Dissolved Organic Matter Biodegradation Research Articles

Ammonium and glucose amendments stimulate dissolved organic matter mineralization in a Lake Superior tributary

Dissolved organic matter (DOM) plays an integral role in the biogeochemical cycles of aquatic ecosystems, and rates of DOM mineralization can be affected by nitrogen (N) and carbon (C) availability in the water column. To determine if DOM mineralization rates were limited by availability of N or C in a small tributary of Lake Superior, we conducted 28-day laboratory experiments where we amended stream water with a microbial inoculum and ammonium (NH4+) and/or glucose in a full factorial design. We repeated these experiments on four dates (July, October, January, April) because we expected nutrient limitation to vary with temporal changes in sources of DOM and nutrients. DOM mineralization rates were stimulated by additions of NH4+ in three of the four experiments and by glucose in all four experiments, even in October when carbon inputs to the stream via leaf litter were greatest. Mean biodegradable dissolved organic C was greater in July (40.6% ± 5.4) than October (10.2% ± 0.9) or January (9.6% ± 10.9) but did not differ from April (18.4% ± 0.7), which suggests the composition of DOM varies temporally. Our results suggest that biodegradable DOM is exported from this forested stream to nearshore Lake Superior throughout the year, but DOM mineralization can be stimulated by additions of both carbon and nitrogen. Nutrient enrichment may alter in-stream processing of DOM in small forested tributary streams, in turn reducing export of biodegradable DOM to nearshore regions of the Great Lakes where it fuels microbial production.

Characterization and removal of dissolved organic matter in a vertical flow constructed wetland

Isolated dissolved organic matter (DOM) fractions and their removal potentials in a vertical flow constructed wetland were characterized and identified. Resin isolation, molecular weight distribution and three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy were used to characterize DOM in raw sewage and treated effluent. The results showed that DOM fractions with molecular weights >10kDa in raw domestic sewage could be removed from the system more preferentially. Compared with hydrophilic organics, hydrophobic organics tended to be removed in the vertical flow constructed wetland more preferentially. Acidic and neutral organic matters featured higher removal rates than that of basic matters. Protein-like substances were representative of the biodegradable DOM, which made up a substantial proportion of the total dissolved organic carbon (DOC) removed from the system, while visible fulvic-like hydrophilic substances represented non-biodegradable DOM, which made up a minor proportion of the total DOC removed from the vertical flow constructed wetland.

Bioavailability of dissolved organic carbon across a hillslope chronosequence in the Kuparuk River region, Alaska

Dissolved organic matter (DOM) represents an important component of carbon and nutrient cycling in arctic ecosystems. In northern Alaska, DOM production and microbial activity differ among landscapes with varied glaciation histories with lower rates on younger landscapes. In addition, within the region, soil DOM concentrations vary at the scale of hillslope toposequences, with higher concentrations in upslope than streamside positions. However, it is unknown whether variation in DOM production quality among and within landscapes linked to patterns in DOM quality. To answer this question, we conducted a study of DOM biodegradability within and among hillslopes of different landscape age. We examined rates of DOM decomposition and several indices of the quality of water-extracted DOM collected from soils in the summer. A variety of methods indicated that DOM quality generally was consistent across hillslope positions and among landscape ages. For example, DOM fluorescence index, an index of quality for chromophoric DOM, did not vary significantly across all hillslope positions or landscape ages. There were no significant differences among landscape ages or hillslope positions in DOM specific UV absorbance, in rates of DOM mineralization, or in DOM decomposition, indicating that DOM quality was consistent regardless of its source or position along hillslope flow paths. This suggests that despite many potential sources of variation within and among arctic hillslopes linked to differences in vegetation, hydrology, microclimate, and microbial activity, there is little variation in growing-season soil DOM quality. Microbial processing of DOM within arctic hillslopes may lead to a convergence in growing season DOM quality resulting in little spatial variation. Approximately 10–20% of the growing season DOM is labile in tundra soils, slightly higher that the proportion that is labile in arctic rivers during the summer.

