Specific Absorption Coefficient Research Articles

A Spatial–Seasonal Study on the Danube River in the Adjacent Danube Delta Area: Case Study—Monitored Heavy Metals

Monitoring and protecting flowing watercourses is a complex and challenging task that requires the collaboration and coordination of various stakeholders such as governments, industries, farmers, consumers and environmental groups. The study of the dynamics of the concentration of polluting factors and especially the concentrations of heavy metals and highlighting a seasonal variation is a necessary element from this point of view. In this article, we present the results of our analyses carried out in two measurement campaigns executed in 10 monitoring points along the Danube River, between Braila city and Isaccea city in the pre-deltaic area, during the summer season and autumn season 2022. The importance of this area is given by the fact that the Danube Delta is part of the UNESCO heritage, and the monitoring of polluting factors is a necessity in the desire to protect this area. The data measured during the July and August 2022 campaign cover a wide range of chemical species: Phosphate, CCO, CBO5, NH4+, N-NO2, N-NO3−, N-Total, P-PO4 3−, SO42−, Cl−, phenols, as well as metals with a harmful effect: Al, As, Cd, Cr, Fe. The study includes an evaluation based on the statistical approach of the results to highlight the significant correlations and differences identified between the two data sets. Next, to highlight the obtained results, a numerical model was considered using HEC-RAS and ESRI ArcGIS applications in a two-dimensional unsteady flow model in order to obtain the non-homogenous concentrations’ distributions in the studied area. These two-dimensional models have been less studied in the specialized literature. In this way, interesting results could be obtained, and prediction methods regarding the dynamics of metal concentrations could be structured. The data obtained were used for the terrain model from the USGS service, and the flows of the Danube and its two tributaries were simulated using the data provided by the national services. In this work, we present the results obtained for the dynamics of the concentrations of the metals Al, As, Cd, Cr and Fe and the evaluation of the specific absorption coefficients for the explanation and correlation with the results of the measurements. Except for the numerical model presented, we would like to highlight the existence of some contributions of the main tributaries of the Danube in the study area. Such a systematic study has not been carried out due to conditions imposed by the border authorities. From this point of view, this study has an element of originality. The study is part of a more complex project in which the spatio-temporal distribution of the polluting factors in the water was evaluated, and the habitats in the study area were inventoried—especially those of community interest. In this way, we were able to expose the self-purification capacity of the Danube and highlight the existence of a concentration reduction gradient along the course of the river. The aspects related to the influence of the distribution of polluting factors on the state of health will be the subject of another article.

Facile preparation of conductive silicone rubber composite foams with tunable cell morphologies and absorption-dominant characteristics

Flexible silicone rubber (SR) foams with tunable cellular morphologies were fabricated via supercritical CO2 foaming. Conductive carbon black (CB) modified at a low cost and with high complex viscosity was preferentially selected. The effects of the pore size and void fraction on the electrical conductivity and dielectric permittivity of the SR/CB composite foams were carefully investigated. The pore size of the foams affected the specific shielding effectiveness (SSE) and absorption coefficient (A), whereas the variation in the void fraction did not generate evident changes. In comparison with its solid counterpart, a foam with a pore diameter of 59.9 μm showed a 50 % decrease in density, 31.6 % increase in absorptivity, and 95.7 % increase in SSE, demonstrating a considerable electromagnetic interference shielding effectiveness (EMI SE). Decreases in the pore size and void fraction of the foams improved compression modulus and strength. In addition, sample preparation process was simplified, making industrial production easier.

