Chromophoric Dissolved Organic Matter Optical Properties Research Articles

Potential impacts of climate and anthropogenic-induced changes on DOM dynamics among the major Chinese rivers

Dissolved organic matter (DOM) is closely linked to human activities in drainage basins and plays a crucial role in maintaining ecosystem functioning and reflecting environmental quality. However, the impacts of climate and anthropogenic-induced changes on DOM in riverine systems under increasingly warming conditions still need to be better understood, particularly at large regional scales. To address this knowledge gap, we analyzed a dataset containing 386 published measurements for nine major Chinese river systems, examining dissolved organic carbon (DOC) concentrations and optical properties of chromophoric DOM (CDOM) under diverse environmental conditions, including mean air temperature, precipitation, surface solar radiation, population density, and land use. Our findings indicate that riverine DOC concentrations are significantly higher in northern China (at ∼46.8%) than in the south. This disparity is primarily due to the high input of soil erosion-induced DOM from drying-affected lands (57.0%), farmland (49.1%), and forests in the north. The high temperate and strong hydrological conditions would lead to DOM degradation easily in the riverine system in the south of China. Our study highlights that various climatic and anthropogenic factors, such as agriculture, vegetation coverage, soil erosion, surface solar radiation, and precipitation, individually or in combination, can affect DOM dynamics in river systems. Therefore, considering alterations in DOM dynamics resulting from climate and environmental changes is crucial for carbon-neutral policies and sustainable river ecosystem assessments.

Photochemical and microbial alteration of chromophoric dissolved organic matter (CDOM) in aquatic ecosystems associated with different sources

城市非点源污染向水生生态系统中输入大量的溶解有机物(DOM)，对生态系统健康产生重要影响. 有色可溶性有机物(CDOM)是广泛分布于自然水体中的一类成分和结构复杂、含有多种高活性化学官能团的大分子聚合物，是DOM的重要组分，对水生生态系统健康、能量流动及生物地球化学循环有重要影响. 光化学反应和微生物代谢过程被认为是控制水体CDOM转化、降解和循环的主要影响因素. 然而，对城市化如何影响CDOM组成以及光化学和微生物如何相互作用影响城市水体CDOM动态的理解是不足的. 因此，为评估光化学过程和微生物代谢对不同城市水体CDOM降解与转化的贡献，解析不同城市水体CDOM光化学/微生物降解作用机理，本研究在英国伯明翰选择3类具有典型DOM来源的水体样本，通过实验室9 d受控培养实验，对比分析光化学以及微生物影响下CDOM来源和组成的变化. 结果表明：(1)城市河流由于接受上游污水排放及较短的水力滞留时间，含有丰富的芳香性碳，其CDOM光化学活性明显高于湖泊，光化学降解率为16.60%;(2)城市湖泊CDOM受人类活动影响，自生源类荧光成分富集，生物活性高，在微生物培养过程中CDOM增加了62.16%，而相较于城市湖泊，非城市湖泊由于接受周围景观土壤输入的大量腐殖质类CDOM，光照对其降解转化作用较为明显; (3)光化学过程促进了陆源CDOM中大分子类腐殖质物质降解成为生物活性高的小分子化合物，刺激微生物代谢生成类蛋白质类有机物; 以类蛋白质组分为主导的CDOM在光照过程中被转化为难降解状态，生物活性降低，CDOM微生物代谢过程被抑制. 研究成果为城市水体不同CDOM来源及活性差异特征研究提供了新的思路，有助于城市河流的可持续开放与管理.;Urban non-point source pollution contributes large amounts of dissolved organic matter (DOM) to aquatic ecosystems and has a significant impact on ecosystem health. Chromophoric dissolved organic matter (CDOM) is a group of macromolecular polymers with complex composition and structure, containing a variety of highly reactive chemical functional groups, which are widely distributed in natural waters. It has an important impact on aquatic ecosystem health, energy flow and biogeochemical cycling. Photochemical reactions and microbial metabolic processes are the main controlling factors on the transformation, degradation and cycling of CDOM in water bodies. However, understanding how urbanization source input impacts CDOM quantity and quality and how photochemical and microbial interact to affect CDOM dynamic are deficient. To assess the contribution of photochemical processes and microbial metabolism to the degradation and transformation of different sources of CDOM in urban waters, and to elucidate the mechanisms of photochemical/microbial degradation of different sources of CDOM in aquatic systems (non-urban lake with humic, mostly terrestrial CDOM; urban lake with autochthonous biological production CDOM; urban river with mixed humic and protein-like CDOM), this study compares and analyses the changes in the sources and composition of CDOM under the influence of photochemistry and microorganisms in a controlled 9-day laboratory incubation experiment in three water bodies with typical urban characteristics, selected in Birmingham, UK. Changes in CDOM concentration, optical properties and chlorophyll concentration were measured at the initial and end of incubations. The results show that: (1) due to the acceptance of upstream sewage discharge and shorter hydraulic retention times, the CDOM of urban rivers is dominated by aromatic substances, with the highest photochemical degradation rate of 16.60%; (2) the CDOM of urban lakes, which is affected by human activities, is dominated by autochthonous substances, and could be increased by 62.16% via microbial metabolism, while compared to urban lakes, non-urban lakes have a more pronounced effect of light on their degradation and transformation due to receiving a large input of humus-like CDOM from the surrounding landscape soils; (3) the photochemical process could degrade terrestrial humic-like substances into small molecular compounds with high biological activity, which could stimulate microbial metabolism to produce protein-like CDOM, however, photochemical degradation could inhibit microbial metabolism by transform the autochthonous protein-like CDOM into a refractory state. The study provides a novel perspective for the differences in the sources and activities of CDOM in different urban aquatic systems and the changes in CDOM characteristics during photochemical and microbial processes.

