Carbon dissolution effects on pH changes of RAMP lakes in northeastern Alberta, Canada

Study region: This study focuses on boreal lakes in the Athabasca Oil Sands Region (AOSR), Alberta, Canada between latitude 55.68N and 59.72N and longitude 110.02W and 115.46W. Study focus This study focuses on interpretation of hydrochemistry from 50 lakes thought to be acid sensitive, and so monitored by the Regional Aquatic Monitoring Program (RAMP) over the last two decades. This study uses basic statistics, principal component analysis, lithological evidence, CO2 saturation estimates, mineral equilibria and delta C-13(DIC) measurements to describe and assess controls on pH and to investigate causal factors of observed pH increase in the lakes. New hydrological insights for the region: Our assessment provides evidence of two main geochemical processes that control pH increase, namely carbonate dissolution and organic matter uptake, the latter a particularly important component of alkalinity in low pH lakes. Lakes in all subregions show strong evidence of dissolution of marine carbonates of undetermined source, and lake water appears to be trending from CO2 super-saturation towards atmospheric CO2 equilibrium. This supports the hypothesis of carbonate input due to permafrost thaw via surface or groundwater pathways, but also reveals likely influence from CO2 dissolution mechanisms related to climatic influence on ice cover duration.