Bulk Dissolved Organic Matter Research Articles

Fluorescence spectroscopic studies of the effect of granular activated carbon adsorption on structural properties of dissolved organic matter fractions

This work investigated the effect of granular activated carbon adsorption (GACA) on fluorescence characteristics of dissolved organic matter (DOM) in secondary effluent, by means of excitation-emission matrix (EEM) spectra, the fluorescence regional integration (FRI) method, synchronous spectra, the fluorescence index defined as the ratio of fluorescence emission intensity at wavelength 450 nm to that at 500 nm at excitation (λex)= 370 nm, and the wavelength that corresponds to the position of the normalized emission band at its half intensity (λ0.5). DOM in the secondary effluent from the North Wastewater Treatment Plant (Shenyang, China) was fractionated using XAD resins into 5 fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). Results showed that fluorescent materials in HPO-N and TPI-N were less readily removed than those in the other fractions by GACA. The relative content of fluorescent materials in HPO-A, TPI-A and HPI decreased whereas that in HPO-N and TPI-N increased as a consequence of GACA. Polycyclic aromatics in all DOM fractions were preferentially absorbed by GACA, in comparison with bulk DOM expressed as DOC. On the other hand, the adsorption of aromatic amino acids and humic acid-like fluorophores exhibiting fluorescence peaks in synchronous spectra by GACA seemed to be dependent on the acid/neutral properties of DOM fractions. All five fractions had decreased fluorescence indices as a result of GACA. GACA led to a decreased λ0.5 value for HPO-A, increased λ0.5 values for HPO-N, TPI-A and HPI, and a consistent λ0.5 value for TPI-N.

Seasonal dynamics of dissolved organic matter on a coastal salinity gradient in the northern Baltic Sea

During the phytoplankton growth season, the vertical distributions of dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) were followed biweekly along with key physical, chemical and biological variables on a shore-to-open-sea salinity gradient in the Gulf of Finland. Moreover, bioavailable shares of DOC and DON were evaluated with natural bacterial surface and deepwater samples. Dissolved organic matter (DOM) accumulated in the surface layer throughout the productive season, and the accumulated DOM was N-rich (molar C:N ratio of 10) compared to the bulk DOM pool (C:N 20–29). Redundancy analysis showed a negative correlation between phytoplankton and DOM concentrations, suggesting that most DOM release occurred during declining phases of spring and late summer algal blooms. During the spring bloom, bioavailable shares of DOM were small, whereas during and after the late summer bloom of filamentous cyanobacteria, 3–9% and 10–20% of the respective total DOC and DON pools were degraded by bacteria within 2 weeks. Vertical mixing over the thermocline was estimated by constructing a steady state budget for water and salt mass flows between key GoF basin compartments (inflows equal outflows). The flow estimates suggested that the net changes in surface DOC and DON pools underestimated the respective total accumulations by ca 40% and 20%, respectively, over the 4-mo thermal stratification period. Thus, integral export of surface DOC and DON after autumn overturn amounted to ca 710mmolCm−2 and 40mmolNm−2, corresponding respectively to ca 12–25% and 11% of reported annual particulate organic carbon and nitrogen sedimentation in our study area.

A molecular perspective on the ageing of marine dissolved organic matter

Abstract. Dissolved organic matter (DOM) was extracted by solid-phase extraction (SPE) from 137 water samples from different climate zones and different depths along an eastern Atlantic Ocean transect. The extracts were analyzed with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionization (ESI). Δ14C analyses were performed on subsamples of the SPE-DOM. In addition, the amount of dissolved organic carbon was determined for all water and SPE-DOM samples as well as the yield of amino sugars for selected samples. Linear correlations were observed between the magnitudes of 43 % of the FT-ICR mass peaks and the extract Δ14C values. Decreasing SPE-DOM Δ14C values went along with a shift in the molecular composition to higher average masses (m/z) and lower hydrogen/carbon (H/C) ratios. The correlation was used to model the SPE-DOM Δ14C distribution for all 137 samples. Based on single mass peaks, a degradation index (IDEG) was developed to compare the degradation state of marine SPE-DOM samples analyzed with FT-ICR MS. A correlation between Δ14C, IDEG, DOC values and amino sugar yield supports that SPE-DOM analyzed with FT-ICR MS reflects trends of bulk DOM. DOM weighted normalized mass peak magnitudes were used to compare aged and recent SPE-DOM on a semi-quantitative molecular basis. The magnitude comparison showed a continuum of different degradation rates for the detected compounds. A high proportion of the compounds should persist, possibly modified by partial degradation, in the course of thermohaline circulation. Prokaryotic (bacterial) production, transformation and accumulation of this very stable DOM occur primarily in the upper ocean. This DOM is an important contribution to very old DOM, showing that production and degradation are dynamic processes.