Dissolved Organic Carbon Source Attribution in the Changjiang Outflow Region of the East China Sea.

The variable optical properties of chromophoric dissolved organic matter (CDOM) under the complicated dynamic marine environment make it difficult to establish a robust inversion algorithm for quantifying the dissolved organic carbon (DOC). To better understand the main factors affecting the relationship between the DOC and the CDOM when the Changjiang diluted water (CDW) interacts with the marine currents on the wide continental shelf, we measured the DOC concentration, the absorption, and the fluorescence spectra of the CDOM along the main axis and the northern boundary of the CDW. The sources of DOC and their impacts on the relationship between the optical properties of the DOC and CDOM are discussed. We reached the following conclusions: There are strong positive correlations between the absorptive and fluorescent properties of the DOC and the CDOM as a whole. The dilution of the terrestrial DOC carried by the CDW through mixing with saline sea water is the dominant mechanism controlling the characteristics of the optical properties of the CDOM. CDOM optical properties can be adopted to establish inversion models in retrieving DOC in Changjiang River Estuary. It is concluded that the introduction of extra DOC from different sources is the main factor causing the regional optical complexity leading to the bias of DOC estimation rather than removal mechanism. As whole, the input of polluted water from Huangpujiang River with abnormally high and Fs(355) will induce the overestimation of DOC. In the main axis of CDW, the impact from autochthonous DOC input to the correlation between DOC and CDOM can be neglected in comparison with conservative dilution procedure. The relationship between the DOC and the CDOM on the northern boundary of the CDW is more complicated, which can be attributed to the continuous input of terrestrial material from the Old Huanghe Delta by the Subei Coastal Current, the input of materials from the Yellow sea by the Yellow Sea Warm Western Coastal Current, and the input of materials from the Changjiang Basin by the CDW. The results of this study suggest that long-term observations of the regional variations in the DOM inputs from multiple sources in the interior of the CDW are essential, which is conducive to assess the degree of impact to the DOC estimation through the CDOM in the East China Sea.

Assessing the potential to use CDOM as an indicator of water quality for the sediment-laden Yellow river, China

Chromophoric dissolved organic matter (CDOM) in rivers is mainly affected by natural conditions and human activities and can reflect the watershed pollution status to a certain extent. The Yellow River is one of the largest contributors to the global riverine sediment flux from the land to ocean, and there is a paucity of information on how the optical properties of CDOM have the potential to serve as an indicator of water quality for the sediment-laden Yellow River. In this study, a three-dimensional fluorescence parallel factor (PARAFAC) analysis method was applied to investigate the seasonal and spatial variations in CDOM fluorescence components and spectral characteristics from the source region to the estuary in the mainstream of Yellow River. The relationships of CDOM with water quality indicators and trophic state were also analyzed. Six PARAFAC components (C1–C6) were identified and grouped into two categories: humic-like components (C1–C4), which accounted for 85.8 %, and protein-like components (C5 and C6), which accounted for only 14.2 %. The CDOM components, spectral parameters, and their clear correlations with the main ions (Na+ and Cl−) all indicated that the humic-like components may be primarily derived from nonpoint source erosion, and the protein-like components were mainly derived from point source discharges in the watershed. The combination of the CDOM absorption coefficient at 254 nm (a(254)), spectral slope ratio (SR), specific UV absorbance SUVA254, and fluorescence index (FI) had a good predictive ability for the key water quality indicators (total nitrogen (TN), dissolved total nitrogen (DTN), total phosphorus (TP), dissolved total phosphorus (DTP), and chlorophyll a (Chl a)) and trophic state index (TSI). Therefore, some fluorophores and UV spectral parameters of CDOM in the Yellow River can be used for rapid water quality monitoring and pollution source indication, especially pollutants related to nitrogen and phosphorus nutrients in the basin.

