Chromophoric Dissolved Organic Matter Absorption Research Articles

Absorption and fluorescence properties of chromophoric dissolved organic matter: implications for the monitoring of water quality in a large subtropical reservoir.

The development of techniques for real-time monitoring of water quality is of great importance for effectively managing inland water resources. In this study, we first analyzed the absorption and fluorescence properties in a large subtropical reservoir and then used a chromophoric dissolved organic matter (CDOM) fluorescence monitoring sensor to predict several water quality parameters including the total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), dissolved organic carbon (DOC), and CDOM fluorescence parallel factor analysis (PARAFAC) components in the reservoir. The CDOM absorption coefficient at 254 nm (a(254)), the humic-like component (C1), and the tryptophan-like component (C3) decreased significantly along a gradient from the northwest to the lake center, northeast, southwest, and southeast region in the reservoir. However, no significant spatial difference was found for the tyrosine-like component (C2), which contributed only four marked peaks. A highly significant linear correlation was found between the a(254) and CDOM concentration measured using the CDOM fluorescence sensor (r(2) = 0.865, n = 76, p < 0.001), indicating that CDOM concentrations could act as a proxy for the CDOM absorption coefficient measured in the laboratory. Significant correlations were also found between the CDOM concentration and TN, TP, COD, DOC, and the maximum fluorescence intensity of C1, suggesting that the real-time monitoring of CDOM concentrations could be used to predict these water quality parameters and trace the humic-like fluorescence substance in clear aquatic ecosystems with DOC <2 mg/L and total suspended matter (TSM) concentrations <15 mg/L. These results demonstrate that the CDOM fluorescence sensor is a useful tool for on-line water quality monitoring if the empirical relationship between the CDOM concentration measured using the CDOM fluorescence sensor and the water quality parameters is calibrated and validated.

The potential applications of real-time monitoring of water quality in a large shallow lake (Lake Taihu, China) using a chromophoric dissolved organic matter fluorescence sensor.

This study presents results from field surveys performed over various seasons in a large, eutrophic, shallow lake (Lake Taihu, China) using an in situ chromophoric dissolved organic matter (CDOM) fluorescence sensor as a surrogate for other water quality parameters. These measurements identified highly significant empirical relationships between CDOM concentration measured using the in situ fluorescence sensor and CDOM absorption, fluorescence, dissolved organic carbon (DOC), chemical oxygen demand (COD) and total phosphorus (TP) concentrations. CDOM concentration expressed in quinine sulfate equivalent units, was highly correlated with the CDOM absorption coefficient (r2 = 0.80, p < 0.001), fluorescence intensities (Ex./Em. 370/460 nm) (r2 = 0.91, p < 0.001), the fluorescence index (r2 = 0.88, p < 0.001) and the humification index (r2 = 0.78, p < 0.001), suggesting that CDOM concentration measured using the in situ fluorescence sensor could act as a substitute for the CDOM absorption coefficient and fluorescence measured in the laboratory. Similarly, CDOM concentration was highly correlated with DOC concentration (r2 = 0.68, p < 0.001), indicating that in situ CDOM fluorescence sensor measurements could be a proxy for DOC concentration. In addition, significant positive correlations were found between laboratory CDOM absorption coefficients and COD (r2 = 0.83, p < 0.001), TP (r2 = 0.82, p < 0.001) concentrations, suggesting a potential further application for the real-time monitoring of water quality using an in situ CDOM fluorescence sensor.

Absorption and fluorescence properties of chromophoric dissolved organic matter of the eastern Bering Sea in the summer with special reference to the influence of a cold pool

