Agricultural Ditch Construction and Land Use Characteristics Change DOM Levels and Spectral features in the Naoli River Basin of the Sanjiang Plain, China

Most of the Sanjiang Plain of China was drained for agriculture under the influence of human activities, which simultaneously created a complex network of agricultural ditches. The role of agricultural ditch network structure and land use characteristics on regional dissolved organic matter (DOM) is still unclear. In current work, ultraviolet-visible (UV-Vis) absorption and the three-dimensional (3D) fluorescence excitation-emission matrix combined with parallel factor analysis (PRAFAC) were used to characterize the structural characteristics of DOM under different ditch density groups. The results indicate that as ditch density increases, the complexity of the ditch network structure also increases. Compared with the low-density group, the content of humic acid substances in the medium and strong groups is higher (medium group: 26.33%; strong group: 27.73%), indicating that humic acid substances are more likely to accumulate in areas with high ditch density. In areas with a high proportion of natural land use (especially forests), protein-like components in water tend to be more abundant. Land use characteristics (independently explained 27%) has a greater impact on DOM than ditch network structure (independently explained 19%). Fluvic acid substances and protein-like substances are mainly controlled by land use characteristics, while humic acid substances are more dependent on ditch network structure. The interaction effect also indicated an antagonistic effect between land use characteristics and ditch network structure on DOM composition and spectral characteristics.