Assessment of Eutrophication and DOC Sources Tracing in the Sea Area around Dajin Island Using CASI and MODIS Images Coupled with CDOM Optical Properties

The sea area around Dajin Island in the Pearl River Estuary is the second-largest habitat in China for the Indo-Pacific humpback dolphin (Sousa Chinensis). However, the rapid economic development of this area brings potential threats to the aquatic ecology around Dajin Island. Real-time monitoring and evaluation of the ecological health of the sea area are urgent. In this study, band ratio and single-band inversion algorithms were performed to obtain Chlorophyll-a (Chl-a) and Suspended Sediment Concentration (SSC), relying on both Compact Airborne Spectrographic Imager (CASI) and Moderate resolution Imaging Spectrometer (MODIS) images. The CASI/Chl-a with high spatial resolution was adopted to assess the eutrophication status, while the dissolved organic carbon (DOC) concentration and chromophoric dissolved organic matter (CDOM) optical properties were used to derive the material composition and sources. The results suggest that the study area is under a low to medium eutrophication state with evenly distributed low Chl-a concentration. However, higher Chl-a is observed in the outer estuary with MODIS/Chl-a. The relatively high DOC concentration, especially in the north, where aquaculture is practiced, and near the estuary’s main axis, i.e., east Dajin Island, indicates that the eutrophication state might be underestimated using satellite chlorophyll alone. CDOM optical properties indicated that terrestrial materials are the DOC’s primary material sources, but the DOC derived from fishery aquaculture cannot be ignored. The low Chl-a concentration is likely due to the turbulent hydrodynamic regime caused by jet flow and reciprocating flow in this marine area. Comprehensive observation, including the assessment of different technological platforms, is suggested for the aquatic environment.

Optical Properties and Photochemical Transformation of the Dissolved Organic Matter Released by Sargassum

Chromophoric dissolved organic matter (CDOM) is the dominant absorber of ultraviolet radiation in the ocean, but its sources within the ocean, as well as its chemical composition, remain uncertain. One source of marine CDOM is Sargassum, an epipelagic marine macro brown alga common to the Gulf of Mexico, Caribbean, and Western North Atlantic. Furthermore, Sargassum contains phlorotannins, a class of polyphenols that may have similar optical properties to terrestrial polyphenols. Here, we analyze Sargassum CDOM optical properties, acquired from absorption and fluorescence spectra of filtered samples collected during Sargassum exudation experiments in seawater tanks. To further evaluate the structural basis of Sargassum CDOM optical properties, Sargassum CDOM was collected by solid phase extraction (SPE) and its chemical composition was tested by pH titration and sodium borohydride reduction. These chemical tests revealed that Sargassum CDOM absorption spectra respond similarly to pH titration and borohydride reduction when compared to terrestrially-derived materials, but Sargassum CDOM has unique absorbance peaks in difference spectra that have not been observed in terrestrially-derived CDOM. These absorbance features are consistent with the deprotonation of modified Sargassum phlorotannins, which are likely highly related phenolic acids and polyphenols. Sargassum CDOM was also more rapidly photodegraded when compared to terrestrial CDOM such as Suwannee River Natural Organic Matter. Similar to terrestrial DOM, ultrahigh resolution mass spectrometry revealed that sunlight decreases relative abundances of m/z ions and molecular formulas with an average O/C ratio of 0.6 and an average H/C ratio of 0.9, suggesting preferential photodegradation and/or phototransformation of hydrogen-deficient and oxygenated compounds, such as Sargassum phlorotannins. Assuming a large fraction of Sargassum CDOM is quickly mineralized to CO2 during its rapid photodegradation, Sargassum could play a major role in marine photochemical carbon mineralization during its annual growth cycle.

Chromophoric dissolved organic matter composition and load from a coastal river system under variable flow regimes

Chromophoric dissolved organic matter (CDOM) exported from riverine catchments can influence biogeochemical processes in coastal environments with implications for water quality and carbon budget. Despite recent efforts to quantify C fluxes during high flow events, knowledge gaps exist regarding the fluxes and yield of terrestrial, reactive vs. recalcitrant CDOM under episodic to base-flow conditions from uplands to downstream estuaries. We used stream dissolved organic carbon (DOC) concentrations and CDOM optical properties using parallel factor analysis to characterize composition and fluxes under variable flow conditions for a coastal river basin in the SE USA. Our findings showed that episodic flows (>75th percentile) were marked by the elevated flux of humic acid-like CDOM and lower in-stream autochthonous production, or microbial degradation. Further, 70% of the terrestrial CDOM was exported during high flows, with a 3-fold increase in CDOM flux during episodic events, including Hurricane Irene in 2011. While, low flows (<25th percentile) were marked by an increased abundance of microbial, humic CDOM that can be easily processed within the estuary. Due to greater wetland coverage in the Neuse, the annual CDOM yield was 5–6 times higher than the larger rivers, such as the Mississippi, USA, and Changjiang, China. We suggest that similar coastal watersheds in SE USA or elsewhere may contribute substantial amounts of reactive CDOM to the estuaries during high flow conditions and can have negative water quality implications for the coastal C dynamics. These findings can help predict the evolution of coastal C cycling under projected climate change and inform the development of appropriate management strategies.

