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Article

Geospatial Analysis of Heavy Metal Concentrations in the Coastal Marine Environment of Beihai, Guangxi During April 2021

by
Chaolu
1,
Bo Miao
2,3 and
Na Qian
4,5,*
1
Guangxi Zhuang Autonomous Region Marine Geological Survey Institute, Beihai 536000, China
2
Institute of Oceanography, Center for Earth System Research and Sustainability, University of Hamburg, 20148 Hamburg, Germany
3
Institute of Coastal Systems-Analysis and Modeling, Helmholtz-Zentrum Hereon, 21502 Geesthacht, Germany
4
Key Laboratory of Polar Geology and Marine Mineral Resources, China University of Geosciences, Ministry of Education, Beijing 100083, China
5
Hainan Institute of China University of Geosciences (Beijing), Sanya 572000, China
*
Author to whom correspondence should be addressed.
Coasts 2025, 5(3), 27; https://doi.org/10.3390/coasts5030027
Submission received: 10 April 2025 / Revised: 7 July 2025 / Accepted: 25 July 2025 / Published: 1 August 2025
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Abstract

Heavy metal pollution from human activities is an increasing environmental concern. This study investigates the concentrations of Cu, Pb, Zn, Cd, Hg, and As in the coastal seawater offshore of Beihai, Guangxi, in April 2021, and explores their relationships with dissolved inorganic nitrogen, phosphate, and salinity. Our results reveal higher heavy metal concentrations in the northern nearshore waters and lower levels in southern offshore areas, with surface waters generally exhibiting greater enrichment than bottom waters. Surface concentrations show a decreasing trend from the northeast to the southwest, likely influenced by prevailing northeast monsoon winds. While bottom water concentrations decline from the northwest to the southeast, which indicates the influence of riverine runoff, particularly from the Qinzhou Bay estuary. Heavy metal levels in southern Beihai waters are comparable to those in the Beibu Gulf, except for Hg and Zn, which are significantly higher in the water of the Beibu Gulf. Notably, heavy metal concentrations in both Beihai and Beibu Gulf remain considerably lower than those observed in the coastal waters of Guangdong. Overall, Beihai’s coastal seawater meets China’s Class I quality standards. Nonetheless, continued monitoring is essential, especially of the potential ecological impacts of Hg and Zn on marine life.

1. Introduction

With rapid economic and social development, large quantities of anthropogenic sources of heavy metals have been discharged into coastal environments [1,2,3,4,5,6,7]. Heavy metals are a group of elements naturally found in the Earth’s crust and are widely used in industrial, domestic, and agricultural activities. Due to the significant increase in these activities, the production and use of heavy metals have also increased [8,9,10,11,12]. Therefore, heavy metals such as mercury (Hg), arsenic (As), cadmium (Cd), lead (Pb), zinc (Zn), and copper (Cu) are often analyzed to assess pollution levels in global coastal areas [11,13,14,15,16,17,18,19,20,21,22,23,24]. Once released into seawater, they can be transported by ocean currents, resulting in the wide spread of heavy metals in the marine environment [25,26,27,28,29].
China has one of the longest coastlines in the world, stretching from Liaoning in the north to Guangxi in the south. Early investigations of heavy metals in the coastal regions have primarily focused on areas such as Bohai Bay, Laizhou Bay, and the Pearl River coast in Guangdong, where intensive urbanization and industrialization have led to well-documented pollution issues. However, the Guangxi coast, particularly the Beihai coastal area, has received considerably less attention, despite its growing economic importance and ecological sensitivity. Situated at the northern boundary of the Beibu Gulf, Beihai is experiencing rapid coastal development driven by major national initiatives, such as the “ASEAN-China Free Trade Zone” and the “Western Land–Sea New Corridor”. These developments are contributing to growing anthropogenic pressures on the marine environment, including potential heavy metal contamination. Therefore, Beihai represents a critical yet understudied region for assessing the environmental impacts of coastal industrialization in southern China and offers valuable insights for sustainable coastal management.
Gan et al. (2013) reported an increasing trend of heavy metal accumulation in sediment cores from coastal wetlands in the northern Beibu Gulf between 1985 and 2008 [30]. Additional studies have documented heavy metal contamination in various coastal zones and bays within the Guangxi region [31,32,33,34], though these studies have focused on sediments. Yet, compared with other heavy metal investigations in China’s coastal regions [35,36,37,38,39,40,41,42,43,44], there is still insufficient research on heavy metal concentrations in the coastal water column of Guangxi, especially under the context of ongoing regional development. This lack of data constrains our understanding of pollution sources, transport mechanisms, and ecological risks in this area.
Thus, this study aims to address this gap by reporting heavy metal concentrations in surface and bottom waters collected from 25 stations along the Beihai coast of Guangxi in April 2021. By comparing these concentrations with data of total dissolved inorganic nitrogen (DIN, including NH4+, NO2−, NO3−), phosphate, and salinity, this study analyzes their linear relationships to explore the factors influencing their spatial distribution. Furthermore, by comparing heavy metal levels in this region with those in the open waters of the Beibu Gulf and other coastal areas in China and worldwide, the study evaluates the degree of pollution along the Beihai coast.
The results reveal a distinct spatial pattern in heavy metal concentrations, with higher levels in the northern nearshore waters and lower concentrations in the southern offshore zones. Surface waters generally show higher concentrations than bottom waters. Notably, heavy metal concentrations in Beihai remain significantly lower than those observed in Guangdong’s coastal waters and consistently meet China’s Class I water quality standards, indicating minimal pollution impact in offshore Beihai. These findings not only offer updated baseline data on heavy metal concentrations in the northern Beibu Gulf of Guangxi but also provide valuable insights for coastal urban development and environmental management.

