Microbial Community of a Hydrothermal Mud Vent Underneath the Deep-Sea Anoxic Brine Lake Urania (Eastern Mediterranean)

The composition of a metabolically active prokaryotic community thriving in hydrothermal mud fluids of the deep-sea hypersaline anoxic Western Urania Basin was characterized using rRNA-based phylogenetic analysis of a clone library. The physiologically active prokaryotic assemblage in this extreme environment showed a great genetic diversity. Most members of the microbial community appeared to be affiliated to yet uncultured organisms from similar ecosystems, i.e., deep-sea hypersaline basins and hydrothermal vents. The bacterial clone library was dominated by phylotypes affiliated with the epsilon-Proteobacteria subdivision recognized as an ecologically significant group of bacteria inhabiting deep-sea hydrothermal environments. Almost 18% of all bacterial clones were related to delta-Proteobacteria, suggesting that sulfate reduction is one of the dominant metabolic processes occurring in warm mud fluids. The remaining bacterial phylotypes were related to alpha- and beta-Proteobacteria, Actinobacteria, Bacteroides, Deinococcus-Thermus, KB1 and OP-11 candidate divisions. Moreover, a novel monophyletic clade, deeply branched with unaffiliated 16S rDNA clones was also retrieved from deep-sea sediments and halocline of Urania Basin. Archaeal diversity was much lower and detected phylotypes included organisms affiliated exclusively with the Euryarchaeota. More than 96% of the archaeal clones belonged to the MSBL-1 candidate order recently found in hypersaline anoxic environments, such as endoevaporitic microbial mats, Mediterranean deep-sea mud volcanoes and anoxic basins. Two phylotypes, represented by single clones were related to uncultured groups DHVE-1 and ANME-1. Thus, the hydrothermal mud of hypersaline Urania Basin seems to contain new microbial diversity. The prokaryotic community was significantly different from that occurring in the upper layers of the Urania Basin since 60% of all bacterial and 40% of all archaeal phylotypes were obtained only from mud fluids. The uniqueness of the composition of the active prokaryotic community could be explained by the complex environmental conditions at the site. The interaction of oxygenated warm mud fluids with the cold hypersaline brine of the Urania Basin seems to simultaneously select for various metabolic processes, such as aerobic and anaerobic heterotrophy, sulfide- and methane-dependent chemotrophy along with anaerobic oxidation of methane, sulfate- and metal-reduction.     

Impact of Anthropogenic Organic Matter on the Distribution Patterns of Sediment Microbial Community from the Yangtze River,China

Abstract

How microbes respond to substantial and increasing anthropogenic disturbance remains an open question in river systems. We tested the hypothesis that the source and distribution of anthropogenic organic matter (OM) were significant factors affecting the spatial variation of the microbial community composition of the Yangtze River sediments. Bulk geochemical proxies and lignin phenols suggested a general decrease of terrestrial C3 plants or soil OM input from the middle to the lower reaches. Fecal sterols inferred higher sewage contamination levels in the middle reaches. Polycyclic aromatic hydrocarbons (PAHs) distribution indicated a dominant biomass and coal combustion signal in the middle reaches, whereas a mixed source including petroleum combustion in the lower reaches. Phylogenetic analysis revealed a large portion of Methanobacteria and Verrucomicrobia enriched in the middle reaches, whereas OM-degrading bacteria, including Flavobacteria, Acidobacteria, and Alphaproteobacteria were dominant in the lower reaches. Quantitative PCR analyses and multivariate analysis further demonstrated that sources and distribution of OM had combined effects in shaping alpha and beta-diversity of sediment microbial communities. Sewage discharge and incomplete OM combustion, respectively, were associated with Methylococcaceae, Chloroflexi, and Bacteroidetes groups. This study provides a foundation for further understanding of the river sediment microbial composition, considering the continued increase of anthropogenic influences.     

