Characteristics Of Chromophoric Dissolved Organic Matter Research Articles

Optical Proxies of Euxinia: Spectroscopic Studies of CDOM, Chlorophyll, and Bacteriochlorophylls in the Lagoon on Zeleny Cape (the White Sea)

Along the shoreline of the White Sea, due to the post-glacial uplift of the coast, some water bodies with stable stratification have been formed. They have been classified as meromictic as they are at different stages of isolation from the Sea. As separation progresses, significant changes occur in the water column, including the composition of chromophoric dissolved organic matter (CDOM) and the structure of the aquatic microbial community. In this work, we searched for optical proxies of euxinia (anoxic conditions with accumulated hydrogen sulfide) in the water column of the meromictic lagoon on Zeleny Cape. The lagoon is separated from the White Sea basin by a shallow threshold that completely isolates the lagoon during low tide, but marine water enters the lagoon during high tide. The ecosystem in the lagoon is characterized by the marine salinity of water and a high organic matter content in the bottom water and sediments. In this study, spectral methods were used to obtain the depth distribution of CDOM, chlorophyll, and bacteriochlorophyll in the lagoon with strong water stratification and euxinic conditions in the bottom water. The measured optical CDOM characteristics were compared with hydrochemical data (water salinity, Eh, pH, dissolved oxygen), phytoplankton (oxygenic phototrophs), and green sulfur bacteria (anoxygenic phototrophs) distribution along the water column. The spectroscopic methods showed to have the advantages of not requiring water sample pre-treatment and allowing rapid sensing of CDOM and photosynthetic pigments at each horizon.

Contrasting effects of different light regimes on the photoreactivities of allochthonous and autochthonous chromophoric dissolved organic matter

Chromophoric dissolved organic matter (CDOM) plays an important role in ultraviolet (UV) light absorption in the ocean. CDOM is known to originate from either an allochthonous or autochthonous source and has varying compositions and levels of reactivity; however, the effects of individual radiation treatments and the combined effects of UVA and UVB on allochthonous and autochthonous CDOM remain poorly understood. Thus, here, we measured changes in the common optical properties of CDOM collected from China's marginal seas and the Northwest Pacific, using full-spectrum, UVA (315–400 nm), and UVB (280–315 nm) irradiation to induce photodegradation over the same time period (60 h). Excitation–emission matrices (EEMs) combined with parallel factor analysis (PARAFAC) identified four components: marine humic-like C1, terrestrial humic-like C2, soil fulvic-like C3, and tryptophan-like C4. Although the behaviours of these components during full-spectrum irradiation exhibited similar decreasing tendencies, three components (C1, C3, and C4) underwent direct photodegradation under UVB exposure, whereas C2 was more susceptible to UVA degradation. The diverse photoreactivities of the source-dependent components to different light treatments led to differing photochemical behaviours of other optical indices [aCDOM(355), aCDOM(254), SR, HIX, and BIX]. The results indicate that irradiation preferentially reduced the high humification degree or humic substance content of allochthonous DOM, and promoted the transformation from the allochthonous humic DOM components to recently produced components. Although values for the samples from different sources overlapped frequently, principal component analysis (PCA) indicated that the overall optical signatures could be linked to the original CDOM source features. The degradation of CDOM humification, aromaticity, molecular weight, and autochthonous fractions under exposure can drive the CDOM biogeochemical cycle in marine environments. These findings can aid in a better understanding of the effects of different combinations of light treatments and CDOM characteristics on CDOM photochemical processes.