2. Materials and Methods

2.1. Study Region

The research area encompassing the offshore waters of Beihai in Guangxi is characterized by a complex interplay of wind fields and hydro-oceanographic processes. The wind regime in this region is predominantly influenced by the East Asian monsoon system. During the winter, the area has strong northeast winds (Figure 1a), while in summer it is characterized by weaker southwest winds. These wind patterns are crucial in driving surface currents and mixing processes, which in turn affect the distribution of heavy metals in water.

2.2. Sample Collection and Analysis

In April 2021, a total of 25 sampling stations were established for the investigation (Figure 1a, Table 1). The purpose of this survey and the designed stations is to assess the marine environmental quality and establish baseline data prior to the construction of wind power demonstrations. Sampling depth varied according to water depth at each station: at sites with depths less than 10 m, only surface seawater samples were collected; at depths between 10 m and 25 m, samples were taken from both the surface and bottom layers; and at stations with depths exceeding 25 m but less than 50 m, samples were collected from three layers. Only four stations (C16, C20, F17, and F20) included sampling from three depth layers.
The water sampling device used was a 5 L open–close type acrylic water sampler. Immediately after collection, the samples were pretreated. For Cu, Pb, Cd, and Zn, the water samples were filtered through a 0.45 μm fiber membrane and then acidified with nitric acid to a pH below 2. For As and Cr, the samples were also filtered through a 0.45 μm fiber membrane, followed by acidification with sulfuric acid to a pH below 2. For Hg, the water samples were not filtered and were directly acidified with sulfuric acid to a pH below 2.
When returning to the laboratory, As and Hg concentrations were determined using atomic fluorescence spectrometry (PF32, Shanghai Puxi, Shanghai, China), with typical detection limits of 0.5 and 0.007 μg/L, respectively. Cu, Pb, Cd, and Cr were analyzed using flameless atomic absorption spectrophotometry (TAS-990AFG, Shanghai Puxi), with detection limits of approximately 0.2, 0.03, 0.01, and 0.4 μg/L, respectively. Zn was measured using flame atomic absorption spectrophotometry [45], with a detection limit of around 3.1 μg/L. The quality control samples used in this study were obtained from the Institute for Environmental Reference Materials (IERM). The uncertainties for the elements were as follows: As (8.0%), Hg (5.9%), Cu (5.5%), Pb (4.0%), Cd (6.0%), Cr (5.2%), and Zn (3.8%).
For nutrient analysis, NO3− is reduced to NO2− using the zinc-cadmium reduction method [46], and NO2− is measured photometrically after reaction with naphthylethylenediamine. While NH4+ is determined by oxidation to indophenol blue. The detection limits were 0.05, 0.02, and 0.03 μmol/L, respectively. PO43− was analyzed using the phosphomolybdenum blue spectrophotometric method, with a detection limit of 0.02 μmol/L.
On-site measurements of water temperature and salinity were carried out using a surface water thermometer and a laboratory salinometer, with accuracies of ±0.01 °C and ±0.01 psu, respectively.

