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[HTT18-P05] Distribution characteristics of lead isotope ratio in organic and mineral soil layers under Japanese forests
Keywords:forest soil, lead isotopes, lead concentration, organic layer, regional survey, factorial analysis
Soil minerals and organic matter preserve lead (Pb) released by human activities and its concentration and stable isotope ratios provide information on the provenance and long-term atmospheric deposition. To understand the contributing factors of geographical distribution pattern of Pb concentration and stable isotope ratios (206Pb/207Pb, 208Pb/207Pb), organic layer (Oa layer, 44 sites) and mineral soils (0-10 and 10-20 cm layers, 59 sites) were collected from forests throughout Japan. For chemical analysis, organic layer was air-dried, powdered, and digested by hydrogen dioxide and nitric acid. Mineral soils were also air-dried, passed through 2 mm-mesh sieve, and extracted bioavailable Pb by EDTA solution (0.05 M, pH 7). Lead concentration was analyzed by ICP-MS. For isotope analysis, Pb was purified by percolation of digestion or extracts containing 200 ng of Pb through anion exchange resin, and isotope ratios were analyzed by MC-ICP-MS.
Geographical coordinates, mean annual temperature and precipitation, geological Pb concentration (Imai et al., 2004; Geological Survey of Japan, AIST), winter precipitation ratio [the ratio of winter precipitation (Dec-Feb) to annual precipitation], chemical properties of litter and soil [total carbon and nitrogen concentrations, C/N, and soil pH(H2O)] were obtained from previous study (Urakawa et al., 2015). PLS-R (Partial Least Squares-Regression) analysis was conducted to assess the contributing factors for geographical distribution of Pb concentration and isotope ratios.
Average ± SD of Pb concentration of litter layer, 0-10 cm, and 10-20 cm of soil layers were 9.7 ± 8.8 mg kg-1, 10.7 ± 10.5 mg kg-1, 5.5 ± 5.4 mg kg-1 respectively. Similarly, 206Pb/207Pb was 1.1617 ± 0.0052 for litter, 1.1674 ± 0.0070 for 0-10 cm layer, and 1.1768 ± 0.0092 for 10-20 cm layer, and 208Pb/207Pb was 2.4468 ± 0.0068 for litter, 2.4554 ± 0.0099 for 0-10 cm layer, and 2.4667 ± 0.0113 for 10-20 cm layer. In most of the sites, both two isotope ratios were the lowest in litter layer and increased to the deeper layers when comparing at the same site.
From PLS regression analysis, winter precipitation ratio and pH(H2O) were the major contributing factors for Pb concentration in litter and soil layers, respectively. For Pb isotope ratios, winter precipitation ratio was the most significant factor for both litter and soil layers. Therefore, influx of transboundary air pollutants was implied to affect geographical distribution of Pb concentration and isotope ratios.
References
Imai N, Terashima S, Ohta A (2004) Geochemical map of Japan.
Geological Survey of Japan, AIST, Geochemical map of sea and land of Japan, https://gbank.gsj.jp/geochemmap/index.html
Urakawa R, Ohte N, Shibata H, et al (2015) Biogeochemical nitrogen properties of forest soils in the Japanese archipelago. Ecol Res 30:1–2.
Geographical coordinates, mean annual temperature and precipitation, geological Pb concentration (Imai et al., 2004; Geological Survey of Japan, AIST), winter precipitation ratio [the ratio of winter precipitation (Dec-Feb) to annual precipitation], chemical properties of litter and soil [total carbon and nitrogen concentrations, C/N, and soil pH(H2O)] were obtained from previous study (Urakawa et al., 2015). PLS-R (Partial Least Squares-Regression) analysis was conducted to assess the contributing factors for geographical distribution of Pb concentration and isotope ratios.
Average ± SD of Pb concentration of litter layer, 0-10 cm, and 10-20 cm of soil layers were 9.7 ± 8.8 mg kg-1, 10.7 ± 10.5 mg kg-1, 5.5 ± 5.4 mg kg-1 respectively. Similarly, 206Pb/207Pb was 1.1617 ± 0.0052 for litter, 1.1674 ± 0.0070 for 0-10 cm layer, and 1.1768 ± 0.0092 for 10-20 cm layer, and 208Pb/207Pb was 2.4468 ± 0.0068 for litter, 2.4554 ± 0.0099 for 0-10 cm layer, and 2.4667 ± 0.0113 for 10-20 cm layer. In most of the sites, both two isotope ratios were the lowest in litter layer and increased to the deeper layers when comparing at the same site.
From PLS regression analysis, winter precipitation ratio and pH(H2O) were the major contributing factors for Pb concentration in litter and soil layers, respectively. For Pb isotope ratios, winter precipitation ratio was the most significant factor for both litter and soil layers. Therefore, influx of transboundary air pollutants was implied to affect geographical distribution of Pb concentration and isotope ratios.
References
Imai N, Terashima S, Ohta A (2004) Geochemical map of Japan.
Geological Survey of Japan, AIST, Geochemical map of sea and land of Japan, https://gbank.gsj.jp/geochemmap/index.html
Urakawa R, Ohte N, Shibata H, et al (2015) Biogeochemical nitrogen properties of forest soils in the Japanese archipelago. Ecol Res 30:1–2.