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The groundwater quality impacts associated with anthropogenic groundwater recharge (AGR) are of great concern for water management. However, the impacts of AGR on the molecular properties of dissolved organic matter (DOM) in aquifers are poorly understood. Herein, Fourier transform ion cyclotron resonance mass spectrometry was used to unravel the molecular characteristics of DOM in groundwaters from recharge areas by reclaimed water (RWRA) and natural water from Southto-North Water Diversion Project (SNWRA). Compared with RWRA groundwater, significantly fewer nitrogenous compounds, more sulfur-containing compounds, higher concentrations of NO 3 −N, and lower pH were observed in SNWRA groundwater, indicating the occurrence of deamination, sulfurization, and nitrification. The occurrence of these processes was further supported by transformations of more molecules related to nitrogen and sulfur in SNWRA groundwater relative to RWRA groundwater. The intensities of most common molecules in all samples were significantly correlated with the water quality indicators (e.g., Cl − and NO 3 −N) and fluorescent indicators (e.g., humic-like components (C1%)), indicating that those common molecules may have the potential to track the environmental impact of AGR on groundwater, especially these specific molecules having great mobility and being significantly correlated with other inert tracers like C1% and Cl − . This study is helpful to understand the environmental risks and regional applicability of AGR.

Chronic kidney disease of unknown etiology (CKDu) becomes a health concern in developing countries. It is urgent to recognize CKDu-related groundwater in CKDu-prevalent areas. Here, spectral indices showed that DOM from CKDu groundwater was characterized by higher molecular weight, stronger exogenous feature, and greater degree of humification and unsaturation than from non-CKDu groundwater. Parallel factor analysis of fluorescence spectra showed that DOM from CKDu groundwater contained significantly more humic-like substances (C1%) and less protein-like substances than from non-CKDu groundwater. Furthermore, C1% was correlated with concentrations of inorganic chemicals associated with CKDu, indicating the feasibility of using C1% for probing CKDu groundwater. According to our self-developed method, both the non-CKDu probability of groundwater with C1% less than the recognizing threshold (RT, 28.8%) and the CKDu probability of groundwater with C1% larger than RT are 70.1%. This indicates that the C1%-based method is a feasible tool for recognizing CKDu groundwater.

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