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ABSTRACTThis study explores microbial community structure in managed aquifer recharge (MAR) systems across both laboratory and field scales. Two field sites, the Taif River (Taif, Saudi Arabia) and South Platte River (Colorado), were selected as geographically distinct MAR systems. Samples derived from unsaturated riverbed, saturated-shallow-infiltration (depth, 1 to 2 cm), and intermediate-infiltration (depth, 10 to 50 cm) zones were collected. Complementary laboratory-scale sediment columns representing low (0.6 mg/liter) and moderate (5 mg/liter) dissolved organic carbon (DOC) concentrations were used to further query the influence of DOC and depth on microbial assemblages. Microbial density was positively correlated with the DOC concentration, while diversity was negatively correlated at both the laboratory and field scales. Microbial communities derived from analogous sampling zones in each river were not phylogenetically significantly different on phylum, class, genus, and species levels, as determined by 16S rRNA gene pyrosequencing, suggesting that geography and season exerted less sway than aqueous geochemical properties. When field-scale communities derived from the Taif and South Platte River sediments were grouped together, principal coordinate analysis revealed distinct clusters with regard to the three sample zones (unsaturated, shallow, and intermediate saturated) and, further, with respect to DOC concentration. An analogous trend as a function of depth and corresponding DOC loss was observed in column studies. Canonical correspondence analysis suggests that microbial classesBetaproteobacteriaandGammaproteobacteriaare positively correlated with DOC concentration. Our combined analyses at both the laboratory and field scales suggest that DOC may exert a strong influence on microbial community composition and diversity in MAR saturated zones.

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18The potential formation of nitrogenous disinfection by-products (N-DBPs) was investigated from the 19 chloramination of nitrogenous and non-nitrogenous aromatic compounds. All molecules led to the 20 formation of known N-DBPs (e.g., dichloroacetonitrile, dichloroacetamide) with various production 21 yields. Resorcinol, a major precursor of chloroform, also formed di-/tri-chloroacetonitrile, di-/tri-22 chloroacetamide, and haloacetic acids, indicating that it is a precursor of both N-DBPs and 23carbonaceous DBPs (C-DBPs) upon chloramination. More detailed experiments were conducted on 24 resorcinol to understand N-DBPs formation mechanisms and to identify reaction intermediates. Based 25 on the accurate mass from high resolution Quadrupole Time-of-Flight GC-MS (GC-QTOF) and 26 fragmentation patterns from electronic impact and positive chemical ionization modes, several 27 products were tentatively identified as nitrogenous heterocyclic compounds (e.g., 3-chloro-5-hydroxy-28 1H-pyrrole-2-one with dichloromethyl group, 3-chloro-2,5-pyrroledione). These products were 29 structurally similar to the heterocyclic compounds formed during chlorination, such as the highly 30 mutagenic MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone) or halogenated pyrroles. To 31 our knowledge, this is the first time that the formation of halogenated nitrogenous heterocyclic 32 compounds is reported from chloramination process. The formation of these nitrogenous by-products 33 during chloramination might be of concern considering their potential toxicity. 34 ABSTRACT ART35 36 37 INTRODUCTION 38

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