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The acceleration of water cycle processes in the context of global warming will exacerbate the frequency and intensity of extreme events and predispose to drought and flood disasters (DFD). The Yellow River Basin (YRB) is one of the basins with significant and sensitive impacts of climate change, comprehensive assessment and prediction of its DFD risk are of great significance for ecological protection and high-quality development. This study first constructed an evaluation index system for drought disaster risk and flood disaster risk based on hazard, vulnerability, exposure and the role of large reservoirs. Secondly, the weights of each evaluation index are established by the analytic hierarchy process. Finally, based on the four-factor theory of disasters, an evaluation model of DFD risk indicators is established. The impact of large reservoirs on DFD risk in the YRB is analyzed with emphasis. The results show that from 1990 to 2020, the drought disaster risk in the YRB is mainly distributed in the source area of the Yellow River and the northwest region (11.26-15.79 %), and the flood disaster risk is mainly distributed in the middle and lower reaches (30.04-31.29 %). Compared to scenarios without considering large reservoirs, the area at risk of high drought and high flood is reduced by 45.45 %, 44.22 % and 31.29 % in 2000, 2010 and 2020, respectively. Large reservoirs in the YRB play an important role in mitigating DFD risk, but their role is weakened with the enhancement of the emission scenario. Under the influence of different scenario models, the DFD risk in the YRB in 2030 and 2060 will increase, and the area of high drought and high flood risk in the middle and upper reaches of the basin will increase by 0.26-25.15 %. Therefore, the YRB should play the role of large reservoirs in DFD risk defense in its actions to cope with future climate change, while improving non-engineering measures such as early warning and emergency management systems to mitigate the impacts of disasters., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The effects of tree species on bacterial community structure have attracted much attention, but few studies have been done in natural mixed forests. In this study, we selected 12 sampling sites in the subtropical natural mixed forest (mainly distributed by Chinese sweet gum, chestnut, Oriental oak, Masson pine, Chinese fir, etc.). The fermentation layer (OF) and humified layer (OH) were mixed as forest floor samples, and the topsoil samples (0-10 cm) were taken. Bacterial composition was studied by 16S rRNA gene sequencing. Coniferous canopy area ratio (P c ), broadleaved and shrubby canopy area ratio (P hwd ), elevation, soil properties were tested. The objective is to reveal which soil properties are significantly affected by tree species characteristics, which soil properties significantly affect bacterial community structure, and whether the bacterial community structure is the same in forest floor and topsoil samples at the same sampling site. The results showed that: (1) P c and P hwd could be used to represent tree species characteristics of natural mixed forests, and they significantly (P=0.05) affected the soil C/N ratio; (2) the soil C/N ratio was the main factor affecting the soil bacterial community composition, especially for the dominant heterotrophic bacteria (Acidothermus, Variibacter, Candidatus Solibacter, Acidibacter, and Bryobacter). The relative abundance (1.11-26.27%) of the dominant heterotrophic bacteria increases with an increase in the C/N ratio (6.33-10.76) within a certain range; (3) the dominant bacteria in topsoil samples were Nitrospira, Acidothermus, Arthrobacter, Bradyrhizobium, and Variibacter, while that in forest floor samples were Jatrophihabitans, Acidothermus, Burkholderia-Paraburkholderia, and Bradyrhizobium. Although the forest floor bacteria came from the topsoil at the same sampling site, the bacterial community structure had changed significantly. This study indicated that tree species drive the change of soil bacterial community by changing the soil C/N ratio, which may provide a new perspective for maintaining the stability of regional ecosystem structure., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Dissolved organic matter (DOM) adsorption on colloid surface occurred ubiquitously in aquatic ecosystems, while variations in molecular weight (MW) distribution during adsorption remained poorly understood. In this study, the adsorption and MW fractionation of aquatic DOMs with different origins (e.g., macrophyte- and algae-derived, MDOM and ADOM, respectively) on colloid surface were examined using total organic carbon, absorption and fluorescence spectroscopy, and flow field flow fractionation (FlFFF) analysis. Both the total organic carbon and spectroscopic results showed the predominant adsorption of DOMs within the first 45 min, which behaved not synchronously with MW fractionation. Quantitative FlFFF analysis further indicated that the organic ligands with different MWs exhibited different adsorption affinities on colloid surface. It was found that 5-15 kDa and 50 kDã0.45 μm were preferential adsorption fraction for humic- and protein-like MDOM, respectively, while 0.3-2 kDa and 0.3-50 kDa were preferential adsorption fraction for humic- and protein-like ADOM, respectively. Therefore, the MW fractionation of DOMs upon adsorption was highly