Abstract. The absorption and fluorescence properties of chromophoric dissolved organic matter (CDOM) are reported for the inner shelf, slope waters and outer shelf regions of the eastern Bering Sea during the summer of 2008, when a warm, thermally stratified surface mixed layer lay over a cold pool (&lt; 2 °C) that occupied the entire middle shelf. CDOM absorption at 355 nm (ag355) and its spectral slope (S) in conjunction with excitation–emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC) revealed large variability in the characteristics of CDOM in different regions of the Bering Sea. PARAFAC analysis aided in the identification of three humic-like (components one, two and five) and two protein-like (a tyrosine-like component three, and a tryptophan-like component four) components. In the extensive shelf region, average absorption coefficients at 355 nm (ag355, m−1) and DOC concentrations (μM) were highest in the inner shelf (0.342 ± 0.11 m−1, 92.67 ± 14.60 μM) and lower in the middle (0.226 ± 0.05 m−1, 78.38 ± 10.64 μM) and outer (0.185 ± 0.05 m−1, 79.24 ± 18.01 μM) shelves, respectively. DOC concentrations, however were not significantly different, suggesting CDOM sources and sinks to be uncoupled from DOC. Mean spectral slopes S were elevated in the middle shelf (24.38 ± 2.25 μm−1) especially in the surface waters (26.87 ± 2.39 μm−1) indicating high rates of photodegradation in the highly stratified surface mixed layer, which intensified northwards in the northern middle shelf likely contributing to greater light penetration and to phytoplankton blooms at deeper depths. The fluorescent humic-like components one, two, and five were most elevated in the inner shelf most likely from riverine inputs. Along the productive "green belt" in the outer shelf/slope region, absorption and fluorescence properties indicated the presence of fresh and degraded autochthonous DOM. Near the Unimak Pass region of the Aleutian Islands, low DOC and ag355 (mean 66.99 ± 7.94 μM; 0.182 ± 0.05 m−1) and a high S (mean 25.95 ± 1.58 μm−1) suggested substantial photobleaching of the Alaska Coastal Water, but high intensities of humic-like and protein-like fluorescence suggested sources of fluorescent DOM from coastal runoff and glacier meltwaters during the summer. The spectral slope S vs. ag355 relationship revealed terrestrial and oceanic end members along with intermediate water masses that were modeled using nonlinear regression equations that could allow water mass differentiation based on CDOM optical properties. Spectral slope S was negatively correlated (r2 = 0.79) with apparent oxygen utilization (AOU) for waters extending from the middle shelf into the deep Bering Sea indicating increasing microbial alteration of CDOM with depth. Although our data show that the CDOM photochemical environment of the Bering Sea is complex, our current information on its optical properties will aid in better understanding of the biogeochemical role of CDOM in carbon budgets in relation to the annual sea ice and phytoplankton dynamics, and to improved algorithms of ocean color remote sensing for this region.

Distribution and spectral characteristics of chromophoric dissolved organic matter in a coastal bay in northern China

The absorption spectra of chromophoric dissolved organic matter (CDOM), along with general physical, chemical and biological variables, were determined in the Bohai Bay, China, in the springs of 2011 and 2012. The absorption coefficient of CDOM at 350nm (a350) in surface water ranged from 1.00 to 1.83m−1 (mean: 1.35m−1) in May 2011 and from 0.78 to 1.92m−1 (mean: 1.19m−1) in April 2012. Little surface-bottom difference was observed due to strong vertical mixing. The a350 was weakly anti-correlated to salinity but positively correlated to chlorophyll a (Chl-a) concentration. A shoulder over 260–290nm, suggestive of biogenic molecules, superimposed the overall pattern of exponentially decreasing CDOM absorption with wavelength. The wavelength distribution of the absorption spectral slope manifested a pronounced peak at ca. 300nm characteristic of algal-derived CDOM. All a250/a365 ratios exceeded 6, corresponding to CDOM molecular weights (Mw) of less than 1kDa. Spectroscopically, CDOM in the Bohai Bay differed substantively from that in the Haihe River, the bay's dominant source of land runoff; photobleaching of the riverine CDOM enlarged the difference. Results point to marine biological production being the principal source of CDOM in the Bohai Bay during the sampling seasons. Relatively low runoff, fast dilution, and selective photodegradation are postulated to be among the overarching elements responsible for the lack of terrigenous CDOM signature in the bay water.

Marine CDOM accumulation during a coastal Arctic mesocosm experiment: No response to elevated pCO2 levels

AbstractA large‐scale multidisciplinary mesocosm experiment in an Arctic fjord (Kongsfjorden, Svalbard; 78°56.2′N) was used to study Arctic marine food webs and biogeochemical elements cycling at natural and elevated future carbon dioxide (CO2) levels. At the start of the experiment, marine‐derived chromophoric dissolved organic matter (CDOM) dominated the CDOM pool. Thus, this experiment constituted a convenient case to study production of autochthonous CDOM, which is typically masked by high levels of CDOM of terrestrial origin in the Arctic Ocean proper. CDOM accumulated during the experiment in line with an increase in bacterial abundance; however, no response was observed to increased pCO2 levels. Changes in CDOM absorption spectral slopes indicate that bacteria were most likely responsible for the observed CDOM dynamics. Distinct absorption peaks (at ~ 330 and ~ 360 nm) were likely associated with mycosporine‐like amino acids (MAAs). Due to the experimental setup, MAAs were produced in absence of ultraviolet exposure providing evidence for MAAs to be considered as multipurpose metabolites rather than simple photoprotective compounds. We showed that a small increase in CDOM during the experiment made it a major contributor to total absorption in a range of photosynthetically active radiation (PAR, 400–700 nm) and, therefore, is important for spectral light availability and may be important for photosynthesis and phytoplankton groups composition in a rapidly changing Arctic marine ecosystem.

