Surface sediment properties and heavy metal pollution assessment in the Shallow Sea Wetland of the Liaodong Bay, China

Effects of cadmium and zinc interactions on the physiological biochemistry and enrichment characteristics of Iris pseudacorus

Compound pollution with cadmium (Cd) and zinc (Zn) is common in nature. The effects of compounded Cd and Zn on the growth and development of Iris pseudacorus in the environment and the plant's potential to remediate heavy metals in the environment remain unclear. In this study, the effects of single and combined Cd and Zn stress on I. pseudacorus growth and the enrichment of heavy metals in I. pseudacorus seedlings were investigated. The results showed that under Cd (160 μM) and Zn (800 μM) stress, plant growth was significantly inhibited and photosynthetic performance was affected. Cd+Zn200 (160 μM + 200 μM) reduced the levels of malondialdehyde, hydrogen peroxide, and non-protein thiols by 31.29%, 53.20%, and 13.29%, respectively, in the aboveground tissues compared with levels in the single Cd treatment. However, Cd+Zn800 (160 μM + 800 μM) had no effect. Cd and Zn800 inhibited the absorption of mineral elements, while Zn200 had little effect on plants. Compared with that for Cd treatment alone, Cd + Zn200 and Cd+Zn800 reduced the Cd content in aboveground tissues by 54.15% and 49.92%, respectively, but had no significant effect on Cd in the root system. Zn significantly reduced the Cd content in subcellular components and limited the content and proportion of Cd extracted using water and ethanol. These results suggest that a low supply of Zn reduces Cd accumulation in aboveground tissues by promoting antioxidant substances and heavy metal chelating agents, thus protecting the photosynthetic systems. The addition of Zn also reduced the mobility and bioavailability of Cd to alleviate its toxicity in I. pseudacorus.

Background construction for tracing metal inputs in estuarine sediments of the Liaodong Bay (NE China): Linear-regression method

Intertidal sediments are a significant reservoir of trace metals originating from human activities and natural weathering. However, the absence of geochemical background levels and the heterogeneity of sediment components are challenging to quantify the extent of trace metal contamination. For distinguishing the contribution of natural and anthropogenic inputs, dynamic background functions were established by linear regressions of trace metals (i.e., Zn, Cr, Ni, Cu, Cd, and Pb) against normalizer Al in three cores of the Daliao River estuary. Lead-210 geochronology indicated that trace metals have accumulated rapidly in the sediments since 1985 CE. The calculation results of enrichment factors and excess fluxes confirmed that the increased contents of Zn and Cd were contaminated by human activities. Conversely, the increased contents of others (i.e., Cr, Ni, Cu, and Pb) were attributed to variations in geological background levels, driven by the combination of grain size and organic matter. Overall levels of trace metals were at medium-low ecological risks (MSQG-Q: 0.19-0.38), and Ni at high-medium ecological risks (PEL-Q_Ni > 0.5) in recent decades. Interestingly, these Ni probably originated from natural weathering rather than anthropogenic inputs because sediment quality guidelines lacked consideration for the differences in regional background levels and grain size. This procedure could provide the fundamental framework for regional investigations of spatial and temporal contamination, applied to other similar intertidal zones of sediment quality management.

Potentially hazardous metals in the sediment of a subtropical bay in South China: Spatial variability, contamination assessment and source apportionment

Potentially hazardous metals (PHMs) in the coastal environment have become a great concern due to their easy bioaccumulation, poor biodegradability and high toxicity. Surface sediment samples were collected in a subtropical bay in South China to analyse the spatial variations, contamination level and potential sources of PHMs. The results indicated that the order of average contents of PHMs in Qinzhou Bay sediment was Zn > Pb > Cr > Cu > As > Hg > Cd. The most important potential ecological risk factor was Hg pollution in the Qinzhou Bay sediments. The positive matrix factorization (PMF) model results indicated that Cu, Pb, Zn, Cd and Cr mainly originated from natural sources while Hg and As were related to coal fired industrial inputs and petroleum production activities. The results could provide a basis for marine management to formulate relevant pollution prevention and control measures.

