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. 2015 Aug 20;5:13323. doi: 10.1038/srep13323

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(A) PCA map showing the 8 sampling sites and their correlation with trace elements. Note: pH, Cl^–, Ca²⁺, Mg²⁺, K⁺, Na⁺, Fe²⁺, Mn²⁺, Cu²⁺, Zn²⁺, total N (nitrogen) and total P (phosphorus) were used to evaluate the influence of each variable. The longer the arrow, the greater the influence; the smaller the angle between two arrows, the closer their correlation. solid squares (■), upright (▲) and inverse (▼) triangles, and diamonds (♦) denote the Qijiaojing (QJJ), Aydingkol (AK), Jiangcheng (JC) and Heijing (HJ) sampling sites, respectively.