Photo- and bio-reactivity patterns of dissolved organic matter from biomass and soil leachates and surface waters in a subtropical wetland

Dissolved organic carbon (DOC) measurements and optical properties were applied to assess the photo- and bio-reactivity of dissolved organic matter (DOM) from different sources, including biomass leaching, soil leaching and surface waters in a subtropical wetland ecosystem. Samples were exposed to light and/or dark incubated through controlled laboratory experiments. Changes in DOC, ultraviolet (UV-Vis) visible absorbance, and excitation-emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC) were performed to assess sample degradation. Degradation experiments showed that while significant amounts of DOC were consumed during bio-incubation for biomass leachates, a higher degree of bio-recalcitrance for soil leachate and particularly surface waters was displayed. Photo- and bio-humification transformations were suggested for sawgrass, mangrove, and seagrass leachates, as compared to substantial photo-degradation and very little to almost no change after bio-incubation for the other samples. During photo-degradation in most cases the EEM-PARAFAC components displayed photo-decay as compared to a few cases which featured photo-production. In contrast during bio-incubation most EEM-PARAFAC components proved to be mostly bio-refractory although some increases and decreases in abundance were also observed. Furthermore, the sequential photo- followed by bio-degradation showed, with some exceptions, a “priming effect” of light exposure on the bio-degradation of DOM, and the combination of these two processes resulted in a DOM composition more similar to that of the natural surface water for the different sub-environments. In addition, for leachate samples there was a general enrichment of one of the EEM-PARAFAC humic-like component (Ex/Em: <260(305)/416 nm) during photo-degradation and an enrichment of a microbial humc-like component (Ex/Em: <260(325)/406 nm and of a tryptophan-like component (Ex/Em: 300/342 nm) during the bio-degradation process. This study exemplifies the effectiveness of optical property and EEM-PARAFAC in the assessment of DOM reactivity and highlights the importance of the coupling of photo- and bio-degradation processes in DOM degradation.

Fate of 14C-labeled dissolved organic matter in paddy and upland soils in responding to moisture

Soil organic matter (SOM) content in paddy soils is higher than that in upland soils in tropical and subtropical China. The dissolved organic matter (DOM) concentration, however, is lower in paddy soils. We hypothesize that soil moisture strongly controls the fate of DOM, and thereby leads to differences between the two agricultural soils under contrasting management regimens.A 100-day incubation experiment was conducted to trace the fate and biodegradability of DOM in paddy and upland soils under three moisture levels: 45%, 75%, and 105% of the water holding capacity (WHC). 14C labeled DOM, extracted from the 14C labeled rice plant material, was incubated in paddy and upland soils, and the mineralization to 14CO2 and incorporation into microbial biomass were analyzed. Labile and refractory components of the initial 14C labeled DOM and their respective half-lives were calculated by a double exponential model.During incubation, the mineralization of the initial 14C labeled DOM in the paddy soils was more affected by moisture than in the upland soils. The amount of 14C incorporated into the microbial biomass (2.4–11.0% of the initial DOM-14C activity) was less affected by moisture in the paddy soils than in the upland soils. At any of the moisture levels, 1) the mineralization of DOM to 14CO2 within 100days was 1.2–2.1-fold higher in the paddy soils (41.9–60.0% of the initial DOM-14C activity) than in the upland soils (28.7–35.7%), 2) 14C activity remaining in solution was significantly lower in the paddy soils than in the upland soils, and 3) 14C activity remaining in the same agricultural soil solution was not significantly different among the three moisture levels after 20days. Therefore, moisture strongly controls DOM fate, but moisture was not the key factor in determining the lower DOM in the paddy soils than in the upland soils.The UV absorbance of DOM at 280nm indicates less aromaticity of DOM from the paddy soils than from the upland soils. At any of the moisture levels, much more labile DOM was found in paddy soils (34.3–49.2% of the initial 14C labeled DOM) compared with that in upland soils (19.4–23.9%). This demonstrates that the lower DOM content in the paddy soil compared with that in the upland soil is probably determined by the less complex components and structure of the DOM.

