Dissolved Organic Carbon Levels Research Articles

Photodegradation of dissolved organic matter in ice under solar irradiation.

The photodegradation behavior of dissolved organic matter (DOM) with different origins in ice under solar irradiation was investigated. Exposure to sunlight at 2.7 × 10(5) J m(-2) resulted in dissolved organic carbon (DOC) reductions of 22.1-36.5% in ice. The naturally occurring DOM had higher photodegradation potentials than the wastewater-derived DOM in ice. Ultraviolet (UV)-absorbing compounds in DOM, regardless of DOM origin, had much higher photodegradation potentials than gross DOC in ice. The susceptibility of UV-absorbing compounds with natural origin to sunlight exposure in ice was higher than those derived from wastewater. Trihalomethane (THM) precursors were more susceptible to photochemical reactions than gross DOC and haloacetic acid (HAA) precursors in ice. THM precursors in naturally occurring DOM were more photoreactive than those in wastewater-derived DOM in ice, while the photoreactivity of HAA precursors in ice was independent of DOM origin. In ice, the photoreactivity of humic-like fluorescent materials, regardless of DOM origin, was higher than that of gross DOC and protein-like fluorescent materials. DOC reductions caused by sunlight irradiation were found to be negatively correlated to DOC levels, and positively correlated to the aromaticity of DOM. The photodegradation of both wastewater-derived and naturally occurring DOM in ice was significantly facilitated at both acid and alkaline pH, as compared to neutral pH. The photodegradation of DOM in ice, regardless of the origin, was facilitated by nitrate ion [Formula: see text] , nitrite ion [Formula: see text] , ferric ion (Fe(3+)) and ferrous ion (Fe(2+)), and on the other hand, was inhibited by chloridion ion (Cl(-)) and copper ion (Cu(2+)).

Effects of nitrogen and dissolved organic carbon on microplankton abundances in four coastal South Carolina (USA) systems

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 76:1-14 (2015) - DOI: https://doi.org/10.3354/ame01764 Effects of nitrogen and dissolved organic carbon on microplankton abundances in four coastal South Carolina (USA) systems Michelle L. Reed1, Giacomo R. DiTullio1, Suzanne E. Kacenas2,5, Dianne I. Greenfield2,3,4,* 1Graduate Program in Marine Biology, College of Charleston, 205 Fort Johnson Road, Charleston, SC 29412, USA 2Belle W. Baruch Institute for Marine and Coastal Sciences, University of South Carolina, Hollings Marine Laboratory, 331 Fort Johnson Road, Charleston, SC 29412, USA 3Marine Resources Research Institute, South Carolina Department of Natural Resources, 217 Fort Johnson Road, Charleston, SC 29412, USA 4Marine Sciences Program, University of South Carolina, Columbia, SC 29208, USA 5Present address: Analytical Services, Service Delivery Division, Sydney Water, 51 Hermitage Road, West Ryde, NSW 2114, Australia *Corresponding author: dgreenfield@belle.baruch.sc.edu ABSTRACT: In blackwater systems of the southeastern US, dissolved organic carbon (DOC) contributes a major portion to the total dissolved organic matter pool. The primary DOC source is terrestrial vegetation, with phytoplankton contributing less. Thus, upland development may reduce terrestrial DOC inputs, thereby affecting bacterial abundances. Conversely, development and runoff may increase nitrogen (N) and phosphorus (P) inputs, fueling phytoplankton growth and algal-derived DOC. Yet, the variability of DOC, bacteria, and phytoplankton has not been fully assessed across diverse land uses. We investigated seasonal (July 2012 to May 2013) levels of DOC, bacteria, and phytoplankton biomass (chl a) in response to N and P additions at 4 coastal South Carolina sites: a forested/agricultural creek, an urbanized creek, a forested creek, and a detention pond. DOC concentrations were highest at the least developed site (forested creek), suggesting the influence of surrounding land. DOC was significantly and positively correlated with precipitation but negatively correlated with salinity, suggesting that rainfall affected DOC mobilization. Chl a was highest during summer and positively correlated with temperature, whereas bacterial abundances were generally negatively correlated with salinity. During experiments, chl a was often greater in addition treatments than controls, especially at the urbanized creek and detention pond. In certain N-amended treatments, particularly those containing urea, both DOC and chl a became elevated following incubation. These results indicate that urea stimulated phytoplankton biomass and possibly a greater contribution of phytoplankton-derived DOC to the total DOC pool. Our findings suggest that biogeochemical cycling of DOC may become altered in developing coastal regions. KEY WORDS: Dissolved organic carbon . Bacteria . Phytoplankton . Estuaries . South Carolina Full text in pdf format NextCite this article as: Reed ML, DiTullio GR, Kacenas SE, Greenfield DI (2015) Effects of nitrogen and dissolved organic carbon on microplankton abundances in four coastal South Carolina (USA) systems. Aquat Microb Ecol 76:1-14. https://doi.org/10.3354/ame01764 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 76, No. 1. Online publication date: August 10, 2015 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2015 Inter-Research.

