| Autor: |
Duan SH; Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing 400715, China., Jiang YJ; Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing 400715, China., Zhang YZ; Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing 400715, China., Zeng Z; Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing 400715, China., Wang ZX; Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing 400715, China., Wu W; Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing 400715, China., Peng XY; Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing 400715, China., Liu JC; Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing 400715, China. |
| Abstrakt: |
Water samples from the two underground rivers (Fenghuang River and Longju River) and samples of the dry and wet deposition of atmospheric dissolved inorganic nitrogen were taken from the Longfeng karst trough valley located in the Zhongliang mountain in the suburbs of Chongqing from May 2017 to April 2018. Anions, cations, δ 15 N(NO 3 - ), δ 18 O(NO 3 - ), δ 18 O(H 2 O), and δ 13 C(DIC) isotope data were used to investigate the NO 3 - source and its environmental effects. The results showed:① The hydrochemistry of the two underground rivers is of the type HCO 3 -Ca. The NO 3 - concentration varied from 17.58 to 32.58 mg·L -1 , with an average of 24.02 mg·L -1 , and was slightly higher in rainy season than the dry season, revealing that the underground rivers were polluted. ② The δ 15 N(NO 3 - ) value ranged from -3.14‰ to 12.67‰, with an average value of 7.45‰. The δ 18 O(NO 3 - ) value ranged from -0.77‰ to 12.05‰ with an average value of 2.90‰, and was higher in the dry season than the rainy season, indicating that animal excreta and domestic sewage were main NO 3 - sources throughout the year. In addition, rainfall, fertilizer, and soil nitrogen were the NO 3 - sources during the rainy season. There are no significant differences between the NO 3 - sources of the two underground rivers, and nitrification is the main nitrogen conversion process. ③ The molar ratio of (Ca 2+ +Mg 2+ )/HCO 3 - varied from 0.65 to 0.82. That of the Fenghuang River was 0.75 and that of the Longju River was 0.70. The δ 13 C(DIC) value ranged from -12.46‰ to -9.20‰, with a mean of -11.10‰ in the Longju River and -10.72‰ in the Fenghuang River. These values indicated that the HNO 3 derived from the nitrification of NH 4 + was involved in the weathering of carbonate rocks. ④ HNO 3 dissolved carbonate rocks and aggravated the chemical weathering of carbonate rock in the basin, contributing 8% of the DIC in groundwater, and 9% and 7% in Fenghuang River and Longju River, respectively. |
