Characteristics and Changing Trend of Water Pollution in North Plain of Shang Yu Lixin Wang, Wanying Guo, Ziming Wang, Pengcheng Yao, Guojian Hu and Aiju You E3S Web of Conf., 406 (2023) 03006 Published online: 31 July 2023 DOI: 10.1051/e3sconf/202340603006