Potential ecological risk of heavy metal contamination in sediments and macrobenthos in coastal wetlands induced by freshwater releases: A case study in the Yellow River Delta, China

Effects of variations in hydrological connectivity on the macrobenthic community structure in reclaimed wetlands

The Nanhui Dongtan Wetland is the most extensively reclaimed part of the Yangtze River Estuary wetland. In recent decades, urbanization has led to the extensive reclamation of the intertidal wetlands of Nanhui Dongtan. Macrobenthos are crucial as secondary production groups in the food web. However, there is a lack of in-depth research on the response mechanisms of macrobenthic communities to environmental disturbances in reclaimed wetlands. This study investigated the impact of hydrological connectivity changes caused by land reclamation on the macrobenthic community based on the macrobenthic community composition in preserved tidal flats and closed and open reclamation areas in Nanhui Dongtan. The results showed that the macrobenthos species richness in the closed reclamation area was significantly lower than that in the other areas. After dividing the functional groups of macrobenthos, structural equation modeling revealed a negative correlation between the salinity and the functional group composition. Analysis of the food sources revealed significant positive correlations between predatory and sediment-feeding populations and sediment organic matter content, between detritivorous group and environmental chlorophyll-a content, and between herbivorous group and suspended organic matter content in water. Therefore, variations in hydrological connectivity in different reclamation areas caused differences in food source distribution, which led to different compositions of macrobenthic functional groups. The results of this study provide a theoretical reference for the study of intertidal wetland habitat restoration.

Single and combined toxicity of polystyrene nanoplastics and arsenic on submerged plant Myriophyllum verticillatum L

The contamination of nanoplastics (NPs) and heavy metals (HM) in water bodies has caused widespread concern, while their effects on submerged plants are poorly reported. Polystyrene nanoplastics (PSNPs) and arsenic (As) were used to assess their toxicity on Myriophyllum verticillatum L. via the orthogonal experiments. PSNPs significantly reduced the accumulation of As (17.24%-66.67%) in plant. Single As and high As-PSNPs treatments significantly inhibited plant growth, with a maximum reduction of 70.09% in the growth rate. The mineral nutrient content was significantly affected by PSNPs and As treatments. The antioxidant system was significantly inhibited, which was more pronounced in the roots. Similar findings were observed for soluble protein and soluble sugar. Some organic acids and amino acids showed down-regulation at high concentrations of As, leading to a decrease in the content of the mineral element and down-regulation of antioxidant enzyme synthesis. Furthermore, PSNPs could alleviate As toxicity under 0.1 mg/L As treatment but exacerbate As toxicity at 1 mg/L As dose. This study has important implications for the study of submerged plants exposed to co-contamination of microplastics and heavy metals, as well as the possible ecological risk assessment in freshwater.

Multigenerational DNA methylation responses to copper exposure in Daphnia: Potential targets for epigenetic biomarkers?

Epigenetic mechanisms are moving to the forefront of environmental sciences, as environmentally induced epigenetic changes shape biological responses to chemical contamination. This work focused on Daphnia as a representative of potentially threatened freshwater biota, aiming to gain an insight into the involvement of epigenetic mechanisms in their response and eventual adaptation to metal contamination. Copper-induced DNA methylation changes, their potential transgenerational inheritance, and life-history traits were assessed. Organisms with different histories of past exposure to copper were exposed to toxic levels of the element for one generation (F0) and then monitored for three subsequent unexposed generations (F1, F2, and F3). Overall, methylation changes targeted important genes for counteracting the effects of metals and oxidative stress, including dynein light chain, ribosomal kinase and nuclear fragile X mental retardation-interacting protein. Also, contrasting overall and gene-specific methylation responses were observed in organisms differing in their history of exposure to copper, with different transgenerational methylation responses being also identified among the two groups, without apparent life-history costs. Taken together, these results demonstrate the capacity of copper to promote epigenetic transgenerational inheritance in a manner related explicitly to history of exposure, thereby supporting the development and incorporation of epigenetic biomarkers in risk assessment frameworks.

Spatial distribution, sources and risk assessment of potentially toxic elements contamination in surface soils of Yellow River Delta, China

The contamination status and ecological risk of soil potentially toxic elements (PTEs) in Yellow River Delta (YRD) are still poorly understood. Thirty surface soil samples were collected in YRD, determined for contents of PTEs, and assessed using four kinds of proxies. Results indicated that PTEs contents basically met the Environmental Quality Standard for Soils, and spatial heterogeneity of PTEs was not distinctive except for a few sampling sites. Results of geo-accumulation index (I_geo) and enrichment factor (EF) indicated significant enrichment of As and Sb in YRD. The multivariate analysis results distinguished the possible sources of these PTEs and demonstrated that sources of Ag, As, Cd, Cu, Pb, Sb and Zn could be influenced by anthropogenic activities (industrial and agricultural sources). Moreover, Ni, Cr and As had relatively high contributions to sum of toxicity units (ΣTUs). This study provides basic information for understanding soil PTEs contamination status of YRD.

