Hydrological seasonality largely contributes to riverine dissolved organic matter chemical composition: Insights from EEM-PARAFAC and optical indicators

•DOM compositions and sources have clearly temporaland spatial changes.•There are higher humification, aromaticity and lignin substances in the wet season.•EEM-PARAFAC identify 4 components in the dry and 3 components in the wet season.•Dry season has more biological and autochthonous sources with protein-like component.•Hydrological seasonality and human activities control DOM composition and source.