Spatio-temporal dynamics variation of dissolved organic matter and water quality parameters in Giheung Reservoir: A vertical perspective.

Water reservoirs in densely populated areas play a crucial role in water supply, irrigation, and flood regulation. This study investigated the spatiotemporal dynamics of dissolved organic matter (DOM) and its interactions with water quality parameters in Giheung Reservoir, South Korea. Monthly water samples were collected at three depths, measuring fifteen physicochemical properties alongside DOM characterization using Excitation-Emission Matrix Parallel Factor Analysis (EEM-PARAFAC), identifying four DOM components: C1 (microbial protein-like), C2 (humic-like), C3 (terrestrial humic-like), and C4 (tyrosine/tryptophan-like). Seasonal stratification influenced DOM distribution, with humic-like DOM (C2, C3) accumulating in deeper layers during summer, while protein-like DOM (C1, C4) dominated surface waters due to enhanced biological productivity, and mixing periods homogenizing DOM across depths. The dimictic thermal regime, with moderate summer stratification and full mixing in spring and autumn, governed these patterns. 2D correlation spectroscopy (2D-COS) identified sequential DOM variation across layers, with humic-like DOM increasing at depth during stratification. Fluorescence indices-Fluorescence Index (FI), Humification Index (HIX), and Biological Index (BIX)-were integrated into structural equation modeling (SEM), showing that temperature and dissolved oxygen strongly drive protein-like DOM, while nitrogen and phosphorus compounds shape DOM reactivity. These findings enhance understanding of DOM biogeochemical processes and provide valuable insights for reservoir management to maintain water quality.