Hydrophilic Dissolved Organic Carbon Research Articles

Cadmium-treatment efficiency and membrane fouling during electrodialysis of wastewater discharged from zinc smelting

Zinc smelting wastewater contains high concentrations of Cd. Here, the treatment efficiency of Cd using electrodialysis was evaluated. In addition, scale accumulation of ion-exchange membrane (IEM) was analyzed, and fouling control was studied. The results showed that spacers effectively improved the limiting current density but accelerated foulant accumulation. The Cd-treatment efficiency improved to 85.4% without a spacer. Dissolved organic carbon (DOC) and hydrophobic DOC levels in diluted water decreased by 0.65 mg L−1 and 2.1 mg L−1, respectively; in contrast, hydrophilic DOC level increased by 1.45 mg L−1. Some of the hydrophobic DOC in the diluted water was converted to hydrophilic DOC and subsequently to low-molecular-weight (LMW) DOC. DOC level in the concentrated water did not change substantially, but the LMW fraction of the hydrophilic DOC increased. In the cation-exchange membrane, a material composed of calcium sulfate accumulated in the bottom layer, and hydroxides of divalent and trivalent ions accumulated on top of it. In contrast, the anion-exchange membrane was fouled by humic substances. In terms of fouling control, physical and acid cleaning of IEMs was more effective than the reversal operation.

Characterisation of groundwater dissolved organic matter using LC[sbnd]OCD: Implications for water treatment

The polarity and molecular weight of dissolved organic matter (DOM) is an important factor determining the treatability of water for domestic supply. DOM in surface water and groundwater is comprised of a mixture of carbon with varying molecular weight ranges, with its composition driven by DOM sources and processing. Here, we present the largest dataset of chromatographic DOM in surface and groundwater samples (n = 246) using liquid chromatography organic carbon detection (LCOCD). Our data represents four categories (surface water, hyporheic zone water, local groundwater, and regional groundwater) from five different sites across Australia. In all environments, high molecular weight hydrophilic DOM such as biopolymers (BP) and humic substances (HS) are present in surface waters and are processed out of groundwater as it moves from surface water and hyporheic zones into shallow local groundwater and deeper regional groundwaters. This results in a higher percentage of low molecular weight neutrals (LMWN) and hydrophobic organic carbon (HOC) in deeper regional groundwaters. Our findings indicate that the presence of sedimentary organic matter strongly influence the character of surface and groundwater DOM, resulting in groundwater with higher HS aromaticity and molecular weight, and reduced percentage of LMWNs. We also observe highly variable hydrophilic / HOC ratios in groundwater at all sites, with 9.60% and 25.64% of samples at sites containing sedimentary peat layers and non-sedimentary peat sites respectively containing only hydrophilic dissolved organic carbon (DOC). We identify average hydrophilic / HOC ratios of 4.35 ± 3.76 and 7.53 ± 5.32 at sites containing sedimentary peat layers and non-sedimentary peat sites respectively where both hydrophilic DOC and HOC are present. Overall our results suggest that fractured rock and alluvial aquifers in sedimentary organic carbon poor environments may contain DOC which is better suited to ozonation, biologically activated carbon filtration powdered activated carbon, suspended ion exchange treatment or magnetic ion exchange resin since DOC is more hydrophilic and of lower molecular weight and lower aromaticity. Aquifers located near sedimentary organic matter layers may benefit from pre-treatment by coagulation/flocculation, sedimentation and sand filtration which have high removal efficiency for high molecular weight and polar compounds.

Effects of soil organic residue amendment on losses of dissolved organic carbon, P, Cu and Zn via surface runoff from arable soils