Impact of heterotrophic bacterium Pseudomonas aureofaciens on the release of major and trace elements from podzol soil into aqueous solution

The release of major and trace elements (TEs) from mineral and organic-rich podzol soil horizons has been studied in batch reactors with live and dead soil heterotrophic Pseudomonas aureofaciens bacteria and in bacteria-free systems. Dissolved organic carbon (DOC) concentrations decreased and dissolved inorganic carbon concentrations increased over the course of experiments with live bacteria due to on-going DOC mineralization processes. Several families of major and trace elements could be distinguished, depending on their release patterns in bacteria-free systems and live bacteria-bearing systems. Live bacteria enhanced the release of Mg, Rb, Cd, Pb, Al, Fe and V from the mineral soil horizon and the release of Rb, Ni, Pb, As, Fe, V and La from the organic soil horizon relative to bacteria-free soil or dead bacteria experiments. Unexpectedly, K, Ca, Sr, Cu, Ti, Mn, Zn and As release from the mineral horizon and Mg, K, Ca, Sr, Ba, Cr, Ti, Mn and Zn release from the organic horizon decreased in the presence of live P. aureofaciens compared to bacteria-free and dead bacteria systems. Finally, live bacteria exhibited no effect on the release of Si, Al, Cu and Mo from the humic horizon and Ni, Mo, Cr, Ba, Si and La from the mineral horizon relative to the bacteria-free system. These results can be interpreted via a combination of several simultaneous processes, which occur in the soil–bacteria suspension and lead to changes in TE speciation and affinities to mineral surfaces and bacteria and include the following: 1) a slight decrease in the pH due to exometabolite production; 2) degradation of DOC and TE organic complexes by heterotrophic bacteria; 3) element adsorption at cell surfaces and biological uptake; and 4) element release from the soil mineral and organic particles.Compared to abiotic systems, the observed decreases in the concentrations of major elements and many heavy metals that leach from the soil in the presence of bacteria have important consequences regarding our understanding of the role of bacteria in element mobilizations from soil to rivers. It follows that chemical weathering in both organic and mineral horizons of podzol soil may not be strongly affected by heterotrophic bacterial activity; rather, the solution pH and DOC levels may control the intensity of element mobilization. The aqueous concentrations of many TEs (Fe, Al, La, Cr, Ni, Cd, Pb, Cu, and Rb) at the end of live-bacteria experiments were comparable with reported compositions of interstitial podzol soil solutions.

