A comprehensive analysis of submarine groundwater discharge and nutrient fluxes in the Bohai Sea, China.

Groundwater discharge and associated nutrient fluxes in the Bohai Sea, China has attracted great attention, but most studies lacked high spatial resolution for the whole sea. As the largest semi-enclosed sea in China, the Bohai Sea is confronted with strong environmental pollution problems such as eutrophication induced by terrestrial nutrient inputs. However, the role of SGD has not been evaluated well for the whole Bohai Sea. In this study, stable isotopes (hydrogen and oxygen), radioactive isotope (228Ra), salinity, and temperature were combined to trace the diluted seawater. Mass balances of 228Ra, oxygen isotope, and salinity were used to quantify SGD and nutrient fluxes to the Bohai Sea. The estimated submarine fresh groundwater discharge (SFGD) and SGD to the Bohai Sea were (6.0 ± 0.5) × 109 and (2.7 ± 1.6) × 1011 m3 a-1, respectively. SFGD represents 10 % to 11 % of the total river discharge and SGD is about 2 to 8 folds of the total river discharge to the sea. Moreover, SGD derived dissolved nutrients to the Bohai Sea were (4.8 ± 4.0) × 1010 mol a-1 for dissolved inorganic nitrogen, (1.9 ± 1.7) × 1010 mol a-1 for dissolved inorganic phosphorus, and (6.7 ± 5.5) × 1010 mol a-1 for silicon. These nutrient inputs were about 10 to 20 folds of the total riverine inputs. Overall, this study underscores the importance of evaluating SGD to better understand the terrestrial imported nutrients in regional scale.

The changing nature of groundwater in the global water cycle.

In recent decades, climate change and other anthropogenic activities have substantially affected groundwater systems worldwide. These impacts include changes in groundwater recharge, discharge, flow, storage, and distribution. Climate-induced shifts are evident in altered recharge rates, greater groundwater contribution to streamflow in glacierized catchments, and enhanced groundwater flow in permafrost areas. Direct anthropogenic changes include groundwater withdrawal and injection, regional flow regime modification, water table and storage alterations, and redistribution of embedded groundwater in foods globally. Notably, groundwater extraction contributes to sea level rise, increasing the risk of groundwater inundation in coastal areas. The role of groundwater in the global water cycle is becoming more dynamic and complex. Quantifying these changes is essential to ensure sustainable supply of fresh groundwater resources for people and ecosystems.

Long-term gridded land evapotranspiration reconstruction using Deep Forest with high generalizability.

Previous datasets have limitations in generalizing evapotranspiration (ET) across various land cover types due to the scarcity and spatial heterogeneity of observations, along with the incomplete understanding of underlying physical mechanisms as a deeper contributing factor. To fill in these gaps, here we developed a global Highly Generalized Land (HG-Land) ET dataset at 0.5° spatial resolution with monthly values covering the satellite era (1982-2018). Our approach leverages the power of a Deep Forest machine-learning algorithm, which ensures good generalizability and mitigates overfitting by minimizing hyper-parameterization. Model explanations are further provided to enhance model transparency and gain new insights into the ET process. Validation conducted at both the site and basin scales attests to the dataset's satisfactory accuracy, with a pronounced emphasis on the Northern Hemisphere. Furthermore, we find that the primary driver of ET predictions varies across different climatic regions. Overall, the HG-Land ET, underpinned by the interpretability of the machine-learning model, emerges as a validated and generalized resource catering to scientific research and various applications.

Uncovering the processes of microbial community assembly in the near-surface sediments of a climate-sensitive glacier-fed lake.

