Control of carbon dioxide exchange fluxes by rainfall and biological carbon pump in karst river-lake systems.

As an important component of inland water, the primary factors affecting the carbon cycle in karst river-lake systems require further investigation. In particular, the impacts of climatic factors and the biological carbon pump (BCP) on carbon dioxide (CO2) exchange fluxes in karst rivers and lakes deserve considerable attention. Using quarterly sampling, field monitoring, and meteorological data collection, the spatiotemporal characteristics of CO2 exchange fluxes in Erhai Lake (a typical karst lake in Yunnan, SW China) and its inflow rivers were investigated and the primary influencing factors were analyzed. The average river CO2 exchange flux reached 346.80 mg m-2 h-1, compared to -6.93 mg m-2 h-1 for the lake. The carbon cycle in rivers was strongly influenced by land use within the basin; cultivated and construction land were the main contributors to organic carbon (OC) in the river (r = 0.66, p < 0.01) and the mineralization of OC was a major factor in CO2 oversaturation in most rivers (r = 0.76, p < 0.01). In addition, the BCP effect of aquatic plants and the high pH in karst river-lake systems enhance the ability of water body to absorb CO2, resulting in undersaturated CO2 levels in the lake. Notably, under rainfall regulation, riverine OC and dissolved inorganic carbon (DIC) flux inputs controlled the level of CO2 exchange fluxes in the lake (rOC = 0.78, p < 0.05; rDIC = 0.97, p < 0.01). We speculate that under future climate and human activity scenarios, the DIC and OC input from rivers may alleviate the CO2 limitation of BCP effects in karst eutrophication lakes, possibly enabling aquatic plants to convert more CO2 into OC for burial. The results of this research can help advance our understanding of CO2 emissions and absorption mechanisms in karst river-lake systems.

Alleviating eutrophication by reducing the abundance of Cyanophyta due to dissolved inorganic carbon fertilization: Insights from Erhai Lake, China.

The eutrophication of lakes is a global environmental problem. Regulating nitrogen (N) and phosphorus (P) on phytoplankton is considered to be the most important basis of lake eutrophication management. Therefore, the effects of dissolved inorganic carbon (DIC) on phytoplankton and its role in mitigating lake eutrophication have often been overlooked. In this study, the relationships between phytoplankton and DIC concentrations, carbon isotopic composition, nutrients (N and P), and hydrochemistry in the Erhai Lake (a karst lake) were investigated. The results showed that when the dissolved carbon dioxide (CO2(aq)) concentrations in the water were higher than 15 µmol/L, the productivity of phytoplankton was controlled by the concentrations of TP and TN, especially by that of TP. When the N and P were sufficient and the CO2(aq) concentrations were lower than 15 µmol/L, the phytoplankton productivity was controlled by the concentrations of TP and DIC, especially by that of DIC. Additionally, DIC significantly affected the composition of the phytoplankton community in the lake (p<0.05). When the CO2(aq) concentrations were higher than 15 µmol/L, the relative abundance of Bacillariophyta and Chlorophyta was much higher than those of harmful Cyanophyta. Thus, high concentrations of CO2(aq) can inhibit harmful Cyanophyta blooms. During lake eutrophication, when controlling N and P, an appropriate increase in CO2(aq) concentrations by land-use changes or pumping of industrial CO2 into water may reduce the proportion of harmful Cyanophyta and promote the growth of Chlorophyta and Bacillariophyta, which may provide effectively assist in mitigating water quality deterioration in surface waters.

In-situ growing of metal-organic frameworks on iron mesh as a recyclable remediation material for removing hexavalent chromium from groundwater.

The recovery and reuse of adsorbents is crucial for the effectiveness and sustainability of mitigation methods for groundwater pollution. Considering the difficulty in recovering powder materials and the low mechanical strength of membrane materials, we developed a sheet material with good recyclability and certain mechanical strength. In this study, an in situ synthesized MIL-100(Fe) film sample was produced by hydrothermal reaction using a commercially available iron mesh as the substrate. The MIL-100(Fe) samples were characterized by SEM, XRD, XPS, and FT-IR. The experiments showed that the material presented excellent removal ability toward Cr(VI) and good recovery performance. In the fourth cycle test, the Cr(VI) removal rate reached more than 95%. The material characterization and adsorption kinetics indicated that the removal mechanism was oxidation-reduction reaction and electrostatic adsorption. The removal experiments at different pH values and with different co-existing ions demonstrated that the material can maintain good removal capacity at pH values between 2 and 8, and common ions in groundwater can promote the removal of Cr(VI) under neutral conditions. The recycling test demonstrated that the sample can be reused. After the sample was recovered and calcined in an inert environment, a network sample containing zero-valent iron was obtained, and it removed Cr(VI) from water at a low pH in 20 min. This study provides a new alternative for the practical removal of Cr(VI) from groundwater.

