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.

Multiple pathways of vanadate reduction and denitrification mediated by denitrifying bacterium Acidovorax sp. strain BoFeN1.

Contamination of aquifers by a combination of vanadate [V(V)] and nitrate (NO3-) is widespread nowadays. Although bioremediation of V(V)- and nitrate-contaminated environments is possible, only a limited number of functional species have been identified to date. The present study demonstrates the effectiveness of V(V) reduction and denitrification by a denitrifying bacterium Acidovorax sp. strain BoFeN1. The V(V) removal efficiency was 76.5 ± 5.41 % during 120 h incubation, with complete removal of NO3- within 48 h. Inhibitor experiments confirmed the involvement of electron transport substances and denitrifying enzymes in the bioreduction of V(V) and NO3-. Cyt c and riboflavin were important for extracellular V(V) reduction, with quinone and EPS more significant for NO3- removal. Intracellular reductive compounds including glutathione and NADH directly reduce V(V) and NO3-. Reverse transcription quantitative PCR confirmed the important roles of nirK and napA genes in regulating V(V) reduction and denitrification. Bioaugmentation by strain BoFeN1 increased V(V) and NO3- removal efficiency by 55.3 % ± 2.78 % and 42.1 % ± 1.04 % for samples from a contaminated aquifer. This study proposes new microbial resources for the bioremediation of V(V) and NO3-contaminated aquifers, and contributes to our understanding of coupled vanadium, nitrogen, and carbon biogeochemical processes.

May microbial ecological baseline exist in continental groundwater?

BACKGROUND: Microbes constitute almost the entire biological community in subsurface groundwater and play an important role in ecological evolution and global biogeochemical cycles. Ecological baseline as a fundamental reference with less human interference has been investigated in surface ecosystems such as soils, rivers, and ocean, but the existence of groundwater microbial ecological baseline (GMEB) is still an open question so far. RESULTS: Based on high-throughput sequencing information derived from national monitoring of 733 newly constructed wells, we find that bacterial communities in pristine groundwater exhibit a significant lateral diversity gradient and gradually approach the topsoil microbial latitudinal diversity gradient with decreasing burial depth of phreatic water. Among 74 phyla dominated by Proteobacteria in groundwater, Patescibacteria act as keystone taxa that harmonize microbes in shallower aquifers and accelerate decline in bacterial diversity with increasing well-depth. Decreasing habitat niche breadth with increasing well-depth suggests a general change in the relationship among key microbes from closer cooperation in shallow to stronger competition in deep groundwater. Unlike surface-water microbes, microbial communities in pristine groundwater are predominantly shaped by deterministic processes, potentially associated with nutrient sequestration under dark and anoxic environments in aquifers. CONCLUSIONS: By unveiling the biogeographic patterns and mechanisms controlling the community assembly of microbes in pristine groundwater throughout China, we firstly confirm the existence of GMEB in shallower aquifers and propose Groundwater Microbial Community Index (GMCI) to evaluate anthropogenic impact, which highlights the importance of GMEB in groundwater water security and health diagnosis. Video Abstract.

High-quality reconstruction of China's natural streamflow.

Reconstruction of natural streamflow is fundamental to the sustainable management of water resources. In China, previous reconstructions from sparse and poor-quality gauge measurements have led to large biases in simulation of the interannual and seasonal variability of natural flows. Here we use a well-trained and tested land surface model coupled to a routing model with flow direction correction to reconstruct the first high-quality gauge-based natural streamflow dataset for China, covering all its 330 catchments during the period from 1961 to 2018. A stronger positive linear relationship holds between upstream routing cells and drainage areas, after flow direction correction to 330 catchments. We also introduce a parameter-uncertainty analysis framework including sensitivity analysis, optimization, and regionalization, which further minimizes biases between modeled and inferred natural streamflow from natural or near-natural gauges. The resulting behavior of the natural hydrological system is represented properly by the model which achieves high skill metric values of the monthly streamflow, with about 83% of the 330 catchments having Nash-Sutcliffe efficiency coefficient (NSE) > 0.7, and about 56% of the 330 catchments having Kling-Gupta efficiency coefficient (KGE) > 0.7. The proposed construction scheme has important implications for similar simulation studies in other regions, and the developed low bias long-term national datasets by statistical postprocessing should be useful in supporting river management activities in China.