Comparison of anaerobic and aerobic biodegradation of mineralized skeletal structures in marine and estuarine conditions

The knowledge of the biodegradation rates is essential to studies of the biogeochemistry and ecology of aquatic systems. It helps us to quantify the production and uptake rates of chemical components and their recycling, and to understand the mechanisms and rates of organic matter accumulation in sediments. Experimental studies of biodegradation processes in six types of mineralized skeletons were performed in shallow-marine waters of Calvi Bay, Corsica and in estuarine waters of Roscoff, Brittany. Three types of mollusk shells, sea urchin skeletal plates, crab cuticle and fish vertebrae were exposed to oxic and anoxic conditions over periods of 15 days to 30 months. After recovery of the substrates, protein assays, bacterial counts and organic carbon analyses were performed.Quantitative protein assays and bacterial counts indicate that biodegradation of mineralized skeletal structures occurs at a slower rate in anoxic conditions than in oxic conditions. Bacterial analysis showed that in anoxic environment, less than 0.5% of the consumed organic matter is converted into bacterial biomass. The aerobic biodegradation rate was positively correlated with the organic content of the skeletons.Anoxic biodegradation of skeletons occurred at much slower rates in estuarine sediments than in shallow marine sediments. Preservation of skeletal structures in estuarine conditions appears to be correlated with the abundance of dissolved organic matter rather than with high sedimentation rates.     

Organic Carbon Degradation in Anoxic Organic-Rich Shelf Sediments: Biogeochemical Rates and Microbial Abundance

Identifying and explaining bottlenecks in organic carbon mineralization and the persistence of organic matter in marine sediments remain challenging. This study aims to illuminate the process of carbon flow between microorganisms involved in the sedimentary microbial food chain in anoxic, organic-rich sediments of the central Namibian upwelling system, using biogeochemical rate measurements and abundances of Bacteroidetes, Gammaproteobacteria, and sulfate-reducing bacteria at two sampling stations. Sulfate reduction rates decreased by three orders of magnitude in the top 20 cm at one sampling station (280 nmol cm^?3 d^?1 – 0.1 nmol cm^?3 d^?1) and by a factor of 7 at the second station (65 nmol cm^?3 d^?1 – 9.6 nmol cm^?3 d^?1). However, rates of enzymatic hydrolysis decreased by less than a factor of three at both sampling stations for the polysaccharides laminarin (23 nmol cm^?3 d^?1– 8 nmol cm^?3 d^?1 and 22 nmol cm^?3 d^?1– 10 nmol cm^?3 d^?1) and pullulan (11 nmol cm^?3 d^?1– 4 nmol cm^?3 d^?1 and 8 nmol cm^?3 d^?1– 6 nmol cm^?3 d^?1). Increasing imbalance between carbon turnover by hydrolysis and terminal oxidation with depth, the steep decrease in cell specific activity of sulfate reducing bacteria with depth, low concentrations of volatile fatty acids (less than 15 μM), and persistence of dissolved organic carbon, suggest decreasing bioavailability and substrate limitation with depth.     

Seasonal Variability of Particulate Organic Matter in a Mountain Stream in Central Spain

The aim of this paper was to study the influence of environmental characteristics of the Mediterranean climate on seasonal variability of particulate organic matter abundance in a mountain stream. Coarse and fine fractions of both suspended and benthic particulate organic matter were determined on 14 occasions between February 1998 and November 1999 in a second‐order Mediterranean stream in Central Spain (Arroyo Mediano). Temporal variability of suspended organic matter followed a seasonal pattern, attributed to litter‐fall inputs, instream processing, and the hydrological regime. Suspended organic matter (SOM) and its seasonal variability fall well within the range reported for streams in temperate non‐Mediterranean deciduous forest. However, we found no seasonal trend in benthic organic matter (BOM) storage, and it seems that the amount of BOM remained fairly constant throughout the year. Reach retention (evaluated as the ratio between BOM and SOM per m²) was higher in summer during reduced stream flow, mainly due to coarse particulate organic matter storage. These observations do not differ from those reported for other headwater streams in temperate forested biomes, from which we conclude that there was no evidence of a Mediterranean influence on particulate organic matter dynamics in the Mediano stream, nor probably in other headwater Mediterranean streams. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Transformation of Organic Matter by a Microbial Community in Sediments of Lake Baikal under Experimental Thermobaric Conditions of Protocatagenesis

Early diagenesis of organic matter in bottom sediments of Lake Baikal is a focus of many geochemical studies, because it is one of the few sites of petroleum formation in a nonmarine environment. Although Baikal is a rift lake and considered one of the prospective fields for deep biosphere investigations, the transformation processes of organic matter by microbial communities from deep bottom sediments and likely entering of the microorganisms from deep sediments into the near-surface sediments were not previously studied in Lake Baikal. The natural microbial community from near-surface sediments of the cold methane seep Goloustnoe (Southern Baikal Basin) was incubated with methane and the diatom Synedra acus at 80°C and 49.5 atm to simulate catagenesis. The 11-month incubation yielded the enrichment culture of viable thermophilic microorganisms. Their presence in low-temperature sediment layers may be indicative of their migration through fault zones together with gas-bearing fluids. After culturing, molecular biological methods allowed for the detection of both widespread microorganisms and unique clones whose phylogenetic status is currently unknown. The sediment after the experiment showed the formation of polycyclic aromatic hydrocarbon, retene. Retene can be either a conifer or algal biomarker, thus, interpretation of paleoclimate data is tenuous.     

