Spatio-temporal characteristics and source apportionment of water pollutants in upper reaches of Maotiao river, southwest of China, from 2003 to 2015

The Maotiao River is playing an indispensable role in protecting water quality of the Yangtze River of China. Its hydro-power development also provides adequate power and clean resources for the local areas. To understand the water quality of the upper reaches (i.e., Maijia River), seven indices such as dissolved oxygen (DO), chemical oxygen demand (CODCr), biochemical oxygen demanded (BOD5), ammonia nitrogen (NH3-N), total nitrogen (TN), total phosphorus (TP) and fluoride of samples collected from 4 sites from 2003 to 2015 were studied using multiple analysis approaches. For winter-spring and summer-autumn seasons, pictures of spatio-temporal characteristics were presented and the reasons behind their variation trend were elaborated. The Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI) was evaluated to concisely mark the water quality. Principal component analysis (PCA) was applied to identify the source of pollutants. The results showed that the water quality status in Maijia River was poor from 2008 to 2011 and acceptable from 2003 to 2007, and 2012 to 2015, respectively. The CODCr, NH4-N and TN were considered to be the primary pollutants during winter-spring and summer-autumn seasons. The quality of Maijia River was influenced strongly by human activities. Environmental treatment and pollution sources of the middle and lower reaches of the river need to be focused. This study paves a way to improve the ecological environment of Maotiao River and overall water quality management of the middle and upper reaches of Yangtze River.