Effects of land use on multi-temporal scales of dissolved organic matter in Three Gorges Reservoir

The Three Gorges Reservoir area has the largest water conservancy project in the world. In this context, it potentially provides water resources and promotes economic development, and yet causes serious impacts on ecological environments in the same time. In order to explore the effects of land use on riverine dissolved organic matter (DOM) at distinct spatial and temporal scales, we investigated a typical backwater area and water level fluctuation zone (Pengxi River basin) in the Three Gorges Reservoir area. Techniques of UV-Vis spectral analysis and 3D fluorescence spectral matrix-parallel factor analysis were used to analyze temporal variations of DOM composition and source characteristics. Landscape patterns reach buffer, riparian buffer and catchment were jointly employed to examine the iniluenees of land use on surface water DOM at distinct spatial scales. The results showed that high protein-like abundance was observed in the dry seasons, whereas fulvic acids were dominated in the wet seasons. Both terrestrial and autochthonous inputs constrained DOM sources in the river basin, while terrestrial signals were particularly pronounced in the wet seasons in comparison to the dry seasons. Land use exhibited significant effects on riverine DOM in the wet seasons; land use indexes explained 90.35% of DOM parameters under the catchment scale. Specifically, shrublands, mudflats and Shannon's Diversity Index (SHDI) largely deciphered DOM variables. High cover grassland, edge density (ED) and dissolved organic carbon (DOC) were positively and negatively correlated with aquatic DOM in the dry and wet seasons, respectively. We found discrepant correlations among shrubland, forested land, rivers and canals, reservoir ponds, mudflats, patch density (PD) and DOM, spatially. At the riparian buffer and catchment scales, shrublands, forested lands, river channels and mudflats were negatively correlated with DOM, whereas reservoir ponds and PD were positively correlated with DOM. Our study may provide basic data for rational land planning, as well as assist understandings for river ecosystem and water resources management in the Three Gorges Reservoir area. © 2023 Science Press. All rights reserved.