Deficiency and excess of groundwater iodine and their health associations.

More than two billion people worldwide have suffered thyroid disorders from either iodine deficiency or excess. By creating the national map of groundwater iodine throughout China, we reveal the spatial responses of diverse health risks to iodine in continental groundwater. Greater non-carcinogenic risks relevant to lower iodine more likely occur in the areas of higher altitude, while those associated with high groundwater iodine are concentrated in the areas suffered from transgressions enhanced by land over-use and intensive anthropogenic overexploitation. The potential roles of groundwater iodine species are also explored: iodide might be associated with subclinical hypothyroidism particularly in higher iodine regions, whereas iodate impacts on thyroid risks in presence of universal salt iodization exhibit high uncertainties in lower iodine regions. This implies that accurate iodine supply depending on spatial heterogeneity and dietary iodine structure optimization are highly needed to mitigate thyroid risks in iodine-deficient and -excess areas globally.

Constrained CMIP6 projections indicate less warming and a slower increase in water availability across Asia.

Climate projections are essential for decision-making but contain non-negligible uncertainty. To reduce projection uncertainty over Asia, where half the world's population resides, we develop emergent constraint relationships between simulated temperature (1970-2014) and precipitation (2015-2100) growth rates using 27 CMIP6 models under four Shared Socioeconomic Pathways. Here we show that, with uncertainty successfully narrowed by 12.1-31.0%, constrained future precipitation growth rates are 0.39 ± 0.18 mm year-1 (29.36 mm °C-1, SSP126), 0.70 ± 0.22 mm year-1 (20.03 mm °C-1, SSP245), 1.10 ± 0.33 mm year-1 (17.96 mm °C-1, SSP370) and 1.42 ± 0.35 mm year-1 (17.28 mm °C-1, SSP585), indicating overestimates of 6.0-14.0% by the raw CMIP6 models. Accordingly, future temperature and total evaporation growth rates are also overestimated by 3.4-11.6% and -2.1-13.0%, respectively. The slower warming implies a lower snow cover loss rate by 10.5-40.2%. Overall, we find the projected increase in future water availability is overestimated by CMIP6 over Asia.

Supercarriers of antibiotic resistome in a world's large river.

BACKGROUND: Antibiotic resistome has been found to strongly interact with the core microbiota in the human gut, yet little is known about how antibiotic resistance genes (ARGs) correlate with certain microbes in large rivers that are regarded as "terrestrial gut." RESULTS: By creating the integral pattern for ARGs and antibiotic-resistant microbes in water and sediment along a 4300-km continuum of the Yangtze River, we found that human pathogen bacteria (HPB) share 13.4% and 5.9% of the ARG hosts in water and sediment but contribute 64% and 46% to the total number of planktonic and sedimentary ARGs, respectively. Moreover, the planktonic HPB harbored 79 ARG combinations that are dominated by "natural" supercarriers (e.g., Rheinheimera texasensis and Noviherbaspirillum sp. Root189) in river basins. CONCLUSIONS: We confirmed that terrestrial HPB are the major ARG hosts in the river, rather than conventional supercarriers (e.g., Enterococcus spp. and other fecal indicator bacteria) that prevail in the human gut. The discovery of HPB as natural supercarriers in a world's large river not only interprets the inconsistency between the spatial dissimilarities in ARGs and their hosts, but also highlights the top priority of controlling terrestrial HPB in the future ARG-related risk management of riverine ecosystems globally. Video Abstract.

Three Gorges Dam: friend or foe of riverine greenhouse gases?

