Fig. 5. Empirical relationships between Hg concentration and organic matter of surface organic horizons in forests: Swedish mor, n = 363 (Håkanson et al., 1990); Norwegian humus, n = 700 (Låg and Steinnes, 1978); Great Lakes forest floor from the north-central USA, n = 133 (Nater and Grigal, 1992). Lines indicate approximate range of data from each study.