First spectroscopic study on the structural features of dissolved organic matter isolated from rainwater in different seasons

The complexity of rainwater dissolved organic matter (DOM) and the large percentage considered uncharacterized has made it difficult to determine the role of rainwater DOM in regional and global carbon budgets. Recent studies have concentrated on determining the structural characteristics of the bulk DOM in rainwater, but a comparison between the structural characteristics of rainwater DOM from different seasons is lacking. In this work, DOM was extracted from rainwater collected in different seasons by a procedure based on adsorption onto DAX-8 resin and a comparison between the spectroscopic characteristics of extracted DOM was performed using UV–visible, excitation–emission matrix (EEM) fluorescence and 1H NMR spectroscopies. Similar structural characteristics were observed for extracted DOM from the different seasons: high content of aliphatic structures, hydroxy and alkoxy groups, carbonyl groups and unsaturated carbon atoms, and low content of aromatic structures when compared with aliphatic structures. The obtained results suggest a model of chemical structures for the extracted DOM from rainwater, as consisting mainly of aliphatic chains, with COOH, –CH2OH, –COCH3, or –CH3 terminal groups, and with only a minor aromatic component. Moreover, this study suggests that the DOM extracted from rainwater has higher aliphatic character and lower aromatic content than aquatic humic substances. Thus, the chemical characteristics of aquatic humic substances may not be good models for DOM extracted from rainwater.

Simultaneous consumption and production of fluorescent dissolved organic matter by lake bacterioplankton

Recent evidence suggests a key role of bacterioplankton in shaping the composition of the dissolved organic matter (DOM) pool in aquatic systems, not only through consumption but also through production of specific compounds, but the latter process is still not well understood. We used a bioassay approach to assess the patterns in bacterial production and consumption of five fluorescent DOM pools in seven lakes and two streams in Southeastern Québec, Canada, and the links these patterns may have with key aspects of bacterial metabolism, DOM origin and nutrients availability. Total dissolved organic C declined by 3-15% during these incubations, whereas the specific DOM pools had very different dynamics: Two humic-like fractions accumulated in all incubations, with rates of production increasing as a function of bacterial growth efficiency, which itself increased with phosphorus concentrations. In contrast, two protein-like fractions and a third humic-like fraction either increased or declined over the course of the experiments. The net production or consumption of these pools appeared to be a function of the contribution of terrestrial C to bulk DOM (derived from δ(13) C of the DOM) and of total bacterial activity. Our results suggest that lake bacterioplankton play a dual role in DOM dynamics, as consumers and also producers, and that the interplay between DOM origin and nutrient availability appears to determine the net outcome of bacterial DOM processing, thus influencing the bulk DOM composition and its fate in these aquatic systems.

Water-extractable soil organic matter characterization by chromophoric indicators: Effects of soil type and irrigation water quality

