Protein-like Fluorescent Dissolved Organic Matter Research Articles

Interaction of reed litter and biochar presences on performances of constructed wetlands

Constructed wetlands (CWs) are frequently used for effective biological treatment of nitrogen-rich wastewater with external carbon source addition; however, these approaches often neglect the interaction between plant litter and biochar in biochar-amended CW environments. To address this, we conducted a comprehensive study to assess the impacts of single or combined addition of common reed litter and reed biochar (pyrolyzed at 300 and 500 °C) on nitrogen removal, greenhouse gas emission, dissolved organic matter (DOM) dynamics, and microbial activity. The results showed that combined addition of reed litter and biochar to CWs significantly improved nitrate and total nitrogen removal compared with biochar addition alone. Compared to those without reed litter addition, CWs with reed litter addition had more low-molecular-weight and less aromatic DOM and more protein-like fluorescent DOM, which favored the enrichment of bacteria associated with denitrification. The improved nitrogen removal could be attributed to increases in denitrifying microbes and the relative abundance of functional denitrification genes with litter addition. Moreover, the combined addition of reed litter and 300 °C-heated biochar significantly decreased nitrous oxide (30.7 %) and methane (43.9 %) compared to reed litter addition alone, while the combined addition of reed litter and 500 °C-heated biochar did not. This study demonstrated that the presences of reed litter and biochar in CWs could achieve both high microbial nitrogen removal and relatively low greenhouse gas emissions.

The removal of dissolved organic matter by marine sponges is a function of its composition and concentration: An in situ seasonal study of four Mediterranean species

Sponges are unique among metazoans in their ability to use dissolved organic matter (DOM), the largest pool of organic matter in the ocean, as a major food source. The effect of variations in DOM abundance and composition on its uptake by sponges has rarely been studied. We examined, in situ, the seasonal uptake of DOM by four sponges [2 species with high microbial abundance (HMA) and 2 with low microbial abundance (LMA)] in the northwestern Mediterranean. Dissolved organic carbon (DOC) showed a strong seasonality with 3-fold higher concentrations in fall-winter (256 ± 16 μmol L−1, mean ± SE) than in spring-summer (88 ± 3 μmol L−1). Dissolved organic nitrogen (DON) showed the opposite trend, with higher summer concentrations (8.9 ± 0.4 μmol L−1) and mean concentrations of 2.5–3.4 μmol L−1 in the other seasons. DOC removal by all sponge species increased linearly with its ambient concentration, but only above a DOC removal threshold that was threefold higher in fall-winter (198 μmol L−1) than in spring-summer (74 μmol L−1). All species showed a concentration-dependent DON removal, but LMA sponges removed more DON than HMA sponges. The DOC removal rate (normalized to sponge volume) was 2–3 times higher in fall-winter, when ambient DOC levels were high, than in spring-summer. Sponges efficiently removed clusters of the fluorescent DOM (FDOM) associated with protein-rich DOM, but not those associated with humic material. The clear threshold for DOC removal and the protein-like FDOM uptake pattern suggest that the quality and quantity of DOM control its removal and transformation by marine sponges. Our results indicate that marine sponges transform the composition of the coastal DOM pool, thereby affecting its fate. It is postulated that the DOM excreted by the sponges is more recalcitrant; consequently, sponge activity enhances carbon sequestration in benthic habitats in a similar fashion to that of the oceanic ‘microbial pump’.

Land use impact on the levels of fluorescent dissolved organic matter, phytoplankton and zooplankton in urban lakes