Bacterial Activity and Preservation of Sedimentary Organic Matter: The Role of Exopolymeric Substances

Although exopolymeric substances (EPS) are associated with the microorganisms contributing to the production/degradation of sedimentary organic matter, their role in theses processes have so far never been mentioned. Using high-resolution microscopical tools (scanning and transmission electron microscopy, atomic force microscopy), fossil organic matter in the Miocene Monterey Formation (California) and Kimmeridgian laminites (France) has been compared with its present-day analogs, i.e., respectively sulphuroxidizing bacteria and cyanobacterial biofilms. This comparison shows that, particularly in the case of Kimmeridgian cyanobacterial mats deposited in a shallow back-reef environment, organic matter preservation is conditioned by exopolymeric substances secreted by bacteria. A model is proposed for the evolution through time of exopolymeric substances in relation to the mechanical constrains they have been exposed to, during lithification and diagenesis. This model is based on the microscopical observation of sulphuroxidizing bacteria and could explain the morphology of fossil organic matter usually referred to as “amorphous” in standard light microscopy. The highly hydrated nature of exopolymeric substances helps to protect organic matter from degradation and remineralization. These substances can be observed only in microscopy and are undetectable through organic geochemical methods, hence the need to combine these two methods in organic matter studies. Consequently, exopolymeric substances must be considered as an important contributing agent to organic matter preservation. These results confirm the complexity of the bacterial role in geoenvironments and add a new parameter in the productivity-vs-preservation debate.     

Sources and Contamination of Heavy Metals in Sediments of Kabul River: The Role of Organic Matter in Metals Retention and Accumulation

In this study, sediment samples were collected from Kabul River (Pakistan) and analyzed for heavy metals including zinc (Zn), cadmium (Cd), chromium (Cr), nickel (Ni) and lead (Pb). The physico-chemical characteristics were also determined which are known to influence the metal accumulation within the sediment matrix. Heavy metal concentrations (mg kg^?1, dry weight basis) in the sediment were in the order of Zn > Cr > Ni > Pb > Cd. Heavy metal concentrations were found in moderately polluted category set by U. S. Environmental Protection Agency (USEPA). However, Cr and Ni concentrations exceeded the screening levels at the sites where a larger volume of industrial effluents enter into Kabul River. Higher concentrations of almost all the tested metals were detected at locations of greater industrial and sewage entry points. Sediment organic matter (OM) exhibited strong correlation with Pb (R² = 0.80), Ni (R² = 0.67) and Zn (R² = 0.46), indicating that OM plays a significant role in metal retention and accumulation. The findings of this study showed that Kabul River is reasonably contaminated with selected heavy metals released from anthropogenic sources. In the study area, sewage discharge was the major source of heavy metals including Zn and Pb, which were observed at locations where sewage effluents enter into the river.     

土壤有机质和外源有机物对甲烷产生的影响

对土壤有机质含量及组分、外源有机物和根系分泌对甲烷产生的影响作了综述。土壤产甲烷量和甲烷排放量随有机质含量增加而提高,与土壤中易矿化有机碳或沸水浸提有机碳含量呈显著相关。外源有机碳加入促进了土壤排放甲,刺激效果与外源有机碳的用量和组成有关。还原力强的有机物如纤维素和半纤维素较还原力弱的有机物如类脂和多糖能够产生更多的甲烷。甲醇、甲基化氨基酸等无其它微生物竞争利用的有机物能被产甲烷菌更多地转化成甲烷。植物根系分泌物也促进甲烷的产生,促进作用大小与植物种类及分泌物的数量和质量有关。外源有机物通过3种方式促进土壤甲烷产生;提高土壤的甲烷底物供应量,降低土壤氧化还原电位,刺激土壤原有有机碳的转化。     