3. Results

All data obtained in this study are presented in Table 2 and Table 3, including in situ measured temperature and salinity, nutrient concentrations (NO2−, NO3−, NH4+, PO43−), and heavy metal concentrations (Cu, Pb, Cd, Zn, Cr, Hg, As).
Water temperature ranged from 25.4 to 27.2 °C, while salinity varied between 22.6 and 34.1 psu. The lowest salinity was observed at Station C1, the only location where salinity dropped below 30 psu. Inorganic nitrogen concentrations ranged as follows: NO2− (0.0056–0.0416 mg/L), NO3− (0.0277–0.1443 mg/L), NH4+ (0.007–0.037 mg/L), and PO43− (0.0036–0.0145 mg/L). Total dissolved inorganic nitrogen (the sum of NO2−, NO3−, and NH4+) ranged from 0.0403 to 0.2121 mg/L. The highest nutrient concentrations were generally observed at Stations C1, C2, C3, and C4, while the lowest values were consistently found at Station C20 (Figure 2 and Figure 3).
Heavy metal concentrations ranged as follows: Cu (0.73–1.57 μg/L), Pb (0.18–0.96 μg/L), Cd (0.021–0.104 μg/L), Zn (4.31–20.53 μg/L), Cr (0.57–1.38 μg/L), Hg (0.0054–0.0239 μg/L), and As (0.391–1.646 μg/L). The highest heavy metal concentrations are primarily detected at Stations C1 and C5, whereas the lowest were found at Stations C20 and F20 (Figure 2 and Figure 3).
Overall, the spatial distributions of salinity, nutrients, and heavy metals exhibit obvious variability, indicating the influence of multiple complex and interacting environmental factors.

4. Discussion

4.1. Spatial Distribution of Heavy Metals and Nutrients (DIN, PO43−) in Surface Seawater

Figure 2 illustrates the spatial distribution of heavy metal concentrations in surface seawater across the study area. Overall, concentrations show a clear decreasing trend from the northeast toward the southwest, with higher levels near the coastline and lower levels farther offshore. This spatial pattern is consistent with the prevailing northeast monsoon in spring, which facilitates the transport of pollutants from land to sea. It should be noted that some data, such as As and Cr, are lacking due to concentrations below the detection limits. But this does not significantly affect the interpretation of spatial distribution trends or related analyses. Because most of the undetected values are concentrated in offshore open-sea areas. This is consistent with the overall coastal-to-offshore decreasing trend in heavy metal concentrations.

4.2. Spatial Distribution of Heavy Metals and Nutrients (DIN, PO43−) in Bottom Seawater

Figure 3 presents the distribution of heavy metals in bottom seawater. On average, heavy metal concentrations in the bottom layer are lower than those in the surface waters. In contrast, salinity is generally higher at depth, with the highest values (~34.1 psu) observed at Stations F17 and F19. Horizontally, heavy metal concentrations decrease from the northwest to the southeast, similar to the distribution trends of phosphate and DIN in the bottom waters.
The northwestern transect, particularly Station C1, is closest to the estuary of Qinzhou Bay. Elevated heavy metal levels in this region likely reflect the influence of river discharge, industrial wastewater, and agricultural runoff.
To further investigate the quantitative relationships among chemical parameters, Figure 4 displays Pearson correlation coefficients (R2) between various heavy metals, as well as between heavy metals and salinity, DIN, and phosphate, for both surface and bottom seawater. In surface waters, strong positive correlations are observed among most heavy metals (R2 > 0.9), suggesting a common source. Some moderate correlations (R2 = 0.62–0.88), such as Zn-Cu and Cd-Cu, may be due to data limitations.
In the bottom layer, limited data, particularly for Cu (only two data points), restricts the correlation analysis, and thus Cu is excluded from Figure 4b. Nevertheless, significant positive correlations are observed among Pb, Cd, Zn, Hg, As, and Cr, reinforcing the likelihood of shared sources.
Weak correlations between heavy metals and salinity suggest that their distributions are not strongly influenced by freshwater input and/or ocean mixing. In contrast, moderate to strong correlations between heavy metals and nutrients (DIN and phosphate) indicate that anthropogenic inputs, especially agricultural wastewater, play a more dominant role. This is consistent with the fact that estuaries often act as sinks for land-derived nutrient discharges [47]. While the lower heavy metal concentrations observed at depth may reflect particle-associated downward transport and subsequent scavenging into surface sediments, coupled with a reduced influence of runoff, as freshwater is generally less dense and tends to remain near the surface. Nevertheless, the complex relationships between heavy metals and nutrients also suggest that additional biological and physicochemical processes may influence their spatial distribution patterns.

