Lower Dissolved Organic Carbon Concentrations Research Articles

Using Extracellular Enzyme Activity as a Pollutant Indicator: a Field Study in Chinchiná River, Caldas – Colombia

The present study investigated the existence of a relationship between Extracellular Enzyme Activity (EEA) of glucosidase and alkaline phosphatase and pollution by carbon and phosphorous at five stations on the Chinchina River in the water main and the biofilm (epilithon/episammon) during three seasons (rainy, dry and transition). Specific substrates were used as sources: 4- Nitrophenyl-β-D-Glucopyranose as a carbon source and 4-Nitrophenylphosphate as a phosphorus source. The product of catalysis (4-nitrophenol) was detected spectrophotometrically at an emission of 405nm. The ratio of EEA to temperature and pH was also determined. All sampling stations displayed EEA; however, reported results were higher for phosphatase, specifically in the biofilm, in all seasons; this indicates that certain associated microorganisms in this matrix can act as a multi-enzyme system which allows for easy disposal of substrate and the presence of catalysis. A relationship could not be established to describe EEA in dissolved organic carbon (DOC), because EEA was not detected in water samples from all stations during the three sampling seasons (E1, E2 and E4), because the bioavailability of nutrients attributed to the discharge of domestic wastewater from the municipalities of Manizales and Villamaria. Additionally, the complexity of the links between the monosaccharides which comprise polymers affects the degradation rate of the material, since the enzymes produced by microorganisms in the water prefer to hydrolyze specific regions (regiospecific) of the molecule. Enzyme activity can be affected by the structure of the polysaccharide being degraded. Therefore, some trends, such as those which occur at lower DOC concentrations, exhibit greater EEA. During the dry season, a correlation was found between phosphatase and glucosidase EEA in samples of water related to the concentration of orthophosphates and filtered COD, respectively. This indicates that higher concentrations of orthophosphates result in higher EEA of the phosphatase, and that higher concentrations of CODs result in higher EEA of the glucosidase.

Manganese removal by hydrogen peroxide and biofiltration

Biofiltration has gained more attention as an alternative filtration for the removal of manganese (Mn) in both groundwater and surface water. This study investigated the potential of biofiltration as pretreatment at the Bennery Lake Water Treatment Plant located in Halifax, Nova Scotia, for the removal of manganese and dissolved organic carbon (DOC) from pH 6 natural lake water. A bench-scale study identified the effect of oxidant enhancement with hydrogen peroxide (H2O2), nutrient enhancement with phosphorus (P) and medium type (granular activated carbon (GAC) and anthracite) on a biofiltration system. Addition of both the nutrient, phosphorus (300–500 µg/l), and the oxidant, hydrogen peroxide (0·5 mg/l) enhanced the biofiltration performance, achieving 98% manganese removal and 27% (1·3 mg/l) DOC removal. Overall, the medium was not a significant factor for manganese removal, while GAC removed significantly more DOC than anthracite, although further treatment would be required for either medium to achieve lower DOC concentrations. These results show direct biofiltration of surface water at pH 6 can remove manganese below the 50 µg/l aesthetic guideline from a manganese loading of over 1 mg/l. This work highlights a potential mechanism and implication of biological roughing filtration technique for the removal of manganese and DOC from natural surface water.

An effective method of UV-oxidation of dissolved organic carbon in natural waters for radiocarbon analysis by accelerator mass spectrometry

Radiocarbon (14C) measurement of dissolved organic carbon (DOC) is a very powerful tool to study the sources, transformation and cycling of carbon in the ocean. The technique, however, remains great challenges for complete and successful oxidation of sufficient DOC with low blanks for high precision carbon isotopic ratio analysis, largely due to the overwhelming proportion of salts and low DOC concentrations in the ocean. In this paper, we report an effective UV-Oxidation method for oxidizing DOC in natural waters for radiocarbon analysis by accelerator mass spectrometry (AMS). The UV-oxidation system and method show 95%±4% oxidation efficiency and high reproducibility for DOC in both river and seawater samples. The blanks associated with the method was also low (about 3 µg C) that is critical for 14C analysis. As a great advantage of the method, multiple water samples can be oxidized at the same time so it reduces the sample processing time substantially compared with other UV-oxidation method currently being used in other laboratories. We have used the system and method for 14C studies of DOC in rivers, estuaries, and oceanic environments and have received promise results.