Dams are often regarded as greenhouse gas (GHG) emitters. However, our study indicated that the world's largest dam, the Three Gorges Dam (TGD), has caused significant drops in annual average emissions of CO2, CH4 and N2O over 4300 km along the Yangtze River, accompanied by remarkable reductions in the annual export of CO2 (79%), CH4 (50%) and N2O (9%) to the sea. Since the commencement of its operation in 2003, the TGD has altered the carbonate equilibrium in the reservoir area, enhanced methanogenesis in the upstream, and restrained methanogenesis and denitrification via modifying anoxic habitats through long-distance scouring in the downstream. These findings suggest that 'large-dam effects' are far beyond our previous understanding spatiotemporally, which highlights the fundamental importance of whole-system budgeting of GHGs under the profound impacts of huge dams.

Microbial selenate detoxification linked to elemental sulfur oxidation: Independent and synergic pathways.

Elevated selenium levels in the environment, with soluble selenate [Se(VI)] as the common chemical species, pose a severe threat to human health. Anaerobic Se(VI) bioreduction is a promising approach for selenium detoxification, and various organic/inorganic electron donors have proved effective in supporting this bioprocess. Nevertheless, autotrophic Se(VI) bioreduction driven by solid inorganic electron donors is still not fully understood. This work is the first to employ elemental sulfur [S(0)] as electron donor to support Se(VI) bioreduction. A batch trial with mixed culture demonstrated the feasibility of this bioprocess, with Se(VI) removal efficiency of 92.4 ± 0.7% at an initial Se(VI) concentration of 10 mg/L within 36 h. Continuous column tests showed that increased initial concentration, flow rate, and introduction of NO3--N depressed Se(VI) removal. Se(VI) was mainly bioreduced to solid elemental Se with trace selenite in the effluent, while S(0) was oxidized to SO42-. Enrichment of Thiobacillus, Desulfurivibrio, and Sulfuricurvum combined with upregulation of genes serA, tatC, and soxB indicated Se(VI) bioreduction was coupled to S(0) oxidation. Thiobacillus performed S(0) oxidation and Se(VI) reduction independently. Intermediate metabolites as volatile fatty acids, hydrogen and methane from S(0) oxidation were utilized by heterotrophic Se(VI) reducers for Se(VI) detoxification, indicative of microbial synergy.

Global syndromes induced by changes in solutes of the world's large rivers.

Solute-induced river syndromes have grown in intensity in recent years. Here we investigate seven such river syndromes (salinization, mineralization, desalinization, acidification, alkalization, hardening, and softening) associated with global trends in major solutes (Ca2+, Mg2+, Na+, K+, SO42-, Cl-, HCO3-) and dissolved silica in the world's large rivers (basin areas ≥ 1000 km2). A comprehensive dataset from 600 gauge stations in 149 large rivers reveals nine binary patterns of co-varying trends in runoff and solute concentration. Solute-induced river syndromes are associated with remarkable increases in total dissolved solids (68%), chloride (81%), sodium (86%) and sulfate (142%) fluxes from rivers to oceans worldwide. The syndromes are most prevalent in temperate regions (30~50°N and 30~40°S based on the available data) where severe rock weathering and active human interferences such as urbanization and agricultural irrigation are concentrated. This study highlights the urgency to protect river health from extreme changes in solute contents.

Perfluoroalkyl substances in the Yangtze River: Changing exposure and its implications after operation of the Three Gorges Dam.