Dissolved organic carbon (DOC) constitutes the largest carbon pool in surface waters, with soil being its main source via surface and subsurface runoff. Amendment with organic residues can reduce soil erosion and surface runoff, but little is known how this affects the amount and composition of DOC losses via surface runoff and the associated transfer of nutrients and pollutants. In this study, artificial rainfall experiments were conducted on three pairs of soil runoff plots with contrasting organic matter management. A mixture of grass and wheat straw residues was incorporated into the topsoil of one plot in each pair (OI treatment) but not into the other (control). Artificial rainfall was applied onto both treatments at an intensity of 49.1 mm h−1, and surface runoff samples were collected at designated time steps for analysis of DOC, total dissolved phosphorus (TDP), copper (TDCu) and zinc (TDZn) concentrations, as well as for characterization of DOC by UV–vis absorbance (SUVA254 and E2:E3) and fluorescence spectroscopy (FI) indexes. The organic amendment reduced the loss rates of DOC, TDP, TDCu and TDZn by reducing surface runoff, although increasing the concentrations of DOC, TDP and TDCu. Regardless of the treatment, DOC, TDP and TDCu concentrations were always maximal at the onset of runoff and then continuously decreased after the initial flush. The observed relationships of TDP and TDCu concentrations with DOC indicate that the export of “dissolved” P and Cu primarily occurred in DOC-bound form, while the concentration of TDZn was not correlated with that of DOC. Surface runoff from the amended soils generally contained more hydrophilic and low molecular weight DOC (as indicated by low SUVA254 and high E2:E3 and FI values), particularly at high DOC concentrations. The ratio between TDCu and DOC concentration showed a positive relationship to DOC aromaticity (as indicated by SUVA254 values) in the OI treatment. The results indicate that organic amendment can reduce total rates of dissolved element losses with surface runoff, but attention should also be paid to the composition of lost DOC and the concentrations of DOC-associated solutes.

Sensitivity of labile carbon fractions to tillage and organic matter management and their potential as comprehensive soil quality indicators across pedoclimatic conditions in Europe

Soil quality is defined as the capacity of the soil to perform multiple functions, and can be assessed by measuring soil chemical, physical and biological parameters. Among soil parameters, labile organic carbon is considered to have a primary role in many soil functions related to productivity and environmental resilience. Our study aimed at assessing the suitability of different labile carbon fractions, namely dissolved organic carbon (DOC), hydrophilic DOC (Hy-DOC), permanganate oxidizable carbon (POXC, also referred to as Active Carbon), hot water extractable carbon (HWEC) and particulate organic matter carbon (POMC) as soil quality indicators in agricultural systems. To do so, we tested their sensitivity to two agricultural management factors (tillage and organic matter input) in 10 European long-term field experiments (LTEs), and we assessed the correlation of the different labile carbon fractions with physical, chemical and biological soil quality indicators linked to soil functions. We found that reduced tillage and high organic matter input increase concentrations of labile carbon fractions in soil compared to conventional tillage and low organic matter addition, respectively. POXC and POMC were the most sensitive fractions to both tillage and fertilization across the 10 European LTEs. In addition, POXC was the labile carbon fraction most positively correlated with soil chemical (total organic carbon, total nitrogen, and cation exchange capacity), physical (water stable aggregates, water holding capacity, bulk density) and biological soil quality indicators (microbial biomass carbon and nitrogen, and soil respiration).We conclude that POXC represents a labile carbon fraction sensitive to soil management and that is the most informative about total soil organic matter, nutrients, soil structure, and microbial pools and activity, parameters commonly used as indicators of various soil functions, such as C sequestration, nutrient cycling, soil structure formation and soil as a habitat for biodiversity. Moreover, POXC measurement is relatively cheap, fast and easy. Therefore, we suggest measuring POXC as the labile carbon fraction in soil quality assessment schemes in addition to other valuable soil quality indicators.

Allochthonous sources and dynamic cycling of ocean dissolved organic carbon revealed by carbon isotopes

AbstractWe present concentration and isotopic profiles of total, size, and polarity fractionated dissolved organic carbon (DOC) from Station ALOHA (A Long‐term Oligotrophic Habitat Assessment), an oligotrophic site in the North Pacific Ocean. The data show that, between the surface and 3500 m, low molecular weight (LMW) hydrophilic DOC, LMW hydrophobic DOC, and high molecular weight (HMW) DOC constitute 22–33%, 45–52%, and 23–35% of DOC, respectively. LMW hydrophilic DOC is more isotopically depleted (δ13C of −23.9‰ to −31.5‰ and Δ14C of −304‰ to −795‰; mean age of 2850 to 15000 years) than the LMW hydrophobic DOC (δ13C of −22‰ to −23‰ and Δ14C of −270‰ to −568‰; 2470 to 6680 years) and HMW DOC (δ13C of ~−21‰ and Δ14C of −24‰ to −294‰; 135–2700 years). Our analyses suggest that a large fraction of DOC may be derived from allochthonous sources such as terrestrial and hydrothermal DOC and cycle on much longer time scales of >10000 years or enter the ocean as preaged carbon.