Urban lakes are vulnerable ecosystems, sensitive to environmental challenges, such as pollution, land use transformation and climate change. Closed and open lakes play relatively different roles in the accumulation, transport and transformation of pollutants and organic matter. Land use can influence the concentration of dissolved organic matter and the abundance of phytoplankton. Little is known about the relationship between fluorescent dissolved organic matter (FDOM), phytoplankton and zooplankton in open and closed lakes, relative to the impact of land use. This study aims to determine the connection between various types of land use and FDOM characteristics, as well as phytoplankton and zooplankton abundances in urban lakes. For the closed lakes samples, results showed positive associations between Bacillariophyceae and Testacea, and the protein-like fraction, while for open lakes, positive associations were found between these groups and the microbial humic-like fraction. Also, copepods and rotifers were associated with the humic-like fraction, in closed lakes, but in open lakes copepods correlated with the biological index, and rotifers with the humification index and fluorescence T/C ratio. Results suggested that discontinuous urban fabric, dump sites and abandoned lands decreased the abundance of protein-like fraction and phytoplankton. However, lakes with the highest quantity of protein-like FDOM also had the highest coverage of continuous urban fabric around the lake. Green urban areas decreased the quantity of humic-like FDOM. No impact by land use type was observed on zooplankton groups, suggesting that zooplankton may be less vulnerable to land use. Our findings will contribute to an improved urban water management and to an effective control of FDOM and phytoplankton abundances in urban lakes.

Does Nitrate Enrichment Accelerate Organic Matter Turnover in Subterranean Estuaries?

Due to the widespread pollution of coastal groundwaters with fertilizers, submarine groundwater discharge (SGD) is often thought to be a large dissolved inorganic nitrogen (DIN) source to the ocean. Whether this N is autochthonous or allochthonous to the subterranean estuary (STE), the availability of large quantities of DIN can nevertheless interact with the cycling of other elements, such as carbon (C). In previous studies, we documented the discharge of large quantities of freshwater and NO3– from the mouth of an STE into the Ria Formosa lagoon (SW Iberian Peninsula). For the period covered in this study (2009–2011), the same STE site was dominated by recirculating seawater due to a prolonged fall in piezometric head in the coupled coastal aquifers. Total SGD rates remained similarly high, peaking at 144 cm day–1 at the lower intertidal during fall. We observed a progressive increase of NO3– availability within the STE associated with the recovery of piezometric head inland. Interestingly, during this period, the highest SGD-derived dissolved organic C and DIN fluxes (112 ± 53 and 10 ± 3 mmol m–2 day–1, respectively) originated in the lower intertidal. NO3– enrichment in the STE influences the benthic reactivity of fluorescent dissolved organic matter (FDOM): when seawater recirculation drives STE dynamics, only small changes in the benthic distribution of recalcitrant humic-like FDOM are observed (from −2.57 ± 1.14 to 1.24 ± 0.19 10–3 R.U. “bulk” sediment h–1) in the absence of DIN. However, when DIN is available, these recalcitrant fractions of FDOM are actively generated (from 1.32 ± 0.15 to 11.56 ± 3.39 10–3 R.U. “bulk” sediment h–1), accompanied by the production of labile protein-like FDOM. The results agree with previous studies conducted with flow-through reactor experiments at the same site and suggest that DIN enrichment in the STE enhances the metabolic turnover of sedimentary organic matter up to the point of discharge to surface waters. DIN pollution of coastal aquifers may therefore promote a contraction of the residence time of particulate organic C within the STE, driving carbon from continental storage into the sea.

Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater

Humic-like fluorescent dissolved organic matter (FDOM) have been widely used as tracers for bio-refractory dissolved organic matter to understand its dynamics in the oceans. Vertical distributions of humic-like FDOM are controlled by microbial production in the ocean interiors and photobleaching in surface layers. Although humic-like FDOM is expected to be actively produced in surface layers with high bacterial activity, its production in surface seawater is not well understood. To examine the diurnal variations in humic-like FDOM due to microbial production and photobleaching in surface seawater, we conducted seven experiments from night to day using surface seawater in the subtropical Pacific and coastal regions. Parallel factor analysis determined that FDOM in the incubated seawater was composed of three components: two types of humic-like FDOM and a protein-like FDOM. The fluorescence intensity of humic-like FDOM increased to 104.0 ± 2.5% of the initial intensity during the night and decreased to 101.2 ± 2.5% under sunlight exposure during the day. Conversely, its intensity significantly increased to 114.0 ± 2.7% under dark conditions during the day. The turnover rates of humic-like FDOM by the increase and decrease in its intensity were estimated to be 0.14 and 0.11 d–1, respectively. These comparable turnover rates indicated that the production and photobleaching of humic-like FDOM were almost in equilibrium in the surface layer, with a low level of humic-like FDOM. Linear correlations between the intensity of humic-like FDOM and concentrations of dissolved oxygen in all experiments under dark conditions indicated that humic-like FDOM were produced as the by-products of microbial respiration processes in the surface seawater. Using global bacterial respiration rates, the net production rate of humic-like FDOM in the global photic layer was estimated as 4.2–5.5 x 1017 R.U. yr–1, contributing to 75% of its production in the entire ocean.

