A 140-year paleolimnological record of climatically and anthropogenically driven eutrophication in Utikuma Lake, Alberta, Canada

Eutrophication brings a plethora of environmental and economic consequences to lakes, including ecosystem degradation, increased health risk due to the emergence of harmful algal blooms, and disrupts tourism, recreation and fishing industries. A 140-year core record from Utikuma Lake, Alberta, Canada (55.87° N, 115.42°W), uncovered the mechanisms contributing to the lake's current hypereutrophic state. ITRAX X-ray fluorescence (XRF) element/ratios and end-member modeling analysis (EMMA) of the core sediment grain size data identified variation in the core profile linked to specific sedimentological processes. XRF results exhibited changes in precipitation, weathering, and catchment runoff (Ti, Fe, K/Rb, Ca/Sr) and in lake productivity over time (P, S, Si/Ti). Five derived end members (EMs) were identified: EM01 (mode = 1 µm), low-energy catchment erosion from moderate precipitation events; EM02 (mode = 9 µm), warm spring low-energy freshet; EM03 (mode = 44 µm), cold spring high-energy freshet; EM04 (primary mode = 84 µm, secondary mode = 42 µm), major storm events; and EM05 (mode = 146 µm), catchment disturbances related to construction earth moving. CONISS clustering analysis of EMMA and XRF data identified five distinct depositional phases (Zones 1–5) spanning from the late 19th century to the present, characterized by varying levels of productivity, rainfall, weathering, and runoff associated with both natural and anthropogenic factors. Spectral and wavelet time series analysis showed that Utikuma Lake's spring freshet has similar spectral content to time series representating the Arctic Oscillation (AO), El-Niño Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO), while rainfall-driven sedimentary processes are mainly affected by ENSO and PDO. The most notable change in the record took place in 1996, characterized by a sudden and significant rise in both biological productivity and runoff from the catchment area. This shift pushed the lake beyond a trophic tipping point, leading to the development of hypereutrophic conditions that persist to this day. This limnological shift was primarily triggered by a significant discharge from a decommissioned sewage treatment lagoon into the lake. Contributing factors also included catchment runoff disturbances linked to phase shifts in the PDO and ENSO teleconnections.