Organic Carbon Weight Research Articles

Estimating the global root exudate carbon flux

Root exudation, the export of low-molecular weight organic carbon (C) from living plant roots to soil, influences microbial activity, nutrient availability, and ecosystem feedbacks to climate change, but the magnitude of this C flux at ecosystem and global scales is largely unknown. Here, we synthesize in situ measurements of root exudation rates and couple those to estimates of fine root biomass to estimate global and biome-level root exudate C fluxes. We estimate a global root exudate flux of 13.4 (10.1–20.2) Pg C y−1, or about 9% (7–14%) of global annual gross primary productivity. We did not find differences in root mass-specific exudation rates among biomes, though total exudate fluxes are estimated to be greatest in grasslands owing to their high density of absorptive root biomass. Our synthesis highlights the global importance of root exudates in the terrestrial C cycle and identifies regions where more in situ measurements are needed to improve future estimates of root exudate C fluxes.

Aggregate stability and carbon and N dymamics in macroaggregate size fractions with different soil texture

Soil nutrient cycling, the distribution of soil aggregates, and their stability are directly influenced by soil texture. Different sizes of soil aggregates provide microhabitats for microorganisms and therefore influence soil carbon (C) and nitrogen (N) mineralization. The purpose of the present study was to assess the aggregate stability and dynamics of carbon and nitrogen in macroaggregate size fractions (1-8 mm) with different clay content from meadow soils. Surface soil samples (0-15 cm) were collected from 4- to 5-year-old forage crops. Four macroaggregate size classes were isolated by dry sieving and analyzed for their mass proportions: fine macroaggregates (FM) (less than 1 mm), medium-fine macroaggregates (MFM) (1-2 mm), medium-coarse macroaggregates (MCM) (2-4 mm), and large-coarse macroaggregates (LCM) (4-8 mm). The dry mean weight diameter (MWD), organic carbon (OC), total nitrogen (TN), carbon and nitrogen of microbial biomass (C-MB, N-MB) were determined. CO2 emission and net nitrogen mineralized (NM) were measured after 14 weeks of incubation. The amounts of FM were significantly lower than those of intermediate macroaggregates (MCM and MFM) and decreased markedly with increasing clay content within soil macroaggregates. In general, the amounts of macroaggregate size fractions were lowest in soils with high clay content. MWD exhibited a significant correlation with particle size distribution, OC, and MB-C. OC, TN, MB-C, and MB-N contents within macroaggregates increased with decreasing macroaggregate size and increasing clay content of macroaggregate fractions. The CO2 emission and NM content increased with increasing macroaggregate size, indicating higher organic C and N mineralization activity in larger macroaggregates. Mineralization of OC was lowest in macroaggregate fractions with the highest clay content. We conclude that clay content can increase the protection of microbial biomass in meadow soils. Small macroaggregates tend to contain more recalcitrant organic matter compared to larger macroaggregates.

Characterization of Lignin Peroxidase from Cryptococcus neoformans for Bioremediation of Pulp and Paper Mill Effluent

Eight fungal strains (F1–F8) isolate from the sediment core and degraded wood of the Pulp and Paper Mill effluent and Phanerochaete chrysosporium are tested for different cellulolytic (CMcase, FPase, Xylanases) and lignolytic (lignin peroxidase) enzyme activity in pulp. F-3 (Cryptococcus neoformans) strain shows higher enzyme activity compare to other fungi isolated from effluent. Weight loss, cellulose loss, and organic carbon contents are found maximum in F-3 (C. neoformans) strain. Reducing sugar, protein content, and color removing potential are also higher in C. neoformans. The culture extract of F-3 strain grows in presence of pulp fractionated into five protein fractions has indicated two fractions of molecular weight, 38,000 and 40,000 Da, having lignin peroxidase activity. Lignin peroxidase has optimum activity at pH 2–3 and temperature 20–30 °C, maximum activity at 6–48 mM veratryl alcohol concentration and 256 mM H2O2, however, sodium azide inhibits the enzyme activity. Different metals (CoCl2, HgSO4, CaCl2, SnCl2, FeSO4, CuSO4, and ZnSO4) also affect the lignin peroxidase activity. Characterization study is performed for significant analysis.

