Spectroscopic and Thermal Investigation Of Hydrophobic and Hydrophilic Fractions Of Dissolved Organic Matter

Hydrophobic (HO) and hydrophilic (HI) fractions of dissolved organic matter (DOM) isolated from several substrates including a source separated urban waste compost, a mechanically separated urban waste compost, an anaerobically digested municipal sewage sludge, a composted sewage sludge and a cow slurry were characterised by Fourier transform infrared spectroscopy (FT-IR), monodimensional fluorescence spectroscopy in the emission, excitation and synchronous scan modes, tridimensional excitation emission matrix (EEM) fluorescence spectroscopy, ¹H nuclear magnetic resonance (¹H-NMR) spectroscopy, and differential scanning calorimetry (DSC). The FT-IR spectra indicated that the HI fractions were rich in both aromatic and aliphatic structures, whereas the HO fractions were rich in carboxylic groups and polysaccharides. The synchronous scan spectra of HO fractions showed the main peak at a wavelength much longer than that of the HI fractions, which indicated a greater molecular complexity of the HO fractions with respect to HI fractions. The ¹H-NMR data indicated a great percentage of aliphatic structures in all samples, whereas the HO samples were also characterised by the presence of aromatic structures. The DSC curves confirmed the more distinct aromatic nature of HO fractions, as compared to the corresponding HI fractions.     

Composting Posidonia oceanica and Sewage Sludge: Chemical and Spectroscopic Investigation

ABSTRACT

In this article composting of 40% Posidonia oceanica, 20% ligno-cellulosic residues, and 40% sewage sludge was monitored by retrieving samples every 2 weeks from the composting pile and by characterizing them both by chemical and spectroscopic analysis in Fourier transform infrared spectroscopy and fluorescence spectroscopy in the emission mode and as EEM spectra. Chemical data indicated the occurrence of extended mineralization and stabilization during the process. The decreasing trend of E₄/E₆ ratios suggested a progressive humification of the substrate. Ratios of peaks of aliphatics to aromatics as a function of composting time showed a decreasing trend due to consumption of aliphatic structures and increase of aromatics during the process. The trend of fluorescence intensity observed on emission spectra showed an increase up until 6 weeks and then a decrease until the end of the process, as a consequence of the decomposition process, which broke down organic macromolecules contained in the fresh substrate followed by the humification process. EEM spectra of all samples produced a peak D in the range 345–355_ex/437–446_em. Samples retrieved at the beginning of the process showed, in addition, a peak B at 280_ex/344_em whose disappearance during the process was consistent with bio-degradation of organic matter. Samples retrieved at the beginning and after 2, 4, 6, 8, 10, and 12 weeks exhibited also a peak C at 255_ex/440_em whose fluorescence intensity trend suggested a progressive humification of the substrates.     

Application of fluorescence spectroscopy in the evaluation of light-induced oxidation in cheese

Light-induced oxidation of semihard cheese has been evaluated by fluorescence spectroscopy. The cheese was packaged in two packaging materials and exposed to different storage conditions, which included light/dark storage, oxygen availability, and storage time (0, 4, 7, 14, 21, 42, 70, or 84 days). Fluorescence excitation-emission matrices (EEM) were analyzed by PARAFAC, which gave an estimation of the pure excitation and emission spectra of the fluorophores and the concentrations of these. This analysis showed the presence of components such as tryptophan, tyrosine, vitamin A, fluorescent oxidation products, and riboflavin. Effects of packaging material, light or dark storage, and storage time were seen. However, there was no effect of the oxygen availability on the fluorescence measurements. The score values obtained by the PARAFAC models and chemical and physical measurements were analyzed together by principal component analysis (PCA). The loadings showed a separation of the variables into three groups; the first group was related to oxidation, the second group was related to the degradation of both riboflavin and vitamin A, and the third group was linked to the protein structure.     