Impacts of haze on the photobleaching of chromophoric dissolved organic matter in surface water

Sunlight plays an important role in the photochemical processes of chromophoric dissolved organic matter (CDOM), which is closely related to water self-purification and primary productivity of healthy aquatic ecosystem health. The fine particles of haze, a widespread air pollutant, absorb natural ultraviolet (UV) irradiation and have an unknown degree of influence on the photochemical transformation of CDOM. Here, an in-situ experiment investigating how the amount and composition of CDOM changes under hazy conditions was conducted in Ningbo, southeastern China, a city that frequently suffers from seasonal haze pollution. The results indicated that haze attenuated UV light under different weather conditions. The UV intensities were reduced from 1124.90 ± 91.58 to 510.26 ± 40.26 μW cm-2 and 748.54 ± 101.68 to 316.32 ± 40.48 μW cm-2 on sunny and cloudy days, respectively; these values approached those on rainy days (186.97 ± 28.58 μW cm-2). Consequently, the loss of dissolved organic carbon during the irradiation test was reduced on hazy days (e.g., from 5.63% to 2.59% on sunny/hazy days). The impact of haze on CDOM photobleaching was further assessed by an excitation-emission matrix (EEM) combined with parallel factor (PARAFAC) analysis. On hazy days, the EEM-PARAFAC components were saved from photobleaching to different degrees; and humic-like substances showed a stronger protective effect from haze than protein-like substances because of their higher photosensitivity. Consequently, haze could cause more terrestrial CDOM to remain in surface water. UV intensity played a critical role in the composition characteristics of CDOM. This study identifies the linkage between atmospheric pollution and water quality and demonstrates that long-term and large-scale haze may adversely influence aquatic ecology through pollutant/nutrient accumulation.

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.

Chromophoric dissolved organic matter (CDOM) in a subtropical estuary (Galveston Bay, USA) and the impact of Hurricane Harvey.

The landfall of Hurricane Harvey in August 2017 provided the opportunity to study the impact of extreme freshwater discharge on chromophoric dissolved organic matter (CDOM) properties in a subtropical estuary (Galveston Bay, Texas). Both fluorescence spectroscopy (excitation-emission matrices) and a three-component parallel factor analysis (PARAFAC) model identified changes in CDOM properties. Comparing to Coble's peaks, component 1 was similar to peak C, component 2 to peak M, and component 3 to peak B. Results clearly show three periods with distinct CDOM properties: a dry season, a wet season, and Hurricane Harvey. The dry season was characterized by higher values of the spectral slope and fluorescence and biological indices. The wet season was characterized by high values of PARAFAC components 1 and 2 (humic-like) and the absorption coefficient at 350 nm. Some CDOM components were highly correlated with salinity, indicating conservative mixing. Component 3 (protein-like) had a low correlation to salinity, suggesting degradation or production processes in the bay. Silicates and NO3- + NO2- had negative relationships with salinity and a positive one with PARAFAC components 1 and 2. PARAFAC component 3 was correlated with dissolved oxygen and chlorophyll a, suggesting a relationship between CDOM fluorescent components and phytoplankton activity. High values of the humification index were observed immediately after Hurricane Harvey, indicating increased input of terrestrial organic matter into the bay. Hurricane Harvey increased CDOM levels and humification, and the variability and changes seem to be mostly due to freshwater discharge from the San Jacinto River and not the Trinity River. The influx of freshwater was sufficient to eliminate the salinity gradient in Galveston Bay and significantly change CDOM properties. Galveston Bay recovered quickly from the hurricane and associated flux of freshwater, returning to pre-hurricane CDOM characteristics in less than 2 months.

Mixing behavior, biological and photolytic degradation of dissolved organic matter in the East China Sea and the Yellow Sea