Glacier-fed lakes are characterized by cold temperatures, high altitudes, and nutrient-poor conditions. Despite these challenging conditions, near-surface sediments of glacier-fed lakes harbor rich microbial communities that are critical for ecosystem functioning and serve as a bridge between aquatic ecology and the deep subsurface biosphere. However, there is limited knowledge regarding the microbial communities and their assembly processes in these sediments, which are highly vulnerable to climate change. To fill this knowledge gap, this study systematically analyzed environmental variables, microbial communities, diversity, co-occurrence relationships, and community assembly processes in the near-surface sediments of a glacier-fed lake in the Tibetan Plateau. The results revealed distinct vertical gradients in microbial diversity and subcommunities, highlighting the significant influence of selection processes and adaptive abilities on microbial communities. Specifically, specialists played a crucial role within the overall microbial communities. Microbial assembly was primarily driven by homogeneous selection, but its influence declined with increasing depth. In contrast, homogenizing dispersal showed an opposite pattern, and the bottom layer exhibited heterogeneous selection and undominated processes. These patterns of microbial assembly were primarily driven by environmental gradients, with significant contributions from processes associated to ammonium and organic matter deposition, as well as chemical precipitation in response to a warming climate. This study enhances our understanding of the microbial communities and assembly processes in the near-surface sediments of glacier-fed lakes and sheds light on geo-microbiological processes in climate-sensitive lacustrine sediments.

A new model to predict soil thermal conductivity.

Thermal conductivity is a basic parameter of soil heat transferring, playing an important role in many fields including groundwater withdrawal, ground source heat pump, and heat storage in soils. However, it usually requires a lot of time and efforts to obtain soil thermal conductivity. To conveniently obtain accurate soil thermal conductivity, a new model describes the relationship between soil thermal conductivity (λ) and degree of saturation (Sr) was proposed in this study. Dry soil thermal conductivity (λdry) and saturated soil thermal conductivity (λsat) were described using a linear expression and a geometric mean model, respectively. A quadratic function with one constant was added to calculate λ beyond the lower λdry and upper λsat limit conditions. The proposed model is compared with five other frequently used models and measured data for 51 soil samples ranging from sand to silty clay loam. Results show that the proposed model match the measured data well. The proposed model can be used to determine soil thermal conductivity of a variety of soil textures over a wide range of water content.

Subglacial Meltwater Recharge in the Dongkemadi River Basin, Yangtze River Source Region.

Glaciers on the Tibetan Plateau play an important role in the local hydrological cycle. However, there are only few studies on groundwater in the alpine basins in the Tibetan Plateau which considered the effects of glaciers. Glaciers are extensively distributed in the Dongkemadi River Basin, which is a representative alpine basin in the Yangtze River source region. This study focuses on building a numerical groundwater flow model with glaciations using HydroGeoSphere (HGS) to simulate subglacial meltwater recharge to groundwater in the Dongkemadi River Basin in response to future climate changes. Effects of hydraulic conductivity, precipitation, and temperature on subglacial meltwater recharge to groundwater were discussed. Glacier changes in the future 50 years were predicted under different climate change scenarios. Results show that: (1) the average thickness of the glacier will change significantly; (2) the simulated rate of annual mean subglacial meltwater recharge to groundwater is 4.58 mm, which accounts for 6.33% of total groundwater recharge; and (3) hydraulic conductivity has the largest influence on subglacial meltwater recharge to groundwater, followed by temperature and precipitation. Results of this study are also important to sustainable water resource usage in the Yangtze River source region.

Health impacts of indoor air pollution from household solid fuel on children and women.

The inefficient and incomplete combustion of solid fuel (SF) is associated with high levels of indoor air pollutants leading to 3.55 million deaths annually. The risk is higher in women and children, due to their higher exposure duration and unique physical properties. The current article aims to provide a critical overview regarding the use of solid fuel, its associated pollutants, their toxicity mechanisms and, most importantly the associated health impacts, especially in women and children. Pollutants associated with SF mostly include polycyclic aromatic hydrocarbons, particulate matter, nitrous oxide, carbon monoxide and sulfur dioxide, and their concentrations are two- to threefold higher in indoor environments. These pollutants can lead to a variety of health risks by inducing different toxicity mechanisms, such as oxidative stress, DNA methylation, and gene activation. Exposed children have an increased prevalence of low birth weight, acute lower respiratory tract infections, anemia and premature mortality. On the other hand, lung cancer, chronic obstructive pulmonary disease and cardiovascular diseases are the major causes of disability and premature death in women. Indoor air pollution resulting from SF combustion is a major public health threat globally. To reduce the risks, it is important to identify future research gaps and implement effective interventions and policies.

Water quality and health risk assessment of the water bodies in the Yamdrok-tso basin, southern Tibetan Plateau.

