Fluorescence spectroscopic characterization of dissolved organic matter fractions in soils in soil aquifer treatment

This work investigated the effect of soil aquifer treatment (SAT) operation on the fluorescence characteristics of dissolved organic matter (DOM) fractions in soils through laboratory-scale soil columns with a 2-year operation. The resin adsorption technique (with XAD-8 and XAD-4 resins) was employed to characterize the dissolved organic matter in soils into five fractions, i.e., hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N), and hydrophilic fraction (HPI). The synchronous fluorescence spectra revealed the presence of soluble microbial byproduct- and humic acid-like components and polycyclic aromatic compounds in DOM in soils, and SAT operation resulted in the enrichment of these fluorescent materials in all DOM fractions in the surface soil (0–12.5 cm). More importantly, the quantitative method of fluorescence regional integration was used in the analysis of excitation–emission matrix (EEM) spectra of DOM fractions in soils. The cumulative EEM volume (Φ _{T, n} ) results showed that SAT operation led to the enrichment of more fluorescent components in HPO-A and TPI-A, as well as the dominance of less fluorescent components in HPO-N, TPI-N, and HPI in the bottom soil (75–150 cm). Total Φ _{T, n} values, which were calculated as $ {\Phi_{{T,n}}} \times {\mathrm{DOC}} $ , suggested an accumulation of fluorescent organic matter in the upper 75 cm of soil as a consequence of SAT operation. The distribution of volumetric fluorescence among five regions (i.e., P _{i, n} ) results revealed that SAT caused the increased content of humic-like fluorophores as well as the decreased content of protein-like fluorophores in both HPO-A and TPI-A in soils.     

Characterization of soil organic matter content of two sample size populations along a climatic transect

Soil organic matter (SOM) content was determined in two populations of soil samples that were taken from 0–2 soil depth. One population represented soil samples that were takenfrom a square of 25 cm² in size (small-S population) and the other population represented soil samples that were taken from a square of 2500 cm² in size (large-L population). Thesamples were collected on hillslopes in different climatic regions: Mediterranean (GIV), semi-arid (MAL), mildly-arid (MIS) and arid (KAL). The results of both S and L populationsshowed decreasing SOM mean and variance from the Mediterranean site to the arid site. Statistical and spatial characteristics of each population were compared between the climatic regions. In addition, comparison between the two populations was made foreach site. The difference in sample size did not significantly affect the mean values of SOM of the two populations in sitesGIV, MAL and KAL, but did affect the mean at site MIS. At all study sites, except for site MAL, the variance increased with decreasing sample size. At sites GIV and KAL the coefficient ofvariation of S population was higher (more than 1.5 times) thanthat of L population, whereas at sites MAL and MIS, the differences were negligible. The relationships between the valuesof S and L samples at the individual sampling points defined thebackground of the study sites, which reflects the effect of vegetation (type), grazing, biological crust and soil properties.It was found that at the extreme sites GIV and KAL the backgroundwas characterized by relatively low SOM content with small areas of high organic matter content. At site MIS the background wascharacterized by relatively high SOM with small areas of low organic matter content. At site MAL the background was not dominated by high values of SOM nor by low ones. The spatial pattern of L population became more simple with increasing aridity. At the relatively wet sites the spatial pattern did notdepend on the sample size while in the more arid sites it was sample size dependent. It was indicated that the spatial structure of SOM at the semi-arid and mildly arid sites is anisotropic whereas at the Mediterranean and arid sites it is isotropic.     