Impact of topsoil mining for unfired mudbricks on soil quality in eastern KwaZulu‐Natal, South Africa

AbstractTopsoil mining associated with informal mud brick making is common in rural villages of South Africa. The impact of topsoil mining on soil quality, however has not been investigated. This study therefore assessed the impact of topsoil mining associated with unfired mud bricks on selected soil quality indicators in two villages of KwaZulu‐Natal, South Africa. First, local miners were interviewed to ascertain information related to topsoil mining, brickfield site identification and soil suitability for mud bricks. Two brickfields per village mined for ≤5 and > 20 years, respectively were used in this study. Experiment consisted of three treatments, that is, unmined, mined and recovering lands replicated three times. Nine soil samples were collected (0–10 cm) from each site (three composite samples per treatment) with corresponding bulk density samples taken at 0–5 cm using core rings. The average topsoil mining depth was 30 cm. Interviews revealed that isidaka (poorly drained sandy clay) and isibomvu (red soil) are preferred over ubumba (clayey) soils. Topsoil mining increased silt fraction across all studied brickfields with an average of 45.2% in mined compared with 30.6% in unmined treatments. The response of clay fractions was variable across villages and mining time. Mining significantly decreased mean weight diameter, exchangeable bases, organic carbon, and nitrogen content and stocks and porosity while it increased bulk density. Results show that topsoil mining for mud brick making results in poor soil physical quality, nutrient availability and carbon storage with implications for land degradation in mud brickfields.

Plastic properties affect the composition of prokaryotic and eukaryotic communities and further regulate the ARGs in their surface biofilms

Plastic wastes are ubiquitous in the offshore and oceans with an increasing quantity, and inevitably, microbial communities colonized the plastics to form biofilms, which have become dispersal vectors for antibiotic resistance genes (ARGs). This study focused on the impact of plastic properties including hardness, wettability, and zeta-potential on the biomass, prokaryotic and eukaryotic communities and ARGs in biofilms formed on specific plastics (polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET)) in an estuarine environment. The results showed that, in comparison to PP, more biomass characterized by more dry weight, chlorophyll a (Chl a) and total organic carbon (TOC) was found in biofilms formed on PE and PET, which may be related to their lower surface wettability. Proteobacteria were the dominant prokaryotic phyla, and they accounted for 53.06%, 81.90%, 37.06%, 76.25%, and 54.27% of the total sequences in biofilms on PE, PP, PET, water and sediment, respectively. Ascomycota were the predominant eukaryotic phyla in biofilms, water, and sediment, and their abundances were elevated in biofilms on PP, which accounted for 34.73%. The biofilms on PP had a higher relative abundance of ARGs (3.13) compared to those on PE (2.59) and PET (0.23). Furthermore, both the plastic-biofilm properties (e.g. dry weight, Chl a, and TOC) and microbial communities (e.g., Fungi and Proteobacteria) may be involved in regulating the abundance of ARGs. Moreover, mobile genetic elements (MGEs) were significantly correlated to both the absolute and relative abundance of ARGs, indicating that MGEs may regulate the migration of ARGs in biofilms. Taken together, this investigation provides the significance of the plastic type, surface properties, and surrounding environments in shaping microbial communities and ARGs in biofilms formed on plastics.

Mechanisms for retention of low molecular weight organic carbon varies with soil depth at a coastal prairie ecosystem

