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Detailed depiction of hydrological process and its associated pollution processes plays a critical role in environment improvement and management at basin scale. It also provides a useful tool to assess impact of potential factors on hydrological and water quality conditions. However, it was still difficult to well capture some typical characteristics of these complicated processes including built-in nonlinearity and time-variation, water infrastructure regulations, particularly for highly regulated basins. In this study, an integrated approach of hydrological and water quality dynamic simulation was proposed to solve these difficulties and assess the impacts of several anthropogenic disturbances. The Huai River Basin which was highly disturbed and seriously polluted, was selected as the study area. The main anthropogenic activities considered were point source pollution emissions, diffuse pollutant losses and dam regulations. Results showed that the integrated simulation could well capture the variations in water level, water discharge, concentrations of permanganate index (COD Mn ) and ammonia nitrogen (NH 4 -N) in high (2007), normal (2008) and low (2004) flow years at 15 stations in the upper and middle streams of Huai River Basin. The regulation rules of downstream sluices played negative roles on water quality improvement if keeping current pollution sources, while those of middle stream sluices played positive roles on water quality improvement. However, the water quality deterioration was mainly attributed to emission of point source pollution (12%–43%), followed by diffuse pollutant loss (0–23%) and water quantity-oriented dam regulation (− 29%–20%). The study was expected to provide technical supports for the implementation of water pollution control and sustainable water resources management in the Huai River Basin, and give a reference of integrated hydrological and hydrodynamic simulation. [ABSTRACT FROM AUTHOR]

Water quality deterioration is a prominent issue threatening water security throughout the world. Huai River Basin, as the sixth largest basin in China, is facing the most severe water pollution and high disturbance. Statistical detection of water quality trends and identification of human interferences are significant for sustainable water quality management. Three key water quality elements (ammonium nitrogen: NH 3 -N, permanganate index: COD Mn and dissolved oxygen: DO) at 18 monitoring stations were selected to analyze their spatio-temporal variations in the highly disturbed Huai River Basin using seasonal Mann–Kendall test and Moran's I method. Relationship between surrounding water environment and anthropogenic activities (point source emission, land use) was investigated by regression analysis. The results indicated that water environment was significantly improved on the whole from 1994 to 2005. COD Mn and NH 3 -N concentrations decreased at half of the stations, and DO concentration increased significantly at 39% (7/18) stations. The high pollution cluster centers for both NH 3 -N and COD Mn were in the middle stream of Shaying River and Guo River in the 2000s. Water quality of Huai River Basin was mainly influenced by point source pollution emission, flows regulated by dams, water temperature and land use variations and so on. This study was expected to provide insights into water quality evolution and foundations for water quality management in Huai River Basin, and scientific references for the implementation of water pollution prevention in China. [ABSTRACT FROM AUTHOR]