Monitoring of chlorophyll content in local saltwort species Suaeda salsa under water and salt stress based on the PROSAIL-D model in coastal wetland

As the invasion of alien species intensifies, the native salt marsh vegetation, especially the ecosystem of Suaeda salsa (S. salsa), in Chinese coastal wetlands has been severely disrupted, significantly impeding its functionality within coastal wetland ecosystems. Chlorophyll content (Cab) is an important parameter for monitoring the growth and health status of vegetation. However, the remote sensing mechanism of Cab for different phenotypes of green and red vegetation influenced by betacyanin under different water and salt conditions is not clear. Therefore, to further clarify the remote sensing mechanism of S. salsa and improve the generality of Cab prediction for different phenotypes under different water and salt conditions, we designed a growth experiment under different groundwater levels and salt concentrations. This experiment was used to simulate the growth of S. salsa in different habitats in nature and investigate the relationship between their physicochemical parameters, spectra, and environmental stress. We propose using the specific absorption coefficient of betacyanin (Beta) to adjust PROSAIL-D to better fit the spectral characteristics of S. salsa. The relationship between Beta and Cab was utilized to further optimize the simulation accuracy of the PROSAIL-D model in different environments. Feature extraction algorithms, including differential enhancement of two-dimensional correlation spectroscopy (FD-2DCOS) and three-band models, were introduced to construct multiple spectral features for establishing a Cab prediction model for S. salsa. The research results showed that: (1) S. salsa had the best response of Cab and spectra to salinity under a higher groundwater level and showed a gradual reddening trend. (2) The spectral curves simulated by the adjusted PROSAIL-D model were more consistent with the spectral characteristics of S. salsa under different water-salt environments, and the simulation effect could be further optimized by using the relationship between Beta and Cab. (3) The FD-2DCOS analysis method we proposed could highlight the useful spectral information related to Cab better than the original 2DCOS algorithm. The final eight spectral features of (1/R701–1/R540)R540, Mean(D590–600), Mean(D660–670), Mean(D677–685), FDVI_NRG, FDVI_NIR, Skewness (D677–750) and Position(D677–750) had the best response to Cab of S. salsa, and had the least influence on LAI and soil background. (4) The particle swarm optimization random forest regression (PSO-RFR) model based on eight spectral features and adding 70% measured spectral data performed the best in predicting the actual Cab of S. salsa, with an RMSE of 2.326 μg·cm−2. Although further optimization and calibration of the adjusted PROSAIL-D model and Cab prediction model of S. salsa are needed in the future, this study extended its application to S. salsa, a special local salt marsh vegetation, and promoted the development of Cab monitoring of salt marsh vegetation in coastal wetlands.

Optoelectronic Digital Dust Meter in Cotton Gining Manufactory

The paper discusses the problems of environmental pollution and requirements for instruments and systems for measuring dust levels. It is demonstrated that among the problems of environmental protection, the most crucial one is the protection of the air basin. Dust is one of the most common types of industrial waste. Human health is affected not only by the type of dust, particle size and mineralogical composition, but also by the duration of exposure. Therefore, high sensitivity of instruments and systems for monitoring atmospheric pollution is required. The problem of environmental pollution can only be solved with the help of automatic, continuously operating analysers. It is advisable to develop and implement portable threshold alarms that have a significantly lower cost than the cost of automatic control and measurement equipment. The operating principle of an optoelectronic device for monitoring the degree of dust in cotton ginning rooms has been developed and presented, which allows simultaneous measurement of the attenuation (extinction) and light scattering of the same passing mass of aerosol. The calculation of specific absorption and dispersion coefficients in the ginning shops of cotton gin plants has been carried out. Experimental curves of the ratio of absorption and attenuation coefficients depending on the presence of the aerosol in the optoelectronic device are presented. Methods to reduce measurement error are revealed.

