Characteristics of Dissolved Organic Matter Impacted by Different Land Use in Haihe River Watershed, China.

It is important to explore characteristics of dissolved organic matter (DOM) in the riverine system due to its critical role in the carbon cycle. This study investigated the distribution characteristics and sources of DOM based on excitation emission matrix three-dimensional fluorescence technology and parallel factor (EEM-PARAFAC) analysis at two rivers in northern China strongly impacted by human activities. The results show that the fluorescence intensity of terrestrial humic-like substances increased during summer in Haihe River. The intensity was significantly higher than in spring due to terrestrial detritus from runoff conveyance. The fluorescence intensity of protein-like substances in spring was the highest and decreased in summer. This feature of DOM in the Duliujian River was related to the increase in precipitation and surface runoff in the wet season and the rapid degradation of mixed DOM in the dry season. An analysis of HIX, BIX and FI showed a low degree of DOM humification and more endogenous contributions from microbial and phytoplankton degradation. Seasonal variations of dissolved organic carbon (DOC) and chromophoric DOM (CDOM, a335, thereinto C1) suggest that chromophores, particularly terrestrial substances, regulate the temporal patterns of DOM in the two rivers. Combined with the analysis of the proportion of land use types in riparian buffers, tillage had a great impact on DOM content and hydrophobicity in Haihe River watershed. Domestic wastewater and industrial sewage discharge contribute more DOM to Duliujian River watershed, which was indicated by more abundant protein-like components (212.17 ± 94.63 QSU in Duliujian River;186.59 ± 238.72 QSU in Haihe River). This study highlights that different land use types resulted in distinctive sources and seasonal dynamics of DOM in rivers. Meanwhile, it should be considered that the estimation of carbon cycling should involve monitoring and evaluating anthropogenic inputs into rivers.

Hierarchical Superhydrophobic Poly(vinylidene fluoride-co-hexafluoropropylene) Membrane with a Bead (SiO2 Nanoparticles)-on-String (Nanofibers) Structure for All-Day Passive Radiative Cooling.

Passive all-day radiative cooling has been proposed as a promising pathway to cool objects by reflecting sunlight and dissipating heat to the cold outer space through atmospheric windows without any energy consumption. However, most of the existing radiative coolers are susceptible to contamination, which may decrease the optical property and gradually degrade the outdoor radiative cooling performance. Herein, we prepared a hierarchical superhydrophobic fluorinated-SiO2/PVDF-HFP nanofiber membrane by a facile and scalable technology of electrospinning and electrostatic spraying. Due to the synergistic effects of the efficient scattering of nanofibers/micropores and the phonon polarization resonance of SiO2 nanoparticles, the membrane achieves up to 97.8% average solar reflectance and 96.6% average atmospheric window emittance. The membrane displays sub-ambient temperature drop values of 11.5 and 4.1 °C in daytime and nighttime outdoor conditions, respectively, exhibiting remarkable radiative cooling performance. Importantly, the unique bead (SiO2 nanoparticles)-on-string (nanofibers) structure forms hierarchical roughness that endows the surface with a superior self-cleaning property. In addition, the obtained membrane exhibits remarkable flexibility and mechanical stability, which are of significant importance in cooling vehicles, buildings, and large-scale equipment.

Microgroove-Structured PDA/PEI/PPy@PI-MS Photothermal Aerogel with a Multilevel Water Transport Network for Highly Salt-Rejecting Solar-Driven Interfacial Evaporation.

Desalination of seawater through solar-driven interfacial evaporation is an efficient approach to solve the freshwater resource shortage problem. However, the salt formation and crystallization during interfacial evaporation limit the long-term stability of the solar evaporator. To further improve the salt-rejecting capability of the solar evaporator, we developed a porous framework photothermal microgroove-structured aerogel (PDA/PEI/PPy@PI-MS MGA, pppMGA) through a combined freeze drying, laser engraving, and chemical polymerization technique. A multilevel water transport network consisting of a three-dimensional (3D) skeleton, a microgroove-structured water channel, and a cotton core is constructed, which can effectively improve the salt-rejecting capability of the aerogel. At the same time, the combination of the 3D porous microgroove structure of the pppMGA evaporative interface and the efficient light absorption capacity of PPy effectively increases the vapor-liquid evaporation area and the light absorption rate (98%). A high evaporation rate (∼1.38 kg m-2 h-1) and high photothermal conversion efficiency (∼93.04%) can be achieved on the pppMGA evaporator under 1 sun illumination, which can operate stably in high salt concentration (20%) water for 8 h. Even under 3 sun illumination and a 20 wt % NaCl solution, the pppMGA evaporator can operate stably without salt crystallization. Such a photothermal aerogel with high salt-rejecting performance provides a new avenue for designing an interfacial evaporation system that can operate stably under high salt concentration conditions.

The Optical Characterization and Distribution of Dissolved Organic Matter in Water Regimes of Qilian Mountains Watershed.

The constituents and content of dissolved organic matter (DOM) in the Qilian Mountain watershed were characterized with a spectroscopic technique, especially 3-DEEM fluorescence assisted by parallel factor (PARAFAC) analysis. The level of DOM in the surrounding area of Qinghai lake (thereafter the lake in this article specifically refers to Qinghai Lake)was highest at 9.45 mg C·L-1 and about 3 times less (3.09 mg C·L-1) in a cropland aquatic regime (the lowest value). In general, DOM was freshly autochthonously generated by plankton and plant debris, microorganisms and diagenetic effects in the aquatic environment (FI > 1.8). Component 1 (humic acid-like) and 3 (fulvic acid-like) determined the humification degree of chromophoric dissolved organic matter (CDOM). The spatial variation of sulfate and nitrate in the surrounding water regime of the lake revealed that organic molecules were mainly influenced by bacterial mediation. Mineral disintegration was an important and necessary process for fluorescent fraction formation in the cropland water regime. Exceptionally, organic moiety in the unused land area was affected by anespecially aridclimate in addition to microbial metabolic experience. Salinity became the critical factor determining the distribution of DOM, and the total normalized fluorescent intensity and CDOM level were lower in low-salinity circumstances (0.2-0.5 g·L-1) with 32.06 QSU and 1.38 m-1 in the grassland area, and higher salinity (0.6~0.8 g·L-1) resulted in abnormally high fluorescence of 150.62 QSU and absorption of 7.83 m-1 in the cropland water regime. Climatic conditions and microbial reactivity controlled by salinity were found to induce the above results. Our findings demonstrated that autochthonous inputs regulated DOM dynamics in the Qilian Mountains watershed of high altitude.