Characteristics of surface microlayer film under different freshwater environments: Physical, chemical, and biological properties

The surface microlayer film (SMF) has been observed worldwide in water environments and its environmental behavior plays a vital role in the migration and transformation of water pollutants. However, there has been little description and explanation of their characteristics in freshwater environments. Here, we investigate the characteristics of SMF under different freshwater trophic status. The results demonstrated that under sufficient nutrition, the interior characteristics of the SMF are densely arranged Fe3O4 skeletal structures, and the enrichment concentration of Fe3+ on the SMF reached 4.66 mu g/mL, the dominant bacteria is Zoogloea. Under the constraint of nitrogen, the interior characteristics of the SMF is a tightly spherical encapsulated organic matter, the maximum enrichment concentration of Fe3+ on the SMF was only 0.75 mu g/mL, Limnobacter and Acidocella are the dominant bacteria in the carbon and nitrogen constraint. Under iron constraint, the interior of the SMF is an entangled organic organism, and the coverage rate of the SMF was only 31.41 %, which decreased by 20.55 % and 8.58 %, compared with carbon and nitrogen constraint respectively, and the main microbial species is Cloacibacterium. These results reveal a strong correlation between water nutrient types and the formation of SMF, and established a connection between water pollution and SMF characteristics, provided a new approach for predicting water types using water surface microlayers, and have important implications for managing freshwater ecosystems.