[Spatial Distribution, Speciation, and Ecological Risk Assessment of Heavy Metals in Surface Sediments of Dongjiang Lake, Hunan Province].

To understand the heavy metal pollution status of Dongjiang Lake, the contents and species of heavy metals in the surface sediments were investigated during September 2021, and the heavy metal pollution level and potential ecological risk were evaluated. The results showed that Cd, Pb, As, Cu, Zn, Ni, and Cr contents were in the range of 0.40-34.1, 14.8-1688, 6.99-1155, 6.89-280, 26.2-1739, 6.29-55.4, and 23.3-44.8 mg·kg-1, respectively, with extremely uneven spatial distributions. The highest contents of Cd, Pb, As, Zn, Cu, and Ni were found in the site adjacent to Yaogangxian tungsten ore. The proportion of metal species with bioavailability was high, in which Cd in acid-soluble species was 46.7%-71.5% and Pb in reducible species was 46.8%-67.0%. The bioavailable species of Cu, Zn, Ni, and Cr were 35%-68%, 42%-72%, 26%-51%, and 6%-30%, respectively, although they primarily existed in residual species. According to the geo-accumulation index (Igeo), there was a moderate or extreme pollution status of Cd in all sites, moderate or extreme pollution status of Pb in 90% of sites, and moderate pollution status of As, Cu, and Zn in 30% of sites. The ecological risk factor (Eri) of Cd showed high potential ecological risk in all sites with significantly high potential ecological risk in 80% of sites. Moreover, As and Pb had significantly high potential ecological risk, and Cu had moderate potential ecological risk in S7, which was adjacent to Yaogangxian tungsten ore. There was a high total potential ecological risk in all sites and significantly high potential ecological risk in 50% of sites. Therefore, the surface sediments of Dongjiang Lake were under the combined pollution of Cd, Pb, As, Zn, and Cu with high bioavailability and high total potential ecological risk.

Autochthonous sources and drought conditions drive anomalous oxygen-consuming pollution increase in a sluice-controlled reservoir in eastern China.

Freshwater reservoirs are an important type of inland waterbody. However, they can suffer from oxygen-consuming pollution, which can seriously threaten drinking water safety and negatively impact the health of aquatic ecosystems. Oxygen-consuming pollutants originate from both allochthonous and autochthonous sources, and have temporally and spatially heterogeneous drivers. Datanggang Reservoir, China, is located in a small agricultural watershed; it is controlled by multiple sluice gates. Anomalously high oxygen consumption indicators were observed in this reservoir in March 2021. Here, it was hypothesized that autochthonous sources were the primary drivers of oxygen-consuming pollution in the reservoir under drought conditions. Datasets of water quality, precipitation, primary productivity, and sediment were used to analyze water quality trends in the reservoir and inflow rivers, demonstrating the effects of allochthonous inputs and autochthonous pollution. No correlation was found between reservoir oxygen consumption indicators and allochthonous inputs; reservoir oxygen consumption indicators and chlorophyll-a concentration were significantly positively correlated (p < 0.05). Substantially lower precipitation and higher water temperature and pH (compared to historical levels) were also observed before the pollution event. Therefore, during this period the hydrological conditions, water temperature, pH, and other variables caused by short-term drought conditions may have facilitated phytoplankton growth in the reservoir. This contributed to a large increase in autochthonous oxygen-consuming pollutants, as reflected by the abnormally high indicators. Sediments contaminated with organic matter may also have been an important contributor. As the effects of environmental management and pollution control continue to emerge, exogenous pollutants imported from the land to reservoirs are currently effectively controlled. However, endogenous pollutants driven by a variety of factors, such as meteorology and hydrology, will likely become the main drivers of short-term changes in oxygen-consuming pollution in freshwater reservoirs in the foreseeable future.

Distribution and pollution risk assessment of heavy metals in the surface sediment of the intertidal zones of the Yellow River Estuary, China.

Eleven heavy metals (V, Cr, Mn, Co, Fe, Ni, Cu, Zn, As, Cd, and Pb) in surface sediment in the intertidal zones of the Yellow River Estuary, China were analyzed by inductively coupled plasma-mass spectrometry in summer and autumn 2019. Results indicated that the 11 heavy metals had the same sources. Sediment particle size and total organic matter were the main factors influencing the distribution of heavy metals. Most sites in the intertidal zones of the study area were not contaminated with V, Cr, Fe, Co, Zn, Pb, Cu, As, Mn and Ni, while Cd was the priority pollutant. Heavy metal pollution risk in autumn was higher than that in summer, which may be due to hydrodynamic effects. The present study showed that the heavy metal concentrations in the study area had a temporal decreasing trend compared to previous studies, which may be due to the reduction in human activities.

