Conclusions and recommendations for the use of sedDNA in
palaeolimnology
Validation of sedDNA against concurrent lake monitoring is crucial to
further its development and evaluate its performance as a
palaeolimnological tool. Our comparison with long-term microscopy-based
monitoring of phytoplankton in the lake surface water revealed broadly
similar trends in the diversity and relative abundance and occurrence of
chlorophytes, dinoflagellates, ochrophytes and bacillariophytes, and up
to 20% of genera detected by microscopy were also detected by sedDNA.
These results support the use of sedDNA as an effective tool for the
reconstruction of past phytoplankton communities, at least within the
time period investigated in this study. However, DNA degradation may
occur in older sediments which could limit the reliability of
reconstructions over longer time periods, and a substantial proportion
of the phytoplankton community detected by microscopy were missed by
sedDNA. Based on these results, we recommend that sedDNA reconstructions
over time periods exceeding 100 years or of groups such as cryptophytes
that were poorly resolved with sedDNA are treated with caution, and
future research should focus on identifying the key determinants of
variable DNA degradation and deposition among taxa. Furthermore, due to
incomplete reference databases, it is important that future studies
consider the fact that phytoplankton sedDNA reconstructions may only
represent a subset of the total community in lakes. Continued
improvements to reference database coverage, in addition to the combined
use of multiple targeted primers may enable the wider phytoplankton
community to be captured with sedDNA.