The importance of structural and functional characteristics of tidal channels to smooth cordgrass invasion in the Yellow River Delta, China: Implications for coastal wetland management.

Understanding the spatiotemporal landscape dynamics and spread pathways of invasive plants, as well as their interactions with geomorphic landscape features, are of great importance for predicting and managing their future range-expansion in non-native habitats. Although previous studies have linked geomorphic landscape features such as tidal channels to plant invasions, the potential mechanisms and critical characteristics of tidal channels that affect the landward invasion by Spartina alterniflora, an aggressive plant in global coastal wetlands, remain unclear. Here, using high-resolution remote-sensing images of the Yellow River Delta from 2013 to 2020, we first quantified the evolution of tidal channel networks by analyzing the spatiotemporal dynamics of their structural and functional characteristics. The invasion patterns and pathways of S. alterniflora were then identified. Based on the above-mentioned quantification and identification, we finally quantified the influences of tidal channel characteristics on S. alterniflora invasion. The results showed that tidal channel networks presented increasing growth and development over time, and their spatial structure evolved from simple to complex. The external isolated expansion of S. alterniflora played a dominant role during the initial invasion stage, and then they connected the discrete patches into the meadow through marginal expansion. Afterwards, tidal channel-driven expansion gradually increased and became the primary way during the late invasion stage, accounting for about 47.3%. Notably, tidal channel networks with higher drainage efficiency (shorter OPL, higher D and E) attained larger invasion areas. The longer the tidal channels and the more sinuous the channel structure, the greater the invasion potential by S. alterniflora. These findings highlight the importance of structural and functional properties of tidal channel networks in driving plant invasion landward, which should be incorporated into future control and management of invasive plants in coastal wetlands.

n-Alkanes in sediments from the Yellow River Estuary, China: Occurrence, sources and historical sedimentary record.

A total of 21 surface sediments from the Yellow River Estuary (YRE) and a sediment core from the abandoned Old Yellow River Estuary (OYRE) were analyzed for n-alkanes using gas chromatography-mass spectrometry (GC-MS). n-Alkanes in the range C12-C33 and C13-C34 were identified in the surface sediments and the core, respectively. The homologous series were mainly bimodal distribution pattern without odd/even predominance in the YRE and OYRE. The total n-alkanes concentrations in the surface sediments ranged from 0.356 to 0.572mg/kg, with a mean of 0.434mg/kg on dry wt. BASIS: Evaluation of n-alkanes proxies indicated that the aliphatic hydrocarbons in the surface sediments were derived mainly from a petrogenic source with a relatively low contribution of submerged/floating macrophytes, terrestrial and emergent plants. The dated core covered the time period 1925-2012 and the mean sedimentation rate was ca. 0.5cm/yr. The total n-alkanes concentrations in the core ranged from 0.0394 to 0.941mg/kg, with a mean of 0.180mg/kg. The temporal evolution of n-alkanes reflected the historical input of aliphatic hydrocarbons and was consistent with local and regional anthropogenic activity. In general, the investigation on the sediment core revealed a trend of regional environmental change and the role of anthropogenic activity in environmental change.

Spatial variation in bacterial community in natural wetland-river-sea ecosystems.