Assessment of maturity degree of composts from domestic solid wastes by fluorescence and Fourier transform infrared spectroscopies.

Methods of assessment of compost maturity are needed so the application of composted materials to lands will provide optimal benefits. The aim of the present paper is to assess the maturity reached by composts from domestic solid wastes (DSW) prepared under periodic and permanent aeration systems and sampled at different composting time, by means of excitation-emission matrix (EEM) fluorescence spectroscopy and Fourier transform infrared spectroscopy (FT-IR). EEM spectra indicated the presence of two different fluorophores centered, respectively, at Ex/Em wavelength pairs of 330/425 and 280/330 nm. The fluorescence intensities of these peaks were also analyzed, showing trends related to the maturity of composts. The "contour density" of EEM maps appeared to be strongly reduced with composting days. After 30 and 45 days of composting, FT-IR spectra exhibited a decrease of intensity of peaks assigned to polysaccharides and in the aliphatic region. EEM and FT-IR techniques seem to produce spectra that correlate with the degree of maturity of the compost. Further refinement of these techniques should provide a relatively rapid method of assessing the suitability of the compost to land application.     

Spectroscopic and thermal investigations on compost improved by iron salt addition

A quality compost obtained from sewage sludge (one part in weight) and yard trimmings and sawdust (two parts) has been investigated as a potential carrier of iron to plants. At the end of the thermophilic phase, the composting materials were added with crystalline FeSO4.7H2O (97%). Chemical properties, respiratory indices, and seed germination tests proved the compost to be suitable as an iron carrier in agriculture. Fourier transform infrared spectroscopy (FT-IR) and fluorescence spectroscopy provided evidence of the effective linking of the iron ion to the organic molecule functional groups, thus preventing the loss of iron ion by leaching and precipitation phenomena and allowing the metal ion to be available to plants as both mineral and organic species. The thermogram obtained on compost without iron was similar to that previously obtained for composted materials of different origins, whereas samples with added iron ion exhibited in addition an exotherm in the medium-temperature region. FT-IR spectra carried out on samples heated at different temperatures indicated a loss of iron ion linked to carboxyl groups.     

Optical characteristic of humic acids from lake sediments by excitation-emission matrix fluorescence with PARAFAC model

Journal of Soils and Sediments - The study aimed to find out whether fluorescence parameters of humic acids (HA), obtained from excitation-emission matrix (EEM) fluorescence spectra, could be used...     

Fluorescence of raw cane sugars evaluated by chemometrics

In a fluorescence study of raw cane sugar samples, two-way and three-way chemometric methods have been used to extract information about the individual fluorophores in the sugar from fluorescence excitation-emission landscapes. A sample set of 47 raw sugar samples representing a varied selection was analyzed, and three individual fluorophores with (275, 350) nm, (340, 420) nm, and (390, 460) nm as their approximate excitation and emission maxima were found. The spectral profiles of the fluorophores were estimated with the three-way decomposition model PARAFAC. Two-way principal component analysis (PCA) of unfolded fluorescence landscapes confirmed the PARAFAC results and showed patterns of samples related to time of storage. Partial least squares (PLS) calibration models of color at 420 nm had a high model error due to the very high color range of the raw sugars, but variable selection performed on the fluorescence data revealed that all three fluorophores were correlated to color. The (275, 350) nm fluorophore is considered as a color precursor to the color developed on storage and the (340, 420) nm and (390, 460) nm fluorophores show colorant polymer characteristics.     