14C and delta13C characteristics of organic matter and carbonate in saltmarsh sediments from south west Scotland

The distribution of contaminant radionuclides from the Sellafield nuclear fuel reprocessing plant was used to establish chronologies for three saltmarsh sediment cores from south west Scotland. delta(13)C and (14)C analyses indicated that the cores provided a useful archive record of variations in input of organic matter and carbonate. The results imply that prior to major releases of contaminant (14)C from Sellafield, the (14)C specific activity of organic matter in Irish Sea offshore sediments was about 24 Bq kg(-1) C, while that of the carbonate component was below the limit of detection. These results provide baseline data for modelling the uptake of contaminant (14)C by the Irish Sea sediment system. The study confirmed that small(13)C analyses provide a sensitive means of apportioning the origin of saltmarsh organic matter between C(3) terrigenous plants, C(4) terrigenous plants and suspended particulate marine organic matter. For the <2 mm fraction of sediment, a clear pattern of decreasing marine organic input was observed in response to increasing elevation of the marsh surface as a result of sediment accumulation. Bulk sediment, including detrital vegetation, had a dominant input from terrigenous plants. The combined use of delta(13)C and (14)C data revealed that organic matter in the marine organic component of the <2 mm fraction of contemporary surface sediments of the saltmarshes is dominated by recycled old organic material.     

Comparison of dissolved organic matter fractions in a secondary effluent and a natural water

This research compared the structural and chemical characteristics among dissolved organic matter (DOM) fractions within the same source and among different origins. Samples taken from the Taiping Wastewater Treatment Plant (TWTP) (Harbin, China) and from the Songhuajing River (SR), Heilongjiang Province, China were chosen to represent waters containing DOM of wastewater origin and of natural-water origin, respectively. DOM was fractionated using XAD resins into five fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). The SR fractions were more UV-sensitive and more reactive with chlorine in formation of trihalomethanes (THMs) than the TWTP secondary effluent (TSE) fractions. The aromatic character peaks in the Fourier-transform infrared (FT-IR) spectra of SR fractions were clearer than those of TSE fractions. On the other hand, the peaks of carbohydrates in TSE fractions were more prominent in comparison with SR fractions. In addition, the amide-2 peak was present in the spectra of all the five TSE fractions but not visible in the spectra of SR fractions. The fluorescence results showed that SR DOM fractions contained more fulvic acid-like fluorescent compounds while TSE DOM fractions had higher amounts of protein-like fluorescent components.     

Changes in labile soil organic matter fractions following land use change from monocropping to poplar-based agroforestry systems in a semiarid region of Northeast China

Labile fractions of soil organic matter (SOM) respond rapidly to land management practices and can be used as a sensitive indicator of changes in SOM. However, there is little information about the effect of agroforestry practices on labile SOM fractions in semiarid regions of China. In order to test the effects of land use change from monocropping to agroforestry systems on labile SOM fractions, we investigated soil microbial biomass C (MBC) and N, particulate organic matter C (POMC) and N (POMN), as well as total organic C (TOC) and total N (TN) in the 0- to 15-cm and the 15- to 30-cm layers in 4-year-old poplar-based agroforestry systems and adjoining monocropping systems with two different soil textures (sandy loam and sandy clay loam) in a semiarid region of Northeast China. Our results showed that poplar-based agroforestry practices affected soil MBC, POMC, and POMN, albeit there was no significant difference in TOC and TN. Agroforestry practices increased MBC, POMC, and POMN in sandy clay loam soils. However, in sandy loam soils, agroforestry practices only increased MBC and even decreased POMC and POMN at the 0- to 15-cm layer. Our results suggest that labile SOM fractions respond sensitively to poplar-based agroforestry practices and can provide early information about the changes in SOM in semiarid regions of Northeast China and highlight that the effects of agroforestry practices on labile SOM fractions vary with soil texture.     

Mobilization and plant accumulation of prometryne in soil by two different sources of organic matter

Prometryne is a selective herbicide of the s-triazine chemical family. Due to its weak absorption onto soil, it readily leaches down through the soil and contaminates underground water. Application of organic manure to soil has become a widespread practice as a disposal strategy to improve soil properties. In this study, we demonstrated the effect of pig manure compost (PMC) and lake-bed sludge (SL) on the sorption/desorption, mobility and bioavailability of prometryne in soil using comprehensive analysis approaches. Downward movement of prometryne was monitored in the packed soil column. Addition of PMC or SL decreased considerably the mobility and total concentration of prometryne in the soil leachate. Bioavailability analyses with wheat plants revealed that addition of the organic matter reduced accumulation of prometryne in tissues and increased plant elongation and biomass. These results indicate that the organic amendments are effective in modifying adsorption and mobility of the pesticide in soil.     