Optical properties of dissolved organic matter (DOM) were used as an indicator of the quantitative and qualitative changes occurring in marine DOM. The spatiotemporal distribution, bioavailability, and photoreactivity of chromophoric DOM (CDOM) and dissolved organic carbon (DOC) were investigated in the East China Sea (ECS) and the Yellow Sea (YS) during spring and summer using absorption spectroscopy and fluorescence excitation-emission matrix–parallel factor analysis. Over a 4-month laboratory study, we measured changes in six commonly used optical indices, including spectral slope (S275–295), slope ratio (SR: S275–295/S350–400), specific ultraviolet absorbance (SUVA254), ratio of the sum of protein-like components to the sum of humic-like components (Cprotein/Chumic), biological index (BIX), and humification index (HIX) to determine their changes following biological and photochemical degradation processes. Significant seasonal variations were observed in the spectral characteristics of CDOM in the ECS and the YS, indicating a stronger influence of the terrestrial origin and highly aromatic content of DOM in summer than in spring; this result was likely the consequence of an increase in the Changjiang River discharge, phytoplankton production, and biological activity, resulting in an increase in DOM production. Significant correlation between salinity and optical parameters (SUVA254, S275–295, S350–400, Cprotein/Chumic) indicated that water mixing strongly influenced the distributions of these optical parameters. The bioreactivity and photoreactivity of DOM varied depending on the source material, and the autochthonous protein-like DOM was more prone to biodegradation than the terrestrial DOM. The photodegradation processes acted preferentially on the CDOM than the colorless DOM. These results demonstrated that the optical parameters exhibited distinct changes during the mixing and the biodegradation and photodegradation processes and explained the seasonal distribution of DOM in the ECS and the YS.

CDOM in the source regions of the Yangtze and Yellow Rivers, China: optical properties, possible sources, and their relationships with environmental variables.

The source regions of the Yangtze and Yellow Rivers on the Qinghai-Tibet Plateau are extremely important water resources and ecological functional areas in China, and the ecological environment is fragile and sensitive to climate change. Chromophoric dissolved organic matter (CDOM) is an important component that plays a crucial role in the biogeochemical cycle in aquatic ecosystems. However, knowledge of the distribution characteristics of CDOM in this area is limited. In this study, the optical properties, possible sources of CDOM, and their relationships with environmental variables were investigated in the two regions. The results indicated that the CDOM absorption spectra of these two source regions had a high degree of consistency, and the absorption coefficient aCDOM(355) was small, with a mean of 2.07 ± 1.10m-1. Two fluorescence components (C1 and C2) were identified and grouped into the humic-like component with parallel factor analysis (PARAFAC) of fluorescence excitation-emission matrices (EEMs), which exhibited highly similar (excitations/emission)max positions between each pair of components in the two regions. Comprehensive CDOM spectral absorption and fluorescence parameters suggested that CDOM was mainly derived from externally input humus, and the source region of the Yellow River showed stronger allochthonous sources. The dissolved organic carbon (DOC) gradients in the water affected the fluorescence intensity and indicated that the humic-like component was an important component of DOC. Water temperature (WT) and turbidity (Turb) positively affected the concentration of CDOM and the ability to absorb light in the aquatic ecosystems. Due to global warming, the rising temperature may lead to an increase in meltwater inflow in the source area and will also bring more external inputs through the runoff.

Temporal and Spatial Distribution Characteristics and Difference Analysis of Chromophoric Dissolved Organic Matter in Sediment Interstitial Water from Gangnan Reservoir

The chromophoric dissolved organic matter (CDOM), the main component of dissolved organic matter, affects the morphological characteristics, migration, and conversion of pollutants in water. Based on UV-vis spectra and excitation emission matrix spectroscopy (EEMs) combined with the parallel factor analysis (PARAFAC), the spatial distribution and spectral characteristics were investigated and source analysis of CDOM was performed. Thus, the spatiotemporal differences in the CDOM in Gangnan Reservoir were analyzed. Results showed that a254, a260, a280, and a355 exhibited significant seasonal differences in Gangnan Reservoir, and the order of CDOM concentrations was summer > spring > autumn > winter. There are significant seasonal differences in the E2/E3, E3/E4, E4/E6, and SR of interstitial water CDOM. The concentrations of E2/E3, E3/E4, E4/E6, and SR were high in winter and low in summer. E2/E3 and E3/E4 in autumn and winter were significantly higher than those in spring and summer, and the E3/E4 in autumn and winter was greater than 3.5, which indicates that the CDOM of the autumn and winter sediments has a smaller molecular weight and a lower degree of humification. Protein-like substances (C1), short-wave fulvic acid (C2), and degraded humic substances (C3) were identified by the PARAFAC model, and there was a significant positive correlation among the three fluorescent components (P<0.001). The total fluorescence intensity of CDOM and the fluorescence intensity of each fluorescent component show significant seasonal differences. The total fluorescence intensity and the fluorescence intensity of each component show the highest levels in spring, followed by autumn and winter, and the lowest levels in summer. The proportion of each fluorescent component in autumn and winter and that of each fluorescent component in spring and summer showed no significant difference. There was a significant difference in the proportion of each fluorescent component between autumn/winter and spring/summer. The BIX and FI of CDOM for autumn and winter were higher than those for spring and summer, indicating that the autogenous source of CDOM in autumn and winter is stronger than that in spring and summer, which was consistent with the result of HIX. PCA and Adonis analysis showed that the spectral characteristics of CDOM exhibited obvious seasonal differences (P<0.001). Moreover, the C1, C2, and C3 and water quality parameters (NH4+, NO3-, NO2-, TDN, and TDP) exhibited significant correlation based on linear regression. The results could provide technical support for the control of organic carbon pollution sources and water quality management in Gangnan Reservoir.