4.3. Comparison with Heavy Metals in Adjacent Coastal Regions

Based on the spatial distribution analysis in Section 3, this section compares average heavy metal concentrations between northern and southern surface and bottom waters. Stations in the northern nearshore region include C1, 2, 3, 4, 5, 6, 7, 8, 9, 13, and 17, while stations in the southern offshore region comprise C10, 11, 12, 14, 15, 16, 18, 19, 20, F14, 16, 17, 19, and 20 (Figure 5a).
As shown in Table 4, average concentrations of Pb, Cd, Zn, Cr, Hg, and As in the northern surface waters are approximately three times higher than those in the south. In the bottom layer, concentrations in the north are about twice those in the south. These findings support previous conclusions that, in addition to terrestrial runoff carrying agricultural and industrial waste, atmospheric deposition driven by the monsoon system also contributes to elevated heavy metal concentrations in nearshore surface waters.
When compared with open water data from the Beibu Gulf in 2021 (Table 4) [34], heavy metal concentrations in the southern offshore area of Beihai are generally consistent with open water levels, except for Zn and Hg (Figure 5d,e), which are significantly higher in the open Gulf waters. In contrast, concentrations along the western Guangdong coast (e.g., Zhanjiang and Yang Mao) [48] are markedly higher than those in Beihai and the Beibu Gulf. This suggests that elevated Zn and Hg levels in the Beibu Gulf may result from coastal current intrusion from Guangdong [31]. It is known that Hg can accumulate in marine organisms, and Zn is one of the essential nutrients for plants and is influenced by marine biological activity and high primary productivity of phytoplankton. Thus, the trace metals in marine organisms need further investigation to figure out the biological influence on Zn and Hg in waters, as shown in Figure 5d,e.
Beihai, having experienced later industrial development than Guangdong cities, is subject to relatively less anthropogenic pressure, which explains the lower heavy metal concentrations observed. According to China’s Class I and Class II water quality standards (Table 4), heavy metal levels along the Beihai coast meet Class I standards, indicating low pollution risk. Despite the low concentrations, potential long-term ecological risks should not be overlooked. Certain heavy metals can persist in the environment, bioaccumulate through the food web, and exert toxic effects on marine organisms, even at low levels. Continuous monitoring and ecological risk assessment are therefore essential to detect early signs and prevent adverse impacts on marine ecosystems.
It is also noteworthy that Cu, Cd, and Zn concentrations in Beihai coast waters are lower than global averages (Table 4) [49]. However, Pb concentrations are approximately five times higher than the global average, likely reflecting atmospheric inputs from industrial emissions and coal combustion across East and South Asian countries. This atmospheric deposition process is supported by historical Pb records in coral archives from the Indian Ocean [51], and atmospheric wet deposition of dissolved trace elements was previously revealed in Jiaozhou Bay [52]. This transport pathway is also supported by a decreasing trend of surface Pb from nearshore to offshore, as shown in Figure 2a, driven by northeast winds.

