Intensive anthropogenic activities had affected Daya Bay in South China Sea since the 1980s: Evidence from heavy metal contaminations

Assessment of benthic ecological status and heavy metal contamination in an estuarine intertidal mudflat in the Northern Bohai Sea

Evaluating the ecological quality and pollution status of coastal mudflats is crucial for environmental protection and management, particularly when these areas serve as major shellfish production hotspots. In this study, we assessed the benthic ecological quality and heavy metals pollution in Geligang, located in the Northern Bohai Sea using the macrobenthos diversity index and the heavy metal pollution index. The Shannon-Wiener index (H'), AZTI marine biotic index (AMBI), multivariate AMBI (M-AMBI) showed that the benthic ecological quality in Geligang is either good or high. The potential ecological risk index and geoaccumulation index highlighted that cadmium (Cd) and mercury (Hg) as the primary heavy metal pollutants in Geligang. Surprisingly, the biomass of the two dominant species other than these indices serve as reliable indicators of heavy metal pollution. This suggests that the biomass of Mactra veneriformis and Potamocorbula laevis could be used to assess heavy metal pollution levels in Geligang.

Sediment record of heavy metals in Xincun Lagoon indicating anthropogenic impact over the last 200 years

Anthropogenic metal pollution is a leading environmental problem in southern China, especially in remote regions where its impact remains poorly understood. This study investigates the historical variation of heavy metal pollution over the last 200 years using a sediment core from Xincun Lagoon, Hainan Island, South China. The temporal evolution of heavy metal pollution aligns with China's socioeconomic development. Prior to the 1950s, heavy metal concentrations were at geochemical background levels, reflecting China's agrarian status. Since the 1950s, the increased heavy metal accumulation may be attributed to intensified human activities linked to rapid urbanization and industrialization. Despite the increase in heavy metal enrichments since the 1950s, Xincun Lagoon currently faces a low ecological risk.

Gut microbiome play a crucial role in geographical and interspecies variations in mercury accumulation by fish

Mercury (Hg) contamination in fish has raised global concerns for decades. The Hg biotransformation can be manipulated by gut microbiome and it is found to have a substantial impact on the speciation and final fate of Hg in fish. However, the contribution of intestinal microbiota in geographical and interspecies variations in fish Hg levels has not been thoroughly understood. The present study compared the Hg levels in wild marine fish captured from two distinct regions in South China sea. We observed a quite "ironic" phenomenon that MeHg levels in carnivorous fish from a region with minimal human impacts (Xisha Islands, 92 ± 7.2 ng g-1 FW) were much higher than those from a region with severe human impacts (Daya Bay, 19 ± 0.41 ng g-1 FW). Furthermore, the results showed that gut microbiome determined Hg biotransformation and played a crucial role in the variances in fish Hg levels across different geographical locations and species. The intestinal methylators, rather than demethylators, were more significant in affecting Hg biotransformation in fish. The carnivorous species in Xisha Islands exhibited a higher abundance of intestinal methylators, leading to higher MeHg accumulation. Besides, the gut microbiome could be shaped in response to the elevated Hg levels in these fish, which may benefit their adaptation to Hg toxicity and overall health preservation. However, anthropogenic activities (particularly overfishing) in Daya Bay have severely affected the fish population, disrupting the reciprocal relationships between fish and intestinal microbiota and rendering them more susceptible to pathogenic microbes. Overall, this study provided a comprehensive understanding of the role of gut microbiome in Hg bioaccumulation in fish and offered valuable insights into the co-evolutionary dynamics between fish and gut microbiome in the presence of Hg exposure.

Distribution and co-occurrence networks of the bacterial community in sediment cores from the subtropical Daya Bay, China

The bacterial community plays an important role in biogeochemical cycles in marine sediment. However, little is known about the vertical profiles and co-occurrence patterns of bacterial community in sediment cores from the marine environment. In this study, five sediment cores were taken from a subtropical bay in China, heavily impacted by anthropogenic activities. The bacterial composition in sediment cores was investigated by using high-throughput sequencing of the 16S rRNA gene. A principal coordinates analysis and an adonis analysis of the operational taxonomic unit (OTU) compositions showed that spatial variation, rather than vertical variation, determined the bacterial structure in sediment cores. The bacterial complexity varied greatly across the five sediment cores, and the rare taxa played an important role in supporting the stability of the bacterial network. This study revealed that sediment properties and anthropogenic activities may induce a shift in the bacterial composition in sediment cores of a subtropical bay.

