The increasing rate of glacier retreat, and turbid glacial runoff can have a strong influence on freshwater ecosystems. Seton and Anderson lakes (British Columbia, Canada) are Sockeye Salmon (Oncorhynchus nerka) nursery systems. Since the 1940s, the Bridge River Diversion (BRD) introduced glacially-turbid water into Seton Lake. To assess the impact of the BRD on the production of Seton Lake, we combined data from limnological surveys with the analysis of sub-fossil cladocerans and diatoms from sediment cores; using Anderson Lake as a reference.
The modern data indicate that the euphotic zone is 14m shallower, and the cladoceran density and biomass are significantly lower in Seton Lake in comparison to Anderson Lake. The paleo-data indicate that following the BRD, the sedimentary fluxes of cladoceran and diatom declined 2- to 10-fold in Seton Lake and remained low thereafter. Together our data support declines in primary and secondary producers following the BRD, likely due to changes in light penetration, and/or other indirect influence, and provides insights into the impact of turbid meltwater on the biological production of downstream lakes. Moreover, diatom compositional changes in Seton Lake were consistent with decreased light penetration due to increased turbidity. These changes did not occur in Anderson Lake, indicating the changes in the Seton Lake cores were likely driven by inflow of the glacially-turbid waters.
Both lakes exhibited diatom compositional changes ca. 1980, with a rise in Lindavia comensis coincident with significant increases in local mean annual air temperatures and presumably associated limnological changes. Modern phytoplankton data provides support for the occurrence of different L. comensis morphs throughout the sampling period (May-October) in Anderson Lake and in the fall in Seton Lake. The rise of L. comensis in both Anderson and Seton lakes is conceivably linked to the recent ice-free conditions enabling this taxon to persist throughout the year.
Barouillet, C., B.F. Cumming, K.R. Laird, C.J. Perrin and D.T. Selbie. 2019. Influence of glacial flour on the primary and secondary production of Sockeye Salmon nursery lakes: a comparative modern and paleolimnological study. Canadian Journal of Fisheries and Aquatic Sciences 76, https://doi.org/10.1139/cjfas-2018-0372
Laird, K. R., Barouillet, C., Cumming, B. F., Perrin C. J., and D. T. Selbie. 2021. Influence of glacial turbidity and climate on diatom communities in two Fjord Lakes (British Columbia, Canada). Aquatic Sciences 83, https://doi.org/10.1007/s00027-020-00767-3