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The intensity of the 340/430-nm peak in the three-dimensional excitation-emission matrix spectra of water samples has been used as an index of the concentration of aquatic humic substance (AHS). However, whether this peak corresponds uniquely to AHS has not been definitively verified. Therefore, in this study, our objectives were: (1) to determine whether the 340/430-nm peak in the spectra of lake and river water samples does, in fact, correspond uniquely to AHS; (2) to determine what type of dissolved organic matter (DOM), in terms of hydrophobicity, accounts for the peak; and (3) to determine the advisability of using excitation-emission matrix spectroscopy to rapidly estimate AHS concentrations. We found that the 340/430-nm peak originates not only from the AHS fraction of DOM but also from a portion of the hydrophilic fraction. By analyzing the quantitative relationship between AHS concentration and 340/430-nm peak intensity for DOM samples, we found the intensity can be used to estimate AHS concentration in lake water when the concentration is strongly affected by influent river water or when the ratio of ultraviolet (UV) absorbance to dissolved organic carbon concentration is relatively high.

Anaerobic digestion effluent (ADE) from aquatic macrophytes (Egeria densa, Elodea nuttallii, Ceratophyllum demersum and Potamogeton maackianus) contains insufficient available magnesium ions (Mg2+) to achieve maximum algal yield and nutrient removal, although Mg concentrations are not scarce at 6–10 mg L−1. Unavailable Mg2+ may be bound into complexes with dissolved organic matter (DOM). We determined the effects of ADE exposure to ultraviolet C (UVC), and degradation of DOM, on Mg availability for growth of Chlorella sorokiniana. Molecular sizes of DOM binding Mg2+ were identified with high-performance size-exclusion chromatography. The results demonstrated that 3 h exposure to UVC can decompose DOM, and release sufficient amounts of available Mg2+, i.e. 0.09 mg from 1 mg of dissolved organic carbon, thus enhancing algal yield and nutrient removal. Almost 50 % of Mg in the ADE was bound by DOM with a molecular size of 400–1170 Da as organic complexes, and the remaining Mg was bound by DOM of

The recalcitrant landfill leachate was anaerobically digested at various mixing ratios with labile synthetic wastewater to evaluate the degradation properties of recalcitrant wastewater. The proportion of leachate to the digestion system was increased in three equal steps, starting from 0% to 100%, and later decreased back to 0% with the same steps. The chemical oxygen demand (COD) for organic carbon and other components were calculated by analyzing the COD and dissolved organic carbon (DOC), and the removal efficiencies of COD carbon and COD others were evaluated separately. The degradation properties of COD carbon and COD others shifted owing to changing of substrate degradability, and the removal efficiencies of COD carbon and COD others were improved after supplying 100% recalcitrant wastewater. The UV absorptive property and total organic carbon (TOC) of each molecular size using high performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) with UVA and TOC detectors were also investigated, and the degradability of different molecular sizes was determined. Although the SEC system detected extracellular polymeric substances (EPS), which are produced by microbes in stressful environments, during early stages of the experiment, EPS were not detected after feeding 100% recalcitrant wastewater. These results suggest that the microbes had acclimatized to the recalcitrant wastewater degradation. The high removal rates of both COD carbon and COD others were sustained when the proportion of labile wastewater in the substrate was 33%, indicating that the effective removal of recalcitrant COD might be controlled by changing the substrate's degradability.

Molecular size and dissolved organic carbon (DOC) distributions of dissolved organic matter (DOM) in seawater were determined qualitatively and quantitatively by high-performance size exclusion chromatography (HPSEC). To estimate the relationship between molecular size distribution and the DOC concentration of seawater DOM, seawater was desalinated with an electric dialyzer. The recent technological advancements of desalination make us possible to recover a high percentage of seawater DOM. Surface coastal seawater samples were collected from three locations in Japan: Tokyo Bay, Kashima Port, and Cape Inubo. Samples were evaluated by a chromatography system coupled with ultraviolet (UV) absorbance, fluorescence, and non-dispersive infrared total organic carbon detectors in series. Two peaks, 1 (1.24 × 105−1.54 × 105 Da) and 2 (9.48 × 102−1.81 × 103 Da), were detected in all sample chromatograms. Peak 1 showed little fluorescence and UV absorption in all samples. It has been shown that carbohydrates, one of the main components of seawater DOM, exhibit almost no fluorescence or UV absorption; thus, Peak 1 could mainly consist of carbohydrates which are usually labile DOM. Total DOC concentrations of the Tokyo Bay, Kashima Port, and Cape Inubo were 1.38, 0.92, and 0.80 mg C L−1, respectively. Peak 2 accounted for 75–80% of the total DOC and showed a substantial humic-like fluorescence and UV absorption in all samples. These results indicate that the photochemical characteristics of seawater DOM significantly differ depending on its molecular size. Thus, analysis of molecular size with our HPSEC provides a new approach for quantitative and qualitative characterization of seawater DOM.

