Habitat selection drives diatom community assembly and network complexity in sediment-laden riverine environments

Microbial communities assemble stochastically and deterministically, but how different assembly processes shape diatom community structure across riverine habitats is unclear, especially in sediment-laden environments. In this study, we deciphered the mechanisms of riverine diatom community assembly in the water column and riverbed substrate with varying sediment concentrations. Water and sediment samples were collected from 44 sampling sites along the Yellow River mainstream during two seasons. Diatom communities were characterized based on high-throughput sequencing of the 18S ribosomal RNA genes coupled with multivariate statistical analyses. A total of 198 diatom species were taxonomically assigned, including 182 free-living and particle-attached species and 184 surface-sediment species. Planktonic communities were structurally different from benthic communities, with Cyclotella being dominant mainly in the middle and lower reaches of the river with higher sediment concentrations. Both stochastic and deterministic processes affected diatom community assembly in different habitats. Species dispersal was more important in the water than in the substrate, and this process was strengthened by increased sediment concentration across habitats. Diatom communities exhibited lower network complexity and enhanced antagonistic or competitive interactions between species in response to higher sediment concentrations compared with lower sediment concentrations mainly in the source region of the river. Differences in the species composition and community diversity of planktonic diatoms were closely correlated with the proportion of bare land area, nitrogen nutrients, precipitation, and sediment concentration. In particular, particle-attached diatoms responded sensitively to environmental factors. These findings provide strong evidence for sediment-mediated assembly and interactions of riverine diatom communities.

The mystery of rich human gut antibiotic resistome in the Yellow River with hyper-concentrated sediment-laden flow

Human gut antibiotic resistome widely occur in anoxic environments characterized by high density of bacterial cells and frequent transmission of antibiotic resistance genes (ARGs). Such resistome is greatly diluted, degraded, and restrained in the aerobic habitats within most natural rivers (regarded as "terrestrial guts") connecting continents and the oceans. Here we implemented a large-scale monitoring campaign extending 5,200 km along the Yellow River, and provide the first integral biogeographic pattern for both ARGs and their hosts. We identified plentiful ARGs (24 types and 809 subtypes) and their hosts (24 phyla and 757 MAGs) in three media (water, suspended particulate matter (SPM), and sediment). Unexpectedly, we found diverse human gut bacteria (HGB) acting as supercarriers of ARGs in this oxygen-rich river. We further discovered that numerous microhabitats were created within stratified biofilms that surround SPMs, particularly regarding the aggregation of anaerobic HGB. These microhabitats provide numerous ideal sinks for anaerobic bacteria and facilitate horizontal transfer of ARGs within the stratified biofilms, Furthermore, the stratification of biofilms surrounding SPMs has facilitated synergy between human gut flora and denitrifiers for propagation of ARGs in the anoxic atmospheres, leading to high occurrence of human gut antibiotic resistome. SPMs play active roles in the dynamic interactions of river water and sediment, thus accelerating the evolution of riverine resistome and transmission of human gut antibiotic resistome. This study revealed the special contribution of SPMs to the propagation of ARGs, and highlighted the necessity of making alternative strategies for sustainable management of large rivers with hyper-concentrated sediment-laden flows.

Distribution, seasonal variation and influencing factors of total dissolved inorganic arsenic in the middle and lower reaches of the Yellow River

The concentrations of dissolved arsenate in natural water has an important impact on human health. The distributions, seasonal variation and major influencing factors of total dissolved inorganic arsenic (TDIAs) were studied in the Yellow River. The concentrations of TDIAs in the middle and lower reaches of the Yellow River ranged from 4.3 to 42.4 nmol/L, which met the standards for drinking water of WHO. The seasonal variation of TDIAs concentration in the middle and lower reaches of the Yellow River was highest in summer, followed by autumn and winter, and lowest in spring. The influencing factors of TDIAs concentration in the middle and lower reaches of the Yellow River mainly include the hydrological conditions, topographical variation, the adsorption and desorption of suspended particulate matter (SPM) and the intervention of human activities. The absorption of TDIAs by phytoplankton in the Xiaolangdi Reservoir (XLD) is an important factor affecting its distributions and seasonal variation. The annual flux of TDIAs transported from the Yellow River into the Bohai Sea ranged from 1.1 × 105 to 4.5 × 105 mol from 2016 to 2018, which is lower than the flux in 1985 and 2009. The carcinogenic risks (CR) of TDIAs for children and adults were all within acceptable levels (<10-6).

Multiple isotopes reveal the driving mechanism of high NO3- level and key processes of nitrogen cycling in the lower reaches of Yellow River

The continuous increase of nitrate (NO3-) level in rivers is a hot issue in the world. However, the driving mechanism of high NO3- level in large rivers is still lacking, which has limited the use of river water and increased the cost of water treatment. In this study, multiple isotopes and source resolution models are applied to identify the driving mechanism of high NO3- level and key processes of nitrogen cycling in the lower reaches of the Yellow River (LRYR). The major sources of NO3- were sewage and manure (SAM) in the low-flow season and soil nitrogen (SN) and chemical fertilizer (CF) in the high-flow season. Nitrification was the most key process of nitrogen cycling in the LRYR. However, in the biological removal processes, denitrification may not occur significantly. The temporal variation of contributions of NO3- sources were estimated by a source resolution model in the LRYR. The proportional contributions of SAM and CF to NO3- in the low-flow and high-flow season were 32.5%-52.3%, 44.2%-46.2% and 36.0%-40.8%, 54.9%-56.9%, respectively. The driving mechanisms of high NO3- level were unreasonable sewage discharge, intensity rainfall runoff, nitrification and lack of nitrate removal capacity. To control the NO3- concentration, targeted measures should be implemented to improve the capacity of sewage and wastewater treatment, increase the utilization efficiency of nitrogen fertilizer and construct ecological engineering. This study deepens the understanding of the driving mechanism of high nitrate level and provides a vital reference for nitrogen pollution control in rivers to other area of the world.

The impacts of water-sediment regulation on organic carbon in the Yellow River

The Yellow River water-sediment regulation (WSR) is a unique hydraulic engineering project that involves the resuspension and rapid discharge of sediment downstream under the influence of density currents. This process leads to short-term high-intensity sediment scouring, which in turn increases the output of organic carbon. The impact of WSR on the biogeochemical cycling of organic carbon in rivers has not been adequately explored. In this study, we applied stable isotope and 3-D fluorescence analyses to investigate the impact of WSR at the Xiaolangdi (XLD) Reservoir on the sources and fluxes of dissolved organic carbon (DOC) and particulate organic carbon (POC) in the Yellow River. The POC and DOC fluxes during WSR (∼51 days) accounted for 95.5 % and 28.3 % of the annual fluxes. According to the Bayesian model used in the study, the fluxes of POC from sediment, terrestrial plants, and sewage increased by 23.2, 13.36, and 56.55 times, respectively, during the WSR period. On the other hand, the flux from various sources of DOC decreased by ∼0.7 times during the WSR process. The three-dimensional fluorescence index (specific UV absorbance [SUVA254], humification index [HIX], biological index [BIX], and fluorescence index [FI]) further reveals that in the WSR process, more DOC comes from sediment and upstream water. This study provides quantitative insights into the effects of WSR on river organic carbon export dynamics and the driving mechanisms behind them. It also has important implications for understanding the impact of anthropogenic disturbance on the global carbon cycle.

A comparative study on the age, growth, and mortality of Gobio huanghensis (Luo, Le & Chen, 1977) in the Gansu and Ningxia sections of the upper Yellow River, China

BALKGROUND

Gobio huanghensis is a small economic fish endemic to the Yellow River at the junction of the Tibetan Plateau and the Huangtu Plateau in China. To understand the impact of environmental changes and human activities on the ecological structure of the G. huanghensis population, a comparative study was conducted on the age composition, growth characteristics, mortality rate, and exploitation rate of the G. huanghensis populations in the Gansu and Ningxia sections of the upper Yellow River.

RESULTS

During the investigation, a total of 1147 individuals were collected, with 427 individuals collected from the Gansu section and 720 individuals from the Ningxia section. The results showed that G. huanghensis in the Gansu section exhibited a total length ranging from 5.00 to 22.80 cm, with an average of 12.68 ± 4.03 cm. In the Ningxia section, the total length of G. huanghensis ranged from 2.15 to 20.65 cm, with an average of 9.48 ± 3.56 cm. The age composition of G. huanghensis in the Gansu section ranged from 1 to 7 years, where female fish were observed between 1 and 7 years old, and male fish between 1 and 6 years old. In the Ningxia section, both female and male fish ranged from 1 to 5 years old. The relationships between total length and body weight were (Gansu section, R2 = 0.9738) and (Ningxia section, R2 = 0.9686), indicating that fish in the Gansu section exhibit positive allometric growth, while fish in the Ningxia section exhibit negative allometric growth. The von Bertalanffy growth equation revealed that G. huanghensis in the Gansu section exhibited an asymptotic total length L∞ of 27.426 cm with a growth coefficient K of 0.225 yr-1, while in the Ningxia section, the asymptotic total length L∞ was 26.945 cm with a growth coefficient K of 0.263 yr-1. The total mortality rate (Z) values of G. huanghensis were 0.7592 yr and 1.1529 yr in the Gansu section and Ningxia section, respectively. The average natural mortality rate (M), estimated by three different methods, in the Gansu section was 0.4432 yr, while it was 0.5366 yr in the Ningxia section. The exploitation rate (E) of G. huanghensis was 0.4163 in the Gansu section and 0.5345 in the Ningxia section, indicating that the population in the Ningxia section may have been overexploited.