Though primary sources of carbon (C) to soil are plant inputs (e.g., rhizodeposits), the role of microorganisms as mediators of soil organic carbon (SOC) retention is increasingly recognized. Yet, insufficient knowledge of sub-soil processes complicates attempts to describe microbial-driven C cycling at depth as most studies of microbial-mineral-C interactions focus on surface horizons. We leveraged a well-studied paleo-marine terrace (90 ka) located near Santa Cruz, CA, to characterize the short-term (days to weeks) and intermediate-term (months to years) fate of two low molecular weight organic carbon. compounds at three depths in the soil profile (∼25 cm, A horizon; ∼75 cm A/B transition; and ∼125 cm, B horizon). We employed isotopically-labeled glucose (GLU) and oxalic acid (OXA) to represent two common classes of rhizodeposits: carbohydrates and organic acids. Using a combination of laboratory (9 d) and field (490 d) incubations, we traced the fate of GLU-C and OXA-C through dissolved-, metal-associated-, and microbially-respired CO2 and bulk SOC pools. Our results suggest new SOC retention (i.e., defined as 13C label identified in solid or aqueous fractions) over intermediate time frames (490 d) is correlated with patterns in short-term (9 d) cycling dynamics, which in turn is related to the theoretical efficiency by which microorganisms process each substrate. For all horizons (A, A/B, and B) GLU-C was converted to CO2 more quickly than OXA-C with modeled decomposition rates ∼2–4 times faster for GLU depending on microbial density (higher in A than B horizon). The faster decomposition rates of GLU-C increased fractional recovery (0.399 ± 0.026 to 0.504 ± 0.030 for GLU-C) compared to OXA-C (0.035 ± 0.003 to 0.127 ± 0.010) among all horizons in our field experiment (490 d). Though the overall proportion of GLU-C recovered in solid fractions did not vary significantly with horizon, based on 13C recovered in aqueous fractions the apparent mechanism for retention did. After the 9-d laboratory incubation, fractional recovery for GLU-C among C pools associated with microbial biomass was almost 20× higher than OXA-C (0.192 versus 0.010, respectively across all horizons). More than a year later, 43–46% of GLU-C retained in the field incubation was extractable with a neutral salt (representing a pool of soil C residing within or available to microbial biomass) among A and A/B horizons, while only 6% of retained GLU-C was similarly extractable in the B horizon. Thus, it appears among depths with higher microbial density (A, A/B horizons), anabolic recycling is the most likely process contributing to the persistence of glucose C, whereas abiotic sinks contributed more to intermediate-term stability for GLU-C in the B horizon. By contrast, most OXA-C was lost, presumably as CO2, over the short-term from the A and A/B horizons (fractional recovery: 0.136 ± 0.011 and 0.091 ± 0.002, respectively). However, though substantially lower than GLU-C recovered at the conclusion of our field experiment, the fraction of oxalic acid C retained in the B horizon over both short- (0.72 ± 0.037) and intermediate-time (0.127 ± 0.010) frames was several-fold higher than for overlying horizons. The specific process(es) (e.g., more efficient microbial utilization, metal-organic complexation, direct adsorption to the mineral matrix, etc.) contributing to higher retention for OXA-C at depth are discussed but remain unresolved.

Effects of plant species on soil quality in natural and planted areas of a forest park in northern Iran.

Reforestation may help protect the health of endangered forest ecosystems. To implement this action, it is important to evaluate the effects of the planted species on soil quality. Previous studies have demonstrated that soil properties are closely driven by the effects of plant roots and plant remains (quantity and quality) reaching the soil surface. However, little research is available about the effects of plant species on soil quality of reforested sites compared to natural forest ecosystems. This study evaluates the changes in the main soil properties between two 30-40year-old stand types in forest areas of northern Iran: i) two stands, each one comprising a natural species (Parrotia persica or Pinus taeda); and ii) two stands, each one with planted trees (Quercus castaneifolia or Alnus glutinosa). Compared to reforested sites, the soils with natural trees showed higher root weight density (+43%), pH (+17%), and organic carbon (+64%). These differences led to higher nutrient contents, microbial respiration, aggregate stability, and water retention in soils with natural trees, as confirmed by the correlation analysis. A principal component analysis provided a meaningful combined factor (the first principal component) that showed a clear discrimination in soil quality and fertility among natural and reforested species. The calculation of a soil quality index confirms that planted species may lead to an overall lower quality of soils with planted species compared to natural forest. Since the lower soil quality of planted forests can be also the result of unsuitable management practices, this study suggest that forest operations in reforested areas should be avoided, since this could lead to negative effects on soil quality and contribute to an increase in the risk of soil degradation.

