Trophodynamics and potential health risk assessment of heavy metals in the mangrove food web in Yanpu Bay, China.

Mangroves are the cradle of coastal water biodiversity and are susceptible to heavy metal pollution. However, the trophic transfer mechanism of heavy metals in the mangrove food web and the resulting human health risks are not fully understood. Heavy metal concentration (Cr, Ni, Cu, Zn, As, Cd, Pb, V, Co) and stable isotope ratios of carbon and nitrogen (δ13C and δ15N) were evaluated in sediments and particulate organic matter, litter, and aquatic organisms (plankton, arthropods, mollusks, omnivorous fish, and carnivorous fish) from the Yanpu Bay mangroves. The results revealed that heavy metals exhibited different trophic transfer patterns. As and Hg were efficiently biomagnified, with trophic magnification factors of 1.17 and 1.42, respectively; while Cr, Ni, Cu, Cd, Pb, V, and Co were efficiently biodiluted. Zn exhibited a trophic magnification factor > 1 and was not significantly correlated with δ15N (p > 0.05), suggesting no biomagnification or biodilution. The heavy metals in the important fishery species (omnivorous fish and carnivorous fish) were below the permissible limits, except for Zn in Ophichthus apicalis. The assessment of probabilistic health risks revealed that fish consumption in adults and children posed an acceptable risk (total target hazard quotient <1).

Assessing heavy metal pollution in sediments from the northern margin of Chinese mangrove areas: Sources, ecological risks, and health impacts.

With the rapid economic development of coastal cities, the discharge of substantial amounts of heavy metal pollutants poses a serious hazard to mangroves; however, the potential sources of heavy metals and the resulting health risks are not fully understood. In this study, we analyzed the contents, sources, and ecological and health risks of heavy metal contamination in mangrove sediments from the northern margin of China. The accumulation of heavy metals in mangroves was primarily driven by five potential sources, namely agricultural (33.5 %), natural sources (21.3 %), industrial (19.1 %), aquaculture (14.3 %), and traffic (11.8 %). The assessment of health risks using a probabilistic approach demonstrated that noncarcinogenic risks were within acceptable limits for all populations. It was worth noting that both noncarcinogenic and carcinogenic risks were greater in children than in adults. Analysis of source-oriented health risks revealed that agricultural sources and As and Cd were priority sources and elements of pollution requiring attention.

Ensemble habitat suitability modeling for predicting optimal sites for eelgrass (Zostera marina) in the tidal lagoon ecosystem: Implications for restoration and conservation.

Seagrass systems are in decline, mainly due to anthropogenic pressures and ongoing climate change. Implementing seagrass protection and restoration measures requires accurate assessment of suitable habitats. Commonly, such assessments have been performed using single-algorithm habitat suitability models, nearly always based on low environmental resolution information and short-term species data series. Here we address eelgrass (Zoostera marina) meadows' large-scale decline (>80%) in Shandong province (Yellow Sea, China) by developing an ensemble habitat model (EHM) to inform eelgrass conservation and restoration strategies in the Swan Lake (SL). For this, we applied a weighted EHM derived from ten single-algorithm models including profile, regression, classification, and machine learning methods to generate a high-resolution habitat suitability map. The EHM was constructed based on the predictive performances of each model, by combining a series of present-absent eelgrass datasets from recent years coupled with oceanographic and sediment data. The model was cross-validated with independent historical datasets, and a final habitat suitability map for conservation and restoration was generated. Our EHM scheme outperformed all single models in terms of habitat suitability, scoring ∼0.95 for both true statistic skill (TSS) and area under the curve (AUC) performance criteria. Machine learning methods outperformed profile, regression and classification methods. Regarding model explanatory variables, overall, topographic characteristics such as depth (DEP) and seafloor slope (SSL) are the most significant factors determining the distribution of eelgrass. The EHM predicted that the overlapping area was almost 90% of the current eelgrass habitat. Using results from our EHM, a LOESS regression model for the relationship of the habitat suitability to both the biomass and density of Z. marina outperformed better than the classic Ordinary Least Squares regression model. The EHM is a promising tool for supporting eelgrass protection and restoration areas in temperate lagoons as data availability improves.

Sediment nitrogen mineralization and immobilization affected by non-native Sonneratia apetala plantation in an intertidal wetland of South China.

