Chromophoric Dissolved Organic Matter Composition Research Articles

Chromophoric dissolved organic matter in the estuaries of populated and mountainous Taiwan

Absorption and fluorescence of chromophoric dissolved organic matter (CDOM) in 16 Taiwan estuaries are reported for the first time, so as to examine the influence of catchment characteristics on the CDOM level and to study the estuarine behavior of CDOM. The absorption coefficient (a350) in the freshwater end-member ranged from 0.15 to 12.5m−1 among estuaries. The a350 and fluorescence intensities correlated positively with population density and the chlorophyll a concentration, likely due to the additions of CDOM from anthropogenic activities and autochthonous production. The freshwater a350 also correlated negatively with precipitation, headwater altitude and freshwater discharge. The a350 generally decreased linearly with increasing salinity in most estuaries. Humic-like fluorescent components had intensities strongly correlated with a350, while protein-like components received notable additions in five estuaries but were removed in another five estuaries. The absorption spectral slope (S275–295) and slope ratio (SR; 275–295nm slope: 350–400nm slope) generally increased with increasing salinity, likely reflecting a decrease in the average molecular weight. The contribution of protein-like components to the total fluorescence changed greatly among different estuaries, which was in part associated with river population density and precipitation. The results showed that both the catchment characteristics and estuarine biogeochemical processes contributed to the variations of CDOM level and composition in estuarine environments.

Abundance, size distributions and trace-element binding of organic and iron-rich nanocolloids in Alaskan rivers, as revealed by field-flow fractionation and ICP-MS

Water samples were collected from six small rivers in the Yukon River basin in central Alaska to examine the role of colloids and organic matter in the transport of trace elements in Northern high latitude watersheds influenced by permafrost. Concentrations of dissolved organic carbon (DOC), selected elements (Al, Si, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Rb, Sr, Ba, Pb, U), and UV-absorbance spectra were measured in 0.45μm filtered samples. ‘Nanocolloidal size distributions’ (0.5–40nm, hydrodynamic diameter) of humic-type and chromophoric dissolved organic matter (CDOM), Cr, Mn, Fe, Co, Ni, Cu, Zn, and Pb were determined by on-line coupling of flow field-flow fractionation (FFF) to detectors including UV-absorbance, fluorescence, and ICP-MS. Total dissolved and nanocolloidal concentrations of the elements varied considerably between the rivers and between spring flood and late summer base flow. Data on specific UV-absorbance (SUVA), spectral slopes, and the nanocolloidal fraction of the UV-absorbance indicated a decrease in aromaticity and size of CDOM from spring flood to late summer. The nanocolloidal size distributions indicated the presence of different ‘components’ of nanocolloids. ‘Fulvic-rich nanocolloids’ had a hydrodynamic diameter of 0.5–3nm throughout the sampling season; ‘organic/iron-rich nanocolloids’ occurred in the <8nm size range during the spring flood; whereas ‘iron-rich nanocolloids’ formed a discrete 4–40nm components during summer base flow. Mn, Co, Ni, Cu and Zn were distributed between the nanocolloid components depending on the stability constant of the metal (+II)–organic complexes, while stronger association of Cr to the iron-rich nanocolloids was attributed to the higher oxidation states of Cr (+III or +IV). Changes in total dissolved element concentrations, size and composition of CDOM, and occurrence and size of organic/iron and iron-rich nanocolloids were related to variations in their sources from either the upper organic-rich soil or the deeper mineral layer, depending on seasonal variations in hydrological flow patterns and permafrost dynamics.

Changes in the Quality of Chromophoric Dissolved Organic Matter Leached from Senescent Leaf Litter during the Early Decomposition