Compositional differences of fluorescent dissolved organic matter in Arctic Ocean spring sea ice and surface waters north of Svalbard

We assessed the qualitative composition of fluorescent dissolved organic matter (FDOM) in Arctic Ocean surface water and in sea ice north of the Svalbard Archipelago (in the Sophia Basin, the Yermak Plateau and the north Spitsbergen shelf) in May and June 2015, during the “TRANSSIZ” expedition (Transitions in the Arctic Seasonal Sea Ice Zone). Samples collected in open lead waters (OW), under-ice waters (UIW) and from the sea ice (ICE) were analyzed by fluorescence spectroscopy and subsequently by multivariate statistical methods using Parallel Factor Analysis (PARAFAC). Statistical analyses of all measured DOM fluorescence excitation and emission matrices (EEMs) enabled four components to be identified and validated. The spectral characteristics of the first component C1 (λEx/λEm 282(270)/335) corresponded to those of tryptophan. The spectral properties of the other three components corresponded to those of humic-like substances: components two (C2 − λEx/λEm 315(252)/395) and three (C3 − λEx/λEm 357(258)/446) corresponded to humic-like substances of marine origin, whereas component four (C4 − λEx/λEm 261(399)/492) resembled terrestrial humic-like substances. Changes in FDOM composition were recorded in OW, in contrast to UIW and sea ice. In the OW the sum of fluorescence intensities of humic-like components (C2, C3 and C4) was two times higher than the fluorescence intensity of protein-like component (C1). Component C2 exhibited the highest fluorescence intensity. In the UIW and particularly in the sea ice the fluorescence intensity of the protein-like component, IC1, was the highest. The IC1 in the sea ice increased toward the sea ice bottom, reaching maximum values at the sea ice-water interface. The calculated spectral indices (SUVA(254) and HIX) and ratios of fluorescence intensities of protein-like to humic-like components, Ip/Ih, suggested that FDOM in water and sea ice was predominantly autochthonous, characterized by low molecular weight organic compounds and low aromatic ring saturation. Enrichment factors Dc, calculated from salinity-normalized values of the optical DOM properties and dissolved organic carbon concentrations, indicated the significant fractionation of FDOM in the sea ice relative to the parent open waters. The humic-like terrestrial component C4 was enriched the least, whereas the protein-like component C1 was enriched the most. A statistically significant (p < 0.0001) and relatively strong (R = 63) correlation between IC1 and the total chlorophyll a concentration Tchla was found in the sea ice, which suggests that sympagic algal communities were producers of the protein-like FDOM fraction.

Dissolved and Particulate Organic Matter Dynamics Relative to Sediment Resuspension Induced by the Tidal Cycle in Macrotidal Estuaries, Kyushu, Japan

The tide-induced resuspension of sediments plays important roles in the efflux of particulate organic carbon (POC) from rivers to the coastal sea. Although dissolved organic carbon (DOC) comprises more than half of the riverine flux of organic carbon to the ocean, the influence of sediment resuspension induced by the tidal cycle on DOC dynamics is largely unknown. This study examined the dynamics of POC, particulate organic nitrogen (PON), DOC, humic-like and protein-like fluorescent dissolved organic matter (DOM) in relation to the tidal cycle in the Chikugo and Hayatsue River Estuaries, Kyushu, Japan. This study is the first to show both the particulate organic matter (POM) and DOM dynamics in relation to the tidal cycle in the macrotidal estuaries. We found that the turbidity changed with the tidal cycle and that there were significant positive correlations of turbidity with POC and PON in the Chikugo River mouth, suggesting that tide-induced sediment resuspension supplied POM to the water column. The DOC concentration, humic-like and protein-like fluorescent DOM were not correlated with turbidity but were negatively correlated with salinity. These results suggest that POM efflux, but not DOM efflux, can be accelerated by tide-induced sediment resuspension in the macrotidal estuaries.

