Spatiotemporal Patterns of Ammonia Nitrogen and Chemical Oxygen Demand in the Huaihe River–Hongze Lake System (Eastern China)

Understanding variations in contaminant concentrations and exploring their driving factors are essential for pollution control water environment improvement. The Huaihe River Basin, as an important region the eastern of China, has attracted much attention to its issues recent years. Therefore, in-depth analysis spatiotemporal patterns quality parameters was carried out on River–Hongze Lake system, period 1998–2018, using Mann–Kendall test (MKT) wavelet transforms (WTs). Significant decrease trends ammonia nitrogen (AN) chemical oxygen demand (COD) were detected (HR) before 2008 MKT. High concentration load a result effect increased construction decreased forest increasing input pollutants during this period. results WT showed how (e.g., streamflow temperature), except land use, affect AN COD concentrations. comparison between HR Hongze (HL) differences transport regimes. contaminants rapidly transported downstream along with high wet season, while these HL less responsive due long residence time body. In addition, rebounds occurred many times at confluence strong river–lake interactions, especially flood season. These have implications future management Basin similar settings worldwide.