Water resources in good quality guarantee the primary condition for the maintenance and development of the natural ecosystem and human society. Water quality status and health risk of the lake water bodies in the national nature reserve, the Yamdrok-tso basin, in the southern Tibetan Plateau are assessed by 25 water parameters including 12 heavy metal(loid)s. Results reveal that the lake water bodies possess relatively high pH (9.68), high concentrations of F (1.66 mg/L), Cu (13.92 µg/L), As (41.60 µg/L), Pb (26.69 µg/L), and U (19.53 µg/L), and a low value of dissolved oxygen (19.30%). The pollution indices (heavy metal pollution index of 0.88-22.88, heavy metal evaluation index of 0.18-3.75, and the degree of contamination of -8.82 to -5.25) demonstrate that the lake water bodies are in a low pollution level with respect to heavy metal(loid)s. The evaluation of water quality based on the fuzzy comprehensive assessment method suggests that 75.56% of the water samples meet the regulation of the China National Standard for water resources in national nature reserves. Health risk assessment shows that potential hazards exist on this region when the residents under long-term exposure to the lake water through oral and dermal pathways, of which children and adults are mostly exposed to As and F for non-carcinogenic and As for carcinogenic risks, especially for children. Results of this study contribute to targeted water resources management in the national nature reserves.

Environmental emission, fate and transformation of microplastics in biotic and abiotic compartments: Global status, recent advances and future perspectives.

The intensive use and wide-ranging application of plastic- and plastic-derived products have resulted in alarming levels of plastic pollution in different environmental compartments worldwide. As a result of various biogeochemical mechanisms, this plastic litter is converted into small, ubiquitous and persistent fragments called microplastics (<5 mm), which are of significant and increasing concern to the scientific community. Microplastics have spread across the globe and now exist in virtually all environmental compartments (the soil, atmosphere, and water). Although these compartments are often considered to be independent environments, in reality, they are very closely linked. Ample research has been done on microplastics, but there are still questions and knowledge gaps regarding the emission, occurrence, distribution, detection, environmental fate and transport of MPs in different environmental compartments. The current article is intended to provide a systematic overview of MP emissions, pollution conditions, sampling and analytical approaches, transport, fates and transformation mechanisms in different environmental compartments. It also identifies research gaps and future research directions and perspectives.

Life stages and morphological variations of Limnocythere inopinata (Crustacea, Ostracoda) from Lake Jiang-Co (northern Tibet): a bioculture experiment.

Limnocythere inopinata (Baird, 1843) is a Holarctic species, abundant in a number of Recent and fossil ostracod assemblages, and has many important taxonomic and (paleo)ecological applications. However, the life cycle and morphological characteristics of the living L. inopinata are still unclear. A bioculture experiment was designed to study life stages and morphological variations from stage A-8 to adult in this species. The living animals were collected from Lake Jiang-Co, in the northern Tibetan Plateau. Results reveal that this species possesses a special growth pattern with the maximum size increase occurring at the transition from the instars A-5 to A-4. The growth pattern deviates from Brooks' rule and one population from Lake Dali, eastern Mongolian Plateau. This suggests that the life history of L. inopinata may be influenced by environmental factors. Some morphological differences between Lake Jiang-Co and European populations of L. inopinata are also uncovered. Therefore, a detailed morphological description of this population is provided, but refrain from erecting a new species at the present stage because those differences appear to be inconsistent.

Localization and characterization of a putative cysteine desulfurase in Chlamydia psittaci.

Chlamydia psittaci is an obligate intracellular pathogen with a biphasic developmental life cycle. It is auxotrophic for a variety of essential metabolites and obtains amino acids from eukaryotic host cells. Chlamydia can develop inside host cells within chlamydial inclusions. A pathway secreting proteins from inclusions into the host cellular cytoplasm is the type III secretion system (T3SS). The T3SS is universal among several Gram-negative bacteria. Here, we show that CPSIT_0959 of C. psittaci is expressed midcycle and secreted into the infected cellular cytoplasm via the T3SS. Recombinant CPSIT_0959 possesses cysteine desulfurase and PLP-binding activity, which removes sulfur from cysteine to produce alanine, and helps chlamydial replication. Our study shows that CPSIT_0959 improve the infectivity of offspring elementary bodies and seems to promote the replication by its product. This phenomenon has inhibited by the PLP-dependent enzymes inhibitor. Moreover, CPSIT_0959 increased expression of Bim and tBid, and decreased the mitochondrial membrane potential of host mitochondria to induce apoptosis in the latecycle for release of offspring. These results demonstrate that CPSIT_0959 has cysteine desulfurase and PLP-binding activity and is likely to contribute to apoptosis of the infected cells via a mitochondria-mediated pathway to improve the infectivity of progeny.