Experimental nitrogen deposition alters the quantity and quality of soil dissolved organic carbon in an alpine meadow on the Qinghai-Tibetan Plateau

Dissolved organic matter (DOM) plays a central role in driving biogeochemical processes in soils, but little information is available on the relation of soil DOM dynamics to microbial activity. The effects of NO3− and NH4+ deposition in grasslands on the amount and composition of soil DOM also remain largely unclear. In this study, a multi-form, low-dose N addition experiment was conducted in an alpine meadow on the Qinghai–Tibetan Plateau in 2007. Three N fertilizers, NH4Cl, (NH4)2SO4 and KNO3, were applied at four rates: 0, 10, 20 and 40kgNha−1yr−1. Soil samples from surface (0–10cm) and subsurface layers (10–20cm) were collected in 2011. Excitation/emission matrix fluorescence spectroscopy (EEM) was used to assess the composition and stability of soil DOM. Community-level physiological profile (CLPP, basing on the BIOLOG Ecoplate technique) was measured to evaluate the relationship between soil DOC dynamics and microbial utilization of C resources. Nitrogen (N) dose rather than N form significantly increased soil DOC contents in surface layer by 23.5%–35.1%, whereas it significantly decreased soil DOC contents in subsurface layer by 10.4%–23.8%. Continuous five-year N addition significantly increased the labile components and decreased recalcitrant components of soil DOM in surface layer, while an opposite pattern was observed in subsurface layer; however, the humification indices (HIX) of soil DOM was unaltered by various N treatments. Furthermore, N addition changed the amount and biodegradability of soil DOM through stimulating microbial metabolic activity and preferentially utilizing organic acids. These results suggest that microbial metabolic processes dominate the dynamics of soil DOC, and increasing atmospheric N deposition could be adverse to the accumulation of soil organic carbon pool in the alpine meadow on the Qinghai-Tibetan Plateau.

Changes in Chemical Composition and Spectral Characteristics of Dissolved Organic Matter From Soils Induced by Biodegradation

Dissolved organic matter (DOM) provides the main energy and C source for soil microorganisms; however, relatively little is known about the dynamics of individual DOM fractions during microbial decomposition. Our objective was to investigate the changes in chemical composition and spectral characteristics of DOM from soils under four different vegetation types, including evergreen broad-leaved forest, coniferous forest, dwarf forest, and alpine meadow along an elevation gradient in the Wuyi Mountains of southeastern China during a 90-day incubation with UV, fluorescence, and Fourier-transform infrared spectroscopic techniques. In synchronous fluorescence spectra, the relative fluorescence intensity (RFI) of fulvic acid–like materials in DOM decreased for evergreen broad-leaved forest and dwarf forest soils after incubation, indicating that fulvic acids, especially when abundant at high initial content, seemed to be an important C source for soil microorganisms. The RFI of humic acid–like materials in DOM increased for all the samples after incubation, indicating that humic acids were resistant to biodegradation. The RFI of protein-like materials in DOM increased for all cases after incubation. Fourier-transform infrared spectroscopy showed that the ratio of absorption intensity of aromatic C=C to that of carbohydrate C-O in DOM increased by twofold to threefold after incubation for all the samples. Increasing values of UV254 absorbance and Humification Index of DOM were found for soils under most vegetation types after incubation. Carbohydrate C concentrations showed a larger fluctuation throughout the incubation, with a change of between 4.5 and 10.4 mg C L−1. Phenol C concentrations increased significantly for all cases. These results indicate that aromatic compounds with an enhanced degree of condensation were accumulated gradually during DOM biodegradation, and that there were considerable amounts of carbohydrates and protein-like materials in the residual DOM.

Fractions and biodegradability of dissolved organic matter derived from different composts

An experiment was conducted to determine the fractions of molecular weights (MW) and the biodegradability of dissolved organic matter (DOM) in mature composts derived from dairy cattle manure (DCM), kitchen waste (KW), cabbage waste (CW), tomato stem waste (TSW), municipal solid waste (MSW), green waste (GW), chicken manure (CM), sludge (S), and mushroom culture waste (MCW). There were distinct differences in the concentration and MW fractions of DOM, and the two measures were correlated. Fraction MW>5kDa was the major component of DOM in all mature composts. Determined 5day biochemical oxygen demand (BOD5) of DOM was correlated to the concentration of DOM and all MW fractions except MW>5kDa, indicating that the biodegradability of DOM was a function of the content and proportion of fraction MW<5kDa. This study suggests that the amount and distribution of low MW fractions affect DOM biodegradability.

