Severe Lake Heatwaves Attributable to Human‐Induced Global Warming

Abstract

Lake heatwaves, prolonged periods of hot surface water temperatures in lakes (Woolway, Jennings, et al., 2021), can have devastating impacts on aquatic ecosystems. Notable implications of lake heatwaves include severe algal blooms (Jöhnk et al., 2008), mass die-off events (Till et al., 2019), and changes to the community composition of microscopic algae (phytoplankton), which form the bases of aquatic food webs (Baker and Geider, 2021;Olalla et al., 2021;Rasconi et al., 2017). Over time, an increase in the exposure of lake ecosystems to hot temperature extremes may lead to an irreversible loss of species as has already been observed in the oceans due to the increased frequency of marine heatwaves (Cheung et al., 2021Smale et al., 2019Smith et al., 2021;Straub et al., 2019). Moreover, heatwaves can influence some of the many benefits that lakes provide to society, including the provision of safe water for drinking and irrigation, recreational use, and economic benefits, such as fisheries and tourism, with knock-on impacts on local economies. Despite a growing appreciation of their importance, scientific understanding of lake heatwaves is in its infancy (Woolway et al., 2021a(Woolway et al., , 2021b, particularly when compared to their atmospheric (

Early Seasonal Increases and Persistence in Relative Abundance of Potentially Toxic Cyanobacteria: Concerning Impacts of Extended Ice-Free Periods in Northern Temperate Lakes

“…This may include identification of the associated implications to human and environmental health through the characterization of cyanobacterial community dynamics in a changing world. This study provided seven important observations: almost 40 years of ice phenology data showed that rising air temperatures have led to significantly longer ice-free periods extending later into the year annually in the TLW, warmer spring air temperatures, increased solar radiation and elevated discharge rates following snowmelt coincided with warming of the water column and initiated the aquatic growing season, cyanobacteria persisted year-round in the oligotrophic, northern temperate lakes of the TLW, cyanobacterial communities during ice-covered months included sequences classified to the recently identified non-photosynthetic, potentially toxic basal lineage, Melainabacteria, cyanobacteria composed a significant portion of the bacterial communities in the study lakes during ice free periods as early as May and persisted into late October, picocyanobacteria were especially dominant during ice-free periods, individual picocyanobacterial populations shifted seasonally—while certain sequences were dominant during ice-free months, other sequences were restricted to either (i) the shoulder seasons of the ice-free period (i.e., spring and fall) or (ii) periods of winter ice cover, and lakes with lower depth ratios and longer water renewal times situated in areas relatively rich in fine grained sediment (i.e., Big Turkey Lake; Table S2) had higher relative abundances of cyanobacteria. Future increases in air temperature are expected to cause further decreases in days of lake ice cover (Woolway et al, 2022), a phenomenon which is being observed in the lakes of TLW. However, in the case of the lakes of TLW, this decrease is caused by a later ice-on date in the autumn where cyanobacteria were not observed in high relative abundances which contrasts with the observance of significant proportions of cyanobacteria as early as May in some systems.…”

Transgenerational plasticity in a zooplankton in response to temperature elevation and parasitism

“…We focused on the crustacean Daphnia dentifera, which is commonly found in stratified lakes in Midwestern Northern America (Tessier et al 1263). Lakes in this temperature region have increased in temperature by 0.5-1.0°C relative to 1951-1980 (Piccolroaz et al 2020), with further increases expected, including a 3 to 25x increased likelihood of severe lake heatwaves with 1.5-3.5°C warming (Woolway et al 2022). D. dentifera are exposed to the fungal parasite Metschnikowia bicuspidata during filter-feeding for algal food, with epidemics typically beginning during late summer/early fall (Shocket et al 2019).…”

Influence of macrophytes on stratification and dissolved oxygen dynamics in ponds

“…Aquatic heatwaves are periods of sustained high surface water temperatures relative to local and seasonal baseline conditions (Hobday et al 2016;Tassone et al 2021; Woolway et al 2021a). The frequency, duration, and intensity of aquatic heatwaves have increased over the past century as a result of anthropogenic climate change, a trend which is anticipated to continue, even under low green-house-gas-emissions scenarios (Oliver et al 2018; Woolway et al 2021a, Woolway et al 2022). Aquatic heatwaves may lower dissolved oxygen (DO) concentrations directly through reduced gas solubility in warmer waters and indirectly through increased ecosystem respiration (Tassone et al 2021).…”

“…Low DO concentrations and thermal stress have been linked to coral bleaching, declines in kelp forests, and mass seagrass mortality in marine systems (Wernberg et al 2016;Hughes et al 2017;Strydom et al 2020). Although heatwaves are well-studied in coastal and marine systems, research on the effects of heatwaves in lakes and ponds is relatively nascent (Woolway et al 2021a; Woolway et al 2022). As such, it remains unclear how aquatic heatwaves affect the structure and function of lentic ecosystems, especially small, vegetated waterbodies.…”