Predicting Metal Release from Peatlands in Sudbury, Ontario, in Response to Drought

Peatlands are often regarded as metal repositories, but under drought conditions may switch from sinks to sources of metals and contaminate downstream ecosystems. To evaluate whether the release of metals into soil solution in peatlands is predictable using simple, widely available soil parameters, six peatlands, with varying levels of metal contamination, including a previously limed peatland, were sampled around the Sudbury, Ontario, region, and were subjected to simulated drought. The simulated drought lowered soil water pH and dissolved organic carbon (DOC) concentrations, which is consistent with field observations. Metal partitioning (K d ) values for Co, Mn, Ni, and Zn, with just one exception at one peatland, could be significantly predicted by just the pH of the soil water, although the strength of the relationship varied considerably among sites. The metal speciation model WHAM VII predicted that the free metal ion concentration of all metals tested, including Cu and Al, increased significantly with decreasing pH. At the same time, DOC-bound metal concentrations were predicted to decrease as DOC levels were lower, which for metals with strong organic matter affinities (Cu and Al) offset the increase in free metal ion concentration in soil solution following summer drought. Climate change forecasts for more frequent and sustained droughts may promote metal release from peatlands and increased mobilization to surface waters, and importantly, for some metals, the potential toxicity of the metals released from peatlands may increase to a greater extent than expected from increases in total metal concentrations because of decreased DOC following drought.

Spatial controls on dissolved organic carbon in upland waters inferred from a simple statistical model

Dissolved organic carbon (DOC) concentrations in upland surface waters in many northern hemisphere industrialised regions are at their highest in living memory, provoking debate over their “naturalness”. Because of the implications for drinking water treatment and supply there is increasing interest in the potential for mitigation through local land management, and for forecasting the likely impact of environmental change. However, the dominant controls on DOC production remain unresolved, hindering the establishment of appropriate reference levels for specific locations. Here we demonstrate that spatial variation in long-term average DOC levels draining upland UK catchments is highly predictable using a simple multiple logistic regression model comprising variables representing wetland soil cover, rainfall, altitude, catchment sensitivity to acidification and current acid deposition. A negative relationship was observed between DOC concentration and altitude that, for catchments dominated by organo-mineral soils, is plausibly explained by the combined effects of changing net primary production and temperature-dependent decomposition. However, the magnitude of the altitude effect was considerably greater for catchments with a high proportion of wetland cover, suggesting that additional controls influence these sites such as impeded respiratory loss of carbon in wet soils and/or an increased susceptibility to water level drawdown at lower altitudes. The model suggests (1) that continuing reductions in sulphur deposition on acid sensitive organo-mineral soils, will drive further significant increases in DOC and, (2) given the differences in the magnitude of the observed altitude-DOC relationships, that DOC production from catchments with peat-dominated soils may be more sensitive to climate change than those dominated by mineral soils. However, given that mechanisms remain unclear, the latter warrants further investigation.

Effects of ozone as a stand-alone and coagulation-aid treatment on the reduction of trihalomethanes precursors from high DOC and hardness water

This study investigates the effect of ozone as a stand-alone and coagulation aid on the removal of dissolved organic carbon (DOC) from the water with a high level of DOC (13.8 mgL−1) and calcium hardness (270 mgL−1) CaCO3.Natural water collected from the Assiniboine River (Manitoba, Canada) was used in this study.Effectiveness of ozone treatment was evaluated by measurement of DOC, DOC fractions, UV254, and trihalomethane formation potential (THMFP). Additionally, zeta potential and dissolved calcium concentration were measured to discern the mechanism of ozone reactions.Results indicated that 0.8 mg O3/mg DOC ozone stand-alone can cause up to 86% UV254 reduction and up to 27% DOC reduction.DOC fractionation results showed that ozone can change the composition of DOC in the water samples, converting the hydrophobic fractions into hydrophilic ones and resulting in the reduction of THMFP. Also, ozone caused a decrease in particle stability and dissolved calcium concentration. These simultaneous ozonation effects caused improved water flocculation and enhanced removal of DOC. This resulted in reduction of the coagulant dosage when ozone doses higher than 0.2 mg O3/mg DOC were applied prior to coagulation with ferric sulfate. Also, pre-ozonation-coagulation process achieved preferential THMFP removal for all of the ozone doses tested (0–0.8 mg O3/mg DOC), leading to a lower specific THMFP in pre-ozonated-coagulated waters than in the corresponding ozonated waters.

