The impact of climate change and extreme weather events on cyanobacteria blooms in lakes

To elucidate the drivers of lake ecosystem structure a combination of instrumental climate and historical population records were integrated and compared with sediment-derived indicators of runoff and storms (i.e., PSA; XRF). Chronological control was established for each sediment record using 210Pb and 14C AMS age-depth modeling, supported by age-equivalence stratigraphic markers. A synchronous shift in lake phytoplankton community composition towards greater cyanobacterial abundance, including those from N2-fixing cyanobacteria, was observed in recent decades.

Similarly fossil microcystin records suggest an expansion of toxigenic cyanobacteria since ca. 1990 in all study lakes. Comparisons of lake production proxies with demographic change and climate variables confirmed that land-use and climate change have been a significant driver in one site (Harvey Lake). However, in reference site (Wheaton Lake), the recent expansion of cyanobacteria was solely attributed to climate forcing, as anthropogenic activity was limited at this site.

This relationship was also broadly observed in the palaeoclimate record (PSA; XRF) in Wheaton Lake, however, poor correlations between precipitation records and sediment core runoff metrics were observed in Harvey Lake. This research contributes to the wider understanding of the timing and the controls of cyanobacterial abundance and toxicity in the Canadian Maritimes and highlights the utility of multi-proxy analysis to investigate the drivers of toxigenic cyanobacteria from sediment core records.<br><br><i>Thesis is embargoed until 31 July 2031.</i>