Response of Chromophoric Dissolved Organic Matter Dynamics to Different Hydrological Scenarios in the Two Largest Freshwater Lakes Connected to the Yangtze River

Poyang Lake and Dongting Lake are the two largest freshwater lakes in China connected to the Yangtze River. Changes in the water quality of the two lakes are critical to the water security of the residents surrounding the lakes. Analyses of the optical properties, including chromophoric dissolved organic matter (CDOM) absorption and fluorescence spectroscopy coupled by parallel factor analysis (PARAFAC), were carried out to investigate the dynamics of CDOM in the two lakes in different hydrological scenarios. Our results indicated that different hydrological scenarios have more notable effects on the CDOM dynamics in Poyang Lake compared to those in Dongting Lake. In Poyang Lake, the mean CDOM absorption a(254) and dissolved organic carbon (DOC) were higher in the wet season than in the dry-to-wet transition season, and higher still than in the dry season (t-test, P<0.01), and the mean of the CDOM absorption spectral slope S275-295 was higher in the dry season than in the dry-to-wet transition season and higher still than in the wet season (t-test, P<0.01). In Dongting Lake, the mean of a(254) was not significantly different between different hydrological periods, and SUVA254 reached its maximum in the dry-to-wet transition season. Four fluorescent components were identified using parallel factor analysis. The contribution percentage of CDOM protein-like components in the two lakes was higher during the dry season, and the protein-like components and humic-like components contributed roughly the same amount in the dry-to-wet season, whereas the humic-like components accounted for the main proportion in both lakes during the wet season. From the perspective of spatial distribution, the fluorescence intensity of the four components of Poyang Lake was lower in the southern upstream than in the northern downstream lake regions during the dry season, whereas in the wet season a contrast pattern was found, i.e., with high values found in the upstream lake regions. The spatial difference of fluorescence intensity of the four components in the east of Dongting Lake during the dry season was greater than that in the wet season. We found that DOC increased with increasing water level (r2=0.99, P<0.01) in Poyang Lake and tryptophan-like C2 decreased with increasing water level (r2=0.99, P<0.05) in Dongting Lake. Therefore, the water quality of the two lakes should be managed in a targeted manner according to the response characteristics of CDOM in the two lakes under different hydrological scenarios.

Absorption characteristics of CDOM in treated and non-treated urban lakes in Changchun, China