This study aimed to clarify the vertical differences in bacterial growth and grazing pressure on bacteria by heterotrophic nanoflagellates (HNF) and to identify the controlling factors of bacterial growth in temperate coastal waters of Sagami Bay, Japan. In addition to environmental factors, the annual monthly variations in bacterial growth rate (BGR) and the relative abundance of bacteria to HNF (BA/HNFA) were investigated in the euphotic and disphotic layers between May 2012 and May 2013. Significant vertical differences in BGR and BA/HNFA were evident between the two layers during the thermal stratification times of May to October 2012 and April to May 2013. BGR indicated significantly stronger limitation of bacterial growth in the euphotic layer compared to the disphotic layer. In contrast, significantly lower BA/HNFA was observed in the euphotic layer, suggesting significantly higher grazing pressure on bacteria by HNF. However, significant differences in BGR and BA/HNFA were not observed between the two layers from November 2012 to Match 2013, when the water column was well-mixed vertically due to the cooling and wind-induced mixing of surface water. This study indicates that bacteria in the euphotic layer grow less actively and are more vulnerable to predatory grazing by HNF relative to the disphotic layer during the stratification period. Further, multiple regression analyses indicate that bacterial growth was most controlled by the concentrations of chlorophyll a and dissolved organic carbon in the euphotic and disphotic layers, respectively.

Understanding the proximate factors and mechanisms driving primary production in manmade reservoirs is crucial because such production can translate into added fish yields that provide people with food and livelihoods. Furthermore, reservoir fish production could potentially compensate for the loss of fish yields due to habitat fragmentation and alterations caused by damming and impoundment. We monitored primary production, identified environmental factors responsible for its variability, and examined the relationship between primary production and fish production in nine large water bodies of the Lower Mekong Basin for 2 years. The estimated primary production ranged from 40 to 302 g C/m2/y and was generally greater in the wet season than in the dry season. Linear mixed-effects modelling identified the concentration of dissolved inorganic carbon as a significant fixed-effect variable regulating primary production, after variability due to random and fixed effects of water body and seasonality, respectively, were taken into account. Fish yields marginally increased with increasing primary production across the water bodies, with the estimated energy transfer efficiency ranging from 0.004 to 0.009. Dissolved inorganic carbon was partly determined by the lithological composition of the water body catchment, suggesting that the geographic locations of proposed dams determine the magnitude of primary production and hence future fish production.

Changes in the characteristics of dissolved organic matter (DOM: the dissolved fraction of natural organic matter) during a series of wastewater treatment plant (WWTP) processes were investigated by using a combination of molecular size analysis and excitation emission matrix (EEM) spectroscopy coupled with parallel factor analysis. The characteristics of DOM were compared following aerobic, anoxic, and anaerobic treatments. Three peaks at about 100,000 Da (high-molecular-size DOM, Peak 1) and about 900–1,100 Da (intermediate-molecular-size DOM, Peak 2; low-molecular-size DOM, Peak 3 as the shoulder of Peak 2) were observed in the distribution of total organic carbon molecular sizes in the influent of the WWTPs. In this study, five fluorescent components (C1 to C5) were identified in the EEM spectra. Molecular size analysis and molecular size fractionation revealed that the C3 (humic-like) and C5 (specific to sewage) fluorophores had intermediate or low molecular sizes. Comparison of the changes of the concentrations of dissolved organic carbon in each reaction tank and investigation of the removal selectivity of each treatment (aerobic, anaerobic, and anoxic) suggested that the heterogenous compounds present in DOM of the influent were homogenized into intermediate-molecular-size DOM with high hydrophobicity and aromaticity, or into C4 fluorophores (DOM-X), during anaerobic or anoxic treatment. DOM-X was able to be transformed or removed by aerobic treatment. The results suggested that introduction of aerobic treatment at the appropriate stage of wastewater treatment or inclusion of physical or chemical treatment should be an effective way to optimize DOM removal.

Summary The free-living, cosmopolitan, freshwater betaproteobacterial bacterioplankton genus Polynucleobacter was detected in different years in 11 lakes of varying types and a river using the size-exclusion assay method (SEAM). Of the 350 strains isolated, 228 (65.1%) were affiliated with the Polynucleobacter subclusters PnecC (30.0%) and PnecD (35.1%). Significant positive correlations between fluorescence in situ hybridization and SEAM data were observed in the relative abundance of PnecC and PnecD bacteria to Polynucleobacter communities (PnecC + PnecD). Isolates were mainly PnecC bacteria in the samples with a high specific UV absorbance at 254 nm (SUVA254), and a low total hydrolysable neutral carbohydrate and amino acid (THneutralCH + THAA) content of the dissolved organic matter (DOM) fraction, which is known to be correlated with a high humic content. In contrast, the PnecD bacteria were abundant in samples with high chlorophyll a and/or THneutralCH + THAA concentrations, indicative of primary productivity. With few exceptions, differences in the relative abundance of PnecC and PnecD in each sample, determined using a high-sensitivity cultivation-based approach, were due to DOM quality. These results suggest that the major DOM component in the field, which is allochthonously or autochthonously derived, is a key factor for ecological niche separation between PnecC and PnecD subclusters.

