Coral trace metal of natural and anthropogenic influences in the northern South China Sea

Influence of habitat utilization strategies on trace element signatures in egg contents of green turtles nesting on Xisha Islands, South China Sea

Habitat utilization significantly influences the accumulation of chemical pollutants, including trace elements (TEs), in the tissues of large marine organisms. Previous research has demonstrated that sea turtles nesting in the same location may employ distinct foraging strategies. This study investigated the influence of habitat use strategies on the concentrations of 16 TEs in the eggs of green turtles (Chelonia mydas) nesting on the Xisha Islands. The analysis incorporated stable carbon (δ13C) and nitrogen (δ15N) isotopes, as well as characteristic elements. Additionally, inter-relationships between TEs were examined. The nesting female green turtles were categorized into two foraging groups based on isotopic signatures, namely oceanic (δ13C values: -21.5 to -17.0 ‰; δ15N values: 7.10 to 12.5 ‰) and neritic (δ13C values: -14.4 to -9.95 ‰ and δ15N values: 5.10 to 10.0 ‰). Different TE patterns were observed in the egg contents of these two groups. The neritic group exhibited elevated levels of V and Cu, which positively corrected with δ13C values. Conversely, the oceanic group displayed higher levels of Zn, Cd, Se, Sn, As and Hg, which positively associated with δ15N values. This distribution pattern is attributed to variations in background TE concentrations in the respective foraging habitats. Additionally, prey items and trophic levels of green turtles may contribute to the observed inter-group differences in TE concentrations (e.g. Zn, As, Se, Sn) found in their eggs, warranting further research. This study provides valuable information about habitat utilization patterns and TE distribution in green turtles nesting on the Xisha Islands. The findings enhance our understanding of TE accumulation mechanisms in turtle tissues and eggs, which is significant for the conservation of this endangered species, the green sea turtle.

Source identification and risk assessment of trace metals in surface sediment of China Sea by combining APCA-MLR receptor model and lead isotope analysis

This study aimed to investigate the distribution, pollution, risk and sources of trace metals in sediments along China Sea. Clear spatial variations were found for Cr, Mn, Co, Ni, Cu, Zn, Se, Mo, Ag, Cd, and Pb, whereas As did not show spatial variation. East China Sea (ECS) contained the highest concentrations of Mn, Co, Ni, Cu, Zn, South China Sea (SCS) shallow sea contained the highest concentrations of Zn, Se, Mo, Ag, Cd, and Pb, whereas coral reefs contained the lowest concentrations of trace metals. Spatial variations could be explained by economic development characteristics along China Sea. As, Se and Cd exhibited low to moderate pollution in China Sea sediment, yet pollution for Cu, Zn, Ni, and Ag appeared in some regions. Sediment in ECS had moderate ecological risks and other regions at low ecological risks. The absolute principle component score-multiple linear regression (APCS-MLR) and Pb stable isotope indicated that 43-74% of trace metals (Ni, Cu, Zn, As, Se, Cd, and Pb) were derived from anthropogenic sources like traffic emission, agricultural activities, industrial source. No pollution and ecological risk were observed in coral reefs, yet 39-71% (Pb) was derived from anthropogenic activities such as motor vessels.

Cumulated influence of natural and anthropogenic drivers on surface seawater barium: Evidence from a high-resolution coral record in the northern South China Sea

Barium (Ba) plays a crucial role as a tracer element in elucidating essential marine biogeochemical processes. However, the limited knowledge regarding Ba sources and variations impedes our comprehension of the diverse array of processes occurring in the marine environment. Although coral Ba/Ca ratios have demonstrated potential as a tracer of oceanic Ba, there remains a scarcity of long-term and high-resolution records to fully utilize this technique. Here, we presented a 32-year record of monthly coral Ba/Ca ratios and δ18O from the Weizhou Island in the northern South China Sea to elucidate the sources and the influence factors on surface seawater Ba. The results indicated no significant correlation between coral Ba/Ca and sea surface temperature or growth rate, implying that coral Ba/Ca ratios could serve as a dependable proxy for surface seawater Ba concentrations. Significant increases and abrupt fluctuations in coral Ba/Ca ratios were observed during the period of oil drilling exploration and engineering construction, indicating that anthropogenic activities might lead to an elevation of surface seawater Ba levels, subsequently affecting coral Ba/Ca ratios. The winter coral Ba/Ca peaks on monthly timescales were confirmed to be caused by resuspended sediment driven by the winter monsoon. Extreme peaks of coral Ba/Ca occurring during the wet season demonstrated the potential of coral Ba/Ca to record tropical cyclones, which has not been found in low-resolution scale studies. The continuous, long-term, and high-resolution coral Ba/Ca time series provides compelling evidence for the combined influence of both natural and anthropogenic factors on seawater Ba concentrations. These findings significantly contribute to the comprehension of the intricate biogeochemical cycling of marine Ba.