CONCLUSION

Prolonged fishing pressures and environmental changes may have led to variations in the ecological parameters of the G. huanghensis population between the Gansu and Ningxia sections.

Occurrence and dissemination of antibiotic resistance genes in the Yellow River basin: focused on family farms

As an emerging contaminant, antibiotic resistance genes (ARGs) have attracted growing attention, owing to their widespread dissemination and potential risk in the farming environment. However, ARG pollution from family livestock farms in the Yellow River basin, one of the main irrigation water sources in the North China Plain, remains unclear. Herein, we targeted 21 typical family farms to assess the occurrence patterns of ARGs in livestock waste and its influence on ARGs in receiving environment by real-time quantitative PCR (qPCR). Results showed that common ARGs were highly prevalent in family livestock waste, and tet-ARGs and sul-ARGs were the most abundant in these family farms. Most ARG levels in fresh feces of different animals varied, as the trend of chicken farms (broilers > laying hens) > swine farms (piglets > fattening pigs > boars and sows) > cattle farms (dairy cattle > beef cattle). The effect of natural composting on removing ARGs for chicken manure was better than that for cattle manure, while lagoon storage was not effective in removing ARGs from family livestock wastewater. More troublesomely, considerable amounts of ARGs were discharged with manure application, further leading to the ARG increase in farmland soil (up to 58-119 times), which would exert adverse impacts on human health and ecological safety.

Accumulation and migration of particulate trace metals by artificial flood event of the Yellow River: From Xiaolangdi reservoir to estuary

Reservoir construction increasingly alters the natural transport of riverine water and sediment to the sea, including the trace metals and other pollutants. In 2018, an intensive flood event and 412 million tons of sediment were released from the Xiaolangdi dam during the water-sediment regulation of Yellow River, one of the world's largest sediment releases. During the artificial flood event, the surface sediments in Xiaolangdi Reservoir (XLD) and the Yellow River estuary, suspended sediments at Lijin Station were collected. The concentration and speciation of particulate Cr, Ni, Cu, Zn, Cd and Pb, as well as the major geochemical composition were analyzed, to characterize the behaviors of the metals from the reservoir to estuary mixing zone, and elucidate the controlling mechanisms. The results showed that for exogenous phases, Cr, Ni, Cu and Zn were likely bound to the FeMn oxides, whereas Pb and Cd were mainly adsorbed in the carbonates. The trace metals in XLD were stably combined with fine-grained bottom sediments at high concentrations before dam release. During the delivery from reservoir to downstream channel, the binding of Cr, Ni and Cu with FeMn oxides was markedly enhanced. Pb and Cu showed obvious migration from carbonates to FeMn oxides, and Cd and Pb were even released into the water. The accumulation and migration of trace metals were controlled by the adsorption of fine-grained components, especially FeMn oxides and carbonates, and influenced by the oxidizing processes. After entering the estuary, the trace metals were greatly scavenged by reservoir-sourced fine particles, tended to bound to organic matter affected by the reducing environment. Our results suggest that dam regulation and artificial flood events will likely alter the existing forms and redox state of trace metals and the potential environmental effects should be considered.

Tidal inundation and plant growth/decay impact redox-sensitive metal geochemistry and fluxes in salt marsh porewater

In dynamic coastal ecosystems, environmental factors can play important roles in the biogeochemical cycle of redox-sensitive metals. This work is focused on the impact of tidal inundation, plant growth and decay on the biogeochemical cycle of redox-sensitive metals (e.g., Fe, Mn, Mo, V and U) in salt marsh wetlands. Samples were collected from the salt marsh wetlands of the Yellow River Estuary under different tidal states and growth stages of plants (Phragmites australis). Compared to the concentration of redox-sensitive metals in the river water and seawater near the study area, Fe, Mn and U were enriched in salt marsh wetland, which might become a potential source of Fe, Mn and U in the coastal sea. Tidal inundation, plant growth and decay can affect redox-sensitive metals through changes in redox conditions; the plant can also affect them directly via root absorption or plant residue decomposition, especially for Mo. Calculations of diffusion flux between sediment porewater and tidal water show that these processes can increase diffusion by at least 16.7 % or decrease it by at least 65.7 %, even reversing the direction of diffusion, which can affect the accumulation of redox-sensitive metals in salt marsh wetlands. The results showed that tidal inundation and the decay of plant residue were not conducive to the accumulation of Fe and Mn but were beneficial to the accumulation of V and U in salt marsh wetlands. The plant growth showed the opposite pattern. The accumulation of Mo in salt marsh wetlands largely depends on ingestion by plants and the decay of plant residue. This research provides a scientific basis for the budget calculation of redox-sensitive metals in salt marsh wetlands.

Suspended particulate matter affects the distribution and migration of heavy metals in the Yellow River

Suspended particulate matter (SPM) is an important heavy metal transporter in water. As a well-known high-SPM river, its impact on the distribution and migration of heavy metals in the Yellow River (YR) deserves special attention. In this study, the spatial distributions of heavy metals in surface water and SPM of the YR were investigated. The results indicate that the concentrations (dissolved and particulate phases) and bioavailability (particulate phase) of most heavy metals were higher during the rainy season than during the dry season. A considerable proportion of heavy metals (>70 %) was transported by SPM and fine particles (clay) controlled the pollution status of heavy metals in the YR. This could lead to higher heavy metal concentrations in the SPM midstream and downstream during the rainy season and higher heavy metal concentrations in upstream during the dry season. Heavy metal adsorption experiments showed that specific combination methods (such as binding with carbonate) between Cd and SPM may cause SPM to act as a source of Cd midstream and downstream. This study provides a new perspective on the effects of SPM on heavy metal distribution and migration in the YR.

Unprecedented phytoplankton blooms in autumn/winter in the southern Bohai Sea (China) due to high Yellow River discharge: Implications of extreme rainfall events

The occurrence of abnormal phytoplankton blooms is one of the significant changes in coastal ecosystems due to climate change. However, the underlying mechanism of such blooms remains poorly understood due to the complexity of the system. In this study, the data from numerous observations was used to elucidate the unprecedented phytoplankton blooms in the autumn and winter of 2021 in Laizhou Bay, a typical aquaculture bay in the southern Bohai Sea of China. The abundance of phytoplankton cells increased by more than tenfold in the southern waters compared to that in the same period from 2019 to 2020. The phytoplankton bloom was first observed in winter in the Bohai Sea, with the cell abundance in the southern bay exceeding 108 cells L-1 in December 2021. The diversity and evenness of phytoplankton communities decreased in the southern area. Cerataulina pelagica was the dominant algae, comprising 69 % of the total phytoplankton in October and 99 % in December. In autumn 2021, the largest flood of the Yellow River in recent decades occurred. This was attributed to extreme rainfall events within the river basin. The input of substantial riverine nutrients played a significant role in promoting phytoplankton blooms. Correlation analysis indicated the important cumulative impact of the Yellow River on phytoplankton blooms rather than a direct short-term effect. Numerical modeling results indicated that exceptionally high Yellow River discharge in autumn could significantly affect the entire bay from autumn to the following spring. This study may contribute to understanding the abnormal phytoplankton blooms in coastal waters and provide valuable insights for environmental management in river basins and coastal waters.

Source-oriented risk assessment of heavy metal(loid)s in agricultural soils around a multimetal smelting area near the Yellow River, China

Heavy metal(loid) (HM) contamination in agricultural soils, particularly in areas severely impacted by smelting industries, has attracted worldwide attention. In this study, agricultural soils were collected in a flourishing multimetal smelting area near the Yellow River in central China. By an integrated approach encompassing the positive matrix factorization model, ordinary kriging interpolation and hierarchical clustering analysis (PMF-OK-HC), a total of four major sources and their mass contributions were identified, namely, soil parent material (56.6%), industrial waste and Mo smelting (24.0%), metal smelting and traffic emissions (12.8%), and coal combustion (6.7%). On this basis, the health risk of HMs was evaluated by Monte Carlo simulations and showed that a higher risk, with a higher proportion of exceeding-thresholds risk, was observed for children than for adults in terms of both noncarcinogenic and carcinogenic risks. Exposure pathways of oral ingestion in children could result in a higher attributed risk than other pathways. Furthermore, source-oriented risk assessment (SORA) revealed that the sources of coal combustion, industrial waste and Mo smelting had the highest contributions to noncarcinogenic and carcinogenic risks. Overall, for effective environmental management in agricultural soil, the framework of SORA was verified as an effective tool in the identification of the priority control of HMs and their sources.