The impact of pine self-afforestation on podzolization process in semi-natural grassland areas of Volyn Polissya (Ukraine)

Background. Several theories have been proposed to explain the podzolization process. Currently, the role of organic matter in both weathering and immobilization in the illuvial horizon is clearly stated. The origin of soil organic matter and, accordingly, the various mechanisms of its influence on the soil material, create the basis of these theories. We assume that in the base-poor sandy soils under rich herbaceous vegetation with a well developed sod layer, the process of podzolization may also depend on CO2 soil formation agent . Materials and Methods. Four localities along a Pinus sylvestris L. self-afforestation chronosequence with pine stands of 10, 20, 40 yrs and an adjacent semi-natural grassland area were investigated in order to determine the patterns of podzolization process on sandy glacial till deposits. Soil pH, exchangeable base, soil cation exchange capacity, total content of soil organic carbon, amorphous Fe, Si and Al and total contents of Al, Fe, Mn, Zn, Cd, Pb, Cu, Co, Ni, Na, K were determined. Statistical analysis of the results was performed using LibreOffice for Linux. Results. During the pine succession, a previously well differentiated into horizons podzolic soil under the grassland vegetation community gradually degrades. Previously well-defined albic and spodic diagnostic horizons disappear, the soil profile becomes more acidic, the soil organic carbon, the base cation content and the base cation saturation decrease, the leaching rate of aluminium and iron increases. Secondary podzolization features in the soil profiles were detected 40 years after the onset of afforestation. The podzolization has not been intensive enough to develop fully fledged albic and spodic diagnostic horizons over such a short period. Conclusions. Based on the obtained soil morphological, physical and chemical properties, three most important agents of podzolization are proposed as principal for the studied area. The main gent under pine forest is fulvic acids that are produced during coniferous litter decomposition. Low molecular weight organic acids and carbon dioxide produced to the rhizosphere by roots and a root associated microbiota are mainly involved in the podzolization process under the grassland ecosystem.

Mechanisms for Retention of Low Molecular Weight Organic Carbon Varies with Soil Depth at a Coastal Prairie Ecosystem

Mechanisms for Retention of Low Molecular Weight Organic Carbon Varies with Soil Depth at a Coastal Prairie Ecosystem

Evaluating the long‐term effects of tillage systems on soil structural quality using visual assessment and classical methods

AbstractCurrent agricultural practices and their impacts on the sustainability of crop production can be evaluated by simple and reliable soil structure assessment tools. The study was conducted to determine the effects of long‐term (2006–2017) tillage systems on structural quality of a clayey soil using the visual evaluation of soil structure (VESS) and classical field and laboratory measurements. A field experiment with seven tillage systems, representing both traditional and conservation tillage methods, was conducted on a clayey soil in the Cukurova region, Turkey. Soil samples from 0–10, 10–20 and 20–25 cm depths were analysed for mean weight diameter (MWD), porosity and organic carbon. Penetration resistance (PR) was determined in each treatment plot. The VESS scores (<2) of upper 0–5 cm indicated a good structural quality for all tillage systems. The VESS scores were positively related to PR and MWD and negatively to macroporosity (MaP) and total porosity. In reduced and no‐till systems, poorer soil structures were observed in subsurface layers where firm platy and angular blocky structures were defined. Mean VESS score (3.29) in 20–25 cm depth where PR was 3.01 MPa under no‐till indicated a deterioration of soil structural quality; thus, immediate physical interventions would be needed. Lower VESS scores and PR values under strategic tillage which was created by ploughing half of no‐till plots in November 2015 indicated successful correction of compaction caused by long‐term no‐till. The results suggest that the VESS approach is sensitive and useful in distinguishing compacted layers within the topsoil.

