|Alternative Title||Preliminary interpretation of water sources in an agricultural watershed during rainstorm events based on Multi-tracer approach|
|Place of Conferral||北京|
|Keyword||紫色土丘陵区 农业小流域 径流分割 暴雨径流过程 水文示踪|
Long-term application of nitrogen fertilizer, coupled with the runoff scouring, aggravated the nitrate nitrogen leaching and loss from hilly area of purple soil. Water quality of downstream water has been severely eutrophicated and nitrate accumulation in groundwater raised serious environmental threats to the safety of local residents' drinking water. Identification of water sources and pathways of runoff is key to catchment hydrology. A good understanding of the mechanism of runoff formation was helpful for the cause of agricultural non-point pollution, assessment and development of water resources, the construction of hydrological models.This study was conducted in the typical agricultural watershed which included comprehensive monitoring during typical rainstorm events at multiple scales (from 3 to 1236 hectares) in hilly area of purple soil. Streamwater hydrograph and chemograph in catchments of Surong（3.2ha）, Jieliu（35ha）, Daxing（480ha）, Wanan（1236ha），water sources’ chemical characteristics （Rainwaters, soil waters, groundwaters, irrigation waters）, identification of hydrological pathways based on different tracers are studied respectively. The tracers include hydrogen and oxygen isotope, and main inorganic ions. The potential of different inorganic tracers were validated based on EMMA assumptions and then the selection of appropriate hydrological tracers helped quantification of the contributions from different water sources in the nested agricultural watersheds. There search results were as follows.（1）In the smaller watersheds, stream runoff has faster response to the rainfall runoff peak. With the increase of catchment area, the runoff peak appeared obvious lag and smoothed phenomenon. Under the same type of rain events, the more moist soil conditions favored early peak runoff. The town sewage outlet (Surong watershed) led to the highest NO3--N concentrations in runoff during heavy rain events, with lowest concentration reaching the Wanan watershed which is the outlet of the whole nested agricultural watershed. The NO3--N concentrations decrease can be attributed to the dilution of forest subwatershed water in larger scale. The hydrochemistry indicators (K+、Na+、Ca2+、Mg2+、Cl-、SO42-、NO3--N、DOC) were significantly transported out with runoff during storm events and appeared several peaks. During the recession of the streamflow, nitrate nitrogen derived from the interflow on farmed hillslope caused multiple peak concentrations.（2）Investigated water chemical characteristics within the nested watershed are as follows: the concentrations of hydrochemistry ions (K+、Na+、Ca2+、Mg2+、Cl-、SO42-、NO3--N、EC、DOC) in the precipitation are lowest, groundwater are higher，soil waters are the highest. The hydrochemistry characteristic values of the soil water in the forest lands are lower than cultivated lands. Moreover, the groundwater chemical properties within Wanan watershed in different positions are also different. Compared with spring water，the chemical index of wells water are higher. The wells with greater human disturbance are higher in all hydrochemistry ions, with Ca2+ and EC index variation being the largest. Influenced by different sources of water vapor and temperature, hydrogen and oxygen isotope in different rainfall water has a significant difference, presenting lower values in summer and higher values in winter. In addition, hydrogen and oxygen isotopes differed greatly in different water sources. The soil water, groundwater are the mixed waters of diferent ages old water. （3）We found that the dissolved inorganic elements (K+、Na+、Ca2+、Mg2+、Cl-、SO42-、NO3--N、EC、DOC) all have the potential of hydrologic tracers, as well as stable isotopes hydrogen and oxygen which can trace the rise of soil water percentage in flow process in many places.The EMMA model analysis results of the 4 storm events show that: For the two end-members mixing model, 18O and nitrate nitrogen can both trace the process of subsurface interflow supply in the runoff recession period. High nitrogen sewage of the dense residential resulted in inaccuracy to nitrate tracer results at Surong watershed. According to the PCA (dimension reduction method), tappropriate inorganic hydrochemical tracer could be selected to better represent the water mixing processes by the different water sources. The situation for the three end- member mixing model is different. The tracing accuracy of nitrate nitrogen is better proved by other tracers. Nitrate nitrogen acts not only as an indicator of water environment but also behave as the hydrologic tracer, but its application needs to get rid of sewage influences. In order to avoid with the bias by single tracer, the author suggests that using mutiple tracers methods combined with integrated hydrological monitoring would be best approach in interpretation of hydrological process in complex agricultural watershed.We found that EC-DOC、O18—NO3--N/ SO42-/Ca2+/Na+/Cl-、Na+/Na++Ca2+—NO3--N、Ca2+—SO42- can trace soil water contribution during storm events. （4）Streamflow during rainy season is mainly composed of rainwater, soil water, groundwater in the agricultural watershed in the hilly area of purple soil. Daxing and Wanan watershed streamflows are mainly affected by groundwater and soil water supply, with proportion even up to 50%. Subsurface interflow release from farmed hillslope with the soil water contribution led to NO3--N peaks of the chemograph. The basin area is bigger (Daxing, Wanan watershed), the phenomenon of soil water flushing is more obvious.
|王芮. 基于多示踪剂的农业小流域暴雨径流水源初步解析[D]. 北京. 中国科学院大学,2016.|
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