The quantitative inversion of the concentrations of water quality parameters could clarify the temporal and spatial distribution characteristic, migration, and conversion of water quality parameters. This study took the Danjiangkou Reservoir as the research object, and established an inversion model based on the reflectance of different band combinations of remote sensing analyses on Sentinel-2 images, combined with the water quality monitoring data of total nitrogen (TN) and ammonia nitrogen (NH3-N) of the sampling sites in February 2016. The inversion results of TN and NH3-N in 2020 were obtained, the variation of TN and NH3-N concentrations in the reservoir area were analyzed, and the factors accounting for the variation were discussed. The results indicated that the fitting accuracy using the established model was high for both TN and NH3-N, and R2 was 0.782 for TN and 0.851 for NH3-N, respectively, showing high predication accuracy, which could be suitable for remote sensing inversion of TN and NH3-N concentrations in the Danjiangkou Reservoir. The NH3-N concentration of the Danjiangkou Reservoir was in line with Class I from 2016 to 2020, while the TN concentration was between Class III and IV. The inter-annual changes indicated that the overall water quality had an upward trend. The main tributary in the northern of the Danjiangkou Reservoir had a heavy load of TN, and after entering the reservoir, the flow velocity decreased, which caused nitrogen to accumulate at the river entrance, leading to a high TN concentration. The large slope of the mountainous area cause soil erosion. The lost soil and water carried a large amount of pesticides and fertilizers, and the ground runoff carried a large amount of nitrogen into water body, which could account for the high NH3-N concentration on the east and west sides of the southern part of the Danjiangkou Reservoir.

中文翻译：

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南水北调中线工程水源中总氮和氨氮的时空变化

水质参数浓度的定量反演可以明确水质参数的时空分布特征、迁移和转换。本研究以丹江口水库为研究对象，结合Sentinel-2影像遥感分析不同波段组合的反射率，结合全氮（TN）和氨氮水质监测数据，建立反演模型。 2016年2月采样点的(NH3-N)。得到2020年TN和NH3-N的反演结果，分析库区TN和NH3-N浓度的变化，以及影响变化的因素进行了讨论。结果表明，使用所建立的模型对 TN 和 NH3-N 的拟合精度较高，TN 和 NH3-N 的 R2 分别为 0.782 和 0.851，预测精度较高，适用于丹江口水库 TN 和 NH3-N 浓度的遥感反演。2016-2020年丹江口水库NH3-N浓度符合I类，TN浓度在III类和IV类之间。年际变化表明水质总体呈上升趋势。丹江口水库北部主要支流TN负荷较重，入库后流速降低，导致河口氮聚集，导致TN浓度偏高。山区大坡度造成水土流失。流失的水土携带了大量的农药化肥，