Seasonal Dynamic of CDOM in a Shelf Site of the South-Eastern Ligurian Sea (Western Mediterranean)

Chromophoric dissolved organic matter (CDOM) is the fraction of the Dissolved Organic Carbon (DOC) mainly absorbing UV and blue radiation, influencing water optical properties, light availability for primary production, and water-leaving radiance. In open seas, phytoplankton is the main source of organic carbon and CDOM. Despite this, the direct or indirect phytoplankton role in CDOM production is not yet fully clarified. From studies about the relationship between CDOM and phytoplankton biomass as Chlorophyll a (Chl) in the epipelagic layer, positive correlations have been highlighted with regional differences and high levels of variability. Seven years of seasonal dynamic and vertical distribution of CDOM in the Ligurian Sea continental shelf waters have been analyzed in order to evidence the main environmental and/or biological factors determining CDOM dynamic, focusing on the CDOM/Chl relationship. CDOM optical properties (absorption at 440 nm, aCDOM (440), and spectral slope, S) allowed to distinguish different pools and to debate their origin. Four different pools were characterized and two of them were directly or indirectly related to phytoplankton biomass and taxonomic composition. Nevertheless, CDOM/Chl confirm a high level of variability These findings suggest some inputs to improve Mediterranean satellite estimates of Chl and CDOM, such as the seasonal differentiation of optical properties, especially S and CDOM/Chl relationships.

Singlet Oxygen Photogeneration in Coastal Seawater: Prospect of Large-Scale Modeling in Seawater Surface and Its Environmental Significance.

Chromophoric-dissolved organic matter (CDOM) acts as the precursor to singlet oxygen (1O2) in natural waters, while water acts as the main scavenger. In this study, we showed that 1O2 in coastal seawater can be successfully predicted from CDOM parameters. The 1O2 steady-state concentration [1O2]ss and photoformation rate (R1O2) varied by a factor of 6 across 13 sampling stations in the Seto Inland Sea, Japan, ranging from 1.2 to 8.2 × 10-14 M and 3.32 to 22.7 × 10-9 M s-1, respectively. Investigation of CDOM optical properties revealed that CDOM abundance measured as the absorption coefficient at 300 nm (a300) had the strongest correlation (r = 0.96, p < 0.001) with [1O2]ss, while parameters indicative of CDOM quality (e.g., spectral slope) did not influence [1O2]ss. A linear relationship between [1O2]ss and a300, normalized to a sunlight intensity of 0.91 kW/m2, was derived as [1O2]ss (10-14 M) = 2.12(a300) + 0.48. This was then used to predict [1O2]ss using a300 values from a subsequent, independent sampling exercise conducted 2 years after the first sampling. There was a good agreement (r = 0.93, p < 0.001) between the predicted values and the experimentally determined values based on a 95% prediction interval plot. Kinetic estimations using [1O2]ss suggest that 1O2 mediates the degradation of tetrabromobisphenol A in surface seawater (t1/2 = 0.63 days) while also contributing to the indirect photolysis of methyl mercury. The findings from this study suggest that large-scale modeling of 1O2 generation in surface seawater from CDOM parameters is possible with useful environmental significance for determining the fate of pollutants.

CDOM Optical Characteristics and Related Environmental Factors of High-turbidity Waters on the Loess Plateau