Wetland-estuarine-marine environments are typical oxic/anoxic transition zones and have complex water flow-paths within the zone of mixing where freshwater interacts with ocean water. Little is known about the impact of this interaction on bacterial community structures or the relationship between bacterial community and geochemical factors in such transitional mixing environments. Hence, we investigated the distribution patterns and diversity in bacterial communities in the Yellow River estuary-coastal wetland-Bohai Sea transition zone by analyzing 39 samples from 13 ordered sites. High-throughput sequencing of the 16S rRNA gene revealed significant shifts in diversity and distribution of bacterial community in sediments from the Yellow River estuary to the Bohai Sea. Yellow River sediment was dominated by hydrogen-, nitrogen-, and iron-cycling bacteria, such as Hydrogenophaga, Nitrospira, Pseudomonas, and Thiobacillus. The coastal wetland had a haloduric community associated with different functions, such as Planctomyces, Marinobacter, Halomonas, Salinivibrio, and Salinibacter. The Bohai Sea sediment had a higher relative abundance of Lutimonas, Desulfococcus, Photobacterium, Propionigenium, and Vibrio. Spatial variation in bacterial community was correlated with pH, salinity and sulfate (SO42-) concentration in such coastal environments. The major bacterial taxa were significantly different across the wetland, estuary, and coastal marine ecosystems, indicating substantial spatial heterogeneity among the three ecosystems. Statistical analysis revealed strong links between variation in bacterial community structure and ecosystem type. Our results demonstrate the importance of geographic and geochemical factors in structuring the bacterial community in natural environments.

Distinct distribution patterns of prokaryotes between sediment and water in the Yellow River estuary.

There are close exchanges between sediment and water in estuaries; however, the patterns of prokaryotic community assembly in these two habitat types are still unclear. This study investigated the bacterial and archaeal abundance, diversity, and community composition in the sediment and the overlying water of the Yellow River estuary. Notably higher prokaryotic abundance and diversity were detected in the sediment than in the water, and bacterial abundance and diversity were remarkably higher than those of archaea. Furthermore, the ratio of bacterial to archaeal 16S rRNA gene abundance was significantly lower in the sediment than in the water. Bacterial communities at different taxonomic levels were apparently distinct between the sediment and water, but archaeal communities were not. The most dominant bacteria were affiliated with Deltaproteobacteria and Gammaproteobacteria in sediment and with Alphaproteobacteria and Betaproteobacteria in water. Euryarchaeota and Thaumarchaeota were the most abundant archaea in both habitats. Although distinct prokaryotic distribution patterns were observed, most of the dominant bacteria and archaea present were related to carbon, nitrogen, and sulfur cycling processes, such as methanogenesis, ammonia oxidation, and sulfate reduction. Unexpectedly, prokaryotes from the water showed a higher sensitivity to environmental factors, while only a few factors affected sediment communities. Additionally, some potential co-occurrence relationships between prokaryotes were also found in this study. These results suggested distinct distribution patterns of bacterial and archaeal communities between sediment and overlying water in this important temperate estuary, which may serve as a useful community model for the further ecological and evolutionary study of prokaryotes in estuarine ecosystems.

Effects of continual burial by sediment on seedling emergence and morphology of Suaeda salsa in the coastal marsh of the Yellow River estuary, China.

A greenhouse study was conducted to determine the impacts of continual burial on seedling emergence and morphology of Suaeda salsa, a pioneer species in the coastal marsh of the Yellow River estuary. From May to June 2012, seeds of S. salsa were artificially buried to depths of 0 cm (no burial), 2 cm (burial of 1 mm d(-1)), 4 cm (burial of 2 mm d(-1)), 6 cm (burial of 3 mm d(-1)), 8 cm (burial of 4 mm d(-1)) and 10 cm (burial of 5 mm d(-1)) in plastic pots filled with unsterilized sediment. Results showed that the percent emergence of seedlings had a significantly negative correlation with continual burial depth (p < 0.001). A large percentage of seedlings emerged from 2, 4 and 6 cm burial depths, with the highest emergence (56.00 ± 6.60%) occurring from 2 cm depth. The shortest emergence time occurred at 4 cm burial depth and seeds buried at 10 cm depth took longer to emerge than those at other depths. At shallow or moderate burials, a stimulatory effect on seedling height, stem diameter, number and length of branch, taproot length and dry mass were observed. With increasing burial depth, root-mass and leaf-mass ratios generally increased while stem-mass ratio decreased. Sediment burial also stimulated part of the hypocotyl below the sediment to form adventitious roots, implying that S. salsa seedlings had a special adaptive strategy in response to the rapid and dynamic burial environment in the coastal marsh of the Yellow River estuary. The use of thin-layer continual burial (1-2 mm d(-1)) to promote the emergence of S. salsa seedlings in degraded marsh was feasible, and our study provided another way for the restoration of S. salsa marsh during the initial stage of seedling establishment and laid a good foundation for the scientific decision-making and management of restoration project at a large scale.

