Phytoavailability of phosphate adsorbed on ferrihydrite,hematite, and goethite

Poorly crystalline Fe in soil has been shown to affect Fe and P availability. Oxalate extractable Fe, a measure of poorly crystalline Fe oxides, has not been compared to soil test methods for Fe and P in rice soils. Twenty eight soils used for rice production were incubated under aerobic and anaerobic soil conditions and extracted for Fe and P with ammonium oxalate, ammonium acetate-EDTA (AA-EDTA), ammonium bicarbonate-DTPA (AB-DTPA) and DTPA. Citrate-dithionite extractable Fe and Fe content of rice plants in a greenhouse experiment were also determined. Soils used in this experiment had a large amount of poorly-crystalline Fe oxide. In some soils, poorly-crystalline Fe constituted 60% of the citrate-dithionite extractable Fe. The amount of extractable Fe and P increased significantly under anaerobic conditions. The relationships between extractants showed that DTPA Fe was highly correlated to AB-DTPA Fe and oxalate Fe was highly correlated to AA-EDTA Fe. There was no relationship between Fe and P extracted by AB-DTPA, while there was a better relationship with ammonium oxalate and AA-EDTA extractants. Poorly-crystalline Fe and P extracted by ammonium oxalate were correlated.     

Cadmium sorption by bacteria and freshwater sediment

Summary Sorption of cadmium by sediment bacteria and freshwater sediment was investigated using diffusion chambers to simulate the water-sediment interface. Diffusion chambers were constructed to provide two compartments separated by a dialysis membrane. Diffusion of cadmium across the membrane was monitored after pure cultures of sediment bacteria or lake sediments were added to the sediment side of a diffusion chamber. Cellular accumulation of cadmium by cadmium-sensitive and cadmium-resistant bacteria removed between 20% and 80% of the dissolved cadmium from the simulated water column and pore water. Cellular accumulation of cadmium was greatest for cadmium-sensitive isolates that were tested. Sediment with an intact microbial community sequestered 80% of the cadmium added to sediment, whereas autoclaved sediment retained 97% of the metal that was added. Addition of glucose to cadmium-amended sediment decreased retention of cadmium by untreated and autoclaved sediments, resulting in elevated concentrations of dissolved cadmium in the simulated water column.     

Mobilization of sediment phosphorus by submersed freshwater macrophytes

SUMMARY. The mobilization of sediment phosphorus (P) by three submersed freshwater macrophyte species was investigated on five different sediments. The study was conducted under controlled environmental conditions in lucite columns that enabled the separation of sediment and plant roots from the overlying P-free 'complete' nutrient solution. The species investigated ( Egeria densa, Hydrilla verticillata , and Myriophyllum spicatum ) had minor root systems (on a biomass basis), but were demonstrated to be fully capable of deriving their P nutrition exclusively from the sediments. Phosphorus absorption and translocation into shoots (i.e., mobilization) was substantial, and in some cases suggested a greater than 1000-fold turnover of interstitial water PO₄-P over a 3-month period. Sediment P mobilization, a function of both plant growth and tissue P concentration, differed considerably among plant species and sediments. Phosphorus release from the species investigated appears to be primarily dependent upon tissue decay rather than excretory processes. The mobilization of sediment P by submersed macrophytes represents an important aspect of the P cycle, and may affect the overall metabolism of lacustrine systems.     

Limited influence of Si on the preservation of Fe mineral‐encrusted microbial cells during experimental diagenesis