Chromophoric dissolved organic matter (CDOM) optical absorption characteristics, CDOM spectral slopes (S275-295), contribution of each component to water absorption, and the effects of environmental factors on them were analyzed to determine the sources and composition of CDOM in high-turbidity waters on the Loess Plateau. Samples in rivers and lakes (saline and freshwater) in the Loess Plateau area of Shaanxi and Inner Mongolia were collected in May 2018. The results demonstrated significant differences in CDOM absorption optical characteristics between rivers and lakes. The average aCDOM(440) (CDOM concentration, 8.45 m-1) in lakes was higher than that of rivers (2.70 m-1), and the saline lakes showed a higher CDOM concentration (13.52 m-1) than the freshwater lakes (3.38 m-1). Moreover, the light utilization efficiency of freshwater lakes is higher than that of saline lakes and turbid rivers. Great differences in pH and dissolved organic carbon (DOC) were observed between different types of water (P<0.01). The differences in electrical conductivity (EC), turbidity (Tur), and total suspended matter concentration (TSM) were significant with no statistical significances (P>0.1). The chlorophyll a concentration (Chla) in saline lakes was close to the Chla concentration in freshwater lakes if extreme values were excluded. In addition, the CDOM molecular weights of lake water were lower than those in the rivers, while CDOM molecular weights in saline lakes were lower than those in freshwater lakes based on the S275-295. Analyses of specific ultraviolet absorbance (SUVA254) were also conducted to determine the sources of CDOM in different water types, and the results showed that the more terrigenous humus were brought into the rivers and saline lakes compared with the freshwater lakes. Redundancy analysis (RDA) indicated that river and lake water quality parameters of the cumulative variance explained rates were 35.2% for river samples and 61.4% for lake samples, and 100% for samples in the saline and freshwater lakes individually. The results of RDA showed that dissolved oxygen (DO), water temperature, and EC exerted significant effects on CDOM optical properties of the river (P<0.01), while DOC, TSM, and Tur had a great influence on the CDOM optical properties of lakes (P<0.01). There was a strong correlation between pH and CDOM in the saline lakes, while DOC was significantly correlated with CDOM in the freshwater lakes (P<0.05).

DOM dynamics in open waters of the Mediterranean Sea: New insights from optical properties

In the Mediterranean Sea (Med Sea), Dissolved Organic Matter (DOM) dynamics shows some peculiarities that can be investigated by using its optical properties. Despite being a marginal sea, the Med Sea behaves as a miniature ocean for DOM concentrations and distribution. Its surface waters are “greener” than it would normally result from their generally low phytoplankton content and in the deep waters DOC is ~1000 years older and more degraded than in the Atlantic Ocean. These observations suggest a greater contribution of allocthonous substances to the DOM pool in this basin. With this work we aim at presenting new data on optical properties of chromophoric DOM (CDOM) and fluorescent DOM (FDOM) in open sea waters of the Med Sea, in order to investigate the main drivers of CDOM and FDOM dynamics in both surface and deep waters and to get insights into their origin.Our data confirm the occurrence of DOM with a different composition with respect to the oceans and suggest some differences with respect to other marginal basins, opening intriguing questions about the source and cycle of allocthonous molecules in the open sea waters of the Med Sea. CDOM absorption in the western Med Sea and Ionian Sea is generally lower than that observed in the other marginal seas, but higher than in the oceans. The parallel factor analysis unveiled the presence of one PAH-like and one terrestrial humic-like component that were found in the other marginal basins but that were not found in the open oceans. In contrast to the oceans and most of the marginal seas, only one protein-like component was found. Net production of humic-like FDOM as function of mineralization was not observed in the intermediate and deep waters of the Med Sea, supporting that in this basin CDOM/FDOM dynamics is different than in the oceans. In the surface layer, photobleaching plays a relevant role in the removal of humic-like fluorescence, and the release of both protein-like and humic-like substances occurs in proximity of the deep chlorophyll maximum.

Formation of planktonic chromophoric dissolved organic matter in the ocean

Chromophoric dissolved organic matter (CDOM) is an important fraction of the marine carbon cycle that controls most light absorption and many photochemical and biological processes in the ocean. Despite its importance, the chemical basis for the formation of oceanic CDOM remains unclear. Currently, CDOM's optical properties are best-described by an electronic interaction (EI) model of charge transfer (CT) complexes which form between electron-rich donors and electron-poor acceptors. While terrigenous compounds such as lignin best fit this model, planktonic sources of CDOM have not yet been tested. Here, we have tested CDOM formed during an incubation experiment using a natural phytoplankton assemblage and throughout active growth, stationary phase and algal biomass decomposition. Absorbance of the derived planktonic CDOM generally decreased with increasing wavelength, similar to the reference Pony Lake (PLFA) and Suwanee River (SRFA) fulvic acid solutions used as models of terrigenous CDOM. Further, after 60 d of microbial degradation in the dark, CDOM exhibited fluorescence emission maxima continuously red-shifted into the visible band, consistent with PLFA and SRFA. Reduction of carbonyl-containing groups, key to CT complex formation, with sodium borohydride (NaBH4) produced coherent results in planktonic CDOM and reference FAs. Absorption at 350 nm decreased by 50% for planktonic CDOM and by 30% for PLFA and SRFA, with corresponding increases in spectral slope (S) values, indicating preferential loss of absorption well into the visible. Fluorescence likewise responded with enhanced emission at shorter wavelengths. Apparent quantum yields (Φ) were similarly affected. Results from our work support prior observations that phytoplankton and bacteria are important sources of CDOM that color the ocean's “twilight zone”. We hypothesize that microbial processing of a variety of source substrates into more complex compounds represented as planktonic CDOM likely represents a semi-refractory pool of DOM in the ocean.