Mixing behavior and bioavailability of dissolved organic matter in two contrasting subterranean estuaries as revealed by fluorescence spectroscopy and parallel factor analysis

Groundwater discharge represents a potentially important source of dissolved organic matter (DOM) for the coastal ocean, but the mixing behavior and bioavailability of DOM in subterranean estuaries are poorly known. This study examined the concentration, chemical composition and bioavailability of DOM in two subterranean estuaries of southwest Taiwan with contrasting pollution degrees, using dissolved organic carbon (DOC) and excitation emission matrix fluorescence spectroscopy-parallel factor analysis. The DOC and fluorescent components were non-conservative and very dynamic in both subterranean estuaries. In the less-polluted Longquanwan (LQW) subterranean estuary, the levels of DOC and fluorescence components were generally low, and the humic-like fluorescent components received significant additions during mixing between freshwater and seawater. In the highly-polluted Sizihwan (SZW) subterranean estuary, the DOC and fluorescence intensities were high in the freshwater end but were subject to active additions and removals during estuarine mixing. The humification index (HIX) and the autochthonous index (BIX) were 1.0–13.4 and 0.73–1.01 for all groundwater samples. The HIX were elevated in the low-to-mid salinity zone of the LQW subterranean estuary in March and increased with salinity in the SZW subterranean estuary. The BIX decreased with salinity in both subterranean estuaries. These results suggested that subterranean estuaries are important zones where both the level and the chemical composition of groundwater DOM change notably. In addition, the DOC, fluorescent intensities, HIX and BIX in groundwater showed limited changes in microbial incubation experiments (≤20%) in 28 days, which suggested low bioavailability of groundwater DOM.

Contrasting vulnerability of drained tropical and high‐latitude peatlands to fluvial loss of stored carbon

AbstractCarbon sequestration and storage in peatlands rely on consistently high water tables. Anthropogenic pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of peat‐forming vegetation and exposure of previously anaerobic peat to aerobic decomposition. This can shift peatlands from net CO2 sinks to large CO2 sources, releasing carbon held for millennia. Peatlands also export significant quantities of carbon via fluvial pathways, mainly as dissolved organic carbon (DOC). We analyzed radiocarbon (14C) levels of DOC in drainage water from multiple peatlands in Europe and Southeast Asia, to infer differences in the age of carbon lost from intact and drained systems. In most cases, drainage led to increased release of older carbon from the peat profile but with marked differences related to peat type. Very low DOC‐14C levels in runoff from drained tropical peatlands indicate loss of very old (centuries to millennia) stored peat carbon. High‐latitude peatlands appear more resilient to drainage; 14C measurements from UK blanket bogs suggest that exported DOC remains young (<50 years) despite drainage. Boreal and temperate fens and raised bogs in Finland and the Czech Republic showed intermediate sensitivity. We attribute observed differences to physical and climatic differences between peatlands, in particular, hydraulic conductivity and temperature, as well as the extent of disturbance associated with drainage, notably land use changes in the tropics. Data from the UK Peak District, an area where air pollution and intensive land management have triggered Sphagnum loss and peat erosion, suggest that additional anthropogenic pressures may trigger fluvial loss of much older (>500 year) carbon in high‐latitude systems. Rewetting at least partially offsets drainage effects on DOC age.

