Dissolved organic matter signatures in urban surface waters: spatio-temporal patterns and drivers

Advances in analytical chemistry have facilitated the characterization of dissolved organic matter (DOM), which has improved understanding of DOM sources and transformations in surface waters. For urban waters, however, where DOM diversity is likely high, the interpretation of DOM signatures is hampered by a lack of basic information. Here we explored the spatiotemporal variation of DOM composition in contrasting urban water bodies, based on spectrophometry and fluorometry, size-exclusion chromatography and ultrahigh-resolution mass spectrometry, to identify linkages between DOM signatures and potential drivers. The highly diverse DOM we observed distinguished lakes and ponds characterized by a high proportion of autochthonous DOM from rivers and streams with more allochthonous DOM. Seasonal variation was apparent in all types of water bodies, driven by the interaction between phenology and urban influences. Specifically, nutrient supply, the percentage of green space adjacent to the water bodies and point source pollution emerged as major urban drivers of DOM composition. Optical DOM properties also revealed the influence of effluents from waste water treatment plants, suggesting their use in water-quality assessment and monitoring. Furthermore, optical measurements inform about processes both within water bodies and in their surroundings, which could improve the assessment of ecosystem functioning and integrity.