Recent increase in atmospheric deposition of mercury to California aquatic systems inferred from a 300-year geochronological assessment of lake sediments

Age-dated sediment cores from 4 remote lakes across California were analyzed for total Hg (Hg_T) concentration as a function of pre- and post-industrialization. Particle size, magnetic susceptibility and organic C and N, were measured to determine if the Hg concentration in sediment cores could be related to atmospheric deposition and/or watershed processes. Results indicate that (a) for each lake modern (1970–2004) Hg_T lake sediment concentrations have increased by an average factor of 5 times more than historic (pre-1850) Hg_T concentrations; (b) the ratio of modern to pre-industrial lake sediment Hg_T for these lakes are higher than estimated for other locations where atmospheric deposition is presumed to be the main source of Hg; (c) 2 of the 4 studied lakes demonstrated significant relationships between Hg_T concentrations and percentage organic material (r² = 0.68 and p < 0.01; r² = 0.67 and p < 0.01) whereas the other two indicated no significant relationship (r² = 0.05 and p = 0.51; r² = 0.12 and p = 0.36).