Anthropogenic impacts on the temporal variation of heavy metals in Daya Bay (South China)

A detailed study of a sediment core from Daya Bay (South China) has revealed three stages of heavy metal deposition over the past century. Prior to the 1980s, heavy metal concentrations were low with limited influence by human activities. From the 1980s to 2000, metal pollution intensified, and anthropogenic activities, such as oil and petrochemical industries, and fuel combustion, had the greatest direct influence on Hg, Ni, Pb, and Zn concentrations, whereas atmospheric deposition and mariculture were also contributors to the continued increase in Cr, Cu, Pb, Zn, and Ni. Since the year 2000, heavy metal concentration has declined and stabilized. It is noteworthy that anthropogenic input of Cu and Pb is ongoing and may result in a moderate pollution risk. Both modified pollution index (MPI) and modified ecological risk (MRI) consistently indicate that the ecological risk in terms of heavy metals in Daya Bay has remained moderate over the past 70 years.

Toxic metal pollution and ecological risk assessment in water and sediment at ship breaking sites in the Bay of Bengal Coast, Bangladesh

Quantification of four toxic metals (As, Cr, Cd, and Pb) in water and sediments at the Sitakunda ship breaking area in Bangladesh was studied. Along with this, sediment quality and ecological risk were evaluated for the metal intrusion to the study area. A total sample number of 120 (water; n = 60 and sediment; n = 60) were analyzed for both winter and summer seasons using atomic absorption spectrophotometer (AAS). The trace metal concentration in both water and sediment showed decreasing trend as follows; Cr (mean-W: 0.118 mg/L; mean-S:121.87 mg/kg) > Pb (mean-W: 0.064 mg/L; mean-S: 65.31 mg/kg) > As (mean-W: 0.03 mg/L; mean-S: 32.53 mg/kg) > Cd (mean-W: 0.004 mg/L; mean-S: 4.81 mg/kg). However, in both segments, the concentrations of the toxic metals exceeded the recommended acceptable limits. As and Cd showed significant variation (water and sediment) between the seasons, while Pb and Cr had no seasonal impact. Metal pollution index (MPI) and contamination factor (CF) was evaluated and revealed that the study area exhibited the critical score of water quality (MPI > 100). The cumulative effect of the metal concentrations was high (CI > 3). The assessed mean geoaccumulaiton index (I_geo) revealed that the study area was moderate to strongly polluted except for Cr. According to the contamination factor (CF), the sediment samples were moderate to highly contaminated by Cd, Pb, and As. Moreover, the explored range of pollution load index (PLI) in all sampling sites in the ship breaking region was from 1.75 to 3.10, suggesting that the sediment in the study area was highly polluted by heavy metals (PLI > 1). The risk index and the potential ecological risk index (PERI) suggested that the study area was at high risk due to metals pollution. Therefore, it is obligatory to maintain some crucial efforts for the betterment of the surrounding environment near the investigated sites.

Distribution, source and risk assessment of heavy metals in the seawater, sediments, and organisms of the Daya Bay, China

Cu, Pb, Zn, Cd, Cr, Hg and As in seawater, sediment and organisms of the Daya Bay, Guangdong province, China were measured to acquire the comprehensive understanding on distribution, sources and risk assessment of heavy metals (HMs) in the marine ecosystem. The concentrations were relatively ideal, and the Pb was the major pollutant in the seawater and sediment. The contents of HMs were highest in spring; the concentrations near the sewage outlet and shore were noticeable. Submarine pipeline sewage, atmospheric deposition and runoff were the main sources of HMs in coastal waters. Studied HMs were preferentially retained by liquid phase; Cd, Cu and Zn were the most accumulated elements in the organisms from the surrounding environment. Cd in shellfish deserved particular attention, but the health risks including non-carcinogenic and carcinogenic risks of all elements were within acceptable limits. The potential health risks of Pb have been confirmed by molecular docking.