Evaluation of ecological risk, source, and spatial distribution of some heavy metals in marine sediments in the Middle and Eastern Black Sea region, Turkey

In the present study, the concentration levels of heavy metals such as Mn, Fe, Ni, Cu, Zn, Cr, and Pb in sediment samples collected from 16 sampling locations in the Middle and Eastern Black Sea regions, Turkey, were measured using energy dispersive X-ray fluorescence spectroscopy (EDXRF). Various pollution parameters and methods, such as the enrichment factor (EF), geo-accumulation index (I_geo), contamination factor (CF), pollution load index (PLI), ecological risk index (RI), and geo-spatial distribution patterns, were used to assess the pollution status, ecological risks, and sources of metals in sediment in detail. The mean concentrations of Mn, Fe, Ni, Cu, Zn, Cr, and Pb were found to be 565.38, 46,000, 34.38, 104.06, 109.88, 87.31, and 32.31 mg/kg, respectively. Results showed that the mean concentrations of Cu, Zn, and Pb exceeded the crustal shale value, with the exception of Mn, Fe, Ni, and Cr. According to the calculated pollution parameters, although minimal or moderate pollution was detected in the area investigated, it was determined that there was a very low ecological risk. Multivariate statistical analysis results showed that Cu, Zn, and Pb levels in the investigated region were slightly influenced by anthropogenic inputs such as mining and agricultural practices. In addition, the geo-spatial distributions of Cu, Zn, Fe, and Pb were found to be higher in this region due to the mining activities carried out in the Eastern Black Sea region.

Evaluation of metals and trace elements in sediments of Kanyakumari beach (southernmost India) and their possible impact on coastal aquifers

Beach sediments of Kanyakumari at the southernmost India were evaluated for metals and trace elements and to assess their possible impact on coastal ecosystems. Positive correlations (except for Cd and Sr) between them indicated metamorphic lithologies and heavy mineral deposits as possible sources. Significant-extremely high enrichment and very high contamination of Th, Zr, Mo, Ti and U reflected the presence of different heavy minerals. The geo-accumulation index, however, mirrored their variable abundances at different sites. Association of Cd with P suggested the influence of anthropogenic solid waste from fishing industry. It might have caused >41-fold enrichment of Cd and the Fe- Mn-oxides possibly acted as scavengers for 13-fold enrichment of As compared to UCC. Concentrations of Zn and Cr between ERL and ERM in 13% and 93% of the samples, and Ni > ERM in 87% of sediments suggest their bioavailability to seawater with a potential risk for coastal aquifers.

Spatial distribution, origin and contamination assessment of heavy metals in surface sediments from Jangsong tidal flat, Kangryong river estuary, DPR Korea

This study aims to investigate spatial distribution, contamination and origin of heavy metals (Pb, Zn, Cu, Ni, Co and Cr) in surface sediments of Jangsong tidal flat (JTF), Kangryong river estuary, DPR Korea, where has been affected by various mining activities. The spatial diverse of heavy metals are due to differences in their sources and sediment properties. Enrichment factor, geoaccumulation index and ecological risk indexes indicate that JTF is not polluted and has low ecological risk, although slight enrichments occur for some metals. Multivariate analyses revealed that Mn, Ni and Cr originated from lithogenic source, whereas other metals were of anthropogenic origin, among which Fe and Co originated from the iron mine settling pond near JTF, while Pb, Zn and Cu originated from AMD effluent by sulfide mining activity in catchment of JTF. The different transport mechanisms of heavy metals from AMD result in diverse distribution of the metals in JTF.

Uptake and concentration of heavy metals in dominant mangrove species from Hainan Island, South China

By investigating three dominant mangrove species, namely Aegiceras corniculatum, Kandelia candel, Ceriops tagal and their rhizosediment in Mangrove wetlands in Hainan Island, this research analyzed absorption, concentration and distribution of heavy metals (Cr, Cu, Zn, As, Cd and Pb) in mangroves. The results found that the concentration of specific heavy metal differs in the different mangrove organs (leaf, stem and root). The content of heavy metals concentrated greatly in roots, but less in leaves and stems. The study also revealed that concentration capacity was weak in all three mangrove species (BCF0.02-0.91), with their organ ranking BCF_root > BCF_stem > BCF_leaf. Among three mangrove species, the transfer factors of leaves and stems in Ceriops tagal were highest, indicating a great distribution capability for heavy metals, followed by Kandelia candel. Transfer factors in Aegiceras corniculatum were the weakest. This ranking was opposite to bioconcentration factors of roots. This study can further reflect bioavailability of heavy metals in sediments, which provides scientific evidence on ecosystem protection and management in mangrove wetlands.