水稻土中水溶性有机碳对铁还原过程的贡献

【目的】 淹水稻田中Fe (Ⅲ) 还原过程与有机质的厌氧分解和氮、磷、硫等营养元素的有效性密切相关。通过探讨水溶性有机碳 (DOC) 对Fe (Ⅲ) 还原过程的贡献,以期为深入理解淹水稻田中铁循环耦联的碳、氮、磷、硫循环提供理论基础。 【方法】 采集我国不同植稻区的20个典型水稻土,通过有机碳分析仪及三维荧光光谱扫描比较分析不同水稻土DOC的含量及荧光特性;并模拟稻田淹水过程对水稻土进行厌氧淹水培养,采用微生物生长模型对不同水稻土厌氧培养过程中Fe (Ⅲ) 还原特征进行表征;依据相关分析和冗余分析,明确水稻土DOC与Fe (Ⅲ) 还原过程的关系。 【结果】 不同水稻土DOC含量为0.250～1.082 g/kg,仅占土壤有机碳的2.06%～6.86%。三维荧光光谱扫描鉴定得到不同水稻土DOC中4个共有的类腐殖酸荧光组分,其中陆源的UVC类腐殖酸和UVC+UVA类腐殖酸组分在不同水稻土中具有较高荧光强度,分别为0.799～4.570和0.830～5.273。水源的可见光区类腐殖酸和UVA腐殖酸的含量相对较低。各类腐殖酸来源以外源输入为主,内源输入为辅。不同水稻土铁还原潜势a、最大Fe (Ⅲ) 还原速率 (V_max) 及达到最大Fe (Ⅲ) 还原速率对应的时间 (T_Vmax) 间均差异显著,淹水5 d时水稻土中易被还原的非晶态氧化铁已基本被还原。DOC的腐殖化系数与Fe (Ⅲ) 还原特征参数存在显著相关性。其中以陆源的大分子量UVC类腐殖酸对a和V_max的贡献最高,陆源的UVC+UVA类腐殖酸和水源的UVA腐殖酸与a和V_max的相关关系也达到显著或极显著水平,而DOC含量的贡献最小。 【结论】 水稻土DOC的腐殖化程度及其中陆源腐殖酸类组分的荧光强度与Fe (Ⅲ) 还原潜势和Fe (Ⅲ) 还原反应速率呈正相关。水稻土DOC除了作为Fe (Ⅲ) 还原过程的电子供体外,其还以电子穿梭体的形式在Fe (Ⅲ) 还原过程中起重要作用。      

Front-face fluorescence spectroscopy as a rapid and nondestructive tool for differentiating various cereal products: a preliminary investigation

The potential of intrinsic fluorescence spectroscopy was investigated for differentiating between processed grains (flours, pasta, and semolinas) of different wheat cereal products. A total of 59 samples (e.g., 20 complete Kamut, semicomplete Kamut, and soft wheat flours, 28 pasta, and 11 semolinas manufactured from complete Kamut, semicomplete Kamut, and hard wheat flours) were analyzed by front-face fluorescence spectroscopy. Tryptophan fluorescence spectra were scanned between 305 and 400 nm on samples following excitation at 290 nm. The principal component analysis (PCA) performed on flour spectra clearly differentiated complete Kamut and semicomplete Kamut samples from those produced from complete and semicomplete soft wheat flours. The PCA performed on pasta spectra discriminated samples manufactured from complete Kamut and complete hard wheat flours from those made with semicomplete Kamut and semicomplete hard wheat flours. The best discrimination was obtained from tryptophan spectra recorded on semolinas since the four groups were well discriminated. Correct classification amounting to 61.9% was obtained for pasta spectra. A better classification was obtained for flour and semolina spectra since correct classification amounted to 86.7% and 87.9%, respectively. Front-face fluorescence spectroscopy has the potential to be a rapid, low-cost, and efficient method for the authentication of cereal products.     

Evaluation of organic matter stabilization in sewage sludge

Abstract

The ratio between non‐humified and humified fractions in pyrophosphate extracts is shown to vary during maturation of sewage sludge. The ratio is higher than 1 in the raw materials but lowers at 1 or less than 1 with the aging of sludge and is assumed to reflect quantitatively the degree of stabilization of organic matter in the sludge. Analytical isoelectrofocusing (IEF) experiments showed that humified fractions in raw sludge focalize only in the pH gradient regions lower than 5.0, whilst in older sludge samples a progressive strengthening of bands occurs in the region between pH 6.5 and 5.0, approaching at least partially IEF patterns of soil organic matter. IEF patterns are suggested to reflect the stabilization of organic matter in sewage sludge from a qualitative point of view.     

