Distribution characteristics and risk assessment of ammonia nitrogen and heavy metal pollution in Longjing river, the upstream of Ganjiang river

Longjing River, one of China's typical rare earth mining areas, in the upper reaches of the Ganjiang River is studied. 15 observation sections was set up to test and analyze the content and correlation of ammonia nitrogen, nitrate nitrogen, nitrous oxide and 8 heavy metals such as Cr, Cd, Zn, Cu, As, Hg, Pb, Mn. N.L.Nemerow comprehensive pollution index evaluation method was adopted to evaluate heavy metal pollution. The results show that: ①The main heavy metal pollutants in the Longjing River Basin are Mn, Hg and Pb, which are 93%, 20% and 6.7% higher than the surface Ⅱ water quality standards respectively; ②Nitrous oxide, Nitrogen, Ammonia and heavy metals such as Zn, Mn, As, Cd and Pb in the surface water have similarities along the process, and heavy metals such as Zn, Mn, As, Cd, Pb and Ammonia have a significant positive correlation. It indicates that there is homology between Zn, Mn, As, Cd and Pb, and the Ammonia nitrogen content is closely related to the distribution of heavy metal in water; ③Water quality of Longjng River is classified into 5 degress from the best, better, good, bad and worse. The probability of each is 6.67%, 26.67%, 33.33%, 6.67% and 26.67%. The water quality is poor in general. Some sampling points show good water quality, and heavy metal pollution in upstream is heavier than that in downstream.