In urban settings, one may find (i) lakes that are non-treated (NT) and impacted by recurrent discharges of pollutants and nutrients, and (ii) lakes that, through restoration measures and active management, are treated (T) from external inputs. The optical properties of chromophoric dissolved organic matter (CDOM) have been used to assess the anthropogenic impact on lakes ecology, but their application in comparative assessments of urban lakes has not been attempted. For 2 years, we measured nutrients and CDOM properties in water samples collected from NT and T lakes in the city of Changchun, China. Significant differences in CDOM properties were found between the two types of lakes, and these results were supported by redundancy analysis. The NT lakes were eutrophic while the T lakes were mesotrophic, with mean trophic status index (TSI) of 74.2 and 50.3, respectively. The CDOM absorption coefficient at 350 nm, a(350), was 2-fold higher in NT than in T lakes (6.59 vs 3.21 m-1). In the NT lakes, CDOM components predominantly comprised large molecular weight (MW > 1000-Da) humus-like substances of allochthonous origin, whereas in the T lakes CDOM was dominated by low MW (<1000-Da) substances from autochthonous production. Seasonal fluctuation has a great influence on the CDOM concentration, but a little influence on its molecular composition. The CDOM concentration were higher in summer than in other seasons. Weather conditions (rainfall, temperature) and biophysical processes (biodegradation, photo-bleaching) likely contributed to these variations. We found the water quality of the treated lakes was getting better from 2016 to 2018. In summary, the study results, not only revealed seasonal effects, but most importantly documented the impact of human activities on the characteristics of CDOM in urban lakes. Most specifically, the sharp difference between the lakes in regard to a(350) (2-fold lower in T than in NT lakes) demonstrated the suitability CDOM absorption coefficient as an early indicator of the impact of treatment measures on the hydrochemistry of DOM in urban lakes.

Characteristics of Chromophoric Dissolved Organic Matter (CDOM) in Natural Rivers of Western Sichuan Plateau

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.

Characterization of DOC and CDOM and their relationship in turbid waters of a high-altitude area on the western Loess Plateau, China.

Dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) in rivers and reservoirs on the western Loess Plateau, which is an area of severe soil erosion, were investigated in September 2017 to analyze the CDOM characteristics and composition, DOC distribution and influence of environmental factors on these parameters. Great differences of water parameters were exhibited between different groups based on the analysis of variance (p < 0.01). The results indicated that rivers exhibited higher DOC concentrations (mean: 3.70 mg/L) than reservoir waters (mean: 2.04 mg/L). Artificial and agricultural lands exert a large influence on DOC concentrations, which verifies the hypothesis that intense anthropogenic activity results in high DOC concentrations. The CDOM absorption at 350 nm [aCDOM(350)] of tributary water samples was 2.73 m-1, which was higher than that in the Yellow River (1.71 m-1) and reservoir waters (1.33 m-1). The effects of DOC, TC and turbulence (Tur) on CDOM are positive and significant (p < 0.05) according to the multiple linear regressions. An analysis of the optical characteristics of CDOM indicated that waters on the Loess Plateau contained abundant humic acid and higher levels of allochthonous DOM with a higher molecular weight (MW) based on the spectral slopes (S) and specific UV absorbance (SUVA254) values.

Characterization of CDOM in reservoirs and its linkage to trophic status assessment across China using spectroscopic analysis

Chromophoric dissolved organic matter (CDOM) represents the optically active component of the DOM pool, and originates from both allochthonous and autochthonous sources. The fluorescent characteristics of dissolved organic matter (FDOM) has been widely used to trace CDOM sources and infer its composition. However, little is known about the optical and fluorescent properties of CDOM in drinking water reservoirs, and the variability of CDOM properties along trophic gradients in these aquatic systems. A total of 536 water samples were collected between 2015 and 2017 from 131 reservoirs across China to characterize CDOM and FDOM properties using both light absorption and fluorescence spectroscopies, and examine relationships with water-quality condition as expressed by the modified trophic state index (TSIM) of the reservoirs (range: 12 < TSIM < 78). With increased reservoir trophic status, CDOM absorption coefficients at 254 nm (aCDOM(254)) and total fluorescence of FRI-EEMs (excitation-emission matrix coupled with fluorescence regional integration) increased significantly (p < 0.01). Our results indicated that the nutrients in aquatic systems and the social economy factors (including wastewater, sewage, cultivated land, GDP, population) and altitude affect the CDOM absorption and fluorescence significantly (p < 0.05). Most importantly, we proposed a new classification standard associated with eutrophic status via CDOM humification index (HIX) due to the significant correlation between each other (p < 0.01). HIX less than 4 was corresponding to TSIM less than 30 as oligotrophic states; 4 < HIX ≤ 12 was corresponding to TSIM less than 50 as mesotrophic states; 12 < HIX ≤ 18 was corresponding to TSIM less than 70 as eutrophic states; HIX more than 18 is defined as hypereutrophic status with TSIM > 70. This method highlights the importance of CDOM fluorescence for aquatic DOM input and strengthens the linkage between the trophic status index and CDOM characteristics, it also contributes to establish a new rapid assessing model with quick experimental measurements to monitor the trophic status of water reservoirs.