The spatial-temporal evolution of heavy metal accumulation in the offshore sediments along the Shandong Peninsula over the last 100 years: Anthropogenic and natural impacts

The anthropogenic and natural impacts on the temporal and spatial variations of heavy metals in sediments under the Shandong Peninsula coastal current are still unclear. Here, the concentrations\burial fluxes of Cr, Cu, Zn, As, and Pb in three sediment cores retrieved from the Bohai Sea and the Yellow Sea along the Shandong Peninsula were analyzed to study the spatial-temporal variability of heavy metal accumulation over the last century. The results showed that the buried heavy metal fluxes were relatively low at the end of the Shandong Peninsula coastal current. The enrichment factor (EF) and geoaccumulation index (I_geo) indicated that those metals did not severely pollute the sediments except As that reached a moderate enrichment. Principal component analysis (PCA) revealed that Cr, Cu, Zn, and Pb were mainly derived from natural weathering and As was determined by anthropogenic contamination. The strength of the Shandong Peninsula coastal current, the Yellow River estuary location, and sediment discharge load significantly influenced the concentrations of natural-origin heavy metals by affecting sediment grain size and the source-sink process. The emission of pollutants from agricultural and industrial activities in the Shandong Peninsula region resulted in As enrichment since the 1950s. Moreover, the EF values of heavy metals in sediment cores from China's coastal seas showed apparent spatial variations of heavy metal pollution but had coherent temporal variability with China's economic development process. Heavy metals pollution has weakened in most coastal seas since the 2000s, likely due to the extensive industrial upgrading and the implementation of pollution control. These results have a reference significance for studying the evolution and source-sink process of the heavy metals in offshore sediments and tracing anthropogenic impacts in different periods.

Characteristics of Heavy Metals in Seawater and Sediments from Daya Bay (South China): Environmental Fates, Source Apportionment and Ecological Risks

In this study, the spatiotemporal distributions, potential sources, and ecological risks of Hg, Cr, and As in seawater, and Hg, As, Zn, Cd, Pb, and Cu in sediments from Daya Bay were investigated. The five-year average concentrations of Hg, Cr, and As in seawater were 0.020 μg/L, 0.79 μg/L, and 2.08 μg/L, respectively. The five-year average concentrations of Hg, As, Zn, Cd, Pb, and Cu in surface sediments were 0.04 mg/kg, 7.34 mg/kg, 63.81 mg/kg, 0.23 mg/kg, 25.60 mg/kg, and 11.78 mg/kg, respectively. Annual variations in Hg, Cr, and As in seawater exhibited different trends. HMs in sediments, such as As, Zn, Pb, and Cu, exhibited similar annual variations, whereas Hg and Cd exhibited different annual variations. The spatial distribution of metal species in seawater and sediments showed significant variability, and the concentrations decreased gradually from the coast to the open sea. The comprehensive potential ecological hazard index (RI) of HMs in sediments indicated a relatively high risk, especially for Hg and Cd contamination. The geoaccumulation indices (Igeo) of As, Zn, Pb, and Cu suggested that these metals did not pollute Daya Bay, whereas those of Cd and Hg indicated mild and moderate pollution. The environmental fates of HMs were discussed based on Pearson correlation analysis, revealing that concentrations of HMs were greatly affected by parameters, such as pH, salinity, dissolved oxygen (DO), and total organic carbon (TOC). Principal component and factor analyses indicated that Hg, Cr, As, and dissolved inorganic nitrogen (DIN) in water originated from similar sources, including domestic sewage and wastewater from fishing ports, runoffs, and outlets. For sediments, it was proposed that Cu, Zn, As, Pb, and TOC exhibited similar sources, including cage culture and waste discharge from outlets. Meanwhile, Hg and Cd originated from other point sources, such as a harbor. The study suggests that sustainable management and economic development be integrated to control pollutant emissions in Daya Bay.

Distribution and potential provenance of trace elements in a 120-year dated sediment core from west Daya Bay, northeastern South China Sea

Eighteen trace elements were analyzed in a 120-year sediment core from Daya Bay. Burial flux history and potential provenance, the relationships among trace elements, and biogenic compositions were analyzed for determining the trend and extent of trace element accumulation and identifying corresponding anthropogenic effects. Additionally, the effects of anthropogenic activities on Daya Bay were reconstructed, and a baseline/background estimation was provided for Daya Bay. The burial fluxes of V, Cr, Cd, Cu, Zn, Mn, Fe, Co, Ni, Pb, Hg, Zn, Mo, Ag, As, Se, and Tl increased from 1960 to 2010, especially after the late 1980s. Our results are useful for understanding pollution and land-sea interactions along the coasts of the South China Sea, especially in the Guangdong-Hong Kong-Macao Greater Bay Area.