Evaluation of carbon mineralization and structural alterations of organic carbon in high-moor peat soils during incubation

The quantity and quality of soil organic matter (SOM) in the wetlands and peatlands are important for evaluating of the effects of environmental changes. This study’s aim was to evaluate the change in the chemical properties of SOM and dissolved organic matter (DOM) during a constant temperature incubation of high-moor peat soil under two types of vegetation. Incubation of high-moor peat soils collected from marsh vegetation and dwarf bamboo was conducted for 108 days at each temperature of 25 °C and 35 °C. The chemical properties of alkaline extract and DOM in soil samples during incubation were analyzed by tetramethylammonium hydroxide thermochemolysis-gas chromatography-mass spectrometry (TMAH-GC/MS) and fluorescence analysis. The cumulative CO2 emission from peat under dwarf bamboo was higher than that of peat under marsh vegetation. During incubation at 35 °C, plant and microbial residues in DOM extracted from dwarf bamboo soil were increased significantly at the early stages of culture. On the other hand, the components of DOM in the marsh vegetation soil sample did not significantly change between incubation at each temperature. The fluorescence spectra showed that protein-like fluorescent DOM contained in dwarf bamboo soil is consumed by microorganisms, which promotes leaching of humic-like fluorescent DOM and carbon mineralization during the incubation period at a higher temperature. Compared with marsh vegetation soil, the DOM in dwarf bamboo soil is susceptible to temperature rises and can be a larger source of CO2 emissions. This study shows that evaluation of DOM properties in soil could be useful to assess the effect of climate change on soil environment.

Dissolved Metal(loid) Concentrations and Their Relations with Chromophoric and Fluorescent Dissolved Organic Matter in an Urban River in Shenzhen, South China

Urbanization is often accompanied by aquatic metal(loid) pollution, which is regulated by dissolved organic matter (DOM). However, the relationships between dissolved metal(loid) concentration and the bulk, chromophoric, and fluorescent DOM in black and odorous urban rivers are still poorly understood. Here, we investigated the dissolved metal(loid) concentrations of Zn, Cu, Cr, As, Pb, and Cd and their correlations with DOM-related parameters in water samples from a polluted urbanized watershed in Shenzhen, China. The results showed that the Zn and Cu concentrations in the mainstream and tributary exceeded the national standards, and the wastewater treatment plant (WWTP) was an important source, as indicated by the abrupt concentration increases downstream of the WWTP. The dissolved metal(loid) concentrations were not always significantly correlated with the dissolved organic carbon (DOC) concentration or the ultraviolet absorbance at 254 nm (UV254); however, they were more likely to be correlated with the maximum fluorescence intensity (Fmax) of protein-like fluorescent DOM components. A strong correlation between the Cu/DOC ratio and specific UV254 (SUVA254) previously reported did not exist in the present study. Instead, the Cu/DOC ratio was positively correlated with the Fmax/DOC ratios for protein-like fluorescent DOM components. Our study highlights that protein-like fluorescent DOM may be more important than humic-like fluorescence DOM and chromophoric DOM in terms of interacting with dissolved metal(loid)s in black and odorous urban rivers.

