[Migration and Source Analysis of Heavy Metals in Vertical Soil Profiles of the Drylands of Xiamen City].

The concentrations of eight heavy metal elements (V, Cr, Co, Ni, Cu, Zn, Sr, and Pb) and the isotopic composition of Pb and Sr were determined in vertical soil profiles of the drylands of Xiamen City using ICP-MS and TIMS. The vertical distributions and leaching migration patterns of the heavy metals were also analyzed. The results showed that most of the heavy metals (except for Sr) were not enriched relative background values at most profile depths, which indicated that heavy metal content is less affected by exogenous sources. The migration coefficients of Sr were greater than 0 throughout the entire soil profile; Zn and Co were enriched in the surface soil; and Cr, Ni, and Cu were depleted throughout the profile. V and Pb were less influenced by external activities. Sr and Pb showed clear vertical migration characteristics, and the migration depth of Sr was greater than that of Pb. Factor analysis showed that the heavy metals mainly originated from natural sources, followed by agricultural activities, transportation, and other complex anthropogenic activities. Enrichment factor analysis showed that Sr was affected by exogenous sources to varying extents. The isotopic composition analysis of Pb and Sr showed that Pb was mainly derived from the parent material, whereas Sr was interpreted as deriving from both the parent material and anthropogenic activities, and tended to migrate to the subsurface soil horizons (30-70 cm).

Quantification of the impact of land-use changes on ecosystem services: a case study in Pingbian County, China.

Pingbian Miao Autonomous County is one of the poorest rural areas in China. Land-use changes, mainly driven by agricultural expansion and deforestation, may significantly impact ecosystem services and functions, but such effects are difficult to quantify. In the present study, Landsat image data were combined with the published coefficients about the world and China ecosystem to quantify land-use and ecosystem service changes in the mountainous area. A sensitivity analysis was employed to determine the effect of manipulating these coefficients on the estimated values. Our results show that during the past decades (from 1973 to 2004) forests and grasslands were converted into shrubland and cropland, respectively, resulting in a continuous decrease in ecosystem service (from 124.5 US$ x 10(6) in 1973 to 100.4 US$ x 10(6) in 2004). We found that the decrease of mixed forest in the study area was the largest contributor (i.e., 25.4 US$ x 10(6)) to the decline of the ecosystem service. Therefore we propose that future land-use policy should pay more attention to the crucial ecosystem functions of these forests (including tropical forest), and that it is necessary to balance the relationship between the livelihood of local farmers and environmental protection in order to maintain a healthy and stable ecosystem.