Relationship of arsenic and chromium availability with carbon functional groups, aluminum and iron in Little Washita River Experimental Watershed Reservoirs, Oklahoma, USA

Sediment from three reservoirs located in the Little Washita River Experimental Watershed (LWREW) in Oklahoma, USA with contrasting dominant land uses were analyzed for total and extractable concentrations of arsenic (As) and chromium (Cr), and the potential ecologic risk to benthic organisms. Extractable As ranged from 0.24 to 1.21 mg kg^-1, in the order grazing>cropland>forest and 0.13-0.58 mg kg^-1 for extractable Cr, in the order of forest>grazing>cropland. However, only approximately < 1.5% of total As and < 4% of total Cr were extractable. Total As ranged from 16.2 to 141 mg kg^-1 and total Cr ranged from 5.06 to 40.1 mg kg^-1 both in the order of cropland>grazing>forest. The sediment exhibited an alkaline pH (8.0-8.7). As sorption exhibited a positive relationship with Al (r = 0.9995; P = 0.0001), Fe (r = 0.9829; P = 0.0001), and C (r = 0.4090; P = 0.0017) and Cr correlated positively with Al (r = 0.9676 P = 0.0001), Fe (r = 0.9818; P = 0.0001), and C (r = 0.3368; P = 0.0111). In addition, both As and Cr exhibited positive relationships with carbon (C) functional groups in the order of O-alkyl C> methoxyl C> alkyl C> aromatic C> carboxyl C> phenolic C. The sediment concentration analysis results illustrated that As in all reservoirs exceeded their respective Threshold Effect Level (TEL) and/or Probable Effect Level (PEL) indicating that existing concentrations of metals in these sediments were sufficiently high to cause adverse effects. However, Cr concentrations in all reservoirs evaluated was lower compared to the TEL and PEL.

Long-term variations in fish community structure under multiple stressors in a semi-closed marine ecosystem in the South China Sea

Daya Bay is an ecologically and economically crucial semi-closed bay along the southern coast of China. It is proven to be a stressed ecosystem and therefore obviously vulnerable to further extrinsic disturbance. This study used fish data from bottom-trawl surveys, conducted from 1985 to 2018, to analyze variations in the fish community structure over the past 30 years. The results showed that warm-water fish species were overwhelmingly dominant during all years, suggesting the bay's tropical to subtropical characteristic. By 2015, the number of fish species had decreased by 29.44% of that caught in 1987, moreover, values of the Shannon-Wiener diversity index and the Margalef richness index were lower in 2015 compared to 2004. There were evident shifts in the fish community composition from pelagic to demersal species, as suggested by the dominant species found in springtime, the dominant families, and percentages denoting the numbers of species in the main orders. Average fish body weight in landings declined from 13.4 g to 7.58 g, the body sizes of four typical commercial fish species decreased by varying degrees over the last 30 years. Abundance-biomass comparison curves suggested that the Daya Bay fish community was more stressed in 2015 than in 2004 during all seasons, except winter. In general, the fish community structure in Daya Bay is consequently in an unsteady state. Multiple anthropogenic disturbances, such as fishing (including overfishing and changes in the main fishing gears), the destruction of natural habitats, pollutants, and anthropogenically induced temperature changes, are likely to have caused obvious shifts in the bay's fish community structure. Therefore, we emphasize the need for integrating management of multiple anthropogenic stressors to achieve ecosystem-based management.

Fractions and mineralization potential of the sediment organic nitrogen in Daya Bay, South China Sea: Anthropogenic influence and ecological implications

Nitrogen mineralization is a critical biogeochemical process that transfers organic nitrogen into inorganic forms using heterotrophic microorganisms. However, few studies have focused on this potential nutrient supplier. In this study, the composition of sediment organic nitrogen (SON) was studied, and nitrogen mineralization flux entering the water column was quantified. The results indicate that acid-hydrolyzable nitrogen (AHN) accounts for more than 40% of the SON, especially in the riverine input and marine aquaculture areas, which had significantly higher concentrations than the bay mouth area. Similar results were found for the ammonium nitrogen (AN), amino-sugar nitrogen (ASN), the total hydrolyzable amino acid (THAA), and unidentified hydrolyzable nitrogen (HUN). The mineralization rate in the marine aquaculture area was as high as 9.03 ± 1.33 mg·kg^-1·d^-1, while those of the riverine input (4.77 ± 1.55 mg·kg^-1·d^-1) and bay mouth (5.12 ± 1.42 mg·kg^-1·d^-1) areas were lower. The SON fractions, including the AHN, AN, ASN, and AAN, could obviously affect the mineralization of the SON. However, the extracellular enzymes, including proteinase and urease, are the predominant factors controlling the SON mineralization process. Anthropogenic activities, including riverine input and marine aquaculture, exert significant influences on the fractions and mineralization of the SON, and thus, they may increase the amount of dissolved inorganic nitrogen in the bottom of the water column in Daya Bay.