Carbon isotopic (14C and 13C) characterization of fossil-fuel derived dissolved organic carbon in wet precipitation in Shandong Province, China

We present results from a 1-year study of radiocarbon and stable carbon isotope measurement of dissolved organic carbon (DOC) of wet precipitation samples collected in the Shandong province of China. A total of 32 rainfall and 4 snow samples were collected from two coastal cities (Qingdao and Yantai) and one inland site (Taian) during 2014. Concentrations of DOC in the rainwater and snow samples varied widely from 28 to 616 μM. In general, rainwater originating from marine sources had relatively low DOC concentrations compared with continentally generated precipitation. Values of δ13C-DOC and Δ14C-DOC in the snow and rainwater ranged from −19.0 to −29.4 ‰ and −23 to −494 ‰, with corresponding radiocarbon ages of 125 to 5410 years before present. The dominant DOC in the wet precipitation had a relatively old 14C age (average 2841 years) and a depleted 13C value (average −24.4 ‰), indicating the mixing of contemporary organic carbon with 14C-depleted fossil fuel-derived soluble organic carbon in the atmosphere. Using a dual isotopic two-endmember model, we calculate that 7 % to 52 % of DOC in the snow and rainfall originated from fossil fuels. It is estimated that the flux of DOC in continental rainfall of China is 23 × 1012 g C yr−1 and of this, 7.1 × 1012 g C yr−1 could be fossil-fuel OC. On a global scale, the DOC flux in rainfall is estimated to be 357 Tg C yr−1, and 110 Tg C yr−1 could be fossil fuel-derived. Our study demonstrates that wet precipitation is an important removal process for old fossil fuel carbon from the atmosphere. This removal mechanism could play an important role in the carbon cycle, especially for the anthropogenically derived fraction, and it should be taken into consideration in global carbon cycle models.

Variations in dissolved organic carbon concentrations across peatland hillslopes

Peatlands are important terrestrial carbon stores and dissolved organic carbon (DOC) is one of the most important contributors to carbon budgets in peatland systems. Many studies have investigated factors affecting DOC concentration in peatland systems, yet hillslope position has been thus far overlooked as a variable that could influence DOC cycling. This study investigates the importance of hillslope position with regard to DOC cycling. Two upland peat hillslopes were studied in the Peak District, UK, to determine what impact, if any, hillslope position had upon DOC concentration. Hillslope position was found to be a significant factor affecting variation in soil pore water DOC concentration, with bottom-slope positions having significantly lower DOC concentrations than up-slope because of dilution of DOC as water moves down-slope and is flushed out of the system via lateral throughflow. Water table drawdown on steeper mid-slopes increased DOC concentrations through increased DOC production and extended residence times allowing a build-up of humic-rich DOC compounds. Hillslope position did not significantly affect DOC concentrations in surface runoff water because of the dilution of near-surface soil pore water by precipitation inputs, while stream water had similar water chemistry properties to soil pore water under low-flow conditions.

Spatial Variation in the Origin of Dissolved Organic Carbon in Snow on the Juneau Icefield, Southeast Alaska.

Dissolved organic carbon (DOC) plays a fundamental role in the biogeochemistry of glacier ecosystems. However, the specific sources of glacier DOC remain unresolved. To assess the origin and nature of glacier DOC, we collected snow from 10 locations along a transect across the Juneau Icefield, Alaska extending from the coast toward the interior. The Δ(14)C-DOC of snow varied from -743 to -420‰ showing progressive depletion across the Icefield as δ(18)O of water became more depleted (R(2) = 0.56). Older DOC corresponded to lower DOC concentrations in snow (R(2) = 0.31) and a decrease in percent humic-like fluorescence (R(2) = 0.36), indicating an overall decrease in modern DOC across the Icefield. Carbon isotopic signatures ((13)C and (14)C) combined with a three-source mixing model showed that DOC deposited in snow across the Icefield reflects fossil fuel combustion products (43-73%) and to a lesser extent marine (21-41%) and terrestrial sources (1-26%). Our finding that combustion aerosols are a large source of DOC to the glacier ecosystem during the early spring (April-May) together with the pronounced rates of glacier melting in the region suggests that the delivery of relic DOC to the ocean may be increasing and consequently impacting the biogeochemistry of glacial and proglacial ecosystems in unanticipated ways.

