Paleolimnological evidence reveals climate-related preeminence of cyanobacteria in a temperate meromictic lake

Abstract

Meromictic lakes provide a physically stable environment in which proxies for potentially harmful cyanobacteria are exceptionally well-preserved in the sediments. In Sunfish Lake, a meromictic lake that has recently become the focus of citizen concern due to the apparent rise in cyanobacteria blooms, we used a multi-proxy paleolimnological approach pairing novel spectral (i.e., VNIRS) and molecular (i.e., qPCR) assessment tools to explore long-term cyanobacteria trends. We hypothesized that climate change over the past 50 years altered the Sunfish Lake environment to favour cyanobacteria dominance, resulting in an increased incidence of bloom events. Spectral and genetic results aligned to reveal an unprecedented abundance of cyanobacteria in modern times and coincided with warmer and wetter climatic conditions in the region. Our findings offer evidence for climate-driven shifts in cyanobacteria abundance and suggest that a shift towards warmer and wetter conditions supports the rise of cyanobacteria in lakes.

Deep Cyanobacteria Layers: An Overlooked Aspect of Managing Risks of Cyanobacteria

“…In meromictic lakes on unmanaged landscapes (without human activity), the lack of intermixing of water layers inhibits the periodical recharge of nutrient-enriched deep water into the surface layer and may restrict deep cyanobacteria layer development . However, meromictic lakes, such as Sunfish Lake, situated on managed landscapes (with human activity) may experience larger external nutrient loads that keep the lake in a moderately enriched state, supporting deep cyanobacteria layer development . Lake mixing strongly influences nutrient concentrations and thermal stability, which dictates the duration and intensity of stratification. , The lack of deep water-column mixing in meromictic lakes may favor stable thermal characteristics, which would be beneficial for deep cyanobacteria aggregating at depth.…”

“…Sunfish Lake (43°28′25″N, 80°38′01″W) is situated in the township of Wilmot, adjacent to Waterloo, Ontario, Canada. A small surface area (about 19 ha) paired with an unusually steep shoreline creates a lake morphology that supports meromixis , (Figure ). A 1,000 m buffer surrounding the lake is dominated by farmland (54.6% area) followed by mixed deciduous forests (36.4% area) .…”

“…A small surface area (about 19 ha) paired with an unusually steep shoreline creates a lake morphology that supports meromixis , (Figure ). A 1,000 m buffer surrounding the lake is dominated by farmland (54.6% area) followed by mixed deciduous forests (36.4% area) . The shoreline is well developed, with high cottage development occurring around the 1970s .…”

“…21 The lake is mesotrophic (i.e., average total phosphorus during the open water season of about 10 μg L −1 ), narrow, and has two deep recesses. The northwestern facing recess reaches a maximum depth of 19.8 m, and the southeastern recess reaches a maximum depth of 16.0 m. 22 2.2. Lake Sampling and Processing.…”

“…Duthie and Carter previously encountered a deep cyanobacteria layer composed predominately of Planktothrix sp. (previously Oscillatoria sp.) in the late 1960s at Sunfish Lake. Further, the paleorecord suggests a contemporary increase in cyanobacteria abundance, specifically Planktothrix sp . The aims of this study are to (a) characterize the deep cyanobacteria layer in Sunfish Lake, (b) evaluate the presence of toxins associated with the deep cyanobacteria layer to establish potential health risks, and (c) isolate the dominant cyanobacteria species and characterize the toxin-producing potential of these species to establish toxin–producer relationships.…”