Sources of Lipids in Anoxic Lacustrine Sediments Using Stable Carbon Isotopes

The origin of organic matter in recent anoxic sediments of the alpine Lake Bled (NW Slovenia) was determined by analyzing the carbon isotope composition of lipid biomarkers, i.e. alkanes, alcohols, sterols and fatty acids, busing compound specific, carbon isotope analysis. The results indicate that, although biomarker analysis indicated mostly plankton and terrestrial sources for lipids, an important part of sedimentary lipids, especially sterols, are autochthonous, of anaerobic microbial (methanotrophic) origin. Marked differences were observed in δ¹³C values of lipid biomarkers in settling particles collected 2 m above the bottom, and in δ¹³C values determined in surface sediment. These results indicate that even some compounds found in both particulate organic matter and sediments are the same in terms of chemical structures, their sources can be different and thus, isotopic composition should be used as a complementary tool for source identification.     

Chemical Characteristics and Origin of Dissolved Organic Matter in the Yukon River

Monthly (or bi-weekly) water samples were collected from the Yukon River, one of the largest rivers in North America, at a station near the US Geological Survey Stevens Village hydrological station, Alaska from May to September 2002, to examine the quantity and quality of dissolved organic matter (DOM) and its seasonal variations. DOM was further size fractionated into high molecular weight (HMW or colloidal, 1 kDa–0.45 μm) and low molecular weight (LMW, <1 kDa) fractions. Dissolved organic carbon (DOC), colored dissolved organic matter (C-DOM) and total dissolved carbohydrate (TCHO) species were measured in the size fractionated DOM samples. Concentrations of DOC were as high as 2830 μmol-C l⁻¹ during the spring breakup in May and decreased significantly to 508–558 μmol-C l⁻¹ during open-water season (June–September). Within the DOC pool, up to 85% was in the colloidal fraction (1 kDa–0.45 μm) in early May. As DOC concentration decreased, this colloidal portion remained high (70–85% of the bulk DOC) throughout the sampling season. Concentrations of TCHO, including monosaccharides (MCHO) and polysaccharides (PCHO), varied from 722 μmol-C l⁻¹ in May to 129 μmol-C l⁻¹ in September, which comprised a fairly constant portion of bulk DOC (24±2%). Within the TCHO pool, the MCHO/TCHO ratio consistently increased from May to September. The C-DOM/DOM ratio and the size fractionated DOM increased from May to September, indicating that DOM draining into the Yukon River contained increased amounts of humified materials, likely related to a greater soil leaching efficiency in summer. The average composition of DOM was 76% pedogenic humic matter and 24% aquagenic CHO. Characteristics of soil-derived humic substances and low chlorophyll-a concentrations support a dominance of terrestrial DOM in Yukon River waters.     

Bacterial Degradation of Dissolved Organic Matter from Two Northern Michigan Streams

This study used high-pressure size exclusion chromatography (HPSEC) to measure the changes in molecular weight distributions of dissolved organic matter (DOM) of two Northern Michigan streams following inoculation with bacterial concentrates from the same locations. During the initial 12 h of the experiment, weight average molecular weight (M _w ) of DOM decreased, as high molecular weight components were lost from solution. After 12 h, the M _w of DOM increased, primarily because of a loss of intermediate to lower molecular weight components. Leucine incorporation showed little or no bacterial metabolism during the first 12 h, but metabolism increased substantially after 12 h. The initial loss of high molecular weight components during the period of little or no bacterial metabolism suggests preferential adsorption of these components to the bacterial surfaces, perhaps followed by metabolism. This suggested interpretation is consistent with previous observations of preferential adsorption of higher molecular weight components to viable but non-metabolizing Bacillus subtilis and to mineral surfaces. The latter loss of lower molecular weight components was most likely due to bacterial metabolism of the DOM, which is consistent with previous observations that lower molecular weight components are more biodegradable. The HPSEC technique uses 254 nm wavelength for detection and focuses primarily on humic- and fulvic-type components rather than low molecular weight organic molecules, such as carbohydrates. Thus, results confirmed that humic/fulvic components are biodegradable, but did not address other DOM components.     