Potential ecological risk from perfluoroalkyl substances (PFASs) under changing exposure in large river systems has become a new challenge recently. Based on systematic monitoring of PFASs at 43 hydrologic stations along a 4300 km continuum of the Yangtze River, we investigated the ecological risk of PFASs under changing exposure resulting from operation of the Three Gorges Dam (TGD). Importantly, perfluorooctanoic acid (PFOA) was found extensively exposed in most mainstream water samples, accounting for about 90% of the total content of PFASs in both spring and autumn, while short-chain PFASs contributed more than PFOA in sediment. The significant inversion of long-chain PFASs occurrence from sediment to water reflected a profound change in exposure due to loss of finer sediments resulting from long-distance and long-term scour of the riverbed downstream of the TGD. The coarsening of bed materials would weaken sorption of long-chain PFASs in sediments and enhance their exposure in water, resulting in substantial increase of ecological risk to representative aquatic organisms. In the long term, particular attention should be paid to reduction of PFOA discharge to downstream of the TGD from typical industries. This also highlights the significance of huge dams to alternative exposures of persistent organic pollutants and the necessity of new strategy for ecological risk management of large river systems.

Vanadium contamination and associated health risk of farmland soil near smelters throughout China.

Whereas there is broad consensus that smelting causes serious soil contamination during vanadium production, little is known about the vanadium content of soil near smelters and the associated health risk at continental scale. This study is the first to map the distribution of vanadium in farmland soil surrounding smelters throughout mainland China, and assess the associated health risk. Analysis of 76 samples indicated that the average vanadium content in such soil was 115.5 mg/kg - far higher than the 82 mg/kg background content in China (p < 0.05). Southwest China (198.0 mg/kg) and North China (158.3 mg/kg) possessed highest vanadium contents. Vanadium content was strongly related to longitude, altitude, and atmospheric temperature. The reducible fraction accounted for the largest percentages in vanadium speciation. The average Pollution Load Index for all samples was 1.51, denoting significant metal enrichment. The Children's hazard index was higher than unity, indicating elevated health risk. The relative contribution of vanadium to the total health risk ranged from 6.02% to 34.5%, while nickel and chromium were the two main contributors in most regions. This work may serve as a model providing an overview of continental vanadium contamination around smelters, and draw attention to their possible health risks.

Sale-based estimation of pharmaceutical concentrations and associated environmental risk in the Japanese wastewater system.

Information on sales and emission of selected pharmaceuticals were used to predict their concentrations in Japanese wastewater influent through a >300 of pharmaceuticals data sink. A combined wastewater-based epidemiology and environmental risk analysis follow was established. By comparing predicted environmental concentrations (PECs) of pharmaceuticals in wastewater influent against measured environmental concentrations (MECs) reported in previous studies, it was found that the model gave accurate results for 17 pharmaceuticals (0.5 < PEC/MEC < 2), and acceptable results for 32 out of 40 pharmaceuticals (0.1 < PEC/MEC < 10). Although the majority of pharmaceuticals considered in the model were antibiotics and analgesics, pranlukast, a receptor antagonist, was predicted to have the highest concentration in wastewater influent. With regard to the composition of wastewater effluent, the Estimation Program Interface (EPI) suite was used to predict pharmaceutical removal through activated sludge treatment. Although the performance of the EPI suite was variable in terms of accurate prediction of the removal of different pharmaceuticals, it could be an efficient tool in practice for predicting removal under extreme scenarios. By using the EPI suite with input data on PEC in the wastewater influent, the PEC values of pharmaceuticals in wastewater effluent were predicted. The concentrations of 26 pharmaceuticals were relatively high (>1 µg/L), and the PECs of 6 pharmaceuticals were extremely high (>10 µg/L) in wastewater effluent, which could be attributed to their high usage rates by consumers and poor removal rates in wastewater treatment plants (WWTPs). Furthermore, environmental risk assessment (ERA) was carried out by calculating the ratio of predicted no effect concentration (PNEC) to PEC of different pharmaceuticals, and it was found that 9 pharmaceuticals were likely to have high toxicity, and 54 pharmaceuticals were likely to have potential toxicity. It is recommended that this is further investigated in detail. The priority screening and environmental risk assessment results on pharmaceuticals can provide reliable basis for policy-making and environmental management.

Sustainability of global Golden Inland Waterways.