Exogenous mobile genetic elements and their associated integrons drive the enrichment of antibiotic-resistant genes in the river of a valley basin city (Lanzhou, China)

River is a unique source of drinking water in valley-type cities, affecting local urban development and human lifestyles. However, the key driving factors for dissemination of antibiotic-resistant genes (ARGs) in valley-type urban environments remain unclear. This study aimed to investigate the distribution of ARGs in the Yellow River and to clarify the driving factors of ARGs in a typical valley basin city (Lanzhou, China). The seven selected ARGs with higher abundances including tetracycline resistance genes (tetM, tetX), macrolide resistance genes (ermB, ermF, ereA), and sulfonamide resistance genes (sul1, sul2) were detected. The results showed that the total absolute abundance of all the selected ARGs varied from 9.97 × 1012 to 1.04 × 1015 copies/L in the water body, with higher abundances in the wet season, relative to the dry season. Among these, sulfonamide resistance genes (sul1, sul2) displayed the highest absolute abundance in the river and soil. The ARGs and mobile genetic elements (MGEs) were significantly correlated with bacterial abundance, dissolved organic carbon (DOC), ammonia nitrogen (NH4+), and total nitrogen (TN) levels in the water environment (Mantel test, P < 0.01). Structural equation modeling revealed the direct input of point-source and nonpoint-source ARGs in this area contributed less to the overall level of the ARGs in the water. Among the multiple drivers, the MGEs derived from wastewater treatment plant and anthropogenic nonpoint area positively and directly affected the ARG profiles in water (P < 0.01), rather than the factors of bacterial abundance and physicochemical properties. According to this study, the exogenous MGEs from anthropogenic activities are the main driver for the enrichment of ARGs in the valley-type urban river environment.

Spatial distribution and partition of polycyclic aromatic hydrocarbons (PAHs) in the water and sediment of the southern Bohai Sea: Yellow River and PAH property influences

The marginal Bohai Sea, connected to the northwestern Pacific Ocean, is threatened by human activity. The Yellow River, the second largest river in China, drains large amounts of water, silts, and polycyclic aromatic hydrocarbons (PAHs) into the southern Bohai Sea; however, to what extent the Yellow River inputs influence the spatial distributions and partitions of PAHs in the southern Bohai Sea is not well known. Therefore, this study collected surface water, bottom water, and sediment samples from the southern Bohai Sea and analyzed them to examine the spatial distributions and partitions of 15 priority PAHs. The results showed that PAH concentrations ranged from 26.9 to 50.1 ng L-1 in surface water, 18.8 to 44.1 ng L-1 in bottom water, and 7.4 to 143.9 ng g-1 in sediment, with higher proportions of four-, five-, and six-ring PAHs in sediment than in water. PAH inputs from the Yellow River and sea coastal currents determined the spatial distribution of PAH concentrations in water and sediment, with an overall decrease from the estuary to the southeast. However, the solid dilution effect of input silts from the Yellow River and the liquid dilution effect of water from the Yellow River and Yellow Sea led to lower PAH concentrations in the water and sediment of the southern Bohai Sea than those in other areas of the Bohai Sea. PAH exchange between the atmosphere and seawater led to significantly higher individual PAH concentrations (except for acenaphthylene) in the surface water than in the bottom water, with ratios significantly related to the PAH n-octanol-water partition coefficient, organic carbon-water partition coefficient, and Henry's law constants. These parameters also determined PAH partitioning between the bottom water and sediment. Individual and total PAH concentrations in the sediment were significantly correlated with organic matter, clay, and silt contents. Therefore, the partitions and spatial distributions of PAHs in the southern Bohai Sea comprehensively depend on PAH properties, PAH inputs from the Yellow River and the atmosphere, sea currents, and seawater and sediment properties. The ecological risks posed by individual PAHs in both water and sediment were negligible or acceptable.

Distribution of microplastic contamination in the major tributaries of the Yellow River on the Loess Plateau

Microplastic pollution in rivers had gained increased attention worldwide. However, the differences in microplastic characteristics among major tributaries of large rivers and the environmental factors influencing these characteristics remain uncertain. Through field investigation and indoor experiments, the distribution of microplastics and their driving factors were investigated at 96 sampling sites along the three main tributaries (Huangfuchuan, Wuding and Yan River) of the Yellow River in the Loess Plateau. The results revealed that the average microplastic abundance followed this order: Yan River (430.30 items kg-1) > Wuding River (145.09 items kg-1) > Huangfuchuan River (253.33 items kg-1). The abundance was lower than that in most parts of the world. There was a generally increasing trend in average microplastic abundance from upstream to downstream in the three rivers. The most frequently observed microplastic colors observed were black and white, and the most common polymer type were PE and PS in all three rivers. The dominant shape and size in the three rivers were fiber and particles measuring 0.5-5.0 mm, all accounting for more than half of the total microplastic content. The microplastic abundance, shape, and size were primarily influenced by mean annual precipitation and population density. This relationship can be attributed to the fact that increased population density driven by higher demand and consumption of plastic products, while augmented rainfall aggravated the occurrence of floods and provided conditions for plastic degradation and accumulation. This study will provide fundamental data for pollution assessing and ecological protection of the Yellow River, and provide a certain reference for future management and protection on the Loess Plateau.

Morphological and molecular characterization of a new freshwater Ceratomyxa species (Cnidaria: Myxozoa) from the yellow catfish, Trachysurus fulvidraco in China

Ceratomyxa Thélohan, 1892 is one of the largest genera of the sub-phylum Myxozoa, and has a worldwide geographical distribution. Ceratomyxa species mainly infect the gallbladder of marine fish and rarely infect histozoically or coelozoically freshwater fish. In the present study, yellow catfish, Trachysurus fulvidraco (Siluriformes, Actinopteri) collected from the low reach of Yellow River was first found to be infected with an unknown Ceratomyxa species in their gallbladder which was identified to be new to science and nominated as Ceratomyxa huangheensis n. sp. by an integrative taxonomic approach for myxosporeans. Spores are typical of the genus Ceratomyxa, and matures spores are arcuate, with posterior angle of 139.2 ± 11.6 (137.0-156.0)° and rounded ends, and measures 4.7 ± 0.6 (3.3-5.5) μm in length, and 10.7 ± 1.3 (8.5-13.3) μm in thickness. Two spore valves are slightly unequal and present elongated ovoid in the lateral view. Two equal spherical polar capsules, measuring 2.2 ± 0.4 (1.4-2.8) μm × 2.0 ± 0.4 (1.0-2.5) μm in size locates adjacent to the straight suture line. The obtained partial small subunit ribosomal DNA (SSU rDNA) sequence was unique among all myxozoans in GenBank, and the highest similarity is 85.3% with Ceratomyxa sparusaurati, a marine fish-infecting congener. Phylogenetic analysis further indicated that this novel species did not cluster with other freshwater fish-infecting congeners from South America to form an independent clade, but was phylogenetically positioned within the marine fish-infecting clade. The possible presence of different radiation trajectories between Ceratomyxa huangheensis n. sp. and Amazonian freshwater Ceratomyxa lineage was discussed. This is the first report of Ceratomyxa species in the Yellow River basin and the second freshwater Ceraotomyxa species in China, even in Asia.

Human activities have more impacts on the recent discharge reduction of the largest tributary of the Yellow River relative to last three centuries

How to quantitatively decouple the impacts of climate change and human activities on river discharge changes is a challenge in current global change research. As the largest tributary of the Yellow River (YR), the Weihe River (WR) is a typical river whose discharge is influenced by climate change and human activities. Here, we first attempt to obtain the normal-flow season and high-flow season discharge in the lower reaches of the WR by using tree rings and historical documents, respectively. The relationship between natural discharge in the two seasons is unstable and complex since 1678. Using an innovative method, we reconstructed the natural discharge from March to October (D_M-O), which explains >73 % of the variance in the observed D_M-O during the modeling period 1935-1970. There were 44 high-flow years, 6 extremely high-flow years, 48 low-flow years and 8 extremely low-flow years from 1678 to 2008. The contribution of WR annual discharge to the YR is 17 % over the past three centuries, and their natural discharge changes synchronously rise and fall. Human activities, such as the construction of reservoirs and check-dams, agricultural irrigation and domestic and industrial water consumption, have more impacts than climate change on the decrease in the observed discharge. In total, 53.5 % of the discharge reduction since 1971 is due to human activities, and 46.5 % is due to climate change. In addition, this study provides an important model for how to quantify the influences of human activities and nature on discharge reduction and to reconstruct seasonal resolution climate in global change studies.

Study of the adsorption behavior of tetracycline onto suspended sediments in the Yellow River, China: Insights into the transportation and mechanism

The increasing usage of household drugs has contributed to the widespread distribution of antibiotic pollutants in the aquatic environment. Although previous studies have proven that sediments could act as an important transport vector of antibiotic pollutants, the crucial impact of suspended sediments (SS) on the migration and fate of antibiotics in water bodies remain unclear. This study systematically investigated the performance and potential mechanism of the adsorption of tetracycline (TC) on SS in the Yellow River. The results show that physisorption (pore filling, hydrogen bonding) and chemisorption (π-π interaction, surface complexation, and electrostatic interaction) activities contributed to the adsorption of TC onto SS. The mineral components (SiO₂, Fe₂O₃, and Al₂O₃) of SS were found to be the main active sites for TC adsorption. The contribution of SiO₂, Fe₂O₃, and Al₂O₃ to the overall TC adsorption could reach up to 5.6 %, 0.4 %, and 73.3 %, respectively. Interestingly, the DFT results suggesting that SiO₂ tends to form intermolecular hydrogen bonds with TC, while FeO and AlO play predominant roles in TC adsorption on SS. The MIKE simulations showed that river temperature, initial pH, and SS concentration would significantly affect the concentration of dissolved TC during SS transport. In addition, the presence of humic acid and more acidic environments favored the adsorption of TC on SS. Conversely, the introduction of inorganic cations inhibited the adsorption of TC on SS. This study provides new insights into the adsorption mechanism and migration of antibiotics in rivers with high SS content.

