Spatial distribution, source identification and pollution assessment of metal content in the surface sediments of Nansi Lake, China

• Geochemical mapping of metal content in lake sediments was established.
• Pollution degree and potential ecological risk of metals were assessed.
• Moderately polluted area and potential ecological risk area were mapped respectively.
• Multivariate statistical analysis was used to reveal possible sources.
• Spatial–vertical distribution of elements was used to confirm the possible sources.

Nansi Lake which consists of four sublakes from north to south: Nanyang, Dushan, Zhaoyang and Weishan sublake is situated at the southwest of Shandong, China. It has been seriously affected by long-term intensive anthropogenic activities in recent years. An extensive survey was conducted in the surface sediments of Nansi Lake to investigate the spatial distribution, source identification as well as pollution assessment of metal contents. Results showed that the enrichment degree of studied metals decreased in the order of Hg > Cd > As > Pb > Cr > Ni > Cu > Zn, and the average contents of Hg, Cd, As and Pb were 2.87-, 2.73-, 1.95- and 1.89-fold higher than their background values respectively. The obtained geo-accumulation index (Igeo) indicated absent to moderate pollution by As and Pb. Cd followed closely, and Hg was in moderate pollution, while the other metals scarcely showed any pollution. Based on geostatistical analyses, small patches of Nanyang sublake and most parts of Dushan sublake and Weishan sublake suffered heavier pollution, and the whole Nansi Lake was almost in a moderate ecological risk state according to potential ecological risk index (RI). Multivariate statistical analyses combined with spatial–vertical distribution of elements contents in sampled core revealed that Fe2O3, Ni, Cr, Be, Li, V, Ti, Al2O3 and partially Zn, Pb and Cu mostly originated from natural sources, Hg and partially Cd, Zn, Pb and Cu mainly came from metals mining and smelting, industry and traffic sources, while As and partially Cd, Zn and Pb represented agricultural activities like fertilizing and pesticide consumption.