Sustainable inland waterways should meet the needs of navigation without compromising the health of riverine ecosystems. Here we propose a hierarchical model to describe sustainable development of the Golden Inland Waterways (GIWs) which are characterized by great bearing capacity and transport need. Based on datasets from 66 large rivers (basin area > 100,000 km2) worldwide, we identify 34 GIWs, mostly distributed in Asia, Europe, North America, and South America, typically following a three-stage development path from the initial, through to the developing and on to the developed stage. For most GIWs, the exploitation ratio, defined as the ratio of actual to idealized bearing capacity, should be less than 80% due to ecological considerations. Combined with the indices of regional development, GIWs exploitation, and riverine ecosystem, we reveal the global diversity and evolution of GIWs' sustainability from 2015 to 2050, which highlights the importance of river-specific strategies for waterway exploitation worldwide.

Global trends in water and sediment fluxes of the world's large rivers.

Water and sediment transport from rivers to oceans is of primary importance in global geochemical cycle. Against the background of global change, this study examines the changes in water and sediment fluxes and their drivers for 4307 large rivers worldwide (basin area ≥1000 km2) based on the longest available records. Here we find that 24% of the world's large rivers experienced significant changes in water flux and 40% in sediment flux, most notably declining trends in water and sediment fluxes in Asia's large rivers and an increasing trend in suspended sediment concentrations in the Amazon River. In particular, nine binary patterns of changes in water-sediment fluxes are interpreted in terms of climate change and human impacts. The change of precipitation is found significantly correlated to the change of water flux in 71% of the world's large rivers, while dam operation and irrigation rather control the change of sediment flux in intensively managed catchments. Globally, the annual water flux from rivers to sea of the recent years remained stable compared with the long-time average annual value, while the sediment flux has decreased by 20.8%.

Homogenization and polarization of the seasonal water discharge of global rivers in response to climatic and anthropogenic effects.

We investigate global trends in seasonal water discharge using data from 5668 hydrological stations in catchments whose total drainage area accounts for 2/3 of the Earth's total land area. Homogenization of water discharge, which occurs when the gap in water discharge between dry and flood seasons shrinks significantly, affects catchments occupying 2/5 of the total land area, and is mainly concentrated in Eurasia and North America. By contrast, polarization of water discharge, associated with widening of the gap in water discharge between dry and flood seasons, occurs in catchments covering 1/6 of the land area, most notably in the Amazon Basin and river basins in West Africa. Considering the major climatic and anthropogenic controlling factors, i.e. precipitation (P), evaporation (E), glacial runoff (G), and dam operations (D), the world's river basins are classified as P, DEP, GEP, and EP types. Contributions from each controlling factor to either the homogenization or polarization of the seasonal water discharge for each type of river have been analyzed. We found that homogenization of discharge is dominated by dam operations in GDEP and DEP river basins (contributing 48% and 64%) and by homogenized precipitation in GEP and EP river basins. Evaporation and precipitation are primary factors behind the polarization of discharge, contributing 56% and 41%. This study provides a basis for a possible decision tool for controlling drought/flood disasters and for assessing and preventing ecological damage in endangered regions.

The role of natural Fe(II)-bearing minerals in chemoautotrophic chromium (VI) bio-reduction in groundwater.

To date, comparatively little is known about the role of natural Fe(II)-bearing minerals in bioremediation of chromium (VI) contaminated aquifers subject to chemoautotrophic conditions. This work employed four kinds of Fe(II)-bearing minerals (pyrite, mackinawite, wustite, and magnetite) as inorganic electron donors to support Cr(VI) bio-reduction. In batch experiments, mackinawite (FeS) performed best, with Cr(VI) removal efficiency of 98.1 ±â€¯1.21 % in 96 h. Continuous column experiments lasting 180 d implied that groundwater chemistry and hydrodynamics influenced the Cr(VI) removal process. A breakthrough study suggested that biotic and abiotic contributions to Cr(VI) reduction were 76.0 ±â€¯1.12 % and 24.1 ±â€¯1.43 %, respectively. Cr(VI) was reduced to insoluble Cr(III), whereas Fe(II) and S(-II) in mackinawite were finally oxidized to Fe(III) and sulfate. Mackinawite evolved progressively into pyrrhotite. High-throughput 16S rRNA gene sequencing indicated that mackinawite-driven Cr(VI) reduction was mediated through synergistic interactions of microbial consortia; i.e. autotrophs as Acidovorax synthesized volatile fatty acids as metabolic intermediates, which were consumed by Cr(VI) reducers as Geobacter. Genes encoding enzymes for S oxidation (soxB) and Cr(VI) reduction (chrA, yieF) were upregulated. Cytochrome c participating in Fe(II) oxidation increased significantly. This work advances the development of sustainable techniques for Cr(VI) polluted groundwater remediation.