Changes of active particulate uranium under the Water-Sediment Regulation Scheme in the lower Yellow River: Potential impact to the uranium flux into the global ocean

With the annual Water-Sediment Regulation Scheme (WSRS) transporting large amounts of suspended particulate matter (SPM) to the sea within several days, the behavior of uranium in the Yellow River during the WSRS is crucial to better understand the uranium flux. In this study, the active forms (the exchangeable, carbonate bounded, Fe/Mn oxides bounded, organic matter bounded) and the residual form of particulate uranium were extracted by the sequential extraction method and their uranium contents were measured respectively. Results show that the content of total particulate uranium was 1.43-2.56 μg/g and the active forms accounts for 11-32 %. Particle size and redox environment are the two main factors controlling the active particulate uranium. The flux of active particulate uranium at Lijin was 4.7 tons during 2014 WSRS, which was about 50 % of the dissolved uranium flux for the same period. Thus, the terrestrial uranium flux is significantly modified by artificial regulation.

Toxicity risks associated with trace metals call for conservation of threatened fish species in heavily sediment-laden Yellow River

Trace metals and metalloids in aquatic ecosystems may lead to adverse effects on the survival of fish, especially in the sensitive life stages of vulnerable species. It is still unknown whether threatened fish species in the heavily sediment-laden Yellow River are exposed to toxicity risks associated with multiple trace metals. Herein, we analyzed the concentrations of trace metals in aquatic environmental media and fish tissues across the Yellow River mainstream and assessed the level of metal toxicity to threatened fish. Significantly different concentrations of trace metals in fish tissues were measured between at least two categories among near-threatened, vulnerable, endangered, and critically endangered fish. No metal showed a higher concentration in demersal fish than in pelagic fish. Substantially low metal toxicity was observed for the gill of Rhinogobio nasutus (near-threatened) in the upper reaches, as well as for the gill and liver of Silurus lanzhouensis (endangered) in the middle reaches. High contents of suspended sediment in water and high metal concentrations in sediment and suspended matter could influence the survival and reproduction of fish, especially those already with threatened status.

Occurrence, distribution, and ecological risk assessment of artificial sweeteners in surface and ground waters of the middle and lower reaches of the Yellow River (Henan section, China)

As a new class of water contaminants, artificial sweeteners (ASs) have attracted much attention due to their environmental persistence and potential adverse effects to human and the environment. This study systematically investigated the occurrence and distribution of four commonly used ASs in the effluent of wastewater treatment plants (WWTPs), surface water and groundwater in the middle and lower reaches of the Yellow River (Henan section). Sucralose (SUC) was dominant in WWTP effluents and had the highest mass loading. Acesulfame (ACE), cyclamate (CYC), saccharin (SAC), and SUC were consistently detected in surface water at concentrations ranging from 1.364 ng/L (CYC) to 7786 ng/L (ACE). Spatial analysis showed that the pollution level of ASs in the trunk stream was lower than that in most tributaries. The total concentrations of ASs detected in surface water ranged between 308.7 and 10,498 ng/L, while in groundwater, the total concentration of ASs detected was between ND-4863 ng/L. ACE and SUC are the main pollutants in surface water and groundwater within this survey area. The risk assessment showed that the risks of the four target ASs to aquatic organisms were negligible (risk quotient (RQ) values < 0.1), and the maximum risk quotient of the mixtures (MRQ) values of all rivers were all much less than 0.1.

Evaluation of river longitudinal connectivity based on landscape pattern and its application in the middle and lower reaches of the Yellow River, China

River connectivity plays an essential role in maintaining the health and stability of river basin ecosystems. It is of great significance to protect river ecosystems to clarify the effect of water conservancy project construction and operation on river hydrological connectivity. The longitudinal connectivity is affected by the landscape patterns of river, such as the convergence and dispersion of the mid-channel bars and the river areas. This study aims to analyze the impacts of construction and regulation of Xiaolangdi Dam on the connectivity of the middle and lower reaches of the Yellow River from the perspective of landscape pattern. An improved longitudinal river connectivity evaluation method was proposed by accounting for the influence of the landscape pattern represented by mid-channel bars based on barrier coefficient method, and then was applied to analyze the connectivity pre- and post-dam construction. The results show that the amplitude and frequency of the oscillation of the river were greatly reduced and tended to be stable. The aggregation degree of mid-channel bars was reduced, and the distribution of mid-channel bars was more dispersed. The river longitudinal connectivity before and after the construction of the Xiaolangdi Dam were 1.35 and 1.50 respectively, indicating an increased river longitudinal connectivity. Overall, there are differences in connectivity before and after Xiaolangdi Dam construction, and connectivity fluctuates after dam construction. Because of the dam regulation of water and sediment, the river connectivity during the flood season increased significantly, and was greater than that before and after the flood season. The longitudinal connectivity evaluation method established in this study is accurate and efficient, and provides an intuitive and reliable new method for quantitatively analyzing the changing laws and characteristics of river connectivity.

Geographical distance, host evolutionary history and diet drive gut microbiome diversity of fish across the Yellow River

Fish represent a large part of the taxonomic diversity of vertebrates and are of high commercial value. However, the factors influencing the gut microbiota composition of freshwater fish over large spatial scales remain unclear. Therefore, this study explored gut microbiome diversity in 24 fish species from the Yellow River, which spans over 1500 km across China. The results showed that geographical distance, host phylogeny and diet significantly influenced gut microbial community diversity, whereas sex, body length and body weight had minimal influence. Geographical distance was the primary factor shaping gut microbiota, and dissimilarity in microbial community structure increased with an increase in geographical distance, which was mainly driven by dispersal limitation. The microbial communities were more homogeneous at higher host taxonomic resolutions due to the dominant role of homogeneous selection in community convergence. Phylosymbiosis was observed across all host species, with a stronger pattern in Cypriniformes, which harbour host-specific microbial taxa. Host diet explained little variation in gut microbiome diversity, although it was significant for all diversity metrics tested. These findings collectively suggest that the geographical and host-based patterns of fish gut microbiota tend to be shaped by different ecological forces across the Yellow River. The present work provides a robust assessment of multiple factors driving fish gut microbial community assembly and offers insight into the mechanisms underlying shifts in fish gut microbiota in rivers across large spatial scales.

Bioaccumulation and health risks of multiple trace metals in fish species from the heavily sediment-laden Yellow River

The health risk caused by metal pollution is a global concern due to potential metal bioaccumulation, toxicity, and carcinogenicity with multiple sources and pathways. Here, the factors influencing metal bioaccumulation in more than a thousand fish individuals were investigated along a 5464 km continuum of the heavily sediment-laden Yellow River and the health risks to humans were evaluated. The average concentrations of Cr, Zn, As, Cu, Cd, and Pb were below the permissible limits established by domestic and foreign organizations. The fish showed biomagnification of Se and Sn through trophic transfer and a growth dilution effect for V, Mn, Co, Ni, Cu, Zn, As, Cd, and Ba. The concentrations and distributions of most metals in fish were mainly influenced by the trophic levels (δ¹⁵N) of fish and the content of the metals in the aquatic environment. The consumption of fish from the Yellow River does not pose a noncarcinogenic risk to the health of adults and juveniles. Cr and As could cause carcinogenic risks, and Cd and Pb also have carcinogenic risks, but these were within an acceptable range. The carcinogenic risks of fish consumption were relatively low in regions with low levels of metal pollution, such as the source region, while the risks were high in regions with heavy pollution and carnivorous fish at high trophic levels. In response to this threat, people can minimize these risks by adjusting their diet and appropriately reducing their consumption of aquatic products from the Yellow River.

Occurrence, spatiotemporal variation, and ecological risks of organophosphate esters in the water and sediment of the middle and lower streams of the Yellow River and its important tributaries

Research on the environmental occurrence and behavior of organophosphate esters (OPEs) is very imperative. In this study, 12 targeted OPEs in the water and sediment samples collected from the middle and lower streams of the Yellow River (YR) and its tributaries during the dry, normal, and wet season were analyzed, to reveal their concentration, spatiotemporal variations, and ecological risks. The results indicated that the total concentration of OPEs (ΣOPE) ranged from 97.66 to 2433.30 ng/L in water, and from 47.33 to 234.08 ng/g in sediment. Tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl)phosphate (TCIPP), and triethyl phosphate (TEP) were the most abundant OPEs in the surface water and sediment. The OPEs levels in river water were ranked as the order of dry &gt; normal &gt; wet season. The ΣOPE concentrations in water and sediment were relatively high in the central and lower sections of the YR. The resorcinol-bis(diphenyl)phosphate (RDP) effectively transferred from the overlying water to the sediment. TCEP and RDP posed relatively higher ecological risk than other OPEs. Municipal and chemical industrial discharge might be sources of OPEs in the middle and lower streams of the YR.