Treponema pallidum flagellins stimulate MMP-9 and MMP-13 expression via TLR5 and MAPK/NF-κB signaling pathways in human epidermal keratinocytes.

Syphilis is a chronic disease caused by Treponema pallidum and the pathogenesis is still unclear. T. pallidum infection induced inflammatory responses are involved in the immunopathological damage in skin and other tissues. Flagellin, the monomeric subunit of bacterial flagella, is a classic pathogen associated molecular patterns (PAMPs) that interacts to TLR5 and induces inflammatory responses. Keratinocytes, as immune sentinels recognize the PAMPs via TLRs, play an important role in skin innate immune response. Matrix metalloproteinases (MMPs) expressed by keratinocytes are involved in skin inflammatory responses and promoting pathogens invasion. In this study, we demonstrate that FlaB1, FlaB2 and FlaB3, the flagellins of T. pallidum, induced MMP-9 and MMP-13 production in human immortalized keratinocytes cell line HaCaT. Silencing of TLR5, but not TLR2 and TLR4 attenuated MMP-9 and MMP-13 expressions induced by T. pallidum flagellins. MMP-9 and MMP-13 expressions were also be abrogated by transfection with a dominant negative (DN) plasmid of MyD88. We also found that treatment of HaCaT cells with FlaB1, FlaB2 and FlaB3 activate the MAPK and NF-κB signaling pathways. Inhibited of ERK, JNK, p38 and NF-κB suppressed MMP-9 expression induced by the FlaB1. MMP-13 expression was found to be suppressed by pretreatment with inhibitors of ERK, JNK and NF-κB, but not p38. These findings demonstrate that T. pallidum flagellins (FlaB1, FlaB2 or FlaB3) can stimulate MMP-9 and MMP-13 expression through TLR5 and MAPK/NF-κB signaling pathways in human epidermal keratinocytes, which could contribute to the pathogenesis of T. pallidum infection.

Treponema pallidum flagellins elicit proinflammatory cytokines from human monocytes via TLR5 signaling pathway.

The tissue damage caused by syphilis infection may be associated with inflammation. However, the virulence factors of Treponema pallidum are still unclear, nor are the molecular mechanisms for leading to the productions of proinflammatory cytokines. Flagellin, a classic pathogen-associated molecular pattern (PAMP), is a potent immunogen that induces inflammation. In the present study, we have demonstrated that stimulations of human monocytes with Treponema pallidum FlaB1, FlaB2, and FlaB3 result in the up regulation of interleukin (IL)-6 and IL-8. Moreover, silencing of the Toll-like receptor 5 (TLR5) gene by using small interfering RNA was found to abrogate the T. pallidum flagellins-induced IL-6 and IL-8 expressions. Similarly, transfection with the dominant negative plasmid encoding MyD88 (pDeNy-hMyD88) was also giving rise to the down regulation of IL-6 and IL-8. We further investigated the relative contributions of mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) signaling to transcriptions and translations of IL-6 and IL-8. Western Blot and immuno fluorescence experiments revealed that flagellins-mediated IL-6 and IL-8 expressions are heavily dependent on ERK, p38, and NF-κB. In addition, inhibitions of p38 kinase, ERK, and NF-κB were found to attenuate the productions of IL-6 and IL-8. Taken together, our results indicate that T. pallidum flagellins can upregulate IL-6 and IL-8 generations via TLR5 and MAPK/NF-κB signaling pathways in THP-1 cells, which will improve our understanding of the pathogenesis of T. pallidum.