The effect of vegetation and soil texture on the nature of organics in runoff from a catchment supplying water for domestic consumption

The influence of vegetation and soil texture on the concentration and character of dissolved organic matter (DOM) present in runoff from the surface and sub-surface of zero order catchments of the Myponga Reservoir-catchment (South Australia) was investigated to determine the impacts of catchment characteristics and land management practices on the quality of waters used for domestic supply. Catchments selected have distinct vegetative cover (grass, native vegetation or pine) and contrasting texture of the surface soil horizon (sand or clay loam/clay). Water samples were collected from three slope positions (upper, middle, and lower) at soil depths of ~30cm and ~60cm in addition to overland flows. Filtered (0.45μm) water samples were analyzed for dissolved organic carbon (DOC) and UV–visible absorbance and by F-EEM and HPSEC with UV and fluorescence detection to characterize the DOM. Surface and sub-surface runoff from catchments with clay soils and native vegetation or grass had lower DOC concentrations and lower relative abundances of aromatic, humic-like and high molecular weight organics than runoff from sandy soils with these vegetative types. Sub-surface flows from two catchments with Pinus radiata had similar DOC concentrations and DOM character, regardless of marked variation in surface soil texture. Runoff from catchments under native vegetation and grass on clay soils resulted in lower DOC concentrations and hence would be expected to have lower coagulant demand in conventional treatment for potable water supply than runoff from corresponding sandy soil catchments. However, organics in runoff from clay catchments would be more difficult to remove by coagulation. Surface waters from the native vegetation and grass catchments were generally found to have higher relative abundance of organic compounds amenable to removal by coagulation compared with sub-surface waters. Biophysical and land management practices combine to have a marked influence on the quality of source water used for domestic supply.

The influence of slope and peatland vegetation type on riverine dissolved organic carbon and water colour at different scales

Peatlands are important sources of fluvial carbon. Previous research has shown that riverine dissolved organic carbon (DOC) concentrations are largely controlled by soil type. However, there has been little work to establish the controls of riverine DOC within blanket peatlands that have not undergone major disturbance from drainage or burning. A total of 119 peatland catchments were sampled for riverine DOC and water colour across three drainage basins during six repeated sampling campaigns. The topographic characteristics of each catchment were determined from digital elevation models. The dominant vegetation cover was mapped using 0.5m resolution colour infrared aerial images, with ground-truthed validation revealing 82% accuracy. Forward and backward stepwise regression modelling showed that mean slope was a strong (and negative) determinant of DOC and water colour in blanket peatland river waters. There was a weak role for plant functional type in determining DOC and water colour. At the basin scale, there were major differences between the models depending on the basin. The dominance of topographic predictors of DOC found in our study, combined with a weaker role of vegetation type, paves the way for developing improved planning tools for water companies operating in peatland catchments. Using topographic data and aerial imagery it will be possible to predict which tributaries will typically yield lower DOC concentrations and which are therefore more suitable and cost-effective as raw water intakes.

Coagulation–flocculation process with ultrafiltered saline extract of Moringa oleifera for the treatment of surface water

The objective of this study was to obtain a natural coagulant from the Moringa oleifera seed that was able to reduce the contamination of surface water with initial turbidity of 75NTU without increasing the organic material in the water treated. The parameters evaluated were color, turbidity and compounds that absorb light UV254nm, dissolved organic carbon (DOC) and reduction of specific absorption of UV254nm (SUVA). For this we used the saline and aqueous extraction processes of coagulant followed by ultrafiltration. In this work the dosage of coagulant was used in terms of concentration of protein coagulant, allowing greater reproducibility and reliability of results. The saline coagulant had a better performance in the removal of color (89.15%), turbidity (88.75%) and compounds with UV254nm absorbance (75.93%), with low DOC concentration in the treated water and with 38% less SUVA concentration, when compared to that by surface water. A decrease in the volume of the concentrated coagulant needed for such results should be underscored. In fact, only one half of the volume was required when compared to non-ultrafiltrated coagulant. The above directly affected DOC in the treated water which was less for concentrated saline coagulant (4.01mg/L) when compared to non-concentrated saline coagulant (8.39mg/L). High efficiency in water treatment, reduced volume of coagulant and decreased concentration in organic matter in the treated water, especially with regard to SUVA, open new perspectives in the use of saline coagulant of M. oleifera as a natural coagulant for the treatment of supply water.