Chromophoric dissolved organic matter (CDOM) leached from leaf litter is a major source of humus in mineral soil of forest ecosystems. While their functions and refractoriness depend on the physicochemical structure, there is little information on the quality of CDOM, especially for that leached in the very early stages of litter decomposition when a large amount of dissolved organic matter (DOM) is leached. This study aimed to better understand the variations/changes in the composition of CDOM leached from senescent leaf litter from two tree species during the early stage of decomposition. Leaf litter from a conifer tree (Japanese cedar, D. Don) and a deciduous broad-leaved tree (Konara oak, Thunb.) were incubated in columns using simulated rainfall events periodically for a total of 300 d at 20°C. The quality of CDOM was investigated based on the fluorescence properties by using a combination of excitation-emission matrix fluorescence (EEM) and parallel factor analysis (PARAFAC). In addition, the phenolic composition of DOM was investigated at a molecular level by thermally assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC-MS) in the presence of tetramethylammonium hydroxide (TMAH). The EEM was statistically decomposed into eight fluorescence components (two tannin/peptide-like peaks, one protein-like peak, and five humic-like peaks). A significant contribution of tannin/peptide-like peaks was observed at the beginning of incubation, but these peaks decreased quickly and humic-like peaks increased within 1 mo of incubation. The composition of humic-like peaks was different between tree species and changed over the incubation period. Since tannin-derived phenolic compounds were detected in the DOM collected after 254 d of incubation on THM-GC-MS, it was suggested that tannins partially changed its structure, forming various humic-like peaks during the early decomposition.

Characterizing chromophoric dissolved organic matter in Lake Tianmuhu and its catchment basin using excitation-emission matrix fluorescence and parallel factor analysis

Chromophoric dissolved organic matter (CDOM) is an important optically active substance that transports nutrients, heavy metals, and other pollutants from terrestrial to aquatic systems and is used as a measure of water quality. To investigate how the source and composition of CDOM changes in both space and time, we used chemical, spectroscopic, and fluorescence analyses to characterize CDOM in Lake Tianmuhu (a drinking water source) and its catchment in China. Parallel factor analysis (PARAFAC) identified three individual fluorophore moieties that were attributed to humic-like and protein-like materials in 224 water samples collected between December 2008 and September 2009. The upstream rivers contained significantly higher concentrations of CDOM than did the lake water ( a(350) of 4.27 ± 2.51 and 2.32 ± 0.59 m −1, respectively), indicating that the rivers carried a substantial load of organic matter to the lake. Of the three main rivers that flow into Lake Tianmuhu, the Pingqiao River brought in the most CDOM from the catchment to the lake. CDOM absorption and the microbial and terrestrial humic-like components, but not the protein-like component, were significantly higher in the wet season than in other seasons, indicating that the frequency of rainfall and runoff could significantly impact the quantity and quality of CDOM collected from the catchment. The different relationships between the maximum fluorescence intensities of the three PARAFAC components, CDOM absorption, and chemical oxygen demand (COD) concentration in riverine and lake water indicated the difference in the composition of CDOM between Lake Tianmuhu and the rivers that feed it. This study demonstrates the utility of combining excitation-emission matrix fluorescence and PARAFAC to study CDOM dynamics in inland waters.

Spatial-seasonal dynamics of chromophoric dissolved organic matter in Lake Taihu, a large eutrophic, shallow lake in China

From 2005 to 2009, the spatial distribution and the seasonal dynamics of chromophoric dissolved organic matter (CDOM) were explored in Lake Taihu in eastern China. The spatial-seasonal dynamics of CDOM absorption and three CDOM composition variables, including spectral slope ( S), spectral slope ratio (S R) and the M value, defined as the ratio of absorption at 250 nm/365 nm, were analyzed and discussed. Furthermore, river input processes and degradation of phytoplankton were studied to assess their impact on CDOM composition and the factors involved in the spatial-seasonal variability of CDOM. The CDOM absorption coefficient at a wavelength of 350 nm, a(350), ranged from 1.37–9.55 m −1 with a mean of 3.33 ± 1.32 m −1. Spatially, higher a(350) values, but lower spectral slope, spectral slope ratio and M values, were recorded in the northern algae dominated bays while lower values were recorded in southeastern macrophyte dominated bays. The a(350) was significantly higher in inshore waters than in offshore waters. Values of S, S R and M decreased during the flood and algal bloom season in spring and summer whereas a(350) increased. In the three river profiles, the gradual decrease of a(350) along the trajectory from the river mouth into the lake during the flood season showed the contribution of allochthonous CDOM. A laboratory phytoplankton degradation experiment was conducted to determine the contribution of CDOM production from phytoplankton. The significant increase of a(350) with time in the CDOM production experiment underlines the importance of autochthonous CDOM production during the algal bloom season. In summary, the significant increase of a(350) in spring and summer (algal bloom season) may be due to both the allochthonous CDOM input from the surrounding rivers and the autochthonous production of CDOM from degrading phytoplankton.