The reconstruction of the history of microbial life since its emergence on early Earth is impaired by the difficulty to prove the biogenicity of putative microfossils in the rock record. While most of the oldest rocks on Earth have been exposed to different grades of diagenetic alterations, little is known about how the remains of micro‐organisms evolve when exposed to pressure (P) and temperature (T) conditions typical of diagenesis. Using spectroscopy and microscopy, we compared morphological, mineralogical, and chemical biosignatures exhibited by Fe mineral‐encrusted cells of the bacterium Acidovorax sp. BoFeN1 after long‐term incubation under ambient conditions and after experimental diagenesis. We also evaluated the effects of Si on the preservation of microbial cells during the whole process. At ambient conditions, Si affected the morphology but not the identity (goethite) of Fe minerals that formed around cells. Fe‐encrusted cells were morphologically well preserved after 1 week at 250 °C‐140 MPa and after 16 weeks at 170 °C‐120 MPa in the presence or in the absence of Si. Some goethite transformed to hematite and magnetite at 250 °C‐140 MPa, but in the presence of Si more goethite was preserved. Proteins—the most abundant cellular components—were preserved over several months at ambient conditions but disappeared after incubations at high temperature and pressure conditions, both in the presence and in the absence of Si. Other organic compounds, such as lipids and extracellular polysaccharides seemed well preserved after exposure to diagenetic conditions. This study provides insights about the composition and potential preservation of microfossils that could have formed in Fe‐ and Si‐rich Precambrian oceans.     

Dissimilatory Fe(III) reduction by Clostridium beijerinckii isolated from freshwater sediment using Fe(III) maltol enrichment

A microorganism which reduces Fe(III) during the fermentation of glucose was isolated from freshwater sediment. The Fe(III) was supplied to enrichment cultures as a soluble complex with the bidentate ligand maltol (3-hydroxy-2-methyl-4-pyrone). Advantages that were afforded by the use of Fe(III)(maltol)3 over previously published methods included negation of the requirement for assays of Fe(II) formation. Because Fe(III)(maltol)3 has a characteristic deep red colour, Fe(III) reduction could be quantified spectrophotometrically by monitoring the disappearance of the complex in liquid cultures. Furthermore, Fe(III) reduction on agar plates containing the complex was apparent by zones of decolourisation around the bacterial colonies. 16S rRNA gene sequencing indicated the isolate to be a strain of Clostridium beijerinckii. Growth experiments were performed on the isolate in batch cultures with varying concentrations of Fe(III) citrate and 50 mM glucose. Increasing the level of Fe(III) citrate present was found to alter the fermentation balance, with less acidic products being formed. The presence of Fe(III) led to increases in the growth rate and growth yield, which were both approximately doubled when the supply of the cation reached 25 mM. A NAD(P)H-dependent Fe(III) reductase activity was localised to the bacterial membrane and found not to be sensitive to respiratory inhibitors. Taken together, these data suggest that dissimilatory Fe(III) reduction by the isolate provides a means of utilising the cation as an electron sink, thus facilitating pyridine nucleotide to be recycled during fermentative metabolism.     

Chemical and biological interactions during nitrate and goethite reduction by Shewanella putrefaciens 200

Although previous research has demonstrated that NO(3)(-) inhibits microbial Fe(III) reduction in laboratory cultures and natural sediments, the mechanisms of this inhibition have not been fully studied in an environmentally relevant medium that utilizes solid-phase, iron oxide minerals as a Fe(III) source. To study the dynamics of Fe and NO(3)(-) biogeochemistry when ferric (hydr)oxides are used as the Fe(III) source, Shewanella putrefaciens 200 was incubated under anoxic conditions in a low-ionic-strength, artificial groundwater medium with various amounts of NO(3)(-) and synthetic, high-surface-area goethite. Results showed that the presence of NO(3)(-) inhibited microbial goethite reduction more severely than it inhibited microbial reduction of the aqueous or microcrystalline sources of Fe(III) used in other studies. More interestingly, the presence of goethite also resulted in a twofold decrease in the rate of NO(3)(-) reduction, a 10-fold decrease in the rate of NO(2)(-) reduction, and a 20-fold increase in the amounts of N(2)O produced. Nitrogen stable isotope experiments that utilized delta(15)N values of N(2)O to distinguish between chemical and biological reduction of NO(2)(-) revealed that the N(2)O produced during NO(2)(-) or NO(3)(-) reduction in the presence of goethite was primarily of abiotic origin. These results indicate that concomitant microbial Fe(III) and NO(3)(-) reduction produces NO(2)(-) and Fe(II), which then abiotically react to reduce NO(2)(-) to N(2)O with the subsequent oxidation of Fe(II) to Fe(III).     

