every 2 cm from 0-42 cm, with additional samples at 1.5 cm and 41.5 cm, in 1 cm thick subsamples. The Russian core (HAT23-2-R) was sampled once per drive, at approximately every 125 cm from 139-806 cm, with additional samples taken at 56.5 cm and 97.5 cm to capture the transition between the two gravity core and the Russian core sequence. A total of 32 samples from the Hatch Mere sediment sequence was treated with warm KOH (10%) to de-flocculate the material, and subsequently rinsed over a 100 µm mesh. Chironomid head capsules (HCs) were picked from the residue using a Bogorov sorting tray, and mounted onto microscope slides using Euparal mounting medium. HCs were identified using Brooks et al. (2007, doi:10.1007/s10933-007-9191-1). Cricotopus (Isocladius) intersectus-type and Cricotopus (Isocladius) laricomalis-type were combined into a single group (C. intersectus-type sensu lato (s.l.)), as they are similar in appearance and ecological role (Brooks et al., 2007, doi:10.1007/s10933-007-9191-1). All samples reached a minimum HC count of 50. However, due to a labelling error, samples at 24.5 and 25.5 cm were merged into a single sample. The final dataset presented here contains 31 samples. All analyses were performed in the laboratory of Birkbeck, University of London, England.