Dissolved Carbon Research Articles

Modelling Dissolved Organic Carbon Production in Coniferous Forest Soils

Core Ideas Mechanisms of DOC production affect the quantities and qualities of SOC and DOC. Three models with different physical and microbial processes were analyzed. Comparisons with experimental data provides no strong discrimination between models. The production of dissolved carbon (DOC) in forest soils is still not well understood as a result of difficulties in isolating co‐occurring processes. We have used an extension of the continuous‐quality theory to analyze the consequences of three modes for DOC production in coniferous forest soils: Model A, the production of DOC occurs through physical leaching of soil organic carbon (SOC) and the composition of DOC is proportional to the composition of SOC with respect to carbon (C) qualities; Model B, the production of DOC occurs when the decomposers use SOC and the composition of DOC will be proportional to the composition of SOC that decomposers extract; and Model C, the production of DOC is associated with mortality of decomposers and the composition of DOC reflects the composition of decomposer biomass. The results from Models B and C resemble each other but differ from Model A. Models B and C lead to a larger fraction of C being lost through leaching, a higher quality of the C leached, and a lower 14C age of the leached C than Model A. Models B and C differ with respect to properties of DOC leached from a horizon. All three models were found capable of describing stores of C in and leaching of DOC from an organic horizon and an underlying mineral soil in three temperate/boreal Norway spruce [Picea abies (L.) Karst.] forests. Microbial activity should always be an important agent for DOC production. Model B and, in particular, Model C suggest a lager contribution of microbially processed C in DOC than Model A.

Removal behaviors and mechanisms of hexavalent chromium from aqueous solution by cephalosporin residue and derived chars

Cephalosporin residue (CR) was used to produce biochar (BC) and activated carbon (AC) at 600°C (BC600 and AC600). To compare the removal behaviors and mechanisms of Cr(VI) by CR and derived chars, batch adsorption tests were performed in Cr(VI) microenvironment like pH, Cr(VI) concentration, adsorbent dosage, combing with the characterization of adsorbents before and after adsorption. Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and Brunauer-Emmett-Teller (BET) techniques were used. Results showed that the Cr(VI) removals by CR and CR-chars fitted Freundlich and Langmuir models. Based on the Langmuir model, the maximum adsorption capacities of CR, BC600 and AC600 towards Cr(VI) were 107.41, 88.19 and 74.07mgg−1, respectively. The CR rich in dissolved carbon (DOC), –NH2 and –COOH, chiefly acted as chelating and reducing agents, while the AC600 with high surface area mainly supported Cr(VI) adsorption during Cr(VI) removal process.

Vertical distribution of soil Fe in typical riparian subzones of the Sanjiang Plain

Sanjiang Plain, in which marshes occupy the largest area of fresh wetlands in China, has historically been considered a key Fe source of the Amur River and the Sea of Okhotsk. Since the 1950s, extensive human activity and wetland reclamation in the Sanjiang Plain has resulted in aggravating fragmentation of marshlands into different hydrological units. In the present study, soil samples were taken from typical riparian subzones of three representative marsh rivers of the Sanjiang Plain (Yalu River, Bielahong River and Naoli River), including the wetland near river (wetland-R), the wetland near cultivated land (wetland-C) and cultivated land. Soil samples from each riparian subzone were collected vertically every 20cm from surface to a depth of 1m and analyzed for total Fe, free Fe oxides, amorphous Fe oxides, acid-soluble Fe(II), water-soluble Fe(II), dissolved carbon (DOC), soil total organic carbon (TOC) and pH. The results showed that the soil total Fe in the 0–60cm layers increased in the sequence of wetland-R<wetland-C<cultivated land. On the contrary, the soil active ratio of Fe, water- and acid-soluble Fe(II) in the profile decreased in the sequence of wetland-R>wetland-C>cultivated land. These implied that the ability of Fe mobilization and export in the three river basins tended to decrease away from the river. DOC was positively correlated with acid-soluble Fe(II) while negatively correlated with total Fe, indicating that DOC might promote the production of acid-soluble Fe(II) and play a key role in export of Fe from riparian zones to adjacent waters. These findings will be useful to better understand the impacts of natural wetland reclamation in the Sanjiang Plain on the regional environment.

