Critical loads of acidity and exceedances for 1138 lakes and ponds in the Canadian Arctic.

Sulphur emissions associated with increased anthropogenic activity, such as resource extraction and marine shipping, may lead to the acidification of aquatic freshwater systems in the Arctic. In the current study, acid sensitivity (based on a critical load (CL(Ac)) approach) of 1138 lakes and ponds in the Canadian Arctic was quantified using the Steady-State Water Chemistry (SSWC) model. Ecosystem protection was based on an Acid Neutralising Capacity limit (ANC _limit ) for Arctic Char. Acidification risk was estimated under modelled sulphur deposition for the year 2010 (two scenarios). Overall, surface water CL(Ac) values for the Canadian Arctic were low (median = 35.8 meq·m ^-2 ·yr ^-1 , mean = 96.3 meq·m ^-2 ·yr ^-1 ), with approximately 40% (n = 455) of sites estimated to be sensitive to acidification (CL(Ac) < 20 meq·m ^-2 ·yr ^-1 ). Higher CL(Ac) values were found in Yukon (434.5 meq·m ^-2 ·yr ^-1 , n = 40), Ellesmere Is. (262.2 meq·m ^-2 ·yr ^-1 , n = 143), and Southampton Is. (251.5 meq·m ^-2 ·yr ^-1 , n = 35), while lower CL(Ac) values were found in Melville Is. (5.5 meq·m ^-2 ·yr ^-1 , n = 48), Banks Is. (18.4 meq·m ^-2 ·yr ^-1 , n = 45), and Bylot Is. (20.4 meq·m ^-2 ·yr ^-1 , n = 36). Under modelled deposition for 2010, 12-12.5% (n = 136-142) of all sites were exceeded. The highest proportion of exceeded sites were observed in Ellef Ringnes Is. (48-60%; n = 12-15), Melville Is. (38-44%; n = 18-21), and Northwest Territories (24-26%; n = 23-26).
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