title: Linking the mobilization of dissolved organic matter in catchments and its removal in drinking water treatment to its molecular characteristics.
abstract: Drinking water reservoirs in the Northern Hemisphere are largely affected by the decadal-long increase in riverine dissolved organic carbon (DOC) concentrations. The removal of DOC in drinking water treatment is costly and predictions are needed to link DOC removal efficiency to its mobilization in catchments, both of which are determined by the molecular composition. To study the effect of hydrological events and land use on the molecular characteristics of dissolved organic matter (DOM), 36 samples from three different catchment areas in the German low mountain ranges, with DOC concentrations ranging from 3 to 32 mg L-1, were examined. Additionally, nine pairs of samples from downstream drinking water reservoirs were analyzed before and after flocculation. The molecular composition and the age of DOM were analyzed using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and radiocarbon (14C) analysis. At elevated discharge in a forested catchment comparatively younger, more oxygenated and unsaturated molecules of higher molecular weight were preferentially mobilized, likely linked to the reductive mobilization of iron. DOM with highly similar molecular characteristics (O/C ratio > 0.5, m/z > 500) could also be efficiently removed through flocculation in drinking water treatment. The proportion of DOM removed through flocculation ranged between 43% and 73% of DOC and was highest at elevated discharge. In catchment areas with a higher percentage of grassland and agriculture a higher proportion of DOM molecules containing sulfur and nitrogen was detected, which in turn could be less efficiently flocculated. Altogether, it was shown that DOM that is released during large hydrological events can be efficiently flocculated again, suggesting a reversal of similar chemical mechanisms in both processes. Since the occurrence of heavy rainfall events is predicted to increase in the future, event-driven mobilization of DOC may continue to challenge drinking water production.
authors.affiliation: Helmholtz Centre for Environmental Research - UFZ, Department of Analytical Chemistry, Permoserstrasse 15, 04318 Leipzig, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Raeke
authors.affiliation: Helmholtz Centre for Environmental Research - UFZ, Department of Analytical Chemistry, Permoserstrasse 15, 04318 Leipzig, Germany; Helmholtz Centre for Environmental Research - UFZ, ProVIS - Centre for Chemical Microscopy, Permoserstrasse 15, 04318 Leipzig, Germany.
authors.forename: Oliver J
authors.initials: OJ
authors.lastname: Lechtenfeld
authors.affiliation: Helmholtz Centre for Environmental Research - UFZ, Department of Lake Research, Brückstrasse 3a, 39114 Magdeburg, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Tittel
authors.affiliation: Helmholtz Centre for Environmental Research - UFZ, Department of Hydrogeology, Permoserstrasse 15, 04318 Leipzig, Germany.
authors.forename: Marieke R
authors.initials: MR
authors.lastname: Oosterwoud
authors.affiliation: TZW: DVGW Water Technology Center, Wasserwerkstrasse 2, 01326 Dresden, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Bornmann
authors.affiliation: Helmholtz Centre for Environmental Research - UFZ, Department of Analytical Chemistry, Permoserstrasse 15, 04318 Leipzig, Germany. Electronic address: thorsten.reemtsma@ufz.de.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Reemtsma
mesh_terms: D000383:Agriculture; D060766:Drinking Water / Q000737:chemistry*; D009584:Nitrogen; D018508:Water Purification
chemical_list: D060766:Drinking Water; D009584:Nitrogen
keywords: Drinking water treatment; FTICR-MS; Flocculation; Mobilization; Radiocarbon; Ultrahigh resolution mass spectrometry