Heavy Metal Contamination in Sediments from Wetlands Invaded by Spartina alterniflora in the Yellow River Delta

Heavy metals are major pollutants that pose threats to wetland environments. In the present study, surface sediments from wetlands vegetated by invasive species Spartina alterniflora in the Yellow River Delta were collected and determined for the mass fractions of Co, Ni, As, Cd and Pb. Results showed mass fractions of Co, Ni, As, Cd and Pb in the sediments of the S. alterniflora communities ranged from 8.5 to 16.0, 13.9−27.9, 3.2−13.8, 0.08−0.24, and 17.6−37.5 mg/kg dw, respectively, generally presenting an order of Pb > Ni > Co > As > Cd. The levels of heavy metals in sediments in the S. alterniflora communities were higher than those in the wetland vegetated by the native plant species Suaeda heteroptera. Correlations among metal elements were highly significant, suggesting that they might have the same sources. Clay and TOC were important factors affecting the spatial distribution of metals. The Igeo values of the investigated elements in the sediments were frequently lower than 0, revealing the slight pollution status of these metals. Relatively slight values of Eri and RI suggested that the potential ecological risks caused by the 5 metals were low. Our findings could provide a better understanding of the correlation between metal pollution and bio-invasion in wetland ecosystems.

Assessment of heavy metals in surface water, sediment and macrozoobenthos in inland rivers: a case study of the Heihe River, Northwest China

Long-term retention and accumulation of heavy metals in surface water and sediment pose a great threat to the sustainable development of aquatic ecosystems and human health. In this research, macrozoobenthos, and surface water and sediment heavy metal (Mn, Cr, Cu, Ni, Pb, Zn, Cd, and As) samples were collected from 23 sites in the upper and middle reaches of the Heihe River in the summers of 2019-2020. The interrelationships between heavy metals and macrozoobenthos were analyzed by Pearson correlation analysis and redundancy analysis (RDA), and the contamination level and potential ecological risk of the heavy metals in surface water and sediments were assessed by comprehensive pollution index (WQI), single potential ecological risk index ([Formula: see text]), and sediment quality guideline-quotient (SQG-Q), respectively. The results showed that the level of heavy metal pollution in the surface water of the Heihe River was extremely low, but the contents of Mn and Pb exceeded the third class of surface water environmental quality standards (GB 3838-2002). The spatial distribution of heavy metals in surface sediments were significantly different, and the average concentration of 8 heavy metals exceeded the background values of Gansu Province. Meanwhile, the pollution level of heavy metals in surface sediments was high pollution, and the ecological risk level was moderate risk. Combining [Formula: see text] and SQG-Q evaluations showed that Cd, Ni, and Cr were the main ecological risk factors. In addition, the distribution coefficients of Cr and Cd were low, indicating that Cr and Cd were easily released from the surface sediments, causing secondary pollution. In terms of the source of the heavy metals, Cu, As, Zn, Cr, and Ni mainly came from industrial and agricultural wastewaters, Pb was from the mining industry and natural sources, and Mn and Cd mainly came from tailings and their landfill leachate. Basommatophora and Araneae can be used as potential indicator organisms for heavy metal pollution in surface water, and Basommatophora, Coleoptera, Hemiptera, and Araneae can be used as indicator species for heavy metal pollution in surface sediments. The study showed that macroinvertebrate community characteristics had a sensitive response to heavy metals in the surface waters and sediments of the Heihe River, which can be used to evaluate the pollution status of heavy metals in inland rivers.

Risk assessment of heavy metals in a typical mangrove ecosystem - A case study of Shankou Mangrove National Natural Reserve, southern China

Mangroves bear enormous ecosystem value, while the ecosystems are facing increasing environmental pressures. In this study, 73 samples of soil sediments in mangroves, paddy fields, grasslands, forests, and shrimp ponds were collected from Shankou Mangrove National Nature Reserve (SKMNNR), Guangxi Zhuang Autonomous Region, China. The pollution status and ecological risks of heavy metal elements of Cr, Ni, Cu, Zn, As, Cd, Pb, V, and Co were determined using the enrichment factor (EF), geoaccumulaton index (I_geo), and potential ecological risk index (PERI). The average concentration is shown to be substantially lower than the background value. In general, the I_geo values indicated that the pollution conditions of different land use types in SKMNNR are relatively minor. Most of the PERI values were at the moderate level. This study demonstrates that the current status of sediment quality in SKMNNR is relatively good, and the pollution level is relatively low. Large-scale coastal aquaculture development and industrial expansion should not no longer be permitted there.