Use of treated wastewater (TWW) for irrigation may affect the concentration and composition of dissolved organic matter (DOM) in the soil solution. Our objectives were (i) to characterize the water-extractable fraction of soil organic matter (SOM) in terms of chromophoric DOM (CDOM) for different soil types and irrigation water qualities, and (ii) to examine the possible relations between DOM composition and various soil properties. Aqueous extracts from four different soil types irrigated with either secondary TWW or fresh water (FW) were characterized for dissolved organic carbon (DOC) concentration and absorbance at 254nm (Abs254). Excitation–emission matrices (EEM) of fluorescence were determined in these aqueous extracts and in extracts where DOM was separated into acid-soluble and acid-precipitated fractions. Parallel factor (PARAFAC) analysis of the EEMs of water-extractable DOM and their fractions identified two humic-like fluorescent components and one tryptophan-like component and provided their concentration scores. The concentration scores revealed that the acid-soluble DOM fraction contained the greater part of the humic-like fluorescent components present in the bulk DOM samples. Statistical examination demonstrated that the ratio of the concentration score of the humic-like substances that emit light at shorter wavelengths to that of humic-like substances that emit light at longer wavelengths was higher in the acid-soluble DOM fraction compared to the acid-precipitated DOM fraction. Among the FW-irrigated soils, the soil extracts varied in terms of concentration of DOM components. Irrigation of the coarse-textured soils with TWW generally increased the concentrations of DOC, fluorescent components and Abs254 in comparison to irrigation with FW. In the fine textured soils TWW application led to a decrease or had no impact on the concentration of DOC and the CDOM components in water-extractable SOM. Thus, the influence of TWW irrigation on water-soluble SOM relative to that of FW irrigation was also soil dependent. Strong linear relations (/r/>0.7) were found within CDOM indicators including concentration scores of fluorescent components and Abs254. Weak or no relations were found (i) between DOC concentration and CDOM indicators, and (ii) between attributes related to DOM properties and basic soil properties. Hence, nor DOC concentration neither SOM content can be used for estimating changes in concentrations of chromophoric components in water-extractable DOM.

Toward understanding the role of individual fluorescent components in DOM-metal binding

Knowledge on the function of individual fractions in dissolved organic matter (DOM) is essential for understanding the impact of DOM on metal speciation and migration. Herein, fluorescence excitation–emission matrix quenching and parallel factor (PARAFAC) analysis were adopted for bulk DOM and chemically isolated fractions from landfill leachate, i.e., humic acids (HA), fulvic acids and hydrophilic (HyI) fraction, to elucidate the role of individual fluorescent components in metal binding (Cu(II) and Cd(II)). Three components were identified by PARAFAC model, including one humic substance (HS)-like, one protein-like and one component highly correlated with the HyI fraction. Among them, the HS-like and protein-like components were responsible for Cu(II) binding, while the protein-like component was the only fraction involved in Cd(II) complexation. It was further identified that the slight quenching effect of HA fraction by Cd(II) was induced by the presence of proteinaceous materials in HA. Fluorescent substances in the HyI fraction of landfill leachate did not play as important a role as HS did. Therefore, it was suggested that the potential risk of aged leachate (more humified) as a carrier of heavy metal should not be overlooked.

Sorptive and Desorptive Fractionation of Dissolved Organic Matter by Mineral Soil Matrices

Interactions of dissolved organic matter (DOM) with soil minerals, such as metal oxides and clays, involve various sorption mechanisms and may lead to sorptive fractionation of certain organic moieties. While sorption of DOM to soil minerals typically involves a degree of irreversibility, it is unclear which structural components of DOM correspond to the irreversibly bound fraction and which factors may be considered determinants. To assist in elucidating that, the current study aimed at investigating fractionation of DOM during sorption and desorption processes in soil. Batch DOM sorption and desorption experiments were conducted with organic matter poor, alkaline soils. Fourier-transform infrared (FTIR) and UV-Vis spectroscopy were used to analyze bulk DOM, sorbed DOM, and desorbed DOM fractions. Sorptive fractionation resulted mainly from the preferential uptake of aromatic, carboxylic, and phenolic moieties of DOM. Soil metal-oxide content positively affected DOM sorption and binding of some specific carboxylate and phenolate functional groups. Desorptive fractionation of DOM was expressed by the irreversible-binding nature of some carboxylic moieties, whereas other bound carboxylic moieties were readily desorbed. Inner-sphere, as opposed to outer-sphere, ligand-exchange complexation mechanisms may be responsible for these irreversible, as opposed to reversible, interactions, respectively. The interaction of aliphatic DOM constituents with soil, presumably through weak van der Waals forces, was minor and increased with increasing proportion of clay minerals in the soil. Revealing the nature of DOM-fractionation processes is of great importance to understanding carbon stabilization mechanisms in soils, as well as the overall fate of contaminants that might be associated with DOM.

