| The rapid industrialization and urbanization development of coastal cities usually lead to the accumulation of heavy metals such as Zn,Ni,Hg,Mn,Pb,Cu,Cr,Cd,As,Fe and other heavy metals in coastal sediments,which in turn leads to serious environmental pollution problems.Therefore,an in-depth understanding of the longterm variation in their pollution levels and their driving forces is crucial for ecological environment governance in coastal waters.Based on the long-term monitoring data from 1987 to 2019,this study used a variety of data mining methods to evaluate the spatiotemporal distribution characteristics,multi-media migration,source apportionment and ecological risks of heavy metals in the marine sediments of the city in the Guangdong-Hong Kong-Macao Greater Bay Area.The results of spatiotemporal characteristic analysis of heavy metal concentrations showed that the average concentrations of Zn,Ni,Hg,Mn,Pb,Cu,Cr,Cd,As,Fe in the sediments were 124.4±75.3,21.0±10.5,0.2±0.3,540.9±192.7,46.6±23.1,62.4±161.6,36.2±25.5,0.4±1.1,8.2±3.2,27942.0±6642.4 mg/kg,respectively.Compared with other coastal areas,the overall concentration of heavy metals in the sediments of the study area is at a moderate pollution level.Mann-Kendall trend analysis was used to study the long-term variation trend of heavy metal concentrations,results showed that the concentrations of Hg,Pb,Cu,Cr and Cd showed a clear downward trend during the study period.The spatial distribution of heavy metals was visualized by kriging interpolation,high concentrations of Zn,Hg,Pb,Cu and Cd were concentrated in the seas close to cities and ports,while Mn,As and Fe were mainly distributed in the seas far from the land.The wavelet analysis results showed that oscillations with high-intensity and short-period were mainly concentrated in 1987–1997.These results indicated that heavy metal pollution in the study area was related to anthropogenic activities,and that the significant decline in pollution levels in recent years might be related to the reduction in the intensity of anthropogenic emission sources.Multimedia transport model was used to explore the transport characteristics of heavy metals in a multi-media environment,the simulated results suggested that heavy metals entering the ER tended to deposit in the sediments.The deposition ability of Fe and Pb is higher,while the deposition ability of Ni,Cd,and As is weak.The results of uncertainty and sensitivity analysis showed that sedimentation rate(0.8–39.7%),sediment burial rate(0.0–54.6%),and in-outflow rate(0.2–32.3%)were the key factors affecting the coastal sediment concentration.In addition,source apportionment by co-occurrence network,self-organized map,and constrained PMF receptor model showed that the heavy metal pollution level in the northwest of the study area gradually increased during the study period,influenced by Pearl River flow and traffic activities.On the other hand,the adverse impacts of industrial activities and urban river discharges on water bodies have declined over time due to pollutant mitigation policies over the past few decades.The source apportionment results of the basic PMF model and the constrained PMF model were compared.The analysis showed that applying the simulation results of the QWASI model as the constraints of the PMF model could improve the accuracy and stability of the source apportionment results.Finally,the spatiotemporal differences in the ecological risk levels of heavy metals in sediments were analyzed by the potential ecological risk index method.The results showed that higher ecological risk levels were concentrated in the middle of CSR,while most areas were at low ecological risk levels.In addition,the ecological risk levels of heavy metals in the sediments of the study area showed a significant downward trend with time.The above research results provided important scientific basis and reference for formulating or adjusting pollution control strategies of heavy metals in coastal sediments. |
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