Heavy metal concentrations in particle size fractions from street dust of Murcia (Spain) as the basis for risk assessment

Street dust has been sampled from six different types of land use of the city of Murcia (Spain). The samples were fractionated into eleven particle size fractions (<2, 2-10, 10-20, 20-50, 50-75, 75-106, 106-150, 150-180, 180-425, 425-850 μm and 850-2000 μm) and analyzed for Pb, Cu, Zn and Cd. The concentrations of these four potentially toxic metals were assessed, as well as the effect of particle size on their distribution. A severe enrichment of all metals was observed for all land-uses (industrial, suburban, urban and highways), with the concentration of all metals affected by the type of land-use. Coarse and fine particles in all cases showed concentrations of metals higher than those found in undisturbed areas. However, the results indicated a preferential partitioning of metals in fine particle size fractions in all cases, following a logarithmic distribution. The accumulation in the fine fractions was higher when the metals had an anthropogenic origin. The strong overrepresentation of metals in particles <10 μm indicates that if the finest fractions are removed by a vacuum-assisted dry sweeper or a regenerative-air sweeper the risk of metal dispersion and its consequent risk for humans will be highly reduced. Therefore, we recommend that risk assessment programs include monitoring of metal concentrations in dust where each land-use is separately evaluated. The finest particle fractions should be examined explicitly in order to apply the most efficient measures for reducing the risk of inhalation and ingestion of dust for humans and risk for the environment.     

An evaluation of grid size uncertainty in empirical soil loss modeling with digital elevation models

This paper presents a study on the effect of topographic variability on grid-based empirical estimation of soil erosion and sediment transport with raster geographic information systems (GIS). An original digital elevation model (DEM) of 10 m resolution for a case watershed is resampled to six realizations of greater grid sizes for a comparative examination. The Universal Soil Loss Equation (USLE) and a distance-based sediment delivery equation are applied to the watershed to calculate soil loss from each cell and total sediment transport to streams, respectively. The results suggest that the selection of the DEM gird size has considerable influence on the soil loss estimation with the empirical models. The estimate of total soil loss from the watershed decreases significantly with the increasing DEM cell size as the spatial variability is reduced by the cell aggregation. The empirical modeling approach is a useful tool for qualitative assessment of soil erosion, provided that spatial variability can be adequately represented by applied DEMs. However, discretion is suggested for its applications to quantitative estimation of soil loss concerning the sensitivity to the grid size selection.     

Structural characterisation of macromolecular organic material in air particulate matter using Py-GC-MS and solid state 13C-NMR

Organic air particulate matter was analysed by applying the techniques of Py-GC-MS (pyrolysis-gas chromatography-mass spectrometry) and solid state 13C-NMR (nuclear magnetic resonance). Particles dislodged from air particulate filters and humic acid extracted from these filters were studied for structural components. The structural components of the air particles and extracted humic acid consisted of compounds originating from biomacromolecules, namely, lignin, carbohydrates, protein and lipids. The main components identified for each class included: (1) methoxyphenols originating from lignin; (2) furans, aldehydes and ketones from carbohydrates; (3) pyrrole, indoles from protein; and (4) many hydrocarbons from lipid structures. Single ion monitoring (SIM) and tetramethyl ammonium hydroxide (TMAH) methylation were utilised for detection of aliphatic hydrocarbons and acidic components, respectively. Hydrocarbons ranging from C9 to C28 were detected by SIM analysis, while aliphatic acids ranged from C9 to C18. The majority of components analysed directly in the air particles were similar to those from the humic acid extracts. Many of the structural components of air particles were typical of humic substances of soil and aqueous systems and these were attributed to both biogenic and anthropogenic sources.     

