Observations of water transparency in China’s lakes from space

Water transparency, usually denoted by Secchi disk depth (SSD), represents the first-order description of water quality and has important implications for the diversity and productivity of aquatic life. In China, lakes supply freshwater and ecosystem services to nearly a billion people. Therefore, real time monitoring of lake transparency is of great significance. Moreover, understanding how and why transparency varies in space and time in response to different driving forces is needed to understand, manage, and predict lake water quality. Based on the time-saving and low-cost Google Earth Engine cloud platform, this study developed a new algorithm for quickly mapping SDDs in Chinese lakes. SDDs were retrieved for 412 Chinese lakes (> 20 km2) for the period 2000–2018. Results demonstrated that lake water depth spatially differentiated transparency. Deep lakes usually had high transparency and water depth explained 88.81 % of the spatial variations. With increasing catchment vegetation coverage and lake water depth, 70.15 % of lakes witnessed increasing transparency during 2000–2018. Of these 42.72 % were significant (p < 0.05). Transparency of deep lakes was generally determined by phytoplankton density not sediment resuspension. Minimum transparency occurred in summer. Future increases in lake water levels in response to factors such as climate change may contribute to further improvements in transparency. Management should focus on controlling eutrophication and increasing vegetation cover in catchments

Surface Modification of Silica Gel by Interfacial Polyelectrolyte Complexes

Two types of modified silica gel have been prepared by constructing layers of a thermolabile interfacial polyelectrolyte complex on the surface of silica gel using diazo resin (DR) as the polycation and poly(sodium styrene sulphonate) (PSS) as the polyanion. Dye adsorption from aqueous solution was employed to estimate the surface properties of the silica gels. It is believed that the diazo resin is anchored on the surface of the silica gel after thermal treatment through covalent bond formation. The adsorption ability of the surface for cationic dyes increases after such modification. Anionic dyes, which cannot be adsorbed by the unmodified silica gel. can be adsorbed by the modified ones. This indicates that a hydrophobic surface has been built up on the silica gel.Chemistry, AppliedChemistry, PhysicalEngineering, ChemicalSCI(E)EI1ARTICLE6459-4671

Interaction of sodium dodecyl sulfate with polyelectrolyte complexes derived from diazoresin and sulfonate-containing polymers

The sulfonate-containing polyelectrolytes (SPE) from sulfonation of polystyrene (PS) and copolymerization of 3-sulfo-propyl methacrylate, potassium salt (SPMS) with styrene (S) were prepared. Photosensitive polyelectrolyte complexes (PECDR) derived from SPE and diazoresin (DR), which does not dissolve in water or organic solvent due to its ionic crosslinking structure, dissolves in aqueous solution of sodium dodecyl sulfate (SDS) due to the dissociation of PECDR and the hydrophobic interaction between SDS and the polymer chain. The photosensitive behavior and thermostability of the PECDR were investigated, and it was found that the thermostability of PECDR increases dramatically in SDS aqueous solution. It was proposed that the higher thermostability of PECDR in SDS aqueous solution is due to an aggregation of SDS molecules around the diazonium group of the PECDR, which protects the - N2+ group of the DR from attack by the nucleophiles. The image-forming behavior of PECDR by ultraviolet (UV) light was examined and considered to be different from other PECs. It was concluded that the photoimaging behavior of PECDR is based on a reaction in which an ionic bond converts to a covalent bond