[Sources and Biogeochemical Processes of Nitrate in the Laolongdong Karst Underground River Basin, Chongqing].

Samples of sewage, well water, and underground river water of the urbanized Laolongdong karst underground river basin in Chongqing, China were collected during July 2019 and October 2020 and measured to determine the nitrate origin and biogeochemical processes based on geochemistry and dual nitrate isotope (N-NO and O-NO) data. The results showed that:① the isotopic nitrate compositions of sewage ranged from -3.3‰ to 14.