Organophosphate esters (OPEs) pollution characteristics, bioaccumulation and human consumption implication in wild marine organisms from the Yellow River Estuary, China.

As the substitutes of polybrominated diphenyl ethers, organophosphate esters (OPEs) with high concentrations have accumulated in the estuaries, bays, and harbors. However, limited information is available about the OPEs in the estuary organism categories, especially under the multiple industrial pressure. This study investigated the occurrence, bioaccumulation and human consumption implication in wild marine organisms from the Yellow River Estuary, where located many petroleum and chemical manufacturing industries. This study found that concentrations of Σ13OPEs ranged from 547 ng/L to 1164 ng/L in seawater (median: 802 ng/L), from 384 to 1366 ng/g dw in the sediment (median: 601 ng/g dw), and from 419 to 959 ng/g dw (median: 560 ng/g dw) in the marine organisms. The congener compositions in the organisms were dominated by alkyl-OPEs (80.7 %), followed by halogenated-OPEs (18.8 %) and aryl-OPEs (0.5 %). Based on the principal component analysis, petrochemical pollution, and industrial wastewater discharge were distinguished as the main plausible sources of OPEs to the YRE ecosystem. Most OPEs had potential or strong bioaccumulation capacity on the organisms, with a positive correlation between log BAF (Bioaccumulation Factor) and log Kow of OPEs. The highest estimated daily intake value of OPEs was tri-n-propyl phosphate, exceeding 300 ng/kg·bw/day via consuming fish. The highest hazard quotients from OPEs ranged from 0.001 to 0.1, indicating a low risk to human health by consuming marine organisms in the YRE. As the consumption of OPEs increases year by year, the risks of OPEs still cannot be ignored.

Exploring source-specific ecological risks of PAHs near oil platforms in the Yellow River Estuary, Bohai Sea.

The Yellow River Estuary (YRE) is one of highly remarkable regions profoundly impacted by human activities, with numerous oil platforms dispersed throughout. In this area, offshore oil exploitation may pose significant ecological risks. To comprehensively evaluate the quantitative impacts of oil field exploitation on the marine coastal ecosystem, this study investigated the occurrence, sources, and ecological risks associated with 16 polycyclic aromatic hydrocarbons (PAHs) in seawater and sediment near oil platforms in the YRE. We found that 1) The concentrations of PAHs decreased from the surface seawater to sediments; 2) The ecological risk level of PAHs in seawater exceeded that in sediments; 3) terrestrial sources (combustion), rather than offshore oil drilling activities, significantly influenced regional ecological risks through processes of atmospheric deposition and surface runoff. These findings provide essential data for future estuarine research efforts while supporting mitigation measures aimed at addressing marine environmental pollution related to oil production activities.

How the Water-Sediment Regulation Scheme in the Yellow River affected the estuary ecosystem in the last 10 years?

