Ecological dynamics of a peri-urban lake: a multi-proxy paleolimnological study of Cultus Lake (British Columbia) over the past ~ 200 years

Abstract

Peri-urban lakes offer many valued ecosystem services, but their vulnerability to climate change and anthropogenic disturbances increases with expanding human populations. As the effects and interactions of multiple stressors on lakes can lead to unexpected outcomes, affecting societal and ecological values, it is necessary to evaluate ecosystem trajectories and respective drivers in peri-urban lakes. BetterPowered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation management practices could thus be applied to preserve ecosystem services of periurban lakes. We conducted a multi-proxy paleolimnological study on Cultus Lake, British Columbia, a Canadian peri-urban lake experiencing cultural eutrophication, to reconstruct a comprehensive ecological trajectory of the lake over the past ~200 years. We also integrated historical data as well as historical archival information to identify the potential drivers of the changes. We identified ca. 1800-1900 CE as a reference period, reflected in muted variations across most paleo-indicators. Minor increases in sedimentary δ 15 N ca. 1880-1940 CE coincided with the onset of anthropogenic modifications to the Cultus Lake watershed. Signs of early eutrophication were evident by ca. 1940 CE, as indicated by increases in all sedimentary pigments. By ca. 1970-1990 CE, elevated concentrations of sedimentary cyanobacterial pigments and changes in diatom species assemblages highlighted the potential interactive effects of multiple stressors, including cultural eutrophication, climate warming and declines in the endangered Cultus Lake sockeye salmon population. Recent (ca. 1990 declines in sedimentary pigments and increases in cladoceran fluxes suggested an increase in top-down control of the lake food web. From the collection of changes observed in the past ~200 years in our study, it is clear that Cultus Lake and its associated ecosystem services would benefit from abatement of nutrient loadings from terrestrial and atmospheric sources. Our study emphasizes the complexity and interactivity of drivers in peri-urban lake ecosystems and the necessity of long-term perspectives to contextualize modern ecological conditions to inform lake and watershed management.

Endangered Cultus Lake sockeye salmon exhibit genomic evidence of hypoxic and thermal stresses while rearing in degrading freshwater lacustrine critical habitat

“…This behavioural cycle exposes them to multiple, spatially disparate water column stresses in Cultus Lake ( DFO, 2020b ). Late-season hypolimnetic DO concentrations have been reduced by more than half in Cultus Lake since the 1920s–1930s ( Shortreed, 2007 ; Putt et al , 2019 ), with the most pronounced depletion occurring in the lake profundal zone, associated with the decomposition of excess organic matter arising from the overlying water column under lake eutrophication ( DFO, 2020b ; Gauthier et al , 2021 ). Juvenile sockeye salmon are sensitive to hypoxia ( Brett, 1964 ; Davis, 1975 ; Ruggerone, 2000 ) and rely upon sufficient levels of DO in hypolimnetic and profundal habitats, which presents a refuge from lake predators ( Scheuerell and Schindler, 2003 In Cultus Lake, hydroacoustic data indicate most juveniles reside in close association with the lake sediments during the daylight hours, despite evident hypoxia.…”

“…It is highly likely that lake eutrophication and hypolimnetic oxygen depletion are leading to increased risk of extirpation for sockeye salmon in Cultus Lake, and possibly the Cultus Pygmy Sculpin, which requires oxic hypolimnetic and profundal habitats. Thus, mitigation of the various identified and quantified nutrient loadings to Cultus Lake, particularly in the watershed and regional airshed, is crucial to restoring deep-water oxic habitats to promote conservation of this species, particularly under climate change ( Putt et al , 2019 ; DFO, 2020b ; Gauthier et al , 2021 ).…”

Sedimentary DNA of a human‐impacted lake in Western Canada (Cultus Lake) reveals changes in micro‐eukaryotic diversity over the past ~200 years

“…1964–1979; ca. 1987–2017; Gauthier, Gregory‐Eaves, et al, 2021). Using the periods of change identified with the PCoA biplot, we performed and indicator species analysis on the ASV time series to evaluate which ASVs were associated with each of these time periods.…”

“…To evaluate the efficiency of sedDNA to track past biological conditions and compare intracellular and extracellular DNA signal, we chose to conduct our study on Cultus Lake (Figure 1) because it has been monitored periodically over the last century (Ricker, 1937, 1938; Shortreed, 2007; DFO unpublished data ), and a multi‐proxy paleolimnological study was recently conducted to identify the major periods of change and related drivers (Gauthier, Gregory‐Eaves, et al, 2021). Cultus Lake was characterized by oligotrophic conditions prior to the 1900s, which was identified as a reference period.…”

“…After ca. 1900, anthropogenic and regional climate changes led to a modest cultural eutrophication of Cultus Lake (Gauthier, Gregory‐Eaves, et al, 2021). From ca.…”