Photochemical Reactivity of Humic Substances in an Aquatic System Revealed by Excitation-Emission Matrix Fluorescence oleh Xin-yuan Wang, Qi-peng Yang, Shi-jie Tian, Fan-hao Song, Fei Guo, Nan-nan Huang, Wei-qiang Tan, Ying-chen Bai, Ying-chen Bai