The Yellow River, renowned as the most sediment-laden river globally, grapples with sediment deposition issues compromising reservoir functionality and elevating downstream riverbeds, posing threats to human life and property safety. In response, the Water-Sediment Regulation Scheme (WSRS) has been innovatively implemented to address these challenges. While effectively mitigating sediment deposition, WSRS has concurrently disrupted the equilibrium of the estuarine ecosystem. This paper addresses the understudied but crucial topic of the interannual impact of WSRS on the estuarine ecosystem. Drawing upon physical, chemical, and biological data gathered through field surveys conducted before, during, and after WSRS from 2011 to 2022, the analysis delves into the interannual changes in the estuarine environment, fish eggs and larvae abundance, and species diversity under the influence of WSRS. The findings reveal an interannual decreasing trend in terrestrial material input due to WSRS, juxtaposed with an interannual increasing trend in fish eggs and larvae around the estuary, as well as the species diversity index. Notably, these trends became more pronounced post-2014. Compared to pre-2014, nutrient concentrations experienced a ~20 % decrease, chlorophyll-a concentration increased by 44 %, fish eggs proliferated approximately 1 time, and the species diversity index transitioned from a declining trend to an ascending trajectory. After 12 years of continuous WSRS implementation, the impact on the estuarine ecosystem has demonstrably diminished. This research aims to furnish reference experience and scientific basis for water and sediment regulation in major rivers around the world in terms of estuarine ecology.

Assessment of the depositional characteristics of the Yellow River estuary from 1960s by 239+240Pu and 137Cs.

The spatial and vertical distribution of 239+240Pu and 137Cs in the sediments of the Yellow River Delta was studied to evaluate the deposition dynamics in the Yellow River estuary from 1960s. The activity of 239+240Pu and 137Cs in sediment core ranged from 0.001 to 0.212 Bq/kg and 0.52-2.53 Bq/kg, respectively. A maximum accumulation peak and two secondary accumulation peaks appeared in the sediment core YR2. The average deposition rate of 8.3 cm/y for the Yellow River estuary from 1964 to 1976 was obtained. The proportion of Pu from the Yellow River net input and direct deposition to the total inventory of Pu in the estuary was assessed, with a total inventory of Pu in the abandoned estuary of 7.4 × 1010 Bq and a net input of 2.2 × 1010 Bq from the Yellow River. Pu deposited in the estuary only accounts for 18 % of the total Pu transported by the Yellow River, and most of the Pu is injected into the Bohai Sea with the Yellow River.

Effects of fresh-salt water interaction on spatial variations of soil organic carbon in reed wetland of Yellow River Estuary.

Estuarine wetlands exhibit significant interaction between fresh and salt water, with long-term carbon sequestration capability. We set up 60 sampling sites in the reed wetlands of the fresh-salt water interaction zone of the Yellow River Estuary, covering four different zones of the weak-intensity fresh-salt water interaction zone (WIZ), medium-intensity fresh-salt water interaction zone (MIZ), high-intensity interaction fresh-salt water zone (HIZ) and strong-intensity fresh-salt water interaction zone (SIZ). We investigated how fresh-salt water interaction affected the spatial variation of soil organic carbon (SOC) storage. The results showed that the area of reed wetland accounted for 17.8% of the total area of the fresh-salt water interaction zone the Yellow River Estuary, which mainly distributed in the WIZ and MIZ. The SOC content of reed wetland in the fresh-salt water interaction zone ranged from 1.09 to 3.65 g·kg-1, the SOC density was between 1.85-5.84 kg·m-2, and the SOC storage was (17.32±3.64)×104 t. The SOC content and SOC density decreased with increasing fresh-salt water interaction. There were significant differences in surface SOC content between different subzones of the fresh-salt water interaction zone. The surface SOC content decreased significantly with the increases of fresh-salt water interaction intensity. SOC density was positively correlated with SOC, TN, NH4+-N, and biomass, but negatively correlated with salt ions, soil bulk density, pH, and EC. SOC storage in the 0-30 cm soil layer accounted for 50.9%-64.2% of that in the 0-60 cm soil layer, while SOC storage in the 0-60 cm soil layer occupied 19.1%-37.7% of that in the 0-400 cm soil layer. The results could provide a scientific basis for accurately evaluating SOC storage of estuarine wetlands, improving carbon sink function and wetland management.

Effects of tidal hydrology on soil phosphorus forms in the Yellow River estuary wetland: A field study of soil core translocation.