Characteristics and sources of chromophoric dissolved organic matter in lakes of the Yungui Plateau, China, differing in trophic state and altitude

The high‐mountain lakes on the Yungui Plateau in China are exposed to high‐intensity ultraviolet radiation, and contain low concentrations of chromophoric dissolved organic matter (CDOM). We determined CDOM absorption, fluorescence, composition, and source in 38 lakes on the Yungui Plateau at altitudes of 1516 to 4591 m above sea level. Total nitrogen (TN), total phosphorus (TP), and chlorophyll a (Chl a) concentrations significantly increased with increasing trophic state, and decreased with altitude. The CDOM absorption coefficient aCDOM(280) significantly increased with increasing trophic state, but not with altitude. There were significant and negative correlations between altitude and TN, TP, Chl a concentrations, and aCDOM(280). Parallel factor analysis identified two humic‐like and two protein‐like fluorescent components. Humic‐like component 1 was terrestrially derived and positively correlated to CDOM absorption. Component 2 was similar to a marine humic‐like substance originating from biological degradation of phytoplankton. Components 3 and 4 were autochthonous tryptophanlike and tyrosine‐like fluorophores. CDOM was, thus, a mixture of material from the catchment and autochthonous material produced by biota in the lake. CDOM fluorescence characteristics of oligotrophic and mesotrophic lakes were dominated by the spectral signatures of protein‐like components, but marine and terrestrial humic‐like components dominated in eutrophic lakes. The fluorescence indices FI255, FI310, and FI370 were useful tools for readily defining and classifying CDOM characteristics in the Yungui Plateau lake waters.

Enumeration of bacteria from a Trichodesmium spp. bloom of the Eastern Arabian Sea: elucidation of their possible role in biogeochemistry

The carbon-flux via algal bloom events involves bacteria as an important mediator. The present study, carried out during the spring inter-monsoon month of April 2008 onboard CRV Sagar Manjusha-06 in the Eastern Arabian Sea, addresses the bloom-specific flow of carbon to bacteria via chromophoric dissolved organic matter (CDOM). Eleven stations monitored were located in the coastal, shelf and open-ocean areas off Ratnagiri (16°59′N, 73°17′E), Goa (15°30′N, 73°48′E) and Bhatkal (13°58′N, 74°33′E) coasts. Visible bloom of “saw-dust” color in the Ratnagiri shelf were microscopically examined and the presence of cyanobacteria Trichodesmium erythraeum and T. thieabautii with cell concentrations as high as 3.05 × 106 trichomes L−1 was recorded. Total bacterial counts (TBC) varied between 94.09 × 108 cells L−1 in the bloom to 1.34 × 108 cells L−1 in the non-bloom area. Chromophoric dissolved organic matter (CDOM) concentrations averaged 2.27 ± 3.02 m−1 (absorption coefficient 325 nm) in the bloom to 0.28 ± 0.07 m−1 in the non-bloom waters respectively. CDOM composition varied from a higher molecular size with lower aromaticity in the bloom to lower molecular size and increased aromaticity in the non-bloom areas respectively. Strong positive relationship of TBC with Chlorophyll a (R2 = 0.65, p < 0.01) and CDOM concentrations (R2 = 0.8373, p = 0.01) in the bloom area indicated hydrolysis and/or uptake of CDOM by bacteria. Absorption by mycosporine-like amino acid palythene (λmax = 360 nm) was recorded in the filtrate of bloom. Morphotypes of Trichodesmium-associated bacteria revealed a higher frequency of Gram-positive rods. The role of bacteria in relation to changing CDOM nature and as a factor in affecting oxygen content of the water column is discussed in context of the Arabian Sea.