Treponema pallidum flagellin FlaA2 induces IL-6 secretion in THP-1 cells via the Toll-like receptor 2 signaling pathway.

Treponema pallidum subsp. pallidum membrane proteins are considered as potent inducers in the initiation and development of inflammation. In the present study, the mechanism that leads to the production of interleukin 6 (IL-6), one of the key proinflammatory cytokines, by human monocytic THP-1 cells when these cells are treated with T. pallidum flagellin FlaA2 was investigated. Stimulation with flagellin FlaA2 can induce IL-6 expression in human monocytes and augment the phosphorylation of ERK, p38, and NF-κB, but has no effect on the phosphorylation of JNK. Likewise, FlaA2-induced IL-6 production was found to be attenuated by inhibitors for ERK, p38, and NF-κB, but not by JNK inhibitor. Immunofluorescence analysis showed that flagellin FlaA2 could stimulate the translocation of IκBα from the cytosol to the nucleus, and this phenomenon could be inhibited by the specific inhibitor BAY11-7082. FlaA2-induced IL-6 expression was also proved to be abrogated by transfection with dominant negative (DN) plasmid of MyD88. We further demonstrated that transfection with DN-TLR2 was sufficient to attenuate IL-6 expression and the phosphorylation of ERK, p38, and IκBα. These results suggest that flagellin FlaA2 induces IL-6 production via signaling pathways involving TLR2, MyD88, ERK, p38, and NF-κB in monocytes, which could contribute to the pathogenesis of T. pallidum.

A novel ELISA using a recombinant outer membrane protein, rTp0663, as the antigen for serological diagnosis of syphilis.

BACKGROUND: The lack of Treponema pallidum-specific antigens with highly accurate diagnosis makes the diagnosis of syphilis challenging. METHODS: A soluble recombinant version of a new diagnostic protein Tp0663 has been produced. The serodiagnostic potential of this protein was assessed by screening 3326 serum samples simultaneously evaluated by rapid plasma reagin and T. pallidum particle agglutination tests. Kappa (κ) coefficients were used to compare the concordance between clinical diagnosis and the Tp0663-based ELISA or the ARCHITECT Syphilis TP chemiluminescent immunoassay (Abbott GmbH and Co. KG). RESULTS: Using the results of clinical diagnosis as the gold standard, the sensitivity and specificity of Tp0663 were found to be 98.83% (95% confidence interval (CI) 96.61-99.60%) and 100% (95% CI 99.88-100%), respectively. In comparison, the ARCHITECT Syphilis TP assay was found to have a lower sensitivity (97.27%, 95% CI 94.46-98.67%) and specificity (99.61%, 95% CI 99.32-99.78%). In particular, the ARCHITECT Syphilis TP exhibited a false-positive rate of 0.39%. Moreover, the ELISA was in perfect agreement with the gold standard, with a κ value of 0.99, comparable to that of ARCHITECT Syphilis TP (0.96). CONCLUSION: These results identified Tp0663 as a novel serodiagnostic candidate with great potential for developing novel tests for the diagnosis of syphilis.

Evaluation of FlaB1, FlaB2, FlaB3, and Tp0463 of Treponema pallidum for serodiagnosis of syphilis.

Syphilis is a multistage disease caused by the invasive spirochete Treponema pallidum subsp. pallidum, and accurate diagnosis is important for the prevention and treatment of syphilis. Here, to identify appropriate diagnostic antigens for serodiagnosis of syphilis, 6 recombinant proteins were expressed in Escherichia coli and purified, including flagellins (FlaB1 [Tp0868], FlaB2 [Tp0792], and FlaB3 [Tp0870]), Tp0463, Tp0751, and Tp1038. The sensitivities were determined by screening sera from individuals with primary (n=82), secondary (n=115), latent (n=105), and congenital (n=65) syphilis. The specificities were determined by screening sera from uninfected controls (n=30) and potentially cross-reactive infections including Lyme disease (n=30), leptospirosis (n=5), and hepatitis B (n=30). Our data showed that FlaB1, FlaB2, FlaB3, Tp0463, and Tp1038 exhibited higher overall sensitivities and specificities for detecting IgG antibody, with 95.4% and 98.9%, 92.6% and 95.8%, 95.1% and 95.8%, 92.6% and 97.9%, and 95.9% and 98.9%, respectively. In contrast, Tp0751 demonstrated only an overall sensitivity of 39.2%. For comparison, the sensitivity and specificity of Architect Syphilis TP were determined to be 98.1% and 93.7%, respectively. In addition, FlaB1, FlaB2, FlaB3, and Tp0463 demonstrated excellent performance for detecting IgM antibody in primary and congenital syphilis, with sensitivities of 76.8% and 83.1%, 72.0% and 87.7%, 74.4% and 89.2%, and 64.6% and 75.3%, respectively. These results indicate that FlaB1, FlaB2, FlaB3, and Tp0463 could be as novel diagnostic candidates for serodiagnosis of syphilis.