Unique bacterial communities and potential function along the vertical gradient in the deepest marine blue hole.

The Sansha Yongle Blue Hole is the deepest blue hole in the world discovered so far, while its great potential and values have not been fully exploited regarding microbial communities. A large-scale sampling was performed at different depths (0-270 m) inside the blue hole. Based on high-throughput sequencing, the diversity and richness of bacterial communities were relatively higher in oxic and euphotic layer, and at depths of 180-230 m in anoxic layer. Proteobacteria was dominant with mean relative abundance of 64.7%. As the representative genera, Thiomicrospira and Arcobacter were detected with higher abundances up to 96.1% and 31.5% in the anaerobic environment. Principal co-ordinates analysis, one-way ANOVA and network analysis highlighted the distinctive species at different depths. Correlation analysis illustrated the significant correlations between the bacteria and environmental elements of dissolved oxygen, temperature, salinity, pH, sulphur and nutrient. Phylogenetic analysis indicated that the microbial ecosystem was characterized with infrequent and unidentified microorganisms in the deep layer. This research revealed the unique microbial ecosystem and potential functions in regulating ecosystem productivity and cycling of carbon, sulphur and nitrogen. Comprehensive and long-term investigations in the Sansha Blue Hole should be taken to conserve the peculiar ecosystem.

Trait-based adaptability of Phragmites australis to the effects of soil water and salinity in the Yellow River Delta.

Phragmites australis is the dominant species in the Yellow River Delta and plays an important role in wetland ecosystems. In order to evaluate the relationship between phenotypic variation and environmental factors, explore how functional traits respond to changes in electrical conductivity and soil water content, and reveal the ecological strategies of P. australis, we investigated the ecological responses of P. australis to soil properties based on 96 plots along the coastal-inland regions in the Yellow River Delta of China. Within the range of soil water content (SWC, 9.39%-36.92%) and electrical conductivity (EC, 0.14-13.29 ms/cm), the results showed that (a) the effects of salinity were more important than the soil water content for the characterization of the morphological traits and that plant functional traits including leaf traits and stem traits responded more strongly to soil salinity than soil water content; (b) compared with morphological traits such as average height and internode number, physiological traits such as SPAD value, as well as morphological traits closely related to physiological traits such as specific leaf area and leaf thickness, showed stronger stability in response to soil water and salinity; and (c) under the condition of high electrical conductivity, P. australis improved its water acquisition ability by increasing indicators such as leaf water content and leaf thickness. In addition, with the increase in plant tolerance to stress, more resources were used to resist external stress, and the survival strategy was inclined toward the stress tolerator (S) strategy. Under low EC conditions, P. australis increased specific leaf area and leaf area for its growth in order to obtain resources rapidly, while its survival strategy gradually moved toward the competitor (C) strategy.

Effects of harvest time and desalination of feedstock on Spartina alterniflora biochar and its efficiency for Cd2+ removal from aqueous solution.

Cadmium (Cd2+), as the primary contaminant in Chinese soils, is dangerous to human health and ecological security. Invasive plant Spartina alterniflora in Chinese coastal wetlands presents a promising feedstock for biochar, which is an efficient adsorbent for heavy metal removal. S. alterniflora harvested in summer, autumn and winter were pyrolyzed to produce biochars. We analyzed the effects of harvest time and desalination of feedstock on biochar properties and Cd2+ adsorption capacity in aqueous solution. Biochars were characterized by pH probe, elemental analyzer, SEM, BJH, BET, and FTIR, and the Cd2+ concentrations were measured using AAS. Except pH (9.85-10.95) and nitrogen contents (0.71-1.59%), other biochar properties had no linear correlations with harvest time. Biochars produced from feedstock harvested in autumn had the highest carbon contents (73.25%) and lowest functional groups diversity (CC and -CHx). The pH and carbon contents (64.44-73.25%) were increased by desalination treatment. The surface area (0.48-2.27 m2/g), total pore volume (0.0015-0.0055 mL/g), mesopore volume (0.0015-0.0052 mL/g), and Cd2+ adsorption capacities (16.29-32.34 mg/g) were affected by desalination treatment, and the effects varied with harvest time. Biochars produced from desalted feedstock harvested in summer and untreated feedstock harvested in winter showed higher surface area, porosity, and Cd2+ adsorption capacity. Moderate salt contents (1.5-3.0% in chloride content) in feedstock promote the formation of biochars with higher surface area and porosity.

[Response Behaviors of Heavy Metals at Tidal Currents Interface and Salinity Interface in the Estuary Area].