The contribution of phytoplankton degradation to chromophoric dissolved organic matter (CDOM) in eutrophic shallow lakes: Field and experimental evidence

Eight field campaigns in the eutrophic, shallow, Lake Taihu in the summers from 2005 to 2007, and a phytoplankton degradation experiment of 33 days, were carried out to determine the contribution of phytoplankton degradation to CDOM. Significant and positive correlations were found between the CDOM absorption coefficient at 355 nm [ a CDOM(355)], normalized fluorescence emission (QSU) at 450 nm from excitation at 355 nm [ F n(355)], and the chlorophyll a (Chl a) concentration for all eight field campaigns, which indicates that the decomposition and degradation of phytoplankton is an important source of CDOM. In the degradation experiment, the CDOM absorption coefficient increased as phytoplankton broke down during the first 12 days, showing the production of CDOM from phytoplankton. After 12 days, a CDOM(355) had increased from the initial value 0.41 ± 0.03 m −1 to 1.37 ± 0.03 m −1 (a 234% increase), and the Chl a concentration decreased from the initial value of 349.1 ± 11.2 μg/L to 30.4 ± 13.2 μg/L (a 91.3% decrease). The mean daily production rate of CDOM from phytoplankton was 0.08 m −1 for a CDOM(355). Parallel Factor Analysis (PARAFAC) was used to assess CDOM composition from EEM spectra, and four components were identified: a terrestrial-like humic component, two marine-like humic components, and a protein-like component. The rapid increase in marine-like humic fluorophores (C3 and C4) during the degradation experiment suggests that in situ production of CDOM plays an important role in the dynamics of CDOM. The field campaigns and experimental data in the present study show that phytoplankton can be one of the important CDOM producers in eutrophic shallow lakes.

Photochemical degradation of chromophoric-dissolved organic matter exposed to simulated UV-B and natural solar radiation

Photochemical degradation of chromophoric-dissolved organic matter (CDOM) by UV-B radiation decreases CDOM absorption in the UV region and fluorescence intensity, and alters CDOM composition. CDOM absorption, fluorescence, and the spectral slope indicating the CDOM composition were studied using 0.22-μm-filtered samples of Meiliang Bay water from Lake Taihu that were exposed to short-term (0–12 h) simulated UV-B radiation and long-term (0–12 days) natural solar radiation in summer. CDOM absorption coefficient and fluorescence decreased with increasing exposure time, which relates to the amounts of absorbed light energy. The decreases of CDOM absorption and normalized fluorescence corresponded to first order kinetics reactions. Different decreases of CDOM absorption and fluorescence at different wavelengths suggested that the composition of CDOM changed when it absorbed ultraviolet radiation. Photochemical degradation increased the spectral slope during 275–295 nm region (S 275–295) but decreased the spectral slope during 275–295 nm region (S 350–400). The slope ratio S R (S 275–295:S 350–400) increased in the photochemical process, which could be used as an indicator of photobleaching and composition change of CDOM. Our results show that photochemical degradation is important in the cycling of CDOM, which indicated change in the composition of CDOM.

Characterization of dissolved organic matter fluorescence in the South Atlantic Bight with use of PARAFAC model: Interannual variability

Systematic water sampling for characterization of chromophoric dissolved organic matter (CDOM) in the coastal South Atlantic Bight, was conducted as part of the long term Coastal Ocean Research and Monitoring Program (CORMP). Water samples were collected during a 3.5 year period, from October 2001 until March 2005, in the vicinity of the Cape Fear River (CFR) outlet and in adjacent Onslow Bay (OB). During this study there were two divergent hydrological and meteorological conditions in the CFR drainage area: a severe drought in 2002, followed by the very wet year of 2003. CDOM was characterized optically by the absorption coefficient at 350 nm, the spectral slope coefficient ( S), and by Excitation Emission Matrix (EEM) fluorescence. Parallel Factor Analysis (PARAFAC) was used to assess CDOM composition from EEM spectra and six components were identified: three terrestrial humic-like components, one marine humic-like component and two protein-like components. Terrestrial humic-like components contributed most to dissolved organic matter (DOM) fluorescence in the low salinity plume of the CFR. The contribution of terrestrial humic-like components to DOM fluorescence in OB was much smaller than in the CFR plume area. Protein-like components contributed significantly to DOM fluorescence in the coastal ocean of OB and they dominated DOM fluorescence in the Gulf Stream waters. Hydrological conditions during the observation period significantly impacted both concentration and composition of CDOM found in the estuary and coastal ocean. In the CFR plume, there was an order of magnitude difference in CDOM absorption and fluorescence intensity between samples collected during the drought compared to the wet period. During the drought, CDOM in the CFR plume was composed of equal proportions of terrestrial humic-like components (ca. 60% of the total fluorescence intensity) with a significant contribution of proteinaceous substances (ca. 20% of the total fluorescence). During high river flow, CDOM was composed mostly of humic substances (nearly 75% of total fluorescence) with minor contributions by proteinaceous substances. The impact of changes in fresh water discharge patterns on CDOM concentration and composition was also observed in OB, though to a lesser degree.

