Abrupt changes in the physical and biological structure of endorheic upland lakes due to 8‐m lake‐level variation during the 20^th century

Abstract

Climate-induced variation in lake level can affect physicochemical properties of endorheic lakes, but its consequences for phototrophic production and regime shifts are not well understood. Here, we quantified changes in the abundance and community composition of phototrophs in Kenosee and White Bear lakes, two endorheic basins in the parkland Moose Mountain uplands of southeastern Saskatchewan, Canada, which have experienced > 8 m declines in water level since $ 1900. We hypothesized that lower water levels and warmer temperatures should manifest as increased abundance of phytoplankton, particularly cyanobacteria, and possibly trigger a regime shift to turbid conditions due to evaporative concentration of nutrients and solutes. High-resolution analysis of sedimentary pigments revealed an increase in total phototrophic abundance (as β-carotene) concurrent with lake-level decline beginning $ 1930, but demonstrated little directional change in cyanobacteria. Instead, significant increases in obligately anaerobic purple sulfur bacteria (as okenone) occurred in both lakes during $ 1930-1950, coeval with alterations to light environments and declines in lake level. The presence of okenone suggests that climate-induced increases in solute concentrations may have favored the formation of novel bacterial habitats where photic and anoxic zones overlapped. Generalized additive models showed that establishment of this unique habitat was likely preceded by increased temporal variance of sulfur bacteria, but not phytoplankton or cyanobacteria, suggesting that this abrupt change to physical lake structure was unique to deepwater environments. Such climate-induced shifts may become more frequent in the region due to hydrological stress on lake levels due to warming temperatures across the Northern Great Plains.

Impacts of a century of land‐use change on the eutrophication of large, shallow, prairie Lake Manitoba in relation to adjacent Lake Winnipeg (Manitoba, Canada)

“…Before the agricultural development of its catchment, the south basin of Lake Manitoba likely exhibited mesotrophic conditions, as suggested by historically low sedimentary concentrations of P, N and C, low fossil pigment concentrations, low concentrations of diatom and cyanobacteria micro‐fossils, and a planktonic diatom assemblage indicative of meso‐eutrophic conditions. Such naturally mesotrophic conditions also have been reconstructed for a variety of presently eutrophic prairie lakes (Bjorndahl et al., 2022; Dixit et al., 2000; Hall et al., 1999; Maheaux et al., 2016; Pham et al., 2008; Vinebrooke et al., 1998), confirming that, despite high baseline fertility, water quality has declined over much of the prairies since the onset of European‐style agriculture.…”

“…Before the agricultural development of its catchment, the south basin of Lake Manitoba likely exhibited mesotrophic conditions, as suggested by historically low sedimentary concentrations of P, N and C, low fossil pigment concentrations, low concentrations of diatom and cyanobacteria micro-fossils, and a planktonic diatom assemblage indicative of meso-eutrophic conditions. Such naturally mesotrophic conditions also have been reconstructed for a variety of presently eutrophic prairie lakes (Bjorndahl et al, 2022;Dixit et al, 2000;Hall et al, 1999;Maheaux et al, 2016;Pham et al, 2008;Vinebrooke et al, 1998), confirming that, despite high baseline fertility, water quality has declined over much of the prairies since the onset of European-style agriculture. Substantial increases in biological production, particularly by diatoms, suggest that horse-drawn and later mechanised tillage mobilised the naturally high amounts of P, N and probably silicon (Si) (Allan & Williams, 1978;Edlund et al, 2009;Gibson et al, 2000), from soils into Lake Manitoba, as seen elsewhere in the Prairies during the late 19th and early 20th centuries (Dixit et al, 2000;Hall et al, 1999).…”

Characterization of lacustrine harmful algal blooms using multiple biomarkers: Historical processes, driving synergy, and ecological shifts

“…First, aliphatic hydrocarbons (particularly n-alkanes) were used to distinguish the relative contributions of organic matter from algae, macrophytes, and terrestrial plants, reflecting major succession of photoautotrophic communities (Meyers, 2003). Second, photosynthetic subfossil pigments are reliable indicators to track the past changes in lake primary productivity and algal community (McGowan, 2013), particularly the abundance and composition of bloom-forming algae (Bjorndahl et al, 2022). On this basis, concentrations of cyanotoxins were measured in the sediments to infer the magnitude of past HABs and their toxin production through time (Waters et al, 2021).…”

“…The complexity and interactivity of stressors on ecosystems further hamper our understanding of how reducing local pressures may increase ecosystem resilience to climate change (Monchamp et al, 2018;Bruel et al, 2021;Carpenter et al, 2022). Retrospective examination of past ecological shifts and variability characteristics using long-term records, therefore, may provide critical insights on how nonlinear and abrupt HABs in response to environmental change may improve lake management and mitigation strategies (Bunting et al, 2016;Ryo et al, 2019;Bjorndahl et al, 2022).…”

Anthropogenic forcing leads to an abrupt shift to phytoplankton dominance in a shallow eutrophic lake

“…Shallow lakes are common in arid regions (Williams, 2000), characterised by a lack of hydrologic inputs and high rates of evaporation, and are likely to exhibit differential responses to external pressures compared to lakes in temperate and subtropical regions (Adrian et al., 2009; Thornton & Rast, 1989). Major shifts in the quantity and periodicity of precipitation produce significant interannual lake level fluctuations in arid regions (Coops et al., 2003) that in turn regulate nutrient concentrations and phytoplankton abundance (e.g., Bjorndahl et al., 2022) separate from alterations in external nutrient loading (Coppens et al., 2020). Water‐level fluctuations can also impact the structure of phytoplankton communities by altering light availability, nutrient loading, and water column stability (Schelske et al., 2010; Yang et al., 2016; Zohary & Ostrovsky, 2011).…”