Detection and quantification of olive oil adulteration using fluorescence spectroscopy and chemometric tools

The increasing incidence of fraud in the olive oil market, particularly through adulteration with cheaper oils, poses a major challenge for the industry. This study examines the effectiveness of fluorescence spectroscopy combined with chemometric tools as a method to detect and quantify olive oil adulteration. Chemical analyses were used to measure parameters such as specific absorption coefficients K232 and K270, peroxide value, and acidity, in accordance with International Olive Council (IOC) standards. These measurements were conducted on samples of olive oil blended with varying percentages of adulterating oils. 3D fluorescence spectra were analyzed to examine the changes induced by adulteration. The results show that free acidity and peroxide value decrease with increasing adulteration degree, while the parameters K232 and K270 increase with the degree of adulteration. Principal component analysis (PCA) was effectively used to differentiate samples based on the percentage of adulterant. A partial least squares (PLS) regression model was developed, achieving a correlation coefficient of 0.999 for predicting the percentage of adulterant in olive oil. This PLS model also proved effective in predicting oil quality parameters such as free acidity and K232 and K270 indices. The results of this study demonstrate the significant potential of fluorescence spectroscopy as a rapid and non-destructive method for olive oil authentication. PCA emerges as a powerful tool for characterizing pure oils without requiring sample preparation or destruction. Furthermore, PLS models provide accurate means to predict both the presence of adulterants and olive oil quality parameters. This approach offers a promising solution to combat fraud in the olive oil industry, ensuring product integrity and quality.

Evaluation of Cretaceous-Tertiary Limestone for Building and Dimension Stones in Erbil, Kurdistan Region of Iraq

In Kurdistan NE of Iraq extensive beddings of well bedded carbonate rocks deposited within Tertiary- Cretaceous age. For this purpose various studies of petrographic, physical, mechanical, and chemical properties for building construction were carried out. Appearance of rocks was measured in the field by thickness of the beddings, joints, fractures, and brightness. The petrographic study achived under transmitted light microscope for diagenesis, weathering, allochems, and matrix. Measuring specific gravity, density, water absorption, moisture content, porosity, and saturation coefficient to qualify the rock according to its physical properties, whereas measuring compressive strength of the rocks were determined for qualifying the mechanical properties, the XRF test for determining the oxides and durability tests for qualifying their chemical properties. Eleven samples selected from Qamchuqa Formation in Binabawi anticline, Aqra-Bekhme Formation in Shakrok anticline, Shiranish Formation in Pirat anticline, Shiranish Formation in Harir anticline, Shiranish Formation in Safin anticline, Shiranish Formation in Shakrok anticline, Pila Spi Formation in Pirmam anticline, Khurmala Formation in Bina Bawi anticline, Fatha Formation in Kori syncline, Anah Formation in South Qara Chugh anticline, and Euphrates Formation in North Qara Chugh anticline. The results in terms of economic demand for building and dimension stones showed that samples of Shiranish Formation from Pirat, Safin, Harir, and Shakrok anticline are highly recommended as dimension stone and building stone, while samples of Qamchuqa, Aqra-Bekhme, Pilaspi, Khurmala, and Euphrates Formations are accepted but not recommended as dimension stone and dimension stone, samples of Fatha and Anah Formations are not accepted as dimension stone, but accepted as building stones as an insulator.

Regulated vs. unregulated rivers: Impacts on CDOM dynamics in the eastern James Bay

The eastern James Bay (EJB) coast harbors numerous rivers, but there is a dearth of knowledge concerning dissolved organic matter (DOM) in the downstream coastal water. Here we report a four-year (2018–2021) and multi-seasons field study on the mixing behavior and characteristics of the chromophoric DOM (CDOM) in the nearshore EJB. Freshwater discharged from the extensively regulated La Grande River (LGR) was constantly depleted in DOM compared with the unregulated rivers (URRs), being on average 3.35 times lower in CDOM absorption coefficient at 440 nm (aCDOM(440)) and 2.50 times lower in dissolved organic carbon (DOC). In contrast, the absorption spectral slope between 275 and 295 nm (S275–295, a proxy of molecular weight) and the specific absorption coefficient at 254 nm (a*CDOM(254), an indicator of aromaticity) of the LGR CDOM were only 10.6% lower and 11.7% higher than those of the URRs CDOM, respectively. Riverine input was found to be the dominant source of CDOM in the study area, with little influence from sea ice formation or melting. CDOM distribution fell into two distinct regimes: the LGR-influenced low-CDOM area in the north and the URRs-influenced high-CDOM area in the south. The two areas showed strong conservative but separate aCDOM(440)–salinity relationships converging at a common marine endmember (salinity ∼25) with little seasonality. The composite data combing both areas and all seasons and years exhibited non-linear relationships between S275–295, a*CDOM(254) and aCDOM(440) and a robust simple linear correlation of DOC to aCDOM(440). This study suggests a strong impact of river regulation on CDOM input into the EJB, reveals low seasonal variability of CDOM mixing dynamics and characteristics, and demonstrates the feasibility of using remote sensing from space for real-time and synoptical assessment of DOM dynamics and the associated biogeochemical cycles in the EJB.