Human activities have created high nutrient surpluses in agricultural lands due to the increasing rate of chemical fertilizer application and the increase in livestock production. To analyse the nutrient characteristics and estimate the nutrient load in streams, we conducted extensive field survey and water quality experiments from 2007 to 2008 in Koise River, a major river of the Lake Kasumigaura watershed, Japan. Water quality indicators of total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) were investigated. The nutrient loads of TN, TP and TOC, as well as dissolved total nitrogen, dissolved inorganic nitrogen, dissolved organic nitrogen, particle organic nitrogen, dissolved total phosphorus, dissolved organic carbon and particle organic carbon were also estimated for the Koise River. Seasonal variation of the nutrient concentration from 2007 to 2008 was analysed considering the river discharge variation and agricultural activities. The results showed that the irrigation...

A new type of high-performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) system with ultraviolet (UV) absorbance detection and non-dispersive infrared (NDIR) detection of total organic carbon is described. The introduction of an online degassing tube and a low-volume HPLC column helped to reduce the analytical time and increase the sensitivity of the SEC system. This study is the first in which linear calibration curves (R(2)>0.99) were obtained for both UV absorbance and NDIR data for polystyrene sulfonate standards, which are the most suitable standards for molecular size analysis of aquatic humic substances as well as dissolved organic matter (DOM). Using the calibration curves, the molecular size distribution of DOM in water collected from Lake Kasumigaura and in pore water from lake sediments was estimated. Most of the DOM had a molecular weight less than 4000 Daltons (Da), and the amount of low-molecular-weight DOM (∼ 2000 Da) with low UV absorbance increased with depth in the sediment pore water. This result shows the importance of combining quantitative analysis by NDIR detection with qualitative analysis by UV detection to determine the chemical and physical properties of DOM. The possible sources and reactivity of DOM in Lake Kasumigaura and its sediment pore water are also discussed.

In an attempt to better characterize dissolved organic carbon (DOC) in several specific sources to Lake Kasumigaura, such as sewage-treatment-plant effluent (STPE), domestic sewage (DS) and forest stream (FS), we analyzed radiocarbon (14C) and stable carbon isotopic compositions (13C) of the DOCs. The measurements of 14C for DOC were performed by an accelerator mass spectrometer (AMS) at the National Institute for Environmental Studies (NIES-TERRA) in Japan. The Δ14C and δ13C values of the DOCs in several sources to Lake Kasumigaura, have low carbon isotopic values, ranging from −470‰ to −79‰ and from −27.9‰ to −24.2‰, respectively. These carbon isotopic values are substantially different from those of Lake Kasumigaura. These results imply different origins for the DOC in Lake Kasumigaura. The 14C and 13C analyses of DOC led to a useful classification for DOCs in Lake Kasumigaura, Japan.

Speciation of aluminum (Al), including inorganic monomeric Al (Ali, the sum of aquo, hydroxy, and inorganically complexed forms), organic monomeric Al (Alo, the organically complexed form), and colloidal mineral Al (Alc, the fine particulate form that passes through a 0.4-μm pore size membrane filter), was investigated in circumneutral (pH 7–9) eutrophic Lake Kasumigaura, Japan. The mean concentrations calculated from the result of monthly observations during the period from January to December 2003 were compared among ten stations. Ali decreased downstream from the mouth of the influent rivers (0.07–0.10 μM) to the mouth of the effluent river (0.03 μM). Alc, which also decreased downstream (from 0.11 to 0.06 μM), was the major fraction (>50%) of total dissolved Al at all stations. Alo remained around 0.02 μM at all stations. In Lake Kasumigaura, a high concentration of Si (average 0.23 mM) seems to be involved in the removal of Ali and formation of Alc. Also, a high concentration of Ca (ave. 0.43 mM) seems to be acting as a competitive cation for complexation with a high concentration of dissolved organic carbon (ave. 0.26 mM), and inhibit the formation of Alo.

Carbon isotopes (14C and 13C) of dissolved organic carbon (DOC) in a Japanese oligotrophic lake (Lake Towada) were measured to study the origin and cycling of dissolved organic matter (DOM) in Lake Towada. Lake water samples were collected at 3 depths (0, 30, and 80 or 85 m) during 4 months (April, June, August, and October) in 2006. 14C measurements of DOC were performed by accelerator mass spectrometry (AMS) at the National Institute for Environmental Studies (NIES-TERRA) in Japan. Δ14C and δ13C values of DOC in Lake Towada showed light carbon isotopic values ranging from –750 to −514‰ and –29.0 to –27.8‰, respectively. These values are similar to those of humic substances reported. The very low carbon isotopic values of DOC in Lake Towada suggest a very small contribution of DOC derived from fresh phytoplankton to the lake DOC. There is an extremely high linear relationship between the Δ14C and δ13C of DOC in Lake Towada when all data points are plotted (r2 =0.818, p < 0.01), suggesting that the DOC in Lake Towada has 2 specific sources contributing heavy and light carbon isotopes. Although the freshly produced DOC of phytoplankton origin can be decomposed easily, the variation in the autochthonous DOC should influence the carbon isotopic values of DOC in Lake Towada.

