Accumulation, risk assessment of trace elements in soil-herbage systems and effects of elevation on subalpine grassland in the northeast of Tibet Plateau

Abstract

Ecological environment of remote grassland has become increasingly serious in many countries due to mining, tourism, grazing and other human activities. In this study, a total of 15 pairs of soil-herbage samples were collected in the northeast of the Tibet Plateau to study the relationship between physicochemical properties and content of trace elements in soils and elevation, and to examine the accumulation and fractionation of heavy metals in soil-herbage systems. In addition, the ecological risk of the subalpine grassland was also assessed. The average concentrations of Hg, As, Cu, Zn, Pb, Cd, Cr and Mn in soil were higher than their background values of Gansu soil, but the average concentrations of these heavy metals in herbage satisfied Hygienical Standard for Feeds. The speciation analysis of heavy metals in soil indicated that the exchangeable content of heavy metal was very low, except Pb, Cd, Mn. There was a linear relationship between pH, CaCO3, total phosphorus (TP), organic matter (OM), concentrations of Hg, As, Zn, Pb, Cr and Mn in soils, dry weight of herbage and elevation, while there was a quadratic curve trend between Cu, Cd in soils and elevation. The results of risk assessment showed that there was no obvious ecological risk in the study area.

Identification of the factors determining the concentration and spatial distribution of Zn, Pb and Cd in the soils of the non-forest Tatra Mountains (southern Poland)

“…In the carbonate soils, Cd was correlated with pH (0.2539) and all three metals were correlated with SOC content (0.4356 for Zn, 0.4925 for Pb, and 0.5960 for Cd, p < 0.05). These relationships may indicate that non-forest meadow soils, especially in montane areas, act as sinks for heavy metals, their accumulation stimulated by the high amounts of organic matter that are usually present in soils in such locations (Ciarkowska, 2018 ; Józefowska et al, 2014 ; Miechówka et al, 2002 ; Tomaškin et al, 2013 , Yang, 2021 ).…”

“…6 C). As Cd is a metal that spreads as small particles that can be transported over large areas, its deposition is more closely related to the wind speed, which increases above the tree line (Ciriaková, 2009 ), and the amount of precipitation, which increases with elevation (Barančoková et al, 2009 ; Magnani et al, 2018 ; Yang et al, 2021 ). A small decrease in Cd content with altitude observed in some non-carbonate soils may be explained by its leaching from adjacent acid soils.…”

“…Kwapuliński et al, ( 2013 ) discussed the speciation of heavy metal forms with reference to the species composition of tree stands in selected areas of TNP, while Paukszto and Mirosławski ( 2019 ) studied the relationship between heavy-metal content in soils and nettles ( Urtica dioica ). Soil altitude has been indicated as an important factor that influences the absorption of air-borne pollutants and their concentrations in mountain soils by various authors (Szopka et al, 2013 ; Tomaškin et al, 2013 ; Yang, 2021 ). Korzeniowska and Krąż ( 2020 ) studied the differences in heavy metal content in soils from around Morskie Oko Lake and the environs of Kasprowy Wierch Mountain in TNP with increasing altitude, while Miechówka and Niemyska-Łukaszuk ( 2004 ) looked for relationships between heavy metal content and altitude in Lithic Leptosols.…”