Concentration and Fluorescence of Chlorophyl a in the Atlantic Sector of Antarctic

The studies were carried out in cruise 79 of the R/V Akademik Mstislav Keldysh. The variability of the chlorophyll a specific light absorption coefficient of phytoplankton and the coefficient of correlation between the fluorescence intensity and chlorophyll a concentration at various optical depths under basic lighting conditions and after dark adaptation was studied. It is shown that in the absence of water stratification, there is no vertical variability in the chlorophyll a specific light absorption coefficient of phytoplankton. It was found that when measuring the intensity of chlorophyll a fluorescence with a submersible sensor, without preliminary dark adaptation, a decrease in the fluorescence intensity signal in the upper layer of water is observed, which is associated with the effect of illumination on the fluorescence quantum yield.

The determination and prediction of the apparent reaction rates between excited triplet-state DOM and selected PPCPs

To determine and predict the reaction rate between 3DOM* and PPCPs in various water bodies, this study defines a reaction rate coefficient (α3DOM∗) to describe the reaction between 3DOM* and PPCPs. As the values also included the inhibition effect of DOM's antioxidant moieties, the calculation of α3DOM∗ is inconsistent with that of a bimolecular rate constant via the steady-state kinetic method. The α3DOM∗ values of 12 selected PPCPs were determined in two DOM solutions and ten DOM-containing water samples collected from typical surface water bodies in Beijing. The Pearson coefficients between nine predictors including the absorbance ratio (E2/E3), specific absorption coefficient at 254 nm (SUVA254), fluorescence index (FI), biological index (BIX), humification index (HIX), pH, total organic carbon (TOC), total fluorescence intensity (TFI) and TOC normalized TFI (TFI/TOC) and α3DOM∗ were examined. Correlation patterns for sulfonamides, β-blockers and diclofenac supported the electron transfer pathway, and was distinctly different from those appeared for FQs where quenching effect played a main part. TFI and TFI/TOC were recognized as the most useful surrogates in empirically predicting α3DOM∗. For PPCPs that went through the electron transfer pathway, α3DOM∗ could be well fit to the Rehm-Weller model assuming a proportional relationship between TFI and △Get. For FQs, α3DOM∗ was found to linearly correlated with TFI/TOC. The α3DOM∗ values determined in this study enrich the database of PPCPs photolysis parameters, and the correlation analysis provides reference for forecasting PPCPs fate in the aquatic environment.

Batch and merging-zone flow injection methods for determination of tetracycline hydrochloride

The objective of the present work is to develop batch and merging-zone flow injection methods for sensitive and accurate spectrophotometric determination of tetracycline hydrochloride. The methods depend on the oxidation of the studied drug with potassium permanganate in an alkaline medium, and the absorbance of the green oxidation product was measured at 610 nm. The calibration graphs in both procedures were linear in the concentration ranges of 0.5 – 25 and 1 – 25 μg mL−1 using the spectrophotometric and merging-zone flow injection methods, respectively. Specific and molar absorption coefficients, limits of detection and quantification, and Sandell’s sensitivity were calculated. The suggested procedures were further applied to the quantitative determination of tetracycline in pharmaceutical formulations.