可溶性有机碳在米槠天然林不同土层中的迁移特征

PDF HTML阅读 XML下载 导出引用 引用提醒 可溶性有机碳在米槠天然林不同土层中的迁移特征 DOI: 10.5846/stxb201310272590 作者: 作者单位: 福建师范大学地理科学学院,湿润亚热带山地生态国家重点实验室培育基地,湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院,湿润亚热带山地生态国家重点实验室培育基地,湿润亚热带山地生态国家重点实验室培育基地 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学青年基金项目(31100467); 福建师范大学优秀青年骨干教师培养基金(fjsdky2012008); 国家自然科学基金重点项目(31130013); 福建省自然科学青年基金项目(2011J05105); 高等学校博士学科点专项科研基金(优先发展领域)(20113503130001) Transport characteristics of dissolved organic carbon in different soil horizons in natural Castanopsis carlesii forest Author: Affiliation: State Key Laboratory of Humid Subtropical Mountain Ecology,State Key Laboratory of Humid Subtropical Mountain Ecology,State Key Laboratory of Humid Subtropical Mountain Ecology,State Key Laboratory of Humid Subtropical Mountain Ecology,State Key Laboratory of Humid Subtropical Mountain Ecology,State Key Laboratory of Humid Subtropical Mountain Ecology Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:选取我国中亚热带典型的常绿阔叶林米槠天然林(Castanopsis carlesii)为研究对象,采集林内米槠凋落物并通过挖剖面法分6个土层采集土样至1 m。通过浸提米槠凋落物得到可溶性有机碳(dissolved organic carbon,DOC)溶液并在室内模拟其在不同土层的淋溶过程,不仅分析了土壤性质对DOC淋溶的影响,还研究了淋溶前后DOC化学结构的变化,以阐明DOC在不同土层中的迁移特征及影响因素,探寻米槠天然林土壤的固碳潜力和DOC在土壤有机碳循环中的作用。结果表明:(1)下层土壤比上层土壤吸附DOC的能力更强,亲水性DOC与疏水性DOC间会争夺土壤颗粒表面的吸附位点,而且芳香化合物和大分子物质等疏水性DOC组分会被优先吸附;(2)红外光谱表明,芳香类和醚类等疏水性物质会优先被吸附,烷烃类物质却不易被吸附,土壤中原有的酚、醇类亲水性物质会被初始DOC中的疏水性物质置换出来;(3)土壤DOC的截留能力与粘粒、游离氧化铁含量呈极显著正相关,而与土壤有机碳和砂粒含量呈极显著负相关,其中土壤有机碳的含量是影响米槠天然林不同土层DOC截留量的关键因素。 Abstract:Dissolved organic carbon (DOC) is a mixture of organic compounds with varying molecular sizes and weights. In forest ecosystems, litterfall is a major aboveground resource of DOC, which supplies soils with carbon as a crucial component of terrestrial biogeochemical cycles. During the migration of litterfall-derived DOC from topsoils to subsoils, soils might retain, transform, or release DOC, depending on the chemical nature of DOC and its interactions with soil surfaces. These physicochemical processes contribute considerably to soil organic carbon (SOC) accumulation. It is generally accepted that soil properties have a great influence on the interaction between soil surface and DOC, with Fe/Al oxides constraining DOC losses and high SOC content being usually negatively correlated to DOC sorption. However, an inconsistency still remains regarding the extent to which soils properties impact DOC movement. In some cases topsoils rich in SOC might demonstrate higher DOC retention capacity. Although subsoils with abundant Fe/Al oxides are considered to have a stronger DOC retention capacity, relatively lower SOC content is often found in subsoils, and direct evidence for their higher carbon sequestration potential is rare. One reason for this maybe the amount of DOC from aboveground litterfall, which is not sufficient and little DOC can reach subsoils. Another reason might be that highly sorptive DOC is preferentially absorbed by topsoils, and DOC that reaches subsoils has a weak affinity for soil surfaces. Supplying individual soil horizons with a common DOC solution is thus a good way to differentiate their carbon sequestration capacities. Natural Castanopsis carlesii forests are dominant evergreen broad-leaf forests in mid-subtropical China, and interaction between litterfall derived DOC and red soil (Ferralic Cambisols, World Reference Base) is now recognized as one of the most important mechanisms of C sequestration in this region. To solve inconsistencies about factors controlling DOC translocation in soils and to provide direct information to differentiate carbon sequestration potential between soil horizons, a 200-year-old natural Castanopsis carlesii forest without human interference was selected for undecomposed litter collection and soil sampling at the depth of 0-10 cm, 10-20 cm, 20-40 cm, 40-60 cm, 60-80 cm, 80-100 cm from each of the three profiles in the site. After extracting DOC from the collected litter with ultrapure water, we supplied individual soil cores with the common DOC in the laboratory. We not only analyzed the influences of soil properties on DOC interception, but also studied the changes in structural composition of DOC before and after leaching. The results showed that: (1) DOC interception in subsoils was greater than that in topsoils. Hydrophilic and hydrophobic DOC competed for binding sites on soil surfaces, and aromatic compounds and macromolecular substances of hydrophobic components were preferentially adsorbed by soils; (2) infrared spectrum suggested that hydrophobic materials such as aromatic substances and ethers were much more ready to be adsorbed than alkane materials, while indigenous hydrophilic substances such as phenols, alcohols could be displaced by hydrophobic components of DOC; (3) there was significant positive correlation between DOC interception and the content of clay and free iron oxide and significant negative correlation between DOC interception and the content of sand and soil organic carbon. Soil organic carbon content was the key factor affecting DOC interception in different soil horizons in natural Castanopsis carlesii forest. 参考文献 相似文献 引证文献

