Combined effects of climatic change and hydrological conditions on thermal regimes in a deep channel-type reservoir.

The thermal regime in large reservoirs plays a significant role in the water quality and ecosystem succession; however, little is known about the impacts of regional climate changes and hydrological conditions on a sizeable stratified reservoir with strong inflow conditions, i.e., the Xiangjiaba Reservoir. Using measured data from 2014 to 2018, the monthly and seasonal variations of the water temperature, thermal stability, and their influencing factors were addressed by using empirical models. The results showed substantial variability and seasonality in the reservoir water temperature, which correlated highly with the air temperature, inflow water temperature, and discharge. Correspondingly, there was a seasonal varying thermal stratification in the reservoir's yearly cycle, with its duration being up to 4 ~ 5 months, the maximum surface-bottom water temperature difference being up to 7 ~ 10 °C. There were significant positive correlations between Schmidt's stability index of the thermal structure and inflow-reservoir temperature difference and the surface-bottom temperature differences, while negative correlations with large discharge. Moreover, the inflow tends to influence thermal stability by retaining hypolimnion cold water, with its maximum bottom hysteresis residence time being up to ~ 4 months. Research findings indicated that climate warming in the recent 30 years (1988 ~ 2017) would cause a 0.213 °C/decade and 0.153 kJ/m2/decade increase in reservoir surface water temperature and Schmidt's stability index, respectively. Among these variations, the inflow temperature increase caused by climate change accounted for the largest proportion, i.e., 0.16 °C/decade and 0.115 kJ/m2/decade. Therefore, climate warming significantly affected the thermal regimes in this large reservoir, and the inflow water temperature increase due to warm air was the main factor altering the reservoir's thermal structure. Findings from the present study provide a fresh perspective on how to best optimize the deep channel-type reservoirs' water quality in the face of anticipated climate change.

Microbial diversity accumulates in a downstream direction in the Three Gorges Reservoir.

Organic and inorganic materials migrate downstream and have important roles in regulating environmental health in the river networks. However, it remains unclear whether and how a mixture of materials (i.e., microbial species) from various upstream habitats contribute to microbial community coalescence upstream of a dam. Here we track the spatial variation in microbial abundance and diversity in the Three Gorges Reservoir based on quantitative PCR and 16S rRNA gene high-throughput sequencing data. We further quantitatively assess the relative contributions of microbial species from mainstem, its tributaries, and the surrounding riverbank soils to the area immediately upstream of the Three Gorges Dam (TGD). We found an increase of microbial diversity and the convergent microbial distribution pattern in areas immediately upstream of TGD, suggesting this area become a new confluence for microbial diversity immigrating from upstream. Indeed, the number of shared species increased from upstream to TGD but unique species decreased, indicating immigration of various sources of microbial species overwhelms local environmental conditions in structuring microbial community close to TGD. By quantifying the sources of microbial species close to TGD, we found little contribution from soils as compared to tributaries, especially for sites closer to TGD, suggesting tributary microbes have greater influence on microbial diversity and environmental health in the Three Gorges Reservoir. Collectively, our results suggest that tracking microbial geographic origin and evaluating accumulating effects of microbial diversity shed light on the ecological processes in microbial communities and provide information for regulating aquatic ecological health.

Spatial variation in bacterial biomass, community composition and driving factors across a eutrophic river.