Phosphorus (P) forms in soil are related to the P cycle and play an important role in maintaining the productivity and function of wetlands. Tidal hydrology is a key factor controlling soil P forms in estuary wetlands; however, the response of soil P forms to tidal hydrological changes remains unclear. A translocation experiment in the Yellow River Estuary wetland was conducted to study the effect of hydrological changes on P forms in the soil, in which freshwater marsh soils in the supratidal zone were translocated to salt marshes in different intertidal zones (up-high-tidal zone, high-tidal zone, and middle-tidal zone). Over a 23-month experiment, soil properties showed varying changes under different tidal hydrology conditions, with an increase in pH, salinity, Ca2+ and salt ions and a decrease in iron oxide and nutrients. Compared with the control, the content of different forms of phosphorus (total phosphorus, inorganic phosphorus, organic phosphorus, and calcium-bound phosphorus) in the cultured soil cores decreased from 3.3 % to 67.0 % in the intertidal zones, whereas the content of ferrum­aluminum-bound phosphorus increased from 58.9 % to 65.1 % at the end of the experiment. According to the partial least squares structural equation model, P forms are influenced by tidal hydrology mainly through the mediation of salt ions and nutrient levels. These results suggest that seawater intrusion promotes the release of P in the supratidal zone soil of estuary wetlands.

Riverine input of suspended particulate matter controls distribution, partitioning and transport of mercury and methylmercury in the Yellow River Estuary.

Riverine mercury (Hg) is the largest global source of Hg in coastal oceans. The Yellow River delivers the majority of Hg to the semi-enclosed Bohai Sea, where Hg contamination adversely affects the surrounding heavily populated provinces in northern China. Mercury distribution patterns in the river-estuary interacting area provides essential information to understand the riverine Hg transport and biogeochemical cycling of Hg in the estuary. Analyzing the spatial distributions of total- (THg) and methyl-Hg (MeHg) in the lower end of Yellow River (∼105 km) and adjacent estuary, we found the dominant role of suspended particulate matter (SPM) in Hg transport, with 99.1% and 86.3% of THg and MeHg being in particulate phase. The SPM dynamics, such as transport, retention, sorting and sedimentation, governs Hg transport with water flow and particle-water partition of Hg. While THg decreased along the water flow to the river mouth with the settlement of particulate THg (about 27.5% onto the riverbed and the rest entering the sea), MeHg and particulate MeHg increased by 110% and 117%, respectively. This study highlights the distinct patterns in THg and MeHg distribution and transport and suggests potential Hg methylation and external MeHg input in the river-estuary mixed zone.

Distribution and Characterization of Typical Antibiotics in Water Bodies of the Yellow River Estuary and Their Ecological Risks.

A total of 34 antibiotics from five major classes of antibiotics, including macrolides, sulfonamides, quinolones, tetracyclines and chloramphenicol, were considered as contaminants, considering the Yellow River Estuary as the study area. The distribution, sources and ecological risks of typical antibiotics in the Yellow River Estuary were investigated using an optimized solid-phase extraction pre-treatment and an Agilent 6410B tandem triple-quadrupole liquid chromatography-mass spectrometer for antibiotic detection. The results show that antibiotics were widely present in the water bodies of the Yellow River Estuary, with 14 antibiotics detected to varying degrees, including a high detection rate for lincomycin hydrochloride. Farming wastewater and domestic sewage were the primary sources of antibiotics in the Yellow River Estuary. The distribution characteristics of antibiotics in the study area were linked to the development of farming and social activities. The ecological risk evaluation of 14 antibiotics in the Yellow River Estuary watershed showed that clarithromycin and doxycycline hydrochloride were present at medium-risk levels, and lincomycin hydrochloride, sulfamethoxazole, methomyl, oxifloxacin, enrofloxacin, sulfadiazine, roxithromycin, sulfapyridine, sulfadiazine and ciprofloxacin were present at low-risk levels in the samples collected from water bodies of the Yellow River Estuary. This study provides novel, beneficial information for the assessment of the ecological risk presented by antibiotics in the Yellow River Estuary water bodies and provides a scientific basis for future antibiotic pollution control in the Yellow River Basin.

