Coefficients of heavy metal accumulation in forest soils.

In a number of publications, it is reported that the surface soil layer in forest territories often contains increased heavy metal quantities, but at present there are lack of criteria for evaluation of their origin. In the present studies is assumed that regarding the forest territories, the determination of heavy metal accumulation coefficients in the surface soil layer is a suitable criterion for distinguishing the natural accumulation processes from the aerosol pollution because the use of norms may lead to incorrect assessment of the contamination caused by atmospheric depositions. The accumulation coefficients of Mn, Zn, Cu, Pb and Cd in the surface soil layers were determined. Data obtained from a 16 х 16 km network in landscape of the Balkan Mountains (40 profiles), Rhodope Mountains (33 profiles), Sredna Gora (22 profiles), obtained in the period from 1986 to 2017, as well as the results obtained at 2 intensive monitoring field stations. Results of litterfall and soil solution analysis were assessed for interpretation of the obtained coefficients. The maximum coefficients (3.00 for Mn, 3.43 for Pb, 2.55 for Cu, 2.25 for Cd and 1.86) are the product of natural accumulation processes and are caused by the high soil acidity.