Quantitative and qualitative characterizations of dissolved organic matter (DOM) were carried out at the watershed level in central Japan by measuring dissolved organic carbon (DOC) concentration and the three-dimensional excitation-emission matrix (3-D EEM). DOC concentration was low (mean 37 ± 19 mM C) in the upstream waters, whereas, in general, it increased toward the downstream areas (mean 92 ± 47 mM C). Significant variations in DOC concentration were detected among rivers and channels. DOC concentration in the epilimnion of Lake Biwa increased during the summer period and decreased during the winter period. The lake hypolimnion has lower DOC concentration (mean 87 ± 7 mM C) compared with the epilimnion (107 ± 15 mM C). Fulvic acid (FA)-like substances in the DOM were directly characterized by 3-D EEM. The fluorescence peak for upstream DOM was found in regions with longer wavelengths (excitation/emission 386 ± 6/476 ± 5 nm) compared with downstream and lake DOM (351 ± 12/ 446 ± 15 nm and 341 ± 6/434 ± 6 nm, respectively). The DOC concentration is correlated with fluorescence peak intensity of FA-like substances in DOM in river waters. Such a relationship was not found in lake DOM. A blueshift of the fluorescence peak from upstream to lake DOM was observed. A decrease in fluorescence intensities was also detected during the summer period. These results may suggest that the degradation of FA-like substances in DOM occurs from natural solar irradiation. Protein-like fluorescence was significantly detected in the lake epilimnion during the summer period. A linear relationship between DOC concentration and protein-like fluorescence indicated that an autochthonous input of DOM gave rise to the increase in DOC concentration in the lake epilimnion during the summer. These results may suggest that the 3-D EEM can be used as a tool for the investigation of DOM dynamics at the watershed level with concurrent measurement of DOC concentration and the fluorescence properties of fulvic acidlike and protein-like substances.
Photodegradation of dissolved organic matter (DOM), collected from two upstream and one downstream sites in the Lake Biwa watershed in Japan, was investigated using fluorescence properties of three-dimensional excitation emission matrix (3-D EEM). Solar irradiation caused a decrease in the dissolved organic carbon (DOC) concentration and in the fluorescence peak intensity (FI) of fulvic acid (FA)-and protein-like substances in DOM. Mineralization of DOC during an irradiation period (13 days) was observed to be higher in upstream samples (32-36%) compared to that in downstream sample (16%). DOC concentration in samples stored in the dark significantly decreased in the downstream sample (16%), while those in upstream samples hardly decreased (1-8%). The FI of FA-like substance decreased by 72-84% during 13-days irradiation (integrated solar intensity = 176 MJ m -2 ). The protein-like fluorescence was only observed in the downstream sample and the net decrease in the FI was 59% in the irradiated sample. The first-order reaction kinetics was applied to analyze the photodegradation of DOM. Two-step photodegradation was suggested for the fluorescent DOM (FDOM), while not for the DOC. Results obtained here suggested that FA-like FDOM is more susceptible to photodegradation compared with those of protein-like substances and DOC.Keywords: dissolved organic carbon, fulvic acid-like fluorescence, protein-like fluorescence, photodegradation, streams as benzene containing carboxyl, methoxylate and phenolic groups, hydroxycoumarin-like structures, and fluorophores containing the Schiff-base system, chromone, xanthone, and quinoline derivatives (Senesi, 1990;Leenheer and Croue, 2003). On the other hand, amino acids in freshwaters have been detected in a combined form, mostly humic bound or colloidal in river waters (Volk et al., 1997;Baker et al., 2007) and affected by anthropogenic sources (Baker, 2001(Baker, , 2002a(Baker, , 2002bMostofa et al., 2005a). FA-and protein-like substances are the major components of the fluorescent dissolved organic matter (FDOM) in natural waters (Senesi, 1990;Coble, 1996; Yamashita and Tanoue, 2003 and references therein). The florescent components such as FA-and protein-like substances have been investigated by the three-dimensional excitation emission matrix (3-D EEM). Due to simplicity of the 3-D EEM technique, it is now widely used for characterization of FDOM and for determinations of the nature, sources and quantity of FDOM in natural waters (Baker, 2001(Baker, , 2002aCoble, 1996;Yamashita and Tanoue, 2003;Mostofa, 2005; Mostofa et al., 2005a, b). The 3D-EEM of FA-or humiclike substances in the aquatic DOM, in general, has been shown a major fluorescence peak within a range of excitation/emission (Ex/Em) wavelengths of 320-390/420-490 nm (Coble et al
