RESUMEN
Accurate source identification/apportionment is essential for optimizing water NO3--N pollution control strategies. This study conducted a meta-analysis based on data from 167 rivers across China from 2000 to 2022 to analyze the spatial and temporal variation patterns of nitrate pollution in seven major river systems and to quantitatively identify the source composition of riverine nitrate. The average ρï¼NO3--Nï¼ in the seven major river systems was ï¼4.54±3.99ï¼ mg·L-1ï¼ with 9.6% of river ρï¼NO3--Nï¼ exceeding 10 mg·L-1. The riverine ρï¼NO3--Nï¼ in eastern China were higher than that in western Chinaï¼ and the highest concentration was observed in the Haihe River system. Additionallyï¼ tributaries experienced more serious NO3--N pollution than that in the main stream. The ρï¼NO3--Nï¼ in most river systems in the dry season was higher than that in the wet seasonï¼ except in the Yellow River system. There was significant nitrification in the Pearl River systemï¼ the middle and lower reaches of the Yellow River systemï¼ the middle reaches of the Liaohe River systemï¼ the Songhua River systemï¼ and the Haihe River systemï¼ whereas there was significant denitrification in the Yangtze River systemï¼ the Huaihe River systemï¼ and the lower reaches of the Pearl River system. Based on the dual stable isotopes-based MixSIAR modelï¼ the major NO3--N source was sewage/manure ï¼ > 50%ï¼ in the Yangtze River systemï¼ Haihe River systemï¼ Liaohe River systemï¼ and Southeast River system. Soil nitrogen was the main NO3--N source in the Songhua River system ï¼56.4%ï¼ï¼ and the contribution of fertilizer nitrogenï¼ soil nitrogenï¼ and sewage/manure to NO3--N pollution in the Pearl River systemï¼ Huai River systemï¼ and Yellow River system was 20%-40%. The contribution rate of sewage/manure to NO3--N in the tributaries was higher than that in the main streamï¼ whereas the contribution rate of soil nitrogen to NO3--N in the main stream was higher than that in the tributaries. The contribution rate of soil nitrogenï¼ fertilizer nitrogenï¼ and atmospheric deposition nitrogen to nitrate nitrogen in the wet season was higher than that in the dry seasonï¼ whereas the contribution rate of sewage/manure to NO3--N pollution in the dry season was higher than that in the wet season. Thereforeï¼ point source pollution such as domestic and production sewage discharge should be controlled in the Haihe River systemï¼ the Yangtze River systemï¼ the Liaohe River systemï¼ the tributaries and the downstream main stream areas of Yellow River systemï¼ and the downstream area of the Pearl River systemï¼ whereas non-point source pollution caused by the loss of fertilizer and soil nitrogen should be controlled in the Huaihe River systemï¼ the Songhua River systemï¼ the middle reaches of the main stream area of the Yellow River systemï¼ and the middle and upper reaches of the Pearl River system. The results can provide a scientific basis for the effective control of nitrate pollution in the river systems in China.