Определение мексидола в таблетках методом производной спектрофотометрии

Mexidol (3-hydroxy-6-methyl-2-ethylpyridine succinate) is a drug that exhibits neuroprotective, antihypoxic, anti-ischemic, nootropic, anti-stress and geroprotective effects and can suppress or slow down oxidation reactions. Оbjective: to develop a selective and simple method for assessing the content of mexidol in tablets. Materials and methods. The objects of the study were mexidol (3-hydroxy-6-methyl-2-ethylpyridine succinate) and Mexidol tablets 0.125 g. Derivative spectrophotometry was used as an analysis method. Results. The ability of mexidol to intensively absorb electromagnetic radiation in the quartz ultraviolet region was revealed. This phenomenon is due to the fact that the analyte molecule contains a number of chromophore groups: a system of conjugated aromatic bonds of the pyridine ring, unpaired electrons at the nitrogen atom, and an enol hydroxyl conjugated with the aromatic system In the region of 292 nm, there is a linear dependence of the derivatives of the 2nd order of the specific absorption coefficient of mexidol on the amount of analyte in the photometric solution (range 2.5-50.0 μg/ml). A calibration graph has been constructed, and its equation has been calculated by the least-squares method. The correlation coefficient exceeds 0.999. The limits of detection and quantification are 1.25 and 2.5 µg/ml, respectively. The technique is characterized by the necessary reproducibility and correctness. The values of the standard deviation and relative standard deviation in the determination of the analyte using the proposed method (n=6; P=0.95) in the tablet mass are 1.16 and 0.012, respectively, in tablets of 0.125 g, 1.32 and 0.013, respectively. Conclusion. A simple and selective method has been developed for estimating the quantitative content of mexidol in 0.125 g tablets based on the calculation of second-order derivatives of spectra.

Investigations on the enhancement of thermomagnetic properties in Fe2.4Ga0.6O4

ABSTRACT The structural, magnetic and calorimetric properties of Fe2.4Ga0.6O4 nanoferrite have been investigated. X-ray and neutron diffraction coupled analyses using Rietveld refinements have shown that the samples under investigation, obtained by different bottom-up methods, crystalize with a cubic structure in the space group (N° 227). The Ga3+ ions preferentially occupying the tetrahedral sublattice of the inverse spinel partly screen the dipole–dipole interactions and lead to the reduction of the magnetic response of Fe3+ ones. Calorimetric measurements confirm that the nanosized Fe2.4Ga0.6O4 system weakly agglomerates and simultaneously collect and release optimal amount of heat under the influence of an alternating magnetic field with the 15.3 kA/m of maximum magnetic field strength and 532 kHz of frequency. The values of the specific absorption coefficients obtained for gallium ferrites, similar to those typical for cobalt ferrites used commercially in biomedicine, together with very low superparamagnetic blocking temperature validated by Mössbauer spectroscopy analysis, make the system an attractive therapeutic material.

Molar absorption coefficients and acid dissociation constants for fluoroquinolone, sulfonamide, and tetracycline antibiotics of environmental concern