Tracing terrestrial versus marine sources of dissolved organic carbon in a coastal bay using stable carbon isotopes

Abstract. The sources of dissolved organic matter (DOM) in coastal waters are diverse, and they play different roles in the biogeochemistry and ecosystems of the ocean. In this study, we measured dissolved organic carbon (DOC) and nitrogen (DON), the stable carbon isotopic composition of dissolved organic carbon (δ13C-DOC), and fluorescent dissolved organic matter (FDOM) in coastal bay waters surrounded by large cities (Masan Bay, Republic of Korea) to determine the different DOM sources in this region. The surface seawater samples were collected in two sampling campaigns (August 2011 and August 2016). The salinities were in the range of 10–21 in 2011 and 25–32 in 2016. In 2011, excess DOC was observed in high-salinity (16–21) waters; the excess DOC source was found to be mainly from marine autochthonous production according to the δ13C-DOC values (−23.7 ‰ to −20.6 ‰), the higher concentrations of protein-like FDOM, and the lower DOC∕DON (C∕N) ratios (8–15). In contrast, excess DOC observed in high-salinity waters in 2016 was characterized by low FDOM, more depleted δ13C values (−28.8 ‰ to −21.1 ‰), and high C∕N ratios (13–45), suggesting that the source of excess DOC is terrestrial C3 plants by direct land–seawater interactions. Our results show that multiple DOM tracers such as δ13C-DOC, FDOM, and C∕N ratios are powerful for determining different sources of DOM occurring in coastal waters.

Combination of self-organizing map and parallel factor analysis to characterize the evolution of fluorescent dissolved organic matter in a full-scale landfill leachate treatment plant

The dissolved organic matter (DOM) characterization in a full-scale landfill leachate treatment plant is of great importance for the design and operation of treatment processes. In this study, the long-term removal behaviors of DOM during landfill leachate treatment were explored using excitation emission matrix fluorescence spectroscopy (EEMs) coupled with parallel factor analysis (PARAFAC) and self-organizing map (SOM). Results indicated that the application of combining PARAFAC and SOM on EEMs analysis effectively characterized long-term removal behaviors of DOM during leachate treatment. The DOM in raw leachate was dominated by humic substances, while its composition exhibited significant seasonal differences. A large proportion of protein-like fluorescent dissolved organic matter (FDOM) and bulk DOM were removed within membrane bioreactor (MBR) system. Meanwhile the humic-like FDOM removal capacity in nanofiltration (NF) process was well comparable with those in the MBR system owing to the bio-recalcitrant nature of humic substances. The protein-like FDOM and bulk DOM were removed synchronously in both the process of MBR and NF. Moreover, samples distribution exhibited obvious differences among NF concentrate samples. In general, the performance of MBR-NF treatment for landfill leachate displayed reasonable stability in DOM removal irrespective of seasonal variations. This study enhanced our understanding of EEMs application in characterizing leachate-derived DOM composition and has potential implications for the associated monitoring investigations in engineered systems.

The remineralization of sedimentary organic carbon in different sedimentary regimes of the Yellow and East China Seas

We investigated the remineralization of sedimentary organic carbon (SOC) at 12 sites in East China Sea mobile-muds (ECSMMs) and South Yellow Sea central mud deposits (SYSMDs) - using a time-sequence sediment incubation experiment. We examined pore-water dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), fluorescent dissolved organic matter (FDOM), dissolved inorganic nitrogen (DIN) nutrients (NH4+, NO3−, and NO2−), redox sensitive elements (Fe2+ and Mn2+), and major anions (SO42− and Cl−) in incubated sediments, to better constrain controlling mechanisms of SOC remineralization under different sedimentary regimes. Lower DIC production rates in SYSMDs (2.36–3.13 mmol m−2 d−1) than those in ECSMMs (2.94–13.5 mmol m−2 d−1), were mainly attributed to cold bottom water masses and a relatively stable sedimentary environment in SYS. Higher DIC production rates were observed mostly at offshore sites of ECSMMs that had relatively enriched 13C of SOC - which indicated preferential degradation of labile SOC of marine origin. When compared with tropical mobile-muds, higher bottom-water temperatures, thicker mobile-muds, and large inputs of reactive terrestrial OC resulted in more intense remineralization of SOC in Amazon mobile-muds than in ECSMMs. Lower ratios of DOC/DIC production rates in ECSMMs (0.11–0.72) were likely indicative of efficient transformation of OC, and largely due to sulfate reduction. A rapid increase in marine protein-like FDOM components during the incubation indicated that less stable marine SOC was preferentially converted to DOC - and then to DIC. Our SOC budget indicates that 16.8% of SOC was decomposed in sediments of ECSMMs, but only about 5.4% of SOC was decomposed in SYSMDs, suggesting lower SOC preservation efficiency in mobile-muds than distal muds.