Seasonal dynamics of light absorption by chromophoric dissolved organic matter (CDOM) in the NW Mediterranean Sea (BOUSSOLE site)

We analyze a two-year time-series of chromophoric dissolved organic matter (CDOM) light absorption measurements in the upper 400m of the water column at the BOUSSOLE site in the NW Mediterranean Sea. The seasonal dynamics of the CDOM light absorption coefficients at 440nm (acdom(440)) is essentially characterized by (i) subsurface maxima forming in spring and progressively reinforcing throughout summer, (ii) impoverishment in the surface layer throughout summer and (iii) vertical homogeneity in winter. Seasonal variations of the spectral dependence of CDOM absorption, as described by the exponential slope value (Scdom), are characterized by highest values in summer and autumn at the surface and low values at the depths of acdom(440) subsurface maxima or just below them. Variations of acdom(440) are likely controlled by microbial digestion of phytoplankton cells, which leads to CDOM production, and by photochemical destruction (photobleaching), which leads to CDOM degradation. Photobleaching is also the main driver of Scdom variations. Consistently with previous observations, acdom(440) for a given chlorophyll a concentration is higher than expected from Case I waters bio-optical models. The total non-water light absorption budget shows that surface waters at the BOUSSOLE site are largely dominated by CDOM during all seasons but the algal bloom in March and April. These results improve the knowledge of CDOM absorption dynamics in the Mediterranean Sea, which is scarcely documented. In addition, they open the way to improved algorithms for the retrieval of CDOM absorption from field or satellite radiometric measurements.

Autumn photoproduction of carbon monoxide in Jiaozhou Bay, China

Carbon monoxide (CO) plays a significant role in global warming and atmospheric chemistry. Global oceans are net natural sources of atmospheric CO. CO at surface ocean is primarily produced from the photochemical degradation of chromophoric dissolved organic matter (CDOM). In this study, the effects of photobleaching, temperature and the origin (terrestrial or marine) of CDOM on the apparent quantum yields (AQY) of CO were studied for seawater samples collected from Jiaozhou Bay. Our results demonstrat that photobleaching, temperature and the origin of CDOM strongly affected the efficiency of CO photoproduction. The concentration, absorbance and fluorescence of CDOM exponentially decreased with increasing light dose. Terrestrial riverine organic matter could be more prone to photodegradation than the marine algae-derived one. The relationships between CO AQY and the dissolved organic carbon-specific absorption coefficient at 254 nm for the photobleaching study were nonlinear, whereas those of the original samples were strongly linear. This suggests that: 1) terrestrial riverine CDOM was more efficient than marine algae-derived CDOM for CO photoproduction; 2) aromatic and olefinic moieties of the CDOM pool were affected more strongly by degradation processes than by aliphatic ones. Water temperature and the origin of CDOM strongly affected the efficiency of CO photoproduction. The photoproduction rate of CO in autumn was estimated to be 31.98 μmol m−2 d−1 and the total DOC photomineralization was equivalent to 3.25%–6.35% of primary production in Jiaozhou Bay. Our results indicate that CO photochemistry in coastal areas is important for oceanic carbon cycle.

Dynamic monitoring of water petroleum substance using HJ-1/CCD remote sensing data

The experiment data used in this paper include CDOM(Chromophoric dissolved organic matter) absorption coefficient, water apparent optical properties and petroleum pollution concentration, which were obtained in May 2008, August 2009 and June 2010 respectively at Liaohe Oilfield in Panjin city, Liaoning province of China. A model between CDOM absorption coefficient and petroleum pollution concentration was developed, and then was applied to eight HJ-1CCD remote sense images obtained from 2009 to 2011, to produce multi-period temporal and spatial distribution maps of petroleum concentration in costal waters. Based on these thematic maps, the dynamic monitoring of petroleum pollution concentration distribution was done. The results showed that (1)There was a decreasing trend of petroleum concentration from costal waters to open sea, which manifest itself as an approximately zonal distribution;(2) due to low precipitation in May and June every year, the concentration of petroleum keeps in a relatively high value state; (3) in September, the concentration of petroleum decreases dramatically as pre increases, most of the area below 0.29 mg/L; (4) compared with that in the same period, the concentration of petroleum in April 2010 is apparently higher than in April 2011, and among the images in September from 2009 to 2011,the highest concentration of petroleum appears in 2010, and the lowest in 2009.

