Impact of human activities on urban river system and its implication for water-environment risks: an isotope-based investigation in Chengdu, China

摘要

To analyze the anthropogenic activities on water-environment conditions, sampling campaigns and isotope measurement for precipitation, river water and groundwater were conducted in Jinjiang River System, Chengdu, China for one year. The results show that runoff is the main factor affecting the isotopic composition in natural-state rivers, while in rivers affected by human activities, the isotopic composition varies greatly due to the influence of impermeable surface and municipal pipe networks on water evaporation and mixing. The warm-and-humid moisture source and "heat island" effect lead to high slope and intercept of local meteoric water line (LMWL), and the characteristics of surface water line (SWL) are closely related to land types. Isotope changes along the flow path indicate significant evaporation effect in wet season, while the operation of municipal pipe networks partially conceals the evaporation effect in dry season. The intensity of river evaporation is positively correlated with the urbanization level along the river. Isotope mixing model shows that precipitation and river water are the recharge sources of groundwater in rain and dry seasons, respectively, and the mixing ratios between Jiangan River and Fuhe River shows significant seasonal variation. The combination of isotopic analysis and pollutant data reveals that the seasonal water contribution is the main factor influencing the water quality. Risks for water safety and environmental health in Chengdu and cities along lower Minjiang River were assessed.