Underestimated heavy metal pollution of the Minjiang River, SE China: Evidence from spatial and seasonal monitoring of suspended-load sediments

Previous assessments on rivers in SE China with highly developed economy and enormous population indicate diverse and relatively low particulate heavy metal pollution levels. However, the controlling mechanisms for heavy metal enrichment and transport remain enigmatic. Here, we target a mesoscale mountainous river, the Minjiang River, and obtain grain size, mineralogical and heavy metal concentration (Pb, Cd, Cr, Mn, Mo, Zn, V, Co, Ni, Cu) data from seasonal suspended particulate matter (SPM) near the river mouth, riverbed sediments and SPM samples from mainstream and major tributaries of the river. The results indicate that SPM samples have higher particulate heavy metal concentrations than riverbed sediments collected in pairs. Heavy metal concentrations of Cd, Zn, Cr, V, Co, Ni and Cu are higher in upstream SPM samples than those in downstream regions, whereas Pb, Mn and Mo concentrations don't show this spatial variation. Most heavy metals (e.g., Pb and Zn) show high concentrations in flood seasons and relatively low concentrations in dry seasons, revealing a hydrologic control. However, Cr and Mn show high concentrations in some dry season samples, suggesting incidental anthropogenic input events. The SPM-based pollution assessments using enrichment factor, geoaccumulation index and potential ecological risk index demonstrate that the Minjiang River is moderately to strongly polluted by particulate Pb, Cd, Mo and Zn contaminations and most particulate heavy metals have moderate to considerable potential ecological risks. We contend that transport and discharge of particulate heavy metals by the Minjiang River are controlled by both natural and anthropogenic forcings and the pollution levels are worse than previously known. Our findings suggest that particulate heavy metal discharge by subtropical mountainous rivers is related to sediment types and hydrologic characteristics. Therefore, high-spatiotemporal-resolution investigations on river SPM samples are highly recommended to better evaluate particulate heavy metal pollution levels and aquatic environmental conditions.

Assessing hydrodynamic effects of ecological restoration scenarios for a tidal-dominated wetland in Liaodong Bay (China)

Estuarine wetlands have experienced a variety of ecological and environmental problems caused by natural and anthropogenic factors. China has proposed a series of measures and made great efforts to control coastal degradation; however, decision makers still urgently need to know which measures to implement and how they will influence the estuarine environment and functions. This study used field observations, a hydrodynamic model, and statistical methods to investigate the effects of potential restoration scenarios on hydrodynamic conditions in the tidal-influenced estuarine wetland system, Liaodong Bay (China). Results reveal that the average total phosphorus, organic carbon, available phosphorus, pH, total nitrogen content, and moisture content in the soil and sediment environment were 0.04 ± 0.003%, 0.84 ± 0.25%, 16.3 ± 4.7 mg/kg, 8.3 ± 0.1, 0.07 ± 0.02%, and 44 ± 2%, respectively, exhibiting an overall trend of degradation. A series of restoration scenarios in regards to hydrodynamic regulation and tidal inputs were used to preserve the ecological value of the estuarine wetland. Model simulations indicate that the significant improvement of hydrodynamic fields (inundation depth and flow velocity) is more likely to occur when the tidal amplitudes reach around 2 m, while relatively weak responses can be observed when the tidal levels are lower than 1 m. Additionally, the construction of floodgates may play a key role in determining the tidal inputs and flowpaths across the wetland. The modifications in micro-topography of the wetland may play a complementary role in enhancing the connectivity condition via increased creek depth of 0.5 m and width up to around 20 m. This work represents a first attempt in exploring hydrodynamic effects of restoration scenarios for a tidal-dominated wetland. An improved understanding of the estuarine system also highlights that the design and implementation of wetland restoration projects should use more comprehensive measures to achieve long-term landscape management, connectivity planning, and ecological sustainability.