Substrate use of Pseudovibrio sp. growing in ultra-oligotrophic seawater.

Marine planktonic bacteria often live in habitats with extremely low concentrations of dissolved organic matter (DOM). To study the use of trace amounts of DOM by the facultatively oligotrophic Pseudovibrio sp. FO-BEG1, we investigated the composition of artificial and natural seawater before and after growth. We determined the concentrations of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), free and hydrolysable amino acids, and the molecular composition of DOM by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). The DOC concentration of the artificial seawater we used for cultivation was 4.4 μmol C L-1, which was eight times lower compared to the natural oligotrophic seawater we used for parallel experiments (36 μmol C L -1). During the three-week duration of the experiment, cell numbers increased from 40 cells mL-1 to 2x104 cells mL -1 in artificial and to 3x105 cells mL -1 in natural seawater. No nitrogen fixation and minor CO2 fixation (< 1% of cellular carbon) was observed. Our data show that in both media, amino acids were not the main substrate for growth. Instead, FT-ICR-MS analysis revealed usage of a variety of different dissolved organic molecules, belonging to a wide range of chemical compound groups, also containing nitrogen. The present study shows that marine heterotrophic bacteria are able to proliferate with even lower DOC concentrations than available in natural ultra-oligotrophic seawater, using unexpected organic compounds to fuel their energy, carbon and nitrogen requirements.

An improved algorithm for remotely sensing marine dissolved organic carbon: Climatology in the northern South China Sea shelf-sea and adjacent waters

By using field in situ observations, data from the NOMAD database, and remotely sensed data from MODIS-Aqua, an improved algorithm has been developed for estimating the surface concentrations of dissolved organic carbon (DOC) in the Northern South China Sea Shelf-sea (NoSoCS) and adjacent waters through a combination of the remotely sensed sea-surface temperature (SST) and the absorption coefficient of colored dissolved organic matter (CDOM). Unlike previously reported algorithms, which were based on only one of these two parameters, this algorithm does not require seasonal tuning and is applicable to both coastal and pelagic waters. The uncertainty in the remotely sensed concentrations of DOC is about ±4–10µM. The climatological distributions of the satellite-derived surface DOC in the NoSoCS and adjacent waters between 2002 and 2012 followed a general trend of increasing concentrations landward, from about 58 and 73μM in the open South China Sea (SCS) in January and July, respectively, to >100μM at the mouth of the Pearl River. The intra-annual changes in the monthly average concentration of DOC in the NoSoCS follow a distinct seasonal cycle, with the lowest and highest concentrations, 56μM and 75μM, in February and July, respectively. The seasonal cycle of DOC was in phase with that of SST but out of phase with that of primary production, suggesting that biological activity was not likely its primary control. Instead, it was consistent with the entrainment of the cold and less DOC-rich sub-surface water in the surface water by enhanced vertical mixing during winter, and the high inflow of organic-rich river water to the NoSoCS in summer. Sub-regionally, lower concentrations of DOC were found in the known upwelling zones in the NoSoCS, where vertical mixing was enhanced. In the inner shelf, the effect of riverine input was indicated by higher concentrations of DOC in the plume of water at the mouth of the Pearl River. This work represents the first attempt to characterize the regional distribution of surface concentration of DOC in the NoSoCS and adjacent waters.