Tracking the environmental impacts of ecological engineering on coastal wetlands with numerical modeling and remote sensing

Coastal wetlands are the most valuable ecosystems on the earth but facing severe degradation and losses owing to climate change and anthropogenic activities. Many ecological engineering projects (EEP) have been conducted to mitigate the degradation of coastal wetlands. However, the geomorphological impacts of EEP on coastal wetlands have not been well documented. In this study, a method employed a process-based hydrodynamic model and remote sensing (RS) was developed to evaluate the impacts of EEP on the geomorphological change of a prototype Ramsar site. Results demonstrated that RS can improve the quality of bathymetry data for the numerical model with a decrease of RMSE of bathymetry data from 0.52 m to 0.3 m. RS data also showed good capacity in trend detection of geomorphological change spatially. Results showed the Chongming Dongtan wetland experienced erosion with an annual rate of -0.035 m/yr from 2013 to 2016 after the implementation of EEP. The deposition rate changed significantly in the area within 200 m of the EEP. It is found that the EEP modified the composition of vegetation, sediment transportation, as well as substrate stability, affecting the geomorphological change of coastal wetlands. The study suggested that the EEP is a direct and effective way to restore the coastal habitats for waterbirds from moderate anthropogenic disturbance. However, the modification of the coastal wetland ecosystem by EEP will potentially increase the vulnerability to global climate change. Therefore, Future studies are needed to further evaluate the advantages and disadvantages of EEP and identify a more sustainable approach for coastal management.

Freshwater Releases Into Estuarine Wetlands Change the Determinants of Benthic Invertebrate Metacommunity Structure

In recent years, the relative importance of the processes driving metacommunity composition has aroused extensive attention and become a powerful approach to identify community patterns and their regulatory mechanisms. We investigated variations in the composition of benthic community in restored wetlands and natural wetlands in the Yellow River Delta (Shandong Province, China). First, spatial structures within each wetland were modeled with Moran eigenvector maps. Next, the variation in community structure among local environmental and spatial variables was partitioned using constrained ordination, and the “elements of metacommunity structure” analysis was used to determine the patterns of best fit for species distributions within metacommunities. Finally, the null model was used to analyze non-random patterns of species co-occurrence. The community structure of benthic invertebrates in restored wetlands and natural wetlands differed significantly. The benthic invertebrate metacommunity structure showed a nested distribution in restored wetlands and a quasi-Clementsian structure in natural wetlands. Pure environmental fractions and pure spatial fractions were critical in regulating benthic invertebrate metacommunities of restored wetlands. In natural wetlands, pure spatial fractions and the interaction between environmental and spatial factors (shared fractions) played a major role in the metacommunity. A species co-occurrence analysis showed that species co-occurred more frequently than expected by chance, demonstrating that biotic interactions were not the main driver of metacommunity structures in both wetland types. Accordingly, the benthic invertebrate metacommunity in estuarine wetlands following freshwater releases was mostly determined by environmental and spatial effects, which resulted in a metacommunity with nested distribution. These results are important for biodiversity protection and ecosystem management of estuarine wetlands in the Yellow River Delta.

Heavy metal pollution in urban river sediment of different urban functional areas and its influence on microbial community structure

In this study, the Songgang River (SR) was selected as a typical contaminated urban river in a highly urbanized city (Shenzhen) that is extensively polluted by heavy metals (HMs). Five representative sampling sites were selected from different urban functional areas along the SR, and the spatial and vertical distributions of HMs and the related environmental risk were investigated. In addition, the distribution variability, composition, and abundance of microbial communities, as well as the correlation between the abundance of the operational taxonomic units (OTUs) and the HM contents were analyzed. The spatial distribution of HMs in the sediment revealed wide variation among the different urban functional areas. Industrial and residential areas had higher HM contents, following the order of Cu > Zn > Ni > Cr > Pb. In addition, the vertical characterization (5-300 cm) of HM content showed a decreasing trend with depth, with a distinct layer around 120-180 cm that might have been caused by anthropogenic activity. An ecological risk assessment indicated that Cu, Ni, and Cr pose high potential risks in these industrial and residential areas (at the depth of 5-180 cm). Furthermore, microbial community analysis indicated that some HM-tolerant bacteria (e.g., Gallionella, Acidovorax, Arenimonas, Curvibacter, and Sideroxydans) were dominant in the 5-120 cm layer, corresponding to high HM contents. A canonical correspondence analysis and co-occurrence network further confirmed that there was a strong correlation among the urban functional areas, HM contents, and the abundance of microorganisms in the urban river sediment. The results of this study have the potential to provide a bio-augmentation strategy for the in-situ bioremediation of sediment contaminated by HMs.