Biological Risk Assessment of Heavy Metals in Sediments and Health Risk Assessment in Marine Organisms from Daya Bay, China

The concentrations of heavy metals in sediments and marine organisms in Daya Bay were investigated, and the Monte Carlo method was used to analyze the uncertainty of the results of geo-accumulation characteristics and ecological and health risks. The mean concentrations of metal elements in sediments were in the following order: Zn > Cr > Cu > As > Cd > Hg, while those in marine organisms were Zn > Cu > As > Cr ≈ Cd > Hg. The geo-accumulation index (Igeo) indicated that the primary pollutant was Hg, with 5.46% moderately polluted, and 39.52% for unpolluted to moderately polluted. Potential ecological risks (RI) were between low and high risks, and the contributions of Hg, Cd, and As to ecological risks were 50.85%, 33.92%, and 11.47%, respectively. The total hazard coefficients (THQ) were less than 1, but on the basis of total carcinogenic risks (TCR), the probability of children and adults exceeded the unacceptable risk threshold of 22.27% and 11.19%, respectively. Sensitivity analysis results showed that the concentrations of carcinogenic elements contributed to risk in the order of As > Cd > Cr. Therefore, in order to effectively control heavy metals contamination in Daya Bay, it is necessary to strengthen the management of Hg, Cd, and As emissions.

Spatiotemporal variation, seasonal variation, and potential risks of sedimentary heavy metals in a new artificial lagoon in eastern China, 2014-2019

The spatiotemporal variation, seasonal variation, and potential ecological risk of eight heavy metals (HMs) in the Meishan Bay (MSB) a new artificial lagoon -from 2014 to 2019 were investigated. The levels of As, Cu, Pb, Cr, Ni, and Zn in winter were higher than in other seasons, Hg in winter and summer were higher than in other seasons, while Cd in summer and spring (wet season) were the highest. The seasonal distribution of HMs was mainly affected by particle size, anthropogenic sources, rainfall, and water characteristics. The concentrations of these HMs showed a general downward trend, while Hg showed an upward trend from2014 to 2019. Higher levels of HMs were found outside the North dyke and some sluice gates. The sources of Cd, Zn, and Pb could be attributed to ship discharges and traffic exhaust, while pesticides and fertilizers were the main sources of Hg. Among all these HMs, Cd and Hg caused moderate pollution in the MSB.

Quantifying Metal Contamination and Potential Uptake by Phragmites australis Adans. (Poaceae) Along a Subtropical River System

Metal pollution is pervasive across terrestrial and aquatic ecosystems owing to anthropogenic activities. Sediments can accrue high concentrations of metals and act as secondary sources, and thus may be valuable indicators of metal contamination across spatiotemporal scales. In aquatic systems, the extent of metal pollution may be further mediated by transference among sediments and living organisms, with plant metal contaminants potentially predictive of underlying sediment concentrations. The present study thus quantifies the extent of metal pollutants (Na, K, Ca, Mg, Cu, Zn, Mn, B, Fe) across multiple study sites and seasons (cool-dry, hot-wet, hot-dry) in a subtropical river system. Furthermore, uptake by a key macrophyte species, Phragmites australis, was examined and correlated with sediment pollution levels among different plant parts. Overall, sediment pollution load indices differed seasonally, being significantly highest during the cool-dry season irrespective of sampling location, suggesting that periods with reduced water flows can exacerbate metal pollution levels in riverine sediments. Also, metal concentrations were highest in upstream wetland sites, indicating a capacity for metal sink effects in these areas. Overall, macrophytes contained high concentrations of select metals, however composition and concentrations differed across plant parts, with roots containing particularly high concentrations of Fe and B. Correlations between sediment and macrophyte concentrations were mostly non-significant, whilst stem Mn and Fe concentrations correlated significantly negatively and positively to sediment concentrations, respectively. The present study identifies key spatiotemporal differences in multiple metal contaminants in an understudied subtropical aquatic system that align with hydrological regime differences. Whilst macrophytes were not found to be major accumulators, or predictors, of metal contaminants in this study, they may collectively play a central role in concentration regulation in aquatic systems.

