Using isotopic lead and strontium in sediments to trace natural and anthropogenic sources in the Bohai Sea

Abstract

The containment history in the coastal zone of the Bohai Sea has not been sufficiently traced because of the difficulty in identifying complex sources of pollutants. This study quantitatively identified various sources of Pb and Sr in two tidal flat sediment cores from Bohai Bay (core BB) and Liaodong Bay (core LB) based on their isotope ratios to trace the natural and anthropogenic disturbance history in the Bohai Sea. The results showed that natural inputs of Pb were the main sources for cores BB and LB; however, core LB was more influenced by anthropogenic inputs. Natural inputs were derived mainly from Chinese loess and Yellow River sediments, whereas anthropogenic sources were mainly a mixture of vehicular exhaust emissions before 2000 and coal combustion after 2000. Anthropogenic influence has declined since the late 1990s, especially in Bohai Bay, but has increased in Liaodong Bay from 1998 to 2006.

Keywords: Historical variation; Pb isotope ratios; Sediment cores; Source identification; Sr isotope ratios.

Fig. 1

Location maps of sampling points showing the marine flow-current patterns of the Bohai Sea (Black dashed lines represent currents). Modified after Hu et al..

Fig. 2

Depth profiles of ¹³⁷Cs of core STZ.

Fig. 3

Vertical variations of Mz (grain size), TOC and pH in the sediment cores.

Fig. 4

Vertical variations of Pb isotopes in the sediment cores. The dote line represents year 2003. in core BB, and 2006, 1997 in core LB.

Fig. 5

Vertical variation of Sr isotopes in the sediment cores.

Fig. 6

Pb contents, EF, I_geo, Pb_A, MF_Pb, and contribution rates in the sediment cores.

Fig. 7

Sr contents, EF, I_geo, and contribution rates in the sediment cores.

Fig. 9

Biplot for indicating potential sources. (a): ²⁰⁸Pb/²⁰⁶Pb vs. ²⁰⁷Pb/²⁰⁶Pb; (b): ⁸⁷Sr/⁸⁶Sr vs. ²⁰⁷Pb/²⁰⁶Pb). References: Yellow River sediment; Loess; Liao River sediment; Coal combustion^,; Automobile exhaust^,; Liaoning Dongsheng Pb Mine; North China aerosol^,; Atmospheric dustfall; Atmospheric aerosols; BB and LB (this study).

Fig. 8

MixSIAR results for mean contribution of Yellow River sediment, Gas and vehicle exhaust particles, Liao River, Loess, coal combustion, Liaoning Pb mine, and North China aerosol, Oyster shell towards core BB and core LB samples. (a) core BB-Pb; (b) core LB-Pb; (c) core BB-Sr and (d) core LB-Sr.

Fig. 10

PCA results of the elements and isotope ratios in core BB and LB. Left: loading plots of the PC1 and PC2; right: scores plots marking the year. The yellow dots represent samples before 2000 and blue dots after 2000 on the right panels.