Oxygen photolysis in the Mauritanian upwelling: Implications for net community production

We carried out 16 photochemical experiments of filtered surface water in a custom‐built solar simulator and concomitant measurements of in vitro gross primary production (GPP) and respiration (R) in the Mauritanian upwelling during a Lagrangian study following three sulfur hexafluoride—labeled patches of upwelled water (P1 to P3). Oxygen photolysis rates were correlated with the absorbance of chromophoric dissolved organic matter (CDOM) at 300 nm, suggesting first‐order kinetics with respect to CDOM. An exponential fit was used to calculate the apparent quantum yield (AQY) for oxygen photolysis, giving an average AQY of 0.00053 µmol O2 (mole photons m−2 s−1)−1 at 280 nm and slope of 0.0012 nm−1. Modeled photochemical oxygen demand (POD) at the surface (3–16 mmol m−3 d−1) occasionally exceeded R and was dominated by ultraviolet radiation (71–79%). Euphotic‐layer integrated GPP decreased with time during both P‐1 and P‐3, whereas R remained relatively constant and POD increased during P‐1 and decreased during P‐3. On Day 4 of P‐3, GPP and POD maxima coincided with high CDOM absorbance, suggesting “new” CDOM production. Omitting POD may lead to an underestimation of net community production (NCP), both through in vitro and geochemical methods (here by 2–22%). We propose that oxygen‐based NCP estimates should be revised upward. For the Mauritanian upwelling, the POD‐corrected NCP was strongly correlated with standard NCP with a slope of 1.0066 ± 0.0244 and intercept of 46.51 ± 13.15 mmol m−2 d−1.

Photooxidation of dimethylsulfide (DMS) in the Canadian Arctic

Abstract. Photolysis of dimethylsulfide (DMS), a secondary photochemical process mediated by chromophoric dissolved organic matter (CDOM), has previously been demonstrated to be an important loss term of DMS in the surface layer of warm seas and the Southern Ocean. The role of photolysis in regulating the DMS dynamics in northern polar seas remains, however, less clear. This study for the first time determined the apparent quantum yield (AQY) spectra of DMS photooxidation in Canadian Arctic seas covering Baffin Bay, the Mackenzie estuary and shelf, and the Canada Basin. The DMS AQY was fairly invariant at salinities &lt; 25 but rose rapidly with further increasing salinity in an exponential manner. Salinity can therefore be used as a quantitative indicator of the DMS AQY. The DMS AQY in the ultraviolet (UV) wavelengths was linearly and positively correlated with the spectral slope coefficient (275–295 nm) of the CDOM absorption spectrum, suggesting that marine CDOM photosensitizes the degradation of DMS more efficiently than does terrestrial CDOM or that coastal waters contain higher concentrations of substrates (most likely dissolved organic matter and redox metals) that compete for DMS-oxidizing radical intermediates. High concentrations of nitrate (~ 12 μmol L−1) in deep water samples boosted DMS photooxidation by 70–80%, due likely to radical chemistry of nitrate photolysis. Coupled optical-photochemical modeling, based on the obtained DMS AQY spectra, shows that UV-A (320–400 nm) accounted for 60–75% of the DMS photolysis in the sunlit surface layer and that photochemistry degraded DMS on an e-folding time from 9 to 100 d (mean: 29 d). The photooxidation term on average accounted for 21% of the DMS gross loss rate and was comparable to the atmospheric DMS ventilation rate estimated for the same geographic regions. The methodology adopted here to study the relationship between CDOM quality/origin and DMS AQYs, if applicable to other ocean areas, may bring results of global significance for DMS cycling and might have implications for probing other CDOM-driven photochemical processes.

