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Dissolved organic matter (DOM) is a complex mixture of organic compounds found across the biosphere. DOM concentration and composition are highly dynamic because of various transformation processes, such as microbial and photochemical degradation and adsorption to mineral particles. These processes are essential for carbon cycling across ecosystems and for water quality. Adsorption is important for DOM cycling, but its role in changing DOM composition and biological reactivity is rarely studied together. Extrinsic controls induced by water residence time can also impact DOM both spatially and temporally, yet these dynamics are poorly known. This thesis aims to fill these knowledge gaps in four studies. In the first study, DOM treatability and biodegradability across lake Mälaren in Sweden were investigated at six time points. The findings show that water residence time (WRT) plays a key role in shaping the composition of DOM. As WRT increases, DOM concentration and composition resist seasonality-driven temporal variations and gradually shift from terrestrial to aquatic origin, which enhances its treatability for drinking water. In the three following studies, batch experiments were sequentially performed to investigate adsorption controls on DOM composition and biodegradability across a range of mineral types and DOM sources from terrestrial and aquatic environments. The experiments (i) quantify adsorption capacities, (ii) evaluate DOM compositional changes due to adsorption using a multi-analytical approach incorporating fluorescence spectroscopy, mass spectrometry, and ¹H NMR, and (iii) assess the biodegradability of the remaining DOM pool. The outcomes highlight that the adsorption capacity depends on the DOM sources, characteristics of mineral surfaces, and water chemistry. Strong adsorption interactions preferentially remove oxygen-rich, aromatic DOM, while weak interactions tend to target more diverse compounds. Moreover, DOM-mineral interactions have varying effects on biodegradability, ranging from strong to moderate and no enhancement after adsorption. The multi-analytical approach improves DOM characterization by reducing individual method biases. Notably, ¹H NMR effectively detects carbohydrate fractions, which are often overlooked by other methods. The thesis has important implications for descriptions of carbon dynamics in terrestrial and aquatic ecosystems, where agricultural, mining, and forestry increase mineral presence and enhance organo-mineral interactions.