Linking chromophoric organic matter transformation with biomarker indices in a marine phytoplankton growth and degradation experiment

The production and transformation of marine chromophoric dissolved organic matter (CDOM) provides a window into the marine biological pump as it is present at all depths and can be measured both in the field and via satellite. However, outside of lignin for terrestrial DOM, few studies have linked marine CDOM characteristics with biomarker indices. In this study, we quantified five fluorescent components of marine CDOM and base-extractable particulate organic matter (BEPOM) in a growth and degradation experiment using a natural plankton assemblage, and compared those results to bacterial abundances, hydrolytic enzyme activities, and amino acid concentrations and associated diagenetic indices. Rotating glass bottles containing plankton were sampled initially (day 0), during the mid-exponential (day 13) and stationary (day 20) growth phases, and again following a dark degradation period that lasted 42 days. Protein-like fluorescence (tryptophan-like and tyrosine-like) was correlated with the total amino acid concentrations for both the DOM and BEPOM through all phases of the incubation. However, tryptophan-like fluorescence showed a stronger correlation for aromatic amino acids. The concentration of particulate organic carbon changed significantly during each phase of the experiment and this substrate correlated with hydrolytic enzyme activities and bacterial abundance. This heterotrophy diagenetically altered the POM during the stationary phase and ultimately resulted in the increased production of more humic-like CDOM after degradation in the dark. Results from this study indicate that CDOM formation and cycling may play a prominent role in the ocean's nitrogen cycle.

Composition, Spatial Distribution Characteristics and Source Analysis of Chromophoric Dissolved Organic Matter in the Lanzhou Reach of the Yellow River

Chromophoric dissolved organic matter (CDOM) in riverine systems can be affected by environmental conditions and land-use, and can thus provide important information regarding anthropogenic activities in surrounding landscapes. It can modify the optical properties of waters and affect the balance and availability of dissolved nutrients and metals in water bodies. However, the characteristics of CDOM in the Lanzhou reach of the Yellow River have not yet been reported. In this study, the optical properties of water samples collected at 32 locations during April 2017 across the Lanzhou reach of the Yellow River were examined using UV-VIS and excitation-emission matrix fluorescence spectroscopy-parallel factor analysis (EEM-PARAFAC), to determine CDOM compositional changes, spatial distribution characteristics, and sources. Cluster analysis was used to categorize samples into groups of similar pollution levels within a study area. Results showed that CDOM was primarily comprised of low molecular weight organic substances with aromatic structure belonging to complex "protein-like-humic-like" substances, and dominated by protein-like substances (organism sources). Two humic-like components (C1, C4), one tryptophan-like component (C2), and one non-humic-like component (C3) were identified by PARAFAC. Tryptophan-like substances were predominant in the components of CDOM, accounting for 51.06% of average total fluorescence intensity. Humic-like materials and non-humic-like substances accounted for 36.74% and 12.20%, respectively. Weak correlations were observed between protein-like substances and humic-like substances, indicating different sources of these components. The distribution of total fluorescence intensity showed a distinct spatial pattern; trends in fluorescence intensity were weak-strong-weak along an upstream to downstream continuum, mainly affected by changes in the content of protein-like substances. The spatial variation of the CDOM in the Lanzhou reach of the Yellow River can therefore be assessed based on protein-like materials dynamics. Public spaces along rivers offer opportunities for community gatherings and recreational activities. However, high-intensity anthropogenic activities strongly influence CDOM concentration and composition in this area in different ways; sources include increased residential/commercial wastewater, catering, water recreation facilities pollution, shipping, and a small amount of industrial discharge. In addition, it was concluded that endogenetic pollution may become the main source of internal loading in the Lanzhou reach of the Yellow River, implying that stronger endogenetic pollution control is needed to alleviate CDOM pollution and improve water quality.

