Deciphering dissolved organic matter from freshwater aquaculture ponds in Eastern China based on optical and molecular signatures

Abstract Aquaculture makes great contribution to global food production. The aquaculture capture scale of China was far ahead of other countries in the world. Despite the potential role of dissolved organic matter (DOM) to affect fish growth and ecological cycle, the characterization of DOM in aquaculture industry was poorly understood. In this study, fluorescence excitation-emission matrix (EEM) spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) were conducted to decipher the optical and molecular signatures of DOM in freshwater aquaculture ponds in Eastern China. The EEM dataset was decomposed by parallel factor analysis (PARAFAC). Three main components including humic/fulvic acid-like (C1 and C3), tryptophan-like (C2) and tyrosine-like substances (C3) were obtained. FT-ICR-MS identified DOM composition at molecular level. In terms of formula classes, the dominant CHO species were followed by CHON and CHOS groups. According to compound classification criteria, the key components of lignins, tannins, proteins and lipids illustrated the primary source from terrestrial sediment, feeding doses and stocked creatures, implying the great influence by the land-based aquaculture ponds. Typical spectral indexes such as humification index (HIX), biological index (BIX) and fluorescence index (FI) consistently reflected the lower humification degree of DOM and greater contribution from protein-like sources. Furthermore, to utilize readily available spectral indexes to predict the time-consuming molecular properties, redundancy analysis and the pairwise correlation analysis was carried out to prove that two spectral indexes (E2:E3 and BIX) were negatively associated with four molecular formula derived parameters (O/Cwa, AImodwa, DBEwa and NOSCwa). The findings expanded our understanding of aquaculture DOM evolved in environmental chemistry.