Variations in some environmental characteristics including C and N stable isotopic composition of suspended organic matter in the Mandovi estuary

Chemical and isotopic (??¹³C and ??¹⁵N) investigation of the Mandovi estuary along the Indian west coast affected strongly by the seasonal monsoon cycle was carried out. The Mandovi estuary is a major waterway for Goa and extensively used for transportation of iron and manganese ore. In addition, with large population centers as well as agricultural fields located on its shores, the estuary is assumed to have been influenced by human activities. Measurements of chemical and isotopic parameters made in the lower part of the estuary during the southwest (SW) monsoon and post-monsoon seasons reveal distinct changes, and it is observed that despite considerable enrichment of macronutrients during the SW monsoon, productivity of the estuary (phytoplankton biomass), as inferred from the chlorophyll-a content, is not as high as expected. This is due to occurrences of high turbidity and cloud cover that limits photosynthetic productivity. The isotopic characterization (C and N isotopes) of suspended organic matter produced/transported during the monsoon and post-monsoon seasons of year 2007 provides a baseline dataset for future isotopic studies in such type of tropical estuaries.     

Assessment of relative accuracy in the determination of organic matter concentrations in aquatic systems

Accurate determinations of total (TOC), dissolved (DOC) and particulate (POC) organic carbon concentrations are critical for understanding the geochemical, environmental, and ecological roles of aquatic organic matter. Of particular significance for the drinking water industry, TOC measurements are the basis for compliance with US EPA regulations. The results of an interlaboratory comparison designed to identify problems associated with the determination of organic matter concentrations in drinking water supplies are presented. The study involved 31 laboratories and a variety of commercially available analytical instruments. All participating laboratories performed well on samples of potassium hydrogen phthalate (KHP), a compound commonly used as a standard in carbon analysis. However, problems associated with the oxidation of difficult to oxidize compounds, such as dodecylbenzene sulfonic acid and caffeine, were noted. Humic substances posed fewer problems for analysts. Particulate organic matter (POM) in the form of polystyrene beads, freeze-dried bacteria and pulverized leaf material were the most difficult for all analysts, with a wide range of performances reported. The POM results indicate that the methods surveyed in this study are inappropriate for the accurate determination of POC and TOC concentration. Finally, several analysts had difficulty in efficiently separating inorganic carbon from KHP solutions, thereby biasing DOC results.     

Sources and the distribution of heavy metals in the particle size of soil polluted by gold mining upstream of Miyun Reservoir,Beijing: implications for assessing the potential risks

Mining has been carried out upstream of Miyun Reservoir, Beijing, for several decades, and has caused metal emissions to the environment, threatening human health. We conducted a soil survey to assess metal contamination in this area and to determine distribution of heavy metals in the particle size. We attempted to determine the possible sources of the metals and the significance of metals in the fine particle fractions to soil risk assessments. Thirty-four soil samples were collected, and eight samples were partitioned into seven size fractions. Most of the metal concentrations in the soils were higher than the background levels in Beijing, and the metal concentrations and total organic matter (TOC) contents generally increased as the particle size decreased. Each metal except Hg significantly positively correlated with the TOC. The metals in the coarse-grained soils were mainly derived from parent materials, but the metals in the fine fractions were mostly anthropogenic. Statistical analyses showed that there were three metal sources: Cd, Cu, Hg, Pb, and Zn had anthropogenic sources; Co, Cr, Ni, and V had mixed anthropogenic and natural sources; and As and Be had natural sources. The trace metals were primarily in the clay and fine silt fractions, and they might pose health risks through the inhalation of resuspended soil particles (PM10 and PM2.5). The elevated accumulation factors, enrichment factors, and ecological risk indices for the metals in the fine fractions suggest that risk assessments should be based on the fine particle size.     