Eutrophication is a global problem, and bacterial diversity and community composition are usually affected by eutrophication. However, limited information on the ecological significance of bacterial community during algae blooms of rivers has been given, more studies should be focused on the bacterial diversity and distribution characteristics in eutrophic rivers. In this study, we explored the spatial variations of bacterial biomass, community structure, and their relationship with environmental factors in the eutrophic Xiangxi River. The content of Chlorophyll (Chl) was about 16 mg/L in the midstream (S2, S3), which was in the range of light eutrophication. Significant spatial variation of bacterial community structure was found at different sites and depths (p < 0.05), and the driving environmental factor was found to be nitrogen, mainly detected as total nitrogen (TN), Kjeldahl nitrogen (KN), and ammonia nitrogen (NH4+) (p < 0.05). The midstream sites had some significantly different bacteria, including algicidal bacteria and dominant lineages during algal blooms. This result was consistent with the functional prediction, where significant higher abundance of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways was associated with algicidal substances in the midstream. At different water depths, some populations adapted to the surface layer, such as the class Flavobacteriia, and others preferred to inhabit in the bottom layer, such as Betaproteobacteria and Acidobacteria. The bacterial biomass was higher in the bottom layer than that in the surface and middle layer, and temperature and pH were found to be the major driving factors. The bacterial diversity increased with the increasing of depths in most sampling sites according to operational taxonomic units (OTUs), Chao1 and ACE indexes, and PO43- was demonstrated to be the most significant factor. In summary, this study offered the evidence for microbial distribution characteristics across different sites and depths in summer, and its relationship with environmental variables in a eutrophic river.

Depth profiles of microplastics in sediments from inland water to coast and their influential factors.

Microplastics, plastic particles with a size smaller than 5 mm, are widely observed in the global environments and pose a growing threat as they accumulate and affect the environments in numerous ways. These particles can be transported from inland water to coast and disperse from surface water to deep sediments, especially the latter, while knowledge of the hidden microplastics in sediment layers is still lacking. Understanding the characteristics and behavior of microplastics in deep sediments from inland water to coast is crucial for estimating the present and future global plastic budget from land to seas. Herein, present knowledge of microplastic sedimentation from inland water to coast is reviewed, with a focus on the physical characteristics of microplastics and environmental factors that affect sedimentation. The abundance, shape, composition, and timeline of microplastics in sediment layers in rivers, floodplains, lakes, estuaries and coastal wetlands are presented. The abundance of microplastics in sediment layers varies across sites and may exhibit opposite trends along depth, and generally the proportion of relatively small microplastics increases with depth, while less is known about the vertical trends in the shape and composition of microplastics. Timeline of microplastics is generally linked to the sedimentation rate, which varies from millimeters to centimeters per year in the reviewed studies. The spatiotemporal characteristics of microplastic sedimentation depend on the settling and erosion of microplastics, which are determined by two aspects, microplastic characteristics and environmental factors. The former aspect includes size, shape and density influenced by aggregation and biofouling, and the latter includes dynamic forces, topographic features, bioturbation and human activities. The comprehensive review of these factors highlights the needs to further quantify the characteristics of microplastic sedimentation and explore the role of these factors in microplastic sedimentation on various spatiotemporal scales.

Longitudinal transport timescales in a large dammed river - The Changjiang River.

As a key component of the global water cycle, river flow transports both freshwater and biotic/abiotic matters from land to sea, while in recent decades its rhythm has been strongly disturbed by human activities, especially damming. Yet little is known about the long-distance transport processes along the world's major fluvial systems and the impact of large dams on their timescales. Here, taking the Changjiang River (Yangtze River) as an example, we built a hydrodynamics-based model to investigate the water age and residence time in the mainstream from the upper reach ~700 km upstream of the Three Gorges Dam (TGD) to the estuary ~1900 km downstream of the TGD. We find that since the mainstream was dammed by the TGD, the water age increases significantly by approximately 2 to 5 times from the estuary to the dam. Downstream of the dam the longitudinal ageing rate of water becomes discordant in an annual cycle, and the replenished discharge in dry season accelerates the water transport. Due to the stationary assumption, the widely applied hydraulic residence time of water is substantially larger and smaller than the age-based dynamic residence time in the large reservoir during the impounding and releasing periods, respectively.

The geochemical behavior of trace metals and nutrients in submerged sediments of the Three Gorges Reservoir and a critical review on risk assessment methods.