Dynamics of soil dissolved organic carbon pools reveal both hydrophobic and hydrophilic compounds sustain microbial respiration

The quality of dissolved organic carbon (DOC) released from soil organic amendments may influence soil microbial activity and the quality of the soil's DOC pools. Measurements of total DOC are often considered in relation to microbial activity levels but here we propose that quantification of DOC fractions is a more informative alternative. In a laboratory incubation, soil received DOC that was extracted from three organic matter sources: fresh compost, mature compost, and a mixture of the two. Soil microbial respiration (CO2 emission), and concentrations of hydrophobic (humic acids (HA), fulvic acids (FA) and neutrals (HoN)) and hydrophilic (Hi) DOC fractions were measured throughout the 35 d incubation. The A254 specific UV absorption of total and HA DOC were measured at the start and end of the incubation as an indicator of aromaticity. Microbial respiration rates were highest in soils amended with fresh compost DOC, which had a higher proportion of Hi compounds. Concentration of Hi was significantly and positively correlated with soil respiration, explaining 24% more variation than total DOC. Humic acid concentrations significantly decreased over 35 d, including a 33% reduction in HA from an unamended control soil. Compost treated soils' HA pools increased in aromaticity, suggesting preferential mineralization of the least aromatic HA molecules. A decrease in SUVA254 values in other HA pools may be the result of HA degradation in the absence of low-aromatic HA. Our observation of depletion of hydrophobic compounds from the HA fraction provides evidence that humic substances can be a relatively reactive pool, which can provide, together with hydrophilic compounds, a readily available C source to the microbial community.

Experimental investigation and modeling of dissolved organic carbon removal by coagulation from seawater

Coagulation removes colloidal matters and dissolved organic carbon (DOC) which can cause irreversible membrane fouling. However, how DOC is removed by coagulant is not well-known. Jar test was used to study the removal of hydrophobic and hydrophilic DOC fractions at various doses (0.5–8.0mg-Fe+3L−1) of ferric chloride (FeCl3) and pH (5.0–9.0). Natural organic matter (NOM) in seawater and treated seawater were fractionated by liquid chromatography-organic carbon detector (LC-OCD). Compared to surface water, the removal of DOC in seawater by coagulation was remarkably different. Majority of DOC could be easily removed with very low coagulant dose (<5.0mg-Fe+3L−1) and the removal efficiency did not vary with pH, but the DOC composition in treated water had significantly changed. Hydrophobic fraction (HB) was better removed at high pH while hydrophilic fraction (HF) was better removed at low pH. A modified model of Kastl et al. (2004) which assumed that the removal occurred by adsorption of un-dissociated compounds onto ferric hydroxide was formulated and successfully validated against the jar test data.

Carbon isotopic characterisation of dissolved organic matter during water treatment

Water treatment is a series of physio-chemical processes to aid organic matter (OM) removal, which helps to minimise the formation of potentially carcinogenic disinfection by-products and microbial regrowth. Changes in OM character through the treatment processes can provide insight into the treatment efficiency, but radiogenic isotopic characterisation techniques have yet to be applied. Here, we show for the first time that analysis of 13C and 14C of dissolved organic carbon (DOC) effectively characterises dissolved OM through a water treatment works. At the sites investigated: post-clarification, DOC becomes isotopically lighter, due to an increased proportion of relatively hydrophilic DOC. Filtration adds ‘old’ 14C-DOC from abrasion of the filter media, whilst the use of activated carbon adds ‘young’ 14C-DOC, most likely from the presence of biofilms. Overall, carbon isotopes provide clear evidence for the first time that new sources of organic carbon are added within the treatment processes, and that treated water is isotopically lighter and typically younger in 14C-DOC age than untreated water. We anticipate our findings will precipitate real-time monitoring of treatment performance using stable carbon isotopes, with associated improvements in energy and carbon footprint (e.g. isotopic analysis used as triggers for filter washing and activated carbon regeneration) and public health benefits resulting from improved carbon removal.