Spatial and temporal variation of soil organic carbon in the North China Plain

The organic carbon, permeability test, grain size, chemical composition, and mineral composition were analyzed for 147 samples collected from the Luan River catchment, Hebei province, China, to quantitatively characterize the effects of land use, climate change, sedimentary environment, mineral composition, and chemical composition on the spatial and temporal variation of soil organic carbon (SOC). The results indicate that there was higher SOC content and stronger variation in the south plain than in the northern low mountain. The effects of land use, climate change, and sedimentary environment on SOC distribution were greater than the effects of mineral composition and chemical composition. The cropping systems in the Luan River catchment resulted in significant difference in SOC concentration between the south plain and north mountain. The precipitation mainly transmitted its effects through the sedimentary environment to SOC, which caused the stronger temporal variation in SOC from June to October in the south plain. The north mountain did not have significant temporal variation because of the lower hydraulic conductivity of the sedimentary sequence. The spatial variation of SOC was correlated with land use, and their temporal variation was attributed to climate change and sedimentary environment. Apart from land use, the decision maker can also affect the organic carbon mineral and sequence through the sedimentary environment.     

A field study of the influence of land management and soil properties on runoff and soil loss in central Spain

Since the 1950s afforestation of degraded land has been the principal means of combatting erosion in a seasonally arid area of central Spain. In the 1970s tree planting of steep hillsides and gully sides was preceded by bench terracing. Experimental sites have been established to monitor runoff and soil losses under mature Pinus forest, 12-year-old Pinus forest, and Cistus matorral. The experiment is being conducted at three scales: large gully or small watershed (c. 3.5 ha), runoff erosion plot (10–21.5 m²), and rainfall simulation plot (1 m²). Monitoring began in October 1992. Discharge was recorded continuously, while sediment loss and soil moisture content were measured on a storm basis. The paper presents summary data on runoff and soil erosion for the three scales and comments on relationships between land management, site characteristics, and these losses. We stress the crucial role of vegetation and its interrelationship with soil properties such as structure and aggregate stability. Matorral was effective in combatting water and soil loss, but we question the practice of afforesting seasonally arid, steeply sided areas that have highly erodible soils.     

Evaluation of the diffusion size classifier (meDiSC) for the real-time measurement of particle size and number concentration of nanoaerosols in the range 20-700 nm

In the frame of assessing exposure to nanostructured particles, the aim of this work is to study the performance of a new device devoted to the real-time measurement of nanostructured aerosol: the meDiSC (Diffusion Size Classifier, Matter Engineering, Switzerland). This instrument is based on unipolar diffusion charging of particles which are then collected successively in diffusion and filtration stages. From currents measured in these stages, the instrument is capable of determining aerosol mean size and number concentration. These data were compared to reference measurements regarding monodisperse aerosols in a range from 20 to 700 nm; the relative biases were found unsatisfying. This led us to investigate the principle of the instrument. Consequently, the charging law of the diffusion charger was experimentally established, as well as the calibration curve allowing the determination of the mean size of the particles. The latter analysis was completed by a model based on diffusion theory. Our results indicate the possibility to improve the range of size measurement up to 350 nm. Measured particle size and number concentration were also used to calculate geometric surface-area concentration; the experimental data were compared to a reference calculated surface-area concentration. The results demonstrate the possibility to evaluate this parameter within acceptable uncertainty. In a second step, the meDiSC was challenged with polydisperse aerosols. It was observed that meDiSC overestimates particle size by a factor 1.7, while particle number concentrations are found within ±40% of the reference. The model applied to polydisperse aerosols indicates that polydispersity little influences particle size up to 300 nm while geometric standard deviation remains below 1.7.     