Characteristics of chromophoric and fluorescent dissolved organic matter in the Nordic Seas

Abstract. Optical properties of chromophoric (CDOM) and fluorescent dissolved organic matter (FDOM) were characterized in the Nordic Seas including the West Spitsbergen Shelf during June–July 2013, 2014, and 2015. The CDOM absorption coefficient at 350 nm, aCDOM(350) showed significant interannual variation (T test, p &lt; 0.00001). In 2013, the highest average aCDOM(350) values (aCDOM(350) = 0.30 ± 0.12 m−1) were observed due to the influence of cold and low-salinity water from the Sørkapp Current (SC) in the southern part of the West Spitsbergen Shelf. In 2014, aCDOM(350) values were significantly lower (T test, p &lt; 0.00001) than in 2013 (average aCDOM(350) = 0.14 ± 0.06 m−1), which was associated with the dominance of warm and saline Atlantic Water (AW) in the region, while in 2015 intermediate CDOM absorption (average aCDOM(350) = 0.19 ± 0.05 m−1) was observed. In situ measurements of three FDOM components revealed that fluorescence intensity of protein-like FDOM dominated in the surface layer of the Nordic Seas. Concentrations of marine and terrestrial humic-like DOM were very low and distribution of those components was generally vertically homogenous in the upper ocean (0–100 m). Fluorescence of terrestrial and marine humic-like DOM decreased in surface waters (0–15 m) near the sea ice edge due to dilution of oceanic waters by sea ice meltwater. The vertical distribution of protein-like FDOM was characterized by a prominent subsurface maximum that matched the subsurface chlorophyll a maximum and was observed across the study area. The highest protein-like FDOM fluorescence was observed in the Norwegian Sea in the core of warm AW. There was a significant relationship between the protein-like fluorescence and chlorophyll a fluorescence (R2 = 0.65, p &lt; 0.0001, n = 24 490), which suggests that phytoplankton was the primary source of protein-like DOM in the Nordic Seas and West Spitsbergen Shelf waters. Observed variability in selected spectral indices (spectral slope coefficient, S300–600, carbon-specific CDOM absorption coefficient at 254 and 350 nm, SUVA254, aCDOM*(350)) and the nonlinear relationship between CDOM absorption and the spectral slope coefficient also indicate a dominant marine (autochthonous) source of CDOM and FDOM in the study area. Further, our data suggest that aCDOM(350) cannot be used to predict dissolved organic carbon (DOC) concentrations in the study region; however the slope coefficient (S300–600) shows some promise in being used.

Sources, fluxes, and behaviors of fluorescent dissolved organic matter (FDOM) in the Nakdong River Estuary, Korea

Abstract. We monitored seasonal variations in dissolved organic carbon (DOC), the stable carbon isotope of DOC (δ13C-DOC), and fluorescent dissolved organic matter (FDOM) in water samples from a fixed station in the Nakdong River Estuary, Korea. Sampling was performed every hour during spring tide once a month from October 2014 to August 2015. The concentrations of DOC and humic-like FDOM showed significant negative correlations against salinity (r2= 0.42–0.98, p &lt; 0.0001), indicating that the river-originated DOM components were the major source and behave conservatively in the estuarine mixing zone. The extrapolated δ13C-DOC values (−27.5 to −24.5 ‰) in fresh water confirm that both components are mainly of terrestrial origin. The slopes of humic-like FDOM against salinity were 60–80 % higher in the summer and fall due to higher terrestrial production of humic-like FDOM. The slopes of protein-like FDOM against salinity, however, were 70–80 % higher in spring due to higher biological production in river water. Our results suggest that there are large seasonal changes in riverine fluxes of humic- and protein-like FDOM to the ocean.