dependent on DOM origins as well as specific components. Results obtained herein can enlarge our insights into adsorption and the resultant behavior and fate of DOMs that were highly related with the MW fractionation in aquatic environments., Competing Interests: Declaration of competing interest None., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Cyanobacterial extracellular polymeric substances (EPSs) in aquatic environments are easily adsorbed onto colloidal particles, whereas the adsorption behavior as affected by molecular weight (MW) properties remained unknown till now. Herein, the bulk cyanobacterial EPS matrix (<0.45 μm) was fractionated into high MW (HMW-, 1 kDa~0.45 μm) and low MW (LMW-, <1 kDa) fractions, with MW-dependent adsorption heterogeneities onto TiO 2 colloids exploring through batch experiment, UV-Vis and fluorescence spectroscopy, and two dimensional Fourier transform infrared correlation spectroscopy (2D-FTIR-COS). About two-thirds of total organic matters within bulk EPS matrix were distributed in the HMW fraction, leaving one-third in the LMW fraction. Compared to LMW-EPS, the HMW counterpart exhibited higher aromaticity and richness of autochthonous protein-like substances, showing evident MW-dependent differences in abundance and composition. The adsorption capacity based on the measurement of total abundance, UV-Vis and fluorescent spectra all decreased in sequence of HMW- > Bulk > LMW-EPS, demonstrating obvious MW-dependent adsorption heterogeneities. During adsorption, the values of SUVA 254 in residual supernatants exhibited an initial decrease followed by gradual increase for all samples, suggesting that the preferentially adsorbed aromatic substances can be subsequently replaced by the non-aromatic moieties. 2D-FTIR-COS further revealed that the carboxylic groups of proteins were preferentially adsorbed onto colloidal surface, followed by the CC functional groups and then the CH groups of polysaccharides, which accounted for the variations of SUVA 254 values in the supernatants. This study demonstrated that the adsorption behavior of EPS matrix was highly MW-dependent, and detailed characterization on size fractionation is thus needed in future studies., Competing Interests: Declaration of competing interest The authors declared that they have no conflicts of interest to this work., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Hydrological cycle changes that occur due to a changing environment is a hot topic in the field of hydrological science. It is of great practical significance to study the response mechanism of hydrological process change for future water resources planning and management. In this study, the effects of climate and watershed characteristic change on the streamflow in a typical tributary of the Yellow River (the Fen River watershed) are studied based on the Budyko hypothesis. The results show that: the sensitivity coefficients of streamflow to precipitation, potential evapotranspiration, and the watershed characteristic coefficient were 0.1809, -0.0551, and -27.0882, respectively. This meant that a 1 mm decrease in the precipitation would induce a 0.1809 mm decrease in the streamflow. Additionally, a 1 mm decrease in the potential evapotranspiration would induce a 0.0551 mm increase in the streamflow, and an increase of 1 in the watershed characteristic coefficient would induce a 27.0882 mm decrease in the streamflow. The streamflow of the Fen River watershed showed a significant decreasing trend during the reference period (1951-1977). In addition, the streamflow of the change period (1978-2010) decreased 26.87 mm; and this was primarily caused by watershed characteristic change which accounted for 92.27%, while climate change only accounted for 6.50%.

Colloidal particles are omnipresent in lake sediments and substantially influence the retention, transportation, and fate of contaminants in lake ecosystems. In this study, the abundance, chemical composition and adsorption behavior of sedimentary colloids (including total and inorganic colloids) from different ecological regions, were for the first time investigated via ultrasonic extraction, spectral analysis and batch absorption experiments. Results showed that the extraction efficiencies of sedimentary colloids showed an ultrasonic energy-dependent enhancement, and the algae-dominated area contained comparable colloidal abundance with the macrophyte-dominated area (i.e., 198.5 vs. 183.3 mg/g). Despite the different ecosystems, these sedimentary colloids usually had a wide size distribution of 30-200 nm, and were characterized with montmorillonite-, kaolin-, volkonskoite-, and quartz-rich chemical compositions. Batch experiment showed that the total pristine colloids exhibited higher adsorption capacity for Pb(II) than the inorganic colloids both for the macrophyte- and algae-dominated sediments, and the adsorption process followed pseudo-second-order kinetics and Langmuir isotherm, irrespective of different colloidal types. Thus, sedimentary colloids can immobilize the heavy metals in sediment and decrease their release into the water column, which can be considered as a sink for contaminants. This study highlighted the significance of sedimentary colloids in determining the physicochemical properties of lake sediments and in evaluating the environmental behavior and fate of contaminants in lake ecosystems., (Copyright © 2018 Elsevier Ltd. All rights reserved.)