Removal of bisphenol A and 17α-ethinyl estradiol from landfill leachate using single-walled carbon nanotubes

In this study, the adsorption of bisphenol A (BPA) and 17α-ethinyl estradiol (EE2) from landfill leachate onto single-walled carbon nanotubes (SWCNTs) was investigated. Different leachate solutions were prepared by altering the pH, ionic strength, and dissolved organic carbon (DOC) in the solutions to mimic the varying water conditions that occur in leachate during the various stages of waste decomposition. The youngest and oldest leachate solutions contained varying DOC and background chemistry and were represented by leachate Type A (pH = 5.0; DOC = 2500 mg/L; conductivity = 12,500 μS/cm; [Ca 2+] = 1200 mg/L; [Mg 2+] = 470 mg/L) and Type E (pH = 7.5; DOC = 250 mg/L; conductivity = 3250 μS/cm; [Ca 2+] = 60 mg/L; [Mg 2+] = 180 mg/L). These solutions were subsequently combined in different ratios to produce intermediate solutions, labeled B–D, to replicate time-dependent changes in leachate composition. Overall, a larger fraction of EE2 was removed as compared to BPA, consistent with its higher log K OW value. The total removal of BPA and EE2 decreased in older leachate solutions, with the adsorptive capacity of SWCNTs decreasing in the order of leachate Type A > Type B > Type C > Type D > Type E. An increase in the pH from 3.5 to 11 decreased the adsorption of BPA by 22% in young leachate and by 10% in old leachate. The changes in pH did not affect the adsorption of EE2 in the young leachate, but did reduce adsorption by 32% in the old leachate. Adjusting the ionic strength using Na + did not significantly impact adsorption, while increasing the concentration of Ca 2+ resulted in a 12% increase in the adsorption of BPA and a 19% increase in the adsorption of EE2. DOC was revealed to be the most influential parameter in this study. In the presence of hydrophilic DOC, represented by glucose in this study, adsorption of the endocrine disrupting compounds (EDCs) onto the SWCNTs was not affected. In the absence of SWCNTs, hydrophobic DOC (i.e., humic acid) adsorbed 15–20% of BPA and EE2. However, when the humic acid and SWCNTs were both present, the overall adsorptive capacity of the SWCNTs was reduced. Hydrophobic (π-π electron donor-acceptor) interactions between the EDCs and the constituents in the leachate, as well as interactions between the SWCNTs and the EDCs, are proposed as potential adsorption mechanisms for BPA and EE2 onto SWCNTs.

Dissolved Organic Carbon in Alaskan Boreal Forest: Sources, Chemical Characteristics, and Biodegradability

The fate of terrestrially-derived dissolved organic carbon (DOC) is important to carbon (C) cycling in both terrestrial and aquatic environments, and recent evidence suggests that climate warming is influencing DOC dynamics in northern ecosystems. To understand what determines the fate of terrestrial DOC, it is essential to quantify the chemical nature and potential biodegradability of this DOC. We examined DOC chemical characteristics and biodegradability collected from soil pore waters and dominant vegetation species in four boreal black spruce forest sites in Alaska spanning a range of hydrologic regimes and permafrost extents (Well Drained, Moderately Well Drained, Poorly Drained, and Thermokarst Wetlands). DOC chemistry was characterized using fractionation, UV–Vis absorbance, and fluorescence measurements. Potential biodegradability was assessed by incubating the samples and measuring CO2 production over 1 month. Soil pore water DOC from all sites was dominated by hydrophobic acids and was highly aromatic, whereas the chemical composition of vegetation leachate DOC varied significantly with species. There was no seasonal variability in soil pore water DOC chemical characteristics or biodegradability; however, DOC collected from the Poorly Drained site was significantly less biodegradable than DOC from the other three sites (6% loss vs. 13–15% loss). The biodegradability of vegetation-derived DOC ranged from 10 to 90% loss, and was strongly correlated with hydrophilic DOC content. Vegetation such as Sphagnum moss and feathermosses yielded DOC that was quickly metabolized and respired. In contrast, the DOC leached from vegetation such as black spruce was moderately recalcitrant. Changes in DOC chemical characteristics that occurred during microbial metabolism of DOC were quantified using fractionation and fluorescence. The chemical characteristics and biodegradability of DOC in soil pore waters were most similar to the moderately recalcitrant vegetation leachates, and to the microbially altered DOC from all vegetation leachates.

