Hydrogen peroxide as a natural tracer of mixing in surface layers

Abstract

Vertical eddy diffusion coefficients (K z ) were estimated for the epilimnion of lakes using hydrogen peroxide (H2O2) as a natural, photochemically produced tracer. Modelled profiles of H2O2 production were combined with observed profiles from the photochemically active region and the waters below in which H2O2 had penetrated to calculate K z values for the epilimnion of Lakes Erie and Ontario, and for two bays in a small lake in Ontario, Canada (Jacks Lake). K z values in both Lake Erie and Lake Ontario were 10−5 to 10−2 m2 s−1 during our study period. Values of K z from Jacks Lake reflected the prevailing wind conditions but also varied with site. In a wide (3 km) bay with relatively clear water, K z values ranged from 10−5 m2 s−1 during calm periods to 10−4 m2 s−1 during windy periods. The K z values were lower in the smaller bay with higher concentrations of dissolved humic material, increasing from 10−6 m2 s−1 during calm periods to 10−4 m2 s−1 during wind-induced mixing. The differences in K z , as determined by this photochemical tracer, a function of lake surface area and wind speed support the applicability of H2O2 in quantifying vertical mixing in the surface layer of small and large lakes.