The dynamic exchange of dissolved organic matter percolating through six diverse soils

The movement of dissolved organic matter (DOM) through forest soils is regulated by a suite of physicochemical and biological processes that retain, transform, and release DOM. While sorptive processes are known to limit DOM losses, there are still uncertainties about what regulates DOM composition. This study examined DOM dynamics in waters percolating through ex-situ soil cores from six diverse forest soils to determine if DOM leaching losses reflected dynamic exchange processes between fresh DOM inputs and soil surfaces or the continual stripping of surface-reactive compounds from recent DOM inputs. There was a net desorption of hydrophilic compounds into soil solutions after 10 cm soil depth that coincided with an increase in DOM biodegradability as solutions percolated to depth. There was also a limited net retention of dissolved organic nitrogen (DON) in surface soils. Taken together, these results support a dynamic exchange model of DOM dynamics where highly sorptive, hydrophobic compounds displace previously sorbed, N-rich hydrophilic compounds from soil surfaces. These soils also demonstrated fairly consistent leaching losses of dissolved organic carbon (DOC) and DON despite their variation in texture, hydraulic conductivity, and Fe and Al mineralogy, removing 72–85% of the DOC added by 50 cm depth. The strong sorption capacity of these soils may be one reason for the fairly uniform DOM chemistry leaching from these soil cores.

Concentration dynamics and biodegradability of dissolved organic matter in wetland soils subjected to experimental warming

Dissolved organic matter (DOM) is the most bioavailable soil organic pool. Understanding how DOM responds to elevated temperature is important for forecasting soil carbon (C) dynamics under climate warming. Here a 4.5-year field microcosm experiment was carried out to examine temporal DOM concentration dynamics in soil pore-water from six different subtropical wetlands. Results are compared between control (ambient temperature) and warmed (+5°C) treatments. UV–visible and fluorescence spectroscopy was performed to reveal DOM structural complexity at the end of the warming incubation. Elevated temperature resulted in initially (1 to 2.5years) high pore-water DOM concentrations in warmed samples. These effects gradually diminished over longer time periods. Of the spectral indices, specific UV absorbance at 280nm and humification index were significantly higher, while the signal intensity ratio of the fulvic-like to humic-like fluorescence peak was lower in warmed samples, compared to the control. Fluorescence regional integration analysis further suggested that warming enhanced the contribution of humic-like substances to DOM composition for all tested wetlands. These spectral fingerprints implied a declined fraction of readily available substrates in DOM allocated to microbial utilization in response to 4.5years of warming. As a negative feedback, decreased DOM biodegradability may have the potential to counteract initial DOM increases and alleviate C loss in water-saturated wetland soils.

Photodegradation‐Induced Changes in the Characteristics of Dissolved Organic Matter with Different Sources and Their Effects on Disinfection By‐Product Formation Potential

Changes in the apparent characteristics of dissolved organic matter (DOM) upon photodegradation and their influences on disinfection by‐products formation potentials (DBPFP) were examined using biodegraded DOM from six different sources (leaf litter, algae, compost, paddy water, treated sewage, and headwater). After seven day UV irradiation, no substantial changes occurred in the dissolved organic carbon (DOC) concentrations, but significant decreases were observed for the specific UV absorbance. In general, fulvic‐like and humic‐like fluorophores appear to be more affected by photodegradation than protein‐like fluorophores (or DOM components) and/or than the DOM structures associated with a shorter excitation wavelength. Size exclusion chromatograms revealed that UV absorbing molecules of intermediate size ranging from 1 to 5 kDa were most vulnerable to the UV irradiation. Except for leaf litter‐derived DOM, UV irradiation did not lead to substantial changes in specific DBPFP (i.e. disinfection by‐product (DBP)/dissolved organic carbon) comparable to those of the DOM characteristics, suggesting that many of the DBP precursors were not easily removed by photodegradation or some photochemically produced compounds could operate as DBP precursors. All the DOM samples exhibited greater formation potential for haloacetic acids per organic carbon than trihalomethanes irrespective of the sources. In general, correlations between DOM properties and specific DBPFP became stronger after photodegradation. The intermediate sized UV‐absorbing moieties appear to be actively involved in forming DBPs for photodegraded DOM. An integrated region of protein‐like fluorescence intensities may be suggested as an estimation index for specific DBPFP independent of the DOM sources.