Potential ecological risks of heavy metals and Cd accumulation characteristics of Suaeda salsa under different Cd input and water logging conditions in the Yellow River estuary, China.

To improve the remediation of heavy metal pollution by typical wetland vegetation and maintain the health of wetland ecosystems under the water-sediment regulation scheme (WSRS) application, we evaluated the potential ecological risk of heavy metals in surface sediment in the Yellow River estuary affected by the WSRS. The ranges of Cr, Cu, Zn, Cd, and Pb content in surface sediment were 52.44-100.80 mg·kg-1 dry weight (DW), 16.38-21.19 mg·kg-1 DW, 64.77-255.50 mg·kg-1 DW, 0.12-0.24 mg·kg-1 DW, and 5.40-8.63 mg·kg-1 DW, respectively, and potential ecological risk coefficients showed that Cd was associated with moderate potential risk. We further examined effects of Cd in a greenhouse experiment to explore the influence of short-term Cd input and water logging condition changes induced by WSRS on the Cd absorption characteristics of Suaeda salsa (L.) Pall in the Yellow River estuary. The results showed that total biomass decreased but Cd content in tissue of S. salsa increased with increasing Cd input and the accumulation factor reached maximum values at 100 µg·L-1 of Cd, indicating that S. salsa efficiently accumulated Cd. Water logging depth significantly affected S. salsa growth and Cd absorption with deeper water logging being detrimental to growth. The interaction effect of Cd input and water logging depth on Cd content and accumulation factor was significant. These results suggest that WSRS caused short-term heavy metal input and changes in water conditions affect wetland vegetation growth and heavy metal absorption in the downstream estuary.

[Effects of Water-salt Environment on Freshwater Wetland Soil C, N, and P Ecological Stoichiometric Characteristics in the Yellow River Estuary Wetland].

Carbon (C), nitrogen (N), and phosphorus (P) are important nutrients, and their ecological stoichiometric characteristics can reflect the quality and fertility capacity of soil, which is critical to understanding the stable mechanisms of estuarine wetland ecosystems. Under global changes, the increase in salinity and flooding caused by sea level rise will lead to changes in biogeochemical processes in estuarine wetlands, which is expected to affect the ecological stoichiometric characteristics of soil C, N, and P and ultimately interfere with the stability of wetland ecosystems. However, it remains unclear how the C, N, and P ecological stoichiometric characteristics respond to the water-salt environment in estuarine wetlands. We differentiated changes in the C, N, and P ecological stoichiometric characteristics through an ex-situ culture experiment for 23 months in the Yellow River Estuary Wetland. The five sites with distinct tidal hydrology were selected to manipulate translocation of soil cores from the freshwater marsh to high-, middle-, and low-tidal flats in June 2019. The results showed that soil water content (SWC); electrical conductivity (EC); and C, N, and P ecological stoichiometric characteristics of freshwater marsh soil significantly changed after translocation for 23 months. SWC decreased on the high- and middle-tidal flats (P<0.05) and increased on the low-tidal flat (P<0.05). EC increased to different degrees on all three tidal flats (P<0.05). Soil total organic carbon (TOC) and total nitrogen (TN) were significantly lower on the high-tidal flat (P<0.05), whereas total phosphorus (TP) was significantly lower on the middle- and high-tidal flats (P<0.05). C:N was decreased on the high- and middle-tidal flats (P<0.05); C:P and N:P were lower on the high-tidal flat; and all C, N, and P ecological stoichiometric characteristics showed no change on the low-tidal flat (P>0.05). Pearson's analysis showed that the ecological stoichiometric characteristics of C, N, and P were related to some properties of soil over the culture sites. The PLS-SEM model showed that the water-salt environment had different effects on soil C:N, C:P, and N:P through the main pathways of negative effects on soil TOC and TP. The results suggest that sea level rise may impact the C, N, and P ecological stoichiometric characteristics in freshwater marsh soil, resulting in some possible changes in the nutrient cycles of estuarine wetlands.