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

In this paper we investigate the seasonal autochthonous sources of dissolved organic carbon (DOC) and nitrogen (DON) in the euphotic zone at a station in the upper Chesapeake Bay using a new mass-based ecosystem model. Important features of the model are: (1) carbon and nitrogen are incorporated by means of a set of fixed and varying C:N ratios; (2) dissolved organic matter (DOM) is separated into labile, semi-labile, and refractory pools for both C and N; (3) the production and consumption of DOM is treated in detail; and (4) seasonal observations of light, temperature, nutrients, and surface layer circulation are used to physically force the model. The model reasonably reproduces the mean observed seasonal concentrations of nutrients, DOM, plankton biomass, and chlorophyll a. The results suggest that estuarine DOM production is intricately tied to the biomass concentration, ratio, and productivity of phytoplankton, zooplankton, viruses, and bacteria. During peak spring productivity phytoplankton exudation and zooplankton sloppy feeding are the most important autochthonous sources of DOM. In the summer when productivity peaks again, autochthonous sources of DOM are more diverse and, in addition to phytoplankton exudation, important ones include viral lysis and the decay of detritus. The potential importance of viral decay as a source of bioavailable DOM from within the bulk DOM pool is also discussed. The results also highlight the importance of some poorly constrained processes and parameters. Some potential improvements and remedies are suggested. Sensitivity studies on selected parameters are also reported and discussed.

Effects of rice straw–derived dissolved organic matter on pyrene sorption by soil

The objectives of the present study were to elucidate the chemical and structural properties of dissolved organic matter (DOM) derived from aerobic decay of rice straw and to quantify the effect of the DOM on the sorption of pyrene on soil. The DOM samples were obtained from microcosms incubated at 0, 21, 63, and 180 d. The bulk DOM samples were fractionated to four fractions: hydrophilic matter (HIM), acid-insoluble matter (AIM), hydrophobic acid (HOA), and hydrophobic neutral (HON) fractions. The bulk DOM and the four DOM fractions were characterized for their elemental compositions and functionalities. The results showed that HIM had the highest H/C atomic ratios, whereas HOA and AIM had the lowest H/C atomic ratios. These DOM samples were used as the background DOMs in the initial aqueous solutions for measuring sorption of pyrene on a paddy soil. The results indicated that, among the four DOM fractions, HOA, HON, and AIM significantly lowered the pyrene sorption coefficients, but HIM had little or no effect on the pyrene sorption by the soil. It appears that less polar AIM and HON had stronger binding affinities for pyrene in water, reducing the sorption coefficient for the soil, whereas more polar and less aromatic HIM had much weaker binding affinity for pyrene in water, causing little or no effect on the pyrene sorption by the soil. The present study showed that rice straw-derived DOM may enhance desorption and transport of organic pollutants in soil-water systems.

Dynamics of dissolved and particulate organic matter during the spring bloom in the Oyashio region of the western subarctic Pacific Ocean

We evaluated the dynamics of dissolved organic matter (DOM) and particulate organic matter (POM) at various stages of the spring bloom in the Oyashio region of the western subarctic Pacific Ocean by means of samples obtained during 3 cruises in April, May, and June 2003. In April, the average concentration (±1 SD) of nitrate plus nitrite ions was 23.3 ± 0.39 µmol l -1 in surface waters, and this decreased to below the detection limit (<0.05 µmol l -1 ) during the bloom period. About 80% of newly accumulated organic carbon was partitioned into POM. Whereas the C:N ratios of bulk DOM ranged from 13 to 20, the average C:N ratio of newly accumulated DOM was 7.3 ± 1.5. The lability of DOM was assessed by seawater culture-type incubation experiments on surface sea- water samples from each observation site. Although the newly accumulated DOM was relatively rich in nitrogen, most of it escaped rapid (d to wk) bacterial consumption in the seawater culture experi- ments.

Sorption of the pharmaceuticals carbamazepine and naproxen to dissolved organic matter: Role of structural fractions

Pharmaceutical compounds and dissolved organic matter (DOM) are co-introduced into the environment by irrigation with reclaimed wastewater and/or application of biosolids. In this study, we evaluate the role and mechanism of interaction of the pharmaceuticals naproxen and carbamazepine with structural fractions of biosolids-derived DOM. Sorption interactions were estimated from dialysis-bag experiments at different pHs. Sorption of naproxen and carbamazepine by the hydrophobic acid fraction exhibited strong pH-dependence. With both pharmaceuticals, the highest sorption coefficients ( K DOC) were at pH 4. With the hydrophobic neutral fraction, pH affected only naproxen sorption (decreasing with increasing pH). Among the hydrophilic DOM fractions, the hydrophilic acid fraction exhibited the highest K DOC value for carbamazepine, probably due to their bipolar character. In the hydrophilic acid fraction-naproxen system, significant anionic repulsion was observed with increasing pH. The hydrophilic base fraction contains positively charged functional groups. Therefore with increasing ionization of naproxen (with increasing pH), K DOC to this fraction increased. The hydrophilic neutral fraction exhibited the lowest K DOC with both studied pharmaceuticals. The K DOC value of carbamazepine with the bulk DOM sample was higher than the calculated K DOC value based on sorption by the individual isolated fractions. The opposite trend was observed with naproxen at pH 8: the calculated K DOC value was higher than the value obtained for the bulk DOM. These results demonstrate that DOM fractions interact with each other and do not act as separate sorption domains.