Antibiotics are priority contaminants of emerging concern due to their pseudo-persistence in the environment and contribution to the development of antimicrobial resistance. In solution, antibiotics undergo (de)protonation reactions that affect their UV absorbance and, therefore, photolytic fate in natural and engineered systems. This study employed enhanced spectrophotometric methods to determine the acid dissociation constants (as pKa values) and molar absorption coefficients for 12 fluoroquinolone, 9 sulfonamide, and 7 tetracycline antibiotics of environmental relevance. Molar absorption coefficient heatmaps were generated for all 28 antibiotics at 200–500 nm and pH 1.8–12.2. The data in the heatmaps were deconvoluted to calculate pKa values and specific molar absorption coefficients at each wavelength. All antibiotics had at least one pKa value in the environmentally relevant range of 5.5–8.5, and pKa values were reported for methacycline, moxifloxacin, nadifloxacin, rolitetracycline, sulfadoxine, and sulfapyridine for the first time. Deprotonation of the carboxylic acid associated with pKa,1 (5.5–6.7) exerted the strongest effects on the UV absorbance of fluoroquinolones. For tetracyclines, deprotonation of the tertiary amine at pKa,3 (7.8–10.2) was responsible for major shifts in UV absorbance. Although sulfonamides have conserved pKa sites, no general trends were observed for the molar absorption coefficients. The structural similarity of fluoroquinolones and tetracyclines supported the potential for a class-based approach to identifying molar absorbance as a function of pH. Overall, the reported pKa values and specific molar absorption coefficients will serve as important resources for future studies on antibiotic fate in natural and engineered systems.

Spectral Retrieval of Eucalypt Leaf Biochemical Traits by Inversion of the Fluspect-Cx Model

Leaf biochemical traits indicating early symptoms of plant stress can be assessed using imaging spectroscopy combined with radiative transfer modelling (RTM). In this study, we assessed the potential applicability of the leaf radiative transfer model Fluspect-Cx to simulate optical properties and estimate leaf biochemical traits through inversion of two native Australian eucalypt species: Eucalyptus dalrympleana and E. delegetensis. The comparison of measured and simulated optical properties revealed the necessity to recalibrate the refractive index and specific absorption coefficients of the eucalypt leaves’ biochemical constituents. Subsequent validation of the modified Fluspect-Cx showed a closer agreement with the spectral measurements. The average root mean square error (RMSE) of reflectance, transmittance and absorptance values within the wavelength interval of 450–1600 nm was smaller than 1%. We compared the performance of both the original and recalibrated Fluspect-Cx versions through inversions aiming to simultaneously retrieve all model inputs from leaf optical properties with and without prior information. The inversion of recalibrated Fluspect-Cx constrained by laboratory-based measurements produced a superior accuracy in estimations of leaf water content (RMSE = 0.0013 cm, NRMSE = 6.55%) and dry matter content (RMSE = 0.0036 g·cm−2, NRMSE = 21.28%). The estimation accuracies of chlorophyll content (RMSE = 8.46 µg·cm−2, NRMSE = 24.73%), carotenoid content (RMSE = 3.83 µg·cm−2, NRMSE = 30.82%) and anthocyanin content (RMSE = 1.69 µg·cm−2, NRMSE = 37.12%) were only marginally better than for the inversion without any constraints. Additionally, we investigated the possibility to substitute the prior information derived in the laboratory by non-destructive reflectance-based spectral indices sensitive to the retrieved biochemical traits, resulting in the most accurate estimation of carotenoid content (RMSE = 3.65 µg·cm−2, NRMSE = 29%). Future coupling of the recalibrated Fluspect with a forest canopy RTM is expected to facilitate retrieval of biophysical traits from spectral air/space-borne image data, allowing for assessing the actual physiological status and health of eucalypt forest canopies.

Glass-forming region and optical properties of TeO2 – MoO3 – La2O3 glasses

Several properties of TeO2 – MoO3 – La2O3 glasses were studied. The glass-forming region in the TeO2 – MoO3 – La2O3 system covers the composition range from 7 to 78 mol.% TeO2, from 7 to 78 mol.% MoO3 and from 0 to 30 mol.% LaO1.5. Optical transmission of glasses was investigated in the wavelength range from 450 to 2000 nm. In this spectral region, the bands of Mo+5 atoms cause the main contribution to light absorption. The presence of these atoms was confirmed by electron paramagnetic resonance method. The specific absorption coefficient attributed to Mo+5 atoms was found (0.009 ± 0.002) cm−1/ppm ((140 ± 30) cm−1/wt.%.) at 990 nm.

