Mercury distribution in the foliage and soil profiles of a subtropical forest: Process for mercury retention in soils

• Published in: Journal of geochemical exploration 2019-10, Vol.205, p.106337, Article 106337
• Main Authors: Du, Buyun, Zhou, Jun, Zhou, Lingli, Fan, Xingjun, Zhou, Jing
• Format: Article
• Language: English
• Subjects: Altitudinal distribution; Atmospheric deposition; Budget; Litterfall; Residence time; Storage
• ISSN: 0375-6742; 1879-1689
• DOI: 10.1016/j.gexplo.2019.106337

Forest canopy can exert great influence on the global mercury (Hg) accumulations and soil Hg pools. However, there exists a debate that forests are net sinks or sources of atmospheric Hg. The current study aimed to study whether forest soils in the southwestern China are net sinks for atmospheric Hg and the soil residence time of Hg in the subtropical forest soils. Foliage samples of fern and pine in sixty-six plots and six soil profiles were sampled at the Tieshanping Forest Park (TFP) in southwestern China. To study the process of Hg budget, the flux of Hg input and the output from the forest soils were estimated and the mean soil Hg residence time (MRT) were calculated using a simple two-box model. The Hg concentrations in foliage (98 ng g−1) was relatively higher than remote areas because the elevated atmospheric Hg concentrations. Mercury concentrations in the understory foliage were positively correlated with altitude, which was resulted from the altitudinal distribution of increasing soil Hg concentrations. The annual Hg deposition flux via litterfall was estimated at 42 μg m−2 and the total Hg input to the forests was approximately 108 μg m−2. The annual Hg retention in forest soil was about at 76 μg m−2. The MRT was longer in surface horizon (0–10 cm, 134 ± 14 yr) than that in the mineral horizon (20–80 cm, 595 ± 34 yr). Subtropical forests in southwestern China act as net sinks for atmospheric Hg and 69% of the total Hg deposition was sequestrated in the forest soils. Short residence time of Hg in surface soil enhanced the deposited Hg output from the forest, which may be the reason for the comparable soil Hg concentration with some other remote forests with lower Hg depositions. •Altitudinal Hg distribution in the foliage of understory and overstory were different.•The Hg retention in forest soil was 74.7 μg m−2 yr−1 in the subtropical forest.•The subtropical forest soil is net sinks of the atmospheric Hg.•The Hg residence time was longer in surface horizon than the mineral horizon.