Sediment core chronology
The chronology of the sediment core was estimated using the age-depth relationship of a separate reference core collected from the same location within Esthwaite Water in 2014 as described by Thorpe et al . (2022). Sample depths for the reference core were corrected to 2021 assuming a constant sedimentation rate (Supplementary Information, Table S1), and the slope and intercept of the age-depth relationship were then used to estimate the age of each sediment core section (Supplementary Information, Table S2). The full length of the 35 cm sediment core was estimated to cover 105 years from 1916 to the date of collection in 2021.
To evaluate whether the reference core chronology was accurately aligned with the 2021 core, 16S rRNA gene amplicon sequencing was carried out on sediments from the core and compared with the bacterial sedDNA record obtained from cores collected from the same location within Esthwaite Water in 2016 (Thorpe et al ., 2022). Temporal trends in the relative abundance of the dominant bacterial groups were closely aligned between the two bacterial sedDNA records, supporting the use of the estimated chronology (refer to the Supplementary Information and Fig. S1 for a detailed comparison).