Permanently submerged sediment samples (SS) were collected in the center stream of eleven tributaries of Changjiang (Yangtze River) and at eight confluence zones in the Three Gorges Reservoir (TGR) in May and December of 2017. The work showed that aqua regia digestion is a simpler, more reliable and robust method compared to total digestion with hydrofluoric acid (HF) for the determination of trace metals (TMs) in sediment for risk assessment purpose. Our study revealed a remarkable accumulation of TMs at the confluence zones and a trend of their gradual increase toward this zone. The presence of iron and manganese (oxy)hydroxides combined with hydrodynamic conditions created by the Three Gorges Dam (TGD) and its operation are believed to play a crucial role. This work also found that concentrations of [Formula: see text] in May sediment were significantly higher than those in December, which could have been caused by both the cyclic hydrodynamic conditions and the warmer water. TOC and TP were both very low in the sediment. Although TN was 2 times higher than the Lowest Effect Level suggested by the Ontario Ministry of Environment, it is uncertain if it reflects a natural background level or due to anthropogenic activities. A critical discussion is made by comparing the conclusions obtained when using different TMs risk assessment models. Necessary precautions are highly recommended when performing this exercise. In this study, no significant risk from either TMs or nutrients was identified.

Association between effective hepatic blood flow and the severity and prognosis of hepatitis B virus-related acute on chronic liver failure.

BACKGROUND: Hepatic inflammation resulted in hepatocyte necrosis and microcirculatory dysfunction in acute on chronic liver failure (ACLF) with cirrhosis or not. The influence of effective hepatic blood flow (EHBF) on the severity of liver failure has not been fully elucidated. AIM: The aim of this study was to assess the correlation between the EHBF and the severity and the prediction of 90-day mortality rate of hepatitis B virus-related ACLF (HBV-ACLF). METHODS: In this retrospective study, patients hospitalized for HBV-ACLF or decompensated cirrhosis and who underwent an indocyanine green (ICG) clearance test between June 2016 and July 2018 were enrolled. EHBF was measured by the ICG clearance test and patients were categorized into the ACLF without cirrhosis (HBV-ACLF-no-Cir), ACLF with cirrhosis (HBV-ACLF-Cir) and decompensated cirrhosis (HBV-De-Cir). RESULTS: A total of 522 patients (HBV-ACLF-no-Cir: 84, HBV-ACLF-Cir: 111 and HBV-De-Cir: 327) were enrolled. The mean EHBF in the HBV-De-Cir was significantly higher than that in the HBV-ACLF-no-Cir and HBV-ACLF-Cir (0.36 vs. 0.21 vs. 0.20 L/min, P < 0.001). EHBF was significantly correlated with the total bilirubin, prothrombin activity and model for end-stage liver disease (MELD) in the HBV-ACLF-no-Cir. The predicted 90-day mortality rate using the MELD, EHBF, ICG-retention rate at 15 min (R15%) and EHBF-R15% scores were similar. The sensitivity and specificity of the EHBF varied between 68.5-80.2% and 45.8-73.7%, respectively. The EHBF-MELD score had the highest specificity. CONCLUSION: EHBF was significantly lower in the patients with ACLF compared to decompensated cirrhosis. The EHBF were closely related to the severity of HBV-ACLF and can be used for predicting the 90-day mortality rate of HBV-ACLF.

Vertical water renewal in a large estuary and implications for water quality.

Estuaries are a special transition zone subject to both riverine and marine processes, where environmental issues, e.g. water pollution, eutrophication and hypoxia, have become an increasing cause of concern in recent decades. The vertical transport of water and material is an intrinsic process in estuarine environments, with the atmosphere and seabed being the upper and lower boundaries. However, vertical water renewal in estuaries is not fully understood despite its significance to the estuarine environment being widely recognized. In the present study, the vertical water renewal process in a large estuary is investigated using the concept of water age. A three-dimensional water age model is built based on a hydrodynamic model, in which the age of a water parcel is defined as the time interval since it last touched the air-water interface, and thus indicates the renewal duration from the free surface. Water renewal durations, especially when relatively long, can provide insight into environmental and water quality issues, e.g. a low dissolved oxygen (DO), that can have a significant impact on ecosystem functioning. Results showed that the water age in the Pearl River Estuary (PRE) was characterized by significant spatial distributions and seasonal variations, which depends heavily on the water density stratification, as indicated by the Richardson number. During the wet season, the bottom water age was large at the lower reach of the estuary, up to 8 days, whereas the maximum bottom age during the dry season was ~1 day at the upper reach. Based on the quantification of vertical renewal, a new approach was proposed, and used to successfully evaluating DO depletion. The data and method would benefit for future environmental management, eco-biological restoration and related policy-making, especially when oxygen-based pollution is considered.