Variations in Spectral Slope in Lake Taihu, a Large Subtropical Shallow Lake in China

Spectral slope (S), describing the exponential decrease of the absorption spectrum over a given wavelength range, is an important parameter in the study of of chromophoric dissolved organic matter (CDOM) dynamics, and also an essential input parameter in remote sensing models. Furthermore, S is often used as a proxy for CDOM composition, including the ratio of fulvic to humic acids and molecular weight. The relative broad range in S values reported in the literature can be explained by the different spectral ranges and fitting methods used. A single exponential model is used to fit the S values for 17 investigations involving 458 samples in Lake Taihu from January to October in 2004. The average S value was 15.18 ± 1.39 μm −1 for the range of 280–500 nm, which fell within the range reported in the literature. The frequency distribution of S value basically obeyed a normal distribution. Significant differences in S values between summer and other seasons showed that phytoplankton degradation was one of the important sources of CDOM in summer, whereas CDOM mainly came from the river input in other seasons. Furthermore, the estimated S value decreased with increasing wavelength range used in regression. The maximum and minimum values derived from the regression were 17.89 ± 1.25 μm −1 and 13.62 ± 2.11 μm −1 for the wavelength ranges of 280–380 nm and 400–500 nm, respectively, a decrease of 23.9%. S values significantly decreased with the increase of CDOM absorption coefficients. CDOM absorption coefficients could be more appropriately estimated from exponential model introducing the variation of S with absorption coefficients, making them useful for a remote sensing bio-optical model of Lake Taihu. DOC-specific absorption coefficient a*(λ) and the parameter M describing molecular size of the humic molecules could also be used as a proxy for the sources and types of CDOM. A general relationship was found between S and a*(λ), and M values. S increased with the decrease of DOC-specific absorption coefficient and the increase of M corresponding to the decrease of molecular weight.

Distribution, characteristics and potential impacts of chromophoric dissolved organic matter (CDOM) in Hudson Strait and Hudson Bay, Canada

The characteristics of chromophoric dissolved organic matter (CDOM) were studied in Hudson Bay and Hudson Strait in the Canadian Arctic. Hudson Bay receives a disproportionately large influx of river runoff. With high dissolved organic matter (DOM) concentrations in Arctic rivers the influence of CDOM on coastal and ocean systems can be significant, yet the distribution, characteristics and potential consequences of CDOM in these waters remain unknown. We collected 470 discrete water samples in offshore, coastal, estuarine and river waters in the region during September and October 2005. Mixing of CDOM appeared conservative with salinity, although regional differences exist due to variable DOM composition in the rivers discharging to the Bay and the presence of sea-ice melt, which has low CDOM concentrations and low salinity. There were higher concentrations of CDOM in Hudson Bay, especially in coastal waters with salinities < 28 , due to river runoff. Using CDOM composition of water masses as a tracer for the freshwater components revealed that river runoff is largely constrained to nearshore waters in Hudson Bay, while sea-ice melt is distributed more evenly in the Bay. Strong inshore–offshore gradients in the bio-optical properties of the surface waters in the Hudson Bay cause large variation in penetration of ultraviolet radiation and the photic depth within the bay, potentially controlling the vertical distribution of biomass and occurrence of deep chlorophyll maxima which are prevalent only in the more transparent offshore waters of the bay. The CDOM distribution and associated photoprocesses may influence the thermodynamics and stratification of the coastal waters, through trapping of radiant heating within the top few meters of the water column. Photoproduction of biologically labile substrates from CDOM could potentially stimulate the growth of biomass in Hudson Bay coastal waters. Further studies are needed to investigate the importance of terrestrial DOM in the Hudson Bay region, and the impact of hydroelectric development and climate change on these processes.

