Natural factors, not land use type, determine topsoil mercury levels in the urbanized mosaic of the Hengduan Mountains, Qinghai-Tibet Plateau, China

Abstract

Context It is widely recognized that contaminants in urban topsoil can present substantial threats to ecosystems and human health. Mercury (Hg) is a persistent pollutant arising from both anthropogenic (industrial and transport emissions) and natural (e.g. biomass burning, weathering, and volcanism) sources, and can reach toxic levels in urban soils. Aims These threats highlight the need to better understand the dynamics of Hg contamination across human-modified and urbanized landscapes, particularly in regions where studies remain scarce. Methods Here, we conducted a topsoil (0–15 cm) survey involving 14 urbanized counties (eight sampling sites per county) in the Hengduan Mountains at the eastern margin of the Qinghai-Tibet Plateau (QTP), traversing an elevational range of 360–3380 m (a.s.l.). Key results Topsoil total Hg (THg) content range was 9.9–773.4 ng/g with an average of 100.7 ng/g across sites. Neither land use type (i.e. parkland, woodland, cropland, or vacant land) nor human population density had any significant effect on topsoil THg concentrations; however, THg levels were affected by climate (temperature, but not precipitation or UV-B), vegetation, and soil organic matter. Conclusions Our findings suggest that natural environmental factors exert stronger influences on topsoil THg concentrations than broad land-use categories across urbanized mosaic landscapes on the QTP. Implications Consideration of natural environmental drivers may improve the interpretation and monitoring of topsoil THg dynamics across broad urbanized landscapes.