Landscape integration of North Patagonian mountain lakes: a first approach using characterization of dissolved organic matter

AbstractNorth‐western Patagonia contains a variety of glacially formed mountain lakes located at different positions from the treeline in the Andean Patagonian forest region. Water chemistry of six North Patagonian lakes located in an altitudinal gradient, above, at and below the treeline (~41°S) were analysed in this study. The relative importance of allochtonous to autochthonous carbon inputs along a marked catchment vegetation gradient encompassing altoandino vegetation and Nothofagus forests was addressed. The dissolved organic carbon (DOC) concentration varied among the study lakes, with the lakes located higher in the landscape exhibiting lower DOC concentrations (&lt;1 mg L−1) than lakes located at or below the treeline (&gt;2 mg L−1). Analysis of coloured and fluorescent dissolved organic matter (CDOM and FDOM, respectively) followed the DOC pattern, despite the contrasting catchments of the study lakes. The results indicated the CDOM in all the lakes had low molecular weight and low aromaticity. The excitation–emission matrices (EEMs) highlighted three distinctive fluorophores in the FDOM, including two humic‐like (peak A and peak C) revealing the presence of humic terrestrial material, and a protein‐like fluorophore (peak T) generally associated with autochthonous DOM. The increased intensities of the humic fluorophores in the lakes located below the treeline suggest higher allochtonous carbon inputs from their catchments. This evidence collectively suggests that mountain lakes exhibit some heterogeneity in terms of DOM, likely attributable to their position in relation to the treeline, which determines the contribution of the catchment. As remote lakes are extremely sensitive to changes in their catchments, these North Patagonian mountain lakes may accurately track the impact of climate and anthropogenic changes on the landscape.

Technical Note: Large overestimation of &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; calculated from pH and alkalinity in acidic, organic-rich freshwaters

Abstract. Inland waters have been recognized as a significant source of carbon dioxide (CO2) to the atmosphere at the global scale. Fluxes of CO2 between aquatic systems and the atmosphere are calculated from the gas transfer velocity and the water–air gradient of the partial pressure of CO2 (pCO2). Currently, direct measurements of water pCO2 remain scarce in freshwaters, and most published pCO2 data are calculated from temperature, pH and total alkalinity (TA). Here, we compare calculated (pH and TA) and measured (equilibrator and headspace) water pCO2 in a large array of temperate and tropical freshwaters. The 761 data points cover a wide range of values for TA (0 to 14 200 μmol L−1), pH (3.94 to 9.17), measured pCO2 (36 to 23 000 ppmv), and dissolved organic carbon (DOC) (29 to 3970 μmol L−1). Calculated pCO2 were &gt;10% higher than measured pCO2 in 60% of the samples (with a median overestimation of calculated pCO2 compared to measured pCO2 of 2560 ppmv) and were &gt;100% higher in the 25% most organic-rich and acidic samples (with a median overestimation of 9080 ppmv). We suggest these large overestimations of calculated pCO2 with respect to measured pCO2 are due to the combination of two cumulative effects: (1) a more significant contribution of organic acids anions to TA in waters with low carbonate alkalinity and high DOC concentrations; (2) a lower buffering capacity of the carbonate system at low pH, which increases the sensitivity of calculated pCO2 to TA in acidic and organic-rich waters. No empirical relationship could be derived from our data set in order to correct calculated pCO2 for this bias. Owing to the widespread distribution of acidic, organic-rich freshwaters, we conclude that regional and global estimates of CO2 outgassing from freshwaters based on pH and TA data only are most likely overestimated, although the magnitude of the overestimation needs further quantitative analysis. Direct measurements of pCO2 are recommended in inland waters in general, and in particular in acidic, poorly buffered freshwaters.

Concentrations of dissolved organic carbon in peat soils as influenced by land use and site characteristics — A lysimeter study

The release of dissolved organic carbon (DOC) from peatlands implies a loss of sequestered carbon. During the last two decades, an increase of DOC exports in Europe and North America has been reported. The influence of land use on DOC has been contradictorily discussed and a lack of knowledge exists particularly for fens in Northeastern Germany. Therefore, we aimed to investigate DOC release from fen soils with differing land use intensity. To exclude climatic influences and water level fluctuations, a lysimeter study was performed. The lysimeter vessels contained three histosols from Northeastern Germany and varied in peat quantity, substrate quality, water table depth, pH and vegetation, as these factors are strongly influenced by land use intensity. Water for DOC analysis was sampled biweekly over a two year period. DOC release ranged from 4 to 123mg/L−1 with a median of 32±22mg/L−1. Lowest DOC concentrations were found at deeply drained gleysols and at relatively slightly decomposed, acidic histosols. Highest concentrations were measured in the most degraded histosols. Degree of decomposition and pH were found to be the major driving factors for DOC release. Long-lasting rewetted lysimeters were not observed to release a lower amount of DOC than drained ones, which may be of importance when restoration of degraded peatlands is intended. As lysimeters from the same site released relatively similar amounts of DOC despite their varying management during the last 50years, it appears that peatlands have an individual potential for DOC release.