Molecular biogeography of planktonic and benthic diatoms in the Yangtze River.

BACKGROUND: Diatoms are of great significance to primary productivity in oceans, yet little is known about their biogeographic distribution in oligotrophic rivers. RESULTS: With the help of metabarcoding analysis of 279 samples from the Yangtze River, we provided the first integral biogeographic pattern of planktonic and benthic diatoms over a 6030 km continuum along the world's third largest river. Our study revealed spatial dissimilarity of diatoms under varying landforms, including plateau, mountain, foothill, basin, foothill-mountain, and plain regions, from the river source to the estuary. Environmental drivers of diatom communities were interpreted in terms of photosynthetically active radiation, temperature, channel slope and nutrients, and human interference. Typical benthic diatoms, such as Pinnularia, Paralia, and Aulacoseira, experienced considerable reduction in relative abundance downstream of the Three Gorges Dam and the Xiluodu Dam, two of the world's largest dams. CONCLUSIONS: Our study revealed that benthic diatoms are of particular significance in characterizing motile guild in riverine environments, which provides insights into diatom biogeography and biogeochemical cycles in large river ecosystems.

Hydrodynamic X Waves.

Stationary wave groups exist in a range of nonlinear dispersive media, including optics, Bose-Einstein condensates, plasma, and hydrodynamics. We report experimental observations of nonlinear surface gravity X waves, i.e., X-shaped wave envelopes that propagate over long distances with constant form. These can be described by the 2D+1 nonlinear Schrödinger equation, which predicts a balance between dispersion and diffraction when the envelope (the arms of the X) travel at ±arctan(1/sqrt[2])≈±35.26° to the carrier wave. Our findings may help improve understanding the lifetime of extremes in directional seas and motivate further studies in other nonlinear dispersive media.

Global heat stress on health, wildfires, and agricultural crops under different levels of climate warming.

The effects of heat stress are spatially heterogeneous owing to local variations in climate response, population density, and social conditions. Using global climate and impact models from the Inter-Sectoral Impact Model Intercomparison Project, our analysis shows that the frequency and intensity of heat events increase, especially in tropical regions (geographic perspective) and developing countries (national perspective), even with global warming held to the 1.5 °C target. An additional 0.5 °C increase to the 2 °C warming target leads to >15% of global land area becoming exposed to levels of heat stress that affect human health; almost all countries in Europe will be subject to increased fire danger, with the duration of the fire season lasting 3.3 days longer; 106 countries are projected to experience an increase in the wheat production-damage index. Globally, about 38%, 50%, 46%, 36%, and 48% of the increases in exposure to health threats, wildfire, crop heat stress for soybeans, wheat, and maize could be avoided by constraining global warming to 1.5 °C rather than 2 °C. With high emissions, these impacts will continue to intensify over time, extending to almost all countries by the end of the 21st century: >95% of countries will face exposure to health-related heat stress, with India and Brazil ranked highest for integrated heat-stress exposure. The magnitude of the changes in fire season length and wildfire frequency are projected to increase substantially over 74% global land, with particularly strong effects in the United States, Canada, Brazil, China, Australia, and Russia. Our study should help facilitate climate policies that account for international variations in the heat-related threats posed by climate change.