The mineralization and immobilization of nitrogen (N) are critical biogeochemical transformations in estuarine and coastal sediments. However, the biotic and abiotic mechanisms that regulate the two processes in different aged mangrove sediments remain poorly understood. Here, we used 15N isotope dilution method to investigate the changes in sediment N mineralization (GNM) and NH4+ immobilization (GAI) of different aged mangrove habitats (including 0, 10, and 20 years Sonneratia apetala, as well as >40 years mature native Kandelia obovata) in Qi'ao Island, Guangdong Province, China. Measured GNM and GAI rates ranged from 2.69 to 17.53 µg N g-1 d-1 and 2.29-21.38 µg N g-1 d-1, respectively, which varied both spatially and seasonally. The ratio of GNM to total N (PAM%, 0.24-0.86%) also varied spatially and seasonally, but the ratio of GAI to GNM (RAI, 0.79-1.54) only varied spatially. Mangrove restoration significantly increased the N mineralization and immobilization rates, but remained lower than those of mature native Kandelia obovata habitat. The sediment bacterial abundance, labile organic matter and temperature are the dominant factors in controlling N mineralization and immobilization. Our findings suggested that exotic mangrove Sonneratia aperale plantation can enhance sediment N mineralization and immobilization rates and improve N stability through accumulated biomass rapidly. Overall, these results provide new insights into sediment N transformation processes and associated influencing mechanisms in such intertidal wetlands profoundly influenced by human activities.

Functional trait responses of macrobenthic communities in seagrass microhabitats of a temperate lagoon.

Understanding the effects of habitat heterogeneity on the functioning of macrobenthic communities is essential to the conservation of biodiversity in coastal ecosystems. However, the effects of habitat heterogeneity on the functional trait composition and diversity of seagrass bed macrobenthos are as scarce. In the present study, functional diversity indices (i.e., functional dispersion, functional richness, and Rao's quadratic entropy), RLQ analysis, and fourth-corner analysis indicated that macrobenthic functional trait composition and diversity differ among seagrass bed microhabitats (interior, edge, and bare sediment). More specifically, functional traits were more evenly distributed in the seagrass bed interior and edge habitats, when compared to bare sediment, and functional diversity was significantly higher (p < 0.01). Functional trait distributions were influenced by environmental parameters (e.g., total organic carbon, organic matter, and grain size). Suspension-feeding and burrowing bivalves preferentially inhabited bare sediment with high sand content and low TOC, whereas herbivorous, small, and sensitive species mainly inhabited muddy sediments with higher organic supply.

Spatial variations and potential risks of heavy metals in sediments of Yueqing Bay, China.

In this study, we determined the spatial variations and potential risks of heavy metals in the sediments of Yueqing Bay by assessing the relationship between metal concentrations and sediment physiochemical factors. We found higher sediment metal concentrations in the inner bay than in the central and outer bay, particularly with respect to Hg, Cu, and Pb concentrations. According to the sediment quality guidelines, the heavy metals had a toxicity incidence probability of 21%. Assessments of heavy metal contamination using the geo-accumulation index and potential ecological risk index suggest that Cr, As, Pb, and Hg likely pose low ecological risks, while Cu, Zn, and Cd were identified as priority pollutants and may pose moderate ecological risks to the ecosystem. Multivariate statistical analysis inferred the high influence of sediment texture, total organic carbon (TOC), and petroleum hydrocarbons (PHCs) on the distribution and fate of metals in sediment.

Response of macrobenthic communities to heavy metal pollution in Laoshan Bay, China: A trait-based method.

The effects of multiple natural and anthropogenic stressors on the functional trait composition and diversity of marine macrobenthic communities in Laoshan Bay were investigated using biological trait analysis (BTA). Seven traits, including 27 trait modalities and four functional diversity indices (functional richness, functional evenness, functional divergence, and Rao's quadratic entropy), were considered. The results of RLQ (environmental variables (R), species taxa (L), and traits (Q)) and variance partitioning analysis (VPA) showed that the trait compositions and functional diversity of macrobenthic communities were influenced by a combination of stressors, among which heavy metals were the major factors. At the sites with high heavy metal pollution, the prevalent traits were infauna, burrower, and deposit feeder, whereas epifauna, carnivores and crawlers were dominant at the sites of low heavy metal contamination. The impact of natural environmental gradients on macrobenthic communities is also worthy of attention.