Sorption of Trace Metals by Standard and Micro Suction Cups in the Absence and Presence of Dissolved Organic Carbon

Both the bioavailability of a trace metal (TM) in a soil and the risk of leaching to the ground water are linked to the metals concentration in the soil solution. Sampling soil solution by tension lysimetry with suction cups is a simple and established technique that is increasingly used for monitoring dissolved TM in soils. Of major concern, however, is the sorption of TM by the walls of the samplers. Metal sorption by different materials used in suction cups can vary widely, depending also on the chemistry of the soil solution. We compared the sorption of Cu, Zn, Cd, and Pb by different standard-size and micro suction cups in the laboratory at two pH values (4.5 and 7.5 or 8.0) in absence and presence of dissolved organic carbon (DOC). In addition, we investigated the sorption of DOC from different origins by the cup materials. At both pH values, the weakest sorption of all four TMs was exhibited by standard-size suction cups based on nylon membranes and by hollow fibers made from polyvinyl alcohol (PVA). At alkaline pH, borosilicate glass, ceramic materials, and polytetrafluorethylene (PTFE) mixed with silicate were characterized by generally strong sorption of all investigated TMs. In addition, Cu and Pb were strongly sorbed at low pH by PTFE-silicate and a ceramic material used for the construction of standard-size suction cups. On the other hand, sorption of Cu, Zn, and Cd by ceramic capillaries produced from pure aluminum oxide was negligible at low pH. Micro suction cups made of an unknown polymerous tube sorbed Cu strongly, but were well suited to monitor Zn, Cd, and Pb at low pH, and, in the presence of DOC, also at high pH. Major cations (Na+, Mg2+, K+, Ca2+) and anions (Cl-, NO3-, SO4(2-)) were not or very weakly sorbed by all cup materials, except for Mg2+, K+, and Ca2+ by borosilicate glass at pH 7.5. Trace metal sorption by suction cups was generally greatly reduced in the presence of DOC, especially at alkaline pH. The sorption of DOC itself depended on its source. Dissolved organic carbon from leaf litter extracts with a probably large hydrophobic fraction was sorbed more strongly than mainly hydrophilic DOC from a mineral soil solution.

Differences in the chemical composition of dissolved organic matter from waste material of different sources

The chemical composition of waste-material-derived dissolved organic matter (DOM) was characterized by chemolytic analyses and 1H, 13C and 31P nuclear magnetic resonance (NMR) spectroscopy. Dissolved organic matter was extracted by water from an aerobic fermented urban waste compost, a sewage sludge and a pig slurry and then fractionated using the XAD-8 method. The amount of water-extractable dissolved organic carbon (DOC) ranged from 3% in the sewage sludge to 22% in the pig slurry. Dissolved organic matter isolated from pig slurry was equally distributed between hydrophilic and hydrophobic DOC, whereas in the sewage-sludge-derived material the hydrophobic fraction was predominant. Dissolved organic C from the urban waste compost was mainly within the hydrophilic fraction. Wet-chemical analysis and 1H- and 13C-NMR spectra showed that both DOM fractions from the urban waste compost were low in neutral, acidic and amino sugars as well as in lignin-derived compounds. In turn, the materials were rich in low-molecular-weight aliphatic compounds. The chemical structure of both fractions is probably the result of the intensive transformation of urban waste compost during its fermentation. The hydrophilic fractions of DOM from sewage sludge and pig slurry contained considerable amounts of carbohydrates but were also rich in low-molecular-weight aliphatics. The respective hydrophobic fractions had the largest contents of CuO-extractable phenols which may in part derive from sources other than lignin. By contrast with the other materials, the hydrophobic fraction from the pig slurry seemed to contain polymeric rather than low-molecular-weight material. The 31P-NMR spectrum of the hydrophilic DOM fraction from urban waste compost did not show signals of inorganic or organic P compounds while the spectrum of the hydrophobic fraction revealed traces of monoester P, diester P, and orthophosphate. 31P-NMR spectroscopy suggested that both the hydrophobic and hydrophilic fractions from pig slurry did not contain organic P. The hydrophilic DOM fraction from sewage sludge contained orthophosphate, organic monoester P and a little pyrophosphate. The hydrophobic fraction contained mainly organic diester P and smaller amounts of teichoic acids and organic monoester P. Considering that water-soluble fractions of urban waste compost contained no easily plant-available P and a low content of labile organics, we conclude that this material contains less labile nutrients and is more refractory than the soluble constituents of pig slurry and sewage sludge.

