RESUMEN

The optical characteristics of colored dissolved organic matter (CDOM) serve as a convenient tool for evaluating coastal processes, e.g., river runoff, anthropogenic inputs, primary production, and bacterial/photochemical processes. We conducted a study on the seasonal and spatial variability of absorbance and fluorescence characteristics of CDOM and nutrients in the coastal waters near the Gauthami estuary of River Godavari, the largest peninsular river of India, for a year. The surface aCDOM(350) showed a significant inverse relation with salinity in the coastal region, indicating a conservative mixing of marine and terrestrial end members. The aCDOM(350) was not conservative in the offshore (100 m isobath) waters due to enrichment by secondary sources. Seasonal variability in optical properties indicated diverse sources for CDOM, as revealed by principal component analysis. The excitation-emission matrix (EEM) spectra followed by parallel factor analysis (EEM-PARAFAC) revealed four distinct fluorophores. The tyrosine (B) fluorophore showed a predominant increase in the post-monsoon season (October to January), while tryptophan (T) was relatively more enriched, coincident with nutrient enrichment and transparency increase during the early monsoon phase (July). The biological index (BIX), which reflects recent photosynthetic activity, also displayed relatively higher values during the early monsoon. The humic fluorophores A and M, and humification index (HIX) were relatively enriched during the later phase of monsoon (July-October). HIX was > 4 in a few samples of the offshore region (100-m isobath) and indicated a probable contamination from drill-mud (bentonite) used in hydrocarbon exploration. During the monsoon, the relationship between T and B with CDOM was not evident due to the masking of B fluorescence in intact protein. However, during the post-monsoon (POM) and pre-monsoon (PRM) periods, this masking effect was not observed, likely due to protein degradation via bacterial and photochemical processes, respectively. Temporal variability in nutrients indicated that high ammonium levels were produced during POM (OM bacterial degradation), and high nitrite levels were observed during PRM (due to primary production). This study provides foundational insights into the use of CDOM for understanding the impact of diverse environmental, river discharge, and anthropogenic factors on coastal ecosystems.

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RESUMEN

The water-rock interaction has a significant effect on the binding characteristics of dissolved organic matter and heavy metals when mine water flows in goaf. This study used fluorescence excitation-emission matrix (EEM) quenching combined with parallel factor (PARAFAC) analysis to characterize the binding properties of DOM with Fe (Ⅲ), Fe (Ⅱ+Ⅲ) and Mn (Ⅱ) in mine water under rock-influenced conditions. Two protein-like components and two humic-like components were identified by PARAFAC, in which protein-like components dominated (75.9%). The fluorescence intensity of each component can all be weakened, especially the stability constant (logKM) value of Fe (Ⅱ+Ⅲ) with fulvic-like acid and humic-like acid was the largest and the binding was more stable. Clay minerals and iron-bearing minerals in rocks had significant effects on the binding characteristics of DOM and metal ions under water-rock interaction. Iron ions released by the oxidation of pyrite and siderite in sandstone can reduce the fluorescence intensity of the derived components. The competitive adsorption effect of clay minerals on metal ions made the fluorescence intensity of the derived components under the action of sandstone containing less clay minerals (19.5%) be lower than that of mudstone (31.3%). Meanwhile, the process of water-rock interaction was accompanied by microbial activities to convert protein-like components into fulvic-like and humic-like components, or higher levels of stable substances. This study shows that when assessing the potential ability of mine water DOM and metal ions binding and migration during the flow of water in goaf it is crucial to take into account the presence of water-rock interaction.

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RESUMEN

The concentration of dissolved organic carbon (DOC) in some rivers in the western Sichuan Plateau is extremely high. Due to the unique optical properties of colored dissolved organic matter (CDOM), a thorough understanding of the photodegradation characteristics of CDOM helps in revealing regional DOC dynamics and carbon cycle at the water-land interface in alpine natural waters. Surface water samples were collected from three rivers (the upper reaches of the Minjiang, Zagunao, and Fubian rivers) in the alpine-gorge region, and the Baihe and Heihe rivers in the plateau planation surface distributed among the watersheds in the western Sichuan plateau, southwest China. Ultraviolet-visible spectra(UV-vis) absorbance and excitation emission matrix (EEM) fluorescence spectroscopy with two-dimensional correlation spectrum (2D-COS) and principal component analysis (PCA) were used to characterize the environmental behavior responses to light irradiation. The first-order decay constants and photodegradation rates of the Baihe and Heihe rivers are 0.167 d-1,0.173 d-1 and 64.85%,63.43%, respectively. Due to the low concentration (0.71 m-1) of the Fubian River CDOM, photodegradation behavior is limited. The photodegradation behavior of CDOM in the Zaogunao and Minjiang rivers is relatively complicated. Exposure to sunlight led to decreases in the chromophores and changes in origin of CDOM from the four rivers, except for the Minjiang River. The aromaticity, hydrophobicity, and humification degree of CDOM in the rivers from the plateau planation surface were decreased with increasing exposure time. PARAFAC produced a four-component model:C2[280(<250)/400 nm], C3 (255/440 nm), and C4[270(360)/492 nm] represented terrestrial UVA humic-like fluorophores, and C1 (275/310nm) belonged to a tyrosine-like substance, as humic-like FDOM was found to be more readily photodegraded. 2D-COS indicated that UVA humic-like FDOM showed a higher susceptibility in the rivers from plateau planation surface. The preferential removal of UVA humic-like FDOM (especially at 500 nm emission wavelength), and delayed response of tyrosine-like fluorescence, were revealed from the five rivers upon irradiation. Two factors were identified in the principal component analysis of the Baihe River, explaining 87.28% of these parameters, which comprehensively reflected the effects of the photodegradation process on CDOM characteristics and fluorescent components.

RESUMEN

The present several humification indexes cannot provide the whole fluorescence information on organic matter composition and the evaluation results from them are inconsistent sometimes. In this study, fluorescence excitation-emission matrix spectra coupled with parallel factor analysis and fluorescence regional integration analysis were utilized to investigate organic matter humification, and the projection pursuit cluster (PPC) model was applied to form a suitable index for overcoming the difficulties in multi-index evaluation. The result showed that the ratio between the volume of humic- and fulvic-like fluorescence region and the volume of protein-like fluorescence region not only revealed the heterogeneity of organic matter, but also provided more accurate information on organic matter humification. In addition, the results showed that the PPC model could be used to characterize integrally the humification, and the projected characteristic value calculated from the PPC model could be used as the integrated humification evaluation index.

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