A novel high-temperature combustion based system for stable isotope analysis of dissolved organic carbon in aqueous samples. I: development and validation.

Traditionally, dissolved organic carbon (DOC) stable isotope analysis (SIA) is performed using either offline sample preparation followed by elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) or a wet chemical oxidation (WCO)-based device coupled to an isotope ratio mass spectrometer. The first method is time-consuming and laborious. The second involves the risks of underestimation of DOC concentration and isotopic fractionation due to incomplete oxidation. The development of an analytical method for accurate and sensitive DOC SIA is described in this study. A high-temperature combustion (HTC) system improves upon traditional methods. A novel total organic carbon (TOC) system, specially designed for SIA, was coupled to an isotope ratio mass spectrometer. An integrated purge and trap technique (peak focusing), flexible injection volume (0.05-3 mL), favorable carrier gas flow, modified ash crucible, new design of combustion tube and optimized drying system were used to achieve the necessary performance. The system can reliably measure concentrations up to 1000 mgC/L. Compounds resistant to oxidation, such as barbituric acid, melamine and humic acid, were analyzed with recovery rates of 100 ± 1% proving complete oxidation. In this initial testing, the δ(13) C values of these compounds were determined with precision and trueness of ≤ 0.2‰ even with 3.5% salinity. Further tests with samples with low DOC concentrations resulted in LOQSIA method values of 0.5 mgC/L and 0.2 mgC/L for LOQSIA instr , considering an accuracy of ± 0.5‰ as acceptable. The novel HTC system coupled to an isotope ratio mass spectrometer resulted in significantly improved sensitivity. The system is suitable for salt-containing liquids and compounds that are resistant to oxidation, and it offers a large concentration range. A second paper (which follows this one in this issue) will present a more comprehensive assessment of the analytical performance with a broad set of solutions and real samples. This highly efficient TOC stable isotopic analyzer will probably open up new possibilities in biogeochemical carbon cycle research.

A novel high-temperature combustion based system for stable isotope analysis of dissolved organic carbon in aqueous samples. II: optimization and assessment of analytical performance.

Dissolved organic carbon (DOC) plays an important role in carbon cycling, making precise and routine measurement of δ(13)C values and DOC concentration highly desirable. A new promising system has been developed for this purpose. However, broad-scale application of this new technique requires an in-depth assessment of analytical performance, and this is described here. A high-temperature combustion Total Organic Carbon analyzer was interfaced with continuous flow isotope ratio mass spectrometry (TOC/IRMS) for the simultaneous analysis of the bulk DOC concentration and δ(13)C signature. The analytical performance (precision, memory effects, linearity, volume/concentration effects, accuracy) was thoroughly evaluated, including realistic and challenging conditions such as low DOC concentrations and natural DOC. High precision (standard deviation, SD predominantly ≤ 0.15 ‰) and accuracy (R(2) = 0.9997) were achieved for the δ(13)C analysis of a broad diversity of DOC solutions. Simultaneously, good results were obtained for the measurement of DOC concentration. Assessment of natural abundance and slightly (13)C-enriched DOC, a wide range of concentrations (~0.2-150 mgC/L) and injection volumes (0.05-3 mL), demonstrated minor/negligible memory effects, good linearity and flexible usage. Finally, TOC/IRMS was successfully applied to determine low DOC concentrations (<2 mgC/L) and DOC from diverse terrestrial, freshwater and marine environments (SD ≤ 0.23 ‰). TOC/IRMS enables fast and reliable measurement of DOC concentrations and δ(13)C values in aqueous samples, without pre-concentration and freeze-drying. Further investigations should focus on complex, saline matrices and very low DOC concentrations, to achieve a potential lower limit of 0.2 mgC/L. Thus, TOC/IRMS will give DOC research in terrestrial and aquatic environments a huge impulse with high-resolution, routine δ(13)C analysis.

