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Linking optical and chemical signatures of dissolved organic matter in the southern Argentine shelf: Distribution and bioavailability
摘要： Fluorescence spectroscopy is commonly used to investigate the distribution and dynamics of dissolved organic matter (DOM) in marine systems. However, the direct comparison with chemical signatures is essential to substantiate the molecular composition of specific fluorescent components. Here we report the relation between optical and chemical signatures of DOM in waters of the Beagle Channel (BCW) (south-east of Tierra del Fuego, in the southern Argentine shelf) at the Pacific-Atlantic connection and neighboring coastal (CW) and oceanic (OW) waters (54.75-55.75°S, 64-68°W). The relationships among concentrations of total dissolved carbohydrates (TDCHO) and amino acids (TDAA), and fluorescent DOM (FDOM), including terrestrial “humic-like” (FDOMC) and “protein-like” compounds (FDOMT), and bioavailability of DOM components were assessed from field measurements acquired in the austral summer 2012. The maximal concentrations of TDCHO, dissolved organic carbon (DOC) and FDOMc intensities were found in BCW, while the minima in OW, displaying a negative correlation with salinity. This spatial distribution of biogeochemical signals suggests that humic compounds contributed by continental runoff contain refractory carbohydrates, and FDOMC resulted as a reliable tracer of carbon pathways in the Pacific-Atlantic connection. Conversely, TDAA and FDOMT showed the opposite distributional trend, with minimal concentrations in BCW and the maxima in CW and OW. The significant positive correlation of TDAA with salinity suggests open water sources of these components, however, phytoplankton biomass (Chla) in CW and OW was significantly lower than in BCW, ruling out the assumption of autochthonous source in open waters. TDAA were negatively correlated with the abundance of heterotrophic bacteria (HB), which displayed a consistent decrease from BCW towards OW, suggesting high bacterial uptake of TDAA in the BCW. This bacterial uptake is supported by the observed variation in carbon contribution of TDAA to DOC (amino acids carbon yield, in %), which is an indicator of DOM lability. The negative correlation found between amino acids carbon yield and HB abundance reflects intense bacterial activity in BCW, where phytoplankton biomass was maximum. Hence, higher DOM “freshness” occurs in the BCW, suggesting a tight coupling between microbial production and consumption.
关键词： Pacific-Atlantic connection.,amino acids,fluorescent dissolved organic matter,carbohydrates
更新于2025-11-14 15:26:12
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Fluorescence as a Surrogate for the Release of Intracellular Material From Cyanobacteria
摘要： Water treatment plants that apply preoxidation before physical cell removal can compromise cyanobacterial cell integrity and cause the release of intracellular organic matter (IOM) containing toxic or odorous metabolites. In this study, fluorescence was evaluated as a surrogate for IOM released from cyanobacterial cells following oxidation with ozone, chlorine, chlorine dioxide, or monochloramine. Oxidation of 200,000 cells/mL of Microcystis aeruginosa led to a significant increase in both the fluorescence index (FI) and the fluorescent dissolved organic matter (FDOM) intensity (excitation wavelength, 370 nm; emission wavelength, 460 nm). FI and FDOM proved impractical for detecting weakly fluorescing IOM released from Oscillatoria sp. and Lyngbya sp., indicating that the viability of fluorescence monitoring is cyanobacteria-specific. For strongly fluorescing IOM, FI and FDOM can serve as qualitative surrogates for the concomitant release of metabolites. Elevated FI and FDOM were not sensitive to the concentration of microcystin-LR but can provide an early warning that a utility’s source water is at risk for metabolite release and accumulation.
关键词： fluorescence index,cyanobacteria,Microcystis aeruginosa,fluorescent dissolved organic matter,intracellular organic matter,microcystin-LR
更新于2025-09-19 17:15:36
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Simulated photo-degradation of dissolved organic matter in lakes revealed by three-dimensional excitation-emission matrix with regional integration and parallel factor analysis
摘要： Simulated photo-degradation of fluorescent dissolved organic matter (FDOM) in Lake Baihua (BH) and Lake Hongfeng (HF) was investigated with three-dimensional excitation-emission matrix (3DEEM) fluorescence combined with the fluorescence regional integration (FRI), parallel factor (PARAFAC) analysis, and multi-order kinetic models. In the FRI analysis, fulvic-like and humic-like materials were the main constituents for both BH-FDOM and HF-FDOM. Four individual components were identified by use of PARAFAC analysis as humic-like components (C1), fulvic-like components (C2), protein-like components (C3) and unidentied components (C4). The maximum 3DEEM fluorescence intensity of PARAFAC components C1eC3 decreased by about 60%, 70% and 90%, respectively after photo-degradation. The multi-order kinetic model was acceptable to represent the photo-degradation of FDOM with correlation coefficient (Radj2) (0.963e0.998). The photo-degradation rate constants (kn) showed differences of three orders of magnitude, from 1.09(cid:1) 10(cid:3)6 to 4.02 (cid:1) 10(cid:3)4 min(cid:3)1, and half-life of multi-order model (Tn1=2) ranged from 5.26 to 64.01 min. The decreased values of fluorescence index (FI) and biogenic index (BI), the fact that of percent fluorescence response parameter of Region I (PI,n) showed the greatest change ratio, followed by percent fluorescence response parameter of Region II (PII,n), while the largest decrease ratio was found for C3 components, and the lowest Tn1=2 was observed for C3, indicated preferential degradation of protein-like materials/components derived from biological sources during photo-degradation. This research on the degradation of FDOM by 3DEEM/FRI-PARAFAC would be beneficial to understanding the photo-degradation of FDOM in natural environments and accurately predicting the environmental behaviors of contaminants in the presence of FDOM.
关键词： Fluorescence regional integration,Parallel factor analysis,Photo-degradation,Fluorescent dissolved organic matter,Multi-order kinetic models,Three-dimensional excitation-emission matrix
更新于2025-09-16 10:30:52