Three-dimensional excitation-emission matrix (EEM) fluorescence spectra were used to evaluate and compare the characteristics of dissolved organic matter (DOM) in lake and river waters as well as effluent from several sewage treatment plants. Our comparisons of the EEMs indicated a substantial difference in the peak profiles among the samples. For example, five peaks (i.e. Ex/Em = 225/280, Ex/Em = 225/340, Ex/Em = 240/420, Ex/Em = 340/430, and Ex/Em = 480/520nm) were observed on the EEM of the sewage treatment plant effluent, but only two peaks (i.e. Ex/Em = 240/420 and Ex/Em = 340/430nm) were observed in the case of the lake and river waters. Furthermore, one of the peaks (i.e. Ex/Em = 340/430), which has been used as an indicator of the humic-like groups of DOM, was actually found in the EEMs of both humic and non-humic fractions prepared by the XAD-8 resin fractionation method. The non-humic fraction consistently accounted for 30-50% of the peak intensity of the DOM . This result suggests that the peak at Ex/Em = 340/430 is not appropriate as an indicator of humic-like groups in DOM.

We determined the monosaccharide composition of dissolved organic matter (DOM) to evaluate the origin of DOM in Lake Kasumigaura. We applied high-performance liquid chromatography coupled with pulsed amperometric detection (HPLC-PAD) for the analysis of monosaccharides. We collected water samples from Lake Kasumigaura in 2004 and prepared samples from culture medium used for growing blue-green algae that are typically found in Lake Kasumigaura. The dissolved total saccharides (DTS) content of the lake water ranged from 1.8 to 3.0 μM. The DTS content of the DOM from lake water ranged from 3 to 6%. The monosaccharide composition in the lake water was uniform all year round. The main monosaccharides were fucose, rhamnose, arabinose, galactose, glucose, mannose, xylose and ribose. The algae released a large amount of DTS during the stationary phase. The concentration and composition of the released DTS differed substantially among the algal species. The released DTS was 43.2 to 126 μM. Glucose was the most predominant among the monosaccharides of the DTS. The DTS content of the algal DOM ranged from 11 to 33% depending on the type of algae. The monosaccharide composition was very different between the lake-water-derived and algal-derived DOMs.

This paper presents the spectral decomposition algorithm (SDA), a new algorithm for estimating chlorophyll-a concentration in case II waters using multi-spectral satellite data, which is based on a simulation in a controlled laboratory experiment. The SDA is composed of two key steps. The first of these is to consider the mixed reflectance spectrum of a given pixel as a linear combination of three basic components: clear water, non phytoplankton suspended sediments (NPSS), and phytoplankton. The second step is to use a decomposition coefficient (Cp ) obtained from the first step as an independent variable in the chlorophyll-a estimation model, instead of the single band reflectance, band ratio or arithmetic calculation of bands used in conventional methods. The simulated results for the Landsat TM data showed that bands 1, 3 and 4 are useful wavelengths for estimating chlorophyll-a concentrations. In the case of a water body with chlorophyll-a concentrations ranging from 0 to 105 µg l-1 and NPSS concentrations ranging from 0 to 100 mg l-1, the RMSE of the estimation model of chlorophyll-a concentrations based on the SDA was 13.7 µg l-1, reduced by nearly half of that for conventional methods (the RMSE was 25.6 µg l-1 for the band ratio, and 25.5 µg l-1 for the arithmetic calculation of bands). The results of a two-factor ANOVA (without replication) highlight that the decomposition coefficient Cp contains information from phytoplankton far more than from NPSS. However, Cp values were still changed with the addition of NPSS, due mainly to the influence of the interaction of optical properties among phytoplankton, NPSS and water, which occurred in both horizontal and vertical directions in the water bodies. Considering the basic components as a nonlinear combination in a water area may reduce the effect of NPSS on Cp values from that of their linear combination. In addition, the influence of coloured dissolved organic matter (CDOM), which is generally considered as one of the optically active substances in case II waters, was ignored according to the practical conditions of our study area, Lake Kasumigaura, Japan in this paper. Users can set the basic components (or endmembers) freely according to the conditions of their own study area when the SDA is used (e.g. considering the CDOM as a basic component in the SDA).