Spatial distribution, source identification, and risk assessment of heavy metals in seawater and sediments from Meishan Bay, Zhejiang coast, China

The aim of this study is to determine the spatial distribution, potential sources, and ecological risks of 8 heavy metals (Zn, Cu, Cr, Ni, As, Cd, Hg, and Pb) in Meishan Bay, Zhejiang coast, China. Surface water (n = 31), bottom water (n = 31), and surface sediments (n = 31) were collected. Water physicochemical properties and sediment resuspension were important factors affecting spatial distributions of heavy metals. The spatial distributions of Cr, Ni, Pb, As, Cu, and Zn were consistent with the clay distribution. Atmospheric deposition was the main source of Cd and Pb, mainly from industrial and transportation exhausts, while Zn was mainly from ship transportation. Agriculture pesticides and sewage wastewater were considered as the main sources for Hg. The geo-accumulation index results indicated that there was limited pollution of Cu, Zn, Cr, Pb, and As, and mild to moderate pollution of Cd and Hg. The potential ecological risk assessment suggested a high ecological risk of Hg in Meishan Bay.

Spatial Variations and Potential Risks of Heavy Metals in Seawater, Sediments, and Living Organisms in Jiuzhen Bay, China

Coastal waters are polluted by heavy metals to varying degrees, posing potential risks to marine ecology and human health. In May 2006, the pollution levels, sources, and ecological risks of heavy metals (Cu, Pb, Zn, Cd, Hg, and As) in seawater, surface sediments, and living organisms were studied in Jiuzhen Bay in Fujian, China. This study identified Hg (0.26–0.72 µg/L) and As (20.3–31.5 µg/L) pollution in the seawater of Jiuzhen Bay. In sediments, heavy Pb pollution (946 µg/g dw) was only detected at one station at a level posing very serious potential risk, while Hg pollution (0.052–0.087 µg/g dw) was observed at three stations at a level posing serious potential risk. No heavy metal pollution was detected in sediments at other stations. The concentrations of five heavy metals (Cu, Zn, As, Cd, and Pb) exceeded the corresponding National Quality Standards for oysters, indicating heavy pollution, based on an ecological risk assessment. In clams, two heavy metals (Pb and As) exceeded the standards, indicating light pollution, based on an ecological risk assessment. No heavy metal pollution was found in fish or shrimps. The heavy metals in the seawater and sediments of Jiuzhen Bay are mainly derived from the river discharges of Luxi and Wujiang Rivers although sewage discharge along the coast of Jiuzhen Bay is another source of heavy metal pollution at some stations. Given the pollution of Pb, Hg, and As in seawater and sediments at some stations within the bay, the potential risks of Pb, Hg, and As in living organisms to both the marine ecology and human health deserve increased attention.

Distribution, ecological risk assessment and source identification of heavy metals in surface sediments of Huixian karst wetland, China

In this study, heavy metals including Cd, Pb, Zn, Mn, Cu, Ni, Cr, As, and Hg, in the surface sediment (0-10 cm) of the Huixian wetland in a karst region were investigated in terms of their spatial distribution, ecological risks, and possible sources. Samples were collected from 13 typical sites throughout the Huixian wetland and were analyzed via inductively coupled plasma-mass spectrometry. The results revealed that the mean concentrations of Cd, Pb, Mn, Cr, As, and Hg were higher than the background and Chinese safe standard values. Based on spatial distribution and ecological risk, the study area was differentiated into three groups of sites with the following order of risk: group 3 > group 2 > group 1. The observed concentrations fluctuated slightly with depth. However, an irregular decreasing trend in the concentration with soil depth was observed among the groups. Multivariate statistical analyses showed that the high accumulation of Cd, Pb, Zn and Cu in the sediments of group 3 sites is due to the natural ancient deposition of minerals rich in heavy metals, while the accumulation of Mn, Cr, As, and Hg is attributed to an anthropogenic origin. Agricultural activities, the use of fertilizers and, pesticides, and local automobile repair stations most probably enriched these heavy metals in the Huixian wetland sediments. Hg and Cd have the highest potential ecological risk, which follows the order Hg > Cd > Pb > As > Ni > Cu > Cr > Mn > Zn. The mean geoaccumulation index (I_geo) values of Pb (0.48) and Hg (1.12) suggested moderate contamination in the study area.