Non-conservative behaviors of chromophoric dissolved organic matter in a turbid estuary: Roles of multiple biogeochemical processes

Chromophoric dissolved organic matter (CDOM) may show notable non-conservative behaviors in many estuaries due to a variety of biogeochemical processes. The partition between CDOM and chromophoric particulate organic matter (CPOM) was examined in the Jiulong Estuary (China) using absorption and fluorescence spectroscopy, which was also compared with microbial and photochemical degradations. The absorption coefficient of water-soluble CPOM (aCPOM(280)) at ambient Milli-Q water pH (6.1) ranged from 0.11 to 7.94 m−1 in the estuary and was equivalent to 5–101% of CDOM absorption coefficient. The aCPOM(280) correlated significantly with the concentration of suspended particulate matter and was highest in the bottom water of turbidity maximum zone. Absorption spectral slope (S275–295) and slope ratio (SR) correlated positively with salinity for both CPOM and CDOM, suggesting decreases in the average molecular weight with increasing salinity. The adsorption of CDOM to re-suspended sediments (at 500 mg L−1) within 2 h was equivalent to 4–26% of the initial aCDOM(280). The adsorption of CDOM to particles was less selective with respect to various CDOM constituents, while the microbial degradation resulted decreases in S275–295 and SR of CDOM and preferential removal of protein-like components. The partition between CPOM and CDOM represented a rapid and important process for the non-conservative behavior of CDOM in turbid estuaries.

A hybrid approach to estimate chromophoric dissolved organic matter in turbid estuaries from satellite measurements: A case study for Tampa Bay

Remote sensing of chromophoric dissolved organic matter (CDOM) from satellite measurements for estuaries has been problematic due to optical complexity of estuarine waters and uncertainties in satellite-derived remote sensing reflectance (Rrs, sr(-1)). Here we demonstrate a hybrid approach to combine empirical and semi-analytical algorithms to derive CDOM absorption coefficient at 443 nm (a(g)(443), m(-1)) in a turbid estuary (Tampa Bay) from MODIS Aqua (MODISA) and SeaWiFS measurements. The approach first used a validated empirical algorithm and a modified quasi-analytical algorithm (QAA) to derive chlorophyll-a concentration (Chla, mg m(-3)) and particulate backscattering coefficient at 443 nm (b(bp)(443), m(-1)), respectively, from which phytoplankton pigment and non-algal particulate absorption coefficient at 443 nm (a(ph)(443) and a(d)(443), m(-1)) were derived with pre-determined bio-optical relationships. Then, the modified QAA was used to estimate the total absorption coefficient at 443 nm (a(t)(443), m(-1)). Finally, a(g)(443) was estimated as (a(t)(443) - a(ph)(443) - a(d)(443) - a(w)(443)) where a(w)(443) is the absorption coefficient of pure water (a constant). Using data collected from 71 field stations and 33 near-concurrent satellite-field matchup data pairs covering a large dynamic range (0.3 - 8 m(-1)), the approach showed ~23% RMS uncertainties in retrieving a(g)(443) when in situ Rrs data (N = 71) were used. The same approach applied to satellite Rrs yielded much higher uncertainties of a(g)(443) (~85%) due to large errors in the satellite-retrieved Rrs(443). When the Rrs(443) was derived from the satellite-retrieved Rrs(550) and then used in the hybrid approach, uncertainties in the retrieved a(g)(443) reduced to ~30% (N = 33). Application of the approach to MODISA and SeaWiFS data led to a 15-year time series of monthly mean a(g)(443) distributions in Tampa Bay between 1998 and 2012. This time series showed significant seasonal and annual variations regulated mainly by river discharge. Testing of the approach over another turbid estuary (Chesapeake Bay, the largest estuary in the U.S.) demonstrated the potential (~25% uncertainties for a limited a(g)(443) range) of using this approach to establish long-term environmental data records (EDRs) of CDOM distributions in other estuaries with similar optical complexity.

Remote determination of chromophoric dissolved organic matter in lakes, China

Chromophoric dissolved organic matter (CDOM) strongly influences the water-leaving radiance from aquatic ecosystems. In most inland waters, the remote determination of CDOM absorption presents a central challenge due to their complex optical conditions. However, identifying the temporal and spatial variability of CDOM is fundamental to the understanding of aquatic biogeochemical dynamics. In the present study, semi-analytical and empirical modeling approaches were used to examine CDOM absorption in four, shallow, inland water bodies using the spectral bands and sensitivities of major satellite observational systems. Of the models examined, an empirical multiband model was found to provide the highest correlation with measured CDOM absorption. The spectral characteristics of the MERIS sensors yielded the best results with respect to the other available satellite sensors. High detrital load was observed to be a major impediment to estimating CDOM absorption, while lakes with elevated phytoplankton biomass did not present similar problems.