Coral skeletons reveal the impacts of oil pollution on seawater chemistry in the northern South China Sea

Oil pollution can release trace metals (TMs) with cumulative toxicity into seawater, harming marine ecosystems in the long term. However, the lack of studies has inhibited our understanding of the effects and mechanisms of oil pollution on TMs in seawater. Hence, we investigated the 10-year monthly variation of TMs in Porites coral skeletons from the northern South China Sea (SCS), complemented by spatial distribution of TMs in seawater, sediments and characterization of TMs in fuel oil. The results of principal component-multivariate linear regression showed that the total contribution of oil pollution as a source to TMs in surface seawater was 77.2%, where the residence time of TMs (Ni, V, Cr, Co, Cu, Mn, Fe, and Mo) released from oil spills in surface seawater was approximately 1.4 months. Due to the geochemical nature of the metals, their seasonal variations are controlled by tropical cyclones (Ni, V, Cr, Co, Cu, Mn, Fe, and Mo), winter monsoons (Pb, Cd, Ba, and Zn) and sea surface temperature (Sr). This study shows that coral skeletons can be used as a new tool to study marine oil pollution. This provides valuable reference data for accurately identifying and quantifying the effects of oil pollution on TMs in seawater from a spatial and temporal perspective.

Interannual variation and sources identification of heavy metals in seawater near shipping lanes: Evidence from a coral record from the northern South China Sea

Heavy metal pollution is a serious environmental problem in the marine ecosystem. Thereinto, marine transportation activities have gradually become an important source of heavy metals in seawater. However, the lack of studies on the temporal dynamics of seawater heavy metals in marine shipping areas has hindered our understanding of the sources and transport mechanisms of heavy metals in seawater of hectic shipping waters. Therefore, we investigated the interannual resolution variation of heavy metals in Porites lutea skeletons during the past 32 years under the rapid development of the shipping sector near Weizhou Island from the northern South China Sea. Results show that most heavy metal concentrations with higher coefficients of variation (≥100 %) in the Porites coral skeletons were higher than those in the uncontaminated or less anthropogenic waters. The results of principal component analysis and multiple linear regression showed that the interannual variations of Ni, V, Cr, Co, Zn, Cu, Mn, Fe and Mo were mainly impacted by marine oil extraction and oil spills generated by shipping activities, accounting for 51.58 %. The effect of sea surface temperature accounts for 13.44 %, and controls the interannual variations of Ba and Sr. The effect of industrial pollution accounts for 13.27 %, and explains the interannual variations of Cd and Y. The fuel consumption of marine shipping accounted for 8.76 %, explaining the interannual variations of Pb. The total contribution of anthropogenic activities reached 73.61 %. The interannual variation of heavy metals indicates that hectic marine shipping activities are the dominant cause of Ni, V, Pb, Cr, Co, Zn, Cu, Mn, Fe and Mo input to surface seawater around Weizhou Island. This provided valuable data for understanding the temporal dynamics and potential sources of heavy metals in the marine environment by using coral skeletons as a high-resolution recording vehicle.

Iron speciation and annual records in black coral as new proxy for mining and environmental impacts

Iron (Fe) is a micronutrient and plays an important role in regulating ocean primary production and consequently changing oceanic CO₂ uptake. However, approaches for high-resolution of Fe records in marine environment has been a great challenge. In this study, we report for the first time an annual Fe record on black coral organic skeleton from the northern South China Sea (SCS) as an archive to study the environmental change during the past century. In situ micro-Raman, synchrotron micro X-ray absorption near edge spectroscopy (μ-XANES) and synchrotron micro X-ray fluorescence (μ-XRF) were applied to investigate the Fe speciation and the radial Fe profile in black coral. The preliminary results from micro-Raman and synchrotron micro XANES analysis demonstrated that Fe in black coral was mainly combined with 3,4-dihydroxyphenylalanine (dopa) as tris-DOPA-Fe complex. Such spatial coordination structure of complexation makes Fe have high affinity with dopa in black coral. Furthermore, elevated Fe concentration in Fe profile recorded on synchrotron μ-XRF spectra with 2.5 μm resolution corresponded well to the exploitation history of the adjacent onshore Tiandu Iron Mine (Sanya, China) from 1939 to 1960. Other distinct Fe peak coincides with the war activities in 1970s. The findings presented in this work indicate that the high-resolution iron record with low annual growth rate (~17.8 μm year^-1) of black coral may serve as a proxy of marine environmental record.