Migration and Diffusion of Heavy Metal Cu from the Interior of Sediment during Wave-Induced Sediment Liquefaction Process

Sediments are an important sink for heavy metal pollutants on account of their strong adsorption capacity. Elevated content of Cu was observed in the Chengdao area of the Yellow River Delta, where the surface sediment is mainly silt and is prone to be liquefied under hydrodynamic forces. The vertical transport of fine particles, along with pore water seepage, during the liquefaction process could promote the migration and diffusion of Cu from the interior of sediment. The present study involved a series of wave flume experiments to simulate the migration and diffusion of Cu from the interior of sediment in the subaqueous Yellow River Delta area under wave actions. The results indicated that sediment liquefaction significantly promoted the release of Cu from internal sediment to overlying water. The variations of Cu concentrations in the overlying water were opposite to the suspended sediment concentrations (SSCs). The sediment liquefaction caused high initial rises of SSCs, but led to a rapid decline of dissolved Cu concentration at the initial period of sediment liquefaction due to the adsorption by fine particles. Afterwards, the SSCs slightly increased and then gradually decreased. Meanwhile, the dissolved Cu concentration generally kept increasing under combined effects of intensively mix of sediment and overlying water, pore water seepage, and desorption. The dissolved Cu concentration in the overlying water during sediment liquefaction phase was 1.5–2.2 times that during the consolidation phase. Sediment liquefaction also caused vertical diffusion of Cu in sediment and the diffusion depth was in accordance with the liquefaction depth. The results of the present study may provide reference for the environmental management in the study area.

The concentration distribution and pollution assessment of heavy metals in surface sediments of the Bohai Bay, China

Three hundred five surface sediment samples from the Bohai Bay in northeastern China were examined for grain size, organic carbon (Corg) concentration, and concentrations of heavy metals (Pb, Zn, Cu, As, Cr, Cd, and Hg). Average metal concentrations were 33 mg/kg (Cu), 27 mg/kg (Pb), 95 mg/kg (Zn), 75 mg/kg (Cr), 0.3 mg/kg (Cd), 13 mg/kg (As), and 72 μg/kg (Hg). In most cases, these concentrations were lower than the China Marine Sediment Quality criteria. Enrichment factors, however, suggested moderate to strong Cd and Hg contamination of the Bohai Bay. The fact that 68.6% of Pollution Load Index (PLI) values exceeded 2 demonstrated strong pollution of the Bohai Bay, Hg contributed the most to the PLI.

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.

Heavy metal contamination assessment of surface sediments of the Subei Shoal, China: Spatial distribution, source apportionment and ecological risk

This study investigated heavy metals (Ni, Zn, Cr, Cu, As, Pb, Cd and Hg) concentrations in surface sediment of Subei Shoal, China, to illustrate their spatial distribution characteristics, sources and potential ecological risk of pollution. Contents of total organic carbon (TOC), clay, silt and sand were 1.7 ± 0.8%, 3.3 ± 3.2%, 13.6 ± 14.2% and 83.1 ± 17.4%, respectively. The spatial distribution of TOC, clay and silt were similar; however, distribution of Hg was inverse. Concentrations of Ni, Zn, Cr, Cu, As, Pb, Cd and Hg were 47.88 ± 8.93, 38.18 ± 8.86, 19.22 ± 5.14, 11.32 ± 5.07, 6.97 ± 2.45, 0.13 ± 0.72, 0.56 ± 0.77 and 0.06 ± 0.02 mg kg^-1 sediment, respectively. Principal component analysis suggested that Cu, Zn, Cd, Cr and Ni were mainly derived from natural sources, whereas Pb, Cd, As and Hg from industrial and agricultural sources. Results of geo-accumulation index, potential ecological risk index (RI), pollution load index (PLI), toxic risk index (TRI) and contamination severity index (CSI) demonstrated that pollution levels of Cd and Hg were moderate, which should attract more attention as main pollution factors. The pollution was mainly distributed in the central and northern parts, and the southern part had a good ecological environment. Moreover, the contaminated stations accounted respective for 33.4%, 25.9%, 33.3% and 70.4% of RI, PLI, TRI and CSI, of which 70.4% of the contamination severity index stations contained 66.7% of much lower severity stations. These findings could contribute to more effective exploitation of tidal flat resources, and the prevention and treatment of tidal marsh environment.