Trends in Levels of Allochthonous Dissolved Organic Carbon in Natural Water: A Review of Potential Mechanisms under a Changing Climate

Over the past several decades, dissolved organic carbon (DOC) in inland natural water systems has been a popular research topic to a variety of scientific disciplines. Part of the attention has been due to observed changes in DOC concentrations in many of the water systems of the Northern Hemisphere. Shifts in DOC levels, and changes in its composition, are of concern due to its significance in aquatic ecosystem functioning and its potential and realized negative effects on waters that might be treated for drinking purposes. While it may not be possible to establish sound cause and effect relationships using a limited number of drivers, through long-term DOC monitoring studies and a variety of laboratory/field experiments, several explanations for increasing DOC trends have been proposed, including two key mechanisms: decreased atmospheric acid deposition and the increasing impact of climate change agents. The purpose of this review is three-fold: to outline frequently discussed conceptual mechanisms used to explain DOC increases (especially under a changing climate), to discuss the structure of DOC and the impact of higher levels of DOC on drinking water resources, and to provide renewed/sustained interest in DOC research that can encourage interdisciplinary collaboration. Understanding the cycling of carbon from terrestrial ecosystems into natural waters is necessary in the face of a variable and changing climate, as climate change-related mechanisms may become increasingly responsible for variations in the inputs of allochthonous DOC concentrations in water.

Scientific basis of dissolved organic carbon limitation for landfilling of municipal treatment sludge – Is it attainable and justifiable?

This study evaluated the scientific and technical basis of the dissolved organic carbon (DOC) limitation imposed on municipal sludge for landfilling, mainly for assessing the attainability of the implemented numerical level. For this purpose, related conceptual framework was analyzed, covering related sewage characteristics, soluble microbial products generation, and substrate solubilization and leakage due to hydrolysis. Soluble COD footprint was experimentally established for a selected treatment plant, including all the key steps in the sequence of wastewater treatment and sludge handling. Observed results were compared with reported DOCs in other treatment configurations. None of the leakage tests performed or considered in the study could even come close to the prescribed limitation. All observed results reflected 10–20 fold higher DOC levels than the numerical limit of 800mg/kg (80mg/L), providing conclusive evidence that the DOC limitation imposed on municipal treatment sludge for landfilling is not attainable, and therefore not justifiable on the basis of currently available technology.

Characteristics of DBPs reduction of AOM by dissolved air flotation

AbstractAlgae increase the concentration of dissolved organic carbon (DOC), which causes unpleasant tastes and odors in water. This DOC is known as algal organic matter, which comprises extracellular organic matter and intracellular organic matter. Carbonaceous disinfection by-products (C-DBPs) and nitrogenous DBP (N-DBPs) are produced from DOC by disinfection processes, and N-DBPs are about 140 times more toxic than C-DBPs. We compared the levels of N-DBPs when dissolved air flotation (DAF) or conventional gravity sedimentation was used to remove algae before/after chlorination. The degradation of algal cells by chlorine treatment increased the DOC level, which was attributable to DBPs/DBP formation precursors (DBPFPs). The levels of N-DBPs such as dechloroacetonitrile DCAN and C-DBPs such as trihalomethanes increased with the amount of chlorine applied. Haloacetonitriles increased continuously after treatment because the residual chlorine reacted with dissolved organic nitrogen. C-DBPs and N-DBPs were r...

Single bacterial strain capable of significant contribution to carbon cycling in the surface ocean.

Marine dissolved organic carbon (DOC) encompasses one of the largest reservoirs of carbon on Earth. Heterotrophic bacteria are the primary biotic force regulating the fate of this material, yet the capacity of individual strains to significantly contribute to carbon cycling is unknown. Here we quantified the ability of a single Alteromonas strain [Alteromonas sp. strain Scripps Institution of Oceanography (AltSIO)] to drawdown ambient DOC in a coastal ecosystem. In three experiments, AltSIO alone consumed the entire pool of labile DOC, defined here as the quantity consumed by the submicron size fraction of ambient microbial assemblages within 5 d. These findings demonstrate that complete removal of the labile DOC pool in coastal surface seawater can be achieved by a single taxon. During long-term incubations (>1 y) testing semilabile DOC consumption, AltSIO entered dormancy but remained viable, while the diverse assemblages continued to consume carbon. Given that AltSIO is a large bacterium and thus subject to increased grazing pressure, we sought to determine the ecological relevance of this phenotype. Growth dynamics in natural seawater revealed that AltSIO rapidly outgrew the native bacteria, and despite intense grazing pressure, was never eliminated from the population. A survey in the California Current Ecosystem revealed that large bacteria (≥40 fg C⋅cell(-1)) were persistent, accounting for up to 12% of total bacterial abundance and 24% of total bacterial biomass. We conclude that large, rapidly growing bacteria have the potential to disproportionately alter the fate of carbon in the mesotrophic ocean and play an important role in ecosystem function.