Reduction of trihalomethane precursors of dissolved organic matter in the secondary effluent by advanced treatment processes

Wastewater effluent collected from the Wenchang Wastewater Treatment Plant (Harbin, China) was used as source water for advanced treatment and reclamation. Since dissolved organic matter (DOM) in the secondary effluent contains a high concentration of trihalomethanes (THMs) precursors, several processes of advanced treatments including granular activated carbon (GAC) adsorption, sand column biodegradation, horizontal subsurface flow wetland (HSFW) treatment, laboratory-scale soil aquifer treatment (SAT) and GAC + SAT were used in this study to compare and differentiate the removal mechanisms of DOM. DOM in the secondary effluent and the treated effluents was fractionated into five classes using XAD resins: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N), and hydrophilic fraction (HPI). Results showed that HPO-A and HPI were two main fractions of the DOM in the secondary effluent, accounting for 30.0% and 45.5% of the bulk DOM, respectively. HPO-A exhibited higher trihalomethane formation potential (THMFP) and specific THMFP (STHMFP) than HPI during the chlorination process. The order of the dissolved organic carbon (DOC) removal with respect to different advanced treatments was observed to be GAC + SAT > SAT > GAC > sand column > HSFW. As for the DOM removal mechanisms, the advanced treatment processes of GAC adsorption, SAT and GAC + SAT tended to adsorb more HPO-A, HPO-N and TPI-A and could reduce the aromaticity of those DOM fractions efficiently. Correspondingly, the advanced treatment processes of sand column, SAT, HSFW and GAC + SAT removed more HPI and TPI-N through biodegradation and each of the DOM fractions had an increased aromaticity. The removal order of the THMs precursor by the advanced treatment processes was GAC + SAT > GAC > SAT> sand column > HSFW. The adsorption reduced the STHMFP of the DOM fractions effectively, whereas the biodegradation mechanism of the treatments (sand column, SAT, GAC + SAT and HSFW) showed a converse trend. Moreover, the THMFP and STHMFP of the DOM in the HSFW effluent were obviously affected by the DOM derived from the leaves and roots.

Use of electrospray ionization (ESI) mass spectrometry to investigate complex dissolved organic matter (DOM) and its potential applications in phytoplankton research

Organic nutrients are one of many factors considered to be important in the growth and proliferation of phytoplankton including many species that cause harmful algal blooms (HABs). Several studies have investigated the effects of known organic compounds on phytoplankton growth, however, the role of natural dissolved organic matter (DOM) in phytoplankton nutrition remains understudied at the compound level. This lack of research is due in part to analytical limitations for the characterization of DOM compounds. Electrospray ionization (ESI) mass spectrometry (MS) provides an unprecedented level of chemical information on thousands of organic compounds that comprise the bulk DOM pool. In this paper we provide a brief overview of some of the benefits and caveats of using ESI to investigate DOM in natural freshwater and marine systems and show an example of ESI-MS DOM characterization for a natural bloom of the raphidophyte Chattonella cf. verruculosa.