Microbial utilization of low molecular weight organic carbon substrates in cultivated peats in response to warming and soil degradation

Peatlands store vast amounts of carbon (C) within the global terrestrial biosphere. Drainage and cultivation of peat soils lead to rapid soil degradation and C losses, and this may worsen under warming as the soils are no longer protected by anaerobic conditions. To predict the rates of soil C loss and design effective mitigation strategies, it is important to understand what controls organic matter mineralization in these soils. Using the 0–10 cm soil depth of thick and thin (degraded) agricultural peat soils, we investigated the fate of low molecular weight organic substrates (LMWOS) and how the microbial biomass consuming these substrates responded to temperature. We incubated the soils under increasing temperatures (4, 10, 20, and 30 °C) for 72 h. Either 14C-labelled glucose or amino acids were added to the soils and their speed of breakdown, partitioning into anabolic/catabolic processes and microbial C use efficiency (CUE) were determined. The total 14CO2 loss from soil increased significantly with increasing temperature during 72-h incubation, regardless of peat layer thickness. Warming altered the dynamics of LMWOS mineralization by changing C allocation and the turnover rate of different microbial C pools. The half-life of LMWOS decreased more than 50% when temperature increased from 4 to 30 °C for both substrates. CUE was always higher for thin than thick peat soil and both declined by 0.002–0.005 °C-1 with increasing temperature. Thin peat decreased substrate C allocation into the fast cycling C pool compared to the thick peat, but had no overall effect on pool turnover rate. Our work suggests that climate warming will accelerate C mineralization and soil loss in drained peat soils, with larger effects expected in thick peat soil. This study provides an important initial step in characterizing the response of the microbial utilization of labile C to temperature change and soil degradation in cultivated peatlands.

Stabilization of exogenous carbon in soil density fractions is affected by its chemical composition and soil management

Low molecular weight organic carbon (LMWOC) can be physiochemically protected by soil particles via sorption and enfolding. Soil management usually changed the soil particle distribution (e.g. upland vs paddy soil). Higher organic carbon stocks in paddy soil than upland soil could partially be because of the greater immobilization and inaccessibility of LMWOC in paddy soil. To assess the effects of soil management and types of LMWOC on its carbon stabilization in soil density fractions, a simulated study was conducted to investigate the distribution of LMWOC (i.e., glucose, acetic acid, and oxalic acid) in soil density fractions based on 13C-labeling experiments in both soils. The results showed that the total 13C recovery was determined by LMWOC types, following the order of glucose> acetic acid > oxalic acid (p < 0.05). Both soil management and types of LMWOC significantly affect carbon distribution in soil density fractions. The 13C from LMWOC was predominant in the 1.85–2.4 g.cm−3 fraction of upland soil, while the highest concentration of LMWOC 13C was found in mineral grains (2.4–2.65 g.cm−3) in paddy soil, suggesting that more LMWOC was preserved in high density fractions in paddy soil than in upland soil. Our results highlighted that the LMWOC was mainly associated with aggregates in upland soil while subjected to mineral adsorption in paddy soil.

Spectral characteristics and sources of rainstorms dissolved organic matter in Zhoucun Reservoir during flood season

运用三维荧光光谱（EEMs）技术结合平行因子分析法（PARAFAC），对周村水库夏季两场暴雨不同降雨历时以及分子量的溶解有机物光谱特征和来源进行分析.结果表明：周村水库不同暴雨荧光光谱中出现了5种组分，分别为类腐殖质（C1、C2）、可见区富里酸（C3）和类蛋白（C4、C5）；相关性分析显示C1与C2、C3、C4以及C5具有显著的相关性，C2与C3具有显著的相关性，C3与C4以及C5具有显著的相关性；同一分子量下的雨水有机质总荧光强度以及各组分荧光强度随着降雨历时的增加均呈下降趋势，并且在各个历时和分子量间差异明显；同一降雨历时下，第一场暴雨总荧光强度随着分子量的减少而增加，第二场暴雨总荧光强度随着分子量的减少而减少；两场暴雨都呈现自生源的特征，其中第一场暴雨具有以陆源输入为主的特征；组分C1和C3与水质参数硝态氮、氨氮、总氮以及有机碳呈显著相关性.通过对暴雨在不同降雨历时以及分子量DOM光谱特征研究，可以进一步分析水库外源输入的天然有机质特征，为水库水质管理提供技术支持.;Based on the three dimensional fluorescence spectra (EEMs) technology combined with the parallel factor analysis (PARAFAC), the spectral characteristics and sources analysis of dissolved organic matter of two rainstorms were investigated for different rainfall duration and molecular weight organic carbon in Zhoucun Reservoir. Two humic-like substances (C1, C2), one fulvic-like substance (C3) and two protein-like substance (C4, C5) were identified by PARAFAC model, and there exhibited significantly correlation coefficient in C1 & C2/C3/C4/C5, C2 & C3 and C3 & C4/C5, respectively. For the same molecular weight organic carbon, total dissolved organic matter (DOM) fluorescence intensity and the fluorescence intensity of each component showed a decreasing trend with the increase of rainfall duration and exhibited significantly differences distribution in two rainstorms. For the same rainfall duration, the total fluorescence intensity of the first rainstorm increased with the decrease of molecular weight organic carbon, while the total fluorescence intensity of the second rainstorm decreased with the decrease of molecular weight. The two rainstorms water both exhibited strong autochthonous component characteristics and first rainstorm exhibited strong terrestrial input characteristic; C1 and C3 exhibited significantly correlation coefficient with nitrate, ammonia, total nitrogen and organic carbon. From all the results, the study could supply a strong support for the managers of Zhoucun Reservoir to explore the DOM characteristic of rainstorm in the future.

