Impacts of mining activities on the spatial distribution and source apportionment of soil organic matter in a karst farmland

Worldwide mining activities produce vast quantities of mine tailings, which pose a threat to soil quality, crop yields, and the regional environment in the adjacent agricultural soil, but little is known about the impact of mining activities on the SOM source and migration. In this study, soil samples of the topsoil (0-15 cm) and soil profiles (0-50 cm), as well as the potential sources samples (C3 plants, C4 plants and mining tailings) were collected from mine -contaminated karst farmland of four different pollution levels (NP, non-polluted; SP, slightly polluted; MP, moderately polluted; and HP, heavily polluted). Total organic carbon (TOC), total organic nitrogen (TON), and stable isotopic com-positions (813Corg and 815Norg) of soil and potential sources samples were determined. In the topsoil, the concentrations of TOC (1.9 +/- 1.4 %) and TON (0.1 +/- 0.1 %), and the value of 813Corg (-25.4 +/- 0.9 parts per thousand) and 815Norg (-3.6 +/- 3.6 parts per thousand), were not significantly different among HP, MP and SP farmland (P > 0.05). C3 plants (42.1 %-49.9 %) and mine tailings (32.3 %-40.1 %) were identified as the dominant source of topsoil SOM. In the soil profile, TOC%, TON%, 813Corg, and 815Norg were affected by soil depth and pollution level. TOC% and TON% in the soil profiles of NP changed slightly with soil depth, while that in the other soil profiles was decreased with the increasing of soil depth. The 815Norg value in the SP soil dropped sharply when the soil depth was >15 cm, while that in the HP and MP soil was fluctuated and no obvious vertical pattern. Our findings provide valuable information regarding the im-pact of mining activities on SOM distribution and source apportionment in karst farmlands. The effects of mine tailings on SOM should be considered when the soil quality was estimated in the mine-grain composite area.