Chemical Characterization of Dissolved Organic Matter in Hiroshima Bay, Japan

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 (0·014mgl−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.

Transformation of Dissolved Organic Matter During Ozonation: Effects on Trihalomethane Formation Potential

Transformation of dissolved organic matter (DOM) during ozonation results in a higher reduction in trihalomethane formation potential (THMFP) relative to dissolved organic carbon (DOC). This study was conducted to determine the effect of DOM transformation after ozonation on THM formation and to elucidate the difference in THMFP and DOC removal. Changes in DOC, THMFP, reactivities of the hydrophilic and hydrophobic DOC, and phenolic-OH were determined to explain the difference in THMFP and DOC removal after ozonation. Higher reduction in THMFP (24–46%) relative to DOC (10–16%) was obtained and was attributed to the following: transformation of DOM from a more reactive hydrophobic DOC (μg THM produced per mg organic carbon) to a less reactive hydrophilic DOC and to the decrease in the reactivities of both the hydrophobic and hydrophilic DOC after ozonation. The results also showed decrease in phenolic-OH indicating the oxidation of some reactive sites like resorcinol or meta-dihydroxy benzene ring structures, which are prone to chlorine substitution, consequently decreasing the reactivity of the organic carbon to form THM. These changes in DOM led to a significant decrease in THMFP with no remarkable removal in DOC.

Dissolved Organic Matter (DOM) in Acid Forest Soils at Gådsjön (Sweden): Natural Variabilities and Effects of Increased Input of Nitrogen and of Reversal of Acidification

Effects of (1) the addition of 35 kg N ha-1yr-1(as NH4NO3) and (2) interception of throughfall and litterfall by means of a roof on concentrations, chemical characteristics and dynamics of dissolved organic matter (DOM) in acid forest soils (podzols) were studied at Gardsjon, Sweden. A non-manipulated catchment served as a reference. After 4 yr of treatment no significant effects of either manipulation were found on concentrations and characteristics of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). The variability of these parameters within catchments appeared to be of the same order of magnitude as the variability between catchments. At all sites, DON contributed more than 70% of the total dissolved nitrogen. In general, the proportion of hydrophilic DOC increased with depth. In contrast, to other studies the C/N ratio of DOM at Gardsjon did not show a clear pattern with depth. Other studies in SE U.S.A. have suggested that relatively low C/N ratios at depth are due to increased contribution of hydrophilic neutrals to DOC. However, this fraction appears to be small in temperate and boreal spruce forest soils, including Gardsjon.

RATES OF DISSOLVED ORGANIC MATTER RELEASE AND SORPTION IN FOREST SOILS

Rapid percolation enhances dissolved organic matter (DOM) transport in soils. One reason for this is nonequilibrium conditions, which make the time-dependence of the sorption/desorption an important parameter. We investigated the time-dependent DOM release and sorption of four soils (one topsoil, three subsoils) with different properties (organic carbon (OC): 2-56 g kg -1 ; dithionite-citrate-bicarbonate-extractable Fe: 2.4-21.9 g kg -1 ; clay: 30-450 g kg -1 ) in batch experiments during a 24-h period. Release of dissolved organic carbon (DOC) when a DOC-free solution was added occurred mainly within the first 15 min and then decreased drastically. After 2 to 4 h, the release almost stopped, but steady-state conditions were not reached within the experimental period. DOM fractionation with XAD-8 adsorber resin showed that the major portion of the released DOC exhibited hydrophilic properties. At an addition of 14 mmol DOC kg -1 , the topsoil still released DOC. One subsoil, which was rich in Al and Fe oxides and low in OC, sorbed both hydrophilic and hydrophobic DOC strongly, with a preference for the hydrophobic fraction. The other two subsoil horizons showed a sorption of hydrophobic DOC that was accompanied by a steadily increasing release of hydrophilic DOC. This indicates competition between the two DOC fractions, with hydrophobic DOC having the stronger affinity to sorbent and displacing soil-bound hydrophilic substances. The reactions approached steady-state conditions after 2 to 4 h. The time-dependency of the release and sorption can be described adequately by the Elovich equation and the fractional-power model. In a few cases, the DOC release from soil was represented better by the parabolic-diffusion equation. The slope of the Elovich equation, which may be considered the apparent rate constant, was higher for the hydrophilic than for the hydrophobic DOC fraction. It is related to the ratio between OC and Al and Fe oxide content.