Multiple benthic indicators are efficient for health assessment of coral reefs subjected to petroleum hydrocarbons contamination: A case study in the Persian Gulf

The ever-increasing anthropogenic activities have adversely impacted coral reef ecosystems and their ecological functions. This calls for an urgent assessment of the health state of these valuable ecosystems to justify the need for mitigation and proper management efforts. In this contribution, we used multiple indicators to assess the impact of intense oil-related activities on coral reefs in two near-by impacted and non-impacted islands in the northwestern Persian Gulf. The efficacy of indices was assessed using estimations of the effect size (omega-squared), precision, and decision trees (Classification and Regression Tree (CART)). The results demonstrated that the combination of bioaccumulation of ƩPAH in coral tissues, the percent of live coral cover, and the Sediment Constituent (SEDCON) Index were the most robust proxies reflecting the influence of human activities on reef's health. Based on sedimentary PAH concentration, the CART classified most of the indicators into two classes consisting of those in impacted and those in non-impacted locations, further supporting the feasibility of the employed indices. The findings of this study provided a warning of degradation in coral reefs of the island subjected to PAH pollution. This encourages decision-makers to execute routine monitoring and mitigation practices to maintain healthy reefs in the study areas.

Quantitative source identification and apportionment of heavy metals under two different land use types: comparison of two receptor models APCS-MLR and PMF

At present, many researchers are increasingly aware of the importance of using models to identify heavy metal (HM) pollution sources. However, on the performance and application of different source identification models to HMs under different land use types had been studied little. In this study, comparison of absolute principal component scores-multiple linear regression (APCS-MLR) and positive matrix factorization (PMF) models and their application characteristics in identifying pollution sources were carried out by using 11 HMs in Zhongwei City farmland and Shizuishan industrial park, Ningxia. The results indicated that HM pollution in farmland mainly came from pesticides, fertilizers, and deposition of the Yellow River, while the pollution in industrial park mainly originated from atmospheric deposition and various industrial productions. The APCS-MLR model had the problem of less identification sources and the difficulty to explain the complex pollution, while the PMF model not only identified more pollution sources, but also distinguished heavy metal-related sources for two different land use types and different industrial production conditions. It is of great significance the formulation of agricultural-related pesticides' and chemical fertilizers' rational use and various industrial production-related raw materials put in and emission control strategies.

Impact of heavy metals on Ciconia boyciana feathers and Larus saundersi egg shells in the Yellow River delta estuary

In this study, the Ciconia boyciana and Larus saundersi, typical wetland birds in the Yellow River estuary, were selected as research objects. The feathers and egg shells of Ciconia boyciana and Larus saundersi were collected to determine the contents of heavy metals Cd, Cr, Cu, Zn, Mn, Ni and Pb in the samples. Correlation analysis (CA), principal component analysis (PCA), principal factor analysis (PFA) and potential ecological risk index (RI) were used to analyse and treat the measured heavy metal content data to determine the heavy metal pollution status, source and potential ecological risk in the Yellow River estuary. The results of CA, PCA and PFA showed that the content of Cd in the Yellow River estuary was much higher than the background value and its pollution was the most serious. Cr pollution was second and Mn pollution was the lowest. Heavy metal pollution mainly came from human activities such as oil exploitation, industrial production, use of pesticides and fertilizers, and the pollution caused by natural sources was relatively low. Based on the RI value of heavy metals in the study area, heavy metal Cd had an extremely high ecological risk status, and other heavy metals were all low. The results of this study can provide some reference and theoretical support for bird protection, heavy metal pollution control and ecological restoration in the Yellow River delta.

In this study, the Ciconia boyciana and Larus saundersi, typical wetland birds in the Yellow River estuary, were selected as research objects.

Distributions, quality assessments and fluxes of heavy metals carried by submarine groundwater discharge in different types of wetlands in Jiaozhou Bay, China

Intertidal groundwater and seawater were sampled to analyze the distribution characteristics, the contamination status and the submarine groundwater discharge (SGD)-associated fluxes of heavy metals Cu, Pb, Zn, Cd, Cr, and Hg as well as the metalloid As at four typical intertidal wetlands (including a sandy beach, a mud flat, a tidal marsh and an estuarine intertidal zone) of Jiaozhou Bay, China. Results show that the surface water near the Dagu River estuary suffers from a severe Cu pollution. The groundwater in the sandy beach and mud flat has stronger enrichment abilities of heavy metals than those at the other two sites. The contents of Pb and Zn in groundwater are mainly controlled by the sulfate reduction. At the mud flat, human activities may cause potential Pb contamination to groundwater. The heavy metal effluxes in the sandy beach are the largest of all the four wetlands.

