Ecological risk of heavy metals in lake sediments of China: A national-scale integrated analysis

Intensive anthropogenic activities, specifically, industrial and agricultural production, have resulted in heavy metal enrichment in lake sediment and threats to aquatic ecosystems and human health. Evaluating the potential ecological risk of heavy metals in lake sediment is essential for promoting appropriate lake management in aquatic ecosystems. Large-spatial scale risk evaluations of heavy metal pollution in lake sediment in densely populated countries such as China are lacking. We compiled sediment heavy metal (Cu, Pb, Zn, Ni, Cr, As, Hg, and Cd) data from 190 lakes distributed across five geographic zones in China published between 2000 and 2019, evaluated the potential ecological risk and identified heavy metal sources through positive matrix factorization. Five conclusions were drawn. (1) Regarding the eight collected heavy metals, 6.1–40.4% of 190 lakes exhibited higher concentrations than the Chinese soil background value, and the concentration in 6.2% of lakes exceeded the probable effect concentration. (2) Based on the potential ecological risk index (PERI) and sum of toxic units (STU), Cd and Hg were the major pollutants. (3) The PERI value notably decreased with increasing lake surface area, and small lakes (<10 km2) generally yielded high PERI values. Among the five Chinese geographic zones, the Eastern Plain Lake Zone and Inner Mongolia-Xinjiang Lake Zone exhibited higher potential ecological risk. Compared to natural lakes, urban lakes and reservoirs posed higher ecological risks, while freshwater lakes yielded higher PERI values than saltwater lakes and saline lakes. (4) In all lakes, lake sediment pollutants Cu and Zn mainly originated from traffic sources; Cd originated from agricultural activities; Pb and Hg were related to industrial activities; and Ni, Cr and As indicated mixed sources. (5) In the Eastern Plain Lake Zone, Yunnan-Guizhou Plateau Lake Zone and Northeast Plain and Mountain Lake Zone, industry was the dominant source of heavy metals in lake sediment, while in the Tibetan Plateau Lake Zone and Inner Mongolia-Xinjiang Lake Zone, except for industrial sources, agricultural sources played an important role. Our national-scale integrated analysis provides valuable references for both macroscale policy formulation and polluted lake restoration.