Microbial transformation of dissolved organic matter from different sources and its influence on disinfection byproduct formation potentials

Biodegradation-induced changes in the characteristics of dissolved organic matter (DOM) and the subsequent effects on disinfection byproduct formation potentials (DBPFPs) were investigated using six different sources of DOM (algae, leaf litter, reed, compost, paddy water, and treated municipal sewage effluent). Microbial incubation of the DOM samples increased the specific ultraviolet absorbance and humic-like fluorescence but decreased the protein/tannin-like fluorescence and relative distribution of smaller-sized DOM components. Comparison of the original versus biodegraded DOM samples using resin fractionation and pyrolysis-gas chromatography/mass spectrometry revealed that the biodegradation-induced changes were highly dependent on DOM sources and exhibited no consistent trends among the different sources. Changes in DBPFPs also differed with DOM source. Vascular plant-derived DOM (leaf litter and reed) demonstrated an enhancement in specific DBPFP after biodegradation, whereas little change or even a slight decrease was observed for the other DOM sources. Correlations that were significant between specific DBPFPs and the aromatic content or humic-like fluorescence for the original DOM samples were no longer significant after microbial degradation. The relative abundance of hydrophobic to hydrophilic structures in DOM is suggested to be a general indicator for the formation potential of trihalomethanes irrespective of DOM source and the state of biodegradation.

Biodegradability of natural dissolved organic matter collected from a UK moorland stream

The fate of dissolved organic matter (DOM) exported from headwaters is a large uncertainty in global carbon models and catchment biogeochemical process understanding. We examined the biodegradability of stream DOM collected during different flow conditions (n = 12) from a heather-dominated moorland headwater in NE Scotland. Freeze-dried DOM isolates were characterised, re-dissolved to 10 mg C L−1, inoculated with indigenous stream sediment microbes and incubated, with and without added nutrients, to assess decomposition rates at different times up to 41 days. Biodegradable DOM ranged from 5.0 to 19% of the total transported DOM, representing 8.54 kg C ha−1 yr−1 (11.1% of the total DOC flux, calculated as 77.2 ± 39.0 kg C ha−1 yr−1). No simple patterns with flow rate were apparent but accumulated antecedent rainfall, specific UV absorbance of DOM and 15N content were significant predictors of the proportion of organic matter decomposed. In headwater streams draining organic-rich catchments, in-stream DOM decomposition processes act as a secondary control on the spatial variability of carbon species, and are important for establishing accuracy of aquatic carbon fluxes and cycling budgets. Moreover, biologically-mediated DOM decomposition represents a net ‘climate forcing effect’ via the soil–stream–atmosphere pathway, drives downstream ecosystem metabolism and should be incorporated in carbon predictive modelling and ecosystem process studies.

Dissolved organic matter composition of winter flow in the Yukon River basin: Implications of permafrost thaw and increased groundwater discharge

Groundwater discharge to rivers has increased in recent decades across the circumpolar region and has been attributed to thawing permafrost in arctic and subarctic watersheds. Permafrost‐driven changes in groundwater discharge will alter the flux of dissolved organic carbon (DOC) in rivers, yet little is known about the chemical composition and reactivity of dissolved organic matter (DOM) of groundwater in permafrost settings. Here, we characterize DOM composition of winter flow in 60 rivers and streams of the Yukon River basin to evaluate the biogeochemical consequences of enhanced groundwater discharge associated with permafrost thaw. DOC concentration of winter flow averaged 3.9 ± 0.5 mg C L−1, yet was highly variable across basins (ranging from &lt;1 to &gt;20 mg C L−1). In comparison to the summer‐autumn period, DOM composition of winter flow had lower aromaticity (as indicated by specific ultraviolet absorbance at 254 nm, or SUVA254), lower hydrophobic acid content, and a higher proportion of hydrophilic compounds (HPI). Fluorescence spectroscopy and parallel factor analysis indicated enrichment of protein‐like fluorophores in some, but not all, winter flow samples. The ratio of DOC to dissolved organic nitrogen, an indicator of DOM biodegradability, was positively correlated with SUVA254and negatively correlated with the percentage of protein‐like compounds. Using a simple two‐pool mixing model, we evaluate possible changes in DOM during the summer‐autumn period across a range of conditions reflecting possible increases in groundwater discharge. Across three watersheds, we consistently observed decreases in DOC concentration and SUVA254 and increases in HPI with increasing groundwater discharge. Spatial patterns in DOM composition of winter flow appear to reflect differences in the relative contributions of groundwater from suprapermafrost and subpermafrost aquifers across watersheds. Our findings call for more explicit consideration of DOC loss and stabilization pathways associated with changing subsurface hydrology in watersheds underlain by thawing permafrost.