The extensive extraction of arsenic (As)-contaminated groundwaters for drinking, household and agricultural purposes represents a serious health concern in many districts of Bangladesh. This laboratory-based incubation study investigated the sources and mechanisms of As mobilization in these groundwaters. Several incubation studies were carried out using sediments collected from the Bangladesh aquifer that were supplemented, or not, with different nutrients, followed by an analysis of the sediment suspensions for pH, ORP (oxidation-reduction potential), EC (electrical conductivity) and As and Fe(II) concentrations. In the substrate-amended sediment suspensions incubated under anaerobic environment, there was a mobilization of As (maximum: 50-67 microg/l) and Fe(II) (maximum: 182 microg/l), while the ORP value decreased immediately and drastically (as much as -468 mV to -560 mV) within 5-6 days. In the sediment suspensions incubated under control and aerobic conditions, no significant As mobilization occurred. The simultaneous mobilization of As and Fe(II) from sediments is a strong indication that their mobilization resulted from the reduction of Fe oxyhydroxide by the enhanced activity of indigenous bacteria present in the sediments; this phenomenon also provides insights on the mobilization mechanism of As in groundwater. The concentrations of As in the sediments used in the incubation studies were strongly linked to the gradients of redox potential development that was stimulated by the quantity of organic nutrient (glucose) used. The penetration of surface-derived organic matter into the shallow aquifer may stimulate the activity of microbial communities, thereby leading to a reduction of iron oxyhydroxide and As release.
Abstract. Ocean acidification, a complex phenomenon that lowers seawater pH, is the net outcome of several contributions. They include the dissolution of increasing atmospheric CO2 that adds up with dissolved inorganic carbon (dissolved CO2, H2CO3, HCO3−, and CO32−) generated upon mineralization of primary producers (PP) and dissolved organic matter (DOM). The aquatic processes leading to inorganic carbon are substantially affected by increased DOM and nutrients via terrestrial runoff, acidic rainfall, increased PP and algal blooms, nitrification, denitrification, sulfate reduction, global warming (GW), and by atmospheric CO2 itself through enhanced photosynthesis. They are consecutively associated with enhanced ocean acidification, hypoxia in acidified deeper seawater, pathogens, algal toxins, oxidative stress by reactive oxygen species, and thermal stress caused by longer stratification periods as an effect of GW. We discuss the mechanistic insights into the aforementioned processes and pH changes, with particular focus on processes taking place with different timescales (including the diurnal one) in surface and subsurface seawater. This review also discusses these collective influences to assess their potential detrimental effects to marine organisms, and of ecosystem processes and services. Our review of the effects operating in synergy with ocean acidification will provide a broad insight into the potential impact of acidification itself on biological processes. The foreseen danger to marine organisms by acidification is in fact expected to be amplified by several concurrent and interacting phenomena.
Fluorescent dissolved organic matters (FDOM) in the groundwater-river-lake environments were investigated using three-dimensional excitationemission matrix (EEM) and measuring the dissolved organic carbon (DOC), inorganic anions and electric conductivity (EC) in shallow groundwater, river and lake waters. DOC concentrations were high and largely varied in groundwater, 16-328 μM C (mean 109±88 μM C), and in river waters, 43-271 μM C (mean 158±62 μM C) and were very low in the lake Biwa waters, 89-97 μM C (mean 93±2 μM C). The fluorescence properties of EEM showed that the fulvic-like components (peak C, peak A and peak M) were dominated in groundwater and river waters, but protein-like components (peak T) was in lake waters. The peak C was observed at Ex=Em ¼ 320 AE 9=424 AE 5 nm in groundwater, and 340±5/ 432±4 nm in river waters, but the lake waters detected the two peaks, 347±7/441±11 nm (peak C) as a minor peak and 304±2/421±8 nm (peak M) as a major peak. Emission wavelength of peak T was observed to shorten in wavelengths from groundwater to river and then lake waters. Peak T in lake waters showed at shorter in wavelengths (279 ± 2/338 ± 11 nm) at the middle point of Lake Biwa compared to those of lake shore site (283±3/350±7 nm). Photoirradiation experiment on upstream waters suggested the changes in the fluorescence peaks of fulvic acidlike substances in lake waters, which might be caused by photo-degradation. DOC concentration was significantly correlated with inorganic anions and EC in river waters. However, such correlations were not observed in groundwater. Anion concentrations in lake waters were low with respect to DOC concentration. These results showed that the optical and chemical properties of FDOM are characteristically varied among groundwater, river and lake waters, indicating the impacts of environments to various FDOM at the same watershed level.
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