Fluorescence quantum yield of CDOM in coastal zones of the Arctic seas

ABSTRACTAlong with traditional optical indices, calculated from absorption and fluorescence spectra to describe chromophoric dissolved organic matter (CDOM) naturally occurring in water, the fluorescence quantum yield (FQY) becomes significant. Knowledge of CDOM optical properties is important for satellite remote sensing as well as for lidar ground-true measurements. The FQY as a function of excitation wavelength within 240–500 nm range for a variety of the Arctic shelf waters was determined for the first time in order to identify the characteristic chromophores peculiar to different regions of the Arctic basin affected by freshwater runoff. The surface water samples were collected during several cruises in 2015–2017 in the following sites: the mouth areas of the Khatanga and Lena Rivers (the Laptev Sea), the delta area of the Northern Dvina River (the White Sea), desalinated waters of the Kara Sea (influenced by freshwater of the Ob and Yenisei Rivers) and the East Siberian Sea (influenced by freshwaters of the Indigirka and Kolyma Rivers), as well the shelf areas of those seas not affected by terrigenous runoff. To characterize DOM, conventional optical indices SR, HIX, and BIX were calculated. In most cases, important humic character of DOM was established, while the contribution of autochthonous organic matter varied from low to intermediate level. For the samples with terrestrial impact, the FQY decreased from excitation at 240 nm to 270–280 nm and then increased, demonstrating two peaks at 340 and 380 nm, with constant decrease towards longer excitation wavelengths; at λex = 380 nm FQY varied from 1.4% to 3.1%. In some cases, additional maximum at 270 nm of FQY-excitation dependency was observed as an indicator of autochthonous nature of biological material. Minimal FQY was measured for the White Sea surface waters, the maximal for the Laptev and East Siberian seas.

Evaluation of CDOM sources and their links with antibiotics in the rivers dividing China and North Korea using fluorescence spectroscopy.

Rivers act as carriers where active cycling of chromophoric dissolved organic matter (CDOM) affected by anthropogenic activities and land cover variation may occur. Little is known about the optical properties of CDOM in relation to antibiotics; these properties could provide valuable insights into CDOM transformation processes and biogeochemical reactivity. The spatial distribution of CDOM absorption, fluorescence intensities of CDOM components, and correlations between fluorescence indices (FI370, humification index (HIX)) and biological index (BIX)) with water quality and antibiotics were investigated in three rivers, namely, two rivers (Yalu River and Tumen River) dividing China and North Korea, and the Songhua River. Four humic-like components (C1 and C3-5), and one tryptophan-like component (C2), were identified via fluorescence excitation-emission matrices-parallel factor analysis (EEM-PARAFAC). The correlation between Fmax for five EEM-PARAFAC extracted CDOM components, C1-C5, FI370, HIX, BIX, and water quality parameters, and four antibiotics (i.e., Norfloxacin, Enrofloxacin, Sulfamethoxazole and Metronidazole), were determined through a redundancy analysis (RDA), with species-environment correlations of 0.887 and 0.833, respectively. The results showed that spatial variation in land cover, pollution sources, and terrestrial contribution in water quality affected Fmax for the fluorescent components C1-C5 and the fluorescence indices, indicating a high diverse chemical composition and transformation history. The Fmax for terrestrial humic-like components, C4 and C5, showed spatial variation depending on land cover and anthropogenic impacts. Further correlation and regression analyses indicated that CDOM soil fulvic-like component C5 correlated with Sulfamethoxazole and Metronidazole (t test, p < 0.01). Our results indicate that the spatial distributions of Fmax for CDOM fluorescent terrestrial components, evaluated by EEM-PARAFAC, have potential implications for the monitoring of Sulfamethoxazole and Metronidazole in surface waters. Further, these findings can be used to understand the biogeochemical cycling of CDOM and its effects on antibiotics pollution in the environment.

Excitation-Dependent Fluorescence Quantum Yield for Freshwater Chromophoric Dissolved Organic Matter from Northern Russian Lakes

Advanced fluorescence analysis within the wide range of excitation wavelengths from 230 to 510 nm accompanied with chromatography was used to study natural chromophoric dissolved organic matter (CDOM) from three freshwater Karelian lakes. The influence of excitation wavelength (λex) on fluorescence quantum yield and emission maximum position was determined. The CDOM fluorescence quantum yield has reached a minimum at λex∼270–280 nm and a maximum at λex∼340–360 nm. It was monotonously decreasing after 370 nm towards longer excitation wavelengths. Analytical reversed-phase high-performance liquid chromatography with multiwavelength fluorescence detector characterized distribution of fluorophores between hydrophilic/hydrophobic CDOM parts. This technique revealed “hidden” protein-like fluorophores for some CDOM fractions, in spite of the absence of protein-like fluorescence in the initial CDOM samples. The humic-like fluorescence was documented for all hydrophilic and hydrophobic CDOM chromatographic peaks, and its intensity was decreasing along with peaks’ hydrophobicity. On contrary, the protein-like fluorescence was found only in the hydrophobic peaks, and its intensity was increasing along with peaks’ hydrophobicity. This work provides new data on the CDOM optical properties consistent with the formation of supramolecular assemblies controlled by association of low-molecular size components. In addition, these data are very useful for understanding the CDOM function in the environment.