Dissolved organic matter (DOM) in lake water can have a harmful effect on algal growth through either direct toxicity or iron limitation induced by its complexation with iron. We assessed the effect of iron complexation with DOM on algal growth in the eutrophic Lake Kasumigaura, Japan, using 2 species of cyanobacteria, Microcystis aeruginosa and Planktothrix agardhii, by combining the algal growth potential (AGP) test and pretreatment of DOM decomposition by UV irradiation. We also determined which nutrient limited the growth of the 2 species in the lake water using the AGP test: iron limited the growth of the 2 species, as did nitrogen and phosphorus in Lake Kasumigaura. Moreover, the growth of the 2 species was inhibited by iron complexation with DOM. This is consis- tent with our results regarding iron speciation in Lake Kasumigaura by cathodic stripping voltam- metry: most (>99.9%) of the dissolved iron was present as organic species in the lake water. Further- more, data from our AGP test suggest that iron requirement or iron availability between the 2 species are different. This difference in growth characteristics between algal species would be an important determinant of the dominance of specific algal species.

The photoalteration of dissolved organic matter (DOM) produced in different growth phases of the blue-green alga, Microcystis aeruginosa, was investigated by comparing the biodegradability and distribution of fractions of algal DOM after different ultraviolet (UV) treatments. The distribution of DOM-fractions (based on hydrophobic-hydrophilic and acidic-basic breaks) showed that two of the fractions, hydrophilic acids (HiA) and bases (HiB), were more abundant in all growth phases of M. aeruginosa than the other three fractions, hydrophobic acids (HoA), hydrophobic neutrals (HoN), and hydrophilic neutrals (HiN). The proportion of HiB increased, while the HiA fraction decreased with aging of the algae. After UV treatment, all algal DOM became recalcitrant to bacterial degradation without complete photo-degradation. This was more pronounced in DOM from older cultures (stationary phase) as compared to DOM from the exponential growth phase. The DOM distribution was also significantly different after UV exposure, implying photoalteration to the chemical composition of algal DOM. The proportions of the HiB fraction decreased as a percent of the total dissolved organic carbon pool by 1.5-8.1 % after UVA treatment and by 5.3-15.8 % after UVB treatment. In contrast, the HiA fraction increased by similar amounts. Analyses of fluorescent properties and some carboxylic acids confirmed the changes to the HiB and HiA fractions. However, the increased HiA fraction may not be linked to the recalcitrance of algal DOM after UV exposure, since there was no difference in the biodegradability of this fraction before and after UV treatments. The initially labile HiB fraction, however, became less available to bacteria after UV exposure depending on intensity and thus may be linked to the recalcitrance of algal DOM after UV exposure. Our results confirm earlier reports that algal DOM can be changed in its chemical composition as well as biodegradability by UV radiation, and suggest that the HiB fraction may be important in the formation of recalcitrant algal DOM.

In the basin of Lake Biwa and Lake Kasumigaura, relationships between fractionation data of dissolved organic matter (DOM) and in inflowing river water and watershed characteristics were investigated by regression analysis and specific unit modeling. Most hydrophobic neutrals were found to originate from domestic sewage. Domestic wastewater treatment plant effluent was found to significantly contribute to the load of hydrophilic acids in river water. Specific unit modeling based on the load of DOM fraction and the ratio of land use contribution in watershed enabled source identification for each DOM fraction including refractory dissolved organic matter. In the north basin of Lake Biwa, forest outflow significantly contributed to the load of aquatic humic substances and refractory fractions. The loads of other DOM fractions were found to be dominated mainly by urban drainage.

Dissolved organic matter (DOM) in water samples from the shallow eutrophic Lake Kasumigaura, the second largest lake in Japan, was fractionated and characterized by using resin adsorbents into 5 classes: aquatic humic substances (AHS), hydrophobic neutrals, hydrophilic acids (HiA), bases (BaS) and hydrophilic neutrals (HiN). Subsequently, the trihalomethane formation potential (THMFP), ultraviolet absorbance to dissolved organic carbon (UV:DOC) ratio, and molecular size distribution of the DOM, AHS and hydrophilic fractions (HiF) (HiF=HiA+BaS+HiN) were examined. The THMFP of HiF, normalized on a DOC basis, was found to be comparable to that of AHS (0.176 microM THM mg C(-1) vs. 0.195 microM THM mg C(-1), respectively). The importance of HiF over AHS as a THM precursor became more pronounced when THMFP was evaluated in terms of concentration. In this case, the THMFP of HiF was much greater than that of AHS (0.374 microM THM l(-1) vs. 0.229 microM THM l(-1), respectively). Molecular size distributions all exhibited a narrow size range and relatively low molecular weights. The weight-averaged molecular weights of DOM, AHS and HiF were 780, 957 and 606 g M(-1), respectively.

Dissolved organic matter (DOM) in Lake Unmun (Korea) and its two inflowing rivers was fractionated using three resin adsorbents (XAD-8 resin, macroporous cation and anion exchange resins) into five classes : aquatic humic substances (hydrophobic acids), hydrophobic neutrals, hydrophilic acids, bases, and hydrophilic neutrals. The characteristics of DOM were investigated by evaluating DOM fraction distribution, ultraviolet ray absorbance of DOM fractions (UV absorbance at 260nm), and molecular size distribution of DOM. Aquatic humic substances (AHS) and hydrophilic acids (HiA) were found to be predominant in both lake and river waters. In particular, AHS were greater in percentage fraction than HiA. The UV to dissolved organic carbon (DOC) ratio (UV/DOC ratio) of AHS was two times higher than that of HiA. The UV/DOC ratios of the total DOM, AHS and HiA were 12.9-32.8, 7.2-29.4 and 5.3-17.1 [m ABS cm-1·l·g C-1], respectively. The molecular weight distribution of the lake water DOM was determined by high-pressure size exclusion chromatography and found to exhibit a relatively narrow size range and low weight-averaged molecular weights ranging from 1,010 to 1,110 g·mole-1.