Trophic transfer of heavy metals through aquatic food web in a seagrass ecosystem of Swan Lagoon, China.

The Swan Lagoon is a national nature reserve and an important spawning ground in China. In this study, we evaluated the concentration of heavy metals (Cd, Cr, Cu, Pb, and Zn) in different aquatic organisms (aquatic plants, crustaceans, mollusks, and fish), in order to examine their trophic transfer in food web. The results showed that the concentrations of Cd, Cu, Pb, and Zn were considerably higher in mollusks, whereas Cr concentrations were significantly higher in aquatic plants than in mollusks, crustaceans, and fish (p < 0.01). Heavy metals exhibit different patterns of trophic transfer in food web. Cd, Cr, Cu, and Pb tended to be efficiently biodiluted with increasing trophic levels in food web (trophic magnification factor, TMF < 1; p < 0.05). The concentration of Zn increased with increasing trophic level; however, it exhibited a TMF of only 1.03, and was not significantly correlated with δ15N (p > 0.05), indicating neither biomagnification or biodilution in the food web.

Macrobenthos functional trait responses to heavy metal pollution gradients in a temperate lagoon.

Biological traits analysis (BTA) can help identify the effect of various contaminants on functional trait composition of macrobenthos. However, the effects of bioavailable heavy metals on functional traits of macrobenthos communities remain to be examined. We sampled macrobenthos communities and assessed environmental variables over gradients of heavy metal pollution in Swan Lagoon, China. The RLQ and fourth-corner approaches were used to investigate the response of functional traits to heavy metal pollution. Our findings suggested that macrobenthic functional traits can be used to distinguish the effects of heavy metals and other environmental variables and isolate the corresponding species associated with heavy metal contamination. The macrobenthos at highly contaminated sites comprised taxa of sub-surface deposit-feeders, second-order opportunistic species, and tube-builders, mainly represented by the polychaeta Cirriformia tentaculata and Cirratulus chrysoderma. At less contaminated sites, indifferent species, species attached to seagrass, and crawlers were observed. The results confirm that BTA can provide new insights into the response of macrobenthic functional traits to heavy metal pollution in coastal lagoons.

Comparative analysis of heavy metal accumulation and bioindication in three seagrasses: Which species is more suitable as a bioindicator?

The present study aimed to assess the utilization of three seagrasses (Zostera marina, Z. japonica, and Z. caespitosa) along the eastern coast of the Shandong Peninsula as bioindicators of heavy metal pollution. Heavy metal concentrations (Cd, Cr, Cu, Pb and Zn) were investigated in the sediments and in the aboveground and belowground tissues of seagrasses. The results show that the aboveground tissues of seagrasses accumulated higher levels of Cd and Cu (excluding Z. caespitosa), whereas other metals, such as Cr, Pb and Zn, were mainly restricted to the belowground tissues. Compared to Z. japonica and Z. caespitosa, Z. marina had a higher enrichment capacity for heavy metals. Overall, the seagrasses can reflect the levels of metals in the sediments, especially Z. marina, whose heavy metal tissue levels were significantly and positively correlated with the levels of all metals in the sediments. This study showed that Z. marina could be used as an effective bioindicator for heavy metal pollution of sediments in ecological quality monitoring programs in the future, at least in the temperate waters of China.

Heavy metal concentrations and chemical fractions in sediment from Swan Lagoon, China: Their relation to the physiochemical properties of sediment.

This study was performed to determine the distribution and chemical fractions of five heavy metals (Cd, Cr, Cu, Pb, and Zn) in sediment from three sampling areas in Swan Lagoon, and their relation to the physiochemical properties of sediment were explored. The results revealed that Cd in sediment from the sand part (SP), muddy sand part (MSP) and sand muddy part (SMP) were potentially highly susceptible and bioavailable since the exchangeable fractions were 21.0%, 27.4%, and 32.1%, respectively, of the total concentrations. A portion of Pb and Zn were observed as reducible fractions owing to their affinity to Fe-Mn; they were able to complex with Fe-Mn oxides and oxyhydroxides in the sediment. A large amount of Cu in the oxidizable fraction may be due to the fact that Cu can easily form stable complexes with organic matter. Cr was overwhelmingly found in the residual fraction, suggesting that Cr was strongly bound in mineral lattices. Enrichment factors (EF) indicated that Cd in three sampling areas suffered severe enrichment, whereas other metals were present in only minor amounts. In addition, Cd may pose a medium to high risk in the MSP and SMP based on risk assessment codes. According to the mean probable effects level quotient, the samples from the MSP and SMP had a 21% probability of toxicity. The multivariate statistical analysis suggested that sediment texture (d0.5, sand and silt), Fe-Mn, and the total organic carbon (TOC) influenced the distribution of the studied metals and their chemical fractions.

