[Dynamic Variations and Sources of Nitrate During Dry Season in the Lijiang River]

Dynamic variations and sources of nitrate during dry season in the Lijiang River were analyzed using the nitrate concentrations and ¹⁵ N and ¹⁸ O isotope techniques, from the samples obtained from 13 sections in the Lijiang River from September 28, 2016 to December 28, 2016. Results show that the nitrate concentrations range from 0.46 to 18.48 mg·L^-1, with an average of 6.18 mg·L^-1, and that the nitrate levels are low during the dry season. Nitrate concentrations in the Lijiang River increase slowly from September to December, mainly being influenced by rainfall, runoff, and human activity. Nitrate concentrations in the Lijiang River from upstream to downstream show a trend of "increase-decrease-increase." Nitrate in the Lijiang River during the dry season mainly originates from organic nitrogen in soil, human and animal feces, sewage (largely living sewage), human and animal waste, and tourism. In order to better protect the water quality of the Lijiang River, the urban sewage pipe network must be expanded, in addition to building small sewage treatment facilities and strengthening tourism management and environmental awareness.