Dissolved organic matter characteristics within the Lake Superior watershed

Within the aquatic carbon cycle, dissolved organic carbon (DOC) plays key roles: as a link between terrestrial and aquatic systems, a major food source for biota, a player in photochemical reactions and a sunscreen/competitor for light for aquatic organisms. The molecular-level composition of the dissolved organic matter (DOM) is believed to determine the efficacy of DOM in these roles. While much detailed compositional information is available on selected DOM isolates from both freshwater and marine systems, relatively few studies have presented molecular information for multiple sites within the same system and few of these have focused upon large lakes. Therefore, we present an initial study of surface water DOM characteristics in a temperate large lake (Lake Superior, USA) and selected tributaries. UV–visible spectroscopy, electrospray mass spectrometry and Fourier transform infrared spectroscopy (FTIR) analyses of bulk DOM, along with FTIR and direct temperature-resolved mass spectrometry analyses of C 18 extracts, illustrate a shift from higher molecular weight organic matter enriched in protein and lignin at the tributary sites toward compositionally different material in the open lake. Differences in optical characteristics and DOC concentration between tributary and open lake sites are consistent with possible photodegradation of tributary DOM. Comparison of our FTIR data with those from a previous Chesapeake Bay study indicates that DOM in both the freshwater tributaries and the open lake contain a wider range of aromatic and carbohydrate components than that in the saltwater tributary and bay. This highlights the need for further cross system comparisons of natural organic matter composition.

Dissolved organic matter (DOM) and bacterial growth in floodplains of the Danube River under varying hydrological connectivity

Inorganic nutrients, distribution of low and high molecular weight dissolved organic matter (DOM), bulk DOM constituents, carbohydrate contents and a fl uorescence index of DOM, along with bacterial secondary production (BSP), were determined in a large river fl oodplain system. The aim was to elucidate the signifi cance of DOM in relation to hydrological conditions. Two fl oodplain segments with varying degree of connection to the main channel (and for some parameters also the main channel) of the Danube River downstream of Vienna (Austria) were investigated during two hydrologically dynamic periods. In most cases, inorganic nutrients were signifi cantly coupled to hydrology, but bulk dissolved organic nutrient species in two DOM size fractions were poorly correlated with changing connectivity with the main river. A more specifi c investigation of DOM properties (fl uorescence in- dex based on fulvic acids, carbohydrate content of dissolved organic carbon) revealed good correlation with hydrol- ogy, thus mirroring more directly the effect of changing fl oodplain connectivity and emphasising the importance of local (autochthonous) carbon sources at lower connectivity. BSP, measured during one of the investigated periods, was highly variable, with low values at high discharge and a signifi cant positive dependency on increasing autoch- thonous DOM-sources indicated by higher fl uorescence indices. Hydrological connectivity between the main river and its fl oodplains appears to be a crucial driving force infl uencing the quantity but in particular the quality of DOM as well as related microbial processes.

Fate of secondary effluent dissolved organic matter during soil-aquifer treatment

The reduction of mass and trihalomethane formation potential (THMFP) of dissolved organic matter (DOM) and its fractions from secondary effluent during laboratory-scale soil-aquifer treatment (SAT) soil columns were studied. Reduction in dissolved organic carbon (DOC), absorbance of ultraviolet light at 254 nm (UV-254), biodegradable dissolved organic carbon (BDOC) and nonbiodegradable dissolved organic carbon (NBDOC) for the bulk DOM averaged 72.35%, 53.98%, 97.49% and 35.33% across the soil columns, respectively. Using XAD-8 and XAD-4 resins, DOM was fractionated into 3 fractions: hydrophobic acid (HPO-A), transphilic acid (TPI-A) and hydrophilic fraction (HPI). HPO-A was removed by 61.06%, TPI-A by 54.86% and HPI by 74.95% as DOC as a consequence of the laboratory-scale SAT, respectively. The reduction of THMFP from HPO-A, TPI-A and HPI was 27.24%, 26.24% and 36.08%, respectively. Proton nuclear magnetic resonance (1H-NMR) spectra revealed that the HPO-A isolated from the secondary effluent contained more aromatic functional groups than the corresponding TPI-A. Fourier-transform infrared (FT-IR) spectrum analysis illustrated that TPI-A had decreased hydrocarbon and increased aromatics content in the SAT columns. Specific ultraviolet light absorbance (SUVA) and specific THMFP for each DOM fraction increased across the soil columns and HPI exhibited greater increase in both than HPO-A and TPI-A. The most problematic THM precursor was found to be HPO-A with its high quantity present in recharged water and high chlorine reactivity.