How do spatial and environmental factors shape the structure of a coastal macrobenthic community and meroplanktonic larvae cohort? Evidence from Daya Bay

We examined the relative importance of spatial processes (dispersal-related) and environmental processes (environmental selection-related) in community structure for macrobenthos (including juveniles and adults) and meroplanktonic larvae in the subtidal areas of Daya Bay, China. We found that both macrobenthos and meroplanktonic larvae showed similar spatial patterns, both following the distance-decay relationship. The results of variation partitioning analysis (VPA) showed the roles of both spatial and environmental factors in governing the assembly of both communities, although both explained only a small (slightly larger for spatial factor) fraction of the community variation. We also found that macrobenthos were more affected by spatial processes than meroplanktonic larvae. In addition, we highlight that the mechanisms determining community structure change according to the spatial extent considered.

Historical evolutions of sediment quality in bays under serious anthropogenic influences in China, basing on fuzzy comprehensive assessment of heavy metals

Fuzzy comprehensive assessment was applied, for the first time, to investigate the sediment environmental quality and compare the historical variations of heavy metal pollution in Daya Bay and Jiaozhou Bay, which are representative for sub-tropical and temperate zone of China, respectively. Results shown the Daya Bay had undergone three contrasting stages in the past 100 years. Before 1980s, the sediment was not contaminated by metals and its quality generally conformed to class I of China National Standard for marine sediment quality. During from 1980s to 2000s, however, Daya Bay's environment had experienced significant deterioration. The metal concentrations were significantly higher than the background values, suggesting that there was a sharp increase of metal input. The category of sediment quality fell to class II and class III. Copper was the dominant pollutant during that time. The good thing is sediment quality of Daya Bay has improved to class I since 2000s, and chromium turned to be the major pollutant. As for the Jiaozhou Bay, enrichment of heavy metal was generally not detected and the sediment quality strictly conformed to class I during the recent 90 years. Chromium and zinc were the major pollutants in this bay.

Distribution of Geochemical Fractions of Phosphorus in Surface Sediment in Daya Bay, China

Surface sediment samples were collected from 19 sites throughout Daya Bay, China, to study the concentrations, and spatial distributions of different fractions of phosphorus through sequential extraction methods. Like many coastal and marine areas, De-P was the dominant form of P, contributing 47.5% of TP, followed by O-P, contributing 25.5% of TP. Ex-P and Fe-P contribute the lowest to TP. The concentration of sedimentary TP ranged from 290.3~525.1 µg/g, with the average of 395.3 µg/g, which was a similar range to other estuaries and coastal areas. Based on the spatial distribution, Pearson correlation and Principal component analysis, different fractions of phosphorus showed different spatial distributions due to different sources. The molar ratio of organic carbon to phosphorus (TOC/O-P) ranged from 199 to 609, with the average of 413, which was much higher than the Redfield ratio, suggesting terrestrial sources of organic matter in Daya Bay surface sediment. The average bioavailable phosphorus was 149.6 µg/g and contributed 37.8% (24.6~56.0%) of TP, indicating that the surface sediments of Day Bay act as an important internal source of P.

Concentrations of porewater heavy metals, their benthic fluxes and the potential ecological risks in Daya Bay, South China

Heavy metal (Cr, Mn, Fe, Ni, Cu, Zn, Cd, Pb) concentrations in surface sediment porewater and their benthic fluxes were investigated in Daya Bay, South China, to study their accumulation and transfer at the sediment-water interface, as well as the impact of human activities on heavy metals. Heavy metals in porewater displayed different patterns in three partitions (top, center and inlet), which was mainly attributed to the difference in the biogeochemical conditions, hydrodynamic force inner the bay and the human activities along the bay. Ecological risk assessment results showed that heavy metals in porewater dramatically exceeded the background values. The average release of heavy metals from sediment were (6.1 ± 3.3) × 10⁴-(2.7 ± 1.6) × 10⁸ g a^-1 in the bay, so they had potential risks to the water environment, and sediment should be paid more attention to as the endogenesis of contamination.