Increased Water Storage in the Qaidam Basin, the North Tibet Plateau from GRACE Gravity Data.

Groundwater plays a key role in maintaining the ecology and environment in the hyperarid Qaidam Basin (QB). Indirect evidence and data from sparse observation wells suggest that groundwater in the QB is increasing but there has been no regional assessment of the groundwater conditions in the entire basin because of its remoteness and the severity of the arid environment. Here we report changes in the spatial and temporal distribution of terrestrial water storage (TWS) in the northern Tibetan Plateau (NTP) using Gravity Recovery and Climate Experiment (GRACE) data. Our study confirms long-term (2003-2012) TWS increases in the NTP. Between 2003 and 2012 the TWS increased by 88.4 and 20.6 km3 in the NTP and the QB, respectively, which is 225% and 52% of the capacity of the Three Gorges Reservoir, respectively. Soil and water changes from the Global Land Data Assimilation System (GLDAS) were also used to identify groundwater storage in the TWS and to demonstrate a long-term increase in groundwater storage in the QB. We demonstrate that increases in groundwater, not lake water, are dominant in the QB, as observed by groundwater levels. Our study suggests that the TWS increase was likely caused by a regional increase in precipitation and a decrease in evaporation. Degradation of the permafrost increases the thickness of the active layers providing increased storage for infiltrated precipitation and snow and ice melt water, which may also contribute to the increased TWS. The huge increase of water storage in the NTP will have profound effects, not only on local ecology and environment, but also on global water storage and sea level changes.

Numerical study of variable-density flow and transport in unsaturated-saturated porous media.

Dense contaminant or solute transport in the unsaturated-saturated aquifer commonly exists in the natural environment. However, the influence of hydraulic properties of the unsaturated soil on penetration process of variable density flow in an unsaturated-saturated aquifer system is rarely investigated. In this study, a variable density, variably saturated flow and transport model based on FEFLOW is used to systematically investigate the penetration process of the solute through the unsaturated-saturated aquifer system, with a focus on the influence of the hydraulic parameters of the unsaturated soil on the penetration process. Vertical center of mass, and its speed and acceleration, are used to identify different stages of the penetration process through the unsaturated-saturated aquifer. The hydraulic parameters in the van Genuchten-Mualem model (VGM) affect the water content distribution in the unsaturated zone, subsequently the penetration time through the unsaturated zone. Through influencing the thickness of the transition zone (0.1-0.9 maximum concentration of the plume) when the plume reaches the water table, the hydraulic parameters affect the accumulation time of the solute at the boundary layer in the saturated zone. Thus, the process in not only the unsaturated but also the saturated zones is influenced by the change of the hydraulic properties of the unsaturated zone. Furthermore, the results show that the instabilities start to occur at the zone with high water content (90% of maximum saturation) in the capillary fringe. Freshwater intrudes into the zone with high water content when fingers are completely developed at the entire system. The length of freshwater intrusion above the water table has a negative correlation with the fitting parameter alpha in the VGM model. The influence of the density difference of the solute on the penetration processes is insignificant in the unsaturated zone but significant in the saturated zone. Sensitive analysis for the hydraulic properties of the unsaturated soil on the penetration process shows that pore size distribution index is the main factor influencing the penetration time through the unsaturated zone, the penetration time through the entire aquifer, the accumulation time at the boundary layer, and the development time of the fingers. Two other parameters, fitting parameter alpha and residual saturation, have minor effects.