A Review of the Different Methods Applied in Environmental Geochemistry For Single and Sequential Extraction of Trace Elements in Soils and Related Materials

A comprehensive review of the single and sequential extraction schemes for metal fractionation in environmental samples such as soil and industrially contaminated soils, sewage sludge and sludge amended soils, road dust and run off, waste and miscellaneous materials along with other approaches of sequential extraction methods are being presented. A discussion on the application of chemometric methods in sequential extraction analysis is also being given. The study of single and sequential extraction methods for various reference materials are also being looked into. The review covers several aspects of the single and sequential extraction methodologies. The use of each reagents involved in these schemes are also discussed briefly. Finally the present upto date information by different workers in various fields of environmental geochemistry along with the possible future developments are also being outlined.     

Effects of sewage sludge stabilization on organic‐N mineralization in two soils

Sewage sludge is a valuable source of organic matter, N, P and certain micronutrients that have beneficial effects on plant growth and biomass production. However, sanitary regulations often require the stabilization of sewage materials prior to applying them to soils as biosolids. Environmental regulations also demand appropriate management of biosolid‐N to avoid groundwater contamination. Because stabilization processes usually make sewage sludge less putrescible, we hypothesized that the mineralization rates of organic‐N from stabilized biosolids would be affected. Therefore, this study aimed to evaluate the mineralization of five biosolids in two soils – a sandy Spodosol and a clayey Oxisol. Digested sludge, composted sludge, limed sludge, heat‐dried sludge and solar‐irradiated sludge were mixed with soil samples at a concentration of 32.6 mg N/kg soil (1.0 dry t/ha of digested sludge) and incubated at 25 °C in a humidity chamber for 23 weeks. Results showed that the stabilization processes generally slowed the release of mineral‐N in soils relative to the digested sludge from which the biosolids originated. However, increments in the levels of mineral‐N were more influenced by soil type than by the type of stabilization process applied to the sewage sludge. Mineralization rates were up to 5‐fold higher in the Oxisol than in the Spodosol soil, and as a result, organic‐N in biosolids mineralized 10–24% in Spodosol and 23–52% in Oxisol. Any appropriate plan for the management of biosolid‐N for plant use should consider the interaction between soil type and biosolid type.     

基于前表面荧光光谱鉴别新鲜与冻融大黄鱼

为研究反复冻融对水产品品质的影响,通过理化方法检测了不同冻融次数处理对大黄鱼解冻损失、pH 值、色泽、硫代巴比妥酸值、羰基含量等指标的影响,并采用前表面荧光光谱结合主成分分析（principal component analysis,PCA）和 Fisher 线性判别分析法（Fisher linear discriminant analysis,FLDA）对不同冻融次数的大黄鱼进行区分。结果显示随着冻融次数增加,大黄鱼的解冻损失显著增加（P<0.05）;pH 值呈先上升后下降的趋势;L*（亮度）值、b*（黄度）值均有不同程度的增加（P<0.05）,a*（红度）值下降（P<0.05）;羰基含量和硫代巴比妥酸反应物值（thiobarbituric acid reactive substances,TBARS）增加（P<0.05）,反复冻融导致大黄鱼的品质下降。色氨酸和烟酰胺腺嘌呤二核苷酸磷酸（nicotinamide adenine dinucleotide,NADH）的荧光光谱分别结合 PCA 和 FLDA 对不同冻融处理组进行分析,结果表明 FLDA 识别效果优于 PCA。通过 FLDA 建立了新鲜大黄鱼与冻融大黄鱼荧光光谱判别模型,发现色氨酸原始判别的准确率和交叉验证的准确率分别为68.3%和66.7%,NADH 原始判别的准确率和交叉验证的准确率均达到100%。由此可见,利用 NADH荧光光谱结合化学计量分析可以鉴别不同冻融处理的大黄鱼。研究结果为水产品新鲜度的快速评价提供参考。     