Chemical properties of colored dissolved organic matter in the sea-surface microlayer and subsurface water of Jiaozhou Bay, China in autumn and winter

The distribution and chemical properties of chromophoric dissolved organic matter (CDOM) in the Jiaozhou Bay, China were examined during four cruises in 2010–2011. The influence of freshwater and industrial and municipal sewage along the eastern coast of the bay was clearly evident as CDOM levels (defined as a 305), and dissolved organic carbon (DOC) concentrations were well correlated with salinity during all the cruises. Moreover, DOC concentrations were significantly correlated with chlorophyll a concentrations in the surface microlayer as well as in the subsurface water. The concentrations of DOC and CDOM displayed a gradually decreasing trend from the northwestern and eastern coast to the central bay, and the values and gradients of their concentrations on the eastern coast were generally higher than those on the western coast. In addition, CDOM and DOC levels were generally higher in the surface microlayer than in the subsurface water. In comparison with DOC, CDOM exhibited a greater extent of enrichment in the microlayer in each cruise, with average enrichment factor (EF) values of 1.38 and 1.84, respectively. Four fluorescent components were identified from the surface microlayer and subsurface water samples and could be distinguished as peak A, peak T, peak B and peak M. For all the cruises, peak A levels were higher in the surface microlayer than in the subsurface water. This pattern of variationmight be attributed to the terrestrial input.

Removal of DOC and its fractions from surface waters of the Canadian Prairie containing high levels of DOC and hardness

In this paper removal of dissolved organic carbon (DOC) and its fractions by chemical coagulation was studied. Raw water was collected from the Red River (Manitoba, Canada). This source water has a DOC concentration ranging from 8 to 12 mg L−1 and total hardness of about 400 mg L−1 CaCO3, which represents a typical surface water quality of the Canadian Prairie. Four coagulants were tested at different pH levels: alum, ferric sulfate, ferric chloride and titanium sulfate. Coagulation effectiveness was evaluated by removal of DOC, DOC fractions, specific UV absorbance (SUVA), and trihalomethane formation potential (THMFP) of the coagulated water. The water DOC was separated into six fractions based on hydrophobicity and acid base functionality: hydrophobic acid (HPOA), hydrophobic base (HPOB), hydrophobic neutral (HPON), hydrophilic acid (HPIA), hydrophilic base (HPIB), and hydrophilic neutral (HPIN). Results showed that ferric sulfate had the highest total DOC removal of 66% while ferric chloride had the lowest DOC reduction of 54%. Although the THMFP was found to be lowered significantly with all four coagulants the ferric chloride showed the greatest THMFP reduction. Fractionation results found a significant reduction in the HPOA fraction for all coagulants with 91% for ferric chloride as the highest removal value. Poor removal of hydrophilic fractions was found for all coagulants. The result of this study showed that total DOC reduction cannot guarantee THMFP reduction and coagulation should be optimized to remove DOC fractions which form most THMs.

