Multiple environmental factors but not land use affect topsoil mercury levels across the urbanized mosaic of the Hengduan Mountain region

Various studies have looked at how patterns of topsoil mercury concentrations related to land-use and influenced by climate, vegetation, elevation, and soil conditions; however, a pivotal question remains for urban land management and toxicology: to what extent do natural factors continue to drive mercury accumulation in the type of moderately populated, urbanized mosaic landscapes that represent the optimal compromise between nature and development. We investigated total mercury (THg) concentrations in urban topsoils across the principal cities of fourteen counties in the Hengduan Mountains at the eastern margin of the Qinghai-Tibetan Plateau, spanning an elevation range from c. 360 m to 3380 m. We found that land use type (i.e., parkland, woodland, cropland, or vacant land) had no significant effect on topsoil THg concentrations; however, THg levels were sensitive to climate (temperature, but no precipitation or UV-B), vegetation, and soil organic matter. These results reveals that natural factors appear to dominate the distribution pattern of urban topsoil mercury in ecologically fragile areas with mild human interference. Therefore, there is likely a threshold of urbanization intensity at which topsoil mercury dynamics shift to become more highly land-use dependent.

诸多研究已探讨表层土壤汞浓度格局与土地利用的关联，及其受气候、植被、海拔与土壤条件的影响；但在城市土地管理与毒理学领域仍存在一个关键问题：在兼具自然与开发最优平衡的中等人口密度城市化镶嵌景观中，自然因子在多大程度上仍主导汞的累积过程。本研究针对青藏高原东缘横断山脉14个县域主要城市的城市表层土壤展开总汞（THg）浓度检测，采样海拔跨度约为360米至3380米。研究结果显示，土地利用类型（即公园绿地、林地、耕地或闲置用地）对表层土壤总汞浓度无显著影响；但总汞含量对气候（仅与温度相关，与降水或UV-B无关）、植被及土壤有机质较为敏感。本研究结果表明，在人类干扰温和的生态脆弱区，自然因子主导了城市表层土壤汞的分布格局。据此推测，可能存在一个城市化强度阈值，当突破该阈值后，表层土壤汞的动态变化将愈发依赖土地利用类型。