Identification of the heavy metal pollution sources in the rhizosphere soil of farmland irrigated by the Yellow River using PMF analysis combined with multiple analysis methods-using Zhongwei city, Ningxia, as an example

In recent years, with the frequent occurrences of heavy metal (HM) pollution in agriculture, the problem of HM pollution in farmland soil, especially in the areas irrigation by the Yellow River, has been attracted increasing attention because of the complex sources of pollution. Qualitative identification of pollution sources and quantification of their contributions to HMs in soil are the key links in the prevention and control of HM pollution. The contents of 11 heavy metals (As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sn, V, and Zn) in the rhizosphere soil of the Ningxia irrigation area were determined by inductively coupled plasma mass spectrometry (ICP-MS). Multiple methods were used for source identification, including positive matrix factorization (PMF) analysis combined with multiple other analyses (single factor index method (Pi), coefficient of variation(CV), correlation analysis(CA), enrichment factor(EF), and principal component analysis(PCA)). The results showed that (1) the over-standard rates of As, Cd, Cr, Mn, Pb, Sn, and Zn in the study area were 100%, of which Cd was seriously polluted, while As, Zn, and Sn were moderately polluted. (2) The HM contributions from irrigation and silt soil formed by the Yellow River sediment were the highest (42.45%), followed by the smelting industry and traffic pollution (16.06%). (3) The contribution of agricultural pollution to HMs in the region was 15.54%, in which As was mainly from pesticides and Cd was mainly from fertilizers.

Multiannual Trend of Micro-Pollutants in Sediments and Benthic Community Response in a Mediterranean Lagoon (Sacca di Goro, Italy)

Long-term variations of ecological status in a Mediterranean coastal lagoon (Sacca di Goro, Northern Adriatic) were investigated, combining data on the concentration of surface sediment contaminants and on the structure of the macrobenthic community. The aim was to assess any amount of chemical contamination and check the response of the macrobenthic community to sediment contamination. Over the studied period, the sediments of the lagoon showed contamination by trace metals and organochlorine pesticides, with most of them exceeding the thresholds indicated by the Italian legislation in many samples. Contamination by polychlorinated dibenzodioxins and dibenzofurans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs) instead never exceeded the threshold. The ecological status based on the macrobenthic community, evaluated through biotic indices (AMBI and M-AMBI), fell below the Good/Moderate threshold in most samples. The results indicate a possible influence of toxic compounds in sediment on benthic organisms, but most of the variability shown by the macrobenthic community is probably due to other factors. The difficulty in establishing a cause/effect relationship was due to the co-occurrence and variability of various stressors (both natural and anthropogenic) and their interactions. The methods currently used for monitoring transitional waters thus seem insufficient to disentangle the effect of pollutants and other environmental variables on the benthos. Integrated approaches (e.g., bioaccumulation and toxicity tests) are thus needed for a more precise identification of the risk posed by a high concentration of pollutants in such environments.

Heavy metals in surface sediments in the trans-Himalayan Koshi River catchment: Distribution, source identification and pollution assessment

Rivers flowing across the Himalayas are important water resources and deliver large amounts of sediment to regional and downstream ecosystems. However, the geochemistry of Himalayan river sediments has been less studied. Surface sediment samples collected from a typical trans-Himalayan river, the Koshi River (KR), were used to investigate the distribution, pollution status and potential sources of heavy metals. Heavy metals did not show significant spatial differences between the upstream and downstream areas of the river, but Cd and Pb displayed higher values in the upstream area. The average heavy metal concentrations in the KR sediments are comparable to the natural background values and are lower than the sediment guidelines. Pollution assessment using the geo-accumulation index (Igeo), enrichment factor (EF) and pollution load index (PLI) suggested negligible anthropogenic disturbances except for slight contamination by Cd, Pb and Cu at a few sites. Principal component analysis revealed that Cr, Co, Ni and Zn were primarily from the parent rock and that Cu, Cd and Pb were derived from both natural and anthropogenic sources. Despite contrasting environmental settings and human activities in the upper and lower reaches of the river, the heavy metals concentrations in the KR sediments showed consistency with natural backgrounds and negligible contamination. The geochemistry of river sediments is a useful indicator of environmental changes, and long-term observations of the geochemistry of trans-Himalayan river sediments are needed to understand the impacts of intensified climate change and human activities on the Himalayan environment.