Modelling the fate and transport of faecal bacteria in estuarine and coastal waters.

This paper details a numerical model developed to predict the fate and transport of faecal bacteria in receiving surface waters. The model was first validated by comparing model predicted faecal bacteria concentrations with available field measurements. The model simulations agreed well with the observation data. After calibration, the model was applied to investigate the effects of different parameters, including: tidal processes, river discharges from the upstream boundaries and bacteria inputs from the upstream boundaries, wastewater treatment works (WwTWs), rivers and combined sewer overflows (CSO), on the concentrations of faecal bacteria in the Ribble Estuary. The results revealed that the tide and upstream boundary bacteria inputs were the primary factors controlling the distribution of faecal bacteria. The bacteria inputs from the WwTWs in the model domain were generally found not to have a significant impact on distribution of faecal bacteria in the estuary.

Modelling importance of sediment effects on fate and transport of enterococci in the Severn Estuary, UK.

The paper detailed a water quality modelling study of a hyper-tidal estuary, undertaken to assess the impact of various bacteria input loads on the receiving waters in a coastal basin in the UK, by using the model developed in previous study of the same authors enterococci, used as the indicators for bathing water quality under the new European Union (EU) Bathing Water Directive, were numerically modelled using a hydro-environmental model. In particular, the numerical model used in this study includes the effects of sediment on bacteria transport processes in surface water. Finally, the importance of sediment bacteria inputs on the bathing water quality was also investigated under different weather and tidal condition. During spring tide, the bacteria input from the bed sediments are dominant for both wet and dry weather conditions. During neap tides and during dry weather conditions the inputs of bacteria from the bed sediment were still dominant, but during wet weather conditions the inputs from river were dominant. Under different tidal flow conditions some parameters had a more significant role than others. During high flow conditions the sediment re-suspensions processes were dominant, therefore the bed bacteria concentrations played a dominant role on the overall bacteria concentration levels in the water column. In contrast, during low flow conditions sediment deposition prevails and bacteria are removed from the water column. The partition coefficient was found to be more important than the bed bacteria concentrations, during low flow conditions.

Amniotic-fluid-derived mesenchymal stem cells overexpressing interleukin-1 receptor antagonist improve fulminant hepatic failure.

Uncontrolled hepatic immunoactivation is regarded as the primary pathological mechanism of fulminant hepatic failure (FHF). The major acute-phase mediators associated with FHF, including IL-1ß, IL-6, and TNF-α, impair the regeneration of liver cells and stem cell grafts. Amniotic-fluid-derived mesenchymal stem cells (AF-MSCs) have the capacity, under specific conditions, to differentiate into hepatocytes. Interleukin-1-receptor antagonist (IL-1Ra) plays an anti-inflammatory and anti-apoptotic role in acute and chronic inflammation, and has been used in many experimental and clinical applications. In the present study, we implanted IL-1Ra-expressing AF-MSCs into injured liver via the portal vein, using D-galactosamine-induced FHF in a rat model. IL-1Ra expression, hepatic injury, liver regeneration, cytokines (IL-1ß, IL-6), and animal survival were assessed after cell transplantation. Our results showed that AF-MSCs over-expressing IL-1Ra prevented liver failure and reduced mortality in rats with FHF. These animals also exhibited improved liver function and increased survival rates after injection with these cells. Using green fluorescent protein as a marker, we demonstrated that the engrafted cells and their progeny were incorporated into injured livers and produced albumin. This study suggests that AF-MSCs genetically modified to over-express IL-1Ra can be implanted into the injured liver to provide a novel therapeutic approach to the treatment of FHF.