A model for remote estimation of ultraviolet absorption by chromophoric dissolved organic matter based on the global distribution of spectral slope

Absorption of ultraviolet radiation (UV, 280–400nm) by chromophoric dissolved organic matter (CDOM) precedes a host of light-sensitized surface ocean processes relevant to global climate. These include photo- and biogeochemical cycling of organic material, release of sulfur and carbon-containing gases to the atmosphere, and the photoprotection of marine microorganisms. Synoptic CDOM absorption data in the UV is highly desired yet difficult to estimate by satellite methods as the atmosphere interferes with direct detection of water-leaving UV radiance. The absorption spectrum of CDOM is typically modeled as an exponential function in which a spectral slope parameter, S, describes the rate of decrease in absorption with increase in wavelength. Significant functional relationships are observed in aquatic environments between S and the CDOM absorption coefficient at 443nm, aCDOM(443). In this paper, we use a large, systematic dataset of spectroscopic CDOM measurements from the U.S. CO2/CLIVAR Repeat Hydrography Survey to examine the relationship between S and aCDOM(443) as a means to model aCDOM(λ) in the UV from ocean color. Our resultant model predicts aCDOM(λ) at wavelengths from 325 to 412nm from the absorption coefficient of colored dissolved and detrital materials (CDM) at 443nm, aCDM(443), retrieved by an existing semi-analytical ocean color algorithm. Expected agreement (near 1:1) with the training dataset was achieved (r2=0.71–0.85, p=0, n=127). Considering inherent satellite data uncertainties as well as the model's limitations in regions with potential terrestrial influence, good correspondence between modeled and in situ values was observed during independent validation with open ocean CDOM data, such as from BIOSOPE (r2=0.77–0.85, p<0.05, n=29). The model has immediate application in global scale assessments of photochemical rate processes and CDOM cycling in the open ocean due to its simplicity and optimization using a large base of field data (>7500 samples) from diverse Case I waters.

Chemical properties of colored dissolved organic matter in the sea-surface microlayer and subsurface water of Jiaozhou Bay, China in autumn and winter

The distribution and chemical properties of chromophoric dissolved organic matter (CDOM) in the Jiaozhou Bay, China were examined during four cruises in 2010–2011. The influence of freshwater and industrial and municipal sewage along the eastern coast of the bay was clearly evident as CDOM levels (defined as a 305), and dissolved organic carbon (DOC) concentrations were well correlated with salinity during all the cruises. Moreover, DOC concentrations were significantly correlated with chlorophyll a concentrations in the surface microlayer as well as in the subsurface water. The concentrations of DOC and CDOM displayed a gradually decreasing trend from the northwestern and eastern coast to the central bay, and the values and gradients of their concentrations on the eastern coast were generally higher than those on the western coast. In addition, CDOM and DOC levels were generally higher in the surface microlayer than in the subsurface water. In comparison with DOC, CDOM exhibited a greater extent of enrichment in the microlayer in each cruise, with average enrichment factor (EF) values of 1.38 and 1.84, respectively. Four fluorescent components were identified from the surface microlayer and subsurface water samples and could be distinguished as peak A, peak T, peak B and peak M. For all the cruises, peak A levels were higher in the surface microlayer than in the subsurface water. This pattern of variationmight be attributed to the terrestrial input.

Inversion of Chromophoric Dissolved Organic Matter From EO-1 Hyperion Imagery for Turbid Estuarine and Coastal Waters

The significant implication of chromophoric dissolved organic matter (CDOM) for water quality and biogeochemical cycle leads to an increasing need of CDOM monitoring in coastal regions. Current ocean-color algorithms are mostly limited to open-sea water and have high uncertainty when directly applied to turbid coastal waters. This paper presents a semianalytical algorithm, quasi-analytical CDOM algorithm (QAA-CDOM), to invert CDOM absorption from Earth Observing-1 (EO-1) Hyperion satellite images. This algorithm was developed from a widely used ocean-color algorithm QAA and our earlier extension of QAA. The main goal is to improve the algorithm performance for a wide range of water conditions, particularly turbid waters in estuarine and coastal regions. The algorithm development, calibration, and validation were based on our intensive high-resolution underwater measurements, International Ocean Color Coordinating Group synthetic data, and global National Aeronautics and Space Administration Bio-Optical Marine Algorithm Data Set data. The result shows that retrieved CDOM absorption achieved accuracy (root mean square error (RMSE) = 0.115 m-1andR2= 0.73) in the Atchafalaya River plume area. QAA-CDOM is also evaluated for scenarios in three additional study sites, namely, the Mississippi River, Amazon River, and Moreton Bay, whereag(440) was in the wide range of 0.01-15 m-1. It resulted in expected CDOM distribution patterns along the river salinity gradient. This study improves the high-resolution observation of CDOM dynamics in river-dominated coastal margins and other coastal environments for the study of land-ocean interactive processes.