Hydroxyl Radical Production from Irradiated Arctic Dissolved Organic Matter

The hydroxyl radical (OH·) plays an important role in the environmental chemistry and biogeochemistry of surface waters. OH· acts as a strong oxidant within the irradiated water column, and affects the bioavailability, cycling, and mineralization of dissolved organic matter (DOM), the speciation and redox state of important trace metals e.g., iron and copper, and the fate of persistent organic pollutants (POPs). The generation of this species from irradiated DOM may be especially important in Arctic surface waters during the boreal summer, which contains high levels of DOM and experiences continual solar irradiance. Here, we investigate the OH· produced from laser irradiated Arctic DOM isolated from Toolik Lake, AK (68°38′ N, 149°43′ W). We measured the wavelength dependence of OH· production for aqueous solutions of DOM and report that the greatest OH· production occurs at wavelengths less than 360 nm. OH· production rates ranged from 1.7 (±0.1)×10⁻⁷ M h⁻¹ to 6.4 (±0.2)×10⁻⁷ M h⁻¹, with the rate depending on both irradiation wavelength and to a lesser degree the method used to isolate the DOM matrix. These findings lead to a better understanding of the potentially important photo-oxidation processes that may impact DOM cycling in the Arctic.     

Microbial Response to Organic Matter Enrichment in the Oligotrophic Levantine Basin (Eastern Mediterranean)

The response of a deep-water benthic microbial community to organic matter (OM) enrichment was studied in the unexplored region of the SW Cretan margin (E. Mediterranean). A food pulse of 0.5 g C m^?2 was simulated by adding ¹³C-labelled diatoms to sediment cores retrieved from 1079 m depth. The diatom addition resulted in a significant increase in the sediment community oxygen consumption (SCOC). After 6 days, ～50 mg C m^?2 of the added material was processed by the microbial community. The major carbon sink was respiration, which accounted for ～96% of the total processed material. The carbon uptake rate (12 mg C m^?2 d^?1) was considerably lower than previously published values in the E. Mediterranean at similar depths. The microbial community in our study site is distinct, as revealed by the unusually high presence of branched phospholipid fatty acids (PLFA). Previous studies have revealed that the slope under investigation may act as a conduit of OM from the shallow shelf to the deep basins, resulting in the prevalence of relatively refractory OM at mid-slope depths. We postulate that sedimentary processes affect the amount of bioavailable sedimentary OM and consequently the structure and physiological state of bacterial community in our study site. The distinct microbial community composition at our station compared to more stable adjacent slopes could explain the limited response of the microbial community to the addition of labile OM. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental file.     

Interactions between Carbon and Nitrogen Mineralization and Soil Organic Matter Chemistry in Arctic Tundra Soils

We used long-term laboratory incubations and chemical fractionation to characterize the mineralization dynamics of organic soils from tussock, shrub, and wet meadow tundra communities, to determine the relationship between soil organic matter (SOM) decomposition and chemistry, and to quantify the relative proportions of carbon (C) and nitrogen (N) in tundra SOM that are biologically available for decomposition. In all soils but shrub, we found little decline in respiration rates over 1 year, although soils respired approximately a tenth to a third of total soil C. The lack of decline in respiration rates despite large C losses indicates that the quantity of organic matter available was not controlling respiration and thus suggests that something else was limiting microbial activity. To determine the nature of the respired C, we analyzed soil chemistry before and after the incubation using a peat fractionation scheme. Despite the large losses of soil C, SOM chemistry was relatively unchanged after the incubation. The decomposition dynamics we observed suggest that tundra SOM, which is largely plant detritus, fits within existing concepts of the litter decay continuum. The lack of changes in organic matter chemistry indicates that this material had already decomposed to the point where the breakdown of labile constituents was tied to lignin decomposition. N mineralization was correlated with C mineralization in our study, but shrub soil mineralized more and tussock soil less N than would have been predicted by this correlation. Our results suggest that a large proportion of tundra SOM is potentially mineralizable, despite the fact that decomposition was dependent on lignin breakdown, and that the historical accumulation of organic matter in tundra soils is the result of field conditions unfavorable to decomposition and not the result of fundamental chemical limitations to decomposition. Our study also suggests that the anticipated increases in shrub dominance may substantially alter the dynamics of SOM decomposition in the tundra. Received 31 January 2002; accepted 16 July 2002.     

森林凋落物淋溶中的溶解有机物与紫外-可见光谱特征

对格氏栲(Castanopsis kawakamii)和杉木(Cunninghamia lanceolat)人工林新近凋落物、半分解层(F层)和分解层(H层)凋落物进行室内模拟淋洗实验,研究了凋落物淋溶过程中溶解有机碳(DOC)浓度变化及紫外-可见(UV-Vis.)光谱特征.结果表明,格氏栲和杉木人工林新近凋落物淋出液的DOC浓度较低,F层淋出液的DOC浓度较高;格氏栲凋落物淋出液的DOC浓度基本上随淋溶次数的增加而降低,杉木的则先升后降.淋出液中溶解有机物(DOM)的紫外吸收值均随波长的增加而减小,且UV-Vis.吸收曲线均在200nm附近出现吸收峰,不同来源DOM的E240/E420存在显著差异;同一样品各次淋出液的DOC浓度与E200有很好的线性关系(P2＞0.90),据此,可用E200值估算DOC浓度.     

