Using a water quality index to assess the water quality of the upper and middle streams of the Luanhe River, northern China

The water diversion project from the Luanhe River to Tianjin city has been a lifeline for the economic and social development of Tianjin city since the 1980s. The water quality of this project has received considerable attention due to the degradation of the river environment during the last decade. A comprehensive water quality index (WQI) was applied to provide a clear understanding of the water quality in the upper and middle streams of the Luanhe River. We utilized 12 water quality parameters from 85 sampling sites along the major tributaries in July 2017 (summer), October 2017 (autumn) and April 2018 (spring) respectively. The results showed that the WQI values ranged from 37.6 to 90.0, indicating bad to excellent water quality in the upper and middle streams of the Luanhe River. The seasonal variations in the WQI were significant and the relationship between land use and WQI also have certain seasonal characteristics, such as WQI of 85 sampling sites were significant negatively correlated with the proportion of cultivated land in summer, and with the proportion of built-up land in three sampling periods. The water quality pollutants, such as organic pollutants (permanganate index), nutrients (total phosphorus), total suspended solid, and chlorophyll-a were significantly influenced by the proportion of forest and grass land and the consumption of phosphate fertilizers in tributaries. The evident variation in the WQI was also found in the tributaries with higher proportions of cultivated land and built-up land. Overall, we think that agricultural and urban related activities are important factors affecting the water quality in this region. Water quality improvements should control the sewage in the urban area and the consumption of fertilizers, especially on the cultivated land along the riverside in the upper and middle streams of the Luanhe River.