In China, trace metals (such as dissolved Cu, Zn, Pb, Cd, and Cr) are the routine mandatory monitoring indicators in existing Freshwater Quality Standard (FWQS, 2002) and Seawater Quality Standard (SWQS, 1997). Using Daliao River estuary as an example, we tried to research the general response patterns of these metals in estuarine system. Firstly, we determined the location of FSI (freshwater-seawater interface) and TCI (tidal currents interface), which were based on biological, chemical and geographic similarities by descriptive and quantitative methods, respectively. Secondly, two hypotheses were proposed to explain the difference based on distribution coefficient Kd along salinity and SS (suspended solids) gradient, these results revealed that the indicators for As, Cd and Cr may be prone to be affected by salinity, and the ones in the second pattern may be more sensitive to SS. Finally, we classified the response behaviors into two patterns based on the changing trends along the distance and magnitudes affected by the FSI and TCI: 1the obvious boundary break point from FSI for As, Cd and Cr; 2 the boundary zones from TCI for Zn, Cu, Pb and Ni. The partitioning behaviors showed similar changing trends at particle and sediment phases, especially for particle phase, depending on the concentration of SS along the salinity. The difference between general behaviors for the two patterns mainly existed at water phase. In general, this paper highlighted the need to consider the background difference of trace metals and identified the sensitive indicators controlled by different environment factors (such as salinity and SS) based on the native estuarine characteristics. Our work will assist the implementation of updating the current water quality standards in China.

Bioassessment of marine sediment quality using meiofaunal assemblages in a semi-enclosed bay.

In order to assess marine sediment quality of a semi-enclosed bay, sediment and meiofaunal samples were analyzed at 35 stations in coastal waters of Bohai Bay, China. Concentrations of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn, Co and Mn) in sediment were measured and the Hakanson potential ecological risk index coupled with the ratio of nematodes to copepods (N/C ratio) was used. Results showed that the concentration of Mn was the highest while Cd was the main risk contributor. The Hakanson potential ecological risk index indicated that all pollutants posed low risks in the study area. However, the N/C ratio exhibited different results compared with Hakanson potential ecological risk index. BIOENV analysis identified the concentration of Ni and sediment grain size as the most important environmental variables influencing meiofaunal assemblages. The present study indicated that, in marine sediment quality assessments, meiofaunal assemblages should be involved besides pollutant concentrations.

Temporal and spatial distribution of red tide outbreaks in the Yangtze River Estuary and adjacent waters, China.

Between 1972 and 2009, evidence of red tide outbreaks in the Yangtze River Estuary and adjacent waters was collected. A geographic information system (GIS) was used to analyze the temporal and spatial distribution of these red tides, and it was subsequently used to map the distribution of these events. The results show that the following findings. (1) There were three red tide-prone areas: outside the Yangtze River Estuary and the eastern coast of Sheshan, the Huaniaoshan-Shengshan-Gouqi waters, and the Zhoushan areas and eastern coast of Zhujiajian. In these areas, red tides occurred 174 total times, 25 of which were larger than 1000 km(2) in areal extent. After 2000, the frequency of red tide outbreaks increased significantly. (2) During the months of May and June, the red tide occurrence in these areas was 51% and 20%, respectively. (3) Outbreaks of the dominant red tide plankton species Prorocentrum dong-haiense, Skeletonema costatum, Prorocentrum dantatum, and Noctiluca scientillan occurred 38, 35, 15, and 10 times, respectively, during the study interval.

[Study on the changes of macrobenthos communities and their causes in Bohai Bay].

Based on the analysis of macrobenthos samples collected from Bohai Bay, China in 2011 and the data obtained from the nearly the same sampling area during last six years, as well as the hydrological conditions, nutrients and dissolved oxygen, the characteristics of the changes in macrobenthos communities and their response to environmental variables were derived. Results showed that the distribution of the values of species number, abundance, biomass, richness index and diversity index reflected a gradient from the coastline to the open sea with the higher values concentrated at the open sea in the north part of Haihe estuary. The macrobenthos communities showed an obvious fluctuation over last six years, composed of three nodes. The first time node was in 2005 and 2008, the total species number, abundance and biomass maintained relatively high; the second time node was in 2009 and 2010, the values of the above three indices were the lowest in the three time nodes due to the increasing anthropogenic disturbances and natural changes; the third time node was in 2011, the values of the above three indices were the highest since many effective environmental protection measures had been carried out, indicating that the macrobenthos communities were recovered to a certain degree. The integrated impacts from the physical, chemical and biological variables induced by natural changes and anthropogenic disturbances, such as over-fishing, coastal land reclamation and sewage discharge were the triggers for the changes of macrobenthos communities. Furthermore, the variation characteristics of macrobenthic communities and environmental factors were generally in accordance with each other.