Comparative study of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) in corals, surrounding sediments and surface water at the Dazhou Island, China

This study investigated polycyclic aromatic hydrocarbons (PAHs) content in corals (Acropora sp.), surficial sediments, and surface seawater, and heavy metals (HMs) contents in corals and sediments from Dazhou Island, Hainan, China. Concentrations of PAHs in seawater and sediment seasonally ranged from 191.5 ng L^-1 to 587.7 ng L^-1, and from 37.9 ng g^-1 to 233 ng g^-1, while levels in corals were higher (185.2-545.0 ng g^-1) compared to those found in sediments, demonstrating bioaccumulation of PAHs by corals. A similar seasonally variation of PAHs was observed in water/sediments and corals, and the proportions of low molecular weight PAHs (LPAHs) in seawater and corals were higher. Pyrolytic and petrogenic contaminations were identified to be the main sources of PAHs. Lower HMs concentrations were detected in corals (9.8-39.4 μg g^-1) than in sediments (65.0-83.3 μg g^-1), but HMs bioaccumulation still occurs in corals. Higher concentrations of HMs in sediment and corals were detected in March and December, especially Mn and Zn. Application of an enrichment factor showed that Cu in corals was delivered from non-crustal materials, and anthropogenic inputs were possibly the main sources. According to Biota Sediment Accumulation Factor, corals could strongly bioaccumulate LPAHs and Cd, and PAHs at a higher (p < 0.05) rate than HMs. There was a lack of correlation between the accumulation of PAHs and HMs in corals based on the cluster analysis. Dual hierarchical clustering analysis result revealed that feeding, instead of symbiosis, might be the main process responsible for the bioaccumulation of PAHs and HMs.

Arsenic pollution of sediments in China: An assessment by geochemical baseline

Arsenic (As) contamination in sediments has been reported worldwide. However, few studies have investigated As contamination on a national scale in China. This study aims to address this gap by analyzing the existing literature on As contamination and sediment samples collected from ten main river basins: the Songhua River Basin (SRB), Liao River Basin (LRB), Hai River Basin (HRB), Yellow River Basin (YRB), Huai River Basin (HuRB), Yangtze River Basin (YtRB), Pearl River Basin (PRB), Southeastern River Basin (SeRB), Southwestern River Basin (SwRB), and Northwestern River Basin (NwRB). Regional geochemical baseline (RGB) values of As in the sediments of river basins were calculated to estimate human contributions of As using normalization and cumulative frequency distribution curves. The established RGB values in the SRB, YtRB, and PRB were higher than the corresponding regional soil background (RSB), possibly because of the high intensity of human activities in the SRB, YtRB, and PRB. Taking RGB and RSB values as the background references, contamination assessment yielded important information on As contamination in China. With high As contributions from Yunnan province, the PRB suffered from the highest level of contamination, and the mean human contribution of As in the PRB was 64.4%. The contamination levels in the less developed southwestern regions were even higher than in some river basins in economically developed regions (e.g., YRB). In addition, As in the PRB and YtRB was found to be partially contributed by industrial wastewater discharge, and the response of As contamination in sediments to industrial wastewater discharge was analyzed. The temporal change (2004-2016) of As in sediments from the PRB, YtRB, and YRB corresponded well with that of As discharged in wastewater within the corresponding river basins. This study thus serves as a valuable foundation for policies focused on ameliorating As contamination in China.

Effect of freshwater inflow on self-restoration of macrobenthic diversity in seaward intertidal wetlands influenced by reclamation projects in the Yangtze estuary, China

The Yangtze estuary is considered as an important eco-region of China, but it has been heavily disturbed by reclamation projects. We evaluated the effect of freshwater inflow on the self-restoration of macrobenthic diversity in 3-year-old vegetated, gravel, and mudflat habitats of reclaimed seaward intertidal wetlands. There was a significant self-restoration of species richness and diversity in vegetated and gravel habitats with no inflow of freshwater, but there were no significant changes in species diversity in three habitats subjected to freshwater inflow. Significant changes in community structures of macrobenthos occurred in vegetated and gravel habitats from pre- to post-restoration. Analysis of benthic health showed that gravel habitats were under moderate to high levels of disturbance in pre-restoration period. In contrast, there tended to be no evidence of disturbance in vegetated and mudflat habitats during two investigations. Restoration of macrobenthos is best achieved in vegetated habitats with on inflow of freshwater.