Age and causes of the Yellow River dissecting the Zoige Basin in the eastern Tibetan Plateau, China

Through extensive field investigation in the Zoige Basin of the eastern Tibetan Plateau, a typical sedimentary profile was found on the front scarp of the second terrace of Maqu reach of the Yellow River at the outlet of the Zoige Basin. This profile contains the stratigraphic sequence of paleolake facies and paleo-riverbed floodplain facies. Field observation and the analysis of particle size characteristics and optically stimulated luminescence dating showed the following results: (1) The profile includes a pale blue-grey paleolake deposit, which formed in a deep-water anoxic environment. This deposit was overlain by a mottled pebble layer with pale yellow-orange lenticular sand, which represents typical paleo-riverbed floodplain deposits, indicating a strong hydrodynamic process. The typical unconformity contact relationship between the two deposits shows that the profile recorded the sedimentary information of the transformation of the Zoige paleolake environment into the Yellow River paleo-river environment, which provides powerful sedimentary evidence for the Yellow River dissecting the Zoige paleolake. (2) The optically stimulated luminescence dating results showed the Zoige paleolake was dissected by the Yellow River at 37 ka BP, resulting in the discharge of lake water. At 35 ka BP, the lake water gradually became shallow and disappeared, and the Yellow River subsequently connected the water system of the Zoige Basin. (3) The East Kunlun fault induced strong tectonic movement in the late Pleistocene, and the Tibetan Plateau had a warm and humid climate at 37 ka BP. Under these conditions, the headward erosion of the Yellow River was aggravated in the faulted wide valley grassland between the Anyemaqen mountains and Xiqing mountains, and the Zoige paleolake was dissected by the Yellow River from west to east in the Maqu bottleneck reach. The results of this study have important scientific significance for in-depth understanding of the evolution of river-lake water systems and the formation of the Yellow River source water system in the eastern Tibetan Plateau.

Distribution and sources of fluvial pollen in the middle reaches of the Yellow River in China and their relationship with vegetation and land use

Understanding the processes determining the composition of alluvial pollen assemblages and its relationship with watershed vegetation is a prerequisite for alluvial palynological study. Palynological analysis of a total of 45 river water samples collected from the middle reaches of the Yellow River and its major tributaries, identifies the distribution patterns, possible sources of pollen and relationship with the catchment vegetation. The results reveal that the pollen assemblages in the middle reaches of the Yellow River is dominated by herbaceous taxa, and the pollen is mainly derived from fluvial sources. Higher concentrations of the pollen tend to occur in the southern part of the study area. The Luo River is the main source of tree pollen in the Wei River Basin, while the Sanchuan River and Xinshui River are the main sources of tree pollen in the mainstream of the Yellow River. Herbaceous pollen mainly originates from the flood plain, and from channel bars and point bars, and there is no obvious relationship between herbaceous pollen and tributary inputs. The relative proportions of the various land use classes in the middle reaches of the Yellow River can be ordered as follows: grassland (GL) > cultivated land (CL) > forest (FO) > shrubland (SH) > water (WA). The herbaceous pollen of the Huangfuchuan River and Kuye River are closely related to the coverage of GL; cereal pollen is not fully representative of the CL coverage in the watershed; and the pollen of woody plants is extremely over-represented compared to the coverage of FO and SH in the watershed. Our results provide basic information about the sources of fluvial pollen and its indicative significance in the lower Yellow River and they are also potentially applicable to other major river basins.

Paleochannel of the Yellow River within the Zoige Basin and its environmental significance on the NE Tibetan Plateau

Paleochannel sedimentary sequences can provide abundant information on regional environmental changes. A typical paleochannel (paleo-oxbow lake type) section of the Yellow River was identified within the Zoige Basin on the NE Tibetan Plateau. A multi-index approach was used to accurately identify sediments of different genetic types, such as riverbed deposits of the Yellow River, paleo-oxbow lake deposits, and overbank flood deposits (OFD) in the section. Based on optically stimulated luminescence (OSL) and AMS ¹⁴C dates, we examined the environmental evolution recorded by the section. The results show that: (1) The section is a record of environmental change since 4.17 ± 0.49 ka. During 4.17 ± 0.49 to 3.24 ± 0.26 ka, the ancient Yellow River occupied the channel. At 3.24 ± 0.26 ka, the paleochannel experienced a neck cutoff, and the fluvial environment began to change into the oxbow lake environment. After 2.45 ± 0.11 ka, the paleo-oxbow lake gradually disappeared. Subalpine meadow soil has developed at this site since 1.31 ± 0.05 ka. (2) Paleoenvironmental proxies indicate that the Zoige Basin was warmer and wetter before ~3.00 ka, and became drier and colder after ~3.00 ka, which may be mainly related to the weakening of the East Asian summer monsoon (EASM) and the strengthening of the Westerlies. (3) Two episodes of extreme overbank flooding occurred at 2.96 ± 0.24 to 2.87 ± 0.27 ka and 1.84 ± 0.20 to 1.70 ± 0.16 ka, correlated with climate shift period from the mid-Holocene climatic optimum to the late Holocene and the Dark Age Cold Period (DACP), respectively. Due to the relatively cold and dry climate in these periods, glaciers generally advanced on the Tibetan Plateau, and the contribution of snow and ice meltwater weakened. Therefore, the strong rainfall caused by the abnormal atmospheric circulation may be the main cause of these extreme overbank flooding.

Phosphorus distribution in the water and sediment of Laizhou Bay and sediment phosphorus release potential

Phosphorus is an integral component of marine biogeochemistry. This research investigated the environmental behavior of P in Laizhou Bay using high-resolution sampling, P fractionation, and isotherm adsorption. The total dissolved P (TDP) concentration ranged from 8.4 to 61.0 μg/L in the bay water, while total P (TP) concentration ranged from 311.6 to 654.5 mg/kg in the sediment. The TDP concentration in the water was high in the estuarine area of the Yellow River and the southwestern bay under the combined effects of riverine inputs, direct wastewater discharge, and limited water exchange ability. High TP concentrations in the sediment were observed near the mouth of the Yellow River and central bay, mainly due to the movement and settlement of fine suspended particles under the influence of ocean currents. The P in the bay sediment was predominantly in the calcium-bound fraction and was associated with small particles such as silt and clay. The equilibrium P concentration (EPC₀) ranged from 1.6 to 131.4 μg/L, and P partition coefficient or buffer intensity (K_d) ranged from 104 L/kg to 880 L/kg. The EPC₀ decreased from the northeastern to southwestern area, while K_d showed an inverse distribution; therefore, the southwestern bay sediment had high buffer intensity for external P loads. Additionally, ECP₀ increased linearly, and K_d decreased with exchangeable P (Exc-P) and Fe-bound P (Fe-P) concentrations in the sediment, demonstrating that P sediment-water exchange in LZB was dominated by contributions from Exc-P and Fe-P. These results can aid the understanding of the P sources and geochemistry of coastal ecosystems, particularly sediment P release potential.

Will a heavy sediment load affect responses of phytoplankton functional groups to aquatic environmental changes in different water body types?

Sediment, as a natural component of rivers, directly affects the abundance and function of phytoplankton by altering water physicochemical properties. Despite mounting evidence for the sensitivity of phytoplankton to environmental factors, the responses of phytoplankton functional groups to complex environmental changes in rivers with a heavy sediment load are still poorly understood. Herein, the effectiveness of phytoplankton functional groups was evaluated as an indicator of aquatic environmental changes in a heavily sediment-laden river. Samples were collected from 44 sites (22 free-flowing river sections and 22 man-made reservoir sections) with a mean annual sediment concentration of 4.69 kg m^-3 in the Yellow River, China. A total of 31 phytoplankton functional groups were classified during spring (April-May) and autumn (September-October) in 2019. Groups C, MP, and D, which are well adapted to strong water disturbances and turbid habitats, showed distinct advantages over other groups. Despite no significant differences in many environmental variables between the river and reservoir sections, these variables (especially nitrogen nutrients) had remarkable effects on the phytoplankton community structure. The phytoplankton functional groups were sensitive to environmental changes even under sediment interference, although geo-climatic variables also exhibited non-trivial effects. The mean niche breadth of the abundant taxa (river: 11.16; reservoir: 7.93) was higher than that of the rare taxa (river: 5.64; reservoir: 4.86) in different water bodies. Thus, growth and diffusion of the abundant taxa played paramount roles in maintaining ecosystem stability. The results indicate that, in a large-scale sediment-laden river, phytoplankton functional groups can effectively indicate changes in the aquatic environment of either a free-flowing river or a man-made reservoir.

Distribution Pattern and Influencing Factors of Heavy Metal Resistance Genes in the Yellow River Sediments of Henan Section

The transformation of heavy metal resistance genes (MRGs) in the environment has attracted increasing attention in recent years. However, few studies have reported the MRG content in the Yellow River, one of the main irrigation water sources in the North China Plain. In this study, we quantified MRG abundance by a metagenomic approach, and assessed the influence on MRGs of both bioavailable and total heavy metal (HM) content. The results indicate that Cu-resistant genes are the most common genes, and the prevalence of arsM needs more attention. Comamonadaceae is the dominant family in the Yellow River, and the presence of organic pollutants may contribute to the prevalence of Vicinamibacteraceae, Nocardioidaceae, and Flavobacteriacea. The results of the Mantel test and Spearman analysis indicate that both the bioavailable fractions and total content of HMs could have little influence on MRGs. Network analysis results indicate that some dominant bacteria could be the potential hosts of some prevalent MRGs, which may exert an adverse impact on human health.