Simulated climate change impact on summer dissolved organic carbon release from peat and surface vegetation: Implications for drinking water treatment

Uncertainty regarding changes in dissolved organic carbon (DOC) quantity and quality has created interest in managing peatlands for their ecosystem services such as drinking water provision. The evidence base for such interventions is, however, sometimes contradictory. We performed a laboratory climate manipulation using a factorial design on two dominant peatland vegetation types (Calluna vulgaris and Sphagnum Spp.) and a peat soil collected from a drinking water catchment in Exmoor National Park, UK. Temperature and rainfall were set to represent baseline and future conditions under the UKCP09 2080s high emissions scenario for July and August. DOC leachate then underwent standard water treatment of coagulation/flocculation before chlorination. C. vulgaris leached more DOC than Sphagnum Spp. (7.17 versus 3.00 mg g−1) with higher specific ultraviolet (SUVA) values and a greater sensitivity to climate, leaching more DOC under simulated future conditions. The peat soil leached less DOC (0.37 mg g−1) than the vegetation and was less sensitive to climate. Differences in coagulation removal efficiency between the DOC sources appears to be driven by relative solubilisation of protein-like DOC, observed through the fluorescence peak C/T. Post-coagulation only differences between vegetation types were detected for the regulated disinfection by-products (DBPs), suggesting climate change influence at this scale can be removed via coagulation. Our results suggest current biodiversity restoration programmes to encourage Sphagnum Spp. will result in lower DOC concentrations and SUVA values, particularly with warmer and drier summers.

입상활성탄에 의한 합성폐수의 용존유기물질의 새로운 흡착등온 모델 및 운동학적 흡착 연구

본 논문은 입상활성탄에 의해서 합성폐수에서의 용존유기탄소의 흡착평형과 회분식 실험을 통해 흡착성질을 파악하고자 하였다. 흡착평형의 새로운 모델식을 제안하였고 이 식을 바탕으로 회분식 실험데이터를 모사하였다. 합성폐수의 유기성분은 Beef extract, Peptone, Humic acid, Tannic acid, Sodium lignin sulfonate, Sodium lauryle sulfate, Arabic gum powder, Arabic acid (polysaccharide), <TEX>$(NH_4)_2SO_4$</TEX>, <TEX>$K_2HPO_4$</TEX>, <TEX>$NH_4HCO_3$</TEX>, <TEX>$MgSO_4{\cdot}7H_2O$</TEX> 등으로 구성되었다. 농도가 낮은 영역 (0~2.5 mg/L)에서는 선형적인 흡착평형을 보여주었고, 농도가 높은 영역 (2.5~6mgl/L)에서는 우호적인 흡착평형을 보여주었다. 사용되어진 생물학적 처리방법에서 나오는 유출수의 합성폐수는 알려진 양으로 준비되어졌다. 흡착평형 모델링은 Freundlich, Langmuir, Sips 및 하이브리드 식을 이용하여 모사하였다. 특히, 선형과 Sips를 이용한 하이브리드 흡착평형식은 낮은 농도와 높은 농도 역에서 매우 좋은 흡착평형식이었다. 용수 및 폐수처리에 활성탄 흡착에 있어서, 선형식과 Sips식을 합친 새로운 하이브리드 식은 새로운 흡착평형식이 될 수 있었다. 하이브리드 흡착평형식 (선형+Sips)을 이용하여 LDFA 운동학적식을 통하여 다양한 흡착제 양에 따른 회분식 반응조에서의 실험데이터를 잘 모사할 수 있었다. In this study, we conducted the adsorption equilibrium and batch experiments of dissolved organic carbon (DOC) in the wastewater by granular activated carbon (GAC). The components of organic compound were Beef extract (1.8 mg/L), Peptone (2.7 mg/L), Humic acid (4.2 mg/L), Tannic acid (4.2 mg/L), Sodium lignin sulfonate (2.4 mg/L), Sodium lauryle sulfate (0.94 mg/L), Arabic gum powder (4.7 mg/L), Arabic acid (polysaccharide) (5.0 mg/L), <TEX>$(NH_4)_2SO_4$</TEX> (7.1 mg/L), <TEX>$K_2HPO_4$</TEX> (7.0 mg/L), <TEX>$NH_4HCO_3$</TEX> (19.8 mg/L), <TEX>$MgSO_4{\cdot}7H_2O$</TEX> (0.71 mg/L), The adsorption characteristics of DOC in synthetic wastewater was described using the mathematical model through a series of isotherm and batch experiments. It showed that there was linear adsorption region in the low DOC concentration (0~2.5 mg/L) and favorable adsorption region in high concentration (2.5~6 mg/L). The synthetic wastewater used was prepared using known quantities of organic and/or inorganic compounds. Adsorption modelling isotherms were predicted by the Freundlich, Langmuir, Sips and hybrid isotherm equations. Especially, hybrid isotherm of Linear and Sips equation was a good adsorption equilibrium in the region of the both the low concentration and high concentration. In applying carbon adsorption for treating water and wastewater, hybrid adsorption equation plus linear equation with Sips equation will be a good new adsorption equilibrium model. Linear driving force approximation (LDFA) kinetic equation with Hybrid (linear+Sips) adsorption isotherm model was successfully applied to predict the adsorption kinetics data in various GAC adsorbent amounts.