Catchment vegetation can trigger lake dystrophy through changes in runoff water quality

Surface runoff can supply lakes with a variety of chemical substances - their type and quantity may significantly vary and depend on the characteristics of the catchment area: geomorphology, phyto- coenosis type and degree of human impact. In this study we investigated the physicochemical properties of the surface runoff water collected from the wooded catchment of Lake Piaseczno Duze (LPD, Drawa National Park, Poland) covered by a monoculture of Scots pine (Pinus sylvestris) and mixed forest with white birch (Betula pubescens) as the dominant tree. Experimentally, we also aimed to study the leaching of nutrients from pine and birch litter. Throughout the investigated period runoff waters had low pH, brown colour and high levels of dissolved organic carbon (DOC) - most likely induced by humic acids. Furthermore, considerable levels of nitrogen (N) and phosphorus (P) were found. The highest concentrations of nutrients were observed in runoff collected after heavy rainfall and snow melting. Runoff from the coniferous area contained sig- nificantly higher levels of DOC but lower concentrations of N and P compared to runoff collected from the birch-dominated forest. Similar physicochemical conditions were observed in the leaching experiment. Moreover, it was found that the release of chemical substances from both coniferous and deciduous litter was rapid. Our study indicates that surface runoff from forest areas can significantly affect lake chemistry. Based on the simultaneous analyses of littoral water chemistry we suggest that it may contribute to LPD dystrophi- cation through the transportation of high levels of acidic compounds.

Dissolved organic carbon in Luvisol under different fertilization and crop rotation

The study was conducted on selected plots of long-term experiments in Skierniewice with different fertilization systems and crop rotation having an effect on the amounts of dissolved organic carbon (DOC) in the soil. The aim of the study was to compare the results of measurements of DOC by two methods, Zsolnayis and Houbais, which use the same extraction solution (0.01 mol◊dm n3 CaCl 2 ), but the extraction is carried out with different proportions of extraction solution and soil, and for different durations. Soil samples for analyses were collected in the spring and autumn of 2011 from three soil horizons: Ap (0n25 cm), Eet (25n45 cm) and Bt (45n65 cm). Using the same solution to extract soil DOC (0.01 mol◊dm n3 CaCl 2 ), but extending the extraction time from 10 minutes to 2 hours and expanding the ratio of extraction solution : soil from 2:1 to 10:1 (Zsolnayis method and Houbais method, respectively) causes an approximately 2.4-fold increase in the amount of DOC extracted from the soil. The results obtained by the two extraction methods were characterized by statistically significant differences in precision and accuracy. The observed differences in the assessment of DOC levels in the soil obtained by the two methods were particularly pronounced at lower concentrations of dissolved organic carbon in the soil. The differences demonstrate that it is not possible to substitute Zsolnayis soil test, dedicated to measuring the DOC content in the soil, with Houbais universal test designed to measure the levels of active forms of nutrients.

Temporal variations in dissolved organic carbon concentrations in upland and lowland lakes in North Wales

AbstractOver a period of 18 months, the dissolved organic carbon (DOC) concentration of a series of four lakes in North Wales was measured monthly. The lake catchment profiles consisted of an upland thin peat/soil (Llyn Cwellyn), an upland thin peat/soil associated with an adjacent area of small bog (Llyn Teyrn), an upland blanket bog (Llyn Conwy), and large lowland fen and fertile agricultural area (Llyn Cefni). The results examine the indirect effect of temperature and precipitation on the DOC concentrations found in the lakes fed by the catchments. The lowest DOC of the four sites was observed for Llyn Teyrn, varying from 1.2 to 3.30 mg/L, and with the highest being recorded for Llyn Cefni (5.45–10.83 mg/L). Temperature and rainfall data were both collected. Correlations with the DOC exhibited significant relationships with temperature for three of the sampled lakes Cwellyn (r 0.490), Teyrn (r 0.640) and Cefni (r 0.472). Recomputation versus 30‐ and 60‐day temperature lag times improved the correlation coefficients. The data showed weak and insignificant correlations for DOC versus rainfall for the three lakes, but the upland lake, Llyn Conwy, with its blanket bog catchment, did not demonstrate any statistical correlation with temperature, although it did show a significant correlation for DOC versus rainfall (r 0.553, P < 0.05). Over the sampling period, although tentative relationships were found among temperature, rainfall and DOC levels, an indirect association tempered by site hydrology is suggested.