Community structure characteristics of ichthyoplankton during the water-sediment regulation scheme in the Yellow River in 2020 and 2021.

The Water-Sediment Regulation Scheme (WSRS) will deliver large amounts of water and sand to the Yellow River basin within a short period of time. This will significantly change the physicochemical environment of the Yellow River estuary and the surrounding marine ecosystem. Its effects on the spatial and temporal distribution patterns of ichthyoplankton are still unknown. In this study, six surface horizontal trawl surveys of ichthyoplankton were conducted during the WSRS in 2020 and 2021 using plankton nets. The results were as follows: (1) the estuarine sedentary fish Cynoglossus joyeri was the main species controlling the succession pattern of summer ichthyoplankton communities in the Yellow River estuary. (2) The WSRS influenced the ichthyoplankton community structure by changing the runoff, salinity, and suspension environment in the estuary. (3) The northern and southeastern parts of the estuary near Laizhou Bay were the main aggregation areas of the ichthyoplankton community.

Occurrence, geochemical characteristics, enrichment, and ecological risks of rare earth elements in sediments of "the Yellow river-Estuary-bay" system.

Recent studies have suggested that rare earth elements (REEs) are contaminants of emerging concern. Moreover, the understanding of the occurrence and risks of REEs in river-estuary-bay systems is limited. The present study investigated the distributions, geochemical characteristics, and ecological risks of Y and 14 REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) in sediments from the Yellow River to its estuary and adjacent Laizhou Bay. The average total concentrations of Y and REEs in the sediments generally increased from the Yellow River (149 mg/kg) to the estuary (165 mg/kg) and Laizhou Bay (173 mg/kg). In the estuarine core sediments, the concentrations of Y, light REEs (LREEs), and heavy REEs (HREEs) were in the ranges of 19.5-31.4 mg/kg, 58.6-156 mg/kg, and 12.3-19.1 mg/kg, respectively, from the 1700s to 2018, showing no obvious increasing or decreasing trends. The surface and core sediments from the river to the bay were characterized by obvious fractionation between LREEs and HREEs. In sediments, Fe minerals and clay are believed to promote the accumulation of REEs, especially HREEs. The enrichment levels of REEs generally increased from the middle reaches of the Yellow River to the bay, and Gd, Tb, Dy, Ho, Yb, and Lu were the most enriched elements in the sediments. Lu had moderate potential ecological risks in sediments of "the Yellow River-estuary-bay" system, and other REEs had relatively low ecological risks. The potential ecological risk indices of Y and REEs ranged from 78.7 to 144, showing increasing trends from the Yellow River to its estuary and adjacent bay, which should raise concerns regarding emerging contaminant management around estuarine and coastal regions.

Spatio-temporal patterns of zooplankton community in the Yellow River estuary: Effects of seasonal variability and water-sediment regulation.

Zooplankton community is ecological important because of its high sensitivity to environmental changes especially in estuarine areas. The Yellow River estuary (YRE) in China is the fifth biggest estuary in the world with significant seasonal characteristics and anthropogenic influence of Water-Sediment Regulation (WSR). This study investigated the spatio-temporal patterns of zooplankton in the YRE to explore the response of zooplankton to seasonal variation and WSR. Results suggested that the temporal patterns of zooplankton were mainly characterized by seasonal shift of dominant species. Hierarchical cluster analysis and non-metric multidimensional scaling determined summer, summer-autumn and winter-spring three zooplankton assemblages. Zooplankton spatial distributions represented seasonal consistency, in which the abundance generally showed a decreasing gradient from the river mouth to sea. WSR caused a high species replacement rate in July-August (80.36%) and a dramatic abundance decline from 4224.60 ind./m3 to 1541.10 ind./m3 with persistency and hysteresis effect. The high zooplankton abundance moved seaward in spatial distribution after WSR. Summer spatial pattern was determined with two and three zooplankton station assemblages, which was more clear after WSR. Redundancy analysis identified SSS, SST and transparency as important factors structuring zooplankton spatio-temporal patterns, in which SSS was the key one. The results provide a necessary reference for understanding the response of zooplankton community in estuarine areas to spontaneous changes and anthropogenic factors, and can help the protection of estuarine ecosystems and the formulation of hydrological regulatory policies.