Study of influencing factors to chromophoric dissolved organic matter absorption properties from fluorescence features in Taihu lake in autumn

In order to identify the components of chromophoric dissolved organic matter (CDOM), confirm the influence of components to the absorption coefficient of CDOM (aCDOM), and estimate aCDOM from fluorescence spectra, fluorescence and optical measurements of CDOM were carried out in November 2008. The results indicate that, the primary component of CDOM is humic-like. The secondary component is tryptophan-like, which is the product of phytoplankton and aquatic debris rather than the wastewater treatment drainaged from city. In this study, six fluorophores with multiple excitation-emission matrices (EEMs) peaks (A, B, C, N, M, T) were identified according to the parallel factor analysis (PARAFAC). The average contribution of each component to the CDOM is 19.93, 18.82, 16.88, 16.39, 12.26, and 15.72%, respectively. Red Shifted phenomenon will happen with the increase of fluorescence intensity for ultraviolet and terrestrially humic-like. Conversely, marine humic-like will appear Reverse Red Shifted with the increase of fluorescence intensity. The primary contributor to the shoulder value of CDOM’s absorption coefficient at 275 nm is phytoplankton productivity, followed by marine humic-like. The main contributors to the shoulder shape are UV humic-like and phytoplankton productivity, followed by marine humic-like and tryptophan-like. A strong correlation between CDOM absorption and fluorescence intensity at emission wavelength of 424 nm and excitation wavelength ranging from 280 to 360 nm was found. The absorption coefficient can be retrieved successfully from the same excitation wavelength’s fluorescence intensity by an exponential model.

Contribution of ferric iron to light absorption by chromophoric dissolved organic matter

This study experimentally determined the contribution of ferric iron (Fe(III)) associated with humic substances (HS) to light absorption by chromophoric dissolved organic matter (CDOM). The associations between Fe(III) and HS (HS‐Fe) were generated by mixing HS standards with Fe(III) in acidic conditions and adjusting pH to 8. HS‐associated Fe was separated from total Fe by filtering (0.7 µm and 0.2 µm filters) and by removing the free Fe ions by cation exchange chromatography. The maximum Fe‐binding capacities (at pH 8) of Suwannee River humic acid, Suwannee River fulvic acid, and Pony Lake (Antarctica) fulvic acid were 13.0, 13.5, and 7.64 µmol Fe [mg C]−1, respectively, indicating that wetland‐derived HS had a higher Fe‐binding capacity than plankton‐derived HS. HS‐associated Fe increased the absorption coefficient of CDOM by up to several fold in the visible range of the spectrum and reduced the spectral slope coefficient of CDOM. The Fe‐induced increase in light absorption was spectrally similar among different HS examined. The Fe‐specific absorption coefficient spectrum for HS‐associated Fe (aλ,Fe*) was calculated from the Fe‐induced increase in light absorption by normalizing it with the concentration of Fe in the HS pool. The aλ,Fe* was adopted in estimation of the contribution of HS‐associated Fe to light absorption by CDOM in 13 circum‐neutral natural waters collected from a spring, 10 major rivers, a lake, and a coastal area. HS‐associated Fe was calculated to be responsible for from 0.6% (Mississippi River) to 56.4% (Löytynlähde spring) of light absorption by CDOM at a wavelength of 410 nm. This study shows that HS‐associated Fe can be an important component in light absorption by CDOM and also influence the spectral slope coefficient of CDOM.

Absorption characteristics of particulates and the CDOM in autumn in Guanting Reservoir

