In recent years, with the development of industries, such as mining, smelting, shipping, and oil and gas exploitation, the discharge of heavy metal pollutants into the marine environment through runoff, atmospheric precipitation, and other channels has increased ( Daniel at al., 2016; Davide et al., 2003; Liang et al., 2018; Waheed et al., 2013). Heavy metals are characterized by extensive sources, resistance to degradation, biotoxicity, proneness to enrichment, etc., and their potential long-term impact on human health and the natural ecosystem through various pathways, such as the food chain, has become a focus of marine environmental research (Bantan et al., 2020; Nemr et al., 2016). Marine sediments originate from surface materials, which are transported to the ocean by rivers. Thus, marine sediments are generally believed to be an important "source-sink" of heavy metals (Ding et al., 2019; Ünlü et al., 2008). Moreover, heavy metals often have higher concentrations in sediments than in the surrounding water (Huo et al., 2017; Windom et al., 1983 ). As marine sediments are sensitive to pollutants and play a crucial role in controlling the concentration of heavy metals in the water environment, they can be used as an indicator of environmental pollution (Adams et al., 1992; Karbassi et al., 2008).
The study area is located in the southwest of Bohai Bay, northwest of Laizhou Bay, and north of Dongying City. It is close to the estuary of Caoqiaogou River and Zhanli River and belongs to the Bohai Rim Economic Circle and the coastal economic belt. The Bohai Rim Economic Circle has gained an important economic and ecological status owing to its rich natural resources. From 1953 to 1976, the Yellow River entered the estuary in the study area through the Shenxiangou River and Diaokouhe River, forming complex underwater deltas. In 1976, the Yellow River changed its course to the current channel, almost cutting off the main sediment sources in this area. Under the action of waves and tidal current, the nearshore area has been in a state of scour for a long time. Therefore, the sedimentary environment in the study area is relatively complex (Tian et al., 2017; Zhang et al., 2016). Within the coastal economic belt, the Chengbei Sea area has abundant oil resources, including the Chengdao Oilfield. Futhermore, with the development of coastal urbanization, pollutants discharged from land and sea by human activities are increasing(Cui et al., 2019; Qu, 2009). Under the influence of human activities and natural processes, this area may have a complex pollution status (Peng et al., 2020). Therefore, the study of heavy metals in the surface sediments of this area is of great significance in understanding the distribution and transport characteristics of heavy metals under the influence of various factors.
The distribution characteristics of heavy metals in seabed surface sediments are often related to grain size, hydrodynamics, sediment transport, organic carbon, and sulfide (Lv et al., 2021; Pan et al., 2012). Previous studies on heavy metals in the study area mostly focused on evaluating the pollution status of heavy metals using various indices, such as the geoaccumulation index, enrichment factor, and potential ecological risk index, or analyzed the sources of heavy metals by combining correlation analysis and principal component analysis (Li et al., 2012; Liu et al., 2017; Zhang et al., 2015). However, the transport and hydrodynamic forcing of surface sediments in this area have rarely been analyzed and discussed. In this study, the distribution, source, and transport of sediments were analyzed and discussed in combination with the hydrodynamic characteristics, sedimentary dynamic environment, human activities, etc. The findings are expected to provide reference for understanding the influencing factors of heavy metal distribution and transport in the complex offshore sedimentary environment.