Characterization of light absorption by chromophoric dissolved organic matter (CDOM) in the upper layer of the Red Sea

The absorption coefficient of chromophoric dissolved organic matter (CDOM) is a major variable used in developing robust bio‐optical models and understanding biogeochemical processes. Over the last decade, the optical properties of CDOM in the open sea have been intensely studied. However, their variations in clear water are poorly documented, particularly in the Red Sea, owing to the absence of in situ measurements. We performed several cruises in the Red Sea to investigate the spatial distribution of the absorption coefficient of CDOM. The spectral absorption coefficients were determined from 400 nm to 740 nm using a WETLabs ac-s hyper-spectral spectrophotometer. In general, we found a latitudinal gradient in the CDOM absorption coefficient at 443 nm (aCDOM(443)) from south to north that is likely influenced by the exchange of water through the strait of Bab-el-Mandeb and the thermohaline circulation of the Red Sea. However, high aCDOM(443) values were observed in the northern Red Sea due to the existence of a sub-mesoscale feature that may induce an increase in phytoplankton production and lead to CDOM production. The aCDOM(443) covaried with the chlorophyll a concentration ([Chl a],) despite a high scatter. Furthermore, the aCDOM(443) for a given [Chl a] concentration was higher than those predicted by global ocean bio-optical models. This study advances our understanding of CDOM concentration in the Red Sea and may help improve the accuracy of the algorithms used to obtain CDOM absorption from ocean color.

Spatio-seasonal variability of chromophoric dissolved organic matter absorption and responses to photobleaching in a large shallow temperate lake

Abstract. The development and validation of remote-sensing-based approaches for the retrieval of chromophoric dissolved organic matter (CDOM) concentrations requires a comprehensive understanding of the sources and magnitude of variability in the optical properties of dissolved material within lakes. In this study, spatial and seasonal variability in concentration and composition of CDOM and the origin of its variation was studied in Lake Balaton (Hungary), a large temperate shallow lake in central Europe. In addition, we investigated the effect of photobleaching on the optical properties of CDOM through in-lake incubation experiments. There was marked variability throughout the year in CDOM absorption in Lake Balaton (aCDOM(440) = 0. 06–9.01 m−1). The highest values were consistently observed at the mouth of the main inflow (Zala River), which drains humic-rich material from the adjoining Kis-Balaton wetland, but CDOM absorption decreased rapidly towards the east where it was consistently lower and less variable than in the westernmost lake basins. The spectral slope parameter for the interval of 350–500 nm (SCDOM(350–500)) was more variable with increasing distance from the inflow (observed range 0.0161–0.0181 nm−1 for the mouth of the main inflow and 0.0158–0.0300 nm−1 for waters closer to the outflow). However, spatial variation in SCDOM was more constant exhibiting a negative correlation with aCDOM(440). Dissolved organic carbon (DOC) was strongly positively correlated with aCDOM(440) and followed a similar seasonal trend but it demonstrated more variability than either aCDOM or SCDOM with distance through the system. Photobleaching resulting from a 7-day exposure to natural solar UV radiation resulted in a marked decrease in allochthonous CDOM absorption (7.04 to 3.36 m−1, 42 % decrease). Photodegradation also resulted in an increase in the spectral slope coefficient of dissolved material.

Surface Gradients in Dissolved Organic Matter Absorption and Fluorescence Properties along the New Zealand Sector of the Southern Ocean