Pathways of mineral-associated soil organic matter formation: Integrating the role of plant carbon source, chemistry, and point of entry.

To predict the behavior of the terrestrial carbon cycle, it is critical to understand the source, formation pathway, and chemical composition of soil organic matter (SOM). There is emerging consensus that slow-cycling SOM generally consists of relatively low molecular weight organic carbon substrates that enter the mineral soil as dissolved organic matter and associate with mineral surfaces (referred to as "mineral-associated OM," or MAOM). However, much debate and contradictory evidence persist around: (a) whether the organic C substrates within the MAOM pool primarily originate from aboveground vs. belowground plant sources and (b) whether C substrates directly sorb to mineral surfaces or undergo microbial transformation prior to their incorporation into MAOM. Here, we attempt to reconcile disparate views on the formation of MAOM by proposing a spatially explicit set of processes that link plant C source with MAOM formation pathway. Specifically, because belowground vs. aboveground sources of plant C enter spatially distinct regions of the mineral soil, we propose that fine-scale differences in microbial abundance should determine the probability of substrate-microbe vs. substrate-mineral interaction. Thus, formation of MAOM in areas of high microbial density (e.g., the rhizosphere and other microbial hotspots) should primarily occur through an in vivo microbial turnover pathway and favor C substrates that are first biosynthesized with high microbial carbon-use efficiency prior to incorporation in the MAOM pool. In contrast, in areas of low microbial density (e.g., certain regions of the bulk soil), MAOM formation should primarily occur through the direct sorption of intact or partially oxidized plant compounds to uncolonized mineral surfaces, minimizing the importance of carbon-use efficiency, and favoring C substrates with strong "sorptive affinity." Through this framework, we thus describe how the primacy of biotic vs. abiotic controls on MAOM dynamics is not mutually exclusive, but rather spatially dictated. Such an understanding may be integral to more accurately modeling soil organic matter dynamics across different spatial scales.

NOM-removal by the SIX®-process

Abstract Some waters can have elevated concentrations of dissolved organic carbon (DOC), especially sources like surface waters that are under the influence of secondary effluent, recreation, heavy population, farming and industry. In a number of locations in north-west Europe, for example the United Kingdom and Scandinavia, DOC levels are increasing over time, most likely due to climate change effects and changes in land use. For these types of water, ion exchange (IX) is of interest as a pre-treatment option because the removal of colour and DOC by IX will increase the efficiency of all downstream processes, including: coagulation, membrane filtration, advanced oxidation processes (AOP) and granular activated carbon filtration (GAC). It will also lead to improved water quality (i.e., less by-product formation) and most likely improvements in biostability within the distribution network. Surface waters also contain suspended and colloidal matter, making it nearly impossible to use standard state-of-the-art, fixed bed IX columns. This is because these beds will foul quickly (i.e., head loss build-up) with suspended matter. When this happens, the IX bed starts to function as a filtration bed rather than as an adsorption media. The newly developed suspended ion exchange process SIX® (suspended ion exchange, PWN Technologies, Netherlands) presents an advanced solution for a world-wide challenge: how to remove natural organic matter (NOM/DOC) as a first step in surface water treatment to improve the efficiency of downstream processes and water quality. In addition to the possibility to treat water that contains suspended matter, another advantage is that the process has advanced to an economically and technically feasible process, requiring low contact times and small resin inventories, with a large tolerance for flow fluctuations. Depending on the water source, adding a relatively low concentration of coagulant after IX removes even greater quantities of DOC, especially in the fraction of the high molecular weight organic carbon (whilst the IX primarily removed the humic and fulvic organic fractions). The most important advancement is that almost any commercially available resin can be used, creating the desired flexibility in resin suppliers for water supply companies. This paper describes the process and its advantages and disadvantages compared to conventional technologies. NOM-characterisation with size exclusion chromatography, liquid chromatography – organic carbon detection (SEC/LC-OCD) before and after this process showed the outstanding performance of the process, especially on water types which contain high colour/DOC-concentrations and low total dissolved solids, which are typical of the majority of the surface waters in the north-west of Europe.