5. Conclusions

By analyzing the spatial distribution of heavy metal concentrations in surface and bottom seawater from 25 stations along the Beihai coast in April 2021, this study found that surface water concentrations were highest in the northeastern nearshore transect and gradually decreased southwestward toward the open sea. In contrast, bottom water heavy metal concentrations were highest in the northwestern transect and decreased southeastward. Despite these directional differences, the overall pattern across both layers indicates higher heavy metal concentrations in the northern, nearshore regions and lower concentrations in the southern, more open waters.
In combination with salinity, dissolved inorganic nitrogen, and phosphate data, the findings suggest that the spatial distribution of heavy metals is influenced primarily by the spring northeast monsoon and the input of agricultural and industrial wastewater from riverine sources. Compared with adjacent coastal areas, the overall concentrations of heavy metals in Beihai coastal waters and the Beibu Gulf are considerably lower than those reported offshore Guangdong. In 2021, all measured heavy metals along the Beihai coast meet China’s Class I water quality standards, indicating minimal anthropogenic pollution at that time.
Nonetheless, as coastal industry and offshore wind energy development continue to expand, attention must be paid to the potential environmental risks they may pose. Moving forward, this study will extend to investigate the seasonal variability of heavy metal distributions and explore the interactions between heavy metals in coastal seawater, biota, and sediments. Such efforts aim to enhance our understanding of the behavior, transport, and fate of heavy metals in the coastal waters of Beihai, Guangxi.

Author Contributions

Conceptualization, C.; methodology, C.; data curation, C.; writing—original draft preparation, C. and N.Q.; writing—review and editing, N.Q.; visualization, B.M.; supervision, N.Q. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (Grant No. 42306086) and the Fundamental Research Funds for the Central Universities (No. 2-9-2024-069). This work is also supported by Bureau of Geology and Mineral Exploration and Development of Guangxi Zhuang Autonomous Region (Sedimentary Dynamics Monitoring and Research Project of the Guangxi Coastal Zone, No. 2022-11).

Data Availability Statement

Data is contained within the article.