Effect of fires on soil organic carbon pool and mineralization in a Northeastern China wetland

Fire occurs frequently over wetland, but little is known of its impact on soil carbon variations and carbon mineralization, process that are potentially important in global carbon cycle. To investigate this issue, we have designed and implemented a two-year field campaign to quality the effects of fire seasonality and frequency on soil carbon abundance and carbon mineralization in a wetland of the Sanjiang Plain in Northeastern China. A total of 4 burning experiments were conducted over 12 wetland plots from autumn 2007 to spring 2009. Our results show that after burning soil organic carbon (OC) increased in the burned soils during the first two growing seasons. Fire effects on dissolved organic carbon (DOC) and microbial biomass carbon (MBC), however, were more subtle. During the first post-burning growing season, the levels of DOC and MBC were higher than in the unburned soil. The increase however was temporary, and there was no significant difference between the burned and unburned soils in the second growing season. Carbon mineralization rate increased after burning, and CO2 emission rates were higher from burned soils than from unburned soils. Our findings suggest that burning increased CO2 emission to the atmosphere not only during the combustion process, but also through biogeochemical processes in an extended post-burning period.

Binding interactions of 1‐naphthol with dissolved organic matter of Lake Biwa and treated sewage wastewater: The role of microbial fulvic acid

The binding interactions of 1-naphthol with effluent and whole natural dissolved organic matter (DOM) samples were analyzed by using a fluorescence quenching technique. Nonfractionated DOM samples from Lake Biwa (Japan), creek water, treated sewage effluents, and an extracted Lake Biwa fulvic acid (LBFA) standard were used as quenchers and compared at the same 1-naphthol with DOM organic carbon ratios found for low natural dissolved organic carbon (DOC) levels (∼4.5 mg/L). Natural and effluent DOM (eDOM) samples were characterized by the DOC level, relative hydrophobicity (RH%), ultraviolet (UV)-visible absorbance and fluorescence excitation emission spectroscopy. These parameters were compared with those of the reference LBFA standard. Concave-up Stern-Volmer plots accounted for both the partitioning and the adsorptive binding in the eDOM-polycyclic aromatic hydrocarbons (PAH) system as compared with the nonspecific partitioning in the natural DOM-PAH system. Strong linear regressions (r(2) > 0.80) between the log K(DOC) values, the RH%, the UV absorbances, and the Fl(340-435) -UV(340) indices for the structural composition and molecular weights of the DOM samples were obtained. These results suggest that low molecular weight microbial fulvic acid (<800 Da) is dominant in the eDOM-PAH binding interactions, as well as in the distinct molecular structure of the eDOM samples, which resulted in fivefold to sixfold higher binding magnitude for 1-naphthol than for the other samples.

Effects of boundary conditions on the cleaning efficiency of riverbank filtration and artificial groundwater recharge systems regarding bulk parameters and trace pollutants

Drinking water is often produced from surface water by riverbank filtration (RBF) or artificial groundwater recharge (AGR). In this study, an AGR system was exemplarily investigated and results were compared with those of RBF systems, in which the effects of redox milieu, temperature and surface water discharge on the cleaning efficiency were evaluated. Besides bulk parameters such as DOC (dissolved organic carbon), organic trace pollutants including iodinated X-ray contrast media, personal care products, complexing agents, and pharmaceuticals were investigated. At all studied sites, levels of TOC (total organic carbon), DOC, AOX (adsorbable organic halides), SAC (spectral absorption coefficient at 254 nm), and turbidity were reduced significantly. DOC removal was stimulated at higher groundwater temperatures during AGR. Several substances were generally easily removable during both AGR and RBF, regardless of the site, season, discharge or redox regime. For some more refractory substances, however, removal efficiency turned out to be significantly influenced by redox conditions.