Coastal water quality assessment and groundwater transport in a subtropical mangrove swamp in Daya Bay, China

Coastal water quality assessment is challenging due to the complex hydrological environment in mangrove swamps. Such assessment requires a good understanding of swamp hydrology and potential solute reactions. In this study, we investigated the concentration variations of a suite of major elements (Na⁺, K⁺, Ca²⁺, Mg²⁺, SO₄^2-, HCO₃^- and Cl^-), nutrients such as dissolved inorganic phosphorous (DIP) and silicate (DSi), and heavy metals (Cu, Zn, As, Hg, Cd, Pb and Cr) along a typical mangrove transect in Daya Bay, China. The transect comprises a tidal creek, a mudflat and two mangrove zones. The major elements exhibited various degrees of dilution and loss, such as losses of K⁺ due to uptake by mangrove trees and of SO₄^2- due to microbial sulfate reduction. Numerical simulations of groundwater flow showed that the inland fresh groundwater can continuously discharge through the landward mangrove zone, where high concentrations of DIP and DSi occurred. However, the middle mangrove zone served as a sink of DIP and DSi due to the weak hydrodynamic environment. The spatial distribution of heavy metal concentrations showed that only Cu pollution occurred in the creek zone. The Metal Pollution Index (MPI) was developed to compare the enrichment capability of heavy metals at the different sampling sites. Results showed that the intertidal groundwater has the strongest heavy metal enrichment capability, followed by sea water, inland groundwater and river water. Within the intertidal zone, the creek zone has the highest MPI, followed by the mangrove zone and the mudflat zone. The local water circulation occurred around the creek should contribute the high MPI in the creek zone.

Pollution indices as useful tools for the comprehensive evaluation of the degree of soil contamination-A review

The paper provides a complex, critical assessment of heavy metal soil pollution using different indices. Pollution indices are widely considered a useful tool for the comprehensive evaluation of the degree of contamination. Moreover, they can have a great importance in the assessment of soil quality and the prediction of future ecosystem sustainability, especially in the case of farmlands. Eighteen indices previously described by several authors (I_geo, PI, EF, C_f, PI_sum, PI_Nemerow, PLI, PI_ave, PI_Vector, PIN, MEC, CSI, MERMQ, C_deg, RI, mCd and ExF) as well as the newly published Biogeochemical Index (BGI) were compared. The content, as determined by other authors, of the most widely investigated heavy metals (Cd, Pb and Zn) in farmland, forest and urban soils was used as a database for the calculation of all of the presented indices, and this shows, based on statistical methods, the similarities and differences between them. The indices were initially divided into two groups: individual and complex. In order to achieve a more precise classification, our study attempted to further split indices based on their purpose and method of calculation. The strengths and weaknesses of each index were assessed; in addition, a comprehensive method for pollution index choice is presented, in order to best interpret pollution in different soils (farmland, forest and urban). This critical review also contains an evaluation of various geochemical backgrounds (GBs) used in heavy metal soil pollution assessments. The authors propose a comprehensive method in order to assess soil quality, based on the application of local and reference GB.

An ecological risk investigation of marine sediment from the northern Mediterranean coasts (Aegean Sea) using multiple methods of pollution determination

The aim of this study is an assessment of metal pollution levels in Aegean Sea sediment. Sediment samples collected from 7 different locations (Yeniköy, Edremit, Ayvalık, Dikili, Aliağa, Hekimadası, and Ildır) along the northern Mediterranean region of Turkey were investigated for 11 elements (Cu, Fe, Zn, V, Cd, Ni, As, Pb, Mn, Co, and Cr). Graphite furnace atomic absorption spectrophotometry (GFAAS) and flame atomic absorption spectrophotometry (FAAS) were used for elemental analysis. The findings were evaluated with sediment assessment methods by taking two different values as a reference and then investigating the adverse biological effects of elemental profiles on living organisms. Pb, Mn, As, Cd, and Cr concentrations were within a moderate to significant range in terms of contamination factor [Formula: see text]), albeit varying according to reference and location. The most problematic region and elements regarding the enrichment factor (EF) was Ayvalık and As, Ni, Cu, Pb, Co, and Cd. However, according to the EF, the anthropogenic effect was not at an alarming level. This was further supported by the results of the geoaccumulation index (Igeo). The findings of the modified degree of contamination (mC _d ) and the pollution load index (PLI) suggested that the accumulation was greatest in Ayvalık, and the least in Hekimadası and Ildır. The location with the highest elemental total toxic unit (ΣTU) was Edremit. The effect of the existing element profile on organisms was 21% in this location when the mean effect range-median quotient (m-ERM-q) was considered. As and Ni concentrations in all stations were found to be higher than threshold effect level (TEL) and Effect Range Low (ERL). Ni levels in Edremit exceeded the probable effect level (PEL) and Effect Range Median (ERM). Toxic unit (TU) values of these two elements in all stations ranged from 59.30 to 80.43%.