Optical properties of low molecular weight and colloidal organic matter: Application of the ultrafiltration permeation model to DOM absorption and fluorescence

Cross-flow ultrafiltration (CFF) is often used to obtain separation and concentration of colloids from bulk natural water samples. Application of the ultrafiltration permeation model allows the quantitative determination of the low molecular weight material (LMW, < 1 kDa) and colloids in bulk dissolved organic matter (DOM) from measurements of time series permeate samples obtained from CFF. Detailed analysis of a Yukon River water sample shows that DOM absorption coefficient and fluorescence follow the permeation model and that the complex spectral optical properties of LMW DOM can be reconstructed from CFF data. A combination of measured and modeled data indicates that the LMW contribution to bulk DOM optical properties obtained from CFF can be grossly underestimated by the use of a low concentration factor (CF, the ratio of initial sample volume to retentate volume). Even at a relatively high CF of 19, optical properties of LMW DOM calculated from measurements of the retentate or integrated permeate would underestimate true values by 5–36%. In the Yukon River sample, LMW dissolved organic carbon represented 26% of the bulk concentration, but only 3–14% of the colored DOM was in the LMW fraction while 31–33% of bulk DOM florescence was due to LMW DOM. The contrasting optical properties of LMW and colloidal DOM support the concept that analysis of bulk DOM absorption and fluorescence properties reveals information about DOM molecular weight.

Isolation and characterization of estuarine dissolved organic matter: Comparison of ultrafiltration and C 18 solid-phase extraction techniques

Characterization of dissolved organic matter (DOM) from aquatic environments has always been constrained by the ability to obtain a representative fraction of the DOM pool for analysis. Ultrafiltration or extraction, commonly using XAD or C 18 sorbents, is therefore generally used to concentrate and desalt DOM samples for further analyses. In this study, we compared ultrafiltration and C 18 solid-phase extraction disks (SPE) as DOM isolation methods for estuarine samples. We also evaluated the use of the C 18 SPE disks to isolate low-molecular-weight DOM (LMW-DOM) in the filtrate from ultrafiltration. The isolates from both methods and the LMW-DOM C 18-extracts were characterized using Fourier transform infrared spectroscopy (FTIR) and direct temperature-resolved mass spectrometry (DT-MS). Based on mass balance and blank measurements, we found that the C 18 SPE disks can be used to isolate bulk DOM and LMW-DOM from estuarine samples. FTIR and DT-MS analysis show that C 18-extracted DOM and ultrafiltered high-molecular-weight DOM (HMW-DOM) differ markedly in chemical composition. The HMW-DOM is enriched in (degraded) polysaccharides along with aminosugars when compared with the C 18-extracted DOM. The C 18-extracted DOM appears enriched in aromatic compounds, probably from lignin and/or aromatic amino acids in proteins. C 18 SPE of LMW-DOM samples from ultrafiltration increases the recovery of DOM from the total sample up to about 70%, compared to around 50% using ultrafiltration alone. Thus, a majority of the DOM can be isolated from estuarine samples by a combination of these techniques.

Changes in dissolved organic matter characteristics in Chincoteague Bay during a bloom of the pelagophyteAureococcus anophagefferens

Aureococcus anophagefferens, the pelagophyte responsible for brown tide blooms, occurs in coastal bays along the northeast coast of the United States. This species was identified in Chincoteague Bay, Maryland, in 1997 and has bloomed there since at least 1998. Time series of dissolved organic matter (DOM) concentrations and characteristics are presented for two sites in Chincoteague Bay: one that experienced a brown tide bloom in 2002 and one that did not. Characteristics of the bulk DOM pool were obtained using dissolved organic carbon (DOC) and ultraviolet-visible (UV-Vis) measurements (spectral slope and specific UV absorbance). High molecular weight DOM (HMW-DOM) was characterized in terms of DOC concentration, carbon: nitrogen (C:N) ratio, isotopic signature, and molecular-level characteristics as determined by direct temperature resolved mass spectrometry (DT-MS). Compositional changes in the DOM pool are associated with brown tide blooms, although a direct relationship between DOM characteristics and bloom development could not be confirmed. DOC measurements suggest that during the brown tide bloom, HMW-DOM was released into the surface water. UV-Vis analysis on the bulk DOM and molecular-level characterization of the HMW-DOM using DT-MS show that this material was optically active and more aromatic in nature. Based upon C:N ratio and HMW-DOC measurements, it appears that this HMW-DOM was more nitrogen enriched. Whether this material was released as exudates or was due to lysis ofA. anophagefferens could not be determined.