Production, degradation, and flux of dissolved organic matter in the subterranean estuary of a large tidal flat

The distributions of dissolved organic carbon (DOC), total dissolved hydrolysable amino acids (THAA), and colored dissolved organic matter (CDOM) were studied in pore-water/groundwater samples (including seeping water) from a subterranean estuary (STE) of a large tidal flat in Hampyeong Bay, Korea, in July 2011. The relatively low alanine D/L ratios and high THAA concentrations in the pore-water closest to the sediment surface (0–10cm) indicate the active production of dissolved organic matter (DOM) from benthic algae, and the relatively low THAA concentrations and high D/L ratios in the subsurface pore-water (10–35cm) indicate a relatively large presence of bio-degraded DOM. In the deep pore-water (35–75cm), relatively low D/L ratios, high DOC concentrations, and intense humic-like fluorescence were observed, suggesting a net accumulation of less-reactive DOC in this layer. Overall, this STE appears to have net DOM sources because the concentrations of DOC (60–1700μM) in the pore-water decreased toward the land, the surface, and the low-salinity waters. The concentrations of DOC in the seeping water (185±52μM) were higher than those in the overlying seawater (144±9μM), resulting in net DOC fluxes of 2–5×109g·C·yr−1 through submarine groundwater discharge (SGD) into Hampyeong Bay. The organic matter compositions in the seeping water indicated that SGD introduced DOM from both the surface and subsurface layers. Our results highlight that tidal flats are important sources for DOM, implying that SGD-driven DOM plays an important role in coastal carbon cycles and biogeochemistry.

Transformation of Dissolved Organic Matter in a Novel Groundwater Recharge System with Reclaimed Water

A novel process, enhanced direct injection-well recharge system (EnDir), can overcome the technical difficulties during the application of conventional surface spreading and has been developed to recharge groundwater with reclaimed water. In this study, removal and transformation of dissolved organic matter (DOM) in the system were investigated in laboratory-scale experiments. Results demonstrated that dissolved organic carbon and trihalomethane formation potential values could be reduced from 6.54 +/- 1.30 mg/L and 267.9 +/- 24.3 microg/L to 1.59 +/- 0.64 mg/L and 104.5 +/- 10.2 microg/L, respectively, as a result of DOM biodegradation in the aerobic short-term vadose soil treatment. Fluorescence spectra showed that aromatic protein-like substances and soluble microbial byproducts could be removed, to a great extent, in the soil system. Despite different removal efficiencies of DOM in different molecular weight fractions, the residual DOM was composed mainly of fulvic acid-like and humic acid-like substances, with molecular weights of 500 Da to 1 kDa.

Leachate dissolved organic matter characterization using spectroscopic methods

This study investigated the use of ultraviolet (UV) and fluorescence spectroscopy to monitor the changes in biodegradability of dissolved organic matter (DOM) in landfill leachates. Experiments to investigate aerobic biodegradation of leachate DOM were carried out using untreated and treated leachate samples collected from two UK municipal solid waste landfills, L1 and L2. Leachate samples collected at different stages of the aerobic treatment processes were characterized by conventional methods (chemical oxygen demand (COD) and dissolved organic carbon content (DOC)) and also by UV spectroscopy and fluorescence excitation-emission matrix. The laboratory-scale aerobic treatment system achieved reductions in COD and DOC in all of the leachates. Results obtained from UV spectrophotometry indicated that the aromatic character of the leachate decreased during aerobic biodegradation. Additionally, the fluorescence intensity of the leachates decreased to various extents, suggesting degradation of humic, fulvic or protein-like structures during biodegradation. Initial results showed strong relations between fluorescent DOC and fluorescent COD and suggest that the strength of these correlations could be a useful tool in distinguishing sources and biodegradability of DOC cheaply and quickly, although further research using different types of leachates is required.