Bioavailability of trace metals in sediments of a recovering freshwater coastal wetland in China's Yellow River Delta, and risk assessment for the macrobenthic community

We investigated the speciation of trace metals and their ecological risks to macrobenthic communities in a recovering coastal wetland of China's Yellow River Delta during the freshwater release project. We established 16 sampling sites in three restoration areas and one intertidal reference area, and collected sediments and macrobenthos four times from 2014 to 2015. The instability index for the trace metals showed a moderate risk for Mn and a high risk for Cd. For both Mn and Cd, the carbonate and FeMn-bound fractions appear to contribute mostly to the instability and bioavailability indexes, but for Cd, the exchangeable fraction also have a much higher contribution. The bioavailability index indicated higher bioavailability of trace metals in freshwater restoration areas than that in the intertidal area. The single-factor contamination index indicated that most trace metal concentrations in the macrobenthos were in excess of the national standard. The biota-sediment accumulation factor suggested that the macrobenthos accumulated most As, Cd, and Cu. Redundancy analysis showed clear relationships between the macrobenthos and sediment metal concentrations. Our results will help wetland managers to assess the bioaccumulation risks based on metal speciation, and to improve management of these recovering freshwater wetland ecosystems.

Health risk assessment of heavy metals in fish and accumulation patterns in food web in the upper Yangtze River, China

This study aims to concern the distribution of As, Cr, Cd, Hg, Cu, Zn, Pb and Fe in surface sediment, zoobenthos and fishes, and quantify the accumulative ecological risk and human health risk of metals in river ecological system based on the field investigation in the upper Yangtze River. The results revealed high ecological risk of As, Cd, Cu, Hg, Zn and Pb in sediment. As and Cd in fish presented potential human health risk of metals by assessing integrated target hazard quotient results based on average and maximum concentrations, respectively. No detrimental health effects of heavy metals on humans were found by daily fish consumption. While, the total target hazard quotient (1.659) exceeding 1, it meant that the exposed population might experience noncarcinogenic health risks from the accumulative effect of metals. Ecological network analysis model was established to identify the transfer routes and quantify accumulative effects of metals on river ecosystem. Control analysis between compartments showed large predator fish firstly depended on the omnivorous fish. Accumulative ecological risk of metals indicated that zoobenthos had the largest metal propagation risk and compartments located at higher trophic levels were not easier affected by the external environment pollution.

CAPSULE

A potential accumulative ecological risk of heavy metal in the food web was quantified, and the noncarcinogenic health risk of fish consumption was revealed for the upper reach of the Yangtze River.

Water Environment Assessment as an Ecological Red Line Management Tool for Marine Wetland Protection

A 'red line' was established, identifying an area requiring for ecological protection in Tianjin, China. Within the protected area of the red line area, the Qilihai wetland is an important ecotope with complex ecological functions, although the ecosystem is seriously disturbed due to anthropogenic activities in the surrounding areas. This study assesses the water quality status of the Qilihai wetlands to identify the pollution sources and potential improvements based on the ecological red line policy, to improve and protect the waters of the Qilihai wetlands. An indicator system was established to assess water quality status using single factor evaluation and a comprehensive evaluation method, supported by data from 2010 to 2013. Assessment results show that not all indicators met the requirement of the Environmental Quality Standards for Surface Water (GB3838-2002) and that overall, waters in the Qilihai wetland were seriously polluted. Based on these findings we propose restrictions on all polluting anthropogenic activities in the red line area and implementation of restoration projects to improve water quality.

Assessment ecological risk of heavy metal caused by high-intensity land reclamation in Bohai Bay, China

The article examines the detailed spatial and temporal distributions of coastal reclamation in the northwest coast of Bohai Bay experiencing rapid coastal reclamation in China from 1974 to 2010 in annual intervals. Moreover, soil elements properties and spatial distribution in reclaimed area and inform the future coastal ecosystems management was also analyzed. The results shows that 910.7 km2 of coastal wetlands have been reclaimed and conversed to industrial land during the past 36 years. It covers intertidal beach, shallow sea and island with a percentage of 76.0%, 23.5% and 0.5%, respectively. The average concentration of Mn is 686.91mg/kg and the order of concentration of heavy metal are Cr>Zn>As>Ni>Cu>Pb>Cd>Hg. We used the "space for time substitution" method to test the soil properties changes after reclamation. The potential ecological risk of heavy metal is in low level and the risk of Cd and As is relatively higher. The ecosystem-based coastal protection and management are urgent to support sustainable coastal ecosystems in Bohai bay in the future.