Percentage Of Dissolved Organic Carbon Research Articles

Sources of dissolved organic carbon in forest soils: evidences from the differences of organic carbon concentration and isotope composition studies

There is considerable discussion and uncertainty in the literature regarding the importance of fresh litter versus older soil organic matter as sources of soil dissolved organic carbon (DOC) in forest floor. In this study, the differences of organic carbon concentration and stable isotope composition were analyzed under different background conditions to identify the origins of DOC in forest soil. The data show that there is no significant difference in SOC content between these collected soil samples (P > 0.05), but the litter-rich surface soils have relatively higher DOC concentration than the litter-lacking (P < 0.01) ones, and the δ 13C values of DOC (δ 13CDOC) are closer to δ 13C of litter than δ 13C values of SOC (δ 13CSOC). In the litter-lacking surface soil samples, the range of δ 13CDOC is between δ 13CSOC and δ 13C of dominant plant leaves. These results suggest that DOC mainly derive from litter in the litter-rich surface soil with, and the main path of DOC sources may change with surrounding conditions. In addition, δ 13CSOC and δ 13CDOC become more positive, and the absolute values of Δ (δ 13CDOC − δ 13CSOC) decrease with depth in the soil profiles, which indicate that the percentage of DOC below 5 cm, derived from degradation of humus, may increase with soil depth.

Characterization of dissolved organic matter (DOM) removed by iron coagulation using spectrofluorimetry and pyrolysis GC/MS analysis

In this study, coagulation experiments were conducted using three coagulants (ferric chloride (FC), poly ferric sulfate (PFS) and poly aluminum chloride (PAC)) to evaluate DOM (dissolved organic matter) removal performance in lake water. DOM removal was characterized not only by comprehensive indices such as dissolved organic carbon (DOC) and UV absorbance at 260 nm (UVA 260 ) but also by spectrofluorimetry and pyrolysis gas chromatography/mass spectrometry (py-GC/MS) analysis, which are useful techniques to obtain information on the structure of organic matter. At a coagulant concentration of 0.3 mM, a higher percentage of DOC was removed by ferric coagulants than by the aluminum coagulant (FC: 53%, PFS: 41%, PAC: 36%). Similar trends were observed in the coagulation-induced decrease of UVA 260 and trihalomethane formation potential (THMFP). Spectrofluorimetry showed that higher concentrations of coagulant increased the removal of DOM with fluorescence components. However, fluorescence intensity was not reduced by increased coagulant concentrations at emission wavelengths shorter than 350 nm. Treatments with ferric coagulants were more effective in removing fluorescent components than PAC. Comparison of pyrochromatograms before and after coagulation revealed that the peak area of propanoic acid decreased most significantly after coagulation by FC among 16 identified fragment compounds. Four fragment compounds differed greatly in their coagulation behaviour, depending on the coagulant used.

Dynamic behaviour of river colloidal and dissolved organic matter through cross-flow ultrafiltration system

Through cross-flow filtration (CFF) with a 1-kDa regenerated cellulose Pellicon 2 module, the ultrafiltration characteristics of river organic matter from Longford Stream, UK, were investigated. The concentration of organic carbon (OC) in the retentate in the Longford Stream samples increased substantially with the concentration factor ( cf), reaching approximately 40 mg/L at cf 15. The results of dissolved organic carbon (DOC) and colloidal organic carbon (COC) analysis, tracking the isolation of colloids from river waters, show that 2 mg/L of COC was present in those samples and good OC mass balance (77–101%) was achieved. Fluorescence measurements were carried out for the investigation of retentate and permeate behaviour of coloured dissolved organic materials (CDOM). The concentrations of CDOM in both the retentate and permeate increased with increasing cf, although CDOM were significantly more concentrated in the retentate. The permeation model expressing the correlation between log [CDOM] in the permeate and log cf was able to describe the permeation behaviour of CDOM in the river water with regression coefficients ( r 2 ) of 0.94 and 0.98. Dry weight analysis indicated that the levels of organic colloidal particles were from 49 to 71%, and between 29 and 51% of colloidal particles present were inorganic. COC as a percentage of DOC was found to be 10–16% for Longford Stream samples.

Influence of eutrophication on the coagulation efficiency in reservoir water

Water from the three reservoirs, Min-ter, Li-yu-ten and Yun-ho-shen, was examined for concentration of chlorophyll a, ultraviolet absorption (UV 254), fluorescence intensity (FI), concentration of dissolved organic carbon (DOC), and fractionation of dissolved molecules by molecular weight. The water samples were collected over the change from spring to summer (May to July but before the typhoon season) when the water temperature and extent of eutrophication increase. Analytical results indicate that the concentration of DOC is proportional to the concentration of chlorophyll a, but not to the values of UV 254 and FI. Therefore, eutrophication, extraneous contaminants of small molecules, and the extracellular products of algae cause an increase in DOC, but a decrease in the proportion of large organic molecules such as of humic substances. The fraction of DOC with a molecular weight of less than 5000 Da increases with the concentration of chlorophyll a. All these data suggest that changes in the quality of water after eutrophication make the treatment of drinking water more difficult. The method of enhanced coagulation was recently developed for removing DOC. However, the results of this paper demonstrate that the efficiency of DOC removal falls as the degree of eutrophication increases. When the percentage of DOC with small molecules excreted by algae increased by 1%, the efficiency of DOC removal decreased by approximately 1%, implying that enhanced coagulation are not able to remove the DOC excreted by the algae during eutrophication, and resulting an increased concentration of trihalomethanes formation in water disinfections process.

Transport and fate of dissolved organic carbon in the Lake Pontchartrain estuary, Louisiana, U.S.A.

Cycling dynamics of dissolved organic carbon (DOC) were examined in Lake Pontchartrain estuary, Louisiana, in relation to changes in freshwater inputs. DOC concen- trations ranged from 5.3 to 8.5 mg C L-' reaching their highest during high river inflow. The percentage of DOC represented by HMW DOC (or colloidal material) was greatest (ca. 11%) at stations where freshwater discharge from rivers and surrounding wetlands was most significant. Moreover, the lignin-phenol content of this material (A ranged from 0.09 to 0.33 and A from 0.11 to 0.39) confirmed that a significant fraction of colloidal organic carbon was derived from terrestrial sources. Riverine and benthic fluxes represented the dominant sources of DOC to the estuary. On an annual basis, riverine and benthic DOC concentrations were estimated to be 2.8 x 1010 g C yr-' and 8.8 x 1010 g C yr-', respectively, while the total DOC pool in the estuary was 3.8 x 1010 g C. Annual average concentrations of dissolved inorganic carbon (DIC) (1298 /iM) and pCO2 (5774 /iatm) were comparable to those found in other freshwater systems that reached CO2 saturation levels. Net losses of DOC in the Lake Pontchartrain estuary appeared to be primarily controlled by heterotrophic consumption (con- version of CO2) - which may have been amplified by the long residence time (approximately 120 days) of DOC in this system.

Copper Speciation and Binding by Organic Matter in Copper-Contaminated Streamwater

Fulvic acid binding sites (1.3−70 μM) and EDTA (0.0017−0.18 μM) accounted for organically bound Cu in seven stream samples measured by potentiometric titration. Cu was 84−99% organically bound in filtrates with 200 nM total Cu. Binding of Cu by EDTA was limited by competition from other trace metals. Water hardness was inversely related to properties of dissolved organic carbon (DOC) that enhance fulvic acid binding: DOC concentration, percentage of DOC that is fulvic acid, and binding sites per fulvic acid carbon. Dissolved trace metals, stabilized by organic binding, occurred at increased concentration in soft water as compared to hard water.