The Southern Ocean plays a critical role in global carbon cycling; dissolved organic matter (DOM), a component in the carbon cycle, can be characterized optically. Sea surface chromophoric dissolved organic matter (CDOM) absorption and fluorescence properties were examined in the New Zealand sector of the Southern Ocean (NZSSO) along a transect encompassing various hydrographic fronts associated with the Antarctic Circumpolar Current (ACC) during summer. Phytoplankton chlorophyll, dissolved organic carbon (DOC) and CDOM absorption were observed to be most elevated off the New Zealand shore and then decreased to low values (chlorophyll: 0.21 ± 0.06 mg m-3; DOC: 54.19 ± 4.02 μM; and CDOM absorption coefficient at 325 nm (ag325): 0.097 ± 0.061 m-1) between the Subtropical (STF) and Antarctic Polar (APF) Fronts. Increases in phytoplankton biomass and DOC concentrations between the fronts were associated with meanders or eddies observed in satellite sea surface salinity and chlorophyll imagery. Overall, CDOM absorption was the dominant contributor to total absorption at 443 nm with implications for ocean color. Beyond the APF in the Antarctic Zone, an elevated chlorophyll band likely associated with upwelled waters transitioned to low chlorophyll in the summer ice edge zone that influenced DOM optical properties. A latitudinal increase in ag325 and corresponding decrease in spectral slope S (µm-1) poleward from the STF could be due to the a number of factors including, decreasing CDOM photooxidation, upwelling of high-CDOM waters or bacterial CDOM production in the Antarctic Zone. Parallel factor (PARAFAC) analysis of fluorescence spectra identified two protein-like (C1 and C2) and two humic-like (C3 and C4) components common in the global ocean. ag325 and the humic-like C4 fluorescent component, were positively correlated to chlorophyll indicating biological control. Surface distribution of the protein-like C1 and C2 and the marine humic-like C3 components showed patterns that appeared to be influenced by both physical and biological processes. This study provides insights into surface CDOM optical properties and its transformation along a complex topographically influenced sector of the Southern Ocean that could be used to trace changes linked to the meridional overturning circulation. I

Spatiotemporal Characterization of Chromophoric Dissolved Organic Matter (CDOM) and CDOM-DOC Relationships for Highly Polluted Rivers

Spectral characteristics of CDOM (Chromophoric dissolved organic matter) in water columns are a key parameter for bio-optical modeling. Knowledge of CDOM optical properties and spatial discrepancy based on the relationship between water quality and spectral parameters in the Yinma River watershed with in situ data collected from highly polluted waters are exhibited in this study. Based on the comprehensive index method, the riverine waters showed serious contamination; especially the chemical oxygen demand (COD), iron (Fe), manganese (Mn), mercury (Hg) and dissolved oxygen (DO) were out of range of the contamination warning. Dissolved organic carbon (DOC) and total suspended matter (TSM) with prominent non-homogenizing were significantly high in the riverine waters, but chlorophyll-a (Chl-a) was the opposite. The ternary phase diagram showed that non-algal particle absorption played an important role in total non-water light absorption (&gt;50%) in most sampling locations, and mean contributions of CDOM were 13% and 22% in the summer and autumn, respectively. The analysis of the ratio of absorption at 250–365 nm (E250:365) and the spectral slope (S275–295) indicated that CDOM had higher aromaticity and molecular weight in autumn than in summer, which is consistent with the results of water quality and the CDOM relative contribution rate. Redundancy analysis (RDA) indicated that the environmental variables OSM (Organic suspended matter) had a strong correlation with CDOM absorption, followed by heavy metals, e.g., Mn, Hg and Cr6+. However, for the specific UV absorbance (SUVA254), the seasonal values showed opposite results compared with the reported literature. The potential reasons were that more UDOM (uncolored dissolved organic matter) from human sources (wastewater effluent) existed in the waters. Terrigenous inputs simultaneously are in relation to the aCDOM(440)-DOC relationship with the correlation coefficient of 0.90 in the summer (two-tailed, p &lt; 0.01), and 0.58 in the autumn (two-tailed, p &lt; 0.05). Spatial distribution of the CDOM parameters exhibited that the downstream regions focused on dry land have high CDOM molecular weight and aromatic hydrocarbon. Partial sampling locations around the cities or countries generally showed abnormal values due to terrigenous inputs. As a bio-optical model parameter, the spectral characteristic of CDOM is helpful in adjusting the derived algorithms in highly polluted environments. The study on organic carbon and pollutants in highly polluted waters had an important contribution to global carbon balance estimation and water environment protection.

Optical properties of chromophoric dissolved organic matter (CDOM) in surface and pore waters adjacent to an oil well in a southern California salt marsh

Chromophoric dissolved organic matter (CDOM) optical properties were measured in surface and pore waters as a function of depth and distance from an oil well in a southern California salt marsh. Higher fluorescence and absorbances in pore vs. surface waters suggest soil pore water is a reservoir of CDOM in the marsh. Protein-like fluorophores in pore waters at distinct depths corresponded to variations in sulfate depletion and Fe(II) concentrations from anaerobic microbial activity. These variations were supported by fluorescence indexes and are consistent with differences in optical molecular weight and aromaticity indicators. Fluorescence indices were consistent with autochthonous material of aquatic origin in surface waters, with more terrestrial, humified allochthonous material in deeper pore waters. CDOM optical properties were consistent with significantly enhanced microbial activity in regions closest to the oil well, along with a three-dimensional excitation/emission matrix fluorescence spectrum peak attributable to oil, suggesting anaerobic microbial degradation of oil.