Key Factors Affecting Mathematics Teachers' Well-Being and Stress Levels: An Extended Engagement Theory.

The mathematics teachers' profession often has many challenges. It also occupies important positions at the K-12 education level, in which mathematics knowledge is the basis of all scientific fields. This tends to cause high-stress levels and a negative effect on well-being. Mathematics teachers' well-being has been less examined, and therefore this study aims to determine the factors affecting mathematics teachers' well-being and stress levels. The 210 data points collected from Chinese mathematics teachers using a web-based questionnaire were analyzed for reliability and validity, then model fit and SEM were applied for model validation after removing 3 invalid data points and incomplete responses. The results showed that behavioral and cognitive engagements significantly affect teachers' well-being, while the affective engagement was insignificant. The TPMK was the strongest significant predictor that had a positive impact on improving well-being and reducing stress levels. In addition, the stress level of mathematics teachers was influenced by gender and age. Finally, it was proven that teachers' well-being significantly reduced stress levels. This study's implication was to provide information on how to reduce stress levels.

Cooperative upconversion luminescence of Er3+ in Gd2O3-xSx phosphor.

Gd2O3-xSx:Er crystals were prepared through high-temperature solid-state reaction method in vacuum, with the vacuum synthesis mechanism determined by thermal analysis. The crystal structure and upconversion luminescence properties were investigated respectively by XRD, TEM and spectrophotometer. Well crystallized Gd2O2S:Er phosphors were prepared under 1000°C in vacuum with a certain excessive amount of sulfur content than stoichiometric. It is confirmed that with the increasing sulfur content the green emission was enhanced and red emission was weakened. The cooperative upconversion luminescence of Er3+ in non-stoichiometric Gd2O3-xSx crystals was interpreted as a result of two photon absorption and the photon avalanche process.

Methane adsorption on porous nano-silica in the presence of water: An experimental and ab initio study.

This study investigated the effects of silanol groups and water content on methane adsorption on hydrophilic nano-silica H-380 through experiments and ab initio calculations. Fourier transform infrared (FTIR) spectroscopy was used to confirm the presence of silanol groups on the solid surface, and the pore size distribution between 0 and 40nm was determined using CO2 and N2 sorption experiments. Ab initio MP2 and complete basis set model (CBS-4) calculations were performed to optimize four different silica surfaces with and without silanol groups using different basis sets. The theoretical calculations and experiments indicated that the adsorption of methane slightly decreased when the water content was low. As the water content increased from 29.03wt% to 40.54wt%, the confined water molecules (water within the pores) promoted the adsorption of CH4 by forming deeper adsorption potential energy wells, thus rendering the system more stable. The experimental isotherms at 308.15-318.15K were obtained over a wide range of water contents up to 75.05wt%. The experimental data are consistent with the theoretical analysis, indicating an increase in the adsorption of CH4 as the water content increased from 39.75wt% to 50.35wt%. Additionally, the adsorption of CH4 sharply decreased when the water content was greater than 63.12wt%. This study contributes essential data on methane-confined H2O interactions on nano-silica surfaces to the scientific literature.

[Degradation mechanism of acid red B by cathodic oxidation].

Acid red B (ARB) solution with pH = 3 was electrolyzed in a two-chamber cell using Pt/C gas diffusion electrode (GDE) as cathode. The color and COD removal ratio in cathode chamber were 94.2% and 66.8% respectively; and the color and COD removal ratio in anode chamber were 73.3% and 56.6% respectively, which indicated that O2 can be reduced to H2O2 and x OH in the cathode chamber, then ARB was degraded. Through IR and GC-MS analysis for the intermediates of ARB in the cathode chamber, 20 intermediates have been detected, including 14 esters, 3 acids and 3 compounds with -NO2 or N-OH groups and the probable degradation pathway of ARB in the cathode chamber was given.