Mercury Inputs to Chinese Marginal Seas: Impact of Industrialization and Development of China

Abstract

In the past decades, China has experienced substantial economic growth and industrialization. However, the effects of vast development of China on Hg input to the nearby oceans are still unclear. In this study, the influx and isotopic compositions of Hg in four 210Pb‐dated sediment cores were examined to investigate changes in Hg deposition to the marginal seas off China over a century. Nearshore cores had higher Hg influxes than offshore cores. Increases of Hg influxes started since the 1950s, which coincides with China's economic development. Dramatic historical changes in Hg isotopic composition were observed in the cores (δ202Hg: −2.01‰ to −0.69‰; Δ199Hg: −0.16‰ to 0.31‰; n = 106). δ202Hg increased from the deep to the surface layers of the cores. The offshore cores mainly showed positive Δ199Hg values, but the pre‐1950 samples had more positive Δ199Hg values than the younger samples. The nearshore cores mainly showed negative Δ199Hg values in the pre‐1950s samples, but the younger samples showed Δ199Hg values close to zero. A triple‐mixing isotope model, used to quantify the contribution of potential Hg inputs (e.g., direct discharge of industrial Hg, soil Hg, and precipitation‐derived Hg), showed clear evidence of enhanced industrial Hg inputs to the ocean margin, but slightly decreased watershed soil Hg inputs in the last few decades. The variations of watershed‐derived Hg were likely caused by the construction of impoundments in major rivers of China. This study demonstrates that mercury inputs to Chinese marginal seas have been largely altered due to the industrialization and economic development of China.

Mercury Inputs Into Eastern China Seas Revealed by Mercury Isotope Variations in Sediment Cores

“…It needs to be noted that both concentrations and influxes of THg exhibited a slight decrease from 2001 to 2010, especially for industrial Hg and atmospheric Hg, while differently, the influxes of riverine Hg kept increasing (Figures 5 and 6). This seems a bit different from other published studies which reported an increasing trend in industrial Hg inputs and a decreasing trend in riverine Hg inputs (Yin et al, 2018). Actually, the observed change indicated by only one data point here may not represent a trend, and maybe it was just a fluctuation induced by uncertainties (e.g., sampling contingency).…”

“…As summarized in the box plot (Figure ), the Δ 200 Hg and Δ 204 Hg signatures in Yellow Sea central core‐3 (in this study) were similar to those in Yellow Sea surface sediments (Meng et al., 2019), Yellow Sea central core (Yin et al., 2018) and gaseous Hg 0 (Fu et al., 2018), rather than East China Sea nearshore core‐1 and offshore core‐2 (in this study), East China Sea surface sediments (Meng et al., 2019), East China Sea nearshore core (Yin et al., 2018), particulate‐bound Hg (Fu et al., 2019), and wet precipitation Hg (Huang et al., 2018). These suggest that part of Hg in sediments from the central mud area of Yellow Sea was likely originally traced back to atmospheric Hg 0 .…”

“…Although core-1 and core-2 were not dated in this study, it is still necessary to find out the probable relationship between their depths and ages in order to provide a temporal variation of Hg source contributions. According to the reported data on sites with similar longitude and latitude, the sedimentation rates were found to vary significantly among the three cores, with approximately 1.29 cm yr −1 in core-1 (Yin et al, 2018;Zeng et al, 2013), 0.31 cm yr −1 in core-2 (Guo et al, 2006), and 0.23 cm yr −1 in core-3 (this study). Based on this, the ages (year) of core slices in core-1 and core-2 were further estimated, as listed in Table S6 and shown in Figure S3.…”

“…According to a previous study by Yin et al. (2018), this may be related to the construction of Three Gorges Dam in the Yangtze River, the largest dam in the world. Because the closure work of the Three Gorges dam was completed in 1997, the water storage and discharge functions controlled by the dam may affect the Hg inputs into the coastal region (M. Liu et al., 2020).…”

Sources of mercury in deep-sea sediments of the Mediterranean Sea as revealed by mercury stable isotopes

“…The aim of the present study is to investigate potential sources of Hg in Mediterranean deep-sea and Adriatic sediments. To our knowledge only a few studies report stable isotope compositions of Hg in deep-sea sediments and most of them were conducted close to estuaries or coastal region 15–18 . Ogrinc et al .…”