The hydrological and limnological characterization of two Canadian water catchments sensitive to anthropogenic influences: Crawford Lake, Ontario and Old Crow Flats, Yukon

Abstract

Crawford Lake, Ontario, and Old Crow Flats, Yukon, provide two unique locations to study interacting hydrological components and the effects of climate and anthropogenically- induced landscape changes on local hydrology, geochemistry, and limnology. Crawford Lake is a small meromictic lake near the Niagara Escarpment, whose bathymetry and wind-protected shores impede seasonal turnover, maintaining density stratification across the chemocline. Chemical and isotopic analysis identified a dense, highly conductive groundwater-fed monimolimnion permanently isolated from a less dense, more dilute mixolimnion. High concentrations of dissolved oxygen were measured in the monimolimnion year-round, with oxic conditions maintained by groundwater seeping through hydraulically conductive units in Silurian dolostones of the Lockport Group. This hydrologic setting facilitates the accumulation of varves below the chemocline where the lack of bioturbation is attributed to the saline, alkaline, and isolated nature of the monimolimnion, allowing the undisturbed laminations to provide an annually resolvable chronology of local and global anthropogenic impact.

The Old Crow Flats (OCF) is a remote Arctic wetland that holds over 8700 shallow thermokarst lakes and drain a 14,000 km2 headwater basin via the Old Crow– Porcupine – Yukon River system. OCF is the traditional territory of the Vuntut Gwitchin First Nations who have observed widespread climate-induced landscape changes, including shoreline permafrost slumping, rapid thermokarst lake drainage, shrub encroachment, water level changes, and forest fires. Long-term analysis (2007 –2009 and 2015 – 2019 CE) of the hydrological response to these landscape changes have shown trends of increasing connectivity between the perched lakes and incised rivers, increased seasonal runoff contributions, and altered water chemistry. Analysis of geochemical records sampled from 24 river stations allowed for the rapidly changing contributions of the hydrological endmembers over time (including precipitation, permafrost thaw, lake water, etc.) to be tracked and cross-referenced with the observed climate-induced landscape changes and regional headwater geology.