The Sources and Potential Hosts Identification of Antibiotic Resistance Genes in the Yellow River, Revealed by Metagenomic Analysis

The fate of antibiotic resistance genes (ARGs) has been revealed in various environmental media in recent years. Namely, the emergence of genes that resist colistin and carbapenems has attracted wide attention. However, the pollution condition of ARGs and sources in the Yellow River is still little understood, despite the river being the second longest in China. The present study determined the levels of ARG pollution in the Henan section of the Yellow River and evaluated the role of the aquaculture industry in the spread of ARGs. As revealed by the results, a total of 9 types of ARGs were detected in the sediments of the Yellow River, and the total ARG content in the Yellow River ranges from 7.27 to 245.45 RPKM. Sul1 and sul2 are the dominant ARGs, and the huge usage of sulfonamides, horizontal gene transfer, and wide bacteria host contribute to the prevalence of these two genes. The results of Spearman correlation analysis indicate that the breeding industry has little influence on ARGs in the Yellow River. Network analysis reveals that the opportunistic pathogen Pseudomonas is the potential host of sul1, tetG, and ANT(3'')-IIa, which can pose a risk to human health.

Did the modern Yellow River form at the Mid-Pleistocene transition?

The incision of the Sanmen Gorge marks the birth of the modern Yellow River, but its timing varies from the late Miocene-early Pliocene to the late Pleistocene (∼0.15 Ma), and the suggested forcing mechanisms vary from the uplift of the Tibetan Plateau to global climate change. Here, we report sedimentologic, geochronologic, and provenance data from a drill core near the Sanmen Gorge, the last gorge along the main course of the Yellow River. Our results indicate that typical river channel deposits, with detritus from the Ordos Block in the upstream regions, started to accumulate in the Sanmen Gorge at ∼1.25 Ma. When integrated with river terrace evidence from the upstream and downstream regions, the results provide robust evidence that the final integration of the modern Yellow River occurred at ∼1.25 Ma, consistent with the beginning of the Mid-Pleistocene transition (MPT). We propose that the accelerated lowering of eustatic sea level during the MPT may play as important a role as tectonism in driving the birth and evolution of the modern Yellow River.

[Evaluation and Source Analysis of Heavy Metal Pollution in Sediments of the Yellow River Basin Based on Monte Carlo Simulation and PMF Model]

As sediment is an essential component of rivers, the enrichment of heavy metals in sediment presents a serious threat to the aquatic environment. Many industrial cities are located along the Yellow River, and heavy metal pollution is a prominent problem in these areas. Thus, the study of heavy metal pollution in sediments of the Yellow River basin is of vital significance to the safety of the Yellow River basin ecosystem. In this study, we collected data on the concentrations of heavy metals (Pb, Cd, Cr, As, Zn, Cu, Ni, and Hg) in the sediments of the Yellow River basin from 2000 to 2020. We first analyzed the spatial distribution characteristics of heavy metals based on descriptive statistics and geostatistics and then used the Monte Carlo method to evaluate the probability of the ground accumulation index(I_geo), potential ecological risk, and toxicity units. Finally, the number of pollution sources and their contribution rates were determined by combining the positive definite matrix factor (PMF) decomposition model and Pearson correlation analysis. It was found that the mean values of ω(Pb), ω(As), ω(Zn), ω(Ni), ω(Cu), ω(Hg), ω(Cr), and ω(Cd) in the Yellow River basin sediments were 26.92, 11.78, 87.17, 31.13, 24.96, 0.07, 73.36, and 0.58 mg·kg^-1, which exceeded the mean soil background values in the Yellow River basin provinces by 1.27, 1.08, 1.26, 1.05, 1.09, 2.32, 1.14, and 5.95 times, respectively, among which Cd exceeded the standard by the largest factor and should be taken seriously. The I_geo was ranked as Cd>Hg>Cr>Cu>Pb>Zn>As>Ni, and Cd and Hg showed medium-severe pollution. The proportions of heavy ecological risk in sediments in the upper, middle, and lower reaches of the Yellow River basin were 18.6%, 15.7%, and 7.1%, respectively, with a decreasing trend. Heavy metals in the sediments of the Yellow River basin were in a low-toxicity state. The PMF-Pearson correlation analysis showed that the four sources of heavy metals in the Yellow River basin sediments were mining sources (42.2%), natural activities (38.3%), agricultural activities (11.6%), and electroplating wastewater (7.9%). The results of this study can provide a basis for developing relevant pollution prevention and control measures in the Yellow River basin.

Organic carbon source tracing and the BCP effect in the Yangtze River and the Yellow River: Insights from hydrochemistry, carbon isotope, and lipid biomarker analyses

Autochthonous organic carbon (AOC) formed by biological carbon pump (BCP) in surface waters may serve as a significant carbon sink. The locations, magnitudes, variations and mechanisms responsible for the terrestrial missing carbon sink by BCP are uncertain, especially in large river systems. In this study, hydrochemical characteristics, carbon isotope compositions of dissolved inorganic carbon (DIC) and organic carbon (OC), n-alkane homologues and C/N ratios of organic matter along the Yangtze River and the Yellow River were investigated to constrain the OC source and the significance of BCP effect. It was found that (1) DIC concentrations in the Yellow River were much higher than those in the Yangtze River, which was controlled primarily by the temperature effect; (2) AOC in the both rivers was characterized by lower C/N ratios and δ¹³C_POC values. Based on calculation of n-alkanes compounds, the AOC proportions ranged from 29 to 88% (49% on average, with a higher proportion (55%) in the rainy season than in the dry season (46%)) and 19-68% (41% on average; with a lower proportion in the rainy season (31%) than in the dry season (51%)) in the Yangtze River and the Yellow River, respectively, indicating intense aquatic production. Low dissolved CO₂ concentration (6.17 μmol/L on average) of the Yangtze River limited the aquatic production and decreased the BCP effect in the dry season, indicated by lower AOC proportion. However, the BCP effect increased in the Yellow River in the dry season mainly due to the increased light penetration; (3) even in high turbidity riverine systems such as the Yellow River, the aquatic photosynthetic uptake of DIC could produce considerable AOC. These findings clearly show the formation of AOC by BCP in both the clear and high turbidity riverine systems, suggesting a potential direction for finding the terrestrial missing carbon sink.

Tissue-specific distribution and bioaccumulation pattern of trace metals in fish species from the heavily sediment-laden Yellow River, China

The Yellow River is one of the largest contributors to the global riverine sediment flux from the land to the ocean. Tissue-specific bioaccumulation of trace metals in fish from heavily sediment-laden rivers remains unclear to date. The concentrations and distributions of trace metals in water, suspended matters, sediments, and various fish tissues were investigated in the mainstem of the Yellow River were investigated. The concentrations of most metals in abiotic media were high in the Gan-Ning-Meng of upstream and downstream segments, and were highest in fine-sized suspended matters. The highest concentrations of most metals were in the gill and liver, followed by the gonad, and lowest in the muscle, and there were a significant overall differences among the tissues. The concentrations of metals in some tissues (e.g., muscle and gill) significantly differed among regions and feeding habits. The highest values of the bioaccumulation factor for suspended matters (BF_SPM) were observed in the midstream region (e.g., reaching to 19.0 for Se in the liver). This was determined by metal type and tissue specificity, food composition, and concentration of metals in abiotic media. The results highlight the significance of suspended matters for the distribution of trace metals in abiotic and biotic media.

[Spatiotemporal variations of fish feeding guilds in Yellow River basin]

Conservation of fish resources is the key to ecological protection and high-quality development of Yellow River basin. From 1960 to 2019, Yellow River basin distributed 201 fish species, belonging to 16 orders, 35 families. The species number of Cypriniformes was the largest (accounting for 60.7%), followed by Perciformes (accounting for 10.0%). From 1960 to 1980, there were 182 fish species belonging to 15 orders, 28 families. During 1980-2019, there were 112 species, belonging to 10 orders, 23 families. The total number of fish species in source area, midstream and downstream decreased significantly, while that in the upper reaches increased slightly. Jaccard's similarity index of source area, upstream, midstream and downstream between two periods were 34.2%, 46.0%, 42.4% and 35.7%, respectively. Based on feeding preference characteristic, fish species could be divided into eight feeding guilds: phytobenthivores, herbivores, phytoplanktivores, zooplanktivores, omnivorous, insectivores, zoobenthivores, and piscivores. Compared with the period from 1960 to 1980, the proportion of insectivores decreased significantly in the Yellow River basin during 1980-2019, while that of phytobenthivores, herbivores, phytoplanktivores, omnivorous and piscivores increased significantly. From 1960 to 1980, the proportion of insectivores was higher than other reaches at source area and upstream, then began to decrease along the river continuum from reaches with elevation of 2000-3000 m; while the proportion of piscivores was lower than other reaches at source area and upstream, then began to increase along the river continuum from reaches with elevation of 2000-3000 m. From 1980 to 2019, the proportion of insectivores decreased along river continuum from source area, and that of piscivores increased from source area to midstream but decreased in downstream. Development of cascade hydropower, water pollution, insufficient water flow, overfishing and invasion of alien fish were important factors causing the spatiotemporal variations of fish feeding guilds in Yellow River basin.

