Straw return is becoming a routine practice in disposing of crop residues worldwide. However, the potential effect of such operation on the chemistry of local groundwater is notwell documented. Here, shallowgroundwater in an area where wheat-maize straw return is practiced was analyzed, and the seasonal changes in the nitrate concentration and the isotope compositions of NO(3)(-)and H2O were determined along two flow paths. Measured delta D and delta O-18 inwaters indicated that the groundwater wasmainly recharged by atmospheric precipitation, while measured d15N and delta O-18 in nitrate suggested that the sources for groundwater NO3-included urea fertilizer, soil nitrogen, and sewage/manure. Reduced NO(3)(-)concentrations coincided with an enrichment of organic matter in the groundwater of the strawreturn area, revealing an environmental condition that facilitates nitrate reduction, whereas increased delta N-15-NO(3)(-)and delta O-18-NO3- along the flowpath suggested the occurrence of denitrification. Further analyses showed that, compared to the cases in the absence of straw return, as much as 80% and 90% of groundwater nitrate was removed in lowand high water seasons in the strawreturn area, pointing to a potential positive effect of straw return to groundwater quality. (C) 2017 Elsevier B.V. All rights reserved.

Publication name	SCIENCE OF THE TOTAL ENVIRONMENT, 592 78-85; 10.1016/j.scitotenv.2017.03.029 AUG 15 2017
Author(s)	Li, Rongfu; Ruan, Xiaohong; Bai, Ying; Ma, Tianhai; Liu, Congqiang
Corresponding author(s)	RUAN Xiaohong   ruanxh@nju.edu.cn    -Nanjing Univ, Sch Earth Sci & Engn, Dept HydroSci, Nanjing 210023, Jiangsu, Peoples R China  -Nanjing Univ, MOE Key Lab Surficial Geochem, Nanjing 210023, Jiangsu, Peoples R China
Author(s) from IGCAS	LIU Congqiang

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