Comparison of rhizosphere bacterial communities of reed and Suaeda in Shuangtaizi River Estuary, Northeast China

Microbial communities in wetland soils play vital roles in biogeochemical cycling of nutrients. In this study, the soil samples were collected from Suaeda, reed and Suaeda-reed hybrid zones in Shuangtaizi River Estuary, Northeast China, and the rhizosphere bacterial communities were compared using Illumina MiSeq sequencing. The microbial richness, diversity and structure of bacterial communities varied greatly in reed and Suaeda. Canonical correspondence analysis and Mantel test indicated that pH was the most significant factor (P < 0.05) in bacterial community assembly. Proteobacteria was the most dominant phylum, accounting for 45.7-58.0% of the total sequences. Thioprofundum, Thiohalomonas and Exiguobacterium were the predominant genera in Suaeda, while Exiguobacterium, Gillisia, Desulfomonile, Citrobacter, Thioprofundum and Acinetobacter were the core species in reed. PICRUSt analysis revealed similar functional profiles of rhizosphere microbiota in reed and Suaeda. Nitrate reduction related genes were abundant for nitrogen metabolism, whereas assimilatory sulfate reduction was the major process for sulfur metabolism.

Interactive effects of single, binary and trinary trace metals (lead, zinc and copper) on the physiological responses of Kandelia obovata seedlings

Heavy metals are considered important environmental contaminants, and their mixture toxicity on plants has complex mutual interactions. The interactive effects of heavy metals on growth, photosynthetic parameters, lipid peroxidation and compatible osmolytes were studied in Kandelia obovata grown for 5 months in sediment treated with combinations of lead (Pb), zinc (Zn) and copper (Cu). The results showed no significant reduction of biomass under heavy metal stresses, except for decreased root biomass under higher Pb + Cu treatment, indicating high tolerance of K. obovata to heavy metal stress. Only the photosynthetic parameters, including net photosynthetic rate (P_n), stomatal conductance (G_s) and transpiration rate (T_r), decreased with increasing concentration of treatments (except for Pb + Cu and Pb + Zn + Cu). Trinary treatment (Pb + Zn + Cu) increased biomass and the photosynthetic parameters when compared to the external addition of binary metals. In the roots, biomass and soluble sugar content were lower under binary than trinary treatments, indicating that the combination of Zn and Cu exhibited improved effects of alleviating toxicity than each of them alone in Pb-containing combined treatments. In the leaves, Zn-containing combined treatments significantly decreased malondialdehyde (MDA), soluble sugar and proline content in low concentration, while Pb + Cu treatments significantly increased these parameters (P < 0.05). The correlation analysis showed that leaf MDA and proline content were negatively correlated with Zn concentration (P < 0.05). Zn could alleviate the effects of combined heavy metal stress, and Pb + Cu treatment showed synergistic effects in leaves. The positive correlations between MDA content and the osmotic parameters showed that osmotic stress and lipid membranes oxidation exist simultaneously under multiple heavy metal stresses. Therefore, biomass, T_r, leaf MDA, leaf proline content and soluble sugar content could indicate metal mixture toxicity to mangrove seedlings.

Spatial distribution and ecological risk assessment of heavy metals in coastal surface sediments in the Hebei Province offshore area, Bohai Sea, China

Seven hundred and nine surface sediment samples, along with deeper sediment samples, were collected from Hebei Province along the coastal section of the Bohai Sea, China, and analyzed for grain size, concentrations of organic carbon (Corg) and heavy metals (Cu, Pb, Zn, Cr, Cd, As, and Hg). Results indicated that the average concentrations in the sediments were 16.1 mg/kg (Cu), 19.4 mg/kg (Pb), 50 mg/kg (Zn), 48.8 mg/kg (Cr), 0.1 mg/kg (Cd), 8.4 mg/kg (As), and 20.3 μg/kg (Hg). These concentrations generally met the China Marine Sediment Quality criteria. However, both pollution assessments indicated moderate to strong Cd and Hg contamination in the study area. The potential ecological risk index suggested that the combined ecological risk of the seven studied metals may be low, but that 24.5% of the sites, where sediments were finer and higher in Corg concentration, had high ecological risk in Hg and Cd pollution.