Landscape and groundwater controls over boreal lake water chemistry and water balance heterogeneity in an esker complex of northeastern Ontario, Canada

Abstract. Water chemistry and water isotopic composition were investigated in a set of 50 boreal lakes located at different elevations in an esker system near Timmins, Ontario, as well as in local streams, groundwater springs and information available from seasonal precipitation values. Analyses focused on stable isotopic ratios of hydrogen and oxygen, as well as specific conductance as indicators of the position of a lake with respect to the influence of groundwater. Both isotopic composition and specific conductance distinguished higher elevation groundwater discharge lakes from lower elevation groundwater recharge lakes. Groundwater recharge lakes characterized by enriched isotopic values and low values of specific conductance are located above the hydraulic midline elevation of the study lakes. In contrast groundwater discharge lakes, were isotopically depleted and had higher values of specific conductance, and occurred below the hydraulic midline of the study lakes. An intermediate group of lakes was also defined (termed seepage lakes) and consisted of either recharge lakes that were alkaline, or discharge lakes that had no outlet. The seepage lakes group had intermediate isotopic and water chemistry characteristics compared to recharge and discharge lakes. A classification scheme for lakes was developed based on the specific conductivity, water isotopic composition, the presence of an outlet, and other characteristic to define three types of recharge lakes, and two types of discharge lakes. Interannual (2013 and 2014) and seasonal differences in water chemistry between (early June and August) revealed that upland groundwater recharge lakes showed evidence of evaporative drawdown, indicating sensitivity to short-term changes in climate, whereas the lower-elevation discharge showed little variation between seasonal samples, and consequently would be affected by hydroclimatological changes of greater duration and persistence.

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Use of water isotopes and chemistry to infer the type and degree of exchange between groundwater and lakes in an esker complex of northeastern Ontario, Canada

Hydrology and Earth System Sciences ◽

10.5194/hess-25-6309-2021 ◽

2021 ◽

Vol 25 (12) ◽

pp. 6309-6332

Author(s):

Maxime P. Boreux ◽

Scott F. Lamoureux ◽

Brian F. Cumming

Keyword(s):

Isotopic Composition ◽

Water Chemistry ◽

Groundwater Recharge ◽

Lake Water ◽

Groundwater Discharge ◽

High Elevation ◽

Specific Conductance ◽

Boreal Lakes ◽

Water Geochemistry ◽

Lower Elevation

Abstract. While interactions between groundwater and lake-water influence water chemistry, water balance, aquatic organisms, biochemical cycles and contamination levels, they remain a poorly studied component of lake hydrology. Identifying the controls of groundwater and lake-water interactions at the landscape level and classifying lakes into categories based on their degree of interaction with the groundwater can provide insights into a lake's sensitivity and vulnerability to environmental stressors. Such information can also provide baseline conditions for comparison to future changes that are important for water management and conservation. To this end, water chemistry and water isotopic composition were investigated in a set of 50 boreal lakes located at different elevations in an esker system near Timmins, Ontario. Analyses focused on stable isotopic ratios of hydrogen and oxygen and specific conductance as indicators of the position of a lake with respect to the influence of groundwater. Both isotopic composition and specific conductance distinguished higher-elevation groundwater-recharge lakes from lower-elevation groundwater-discharge lakes. Groundwater-recharge lakes were high-elevation lakes characterized by enriched isotopic values and low values of specific conductance. In contrast, groundwater-discharge lakes were isotopically depleted and had higher values of specific conductance and occurred at lower elevations. An intermediate group of lakes was also defined (termed seepage lakes) and had intermediate isotopic and water-chemistry characteristics compared to recharge and discharge lakes. Differences in water geochemistry between field campaigns revealed that upland groundwater-recharge lakes showed evidence of evaporative drawdown, indicating sensitivity to short-term changes in climate, whereas the lower-elevation groundwater-discharge lakes showed little variation between seasonal samples and consequently would likely be affected only by hydroclimatological changes of greater duration and magnitude.

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