Winter nitrification rates and associated data for Lake Superior (near surface at 2 m depth, in winter but without ice-cover; [40]).

Summer values of nitrification rates are reported for the two lakes (Western Basin of Lake Superior and Lake Croche) where cross-season study has been performed. Values below limits of quantitation (LOQ) for nitrification rates are reported, including negative values (following [40]) and sample-specific LOQ (as described in Methods and calculated as per [43,44]) are reported.