Discrimination between Shiraz wines from different Australian regions: the role of spectroscopy and chemometrics

This study reports the use of UV-visible (UV-vis), near-infrared (NIR), and midinfrared (MIR) spectroscopy combined with chemometrics to discriminate among Shiraz wines produced in five Australian regions. In total, 98 commercial Shiraz samples (vintage 2006) were analyzed using UV-vis, NIR, and MIR wavelength regions. Spectral data were interpreted using principal component analysis (PCA), linear discriminant analysis (LDA), and soft independent model of class analogy (SIMCA) to classify the wine samples according to region. The results indicated that wine samples from Western Australia and Coonawarra can be separated from the other wines based on their MIR spectra. Classification results based on MIR spectra also indicated that LDA achieved 73% overall correct classification, while SIMCA 95.3%. This study demonstrated that IR spectroscopy combined with chemometric methods can be a useful tool for wine region discrimination.     

Authentication of the botanical origin of honey by front-face fluorescence spectroscopy. A preliminary study

The potential of front-face fluorescence spectroscopy for the authentication of unifloral and polyfloral honey types (n = 57 samples) previously classified using traditional methods such as chemical, pollen, and sensory analysis was evaluated. Emission spectra were recorded between 280 and 480 nm (excit: 250 nm), 305 and 500 nm (excit: 290 nm), and 380 and 600 nm (excit: 373 nm) directly on honey samples. In addition, excitation spectra (290-440 nm) were recorded with the emission measured at 450 nm. A total of four different spectral data sets were considered for data analysis. After normalization of the spectra, chemometric evaluation of the spectral data was carried out using principal component analysis (PCA) and linear discriminant analysis (LDA). The rate of correct classification ranged from 36% to 100% by using single spectral data sets (250, 290, 373, 450 nm) and from 73% to 100% by combining these four data sets. For alpine polyfloral honey and the unifloral varieties investigated (acacia, alpine rose, honeydew, chestnut, and rape), correct classification ranged from 96% to 100%. This preliminary study indicates that front-face fluorescence spectroscopy is a promising technique for the authentication of the botanical origin of honey. It is nondestructive, rapid, easy to use, and inexpensive. The use of additional excitation wavelengths between 320 and 440 nm could increase the correct classification of the less characteristic fluorescent varieties.     

Effects of sewage sludge stabilization on fertilizer value and greenhouse gas emissions after soil application

Application of sewage sludge on agricultural land becomes more and more common in many parts of the world in order to recycle the nutrients from the sludge. A range of sewage sludge stabilization techniques are available to make the sludge more stable prior to storage, transportation, and application. These stabilization techniques include dewatering, drying, anaerobic digestion, composting, and reed bed sludge treatment. However, very few studies have investigated the effect of these techniques after the sludge has been applied to agricultural land. The objective of the current study was therefore to investigate the effect of sewage sludge stabilization techniques on the C and N mineralization and gaseous emissions from soil. A soil incubation was conducted to determine the rate of C and N mineralization and N₂O and CH₄ emissions of sewage sludge stabilized using different techniques. Unstabilized sludge released up to 90% of their C content as CO₂, part of which could be caused by release of CO₂ from carbonates. Compared with this, sludge stabilization including anaerobic digestion and drying resulted in a reduction of the C mineralization rate of about 40%. Liming reduced C mineralization with around 29%, while treatment in a reed bed system reduced it by 74%. The current study thus clearly demonstrated that stabilization techniques resulted in sludge that was more stable once they were applied to agricultural land. Stabilization also reduced the N immobilization phase, potentially improving the value of the sludge as a fertilizer. Emissions of CH₄ were also reduced through sludge stabilization and mainly occurred after application of easily degradable sludge types, which is likely to have enhanced the creation of anaerobic microsites. The stabilization processes also decreased emissions of N₂O. The results for both CH₄ and N₂O indicate that the stabilization tends to reduce the chance of developing conditions where these gases could be produced.     

