Contaminant Characteristics and Influencing Factors of Heavy Metals in Seawater and Sediments in a Typical Mariculture Bay in South China

Abstract

Heavy metal pollution in the mariculture areas is of considerable attention due to its potential ecological effects and public concern for seafood safety. A better understanding of the current contamination status and historical trend of heavy metals in the ecosystems of mariculture areas has an important implication for the sustainable development of marine ecosystems and for public health concerns. To assess the impact of human activities on heavy metal pollution in the mariculture area, seven metals (Cu, Pb, Zn, Cd, Hg, As, and Cr) and the environmental parameters were seasonally investigated in the surface seawater and sediments in Qinzhou Bay, a typical mariculture bay in South China. Seasonal variations in the concentration of heavy metals were found in both seawater and sediment, which are mainly influenced by seasonal hydrological change, biological activity, and human influence. The concentration of heavy metals in the seawater was at a relatively higher level than that of other mariculture areas in China, while a lower level was found in the sediment. The concentration of Cu increased in both seawater and sediment for the past decades (by nearly 2 times), which is mainly influenced by the mariculture and shipping activities. The concentration of Hg decreased significantly in the seawater for the past 40 years (decreased by 13 times) due to the decrease in production and usage of Hg. However, the concentrations of Pb, Zn, and Cd in seawater showed an increasing trend in the mariculture bay, while the concentrations of Pb, Zn, As, and Cr decreased in the sediment over the past decades. The decrease in pH value (decreasing by 4.7% for the past 20 years) was responsible for the different trend of those metals between seawater and sediment because the decrease in pH could re-release metals from sediments into the water column. Hg and As are the main ecological risk factors in the mariculture bay. This study suggests that environmental changes, such as ocean acidification, affect the distribution of metals in seawater and sediments, which we should be more vigilant and concerned about under the global climate change.

Quantification of the Seasonal Intrusion of Water Masses and Their Impact on Nutrients in the Beibu Gulf Using Dual Water Isotopes

“…Transport of the water masses is an important contribution to nutrient, primary productivity, phytoplankton and zooplankton community abundance in locally mixed seawater (Churchill et al, 2005;Gaughan et al, 2009;Kusum et al, 2019). Thus, nutrients and other materials in the BG are influenced not only by terrestrial pollution from coastal cities (Lao, Su et al, 2019;Lao et al, 2021Lao et al, , 2022 but also by pollution sources from other areas that enter the gulf with the transport of the water masses, such as the coast of western Guangdong (Chen, Dong, et al, 2019). Based on the proportional contribution of different water masses and nutrient concentrations in each water mass, the proportion of nutrient inputs into the BG with water masses can be quantified.…”

“…This indicated that water in the BG was considerably affected by WGCC intrusion. During winter, the runoff input into the BG decreases remarkably (Lao et al, 2020(Lao et al, , 2022, and water in the BG is evenly mixed. It forms an anti-clockwise circulation under the influence of the northeastern monsoon, with saline water intruding northward from the southern bay mouth and eastern QS (Xia et al, 2001).…”

Spatial and seasonal characteristics of dissolved heavy metals in the seawater of Beibu Gulf, the Northern South China Sea

“…Particularly in the marine environment, with the rapid economic and social development, large quantities of anthropogenic sources of heavy metals are discharged into the coastal environment, and those metals can be bioaccumulated by the marine organisms and biomagnified through the food chain, and ultimately endanger human health (Rainbow and Luoma, 2011;Kumar et al, 2019;Lao et al, 2019a;Liu et al, 2020;Huang et al, 2021). Thus, a better understanding of the current status of heavy metal contamination in marine ecosystems has a significant implication for the sustainable development of marine ecosystems, the seafood industry, and public concerns (Wang et al, 2013;Zhu and Zheng, 2017a;Zhu and Zheng, 2017b;Zhu and Zheng, 2018;Liu et al, 2020;Lao et al, 2022a).…”

“…Many researches have been increasingly concerned about the heavy metals in the marine environment. For example, increasing anthropogenic inputs of heavy metals into the seawater of mariculture areas have been reported due to the continuous expansion of the mariculture scale for the past decades (Wang et al, 2019;Liu et al, 2020;Lao et al, 2022a;Mohsen et al, 2022). Moreover, the coastal currents play an important role on the distribution of materials, and greatly impact on the local marine environment (Dong et al, 2012;Li et al, 2018;Lv et al, 2021;Hu et al, 2022;Lao et al, 2022b;Lao et al, 2022c).…”

“…Once the heavy metals input into the seawater, they can transport along with ocean currents to other areas, resulting in the wide spread of heavy metals in the marine environment (Li et al, 2018). Environmental change, such as ocean acidification and seasonal hypoxia, could change heavy metal status in the marine environment (Atkinson et al, 2007;Chakraborty et al, 2016;Ma et al, 2016;Lao et al, 2019a;Lao et al, 2022a). For example, the decrease of pH value in the marine environment leads to the re-release of heavy metals from sediments into the overlying water with linkage variation of metal concentrations in seawater and sediment environment, resulting in the decrease of heavy metals in sediments and the increase in seawater (Lao et al, 2022a).…”