Otolith fingerprints reveals potential pollution exposure of newly settled juvenile Sparus aurata

Coastal ecosystems are increasingly threatened by a wide range of human activities. Fish otolith chemistry, by creating a unique specific signature, can be used as a natural tag for determining life stage dispersal, spatial connectivity and population structure. In this study, we tested whether differences in otolith composition among juveniles of gilthead sea bream, Sparus aurata, could enable their proper allocation to polluted areas based on higher concentrations of elements related to contaminants. Otoliths were embedded, sectioned and analysed by LA-ICP-MS in line scan mode. Multivariate analysis confirmed clear separation between sites and elements. Samples from the site under the strongest anthropogenic impact from industrial and agricultural river input were characterized by higher values of Pb/Ca and Zn/Ca. However, these relatively low values likely do not have a negative effect on S. aurata recruitment, though they could serve for identifying the contribution of polluted nurseries to stock dynamics.

Speciation and risk assessment of selected trace metals in bottom sediment of coral reef ecosystems of the Persian Gulf

To evaluate the hazard assessment of anthropogenic activities on coastal ecosystems, fractionation and bioaccumulation of trace metals were carried out for sediment and coral samples of three distinct habitats including petroleum exploration area of Kharg, the rural harbor of Chirouyeh, and unpopulated area of Hendorabi. Fractionation results suggested that Ni (~ 51%), Pb (~ 49%), and V (~ 45%) in Kharg; Ni (~ 46%), Pb (~ 84%), and Zn (~ 47%) in Chirouyeh; and Cd (~ 51%) in Hendorabi were the predominant metals in the non-resistant fractions of the sediment samples. Risk Assessment Code (RAC), individual contamination factor (ICF), and global contamination factor (GCF) were derived. The highest relative risk for Cd, Cu, and Ti was observed in Kharg, whereas the highest relative risk for Ni, Pb, V, and Zn was recorded in Chirouyeh. The lowest risk for almost all of the trace metals was observed in Hendorabi. Biota-sediment accumulation factor (BSAF) values of coral samples revealed that species examined in the present study are reliable biomonitors for Cd, Ni, Pb, and Zn contamination. Principal component analysis (PCA) and Pearson's correlation coefficient (PCC) suggested that Pb, Ni, and Zn can be considered the main pollutants of the Persian Gulf which originated mainly from petroleum industries. Furthermore, the metal uptake rates of coral samples seemed to be dependent on bioabsorption pathways and coral species. Overall, the present work constitutes a good basis for further studies on trace metal fractionation, risk assessment, and source apportionment in the Persian Gulf, which could contribute to more effective decisions for reducing the anthropogenic trace metal pollution.

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.

Seasonal to decadal scale influence of environmental drivers on Ba/Ca and Y/Ca in coral aragonite from the southern Great Barrier Reef

Extensive catchment modification since European settlement on the eastern coast of Australia results in poor coastal water quality, which poses a major threat for near shore coral communities in the iconic Great Barrier Reef (GBR). Long lived inshore corals have the potential to provide long-term temporal records of changing water quality both pre- and post-anthropogenic modification. However, water quality proxies require more study and validation of the robustness of coral-hosted geochemical proxies for a specific site is critical. This study investigated the long-term (1958-2010) influence of environmental drivers on high-resolution Ba/Ca and Y/Ca proxies obtained from Porites sp. coral from Great Keppel Island, southern GBR, Australia. Geochemical proxy records were influenced by environmental change on a seasonal to decadal scale. Although seasonal oscillations of Ba/Ca and Y/Ca were related to rainfall and discharge from the Fitzroy River catchment, some uncorrelated anomalous peaks were evident throughout the time series. Regardless, the behaviour of these proxies was significantly consistent over the longer time scale. Most long-term drought-breaking floods, including one that occurred in winter, resulted in significant increase in the targeted elemental ratios owing to higher terrigenous sediment flux to the near shore marine environment from a catchment with reduced groundcover. Following this intense flushing event, elemental ratios were reduced in subsequent wet periods as a result of less sediment being available for transport to coastal seawater. Ba/Ca and Y/Ca proxies can be valuable tools in reconstructing multiyear variations in terrestrial runoff and associated inshore water quality. As these proxies and their regional and local controls are better understood they will aid our understanding of how reefs have responded and may respond to changing water conditions.