Seasonal variation of potential denitrification rate and enhanced denitrification performance via water-lifting aeration technology in a stratified reservoir—A case study of Zhoucun reservoir

Zhoucun reservoir is one of the major water resources in Zao Zhuang city, northern China. The seasonal distribution of surface sediment denitrification rate and enhanced performance of denitrification via water-lifting aeration technology were explored using the acetylene-inhibition technique. Surface sediment denitrification rates ranged from 2.57 ± 1.32 to 923.90 ± 86.81 nmol N2/(g dw·h), with the highest rates in November (ANOVA, p < 0.05) and significantly low rates in June, July, and August (ANOVA, p < 0.05), mainly because of the seasonal differences in nitrate concentration, water temperature, and sediment total nitrogen (STN). Meanwhile, the N2/(N2+N2O) ratio (83.44–91.70% for the highest sediment denitrification period) indicated that N2 accounted for a majority of denitrification. Correlation analysis between various environmental factors and denitrification was conducted, and nitrate concentration, STN, low molecular weight organic carbon, the number of aerobic denitrifying bacteria, and the environmental parameters of oxidation-reduction potential (ORP), pH, electrical conductivity (EC), and chlorophyll a (Chl-a) presented significant relationships during the entire study period. On the basis of the multiple regression model, nitrate and low molecular weight organic carbon concentration were the most influential factors on denitrification variability. Moreover, the denitrification rates of the surface sediment clearly increased, from 5.28 to 13.22 nmol N2/(g dw·h) to 1117.02–3129.47 nmol N2/(g dw·h), which were higher than those in the non-operating year. This suggests that the denitrification in the sediment system could be enhanced in situ by water-lifting and aeration technology in the reservoir ecosystem.

Contrasting seasonality in optical-biogeochemical properties of the Baltic Sea.

Optical-biogeochemical relationships of particulate and dissolved organic matter are presented in support of remote sensing of the Baltic Sea pelagic. This system exhibits strong seasonality in phytoplankton community composition and wide gradients of chromophoric dissolved organic matter (CDOM), properties which are poorly handled by existing remote sensing algorithms. Absorption and scattering properties of particulate matter reflected the seasonality in biological (phytoplankton succession) and physical (thermal stratification) processes. Inherent optical properties showed much wider variability when normalized to the chlorophyll-a concentration compared to normalization to either total suspended matter dry weight or particulate organic carbon. The particle population had the largest optical variability in summer and was dominated by organic matter in both seasons. The geographic variability of CDOM and relationships with dissolved organic carbon (DOC) are also presented. CDOM dominated light absorption at blue wavelengths, contributing 81% (median) of the absorption by all water constituents at 400 nm and 63% at 442 nm. Consequentially, 90% of water-leaving radiance at 412 nm originated from a layer (z90) no deeper than approximately 1.0 m. With water increasingly attenuating light at longer wavelengths, a green peak in light penetration and reflectance is always present in these waters, with z90 up to 3.0–3.5 m depth, whereas z90 only exceeds 5 m at biomass < 5 mg Chla m-3. High absorption combined with a weakly scattering particle population (despite median phytoplankton biomass of 14.1 and 4.3 mg Chla m-3 in spring and summer samples, respectively), characterize this sea as a dark water body for which dedicated or exceptionally robust remote sensing techniques are required. Seasonal and regional optical-biogeochemical models, data distributions, and an extensive set of simulated remote-sensing reflectance spectra for testing of remote sensing algorithms are provided as supplementary data.