The seasonal patterns of dissolved organic matter (DOM) in Lake Kasumigaura, a shallow, eutrophic lake, and serveral DOM sources in its catchment area were investigated. DOM was fractionated using three resin adsorbents into classes: aquatic humic substances (AHS=humic acid+fulvic acid), hydrophobic neutrals (HoN), hydrophilic acids (HiA), bases (BaS) and hydrophilic neutrals (HiN). The DOM produced significantly different fraction distributions depending on the origin of sample. AHS and HiA prevailed over AHS in the lake while AHS and HiA existed at almost the same concentration levels in the rivers. AHS seems to be a more dominant component in rever water than lake water. The dominance of organic acids was also observed in the DOM sources: forest stream (FS), plowed field percolate (PFP), domestic sewage (DS) and sewage treatment plant effluent (STPE).

Dissolved organic matter (DOM) in effluents from sewage and human-wastes treatment plants (STPEs and HWTPEs) was fractionated using resin adsorbents into six classes: aquatic humic substances (AHS), hydrophobic bases (HoB), hydrophobic neutrals (HoN), hydrophilic acids (HiA), hydrophilic bases (HiB), and hydrophilic neutrals (HiN). DOM-fraction distribution varied substantially depending on the kind of wastewater and the type of treatment process. AHS and HiA dominated in all effluents, collectively accounting for more than 55% of the DOM measured as dissolved organic carbon (DOC). In particular, HiA were the most abundant fraction in the effluents, constituting 32-74% of the DOM. AHS appeared to be the second most dominant fraction and varied considerably, accounting for 3-28% of the DOM. The HoN fraction also varied from 0-21%. AHS, HoN, and HiA were the fractions that changed substantially and differed characteristically among the samples studied. The ratios of ultraviolet absorbance to DOC (UV: DOC ratio) in all effluents exhibited a common relationship: AHS> total DOM > HiA. Nevertheless, the ratios were substantially different between STPEs and HWTPEs and among HWTPEs. For HWTPEs, the effluent from the chemical coagulation process had the highest UV: DOC ratios. On the other hand, the effluent from the ultrafiltration and activated carbon adsorption processes had the lowest ratios. Molecular size distribution of the effluents was determined by size exclusion chromatography and found to exhibit a relatively narrow size range and low weight-averaged molecular weights ranging from 380 to 830 g mol(-1). The weight-averaged molecular weight of DOM increased as the UV: DOC ratio of total DOM increased.

The concentrations of dissolved organic carbon (DOC) and hydrophilic DOC (Hil-DOC) in Hiroshima Bay showed clear seasonal changes (high in summer and low in winter), suggesting the autochthonous production of Hil-DOC. The percentages of hydrophobic DOC (Hob-DOC) fractionated by XAD-8 resin were 33% for the bay waters and 41% for the river waters, whereas those of labile DOC (which decomposed during an incubation period of 100 days) were 20% and 24%, respectively. The increment of DOC to Chlorophyll a was calculated to be (0·014 mgl −1 )/(μgl −1 ). The mixing experiments suggested a negligible deposition of DOC at the estuaries of inflowing rivers. The Hob-DOC went through the bay with negligible changes in concentration in both summer and winter, but its chemical characteristics, e.g. spectrophotometric properties and mean molecular weight, differed from those of riverine origin. In contrast, both labile and refractory components of Hil-DOC were produced mainly in the inner part of the bay during summer, and although a significant percentage of the labile component was subjected to biodegradation during transport to the outer part of the bay, its chemical characteristics did not change dramatically.

In order investigate the dynamics of dissolved organic carbon (DOC) in Hiroshima Bay, water samples from 7 stations in the bay, its three inflowing rivers and two wastewater treatment plants (WWP) were taken from Aug. 1997 to Aug. 1998. The filtrated organic matter was fractionated into hydrophobic (Hob-DOC) and hydrophilic (Hil-DOC) components using XAD-8 resin. Biodegradation tests by a 100-day incubation and mixing experiments of those samples for evaluating the sedimentation of DOC were also conducted.The concentrations of DOC and Hil-DOC in the bay showed clear seasonal changes (high in summer and low in winter), suggesting aquagenic production of Hil-DOC. Those of river waters had similar seasonal changes, but not so clear. The percentages of Hob-DOC were 31-35% for the bay waters, 34-46% for the river waters, and 31-35% for the effuent from the WWP waters, whereas those of labile DOC were 9-25%, 18-51%, and 17-30%, respectively. The DOC concentrations had positive correlation with chlorophyll a (increments of DOC to Chlorophyll a : 0.01-0.04mg · l-1/μg · l-1), and negative correlation with salinity. The mixing experiment suggested negligible deposition of DOC at the estuaries of inflowing rivers. In conclusion, Hob-DOC went through the estuaries and the bay with negligible change in the concentration in both summer and winter. In contrast, both labile and refractory components of Hil-DOC were produced mainly in the inner part of the bay during summer, and a large part of the former component was subjected to biodegradation during the transport to the outer part.