Study of phytopigments in river bed sediments: effects of the organic matter, nutrients and metal composition

Phytopigment estimation has a considerable interest in the evaluation of freshwater bodies' quality, because it takes into account the synergistic effect of nutrients like phosphorus or nitrogen on algal growth producing eutrophication. Furthermore, their increasing concentration constitutes the first step in the formation of biofilms on the surface sediments, adding a new and very important element to the dynamic nature of the surface sediments. In this study the distribution of phytoplankton--in terms of chlorophyll-a, chlorophyll-b, phaeophytin-a, phaeophytin-b, total carotenoids, total chlorophyll, and total phaeophytin--was evaluated in river bed sediments. Samples collected at sites with low levels of nutrients (P,N) and metal concentrations showed lower phytopigment concentrations than those collected at the sampling sites affected by sources of pollution. Phytoplankton concentrations were directly and highly related to the organic matter concentrations--in particular to the humic fraction--as well as to the total nitrogen (N), total phosphorus (P(T)) and available phosphorus (P(A)) concentrations in sediments. In addition, phytoplankton also correlates positively with Cu, Zn, Fe and Al extracted in oxalate, being Cu the variable that most influences the phytopigment growth. These are essential metals for the metabolism of the phytoplankton, so therefore the increase in metal concentrations can increase algal growth, unless they reach toxic levels.     

Visualising the equilibrium distribution and mobility of organic contaminants in soil using the chemical partitioning space

Assessing the behaviour of organic chemicals in soil is a complex task as it is governed by the physical chemical properties of the chemicals, the characteristics of the soil as well as the ambient conditions of the environment. The chemical partitioning space, defined by the air-water partition coefficient (K(AW)) and the soil organic carbon-water partition coefficient (K(OC)), was employed to visualize the equilibrium distribution of organic contaminants between the air-filled pores, the pore water and the solid phases of the bulk soil and the relative importance of the three transport processes removing contaminants from soil (evaporation, leaching and particle erosion). The partitioning properties of twenty neutral organic chemicals (i.e. herbicides, pharmaceuticals, polychlorinated biphenyls and volatile chemicals) were estimated using poly-parameter linear free energy relationships and superimposed onto these maps. This allows instantaneous estimation of the equilibrium phase distribution and mobility of neutral organic chemicals in soil. Although there is a link between the major phase and the dominant transport process, such that chemicals found in air-filled pore space are subject to evaporation, those in water-filled pore space undergo leaching and those in the sorbed phase are associated with particle erosion, the partitioning coefficient thresholds for distribution and mobility can often deviate by many orders of magnitude. In particular, even a small fraction of chemical in pore water or pore air allows for evaporation and leaching to dominate over solid phase transport. Multiple maps that represent soils that differ in the amount and type of soil organic matter, water saturation, temperature, depth of surface soil horizon, and mineral matters were evaluated.     

Effects of composition of labile organic matter on biogenic production of methane in the coastal sediments of the Arabian Sea

Coastal regions are potential zones for production of methane which could be governed by ecological/environmental differences or even sediment properties of a niche. In order to test the hypothesis that methanogenesis in most marine sediments could be driven more by proteins than by carbohydrates and lipid content of labile organic matter (LOM), incubation experiments were carried out with sediments from different environmental niches to measure methane production. The methane production rates were examined in relationship to the sediment biochemistry, i.e., carbohydrates, proteins, and lipids. The gas production measured by head space method ranged from 216 ng g(?-1) day(?-1) in the mangrove sediments to 3.1 μg g(?-1) day(?-1) in the shallow Arabian Sea. LOM ranged from 1.56 to 2.85 mg g(?-1) in the shallow Arabian Sea, from 3.35 to 5.43 mg g(?-1) in the mangrove estuary, and from 0.66 to 0.70 mg g(?-1) in the sandy sediments with proteins contributing maximum to the LOM pool. Proteins influenced methane production in the clayey sediments of shallow depths of the Arabian Sea (r = 0.933, p < 0.001) and mangrove estuary (r = 0.981, p < 0.001) but in the sandy beach sediments, carbohydrates (r = 0.924, p < 0.001) governed the net methane production. The gas production was more pronounced in shallow and surface sediments and it decreased with depth apparently governed by the decrease in lability index. Thus, the lability index and protein content are important factors that determine methane production rates in these coastal ecosystems.