Bottom-up and Top-down Strategies for Fabrication of Silicon Nanowires

Silicon (Si) is an important technological material with widespread applications, especially in electronics and . Due to its specific and low light absorption coefficient, the efficiency of Si-based and solar cells is not sufficient for growing industrial needs. By patterning Si into structures, not only the light-trapping efficiency of the Si can be increased for solar cell and applications, but the process also imparts other functionalities to suitable for applications such as antibacterial surfaces, sensing, batteries, etc. Large scale applications of Si depend on their fabrication. In this article, we summarize the most commonly used fabrication techniques for Si and discuss their advantages and disadvantages.

Seasonal variability in phytoplankton light absorption properties: Implications for the regional parameterization of the chlorophyll a specific absorption coefficients

Data of in vivo absorption of particulate material in water column obtained from multiple research cruises performed in the Alboran Sea (Western Mediterranean Sea) were used to investigate seasonal variability of the phytoplankton light absorption properties. Specific absorption coefficients of phytoplankton, aph∗ (λ) were calculated and used to determine the performance of aph∗ (λ) parameterizations based on chlorophyll a concentration for each season. aph∗ (λ) in the blue spectral bands for the euphotic layer decreased by 20% in spring and summer compared with autumn and winter. These changes might reflect stronger dominance of diatoms during these periods, since these cells are characterized by a high degree of pigment packaging that leads to flattening of the absorption spectrum. Surface temperature and salinity, which are proxies for modifications of the surface layer by vertical mixing, explained more than 50% of the variability in the absorption properties, suggesting that the communities also presented high photo-acclimation capacity in response to short-term hydrological variability. The biases between measured and parameterized aph∗ (λ) decreased when the seasonal relationships between chlorophyll a concentration and aph∗ (λ) were used for estimating the parameterization coefficients instead of using the whole dataset. The regional parameterization using seasonal data performed better that parameterizations using global data. These seasonal and regional parameterizations can be useful for developing more refined bio-optical models of primary production for the study area, although it has to be taken into account that a significant percentage of variability in aph∗ (λ) related to short-term hydrological changes remained still unexplained by the seasonal parameterization.

Photochemistry of dissolved organic matter in water from the Pearl river (China): Seasonal patterns and predictive modelling

Photochemical properties of dissolved organic matter (DOM) vary widely in natural and engineered water systems due to the different dominant compositions. However, seasonal patterns of DOM photochemical properties in urban rivers remain unclear. In this study, two seasons (wet and dry) of water samples were collected from eleven sites throughout the Pearl River (China) to investigate the spatiotemporal variability of DOM optical and photochemical properties. The optical properties of DOM in the Pearl River were characterized by UV–vis and fluorescence spectroscopies, which showed the substantial decrease in absorption coefficient and fluorescence intensity and increase in absorbence ratio (E2/E3) and specific absorption coefficient (SUVA) from the wet to dry season. The photochemical properties in terms of the apparent quantum yields of 3DOM*, 1O2 and ·OH from DOM (Φ3DOM*, Φ1O2 and Φ·OH, DOM) under illumination also displayed a significant decrease from the wet to the dry season. Spearman's rank correlation analysis revealed the strongest relationships between Φ3DOM*, Φ1O2 and Φ·OH, DOM and the relative abundance of microbial humic-like component (C2%) derived from parallel factor analysis (PARAFAC). Partial least squares regression (PLSR) modelling exhibited an excellent prediction strength for steady-state concentrations of 1O2 ([1O2]ss) and ·OH ([·OH]ss) with adjusted R2 values of 0.85 and 0.91, respectively, by using DOC concentration ([DOC]), optical properties, nitrate and nitrite concentrations as the response variables. In addition, the model identified that the Fmax of humic-like component C4 (Fmax-C4) was the most effective predictor amongst the used response variables. This study provides an approach to describe and predict the seasonal patterns of DOM photochemical properties in urbanized rivers, offering a good understanding of the formation mechanism of reactive species from river DOM.