The removal efficiency of refractory landfill leachate organics by the biological activated carbon fluidized bed (BACFB) process was compared with and without pre-ozonation. Furthermore, the effects of ozonation upon the characteristics of the refractory leachate such as UV absorbance, dissolved organic carbon (DOC), BOD5, adsorbability, molecular size distribution and the content of humic substances were evaluated. The effectiveness of pre-ozonation in treating a refractory landfill leachate through the BACFB process was confirmed. The steady-state DOC removal was enhanced from 42% to 57% at a hydraulic retention time of 24 h. This improvement was due mainly to the pre-ozonation-enhanced biodegradability of the high-molecular-weight organics that could not be removed by the BACFB process alone. Ozonation of the leachate resulted in an exponential decrease in UV absorbance and a linear decrease in DOC with increasing the contact time. High-molecular-weight leachate organics degraded through ozonation to o...

琵琶湖北湖湖水および流入河川水を対象として,疎水性―親水性,酸性―塩基性の違いに基づいた溶存有機炭素(DOC)分画手法を適用し,湖水および河川水溶存有機物の特性や起源について検討した。湖水と河川水,および流域特性の異なる河川水ではDOC分画分布および紫外部吸光度(UV):DOC比に有意な違いが認められた。琵琶湖北湖湖水および流入河川水ともに,DOC成分として有機酸(疎水性酸(フミン物質)+親水性酸)が卓越していた。湖水では親水性酸(フミン物質:25-27%,0.37-0.41mg Cl-1;親水性酸:40-48%,0.58-0.78mg Cl-1),河川水ではフミン物質が優占した(フミン物質:37-73%,0.32-0.71mg Cl-1;親水性酸:23-35%,0.11-0.45mg Cl-1)。特に,森林自然系河川でフミン物質の存在比が最大となった。湖水のUV:DOC比は親水性酸,湖水DOC,フミン物質の順に高くなった。湖水DOCおよび湖水フミン物質のUV:DOC比は既報の藻類由来とする値とほぼ同じ低い値を示し,琵琶湖北湖水中の溶存有機物は主に藻類由来ではないかと推測された。河川水DOCのUV:DOC比は湖水よりも約60%高く,土壌由来DOCの影響が大きいと考えられた。しかしながら,分離された河川水フミン物質のUV:DOC比は河川水フミン物質としてはかなり低く,湖水フミン物質のUV:DOC比より顕著に高いものではなかった。特に都市系河川のフミン物質のUV:DOC比は湖水フミン物質より低かった。

Incubation experiments using filtered waters from Lake Kasumigaura were conducted to examine bacterial contribution to a dissolved organic carbon (DOC) pool. Bacterial abundance, bacterial production, concentrations of DOC, total dissolved amino acids (TDAA), and total dissolved neutral sugars (TDNS) were monitored during the experiments. Bacterial production during the first few days was very high (20 to 35 μg C liter −1 day −1 ), accounting for 40 to 70% of primary production. The total bacterial production accounted for 34 to 55% of the DOC loss during the experiment, indicating high bacterial activities in Lake Kasumigaura. The DOC degradation was only 12 to 15%, whereas the degradation of TDAA and TDNS ranged from 30 to 50%, suggesting the preferential usage of TDAA and TDNS. The contribution of bacterially derived carbon to a DOC pool in Lake Kasumigaura was estimated using d -amino acids as bacterial biomarkers and accounted for 30 to 50% of the lake DOC. These values were much higher than those estimated for the open ocean (20 to 30%). The ratio of bacterially derived carbon to bulk carbon increased slightly with time, suggesting that the bacterially derived carbon is more resistant to microbial degradation than bulk carbon. This is the first study to estimate the bacterial contribution to a DOC pool in freshwater environments. These results indicate that bacteria play even more important roles in carbon cycles in freshwater environments than in open oceans and also suggests that recent increases in recalcitrant DOC in various lakes could be attributed to bacterially derived carbon. The potential differences in bacterial contributions to dissolved organic matter (DOM) between freshwater and marine environments are discussed.