The biogeochemistry of carbon across a gradient of streams and rivers within the Congo Basin

Dissolved organic carbon (DOC) and inorganic carbon (DIC, pCO2), lignin biomarkers, and theoptical properties of dissolved organic matter (DOM) were measured in a gradient of streams and rivers within the Congo Basin, with the aim of examining how vegetation cover and hydrology influences the composition and concentration of fluvial carbon (C). Three sampling campaigns (February 2010, November 2010, and August 2011) spanning 56 sites are compared by subbasin watershed land cover type (savannah, tropical forest, and swamp) and hydrologic regime (high, intermediate, and low). Land cover properties predominately controlled the amount and quality of DOC, chromophoric DOM (CDOM) and lignin phenol concentrations (∑8) exported in streams and rivers throughout the Congo Basin. Higher DIC concentrations and changing DOM composition (lower molecular weight, less aromatic C) during periods of low hydrologic flow indicated shifting rapid overland supply pathways in wet conditions to deeper groundwater inputs during drier periods. Lower DOC concentrations in forest and swamp subbasins were apparent with increasing catchment area, indicating enhanced DOC loss with extended water residence time. Surface water pCO2 in savannah and tropical forest catchments ranged between 2,600 and 11,922 µatm, with swamp regions exhibiting extremely high pCO2 (10,598–15,802 µatm), highlighting their potential as significant pathways for water-air efflux. Our data suggest that the quantity and quality of DOM exported to streams and rivers are largely driven by terrestrial ecosystem structure and that anthropogenic land use or climate change may impact fluvial C composition and reactivity, with ramifications for regional C budgets and future climate scenarios.

Spatial and Seasonal Variation of Dissolved Organic Carbon (DOC) Concentrations in Irish Streams: Importance of Soil and Topography Characteristics

Dissolved organic carbon (DOC) concentrations have increased in many sites in Europe and North America in recent decades. High DOC concentrations can damage the structure and functions of aquatic ecosystems by influencing water chemistry. This study investigated the spatial and seasonal variation of DOC concentrations in Irish streams across 55 sites at seven time occasions over 1year (2006/2007). The DOC concentrations ranged from 0.9 to 25.9mg/L with a mean value of 6.8 and a median value of 5.7mg/L and varied significantly over the course of the year. The DOC concentrations from late winter (February: 5.2±3.0mg/L across 55 sites) and early spring (April: 4.5±3.5mg/L) had significantly lower DOC concentrations than autumn (October: mean 8.3±5.6mg/L) and early winter (December: 8.3±5.1mg/L). The DOC production sources (e.g., litterfall) or the accumulation of DOC over dry periods might be the driving factor of seasonal change in Irish stream DOC concentrations. Analysis of data using stepwise multiple linear regression techniques identified the topographic index (TI, an indication of saturation-excess runoff potential) and soil conditions (organic carbon content and soil drainage characteristics) as key factors in controlling DOC spatial variation in different seasons. The TI and soil carbon content (e.g., soil organic carbon; peat occurrence) are positively related to DOC concentrations, while well-drained soils are negatively related to DOC concentrations. The knowledge of spatial and seasonal variation of DOC concentrations in streams and their drivers are essential for optimum riverine water resources management.