Impact of water-sediment regulation on the concentration and transport of dissolved heavy metals in the middle and lower reaches of the Yellow River

Anthropogenic activities in river basins, especially large-scale water conservancy projects, have notably impacted the physical, chemical and ecological environments of estuaries and coastal areas. In this paper, the effects of water and sediment regulation (WSR) on the concentration and transport of heavy metals in the Yellow River were studied based on a continuous daily heavy metal survey in both the middle reaches (Xiaolangdi station) and lower reaches (Lijin station) of the Yellow River during the WSR period in 2019. The results indicated that the variation in the water oxidation-reduction environment of the Xiaolangdi reservoir during the WSR process exerted an important impact on the concentrations of dissolved Cu, Cd, Pb, Cr and As at the Xiaolangdi station but exerted almost no influence on the concentration of dissolved Ni. At Lijin station, the dissolved heavy metal content first increased and then decreased in the first stage, which mainly depended on the release of heavy metals from resuspended sediments. In the second stage, the heavy metal content gradually decreased due to adsorption onto fine particles discharged from the reservoir. The dissolved heavy metal flux during the water-sediment regulation scheme (WSRS) period accounted for 16.9-33.4% of the annual total dissolved heavy metal flux. WSRS changed transport of water and sediment. The dissolved heavy metal concentrations at the Xiaolangdi station were mainly controlled by the discharge of water and sediments from the Xiaolangdi reservoir, while the dissolved heavy metal concentration at the Lijin station was largely affected by the sediments resuspended from downstream riverbeds and the water and sediment scheduling mode of the Xiaolangdi reservoir. Dissolved heavy metal transportation was highly influenced by the WSR process within a short time. Human intervention, especially WSRS operation, apparently alters the natural states of both the mainstream and estuarine environments of the Yellow River.

Dynamic and Full-Time Acquisition Technology and Method of Ice Data of Yellow River

Regarding the ice periods of the Yellow River, it is difficult to obtain ice data information. To effectively grasp the ice evolution process in the ice periods of the typical reach of the Yellow River, a fixed-point air-coupled radar remote monitoring device is proposed in this paper. The device is mainly composed of an air-coupled radar ice thickness measurement sensor, radar water level measurement sensor, temperature measurement sensor, high-definition infrared night vision instrument, remote switch control, telemetry communication machine, solar and wind power supply, lightning protection, and slewing arm steel tower. The integrated monitoring device can monitor ice thickness, water level, air temperature, ice surface temperature, and other related parameters in real time. At present, devices have obtained the ice change process of fixed points in ice periods from 2020 to 2021. Through a comparison with manual data, the mean error of the monitoring results of the water level and ice thickness was approximately 1 cm. The device realizes the real-time monitoring of ice thickness and water level change in the whole cycle at the fixed position. Through video monitoring, it can take pictures and videos regularly and realize the connection between the visual river and monitoring data. The research results provide a new model and new technology for hydrological monitoring in the ice periods of the Yellow River, which has broad application prospects.

Impacts of water-sediment regulation on spatial-temporal variations of heavy metals in riparian sediments along the middle and lower reaches of the Yellow River

The water-sediment regulation scheme (WSRS) of dams influences the desorption, resuspension, and deposition processes of riparian sediments, which in turn affect the spatial-temporal variations of heavy metals (HMs) in riparian sediments and leads to severe degradation of soil and water quality. However, the difference between the trapping effect of dams and the redistribution effects of the WSRS on HMs in riparian sediments, as well as the consecutively seasonal change of HMs after the WSRS, are rarely reported. To fill this gap, the concentrations of six HMs including Cd, Cr, Cu, Ni, Pb, and Zn in riparian sediments along the Xiaolangdi Dam (XLD) Reservoir and its downstream reach were investigated, and the contamination level and potential ecological risk of HMs were assessed, to differentiate the effects of the XLD and its WSRS on the concentration, contamination level, and potential ecological risks of HMs. The results indicated that the mean HM concentrations in riparian sediments were higher than the background values in the study area and showed significant spatial and temporal variations. However, the regional differences of HM concentrations caused by the trapping effect of the XLD were less than the seasonal differences caused by the redistribution effects of the WSRS. The contamination and ecological risk assessment indicated that riparian sediments in the study area were contaminated by the six HMs, particularly by Cd and Pb, which overall exhibited a high and moderate ecological risk, respectively. The sources for Pb were likely agricultural inputs, while the sources for Cd should be attributed to both industrial and agricultural inputs. Overall, the trapping effect of the XLD led to the accumulation of HMs in riparian sediments along the reservoir area, while the regulation effects of the WSRS resulted in the redistribution of HMs in riparian sediments from the reservoir area to the downstream reach.

Transport and environmental risks of perfluoroalkyl acids in a large irrigation and drainage system for agricultural production

The quality of irrigation water and drainage water is essential for local ecosystem and human health in agricultural regions. In this study, the transport analysis, source identification, and environmental risk assessment of perfluoroalkyl acids (PFAAs) were conducted in the largest irrigation area in northern China. The concentrations of the total PFAAs (ΣPFAA) ranged from 41.5 to 263 ng/L in surface water, and the short-chain perfluoroalkyl carboxylic acids (PFCAs) and perfluorooctanoic acid (PFOA), were dominant with a total contribution of 94%. Generally, the ΣPFAA levels increased from irrigation waters to drainage and receiving lake waters. PFOA showed the highest increase, with potential emission sources located in the catchment of the sub main drainage ditch D5. More PFOA (36.8 kg/y) was outflowed from Ulansuhai Lake to the Yellow River than that inflowed from the Yellow River to the irrigation district (6.15 kg/y). The results of a risk assessment indicated that avian wildlife living in Ulansuhai Lake were threatened by the PFOA and perfluorobutane sulfonate (PFBS) pollution. The estimated daily intakes (EDIs) of the sum of the PFOA, perfluorononanoic acid (PFNA), perfluorohexane sulfonic acid (PFHxS), and perfluorooctane sulfonic acid (PFOS) through aquatic food consumption for people with the different aquatic food preferences accounted for 6-42% (urban) and 4-27% (rural) of the strictest tolerant daily intake (TDI) value. The results of this study highlight the impact of local emissions of PFAS on massive irrigation and drainage systems, and ultimately, the ecosystem and human health.

Variability of heavy metal transport during the water-sediment regulation period of the Yellow River in 2018

To understand the impacts of the human-induced flood event on heavy metal (HM) transport, spatiotemporal variations in contents and fluxes of metals (Cr, Ni, Cu, Zn, As, Pb, Cd), Pb stable isotopes and characteristics of water and sediment transport into the sea during Water-Sediment Regulation Scheme (WSRS) in Yellow River (YR) were studied based on field investigation at Xiaolangdi Reservoir (XLD), Lijin Station and Yellow River estuary (YRE). The HM transport was significantly controlled by hydrological process and dominated by particulate form with strong associations with particle size and suspended sediment concentration (SSC). In first stage, dissolved heavy metal (DHM) and particulate heavy metal (PHM) contents both increased significantly as coarser sediment with a mixed source of downstream river channel and XLD, while that maintained higher value for stable source of fine-grained XLD sediment in second stage. The HMs into the sea were mainly originated from upper and middle reaches but also contributed by human emissions from downstream area. As the source of HMs into the sea, the downstream area also acted as an important sink, especially in first stage, playing a role of buffering and filtration. During WSRS, the YR discharged 49%-60% of annual HM flux into the sea, and the second stage is the main transport period, leading to a great alternation in geochemical composition of the YRE sediment.

The spatial-temporal evolution of heavy metal accumulation in the offshore sediments along the Shandong Peninsula over the last 100 years: Anthropogenic and natural impacts

The anthropogenic and natural impacts on the temporal and spatial variations of heavy metals in sediments under the Shandong Peninsula coastal current are still unclear. Here, the concentrations\burial fluxes of Cr, Cu, Zn, As, and Pb in three sediment cores retrieved from the Bohai Sea and the Yellow Sea along the Shandong Peninsula were analyzed to study the spatial-temporal variability of heavy metal accumulation over the last century. The results showed that the buried heavy metal fluxes were relatively low at the end of the Shandong Peninsula coastal current. The enrichment factor (EF) and geoaccumulation index (I_geo) indicated that those metals did not severely pollute the sediments except As that reached a moderate enrichment. Principal component analysis (PCA) revealed that Cr, Cu, Zn, and Pb were mainly derived from natural weathering and As was determined by anthropogenic contamination. The strength of the Shandong Peninsula coastal current, the Yellow River estuary location, and sediment discharge load significantly influenced the concentrations of natural-origin heavy metals by affecting sediment grain size and the source-sink process. The emission of pollutants from agricultural and industrial activities in the Shandong Peninsula region resulted in As enrichment since the 1950s. Moreover, the EF values of heavy metals in sediment cores from China's coastal seas showed apparent spatial variations of heavy metal pollution but had coherent temporal variability with China's economic development process. Heavy metals pollution has weakened in most coastal seas since the 2000s, likely due to the extensive industrial upgrading and the implementation of pollution control. These results have a reference significance for studying the evolution and source-sink process of the heavy metals in offshore sediments and tracing anthropogenic impacts in different periods.

Active dissolved organic nitrogen cycling hidden in large river and environmental implications

Large rivers are important terrestrial dissolved organic matter (DOM) sources to marginal seas, and dissolved organic nitrogen (DON) plays an essential role in DOM cycling. The Yellow River ranks as the fifth largest river (in length) in the world and is well-known for its high dissolved inorganic nitrogen (DIN) concentration and relatively low DON concentration, leading to extreme measuring uncertainties in DON and nitrogen isotopic composition (δ¹⁵N), consequently leaving its DON cycling as an unresolved puzzle. To fill such a knowledge gap, we analyzed 17 samples from the middle to downstream with a combination of spectroscopy, tangential flow filtration, nitrogen isotope, and DNA sequencing. DON_<1kDa dominated the DON pool and significantly correlated inversely with DIN, indicating the DON_<1kDa mineralized into nitrate. This finding was further supported by the observed Rayleigh fractionation in δ¹⁵N_DON<1kDa and the spatial distribution pattern of ammonia-oxidizing bacteria/archaea abundance. The redundancy analysis revealed that the geographical features and the microbial community were closely related, which joined together to drive the DON cycling. In addition, we propose a rational method to quantify the flux of mineralized DON in large rivers. This study discovered the active DON cycling hidden in high DIN large river and highlighted the importance of DON mineralization as well as its role in marginal seas carbon cycling.