Photocatalytic Active Coatings for Lignin Degradation in a Continuous Packed Bed Reactor

The synthesis of immobilized catalyst on porous glass support material via the sol-gel route is reported. TiO2-P25-SiO2+ Pt, TiO2-P25-SiO2, TiOSO4_30.6 wt%, and ZnO + TiO2-P25-SiO2catalysts were synthesized and a comparative study is done regarding morphology of coatings, degradation rates, reaction rates, dissolved carbon (DC), formation of peaks, and fluorescence of products formed from the photocatalytic degradation of lignin sulfonate obtained from a local paper plant. Through simultaneous reaction-extraction pathways applying dialysis filtration and highly porous polystyrene divinylbenzene adsorbent resin (HR-P) for solid phase extraction (SPE), an attempt has been made to isolate smaller molecules produced from photocatalytic degradation. Moreover relatively high lignin sulfonate (0.5 g/L) concentrations are used in the reactions. UV-Vis spectroscopy revealed a faster reduction in the concentration values for the aliphatic moiety compared to the aromatic moiety. Peaks were observed by both fluorescence spectroscopy and HPLC suggesting the production of new substances and fluorophores.

Export of dissolved carbon from watersheds of the Central Siberian Plateau

The influence of climatic and forest conditions on space and time variations in the concentrations and export of two forms of dissolved carbon (DOC) and dissolved inorganic carbon (DIC) in rivers of the Central Siberian cryolithic zone (Yenisei River basin) draining territory characterized by relatively homogeneous composition of parent rocks was analyzed. Rivers of the northern (Tembenchi and Kochechum rivers), central (Nidym River), and southern parts (Lower Tunguska and Podkamennaya Tunguska rivers) of the Central Siberian Plateau traps were selected as objects of investigation. Along with growth of the water flow rate, increase in the productivity and reserves of carbon in the biogeocenosis of the cryolithic zone leads to significant (more than twice) increase in export of terrigenous DOC and DIC to the hydrographic network.

Rates, controls and potential adverse effects of nitrate removal in a denitrification bed