In-situ production of humic-like fluorescent dissolved organic matter during Cochlodinium polykrikoides blooms

We investigated phytoplankton pigments, dissolved organic carbon (DOC), and fluorescent dissolved organic matter (FDOM) during the summers of 2013 and 2016 in the coastal area of Tongyeong, Korea, where Cochlodinium polykrikoides blooms often occur. The density of red tides was evaluated using a dinoflagellate pigment, peridinin. The concentrations of peridinin and DOC in the patch areas were 15- and 4-fold higher than those in the non-patch areas. The parallel factor analysis (PARAFAC) model identified one protein-like FDOM (FDOMT) and two humic-like FDOM, classically classified as marine FDOM (FDOMM) and terrestrial FDOM (FDOMC). The concentrations of FDOMT in the patch areas were 5-fold higher than those in the non-patch areas, likely associated with biological production. In general, FDOMM and FDOMC are known to be dependent exclusively on salinity in any surface waters of the coastal ocean. However, in this study, we observed strikingly enhanced FDOMC concentration over that expected from the salinity mixing, whereas FDOMM increases were not clear. These FDOMC concentrations showed a significant positive correlation against peridinin, indicating that the production of FDOMC is associated with the red tide blooms. Our results suggest that FDOMC can be naturally enriched by some phytoplankton species, without FDOMM enrichment. Such naturally produced FDOM may play a critical role in biological production as well as biogeochemical cycle in red tide regions.

Inputs of humic fluorescent dissolved organic matter via submarine groundwater discharge to coastal waters off a volcanic island (Jeju, Korea)

The abundance of fluorescent dissolved organic matter (FDOM) in the surface ocean plays a critical role in the growth of marine microorganisms and corals by affecting the optical properties (i.e., the penetration of UV radiation) of seawater. In general, it is known that rivers are the main source of FDOM to surface ocean waters. Here, however, we show that the concentrations of FDOM in coastal seawater off a volcanic island, Jeju, Korea, are dependent primarily on submarine groundwater discharge (SGD). Based on a significant correlation between 222Rn and salinity in seawater, fresh groundwater was found to be the main source of groundwater as well as fresh water in the bay. The addition of dissolved organic carbon (DOC) and protein-like FDOM to the bay via SGD was generally negligible or negative. However, SGD enhanced the inventory of humic-like FDOM (FDOMH) in seawater by 2–3 times over all seasons, with conservative behavior of FDOMH in bay seawater. These results suggest that SGD-driven fluxes of FDOM regulate its inventory in seawater and consequently play a significant role in determining the optical properties of coastal waters off islands and associated coastal ecosystems (i.e., corals).

Production and degradation of fluorescent dissolved organic matter derived from bacteria

Dynamics of fluorescent dissolved organic matter (FDOM) in ocean environments has received attention over the past few decades. Although it has appeared that in situ production of oceanic FDOM is mainly due to bacteria, the production and bio- and photodegradation processes of bacterial FDOM have not been elucidated. In this study, a culture experiment with bacteria was carried out to assess the production and biodegradation processes of bacterial FDOM. Photodegradation of bacterial FDOM and dissolved organic carbon (DOC) was also examined by exposure to a solar simulator. Bacterial FDOM consists of six components which were determined by parallel factor analysis (PARAFAC). Fluorescence intensities of protein-like FDOM increased with the bacterial biomass, but the increases of humic-like FDOM lagged behind the protein-like FDOM by 5–10 days. Exposure to simulated sunlight caused significant decreases in fluorescence intensities of all components; 52–94% of the initial intensities were lost during 24 h. While, the DOC concentration exhibited a small decrease through the experiment (1.9–11.1%). These results showed that photodegradability of bacteria derived DOC was much less than the fluorescence, indicating that the lifetime of bacteria-derived DOC is much longer than the length estimated by the fluorescence. The role of photobleached FDOM derived from bacteria may be significant in the biogeochemical cycle at the surface layer.