Enhancing microalgal biomass productivity by engineering a microalgal–bacterial community

This study demonstrates that ecologically engineered bacterial consortium could enhance microalgal biomass and lipid productivities through carbon exchange. Phycosphere bacterial diversity analysis in xenic Chlorella vulgaris (XCV) confirmed the presence of growth enhancing and inhibiting microorganisms. Co-cultivation of axenic C. vulgaris (ACV) with four different growth enhancing bacteria revealed a symbiotic relationship with each bacterium. An artificial microalgal–bacterial consortium (AMBC) constituting these four bacteria and ACV showed that the bacterial consortium exerted a statistically significant (P<0.05) growth enhancement on ACV. Moreover, AMBC had superior flocculation efficiency, lipid content and quality. Studies on carbon exchange revealed that bacteria in AMBC might utilize fixed organic carbon released by microalgae, and in return, supply inorganic and low molecular weight (LMW) organic carbon influencing algal growth and metabolism. Such exchanges, although species specific, have enormous significance in carbon cycle and can be exploitated by microalgal biotechnology industry.

Removal of total organic carbon (TOC) residues from power plant make-up water by activated carbon

Organic compounds decomposing in high temperature and pressure of a steam boiler plant water–steam cycle result in low molecular weight (LMW) organic acids and carbon dioxide. Subsequently a drop of pH value is observed in condensate which ultimately can cause corrosion. Organics may also contain for example chloride and release it to condensate. Thirdly decomposition products mask online cation conductivity measurements. This paper evaluates the use of activated carbon (AC) filtration as an option to remove the residues of organic compounds present in deionized make-up water. The experimental part was done using continuous flow bench scale AC filters (AC dry volume 3.75l, flow rate 25l/h, water temperature approximately 20°C) at a steam boiler desalination plant. Four commercial ACs were tested and all proved equally efficient removing approximately 42–45% of total and 58–68% of dissolved organic carbon after 30 days of operation. The most efficiently removed organic fractions were LMW neutral compounds, decomposition products of humic substances and hydrophobic compounds. Biopolymers were not effectively removed. Coconut shell based ACs leached more Ca, Mg and Na ions compared to coal based while for silica there were no differences. Pre-acid washing of ACs was efficient in reducing the initial leaching of impurities. However, the differences between acid washed and non-acid washed AC diminished with time. A mixed bed (MB) ion exchanger as a polishing treatment after AC filters is required to control the leaching of impurities.

Managing compost stability and amendment to soil to enhance soil heating during soil solarization

Soil solarization is a method of soil heating used to eradicate plant pathogens and weeds that involves passive solar heating of moist soil mulched (covered) with clear plastic tarp. Various types of organic matter may be incorporated into soil prior to solarization to increase biocidal activity of the treatment process. Microbial activity associated with the decomposition of soil organic matter may increase temperatures during solarization, potentially enhancing solarization efficacy. However, the level of organic matter decomposition (stability) necessary for increasing soil temperature is not well characterized, nor is it known if various amendments render the soil phytotoxic to crops following solarization. Laboratory studies and a field trial were performed to determine heat generation in soil amended with compost during solarization. Respiration was measured in amended soil samples prior to and following solarization as a function of soil depth. Additionally, phytotoxicity was estimated through measurement of germination and early growth of lettuce seedlings in greenhouse assays. Amendment of soil with 10%(g/g) compost containing 16.9mg CO2/gdry weight organic carbon resulted in soil temperatures that were 2–4°C higher than soil alone. Approximately 85% of total organic carbon within the amended soil was exhausted during 22days of solarization. There was no significant difference in residual respiration with soil depth down to 17.4cm. Although freshly amended soil proved highly inhibitory to lettuce seed germination and seedling growth, phytotoxicity was not detected in solarized amended soil after 22days of field solarization.