Spatial and temporal variation characteristics of water pollution in Hailaer River, Inner Mongolia

Taking the Hailaer River, the upstream tributary of the Erguna River between China and Russia, as the research object, the main water quality indexes of 6 monitoring sites from 2005 to 2015 were analyzed to study the spatial and temporal variation characteristics of water pollution. The results indicated that COD_Mn, COD_Cr and TN were the main pollution indexes of the mainstream of the Hailaer River, and the ammonia nitrogen basically met the Class Ⅲ requirement of Surface Water Environmental Quality Standards (GB 3838-2002). The overall water quality of the main and tributaries of the Hailaer River showed an improvement trend from 2005 to 2015 and a significant improvement occurred from 2005 to 2009. COD_Mn showed a decreasing trend in the four monitoring sites of Hailaer mainstream and COD_Cr showed a decreasing trend in the Taohai and Cuogang sites of Hailaer downstream, while COD_Cr of the four monitoring sites increased in 2010 and 2013. COD_Mn and COD_Cr of the mainstream of the Hailaer River changed significantly within a year, and the pollution was significantly aggravated from March to May every year. In addition, the mainstream was more seriously polluted than the tributaries, the downstream of the mainstream was more seriously polluted than the upstream, and the downstream Taohai monitoring site was the most polluted. The water quality in the Hailaer River was influenced by local meteorology, hydrology and human activities. The special environmental protection programme initiated in 2005 played beneficial effects on the water quality, while the abnormal climate in the years of 2010 and 2013 showed adverse influences on the mainstream water quality.