A Review of Dissolved Organic Matter Transport Processes Affecting Soil and Environmental Quality

Dissolved organic matter (DOM) affects several processes in soil and water including nutrient cycling, soil and water pollution and CO2 flux between the soil and atmosphere. The aim of this review is to collate and synthesize the literature on the transport processes of DOM in soil. The DOM normally comprises of only a small fraction of soil organic matter (SOM) and originates mainly from the decomposition and solubilization of SOM, which is accumulated on soil surface or soil profile from plant residues and additions of organic amendments such as animal and poultry manures and other biosolids. The DOM is one of the most reactive and mobile SOM fractions and has a major influence on biogeochemical processes in both terrestrial and aquatic environments. Terrestrially borne DOM is subjected to microbial decomposition, photodegradation and adsorption on soil mineral surfaces. It is sorbed on mineral surfaces and high adsorption capacities of clay minerals and oxides for DOM sorption are demonstrated in laboratory studies. However, these high sorption values are not reproduced in limited field studies. Similarly, a few data available on the transport of DOM through macropores also demonstrate the limited control of sorption on DOM retention in soil profile. Thus, there is a need to further investigate the physical and chemical protection mechanisms, as well as the biodegradability of DOM shown in laboratory studies. There is an increasing need to clearly understand the formation, fate and transport of DOM at field scales. The environmental factors such as precipitation and temperature, land use change, land management, and biological factors have profound and discrete influences on DOM dynamics in soil profile. Future research efforts must focus on the assessment of the influences of these factors by conducting field studies in different climatic zones, soils, and land use and management systems.

Spectroscopic and chromatographic characterization of wastewater organic matter from a biological treatment plant.

Spectroscopic and chromatographic changes in dissolved organic matter (DOM) characteristics of influent and treated sewage were investigated for a wastewater treatment plant (WWTP) with a biological advanced process. Refractory DOM (R-DOM) was defined as the dissolved organic carbon concentrations of the samples after 28-day incubation for this study. Specific UV absorbance (SUVA), hydrophobicity, synchronous fluorescence spectra and molecular weight (MW) distributions were selected as DOM characteristics. The percent distribution of R-DOM for the effluent was much higher than that of the influent, indicating that biodegradable DOM was selectively removed during the process. Comparison of the influent versus the effluent sewage revealed that SUVA, fulvic-like fluorescence (FLF), humic-like fluorescence (HLF), the apparent MW values were enhanced during the treatment. This suggests that more aromatic and humic-like compounds were enriched during the biological process. No significant difference in the DOM characteristics was observed between the original effluent (i.e., prior to the incubation) and the influent sewage after the incubation. This result suggests that the major changes in wastewater DOM characteristics occurring during the biological advanced process were similar to those for simple microbial incubation.

Impact of Wastewater Treatment Processes on Organic Carbon, Organic Nitrogen, and DBP Precursors in Effluent Organic Matter

Unintentional, indirect wastewater reuse often occurs as wastewater treatment plant (WWTP) discharges contaminate receiving waters serving as drinking-water supplies. A survey was conducted at 23 WWTPs that utilized a range of treatment technologies. Samples were analyzed for typical wastewater and drinking-water constituents, chemical characteristics of the dissolved organic matter (DOM), and disinfection byproduct (DBP) precursors present in the effluent organic matter (EfOM). This was the first large-scale assessment of the critical water quality parameters that affect the formation of potential carcinogens during drinking water treatment relative to the discharge of upstream WWTPs. This study considered a large and wide range of variables, including emerging contaminants rarely studied at WWTPs and never before in one study. This paper emphasizesthe profound impact of nitrification on many measures of effluent water quality, from the obvious wastewater parameters (e.g., ammonia, biochemical oxygen demand) to the ones specific to downstream drinking water treatment plants (e.g., formation potentialsfor a diverse group of DBPs of health concern). Complete nitrification reduced the concentration of biodegradable dissolved organic carbon (BDOC) and changed the ratio of BDOC/DOC. Although nitrification reduced ultraviolet absorbance (UVA) at 254 nm, it resulted in an increase in specific UVA (UVA/DOC). This is attributed to preferential removal of the less UV-absorbing (nonhumic) fraction of the DOC during biological treatment. EfOM is composed of hydrophilic and biodegradable DOM, as well as hydrophobic and recalcitrant DOM, whose proportions change with advanced biological treatment. The onset of nitrification yielded lower precursor levels for haloacetic acids and nitrogenous DBPs (haloacetonitriles, N-nitrosodimethylamine). However, trihalomethane precursors were relatively unaffected by the level of wastewater treatment Thus, one design/operations parameter in wastewater treatment, the decision to have a long enough solids retention time to get reliable nitrification, affected much beyond its immediate goal of ammonium oxidation.