Acknowledgments

We are grateful to teachers and students who participated in the field collection of samples and data in April 2021.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) Seawater sampling sites in the offshore area of Beihai, Guangxi, China. Black arrows indicate seasonal monsoon patterns, i.e., northeast winds in winter and southeast winds in summer. In April, the study region was dominated by northeast winds. Blue arrows represent river discharges into the northern Beibu Gulf, including the Fangcheng River, Qin River, and Nanliu River. (b,c) show the distributions of salinity measured on-site in the surface and bottom waters, respectively.
Figure 1. (a) Seawater sampling sites in the offshore area of Beihai, Guangxi, China. Black arrows indicate seasonal monsoon patterns, i.e., northeast winds in winter and southeast winds in summer. In April, the study region was dominated by northeast winds. Blue arrows represent river discharges into the northern Beibu Gulf, including the Fangcheng River, Qin River, and Nanliu River. (b,c) show the distributions of salinity measured on-site in the surface and bottom waters, respectively.
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Figure 2. Distribution of heavy metals in surface seawater, including (a) Pb, (b) Cd, (c) Zn, (d) Hg, (e) As, (f) Cr, (g) Cu, (h) DIN, and (i) PO43−. Heavy metals exhibit a clear decreasing trend from the northeast toward the southwest.
Figure 2. Distribution of heavy metals in surface seawater, including (a) Pb, (b) Cd, (c) Zn, (d) Hg, (e) As, (f) Cr, (g) Cu, (h) DIN, and (i) PO43−. Heavy metals exhibit a clear decreasing trend from the northeast toward the southwest.
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Figure 3. Distribution of heavy metals, including (a) Pb, (b) Cd, (c) Zn, (d) Hg, (e) As, (f) Cr, (g) Cu, and DIN (h), and PO43− (i) in bottom seawater. Heavy metals exhibit a clear decreasing trend from the northwest toward the southeast, consistent with the trends of DIN and PO43−.
Figure 3. Distribution of heavy metals, including (a) Pb, (b) Cd, (c) Zn, (d) Hg, (e) As, (f) Cr, (g) Cu, and DIN (h), and PO43− (i) in bottom seawater. Heavy metals exhibit a clear decreasing trend from the northwest toward the southeast, consistent with the trends of DIN and PO43−.
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Figure 4. The correlation analysis of heavy metals and salinity (S), DIN, PO43− in the surface (a) and bottom (b) seawater offshore Beihai in the Beibu Gulf. Asterisks in the figure denote statistical significance: * for p < 0.05, and *** for p < 0.001.
Figure 4. The correlation analysis of heavy metals and salinity (S), DIN, PO43− in the surface (a) and bottom (b) seawater offshore Beihai in the Beibu Gulf. Asterisks in the figure denote statistical significance: * for p < 0.05, and *** for p < 0.001.
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Figure 5. Average heavy metal concentrations of Pb (b), Cd (c), Zn (d), Hg (e), As (f), Cr (g) in surface waters between the northern and southern coastal areas of Beihai (a) and comparisons with heavy metal levels in the Beibu Gulf and Guangdong coastal waters.
Figure 5. Average heavy metal concentrations of Pb (b), Cd (c), Zn (d), Hg (e), As (f), Cr (g) in surface waters between the northern and southern coastal areas of Beihai (a) and comparisons with heavy metal levels in the Beibu Gulf and Guangdong coastal waters.
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Table 1. Seawater sampling stations in this study.
Table 1. Seawater sampling stations in this study.
StationDepth/mLatitudeLongitude
C1921°36.3213′108°40.4959′
C25.821°32.0214′108°37.8169′
C315.321°27.1675′108°34.8850′
C420.421°23.6146′108°31.7859′
C56.721°34.7318′108°44.6104′
C612.721°30.1876′108°42.7251′
C714.321°25.3352′108°39.7912′
C816.321°21.5483′108°35.9986′
C96.221°32.9055′108°49.1849′
C101121°28.1258′108°47.3539′
C1117.921°22.4029′108°44.4931′
C1220.121°18.2397′108°40.1305′
