Contrasting histories of microcystin-producing cyanobacteria in two temperate lakes as inferred from quantitative sediment DNA analyses

Abstract

Abstract Pilon S, Zastepa A, Taranu ZE, Gregory-Eaves I, Racine M, Blais JM, Poulain AJ, Pick FR. 2018. Contrasting histories of microcystin-producing cyanobacteria in two temperate lakes as inferred from quantitative sediment DNA analyses. Lake Reserv Manage. 35:102–117. The incidence and abundance of microcystin-producing cyanobacteria were compared between 2 temperate lakes over the past ∼150–175\u2009yr by combining analyses of sediment DNA (qPCR of 4 target genes and high-throughput sequencing of a cyanobacterial 16S rRNA gene fragment) and sediment microcystin concentrations. In Lake of the Woods (LoW), toxic cyanobacteria were only detected beginning in the early 1980s based on gene copy numbers of the microcystin-synthesizing gene (mcyD), and by the early 2000s based on sediment microcystins; both these proxies for toxic cyanobacteria were significantly correlated. In contrast, in Baptiste Lake (Alberta), both mcyD gene copy numbers and microcystins were detected as far back as ∼1830, before European settlement of the region. Total sediment microcystins in this lake were not correlated with mcyD gene copy numbers, but the latter correlated with 2 other cyanobacterial genes targeted. These results point to a relatively recent emergence and increasing dominance of microcystin-producing cyanobacteria in LoW that coincides with the documented rise in regional temperatures rather than changes in nutrient loading. In contrast, toxic blooms are not a new phenomenon in Baptiste Lake, as microcystin-producing cyanobacteria were clearly part of the ecosystem prior to anthropogenic perturbations; this lake has also experienced a recent increase in microcystins coincident with further nutrient enrichment. High-throughput sequencing of the cyanobacterial 16S rRNA gene indicated that bloom-forming and potentially toxigenic Dolichospermum (including related Nostocales) and Microcystis were present but the former has been the dominant genus over the past 175\u2009yr.