Effect of electron acceptor addition on the temperature sensitivity of soil anaerobic carbon mineralization in the Yellow River Estuary wetland, China.

The temperature sensitivity of soil carbon mineralization (Q10) is an important index to evaluate the responses of ecosystem carbon cycling to climate change. We examined the effects of three electron acceptors [SO42-, NO3- and Fe(Ⅲ)] addition on the Q10 value of anaerobic carbon mineralization of Phragmites australis community soil (0-10 cm) in the Yellow River Estuary wetland with the closed culture-gas chromatography method. The results showed that the three electron acceptors addition inhibited the production of CO2 and CH4 during the 48-day culture period, with a decrease of 17.3%-20.8% for CO2 and 29.2%-36.2% for CH4. Generally, the CO2 production differed with the concentrations of electron acceptors, while CH4 production differed with the type of electron acceptors. The CO2:CH4 ratios were significantly different with temperature, indicating an obvious temperature dependence for the anaerobic carbon mineralization pathway. The Q10 values of CO2 and CH4 production under three electron acceptor additions ranged from 1.08 to 1.11 and from 1.19 to 1.37, respectively, showing an increasing trend compared with the control. The type and concentration of electron acceptors affected the temperature dependence of CO2 production, while electron acceptors affected that of CH4 production. It is suggested that the input of reducing salts would retard the mineralization loss of organic carbon in estuary freshwater wetlands under the background of climate change, but enhance the sensitivity of carbon mineralization to increasing temperature.

Influence of heavy metals on Saunders's Gull (Saundersilarus saundersi) reproduction in the Yellow River Estuary: risk assessment and bioaccumulation.

The heavy metal migration in the food chain exerted significant influence on the survival and reproduction of wetland birds and then disturbed and threatened the balance and health of the estuary ecosystem. In this study, the concentration of heavy metals (Cu, Cr, Fe, Mn, Cd, Ni, and Pb) in surface sediment of the Yellow River Estuary (YRE), the food sources of Saunders's Gull (Saundersilarus saundersi) nestlings, and the egg structure of birds were analyzed to determine the bioaccumulation and reproductive influence on wetland bird. The results indicated higher mean concentrations of sediment heavy metals than their corresponding background values in 2019, with the exception of Fe. Notably, the metal Cd exceeded geochemical background value by 1561.5% in 2018 and 1353.9% in 2019, resulting in severe contamination associated with Cd in the YRE (with geo-accumulation indexes of 3.44 and 3.23). Biomagnification factor (BMF) of heavy metals demonstrated that the concentrations of Cr, Ni, and Cu decreased with the trophic level rising while Cd, Mn, Pb, and Fe denoted bio-amplification in the food chain. The residual indexes showed that the food resources of Saunders's Gull were polluted by Cr, Pb, and Cu. Additionally, a higher enrichment of heavy metals was observed in the eggshell membrane. Metal concentrations had significant influences on the reproduction of Saunders's Gull, except for Cd, among which Ni, Pb, Cu, and Fe may have contributed to the reproductive success of birds, whereas the hatching failure of birds may be caused by Cr and Mn. It is of great importance to monitor the contamination of the wetland ecosystem and provide effective management and protection of the wildlife in the YRE.