C138.321°30.8257′108°53.6273′
C1411.921°25.6488′108°52.5277′
C1519.221°20.5087′108°49.4039′
C1625.321°14.7417′108°45.7000′
C176.821°28.4784′108°58.9844′
C181021°23.6137′108°57.6413′
C1916.221°18.1637′108°54.7561′
C2025.821°11.7338′108°51.3855′
F1424.221°10.0274′108°32.2898′
F1622.521°17.1288′108°34.6947′
F1727.521°08.2742′108°37.0892′
F1922.521°14.4520′108°38.7602′
F202621°09.6830′108°43.1785′
Table 2. Temperature (T) (°C), salinity (S) (psu), and nutrients (NO2−, NO3−, NH4+, DIN, PO43−) (mg/L) in seawater. DIN is the sum of NO2−, NO3−, and NH4+.
Table 2. Temperature (T) (°C), salinity (S) (psu), and nutrients (NO2−, NO3−, NH4+, DIN, PO43−) (mg/L) in seawater. DIN is the sum of NO2−, NO3−, and NH4+.
StationLayer/mTSNO2−NO3−NH4+DINPO43−
C1Surface (0.5)26.822.60.04160.13820.03230.21210.0134
C2Surface (0.5)26.4300.03510.12970.0270.19180.0145
C3Surface (0.5)26.2310.01920.11030.02860.15820.0137
C3Bottom (13)25.532.90.03160.14430.01930.19530.0145
C4Surface (0.5)26.131.30.01040.11230.03050.15320.0132
C4Bottom (18)25.7320.02790.13170.0370.19660.0141
C5Surface (0.5)25.429.80.03620.12850.02610.19080.0141
C6Surface (0.5)26.830.30.03110.10730.03570.17410.0137
C6Bottom (10)25.931.30.03860.11530.03640.19030.0142
C7Surface (0.5)25.831.90.01830.0890.02360.13090.0136
C7Bottom (12)25.731.70.03860.13070.02610.19540.0142
C8Surface (0.5)25.832.10.01830.07170.02070.11060.0115
C8Bottom (14)25.532.60.02440.1090.0280.16140.014
C9Surface (0.5)26.3310.02520.13680.03120.19320.0138
C10Surface (0.5)26.831.50.01170.0560.01430.0820.0089
C10Bottom (9)25.632.30.01430.06430.01680.09550.0103
C11Surface (0.5)26.132.20.01780.08170.02160.12110.0125
C11Bottom (15)25.433.10.01460.07430.01980.10870.0115
C12Surface (0.5)2632.50.01520.0670.01840.10060.0108
C12Bottom (18)25.433.10.01350.0620.01610.09160.0096
C13Surface (0.5)25.630.60.02140.13210.02060.17410.0144
C14Surface (0.5)26.432.70.01420.0750.01980.1090.0115
C14Bottom (10)26.332.70.01520.07430.02090.11040.0115
C15Surface (0.5)26.230.50.01330.0670.01860.09890.0103
C15Bottom (17)25.633.90.01380.07030.02090.1050.0103
C16Surface (0.5)26.3330.01250.0620.01860.09310.0096
C16Middle (10)2633.30.01090.05230.01340.07660.0082
C16Bottom (23)25.633.90.01340.06730.01750.09820.0103
C17Surface (0.5)25.430.80.03690.1030.03010.170.0135
C18Surface (0.5)26.830.50.01340.0670.01750.09790.0103
C18Bottom (8)25.632.60.01420.0750.01860.10780.0115
C19Surface (0.5)26330.01250.05870.01860.08980.0096
C19Bottom (14)25.833.30.01380.06070.02090.09540.0103
C20Surface (0.5)25.832.90.00870.05230.01340.07440.0082
C20Middle (10)25.633.30.00560.02770.0070.04030.0036
C20Bottom (23)25.433.70.01120.0570.01480.0830.0089
F14Surface (0.5)26.633.10.01470.07430.01860.10770.0114
F14Bottom (22)26.233.60.01610.08230.02180.12030.0126
F16Surface (0.5)27.2320.02140.11070.03020.16230.0145
F16Bottom (20)25.633.90.01920.10030.02680.14640.0132
F17Surface (0.5)26.933.10.01620.06830.02160.10610.0125
F17Middle (10)26.533.80.01410.07130.01860.10410.011
F17Bottom (25)26.334.10.01470.07430.01950.10860.0114
F19Surface (0.5)27.232.10.01980.10370.02770.15120.0117
F19Bottom (20)25.534.10.01670.08570.0230.12530.0101
F20Surface (0.5)26.632.90.02410.08730.02410.13550.0138
F20Middle (10)25.9340.03990.0670.01730.12420.0103W
F20Bottom (24)25.933.80.00950.07130.01860.09950.011
Table 3. Heavy metal concentrations (µg/L) in seawater.
Table 3. Heavy metal concentrations (µg/L) in seawater.
StationLayer/mCuPbCdZnCrHgAs
C1Surface (0.5)1.570.950.10418.641.320.02371.646
C2Surface (0.5)0.960.560.06310.880.880.01440.928
C3Surface (0.5)—0.320.0326.830.570.00860.682
C3Bottom (13)0.750.550.05610.450.820.01390.993
C4Surface (0.5)—0.310.0386.98—0.00860.58
C4Bottom (18)—0.480.05611.970.810.01350.969
C5Surface (0.5)1.520.960.10417.131.380.02391.591
C6Surface (0.5)—0.530.04410.040.680.01140.823
C6Bottom (10)0.730.50.05611.050.810.01350.868
C7Surface (0.5)—0.560.0285.77———
C7Bottom (12)—0.430.04410.250.680.01140.823
C8Surface (0.5)—0.260.0285.97———
C8Bottom (14)—0.320.0287.81—0.00790.58
C9Surface (0.5)1.360.860.10420.531.320.02341.532