Characterization of Chromophoric Dissolved Organic Matter in the Littoral Zones of Eutrophic Lakes Taihu and Hongze during the Algal Bloom Season

Chromophoric dissolved organic matter (CDOM) is a key component with a critical role in the littoral zones of eutrophic shallow lakes; yet the characteristics of CDOM in these zones remain seldom systematically reported. In this study, the differences in sources, biogeochemical characteristics, and fates of CDOM between the littoral zones of eutrophic lakes Taihu (LLT; frequently occurring algal blooms and longer lake residence time) and Hongze (LLH; no obvious algal blooms and shorter residence time) were compared during the algal bloom season using ultraviolet-visible spectra and excitation and emission matrix spectroscopy combined with parallel factor analysis. Three humic-like fluorescent dissolved organic matter (FDOM) components (C1, C3, and C4) and one protein-like component (C2) were identified. Results showed that FDOM components were dominated by protein-like fluorescent substances in LLT, and humic-like materials in LLH, respectively. The CDOM in LLT had a lower relative aromaticity and molecular weight, humification degree and a higher autotrophic productivity because of algal blooms. Furthermore, CDOM depletion rates in LLT were higher than those in LLH due to a longer lake residence time in LLT. In addition, CDOM shifted from high molecular weight to low molecular weight as the humification degree decreased during the CDOM depletion process. This comparative study showed that algal blooms and lake residence time were the significant factors for distinguishing characteristics of CDOM between littoral zones of shallow lakes on a similar trophic level. This study provides field-based knowledge for remote sensing CDOM measurement and serves as a reference for lakeshore aquatic environmental management.

The Human Health Assessment to Phthalate Acid Esters (PAEs) and Potential Probability Prediction by Chromophoric Dissolved Organic Matter EEM-FRI Fluorescence in Erlong Lake.

Phthalate acid esters (PAEs) are suspected to cause wide environmental pollution and have adverse effects on human health. Three priority control phthalates, namely dimethyl phthalate (DMP), diethyl phthalate (DEP), and dibutyl phthalate (DBP), were determined in 45 water samples from the largest drinking water source in Jilin Province. Chromophoric-dissolved organic matter (CDOM), which are composed of complex compounds and are a proxy for water quality, can be monitored using a fluorometer. This study attempted to understand the correlations of the CDOM fluorescence regional integration (FRI) components with PAEs and CDOM characteristics under seasonal and spatial variations in the Erlong Lake. The characteristics of the CDOM absorption parameters in different water samples showed a higher aromatic content and molecular weight in October because of increased terrestrial inputs. The Σ3PAEs concentrations ranged from 0.231 mg L−1 to 0.435 mg L−1 in water, and DEP contributed to more than 90% of the Σ3PAEs. The FRI method identified five fluorescence components: one tyrosine-like (R1), one tryptophan-like (R2), one fulvic-like (R3), one microbial protein-like (R4), and one humic-like (R5) component. However, significant relationships exist between DEP and R3 (R2 = 0.78, p < 0.001), R4 (R2 = 0.77, p < 0.001), and R5 (R2 = 0.58, p < 0.001). Quantifying the relationship between CDOM and PAEs was highly significant, because the results will simplify the componential analysis of pollutants from a spatiotemporal perspective as compared to traditional chemical measurements. The human health risk assessment results revealed no human health risk (HQ < 1) in the Erlong Lake basin.

