Surface Water and Groundwater Controls on Local Lake Water Chemistry and Water Balance in a Boreal Esker Complex

English Abstract:

Hydrological water balance and chemistry in lakes are critical to biogeochemical cycles and influence aquatic biota. Understanding the climatic controls on water balance and lake water chemistry is essential for ecosystem management and conservation, especially in a time of rapid climate change from human activities. These controls were investigated in a set of 50 lakes located in an esker system near Timmins, Ontario. Water samples were collected in June 2013, June 2014 and August 2014 for stable isotopes of water (δ18O and δ2H), solutes, alkalinity, and dissolved organic carbon to assess how isotopic composition and water chemistry indicate variations in localized water balance between adjacent lakes.

Statistical analyses of the water from the studied lakes indicated a clear separation between two clusters of lakes based on water geochemistry along an elevation gradient: (1) recharge lakes located at higher elevations that were low in solutes and isotopically enriched, and (2) discharge lakes situated at lower elevations that were high in dissolved solutes and isotopically depleted. Differences in lake trophic status and primary production were also observed between these two groups of lakes. Precipitation-fed upland lakes had higher trophic status and dissolved organic carbon concentrations compared to lower elevation groundwater discharge systems presumably in relation to longer water residence times in upland lakes that contribute to local groundwater recharge.

Results suggest that upland recharge lakes will be more prone to evaporative drawdown and therefore more sensitive to short-term climate change and droughts, while discharge lakes will be buffered by groundwater inflow and affected by hydroclimatological changes of greater duration and persistence.