C10Surface (0.5)———————
C10Bottom (9)—0.18—————
C11Surface (0.5)—0.220.0285.83—0.0061—
C11Bottom (15)—0.180.0214.97—0.0057—
C12Surface (0.5)—0.180.0216.46—0.0054—
C12Bottom (18)———————
C13Surface (0.5)1.320.820.10418.291.210.02241.484
C14Surface (0.5)—0.210.0284.99———
C14Bottom (10)—0.240.0285.4———
C15Surface (0.5)—0.180.0214.63———
C15Bottom (17)—0.210.0214.88———
C16Surface (0.5)—0.18—4.34———
C16Middle (10)——— ———
C16Bottom (23)—0.18—4.85———
C17Surface (0.5)1.440.860.08818.141.180.02211.567
C18Surface (0.5)—0.180.0214.75———
C18Bottom (8)—0.210.0214.93———
C19Surface (0.5)—0.18 4.31———
C19Bottom (14)—0.210.0214.52———
C20Surface (0.5)———————
C20Middle (10)——————0.982
C20Bottom (23)—0.18—4.31———
F14Surface (0.5)—0.180.021——0.00560.422
F14Bottom (22)—0.210.0214.4—0.00610.456
F16Surface (0.5)—0.320.0384.95—0.00790.58
F16Bottom (20)—0.260.0214.63—0.00720.53
F17Surface (0.5)—0.210.021——0.00620.453
F17Middle (10)—0.180.021———0.411
F17Bottom (25)—0.180.021——0.00550.422
F19Surface (0.5)—0.260.0385.45—0.00740.544
F19Bottom (20)—0.210.0214.95—0.00630.47
F20Surface (0.5)—0.210.0214.8—0.00660.419
F20Middle (10)——0.021———0.391
F20Bottom (24)—0.180.021———0.422
“—“ indicates heavy metal concentrations are below the detection limit.
Table 4. Comparison with heavy metal concentrations in this study and other ocean regions.
Table 4. Comparison with heavy metal concentrations in this study and other ocean regions.
Ocean Region Cu (μg/L) Pb (μg/L) Cd (μg/L) Zn (μg/L) Cr (μg/L) Hg (μg/L) As (μg/L) Reference
Beihai coast: north surface1.36 ± 0.22
(n = 6)		0.64 ± 0.27
(n = 11)		0.07 ± 0.03
(n = 11)		12.66 ± 5.90
(n = 11)		1.07 ± 0.31
(n = 8)		0.02 ± 0.007
(n = 9)		1.20 ± 0.44
(n = 9)		this study
Beihai coast: south surface* 0.21 ± 0.04
(n = 12)		0.03 ± 0.007
(n = 10)		5.05 ± 0.68
(n = 10)		* 0.006 ± 0.001
(n = 7)		0.48 ± 0.07
(n = 5)
Average surface1.36 ± 0.22
(n = 6)		0.41 ± 0.28
(n = 23)		0.047 ± 0.032
(n = 23)		9.034 ± 5.722
(n = 21)		1.068 ± 0.314
(n = 8)		0.013 ± 0.008
(n = 16)		0.947 ± 0.499
(n = 14)
Beihai coast: north bottom0.74
(n = 2)		0.46 ± 0.09
(n = 5)		0.05 ± 0.01
(n = 5)		10.31 ± 1.55
(n = 5)		0.78 ± 0.07
(n = 4)		0.012 ± 0.003
(n = 5)		0.85 ± 0.17
(n = 5)
Beihai coast: south bottom* 0.20 ± 0.03
(n = 13)		0.022 ± 0.002
(n = 10)		4.78 ± 0.32
(n = 10)		* 0.006 ± 0.001
(n = 5)		0.46 ± 0.04
(n = 5)
Average bottom0.74
(n = 2)		0.27 ± 0.13
(n = 18)		0.03 ± 0.02
(n = 15)		6.63 ± 2.83
(n = 15)		0.78 ± 0.07
(n = 4)		0.009 ± 0.004
(n = 10)		0.65 ± 0.23
(n = 10)
Beibu Gulf1.060.230.0312.120.650.080.62[34]
West Guangdong coastal1.911.810.0911.861.27—1.86[48]
Global average1.680.0790.080.6——0.62[49]
Grade I51120500.0520GB 3097-
1997 *
Grade II1055501000.230
* Cu and Cr were not detected in both surface and bottom waters in the offshore southern area, as their concentrations were below the detection limit. This indicates that there is no Cu and Cr pollution along the Beihai coast. Grades I-II are the National Standard of China for Seawater Quality GB3097-1997 [50].
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Chaolu; Miao, B.; Qian, N. Geospatial Analysis of Heavy Metal Concentrations in the Coastal Marine Environment of Beihai, Guangxi During April 2021. Coasts 2025, 5, 27. https://doi.org/10.3390/coasts5030027

AMA Style

Chaolu, Miao B, Qian N. Geospatial Analysis of Heavy Metal Concentrations in the Coastal Marine Environment of Beihai, Guangxi During April 2021. Coasts. 2025; 5(3):27. https://doi.org/10.3390/coasts5030027

Chicago/Turabian Style

Chaolu, Bo Miao, and Na Qian. 2025. "Geospatial Analysis of Heavy Metal Concentrations in the Coastal Marine Environment of Beihai, Guangxi During April 2021" Coasts 5, no. 3: 27. https://doi.org/10.3390/coasts5030027

APA Style

Chaolu, Miao, B., & Qian, N. (2025). Geospatial Analysis of Heavy Metal Concentrations in the Coastal Marine Environment of Beihai, Guangxi During April 2021. Coasts, 5(3), 27. https://doi.org/10.3390/coasts5030027

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