Assessing the ecological quality status of transplanted mangrove wetland in the Oujiang estuary, China.

Although numerous studies have performed ecological quality status (EcoQS) assessments in aquatic ecosystems, knowledge regarding the assessment of the EcoQS of mangrove transplant wetlands is still lacking. Therefore, we investigated the influence of mangrove transplants on the EcoQS by comparing the sediment quality status and benthic quality status in mangroves with those of reference sites (Spartina alterniflora stand and mudflat). The findings confirm that the benthic quality status of mangroves was superior to those of the reference sites. Subsequently, we tested the performances of various indices (AMBI, BENTIX, H', EX, Δ+, and Ʌ+). BENTIX, H', EX and Ʌ+ seemed be more suitable than AMBI and Δ+ for assessing the benthic quality status. The results also confirm that mangrove transplants may not facilitate or restrain the accumulation of heavy metals (except Cu and Hg) in sediments. Moreover, mangrove transplants posed a low ecological risk.

Evaluation of four seagrass species as early warning indicators for nitrogen overloading: Implications for eutrophic evaluation and ecosystem management.

Seagrasses are major coastal primary producers and are widely distributed on coasts worldwide. Seagrasses show sensitivity to environmental stress due to their high phenotypic plasticity, and therefore, we evaluated the use of constituent elements in four dominant seagrass species as early warning indicators for nitrogen eutrophication of coastal regions. A meta-analysis was conducted with published data to develop a global benchmark for the selected indicator, which was used to evaluate nitrogen loading at a global scale. A case study at three bays was subsequently conducted to test for local-scale differences in leaf C/N ratios in four seagrasses. Additionally, morphological and physiological metrics of seagrasses were measured from the three locations under varied nitrogen levels to develop further assessment indexes. The benchmark and local study showed that leaf C/N ratios of Zostera marina were sensitive to nitrogen discharge, which could be a highly valuable early warning indicator on a global scale. Moreover, the threshold value of seagrass leaf C/N was determined according to the benchmark to differentiate eutrophic and low nitrogen levels at a local scale. Of the eight phenotypic metrics measured, leaf width, total chlorophyll (a + b), chlorophyll ratio (a/b), and starch in the rhizome were the most effective at discriminating between the three locations and could also be promising indicators for monitoring eutrophication.

[Niche and interspecific association of nekton in the south coastal waters of Cangnan, Zhe-jiang, China].

In this paper, the interaction between the species Population were analyzed based on the data of major nekton species in the south coastal waters of Cangnan in spring and autumn 2014. A series of methods including niche breadth, niche overlap, χ2 - test and association coefficient (AC) based on a 2x2 contingency table were used. The results showed that the major nekton species in the south coastal waters of Cangnan were classified into three groups, i.e. wide niche breadth species, moderate niche breadth species and narrow niche breadth species based on the niche breadth values. The wide niche breadth species of nekton were Harpodon nehereus, Portunus trituberculatus, mantis shrimp and other 2 species. The moderate niche breadth species of nekton were Collichthys lucidus, Parapenaeopsis hardwickii, Parapenaeopsis tenella and other 5 species. While the species with narrow niche breadths were Charybdis japonica, Amblychaeturichthys hexanema, Palaemon gravieri and other 7 species. There were great differences in the niche overlap values among the major nekton populations, with the maximum value of 0.93 and the minimum of 0, which indicated that resource utilization competition in some nekton might exist. The results of variance ratio analysis for major nekton in the south coastal waters of Cangnan showed that they were significantly positively correlated. χ2 - test results showed that there were significantly interspecific association for 78 species pairs (χ2≥3.841), among which more association coefficients (AC) of species pairs are positive.