Study on the Physico-chemical Properties of Rural Black and Odorous Water Bodies Based on DOM Fluorescence Characterization: A Case Study of Yueyang City

Dissolved organic matter (DOM) is a key component for characterizing the physico-chemical properties of rural black-odorous water bodies. This study focused on 29 rural black-odorous water bodies in Yueyang City, covering both domestic and mixed pollution sources. The fluorescence features of DOM in the water bodies were elucidated using three-dimensional Excitation-Emission Matrix-Parallel Factor Analysis (EEM-PARAFAC) technology, and the correlation between water quality characteristics and DOM fluorescence features was analyzed. The results indicate that the proportion of dissolved oxygen concentration in domestic source water samples qualifying as black-odorous values (< 2 mg·L^-1) was 38.5%, which was higher than that for mixed source samples. The concentrations of ammonia nitrogen (NH₃-N) in all samples were below the black-odorous threshold (< 15 mg·L^-1). The concentration ranges for total organic carbon (TOC) and total phosphorus (TP) in the samples were 5-15 and 0-2 mg·L^-1, respectively. The average values for the biological index, fluorescence index, and humification index in the samples were 0.80, 2.26, and 4.39, respectively, indicating a strong autogenic characteristic of the water body DOM. The DOM in the water bodies primarily consisted of terrestrial humic-like substances, microbial activity-related humic-like substances, and protein-like components. C1 and C2 together accounted for 73.5%, which suggests that the DOM in the water bodies was predominantly humic-like. The total fluorescence intensity and the fluorescence intensity of component C3 could be used to predict changes in TP and NH₃-N concentrations in domestic source water samples.