Selective elimination of chromophoric and fluorescent dissolved organic matter in a full-scale municipal wastewater treatment plant

Effluent organic matter (EfOM) from municipal wastewater treatment plants potentially has a detrimental effect on both aquatic organisms and humans. This study evaluated the removal and transformation of chromophoric dissolved organic matter (CDOM) and fluorescent dissolved organic matter (FDOM) in a full-scale wastewater treatment plant under different seasons. The results showed that bio-treatment was found to be more efficient in removing bulk DOM (in term of dissolved organic carbon, DOC) than CDOM and FDOM, which was contrary to the disinfection process. CDOM and FDOM were selectively removed at various stages during the treatment. Typically, the low molecular weight fractions of CDOM and protein-like FDOM were more efficiently removed during bio-treatment process, whereas the humic-like FDOM exhibited comparable decreases in both bio-treatment and disinfection processes. Overall, the performance of the WWTP was weak in terms of CDOM and FDOM removal, resulting in enrichment of CDOM and FDOM in effluent. Moreover, the total removal of the bulk DOM (P<0.05) and the protein-like FDOM (P<0.05) displayed a significant seasonal variation, with higher removal efficiencies in summer, whereas removal of CDOM and the humic-like FDOM showed little differences between summer and winter. In all, the results provide useful information for understanding the fate and transformation of DOM, illustrating that sub-fractions of DOM could be selectively removed depending on treatment processes and seasonality.

Quantity and composition of stream dissolved organic matter in the watershed of Conesus Lake, New York

Abstract Dissolved organic matter (DOM) is a complex mixture of soluble organic compounds that plays important roles in stream ecosystem function. We examined temporal and spatial variation in stream DOM characteristics in the small watersheds draining into Conesus Lake, New York, USA. While all watersheds were impacted by human activity, our study sites spanned multiple land uses, with distinct differences in the proportion of agriculture and natural land cover. Concentrations of dissolved organic carbon and inorganic and organic nitrogen and phosphorus were measured seasonally, with a more detailed analysis during the growing season. DOM composition was assessed with a suite of optical indices and multidimensional fluorescence with parallel factor analysis. Seasonal shifts in the composition and quantity of DOM, characterized by increased protein-like fluorescence in the growing season and maximum DOC concentrations in the fall, were consistent with abiotic seasonal controls and the seasonal influx of allochthonous organic matter to all streams. However, agriculturally dominated streams had higher inorganic nutrients, along with less-humified, less-molecularly complex, and more protein-like fluorescent DOM than those with less agriculture, suggesting that nutrients may be stimulating greater in-stream DOM production. Stream order also played a strong role, with more similarity in the DOM pools in second order streams, consistent with high in-stream processing of both allochthonous and autochthonous DOM. We conclude that agriculture is an important driver of stream water nutrients and the quantity and composition of DOM, in conjunction with abiotic seasonal drivers and in-stream processing time.

What's in an EEM? Molecular signatures associated with dissolved organic fluorescence in boreal Canada.

Dissolved organic matter (DOM) is a master variable in aquatic systems. Modern fluorescence techniques couple measurements of excitation emission matrix (EEM) spectra and parallel factor analysis (PARAFAC) to determine fluorescent DOM (FDOM) components and DOM quality. However, the molecular signatures associated with PARAFAC components are poorly defined. In the current study we characterized river water samples from boreal Québec, Canada, using EEM/PARAFAC analysis and ultrahigh resolution mass spectrometry (FTICR-MS). Spearman's correlation of FTICR-MS peak and PARAFAC component relative intensities determined the molecular families associated with 6 PARAFAC components. Molecular families associated with PARAFAC components numbered from 39 to 572 FTICR-MS derived elemental formulas. Detailed molecular properties for each of the classical humic- and protein-like FDOM components are presented. FTICR-MS formulas assigned to PARAFAC components represented 39% of the total number of formulas identified and 59% of total FTICR-MS peak intensities, and included significant numbers compounds that are highly unlikely to fluoresce. Thus, fluorescence measurements offer insight into the biogeochemical cycling of a large proportion of the DOM pool, including a broad suite of unseen molecules that apparently follow the same gradients as FDOM in the environment.