Geo-climatic factors weaken the effectiveness of phytoplankton diversity as a water quality indicator in a large sediment-laden river

The study aims to determine whether phytoplankton diversity can be used as an indicator of water quality in large-scale sediment-laden rivers with heterogeneous environmental conditions. We hypothesized that environmental factors, such as sediment load, water surface slope, and precipitation, may impact the effectiveness of using phytoplankton diversity as a water quality indicator. To test this hypothesis, the Yellow River was selected for phytoplankton diversity and water quality assessments. We measured water quality parameters, calculated phytoplankton diversity indices, and collected data on geo-climatic variables at 130 sampling points in the Yellow River mainstream over two seasons (spring and autumn) in 2019. The results of the water quality assessment based on phytoplankton diversity indices were compared with those based on water quality index (WQI). Correlation analysis, multiple stepwise regression, distance-based redundancy analysis, and regression modeling were used to explore the biogeographical patterns and drivers of phytoplankton diversity. According to the WQI, the water quality gradually deteriorated from the source to the estuary of the river. Three biodiversity indices (Margalef, Pielou, and Shannon-Wiener) indicated that the water quality varied dynamically in the middle reaches of the river. The actual relationships between the biodiversity indices and WQI did not fit well with the standard curves of water quality classification based on the respective biodiversity indices and WQI. Variation partitioning analysis indicated that water quality parameters, such as sediment and nutrient load, were the dominant drivers of variation in phytoplankton diversity in most cases, with the contribution ranging from 11.0% to 25.7%. Geo-climatic factors, such as water surface slope and annual mean precipitation, also affected phytoplankton diversity, with the contribution reaching 27.8%. Therefore, in sediment-laden rivers with a large geographical span and complex environment, phytoplankton diversity cannot be used as a suitable water quality indicator, albeit it can reflect habitat changes to a certain extent.

Ecological Water Requirement in Upper and Middle Reaches of the Yellow River Based on Flow Components and Hydraulic Index

Deterioration of the ecological environment in the upper and middle reaches of the Yellow River in China substantially impacts the growth and development of aquatic organisms in the drainage basin. This paper builds a conceptual model by applying flow components and fish ecological requirements relation with a relevant object of main fish in the upper and middle reaches of the Yellow River. The paper utilized the flow restoration method by employing the River2D model (two-dimensional model of river hydrodynamics and fish habitat), and a one-dimensional hydrodynamics HEC-RAS (hydrologic engineering center's-river analysis system). The calculation result showed that the runoff condition required for Silurus lanzhouensis survival is that the monthly lowest flow in a year is 150 m³·s^-1, and the lowest flow for suitable flow from April to October is 150 m³·s^-1, and 300 m³·s^-1 from November to March. The research result is closer to the actual condition and has more outstanding operability. Meanwhile, the results proposed the coupling method of ecological water requirement for the mainstream of the Yellow River. Moreover, the results portrayed the ecological flow process according to the upper envelope of minimum and maximum ecological water requirements of each fracture surface. It is regarded that the ecological flow process is deemed as the initial value of the reservoir regulation model.

Distribution, sources, and ecological risks of potentially toxic elements in the Laizhou Bay, Bohai Sea: Under the long-term impact of the Yellow River input

Potentially toxic element (PTE) contamination is a common environmental issue in offshore regions worldwide. Water and sediment samples were collected from the Yellow River downstream and adjacent Laizhou Bay to investigate the residues, sources, and ecological risks of 11 typical PTEs (As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sc, V, and Zn). The results indicated that the concentrations of PTEs in the sediments decreased from the Yellow River Estuary to the inner Laizhou Bay under the long-term effect of the Yellow River input. Principal component analysis (PCA) identified three potential sources: natural origins, coastal anthropogenic activities (e.g., oil exploration and steel refining), and marine production (e.g., marine aquaculture and transportation). Among the PTEs, Cd was the most significant contaminant, with a contamination factor (CF) of 2.06 ± 0.78. Furthermore, Cd was the most sensitive factor used in evaluating the overall ecological risk using Monte Carlo analysis, with a contribution of up to 96%. Although the overall contamination and risk levels were low in the bay, a higher pollution load index (PLI) and risk index (RI) adjacent to the Yellow River Estuary indicated that the Yellow River remained the primary contributor to the PTEs contamination in the bay.

[Hydrochemistry and Its Controlling Factors and Water Quality Assessment of Shallow Groundwater in the Weihe and Jinghe River Catchments]

The Weihe and Jinghe Rivers catchments are important tributaries of the Yellow River, where it is of great significance to evaluate groundwater hydrochemistry and quality for ecological protection and sustainable development. Piper diagrams, Gibbs, Na-normalized molar ratios, and ion correlation methods were used to analyze the chemical composition of groundwater in these two catchments. Furthermore, the WQI method, Wilcox diagrams, USSL diagrams, and Doneen diagrams were used to evaluate the suitability of groundwater quality for drinking and irrigation. The results showed that the Weihe and Jinghe River catchments are dominated by fresh and weakly alkaline water. Groundwater ion concentration in the Weihe River are higher than in Jinghe River except for Na⁺, and the major groundwater types are HCO₃-Ca-Mg(accounted for 50%), and HCO₃-Ca-Mg and HCO₃-Na-K (accounted for 32.5%), respectively. The hydrochemistry of the Weihe and Jinghe River catchments is mainly controlled by rock weathering, primarily silicate weathering. Moreover, the groundwater chemistry in the research area is affected by mining and chemical fertilizer application for agriculture. Furthermore, the hydrochemistry of the Weihe River catchment is affected by cation exchange, although this was not obvious in some regions of the Jinghe River catchment. The overall groundwater quality of the two catchments was good, with the Jinghe River water quality being better than in the Weihe River catchment. Based on SSP, SAR, and PI, the groundwater in some parts of the study area cannot be directly used for irrigation as this would result in salinization and, thus, inhibit plant growth. Overall, the groundwater quality in the south of the study area is better than in the north, and is better in the Jinghe River catchment than in the Weihe River catchment according to these three indicators. This study provides a basis for the sustainable development of two catchments, providing baseline data for groundwater quality management.

[Hydrochemical and Isotopic Characteristics in the Shallow Groundwater of the Fenhe River Basin and Indicative Significance]

The Fenhe River basin is the second largest tributary of the Yellow River. Piper diagrams, Gibbs, PCA, correlation analysis and forward derivation modeling were used to analyze the distribution characteristics and the controlling factors of the groundwater chemistry and stable isotopes in the Fenhe River basin, which revealed the water cycle and water quality evolution process. The results indicated that the groundwater is a weakly alkaline, micro-hard water, the dominant anions and cations are HCO₃^- and Ca²⁺, the major groundwater types are Mg-Ca-HCO₃ and Mg-Ca-Cl-SO₄, the groundwater quality is good, and more than 94% of the samples belong to classes Ⅰ-Ⅲ. The average values of δD and δ¹⁸O of the Fenhe River groundwater are -70.2‰ and -9.6‰, which are similar to the isotope values of the precipitation from July to September, indicating that the groundwater may have originated from this period and that the groundwater recharge mode (dominant flow and piston flow) has a spatial variation. Rock weathering is the dominant source of ions in the groundwater, with an average contribution of 87%, while the contributions of atmospheric input and human activity are 8% and 5%, respectively. For rock weathering, silicate, evaporate, and carbonate rock contribute equally to the groundwater solutes, accounting for 32%, 28%, and 26%, respectively. The results of this study provide the basis for promoting the sustainable development and utilization of groundwater resources in the Fenhe River basin.

Variability of annual sediment load and runoff in the Yellow River for the last 100 years (1919-2018)

The sediment load of the Yellow River, once the highest in the world, has decreased to a record low. The annual sediment load (ASL, t·yr^-1) in the main stream of the Yellow River in the past 100 years (1919-2018) shows that the ASL was consistently high for the first 60 years and then decreased gradually until 1999, when the Green for Grain Project (GGP) launched on the Loess Plateau caused ASL to drop sharply. The annual runoff did not decrease as much as ASL from 1919 to 2018, while it decreased significantly in the middle reaches. With the construction of sediment storage dams, terraces, and reservoirs, especially after the GGP launched, the ASL of the Yellow River has been reduced to historic lows. For example, the annual average Normalized Difference Vegetation Index (NDVI) of the Yellow River Basin increased significantly from 1982 to 2016, and the ASL decreased exponentially with increasing NDVI. Although the annual precipitation has a stationary behavior in the Yellow River, the daily precipitation extremes affecting erosion showed an increase of 7% per degree of warming but did not change the trend of ASL reduction. Therefore, the effective management on the Loess Plateau can control the trend of the sediment load of the Yellow River. Erosion, sediment load, and runoff in changing environments are affected by flood control and drought resistance, so more attention should be paid to these hydrologic processes.