As a part of the global material flow, the global dispersion of persistent organic pollutants (POPs) is also regulated by forests. In theory, the forest plays as a "sink" and delays the transport of POPs to remote/cold regions. Nevertheless, previous studies have not yet answered some important scientific issues. For example, from a global perspective, what is the distribution of POPs in forests? How will forest changes influence the global transport of POPs? To answer these questions,
Dr. Ping Gong from the Institute of Tibetan Plateau Research, Chinese Academy of Sciences, and his colleagues systematically reviewed the cycling mechanism of POPs in forests (Figure 1), and emphasized the acceleration of POP deposition from air to soil under forest foliage by leaves absorption, litterfall, and rain washing.
Figure 1. Global pattern of POPs transport (left panel) and POP cycling in forests (right panel)
The author also collected the published data to explore the distribution of POPs in the global forests (Figure 2). The results of statistics showed that organic carbon was a key factor in controlling the accumulation of POPs in forest soils, while the relatively high levels of forest soils in middle and high latitudes reflected the role of forests on hindering POPs transmission to the Arctic. Based on this statistics, the global storage of POPs in vegetation and soil of forests, POP deposition flux under forest canopy, and storage changes of POPs caused by forest changes (the increase or decrease of forest area and the release from forest fires) were estimated. Generally, the annual release of POPs caused by forest changes is about 10% of the annual deposition flux in forest regions, but for some compounds (such as polychlorinated biphenyls and polycyclic aromatic hydrocarbons), their annual release has been close to or even exceeded the annual deposition flux. It indicated that forest changes were significantly changing the "source-sink" relationship of POPs and the processes of global transport, and thus partially offsetting the effect of the implementation of the Stockholm Convention.
Figure 2. The influence of soil organic carbon (TOC) and latitude on the distribution of POPs in forest soil
Finally, by scanning the gaps of forest POPs studies, the researchers proposed to strengthen the research in key areas (tropical rainforests and boreal forests) and of key processes (such as dry and wet deposition, POPs transmission in forest food webs) at macroscale.
This study was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, Pan-Third Pole Environment Study for a Green Silk Road (Pan-TPE) (XDA2004050202), the National Natural Science Foundation of China (41877490 and 41925032), the Second Tibetan Plateau Scientific Expedition and Research (STEP) Programme (2019QZKK0605), and the Youth Innovation Promotion Association Chinese Academy of Sciences (CAS2017098).
Media Contact: Ping Gong 010-84097109