Heavy metals of sediment cores in Dachan Bay and their responses to human activities

The grain-size distributions and heavy metal content in two sediment cores from Dachan Bay were analyzed, and the vertical distribution, provenance, and ecological risk of heavy metal were evaluated. The concentrations (μg g^-1) of Cu, Pb, Zn, Cd, Cr, Hg, As, and Ni in the sediment samples were 14.8-408, 33.0-130, 78.6-256, 0.193-1.79, 47.5-192, 0.052-1.39, 8.94-25.2, and 26.0-89.6, respectively. Most heavy metal concentrations increased from the bottom to the upper layers. On the basis of two sediment cores, the potential ecological risk of heavy metals was determined to be low, and the degree of potential ecological harm of heavy metals was in the order of Hg > Cd > As>Cu > Pb > Cr > Zn. Principal component analysis and correlation analysis yielded similar results, which indicated that heavy metals were closely related to the input of anthropogenic pollution (i.e., industrial pollutants and sewage discharge).

Concentration and pollution assessment of heavy metals within surface sediments of the Raohe Basin, China

Surface sediment samples were collected from four areas (the Jingdezhen Industrialized Area (JDZ), Upstream (UP), the Dexing Mining Area (DX), and Downstream (DM)) to investigate the concentration and chemical composition of heavy metals. The sediments were analysed for Cu, Zn, Pb, Cd, Cr, As, and Ni using a sequential extraction scheme according to the improved BCR (European Community Bureau of Reference) method. The obtained results show that the maximum values of Cu (793.52 μg·g-1), Zn (72.09 μg·g-1), Pb (222.19 μg·g-1), and Cd (1.60 μg·g-1) were collected from the DX sampling area, while the JDZ area had the highest concentrations of Cr (97.09 μg·g-1), As (318.05 μg·g-1), and Ni (66.35 μg·g-1). The majority of metal values far exceeded their corresponding background values. The risk analysis of geo-accumulation index (Igeo) indicated that the heavy metals Cu and As were the main pollution factors and each element of the pollution degree followed the order of: Cu > As > Pb > Cd > Cr > Zn. Metal partitioning characteristics were also considered and more than 80% of metals show potential bioavailability and toxic effects.

Evaluation of the total maximum allocated load of dissolved inorganic nitrogen using a watershed-coastal ocean coupled model

Due to the recent rapid increase in human activity and economic development, many coastal areas have recently experienced a high degree of land-based pollution. Evaluating the total maximum allocated load (TMAL) of dissolved inorganic nitrogen (DIN) nutrients and the remaining capacity is of importance for improving water quality. A considerable amount of nutrients derived from the coastal watershed can be found in wet seasons, which is non-negligible for the estimation of remaining capacity. Therefore, we use a watershed-coastal ocean coupled model combined with an optimization algorithm to tackle this issue. In contrast with previous studies, this study provides a method to estimate the spatiotemporal variations in TMALs and we then compare it to the current DIN nutrient load, including both point sources and non-point sources. Our results suggest that the TMAL of Daya Bay (DB), which is located in the northern part of the South China Sea, is about 7976 metric tons per year (t/yr) and ranges from 191 metric tons per month (t/month) to 1072 t/month. The increase of non-point source (NPS) DIN input also plays an important role in daily overload events during wet seasons. Moreover, the TMALs show an inverse exponential correlation with the water age, but only about 65% of the variance is explained. This suggests that the variations from the optimization algorithm and from local water function zoning plans are also important. According to our prediction of the DIN input, the TMAL of DB will soon be exhausted in the next several years. Consequently, prompt actions are necessary to consider the distribution of TMALs in urban developments and to decelerate the rapid growth of DIN input. Therefore, the results of this study will be helpful for both local pollution control and future urban planning.

Is fish bone subfossil a good archive of heavy metal pollution on Nandao Island, South China Sea?

To examine whether historical fish bones can record the magnitude of heavy metal pollution, we analyzed up to 700 years old fish bone remains extracted from an ornithogenic sediment profile on Nandao Island, South China Sea. Bulk sediments and subfossil fish bones were analyzed for elemental and mineralogical composition, as well as stable carbon and nitrogen isotopes. The results showed that pre-1850 CE fish bones experienced significant diagenesis, and could not be used to reconstruct historical record of heavy metal pollution. Fish bone diagenesis was mainly attributed to the erosion from guano in sediment profile. In contrast, the fish bones from in post-1850 CE time were well preserved and could provide useful information on historical pollution loads over the past 160 years. Since 1850 CE, relatively high concentrations of heavy metals from anthropogenic sources, especially Zn, were recorded in fish bone subfossils on Nandao Island, South China Sea.