Denitrification beds are a simple approach for removing nitrate (NO 3 −) from a range of point sources prior to discharge into receiving waters. These beds are large containers filled with woodchips that act as an energy source for microorganisms to convert NO 3 − to nitrogen (N) gases (N 2O, N 2) through denitrification. This study investigated the biological mechanism of NO 3 − removal, its controlling factors and its adverse effects in a large denitrification bed (176 m × 5 m × 1.5 m) receiving effluent with a high NO 3 − concentration (>100 g N m −3) from a hydroponic glasshouse (Karaka, Auckland, New Zealand). Samples of woodchips and water were collected from 12 sites along the bed every two months for one year, along with measurements of gas fluxes from the bed surface. Denitrifying enzyme activity (DEA), factors limiting denitrification (availability of carbon, dissolved organic carbon (DOC), dissolved oxygen (DO), temperature, pH, and concentrations of NO 3 −, nitrite (NO 2 −) and sulfide (S 2−)), greenhouse gas (GHG) production – as nitrous oxide (N 2O), methane (CH 4), carbon dioxide (CO 2) – and carbon (C) loss were determined. NO 3 −-N concentration declined along the bed with total NO 3 −-N removal rates of 10.1 kg N d −1 for the whole bed or 7.6 g N m −3 d −1. NO 3 −-N removal rates increased with temperature ( Q 10 = 2.0). In laboratory incubations, denitrification was always limited by C availability rather than by NO 3 −. DO levels were above 0.5 mg L −1 at the inlet but did not limit NO 3 −-N removal. pH increased steadily from about 6 to 7 along the length of the bed. Dissolved inorganic carbon (C-CO 2) increased in average about 27.8 mg L −1, whereas DOC decreased slightly by about 0.2 mg L −1 along the length of the bed. The bed surface emitted on average 78.58 μg m −2 min −1 N 2O-N (reflecting 1% of the removed NO 3 −-N), 0.238 μg m −2 min −1 CH 4 and 12.6 mg m −2 min −1 CO 2. Dissolved N 2O-N increased along the length of the bed and the bed released on average 362 g dissolved N 2O-N per day coupled with N 2O emission at the surface about 4.3% of the removed NO 3 −-N as N 2O. Mechanisms to reduce the production of this GHG need to be investigated if denitrification beds are commonly used. Dissolved CH 4 concentrations showed no trends along the length of the bed, ranging from 5.28 μg L −1 to 34.24 μg L −1. Sulfate (SO 4 2−) concentrations declined along the length of the bed on three of six samplings; however, declines in SO 4 2− did not appear to be due to SO 4 2− reduction because S 2− concentrations were generally undetectable. Ammonium (NH 4 +) (range: <0.0007 mg L −1 to 2.12 mg L −1) and NO 2 − concentrations (range: 0.0018 mg L −1 to 0.95 mg L −1) were always very low suggesting that anammox was an unlikely mechanism for NO 3 − removal in the bed. C longevity was calculated from surface emission rates of CO 2 and release of dissolved carbon (DC) and suggested that there would be ample C available to support denitrification for up to 39 years. This study showed that denitrification beds can be an efficient tool for reducing high NO 3 − concentrations in effluents but did produce some GHGs. Over the course of a year NO 3 − removal rates were always limited by C and temperature and not by NO 3 − or DO concentration.

Bacterial Substrates and Productivity in Marine Ecosystems

The classic food pyramids in sea consist of a plant-microbial base nurtured by sunlight or debris, which is consumed by invertebrates, which in turn are eaten by carnivores. This food pyramid can be based on neustonic ecosystems at sea-air interface, on planktonic ecosystems living free in water, on epibiotic ecosystems attached to surfaces, or on benthic ecosystems within sea floor. As a result of feeding processes in and on each of these ecosystems, a very large amount of excrement is released into environment. As organisms are eaten and transformed from ingesta to feces or pseudofeces to sedimenting debris, or die to follow a similar fate, they form a fifth and often overlooked or misunderstood series of fecal-sestonic ecosystems. If it were not for bacteria which solubilize particulate matter and utilize soluble matter, and bacteria-eating protozoa and larger forms that feed upon them, waste products resulting from excretion, defecation, and death could be considered a loss to food pyramid (234). But bacteria and bacteria-eating forms are present in considerable numbers throughout lengths and depths of seas and occur as indispensable components in all five ecosystems. The bacterial-protozoan partnership that utilizes dissolved carbon (DOC) and particulate carbon (POC) is not separate from the mainstream of as believed by Strickland (234), but is a mechanism for keeping DOC and POC in mainstream of tropho-dynamics by connecting ecosystems and maintaining long-term steady state of life in sea. A detailed reevaluation of nature of suspended and sedimenting debris, also known as POC or seston, is needed because currently accepted notions may be incorrect and preventing development of more accurate working hypotheses. Evaluations of nature of POC in seawater (72, 185) assume that most of this material is produced from DOC that comes out of solution to form organic

In situ accumulation of marine algal exudate by a polychaete worm (Schizobranchia insignis)

For the first time, heterotrophic accumulation of dissolved carbon by a soft-bodied marine invertebrate under in situ conditions has been demonstrated. The polychaete wormSchizobranchia insignis Bush concentrated14C-labelled dissolved carbon (DC) exudated by the large brown alga,Macrocystis integrifolia Bory, 14 times over the killed controls. Our evidence suggests that algal exudate may be a significant nutritional supplement to some invertebrates cohabitating withM. integrifolia.