A Novel prognostic scoring system to predict 3-month mortality risk in patients with acute-on-chronic liver failure in hepatitis B: a retrospective cohort study.

PURPOSE: The present study was done to establish an objective, sensitive prognostic scoring system and to determine the applicability of this model in predicting the 3-month mortality of patients with acute-on-chronic liver failure in hepatitis B (ACLFB). METHODS: We developed a novel prognostic scoring system, calculated from six clinical indices including serum total bilirubin, prothrombin activity, serum creatinine, hepatic encephalopathy, infections, and the depth of ascites from 499 patients with ACLFB. Differences in the sensitivity, specificity, and practicality of a Novel prognostic scoring system and the model of end-stage liver disease (MELD) were analyzed. RESULTS: The areas under the receiver operating characteristic curve (ROC) for the Novel scoring systems and MELD scoring systems were 0.967 (95% CI, 0.956-0.977) and 0.900 (95% CI, 0.878-0.922), respectively. The analysis of the ROC curve indicated that the Novel scoring systems were an exact, pertinent, and objective prognostic model with greater accuracy than the MELD. In the Novel scoring systems, the survival rate of these patients whose scores ranged from 2 to 6 was 98.80%, while for those whose scores point at 7 and 15, the mortality rates were 8.70% (2/23) and 95.45% (21/22), respectively, and the mortality rate of these patients whose scores were 16 and above was 100.00%. However, in the MELD prognostic scoring systems, there were no score ranges with 100.00% survival rate. CONCLUSIONS: We developed an objective, pertinent, and sensitive prognostic scoring system that predicted the 3-month mortality of patients with ACLFB with greater accuracy than the MELD.

Numerical modelling of sediment-bacteria interaction processes in surface waters.

Faecal bacteria exist in both free-living and attached forms in surface waters. The deposition of sediments can take faecal bacteria out of the water column and to the bed. The sediments can subsequently be re-suspended into the water column, which can then lead to the re-suspension of the faecal bacteria of the attached form back into the water column, where it may desorb from the sediments. Therefore, the fate and transport of faecal bacteria is highly related to the governing sediment transport processes, particularly where these processes are significant. However, little attempt has been made to model such processes in terms of predicting the impact of the sediment fluxes on faecal bacteria levels. Details are given of the refinement of a numerical model of faecal bacteria transport, where the sediment transport processes are significant. This model is based on the model DIVAST (Depth Integrated Velocities And Solute Transport). Analytical solutions for steady and uniform flow conditions were derived and used to test the sediment-bacteria interaction model. After testing the sediment-bacteria interaction model favourably against known results, the model was then set up for idealized case studies to investigate the effects of sediment on bacteria concentrations in the water column. Finally the model was applied to a simplified artificial flooding study to investigate the impact of suspended sediment fluxes on the corresponding bacteria transport processes. The model predictions have proved to be encouraging, with the results being compared to field measurements.

Modelling the fate and transport of nickel in the mersey estuary.

Modelling heavy metals in estuarine environments is extremely complex for various reasons; one of the primary complicating factors is that metals exist in two phases, dissolved and particulate bound. Dynamic changes in water chemistry, and in particular salinity, affect the partitioning of metals between the two phases and hence make it difficult to determine the relative fractions of each phase. A relatively simple approach was developed to relate variations in partition coefficient for Ni to salinity fluctuations in the Mersey Estuary. The functional relationship developed between partition coefficient and salinity departs from the traditional exponential type curve, providing a more realistic relationship.A numerical model was then developed for predicting the transport and distribution of Ni about the Mersey Estuary. The model couples transport of metals throughout the water along with incorporating the chemical processes controlling how nickel is fractioned between dissolved and particulate phases through the newly developed partition coefficient relationship. Model predictions of dissolved Ni along the longitudinal axis of the estuary were compared with measurements of Ni for two events; very good correlation was obtained between the model results and the data.