Estimation of Standing Stock and Decomposition Rates of Labile Organic Matter in Waters of Novorossiisk Bay,Black Sea

The annual dynamics of the decomposition rate, standing stock, and residence time of labile organic matter as an index of full self-purification were investigated in Novorossiisk Bay, Black Sea. The results are suggestive of fairly effective processes of biological self-purification in polluted waters of the bay. The decomposition rate was highest (0.3–0.7 mgO₂/l per day) during the summer, and it decreased by 4–8 times in winter. The residence time of labile organic matter was 97–104 days in winter and 8–11 days in summer. Oxygen consumption rates measured in different areas of the bay conformed to their trophic status and were not above the normal level for summer.     

Microbial destruction of organic matter in the bottom sediments of Lithuanian lakes

The rates of the processes of bacterial sulfate reduction (SR) and total destruction of organic matter (D_total) were studied in the bottom sediments (BS) of 14 lakes in Lithuanian national and regional parks in the summers of 1998–2002. Anaerobic processes accounted for an average of 92% of D_total in the depressions of deep-water lakes; for the sediments of shallow lakes, high rates of oxygen uptake were noted. The SR rate in different lakes varied from 0.09 to 2.60 mg S^2?/(dm³ day). At low sulfate concentrations (13.3–70.6 mg S-SO ₄ ^2? /dm³), characteristic of the BS of freshwater ecosystems, the main factor that affected the SR rate in the BS of the lakes studied was the content of readily available organic matter; only in special cases, was it affected by a change in the sulfate ion concentration. In shallow lakes, temperature-dependent activation of sulfate-reducing bacteria and their inhibition by acidification of the environment were recorded. The contribution of SR to D_total was 0.2 to 11.0%.     

Characteristics of Soil Organic Matter and Sorption of Phenanthrene,Naphthalene 1,3,5-TCB and o-Xylene

Nonlinear isotherm behavior has been reported for the sorption of hydrophobic organic compounds (HOCs) in soil/water systems, but the mechanisms are unclear. The model of “soft” and “hard” carbon domains has been extensively cited in the sorption literature to account for nonlinear sorption behaviors, but the structural compositions of soil organic matter (SOM) are not well understood. The objective of this study was to examine the characteristics of SOM and the effect of SOM heterogeneity on sorption isotherm by elemental analysis, organic petrographic examination, scanning electron microscopy, ¹³C nuclear magnetic resonance and studying the sorption behaviors of phenanthrene, naphthalene, 1,3,5-trichlorobenzene and o-xylene in soil and its isolated fractions, humic acid (HA) and humin (denser particulates and lighter particulates). DP mainly contained low maturation and high paraffinic carbon huminite. LP was composed of inertinite, huminite, vitrinite and exinite, with smaller particle size and higher maturation than DP. Humic acid approached the lignite coal rank.

All isotherms were nonlinear, and nonlinearity increased in the following order: HA > DP > soil > BE > LP. The sorption of HOCs in soil was primarily regulated by SOM. Humic acid seemed to be the soft carbon domain and insoluble condensed organic matter (humin) the hard carbon domain. Isotherm nonlinearity was negatively correlated with hydrophobicity and molecular size, while sorption capacity increased with increase of these parameters. Aliphatic structures of SOM, as observed for LP, could also contribute to both isotherm nonlinearity and large sorption capacity.     

人工湿地运行过程中有机物质的积累

研究了杭州西湖边人工湿地污水净化生态工程经一年多运行后有机质的积累情况,同时测定了基质的孔隙度和水力传导性,结果表明,人工湿地在运行一年后总有机质积累达到0.658kg/m^2,60%有机质积累主要在0-100mm。湿地上,下池有机质积累有明显差异。且随着基质中的深度和离入水口的距离都呈下降趋势。两池中下层孔隙度均高于上层,并存在显著差异。有机质积累对水力传导性和净化效果均有一定影响,可通过定期收割植物和清除枯落物来维持湿地的长期运作能力。