Identifying sources of dissolved organic matter in sediments of a shallow lake by fluorescence and ultraviolet spectral characteristics of water and alkali extractable organic matter (WEOM and AEOM)

This study investigates the potential of fluorescence characteristics of dissolved organic matter (DOM) to identify sediment organic matter (OM) sources in shallow lakes. Spectral analyses were performed on water and alkali extractable organic matter (WEOM and AEOM) from Lake Taihu sediments. The lake was divided into seven distinct regions: R1 and R2 strongly influenced by inflowing rivers, R3 and R4 were characterized by submerged macrophytes, and R5-R7 were dominated by cyanobacterial blooms. The investigation illustrated that the highest values of water and alkali extractable organic carbon (WEOC and AEOC) were found in region R4. Specifically, the Humification Index (HIX) values consistently exceeded 2.0 in the northwest regions, contrasting with values predominantly below 1.0 in most southeastern regions. Moreover, the Fluorescence Index (FI) of WEOM in regions R5, R6 and R7 reached 2.10, markedly higher than the values observed in other regions. The horizontal distribution of the four spectrographic indices of AEOM exhibited partial similarity to the distribution pattern of WEOM. Although the WEOC content marginally trailed AEOC, there was a significant correlation between WEOM and AEOM in three indices including slope ratio (SR), HIX and FI. The identification of sources implied that organic matter in sediments of regions R1 and R2 originated from terrestrial sources, while regions R3 and R4 were largely derived from submerged macrophyte and the regions R5-R7 were notably impacted by cyanobacteria-derived organic matters. Notably, the identification results aligned perfectly with the distribution of inflowing rivers, cyanobacterial blooms and submerged macrophyte coverage within Taihu Lake, underscoring the potential use of dissolved organic matter's spectral characteristics for organic matter source analysis within sediments. Synopsis: This study identifies distinct sources and spatial distributions of organic matter in Lake Taihu's sediments, using fluorescence characteristics to highlight influences from terrestrial input, submerged macrophytes, and cyanobacterial blooms.