Abstract: Background, aim, and scope The Yellow River has always been regarded as the mother river of the Chinese nation. The water environment quality in Yellow River has an important significance for coastal resident health because they directly take water from yellow river for drinking nearly 100 million people. Recent years, with the rapid economic development and urbanization of Yellow River watershed, the pollution became more and more critical which caused by the cities along the river, especially three nitrogen pollution. By 2020, the state clearly requires that the water quality of the Yellow River watershed must be improved water quality and reduce pollutions discharge, more than 63% of the water should reach the national standard, and poor water quality area cannot exceed 6%. Nowadays, what status is of yellow river water quality is unknown. This study was aim to answer this question by assessed the water quality and analyzed the source of pollutants in upstream, midstream, and downstream of the Yellow River watershed at the wet season, and to provide theoretical basis for the protection of ecological environment in the Yellow River. Materials and methods Four typical sampling points were taken along the Yellow River from upstream to downstream in the wet water period, water physico-chemical properties were determined, such as pH, dissolved oxygen, suspended solid, ammonia nitrogen, nitrate nitrogen, total nitrogen, nitrite nitrogen, total organic carbon, total inorganic carbon, total carbon, total phosphorus, chemical oxygen demand, five day biochemical oxygen demand, coliform group, volatile phenol, the principal component analysis （PCA） were used to analysis source of water pollution of the Yellow River, then the water quality in different samples was evaluated by the calculation of water quality index （WQI）, the source of pollutants were indicated by cluster analysis （CA）. Results: （1） the change trend of suspended solid was Dongying （DY） > Lanzhou （LZ） > Sanmenxia （SMX） > Guide （GD）. （2） The change trends were SMX > LZ > DY > GD for the concentrations of ammonia nitrogen, nitrate nitrogen, total nitrogen, total organic carbon, total inorganic carbon, total carbon, total phosphorus, chemical oxygen demand, five day biochemical oxygen demand and coliform group. （3） The change trends of nitrite nitrogen and volatile phenol were LZ > SMX >DY > GD. （4） although average water quality in this study was poor, the water quality of sample one （GD） was really fine, the water were not satisfactory with standard in the other samples. Overall merit, water quality indexes （WQI） in the different samples of the Yellow River was GD>DY>LZ>SMX. Nitrogen pollutants was particularly prominent, it showed that the situation of nitrogen pollution in the Yellow River basin is still very severe. Discussion Nitrogen pollutants serious exceeded the national standard in sample points of Lanzhou and Samenxia, mainly reasons was due to the pollution of industrial cities and the inflow of serious pollution tributaries. Dongying sample point was at the most downstream, it taken in the water from upland, but it was far away from cities and the water has self-purification capacity, so the water quality at this point has been diluted, in spite of this, nitrogen pollution was still ignored issue. This research showed the nitrogen discharge from industrial and domestic sewage could not be controlled and it great impacted on the water quality of the Yellow River, water management of yellow River should strengthen by national lay. Conclusions Industrial cities, densely populated areas and heavily polluted tributaries pose a great threat to the Yellow River's water quality, we should strictly monitor and focus on these areas, especially three nitrogen pollution. Recommendations and perspectives In order to realize the overall plan of the country in 2020, we should implement rigorously environment policies for controlling artificial emission.
Keywords: nitrogen pollutants;; nitrogen emissions;; industrial sewage;; domestic sewage;; Yellow River water quality;