Absorption and fluorescence of chromophoric dissolved organic matter in the Pearl River Estuary, South China

The Pearl River is a complex river network under the influence of heavy urbanization and industrialization. The Pearl River Estuary receives freshwater from eight major sources, each containing various pollutants. The spectral absorption and fluorescence properties of chromophoric dissolved organic matter (CDOM) in the Pearl River Estuary were studied during November 2002, a low flow (dry) season. Over a salinity range of 33–0, CDOM absorption coefficients at 355 nm ( a(355)) ranged from 0.24 to 1.93 m − 1 , lower than several other American and European estuaries. In contrast to the wet season, conservative mixing was evidenced by a linear, inverse relationship between a(355) and salinity. CDOM, primarily of terrestrial origin, contained more anthropogenic organic matter than natural plant decay matter: tryptophan-like fluorophore T had the strongest signal among all fluorophores for the entire study region. The absorption spectral slope ( S), determined between 300 and 500 nm, ranged between 0.0138 and 0.0184 nm − 1 and did not show distinguishable patterns except in the transition zone between the estuary and the South China Sea. The relative composition of fluorophores was found to vary among different sources. This result demonstrated the potential for using fluorophores to characterize the composition of CDOM and trace pollutants to their various freshwater sources.

Characterization of chromophoric dissolved organic matter (CDOM) in the Baltic Sea by excitation emission matrix fluorescence spectroscopy

Chromophoric dissolved organic matter (CDOM) is the major light absorber in the Baltic Sea. In this study, excitation emission matrix (EEM) fluorescence spectra and UV–visible absorption spectra of CDOM are reported as a function of salinity. Samples from different locations and over different seasons were collected during four cruises in 2002 and 2003 in the Baltic Sea in both Pomeranian Bay and the Gulf of Gdansk. Absorption by CDOM decreased with increased distance from the riverine source and reached a relatively stable absorption background in the open sea. Regression analysis showed that fluorescence intensity was linearly related to absorption by CDOM at 375 nm and a CDOM(375) absorption coefficients were inversely related to salinity. Analysis of CDOM-EEM spectra indicated that a change in composition of CDOM occurred along the salinity gradient in the Baltic Sea. Analysis of percent contribution of respective fluorophore groups to the total intensity of EEM spectra indicated that the fluorescence peaks associated with terrestrial humic components of the CDOM and total integrated fluorescence decreased with decreasing CDOM absorption. In contrast, the protein-like fraction of CDOM decreased to a lesser degree than the others. Analysis of the percent contribution of fluorescence peak intensities to the total fluorescence along the salinity gradient showed that the contribution of protein-like fluorophores increased from 2.6% to 5.1% in the high-salinity region of the transect. Fluorescence and absorption changes observed in the Baltic Sea were similar to those observed in similar transects that have been sampled elsewhere, e.g. in European estuaries, Gulf of Mexico, Mid-Atlantic Bight and the Cape Fear River plume in the South Atlantic Bight, although the changes in the Baltic Sea occurred over a much smaller salinity gradient.

Modeling the spectral shape of absorption by chromophoric dissolved organic matter

A single exponential model of the form a g ( λ)∝e − s e λ was evaluated in the context of its application and interpretation in describing absorption by chromophoric dissolved organic matter (CDOM), a g , as a function of wavelength, λ. The spectral slope, s e , is often used as a proxy for CDOM composition, including the ratio of fulvic to humic acids and molecular weight. About three-quarters of the variability in s e values from the literature could be explained by the different spectral ranges used in each study. Dependency on different spectral ranges resulted from the relatively weak performance of the single exponential as a descriptor of a g ( λ) in comparison to other models that allow for greater spectral curvature. Consequently, actual variability in the spectral shape of absorption, and thus the composition of CDOM, from widely varying water types appears less than currently thought. The usefulness of five other models in describing CDOM absorption spectra in the visible domain was also evaluated. Six data sets collected with an ac9 in-situ spectrophotometer from around the coastal United States were used in the analysis. All models considered performed better than the conventional single exponential model, with the exception of a double exponential model, where the second exponential term contributed little new information in the fit. Statistically, the most “useful” model (judged by an analysis of variance) in the visible range was a hyperbolic model of the form: a g ( λ)∝ λ − s h . Although the hyperbolic model was less dependent on the spectral range used in the fit, some dependency remained. The most representative model for describing a g ( λ) from the six regions considered in this study, with a g at 412 nm as input, was: a g ( λ)= a g (412)( λ/412) −6.92. This spectral relationship may be suitable for remote sensing semi-analytical models which must compute a spectrum from a single estimate of CDOM absorption in the blue derived from a remotely sensed water-leaving radiance signal.