EFFECT OF SOLAR-RADIATION ON THE FORMATION OF DISSOLVED GASEOUS MERCURY IN TEMPERATE LAKES

We have assessed the effect of solar radiation on the formation of dis solved gaseous mercury (DGM) in lake water samples incubated in situ. In temperate forested lakes, solar radiation induced the formation of DGM, whereas in Lake Erie, light had no effect. Tn lakes where photo-i nduced DGM production was found, DGM concentrations were higher near t he surface, whereas in Lake Erie, DGM levels peaked in the metalimnion . In high DOC lakes, removal of UVB radiation did not affect DGM proje ction, whereas in a low DOC lake, DGM production rates were significan tly lower in the absence of UVB radiation, suggesting that DOC compoun ds are reducing the availability of UVB radiation for photoreduction o f Hg. The relationship between light intensity and DGM production was nonlinear in Ranger Lake. Above similar to 3 MJ m(-2) total incident r adiation, a plateau was reached at about 400 fM during the summer and about 150 fM during the fall. In this lake, a clear diel pattern of DG M levels was found which paralleled that for total solar radiation. Sp iking of samples with Hg(II) prior to incubation in Ranger Lake greatl y increased the DGM production rate, suggesting that photoreducible Hg (II) complexes were limiting DGM production. Filtration through GF/F f ilters or sterilization by heating prior to incubation did not decreas e DGM production rates, suggesting that agents promoting DGM formation in Ranger Lake were either dissolved or colloidal. DGM levels in outf lows of two high DOC drainage lakes were higher than in inflows, confi rming that the lakes were sites of DGM production. Copyright (C) 1997 Elsevier Science Ltd.