横跨中国崇明岛河岸湿地缓冲区土壤中溶解性有机碳的空间分布及其荧光特征

The migration of soil dissolved organic carbon(DOC) from terrestrial to aquatic environments has important impacts on the adjacent water quality and the transport of organic and inorganic contaminants.However,few studies have investigated the sources and properties of DOC in riparian zones.A total of 34 soil samples were collected across four riparian buffer zones(Zones A-D) on Chongming Island,China.The vertical distributions of soil organic carbon(SOC) and DOC,fluorescence excitation-emission matrix(EEM) spectra of DOC and the optical indices,including fluorescence index(FI),index of recent autochthonous contribution(BIX),and humification index(HIX),were measured across the riparian environment to investigate the sources and fluorescence properties of DOC.The results showed that SOC stored in the surface soil(0-30 cm) accounted for 40%of the total soil profile SOC.The DOC accumulated in Zones A-C,which accounted for 5%of the SOC.The fluorescence EEM spectra of DOC showed that DOC contained humic-like and protein-like substances,which were mainly derived from recent plant debris by microbes.A large amount of humic-like substances were sorbed to minerals in the surface soil(0-30 cm).In addition,the riparian topography and soil physico-chemical properties(pH,EC and moisture) dictated the transformation and transport of DOC.The results suggested that EEMs could reveal the source of DOC in riparian soil systems,and that optical indices were complementary tools that revealed the characteristics of soil DOC and provided supplemental evidence about DOC sources.     

Occurrence of Polycyclic Musks in Sewage Sludge and their Behaviour in Soils and Plants. Part 1: Behaviour of Polycyclic Musks in Sewage Sludge of Different Treatment Plants in Summer and Winter (5 pp)

Background, Aim and Scope   Part 1: Behaviour of Polycyclic Musks in Sewage Sludge of Different Treatment Plants in Summer and Winter Part 2: Investigation of Polycyclic Musks in Soils and Plants -  Preamble. In Part 1 of the study, screening tests were performed to investigate the occurrence of PCMs in sewage sludges. For a preliminary risk assessment, further information is needed about their behaviour in the terrestrial environment. Hence, Part 2 examined the adsorption of PCMs to soil, their dissipation and leaching in soil and their uptake by plants. Background, Aim and Scope   Polycyclic Musks (PCMs) enter the environment via the waste water system. Because of their persistence, they can accumulate in different matrices like sewage sludge or biota. By the use of sewage sludge as a fertilizer, PCMs are transferred to agricultural soils. Therefore, in Part 1 of the study, screening tests were performed to investigate the occurrence of PCMs in sewage sludge. For a preliminary risk assessment, further information is needed about their behaviour in the terrestrial environment. Hence, Part 2 of the study examined the adsorption of PCMs to soil, their dissipation and leaching in soil, and their uptake by plants. Materials and Methods: In the screening study, samples of activated sewage sludge were taken both in summer and in winter at 21 treatment plants. In order to get an overview of the contamination situation, sampling covered different types of treatment plants (in rural, urban, industrial areas). Analytical methods for the determination of HHCB, AHTN, ADBI, ATTN, AHDI and ATII in the sludge samples were developed and applied. Results: The analytical screening of PCMs showed their presence in activated and dried sewage sludge samples. HHCB and AHTN represented about 95% of the PCMs investigated. Their concentrations in the activated sludge samples varied between 2.9 and 10.4 mg/kg dry mass (dm) and 1.1 to 4.2 mg/kg dm, respectively. Although different types of sewage treatment plants were investigated, similar PCM levels were found, showing the widespread input of these compounds into domestic waste water. Discussion: PCM concentrations in activated sludge varied widely. The variation drops substantially when concentrations are related to the varying dry mass. In dehydrated sludge, PCM concentrations were up to 24 mg/kg dm for HHCB and up to 6.9 mg/kg dm for AHTN. These high values are comparable to those obtained in other investigations analysing PCMs. If the degradation of organic mass during anaerobic decomposition is included in the evaluation, the figures obtained are comparable to those for activated sludge. Elimination in sewage sludge was higher in summer than in winter. Therefore, the contamination of the sludges in winter reached higher levels compared to the summer. Conclusions: The results show that PCMs are widespread contaminants in sewage sludge. Recommendations and Perspectives: PCM should be considered in a risk assessment as potential contaminants of sewage sludge destined for agricultural use. Due to the high PCM levels in sewage sludge, further investigations into the degradation and elimination behaviour in sewage sludge have to be carried out, including that involving PCM metabolites such as lactone derivatives.     