Fractionation of dissolved organic matter affected by polyvalent metal cations

The purpose of the study was to evaluate the influence of polyvalent cations known to form complexes with natural organic substances on the operational fractionation of dissolved organic matter (DOM) using XAD-8 adsorber resin. Dissolved organic matter solutions from a forest floor were treated with increasing concentrations of polyvalent metal cations (Ca 2+, Al 3+, Fe 3+) at different pH levels. Then the concentrations of total dissolved organic carbon (DOC) and the distribution between hydrophilic and hydrophobic DOC were determined. The concentrations of total DOC decreased slightly when the C/metal ratio was less than 10, especially for Al and Fe. Hydrophilic DOC increased and hydrophobic DOC decreased with increasing concentrations of metal cations. Effects increased in the order Ca<Al<Fe and were more pronounced at low DOC concentrations and high pH values. The reason for the reduction of the DOC concentrations seemed to be the formation of insoluble metal–DOM complexes, while soluble metal–DOM complexes may induce an alteration of the distribution between hydrophilic and hydrophobic DOC. Thus, the polyvalent cations and their concentration need to be considered when DOM fraction distributions, determined with XAD-8 resin, of different waters are compared, especially at low DOC contents and high pH.

Soil Dissolved Organic Matter Sorption as Influenced by Organic and Sesquioxide Coatings and Sorbed Sulfate

AbstractThe sorption of dissolved organic carbon (DOC) and its fractions as influenced by organic C (OC), sesquioxides [amorphous Al(OH)3, ferrihydrite, goethite], and extractable SO2−4 was investigated by modifying the properties of the Bs horizon of an Entic Haplorthod. Coating the Bs material with OC extracted from the Oa horizon of a mor forest floor layer decreased the sorption of total DOC. The effects on the sorption of the hydrophobic DOC fraction were little, whereas the sorption of the hydrophilic fraction was strongly reduced. At the highest OC coating levels, a net release of hydrophilic DOC occurred, indicating a displacement of indigenous hydrophilic substances from the soil by the sorbing hydrophobic dissolved organic matter (DOM). Coating of the soil material with sesquioxides clearly increased the sorption of DOC and its fractions. The strongest effects occurred when amorphous Al(OH)3 was added, followed by ferrihydrite and goethite. Increased contents of extractable SO2−4 did not affect the sorption of DOC on soil material. With increasing addition of DOC, however, the concentrations of SO2−4 in the equilibrium solution increased. Adsorbing DOM seems to displace SO2−4 bound to soil materials. Thus, DOM shows a higher affinity to sorb on soil material than SO2−4.

Sorption of DOM and DOM fractions to forest soils

The sorption of total, hydrophilic, and hydrophobic dissolved organic matter (DOM) on 125 forest soil samples was studied in batch experiments. The soil samples represented the main soil orders of temperate climatic zones: Entisols, Inceptisols, Alfisols, Mollisols, and Spodosols. In general, sorption was adequately described by the linear initial mass isotherm. At zero addition of DOM, the release of dissolved organic carbon (DOC) into solutions depended on the soil organic C (OC) content. The DOC released was comprised primarily of hydrophilic substances (61–100%). High contents of OC reduced DOC sorption, notably that of hydrophilic DOC. In soils free of carbonates, sorption was related to oxalate-extractable aluminum (Al o) and dithionite-extractable iron (Fe d); however, in carbonatec soils DOC retention was correlated with Fe d only. Consequently, soils with high OC content and/or low contents of extractable Al and Fe showed low DOC retention (e.g. E horizons), whereas subsoil horizons had high DOC sorption capacities. The majority of the soils preferentially sorbed hydrophobic DOC. This was caused by the higher affinity of hydrophobic DOC to oxide/hydroxide soil components. There was also a strong competition effect between hydrophilic and hydrophobic DOC, especially in soils with a limited number of binding sites. sorption of hydrophobic DOC in some soils was even accompanied by the displacement of indigenous hydrophilic substances. In carbonate-free soils, multiple regression analysis including Al o, Fe d, and OC explained 75 and 77% of the variance of the partition coefficient ( m) of the initial mass isotherm for the sorption of total and hydrophobic DOC, respectively. Due to the competitive effect of hydrophobic DOC on hydrophilic DOC retention, the relation was weaker for the hydrophilic fraction. In the carbonate-containing soils, multiple regression analysis including Fe d and OC explained 67, 58, and 59% of the variance of m for total, hydrophilic, and hydrophobic DOC, respectively.