Two methods were compared for the measurement of dissolved organic carbon (DOC) in waters collected from lakes, rivers and several pollution sources. Both the differential method (D-DOC method), derived from dissolved total carbon (DTC) minus DIC (dissolved inorganic carbon), and the purging method (P-DOC method), which purges DIC, were evaluated with a Shimadzu TOC-5000 with a high temperature catalytic oxidation system. Particularly in cases of gray water and/or water which had seeped through soil-layers, considerably lower concentrations were noted for P-DOC purged at around pH 2 than those measured by the D-DOC method or the P-DOC method at pH 4. DOC measurements for both field samples and specific compounds decreased due either to precipitation or flotation of colloidal organic particles insolubilized during sparging at pH 2 or 3 or to their incomplete combustion. The D-DOC method, exhibiting lower precision than the P-DOC method particularly for samples with high DIC vs DOC ratios, is, however, recommendable because of its accuracy.

The seasonal and spatial changes in dissolved organic carbon (DOC) in Lake Kasumigaura, a shallow, eutrophic lake, were analyzed and the lability of DOC was tested by long-term incubations. There was a nearly 1 mgCl−1 downstream increase in refractory DOC in the lake; at the center it fluctuated little seasonally. The characteristic UV-absorbance: DOC ratios were determined for samples from the influent rivers (pedogenic: used interchangeably with “allochthonous”) and outdoor experimental ponds (autochthonous) during incubations. These ratios were then used to calculate the proportion of total measured lake water DOC in each of four components: pedogenic-refractory (PR), pedogenic-labile (PL), autochthonous-refractory (AR) and autochthonous-labile (AL). PR was uniform (around 1.5 mgCl−1) or diminished very slightly over time. AR increased from nearly zero at the station closest to an influent river to 1 mgCl−1 at the lake center. PL declined downstream from 0.3 mgCl−1 to zero. AL was virtually constant at 0.8 mgCl−1 except at the station closest to the influent river. The constancy of the UV-absorbance: DOC ratio during the biodegradation process was confirmed for Lake Kasumigaura; hence a two-component model (pedogenic-autochthonous) could be applied here without consideration of DOC lability. However, this assumption is not always met for other water bodies, and therefore it should be checked before applying a two-component model elsewhere.

A real leachate from a landfill site of old landfill-age was treated by the biological activated carbon fluidized bed (BACFB) process. Steady-state removal of dissolved organic carbon (DOC) and changes in molecular size distribution, adsorption characteristics and amount of humic substances of the leachate were evaluated as a function of the hydraulic retention time (HRT). The steady-state removal of the leachate DOC was enhanced from 42 to 58% when the HRT was increased from 24 to 96 h, indicating that biological oxidation was indeed responsible for the removal of the leachate organics. This increase was found to be due primarily to the biodegration of the leachate organics of low molecular weight (LMW); the high-molecular-weight organics may be highly refractory. Activated carbon preferentially adsorbed the LMW organics of both the leachate and the BACFB-treated effluents. This preferential adsorption was consistent with the removal of the LMW organics by the BACFB process. Adsorption may act as a prerequisite step toward biodegradation. Humic substances accounted for about 30% of the leachate DOC. The BACFB process removed about 70% of the humics with a HRT of 24 h; however, the concentration of the humics remained constant (about 10 mg l−1) with increasing HRT.

Aquatic dissolved organic matter (DOM) sampled from lakes and rivers was fractionated by Sep-Pack mini-cartridges (PS-2 : polystyrene nonionic resins and tC18 : ODS reverse-phase resins) and the characteristics were discussed with the results of bio-degradability tests. Our experiments showed that trapped organic matter had very low bio-degradability./ The trapped rate increased with incubation time during the degradation tests./ The trapped percentages of DOM were nearly the same as the proportions of refractory DOM in the samples obtained from various waters./ These cartridges could trap more than 70% of fulvic acids extracted from L. Kasumigaura's water. Therefore, we suggest that the trapped rate of DOM by such mini-cartridges gives a useful index of bio-degradability of aquatic DOM.

Dissolved organic matter (DOM) in water from eutrophic Lake Kasumigaura, its inflowing rivers, and several other DOM sources in the lake catchment area was fractionated using resin adsorbents into five classes: aquatic humic substances (AHS), hydrophobic neutrals (HoN), hydrophilic acids (HiA), bases (BaS), and hydrophilic neutrals (HiN). The DOM-fraction distribution pattern and the ultraviolet absorbance to dissolved organic carbon ratio (UV/DOC ratio) were found remarkably effective for evaluating the characteristics of DOM in water. DOM-fraction distribution patterns were significantly different depending on the origin of the sample. AHS and HiA were found to be the dominant fractions in DOM in all samples studied. HiA prevailed over AHS in the lake water, whereas AHS were slightly more abundant than HiA in the river waters. AHS were in the great majority in forest streams and plowed-field percolates. HiA abounded in paddy-field outflow, domestic sewage, and sewage-treatment-plant effluent. Only domestic sewage contained a significant amount of HoN. The UV/DOC ratio also varied depending on the origin of the sample: the ratios in total DOM, AHS, and HiA were greater in river waters than in the lake water. The greatest ratio of AHS was found in paddy-field outflow and the lowest in domestic sewage. The UV/DOC ratios in the sewage-treatment-plant effluent were very similar to those in the lake water.