Ross Sea Dissolved Organic Matter Optical Properties During an Austral Summer: Biophysical Influences

The Ross Sea, one of the most productive regions in the Southern Ocean, plays a significant role in deep water formation and carbon cycling. Dissolved organic carbon (DOC) concentrations and chromophoric dissolved organic matter (CDOM) absorption and fluorescence (FDOM) properties were studied in conjunction with biophysical properties during austral summer. Elevated values of both DOC (mean 47.82 ± 5.70 μM) and CDOM (absorption coefficient at 325 nm, acdom325: mean 0.31 ± 0.18 m–1) observed in the upper shelf waters in the southwest (SW), north of the Ross Ice Shelf (RIS), the northwest and along a transect inward of the shelf break, suggested in situ production and accumulation linked to the productive spring/summer season. However, regional differences were observed in CDOM with acdom325 higher (0.63 ± 0.19 m–1) and its spectral slope S275–295 lower (24.06 ± 2.93 μm–1) in the SW compared to other regions (0.25 ± 0.08 m–1 and 28.92 ± 2.67 μm–1, respectively). Similarly, the specific UV absorption coefficient or SUVA254 determined at 254 nm was greater (1.85 ± 0.55 m2 mg–1 C) compared to other regions (1.07 ± 0.24 m2 mg–1 C), indicating CDOM of greater molecular weight and aromaticity in the SW. Phytoplankton absorption spectra indicated the shallow mixed layer of SW Ross Sea to be dominated by diatoms (e.g., Fragilariopsis spp.), a preferential food source for grazers such as the Antarctic krill, which in large numbers have been shown to enhance CDOM absorption, a likely source in the SW. Excitation-emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC) retrieved one protein-like and two humic-like FDOM fractions commonly observed in the global ocean. In contrast to acdom325 which was uncorrelated to DOC, we observed weak but significant positive correlations between the humic-like FDOM with salinity and DOC, high value of the biological index parameter BIX and an instance of increasing FDOM with depth at a location with sinking organic matter, suggesting autochthonous production of FDOM. The absorption budget showed a relatively higher contribution by CDOM (70.7 ± 18.3%) compared to phytoplankton (22.5 ± 15.2%) absorption coefficients at 443 nm with implications to ocean color remote sensing. This first study of DOM optical properties provides additional insights on carbon cycling in the Ross Sea.

Phytoplankton Genera Structure Revealed from the Multispectral Vertical Diffuse Attenuation Coefficient

The composition of phytoplankton and the concentration of pigments in their cells make their absorption and specific absorption coefficients key parameters for bio-optical modeling. This study investigated whether the multispectral vertical diffuse attenuation coefficient of downward irradiance (Kd) gradients could be a good framework for accessing phytoplankton genera. In situ measurements of remote sensing reflectance (Rrs), obtained in an Amazon Floodplain Lake (Lago Grande do Curuai), were used to invert Kd, focusing on Sentinel-3/Ocean and Land Color Instrument (OLCI) sensor bands. After that, an analysis based on the organization of three-way tables (STATICO) was applied to evaluate the relationships between phytoplankton genera and Kd at different OLCI bands. Our results indicate that phytoplankton genera are organized according to their ability to use light intensity and different spectral ranges of visible light (400 to 700 nm). As the light availability changes seasonally, the structure of phytoplankton changes as well. Some genera, such as Microcystis, are adapted to low light intensity at 550–650 nm, therefore high values of Kd in this range would indicate the dominance of Microcysts. Other genera, such as Aulacoseira, are highly adapted to harvesting blue-green light with higher intensity and probably grow in lakes with lower concentrations of colored dissolved organic matter that highly absorbs blue light (405–498). These findings are an important step to describing phytoplankton communities using orbital data in tropical freshwater floodplains. Furthermore, this approach can be used with biodiversity indexes to access phytoplankton diversity in these environments.