利用2012年9月5日在官厅水库采集的水体吸收系数数据,对总悬浮颗粒物、浮游植物色素颗粒物、非色素颗粒物和有色可溶性有机物的吸收特性进行研究.结果表明:秋季官厅水库的颗粒物吸收以浮游植物色素吸收为主,总颗粒物吸收光谱与浮游藻类吸收光谱相似;非色素颗粒物和有色可溶性有机物的吸收系数随波长的增大接近指数规律衰减;a_d(440)、a_d(675)与C_Chl.a呈显著相关,表明官厅水库秋季的非色素颗粒物主要来源于浮游藻类降解产物,陆源性输入较少;a ph(440)、a ph(675)与C_Chl.a存在显著线性关系,但其比吸收系数较为恒定,与C_Chl.a基本无关;不同采样点的不同组分吸收系数对总吸收系数的贡献不同,大致有4种表现类型.在富营养程度较高的妫库区,浮游植物色素是水体光谱吸收的主导因子;在富营养程度较低的中库区,颗粒物与有色可溶性有机物共同主导水体光谱吸收.;Field work was carried out in Guanting Reservoir on September 5,2012 to study the absorption characteristics of total particulates,phytoplankton pigment,tripton and chromophoric dissolved organic matter (CDOM).The results show that: (1) In autumn,phytoplankton pigment absorption plays a major role in total particulates absorption,thus the absorption of total particulates has the similar characteristics as that of phytoplankton pigment.(2) The absorption coefficients of CDOM and tripton decreased exponentially with wavelength increasing.The slope coefficient of tripton absorption spectral Sd is much smaller than that of other eutrophic waters (eg.Lake Taihu,Lake Dianchi,Lake Chaohu).The slope coefficient of CDOM absorption spectral S_g is similar to Lake Taihu and Lake Chaohu.(3) Significant linear relationship was found between a_ph (440),a_ph (676) and C_Chl.a , but the specific absorption of phytoplankton (a_ph^*) at 440 nm and 675 nm keeps a stable level and has no obvious relationship with C_Chl.a.(4) Significant linear relationship was also found between a_d (440),a_d (676) and C_Chl.a ,which indicates tripton in autumn Guanting Reservoir mainly comes from the degra_dation of phytoplankton.(5) Absorption coefficients of different components from different sites of Guanting Reservoir show four different types of contributions to the total absorption coefficients.In more eutrophic area (Gui Area),phytoplankton dominates water's light absorption,while in less eutrophic area (Zhong Area),particles and CDOM play the same important roles in light absorption.

Chromophoric dissolved organic matter (CDOM) in the Equatorial Atlantic Ocean: Optical properties and their relation to CDOM structure and source

Extensive data exist on the optical properties of CDOM from terrestrial and coastal environments, yet the open oceans have been historically under-sampled. Consequently, the source and structural basis of marine CDOM optical properties are still debated. To address this issue, detailed optical measurements were acquired for both untreated and sodium borohydride (NaBH4) reduced natural waters and C18 extracts (C18-OM) across the Equatorial Atlantic Ocean. Except in regions of upwelling or in the vicinity of the Congo River outflow, CDOM absorption coefficients and visible emission intensity were far smaller for surface waters (aCDOM(355): 0.057–0.162m−1; λex/λem=350/450nm: 0.396–1.431 qse) than for waters below the mixed layer (aCDOM(355) 0.084–0.344m−1; λex/λem=350/450nm: 0.903–3.226 qse), while spectral slopes were higher (surface: 0.019 to 0.025nm−1; deep: 0.013 to 0.019nm−1), consistent with photobleaching of CDOM in surface waters. Distinct emission bands were observed in the ultraviolet, primarily at excitation/emission wavelengths (λex/λem)=280/320nm, but also at λex/λem=300/340, 300/405 and 320/380nm for some stations and depths. In contrast, visible emission exhibited maxima that continuously redshifted with increasing λex (>330nm), a property characteristic of CDOM from estuarine and coastal environments. Further evidence that CDOM in the offshore waters of this region is composed of a major terrestrial component includes: 1) similar spectral dependencies of the emission maxima and fluorescence quantum yields; 2) a large Stokes shift in the emission maxima with short-wavelength excitation (λex=280nm); 3) correlation of visible emission intensities with absorption at λex=280, 320 and 450nm, with absorption to fluorescence ratios comparable to those found in estuarine and coastal environments; 4) affinity of C18 cartridges for the long wavelength (visible) absorbing and emitting material, but not the UV emitting material; 5) preferential loss of visible absorption and substantially enhanced blue-shifted emission in the visible following borohydride reduction of both the Equatorial Atlantic waters and the C18-OM of these waters. These results support the occurrence in offshore waters of a major terrestrial CDOM component that absorbs in the UV and visible and emits in the visible, as well as marine CDOM components that absorb and emit in the UV. The results further demonstrate that the simultaneous acquisition of complete spectral absorption and emission properties, combined with chemical tests (C-18 extractions, borohydride reduction) can provide a far clearer picture of the sources and cycling of CDOM within the oceans.