Response of dissolved organic matter optical properties to net inflow runoff in a large fluvial plain lake and the connecting channels

Fluvial plain lake watersheds are usually highly urbanized and have high concentrations of chromophoric dissolved organic matter (CDOM). CDOM derived from the connecting urban channels usually share strong terrestrial and anthropogenic signals and net inflow runoff (Qnet) to the lake serves as a proxy of residential household sewage input. We investigate how Qnet controls the optical characteristics of CDOM in fluvial plain Lake Taihu and the connecting channels. CDOM absorption coefficient a(350), dissolved organic carbon (DOC), the fluorescence intensity (Fmax) of seven PARAFAC components C1-C7, and δ15N-TDN were higher in the northwestern relative to the other lake regions, and a(250)/a(365), spectral slope S275–295, and δ13C-DOM relative low in the northwestern lake, all indicating strong terrestrial and anthropogenic effects. Conversely, the urban land cover (%Cities), gross domestic product (GDP), and population density were relatively low in the western sub-watersheds and high in the eastern sub-watersheds. This apparent paradox reflects variations in Qnet from different sub-watersheds. Thus, significant positive relationships were found between Qnet and a(350), DOC, chemical oxygen demand (COD), chlorophyll-a (Chl-a), Fmax of C1-C3 and C6-C7, and %C2-%C3 in the five hydraulic sub-watersheds. We revealed significant positive relationships between mean a(350), DOC, COD, Chl-a, C1-C3 and C6, %C2-%C3, and the products of Qnet × %Cities, Qnet × GDP, and Qnet × population density. We further found dominant contribution of lignin to the total number of assigned formulas for the samples collected from the channels in the Huxi watershed and the central lake using high resolution mass spectroscopy. We conclude that Qnet is of key importance for the optical properties of CDOM molecules in the various regions of Lake Taihu and the connecting channels.

Dissolved organic matter characteristics along sabo dammed streams based on ultraviolet visible and fluorescence spectral properties.

Changes in dissolved organic matter (DOM) characteristics were investigated in two mountainous streams with closed-type sabo dams. Surface water was collected from four stations along the two mountainous streams and analyzed using ultraviolet-visible spectrophotometry and excitation-emission fluorescence matrix (EEM) methods. Optical properties of DOM indicated an increase in molecular weight and aromaticity at stations near the sabo dams. Average spectral ratio values were low before and after the dam (i.e., < 0.72) compared to other sections of the stream. Specific ultraviolet absorbance (SUVA254) increased in the vicinities of the dams. While chromophoric DOM characteristics from two sites were influenced by the dam, fluorescence components, however, did not show notable changes around dams. Instead, the three chromophoric components distinguished by EEM-parallel factor analysis, that is, humic-like (C1 and C2) and protein-like (C3) increase along the stream. Fulvic-like component (C1) had a high fluorescence intensity at all stations; all the three components were more abundant in the downstream section. Chromophoric DOM properties varied along the stream based on alterations in molecular size and aromaticity. Using multivariate analysis, the studied sites were grouped into three clusters related to sabo dams and other activities. We conclude that sabo dams modify DOM characteristics which influence the behavior of DOM transported along the stream.

Characteristics, sources, and photobleaching of chromophoric dissolved organic matter (CDOM) in large and shallow Hongze Lake, China

Abstract Hongze Lake, the fourth largest freshwater lake in China, is located on the eastern route of the South-to-North Water Diversion Project. The current study provides a first look at the source and composition of chromophoric dissolved organic matter (CDOM) in Hongze Lake through the combination of excitation emission matrix fluorescence spectra and parallel factor (PARAFAC) analysis. Six fluorescence components were identified by the PARAFAC model: three humic-like components (C1, C2, and C3), two autochthonous protein-like components (C4 and C6), and one photoproduced humic-like component (C5). The results of fluorescence indices and principal component analyses of fluorescence components demonstrate that CDOM is primarily of autochthonous origin, specifically comprising C4 and C5 in surface and bottom waters and C6 in sediment pore water. Sediment pore water contained CDOM of relatively lower aromaticity and molecular weight than that of surface and bottom waters, suggesting various biogeochemical processes involving CDOM in the lake. Moreover, the decrease in fluorescence intensities (primarily humic-like), aromaticity, and the molecular weight suggested photobleaching of CDOM. However, the hydrological conditions in Hongze Lake were strongly affected by human activities due to the urgent demands for water resources. Therefore, the hydrological controls may affect the CDOM characteristics and biogeochemical processes (e.g., photochemical), which should be investigated in further studies.