Effect of cultivated plants on physico‐chemical characteristics of humic substances of soils amended by sewage sludge

Abstract

Humic substances were extracted from raw sewage sludge samples as well as an alluvial slightly alkaline soil [Typic Xerofluvent (So)], a clay loam soil [Calcixerollic Xerochrept (M)] and the corresponding field plots amended with different rates of sewage sludge and cultivated with corn and cotton respectively, in a two‐year field experiment. These substances have been characterized by chemical and spectroscopic methods. The chemical analyses showed that humic acids (HAs) and fulvic acids (FAs), were effected by the cultivated plant. Humic substances extracted from field plots with cotton showed higher carbon, but less nitrogen (N), total acidity and carboxylic groups content, as compared with those under corn. Generally HAs and FAs extracted from the fields plots amended with sewage sludge had higher N content, lower values of total acidity, carboxylic groups and carbon contents than those from the unamended soils. The FT‐IR spectra of humic (HAs) and fulvic (FAs) acids extracted from sewage sludge indicated the presence of high percentage of aliphatic carbon, polysaccharides and proteinaceous materials. The spectra of the humic matter in the field plots showed less aliphatic but increased amide stretch in comparison with the sludge. The absorption due to C=O in carboxylic groups of the FAs was not pronounced, though the presence of polysaccharides and protein decomposition products was clearly indicated.     

Processes controlling the production of aromatic water-soluble organic matter during litter decomposition

Dissolved organic matter (DOM) plays a fundamental role for many soil processes. For instance, production, transport, and retention of DOM control properties and long-term storage of organic matter in mineral soils. Production of water-soluble compounds during the decomposition of plant litter is a major process providing DOM in soils. Herein, we examine processes causing the commonly observed increase in contribution of aromatic compounds to WSOM during litter decomposition, and unravel the relationship between lignin degradation and the production of aromatic WSOM. We analysed amounts and composition of water-soluble organic matter (WSOM) produced during 27 months of decomposition of leaves and needles (ash, beech, maple, spruce, pine). The contribution of aromatic compounds to WSOM, as indicated by the specific UV absorbance of WSOM, remained constant or increased during decomposition. However, the contribution of lignin-derived compounds to the total phenolic products of ¹³C-labelled tetramethylammonium hydroxide (¹³C-TMAH) thermochemolysis increased strongly (by >114%) within 27 months of decomposition. Simultaneous changes in contents of lignin phenols in solid litter residues (cupric oxide method as well as ¹³C-TMAH thermochemolysis) were comparably small (−39% to +21% within 27 months). This suggests that the increasing contribution of lignin-derived compounds to WSOM during decomposition does not reflect compositional changes of solid litter residues, but rather the course of decomposition processes. In the light of recently published findings, these processes include: (i) progressive oxidative alteration of lignin that results in increasing solubility of lignin, (ii) preferential degradation of soluble, non-lignin compounds that limits their contribution to WSOM during later phases of decomposition.