HYDROGEN-PEROXIDE AS A NATURAL TRACER OF MIXING IN SURFACE-LAYERS

Vertical eddy diffusion coefficients (K-z) were estimated for the epil imnion of lakes using hydrogen peroxide (H2O2) as a natural, photochem ically produced tracer. Modelled profiles of H2O2 production were comb ined 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 s mall lake in Ontario, Canada (Jacks Lake). K-z values in both Lake Eri e and Lake Ontario were 10(-5) to 10(-2) m(2) s(-1) during our study p eriod. Values of K-z from Jacks Lake reflected the prevailing wind con ditions but also varied with site. In a wide (3 km) bay with relativel y clear water, K-z values ranged from 10(-5) m(2) s(-1) during calm pe riods to 10(-4) m(2) s(-1) during windy periods. The K-z values were l ower in the smaller bay with higher concentrations of disserved humic material, increasing from 10(-6) m(2) s(-1) during calm periods to 10( -4) m(2) s(-1) during wind-induced mixing. The differences in K-z, as determined by this photochemical tracer, a function of lake surface ar ea and wind speed support the applicability of H2O2 in quantifying ver tical mixing in the surface layer of small and large lakes.