Limited sinking of Phaeocystis during a 12 days sediment trap study

There is a controversy discussion about the contribution of the genus Phaeocystis to the vertical carbon export with evidence for and against sedimentation of Phaeocystis. So far, the presence of Phaeocystis in sinking matter was investigated with methods depending on morphological features (microscopy) and fast degradable substances (biochemical analyses). In this study, we determine the occurrence and abundance of Phaeocystis antarctica in short‐term sediment traps and the overlying water column during a 12‐day time period in the Atlantic sector of the Southern Ocean with 454‐pyrosequencing and microscopy counting. In the sediment trap samples, we only found few sequences belonging to Phaeocystis, which was not reflecting the situation in the water column above. The cell counts showed the same results. We conclude that Phaeocystis cells are not generally transported downwards by active sinking or other sinking processes.     

Effects of sediment loading on food perception and ingestion by freshwater copepods

Seasonal influx of suspended sediments to lakes is common in many aquatic systems, particularly during periods of high flow. Suspended particles not only affect visibility and net primary productivity, as light penetration is reduced, but may also affect the ability of herbivorous zooplankton to locate and ingest food. In Swan Lake, an oligotrophic lake in northwestern Montana, the dose association between zooplankton population development and seasonal maxima in turbidity levels suggests that the community present during peak turbidity is minimally impacted by suspended sediments. This report presents the results of laboratory investigations into the effect of suspended sediments on feeding by the copepod Diaptomus ashlandii, the dominant zoo‐plankter in Swan Lake. Ingestion rate for copepods feeding on ³²P labeled algae was significantly reduced in the presence of suspended particles at all turbidity levels tested (5 to 200 NTU's) compared to ingestion rate in the absence of suspended particles (0 NTU's).     

Response of tidal freshwater macrobenthos to sediment disturbance

The macrobenthic fauna in the tidal freshwater James River, Virginia, USA, exhibited a high degree of resilience and limited temporal response to sediment disturbance caused by large quantities of low bulk density (< 1.3 g cm^–3) fluid mud. The fluid mud was produced by hydraulic dredge deepening of a ship channel with disposal of dredged sediments onto a nearby shoal. The response of tidal freshwater communities to fluid mud was limited to mainly quantitative changes in abundance of dominant taxa (Limnodrilus spp., L. hoffmeisteri, Ilyodrilus templetoni, Corbicula fluminea, Coelotanypus scapularis) and was directly related to the thickness of fluid mud layers. Disturbance effects were short lived and for tubificids most obvious in areas with > 0.3 m fluid mud. In areas that received < 0.3 m fluid mud, acute effects were limited to chironomids and small (< 10 mm) C. fluminea. The fauna colonizing the areas disturbed by fluid mud was the same as that inhabiting the shoal prior to disturbance. There was no indication of a successional sequence, as reported for other freshwater and marine habitats. Three weeks after the disturbance ended, all but a few insect taxa had recolonized. Changes in community structure from fluid mud disturbance were slight with total taxa best characterizing the disturbance. The insensitivity of community structure measures reflects the high resiliency of macrobenthic communities to physical stresses in tidal freshwater systems.     

Enhancement of cellulose degradation in freshwater sediments by a sediment microbial fuel cell

Objective

To demonstrate that an enhanced sediment microbial fuel cell (SMFC) system can accelerate the degradation of cellulose in fresh water sediments as the accumulation of cellulose in lake sediments may aggravate the lake marsh, increase organic matter content and result in rapid deterioration of water quality and damage the ecosystem.

Results

After 330 days the highest cellulose removal efficiency (72.7 ± 2.1 %) was achieved in the presence of a SMFC with a carbon nanotube decorated cathode, followed by a SMFC without the cathode decoration (64.4 ± 2.8 %). The lowest cellulose removal efficiency (47.9 ± 2.1 %) was in the absence of SMFC. The sediment characterization analysis confirmed that the carbon nanotube decorated cathode enhances the electron transfer rate in the SMFC and improves the dissolved organic matter oxidation rate.

Conclusion

This study offers a relatively simple and promising new method for cellulose degradation in sediment.

     

The characterization of amidohydrolases in a freshwater lake sediment

The properties of three amidohydrolases, i.e., urease (I) EC 3.5.1.5, L-asparaginase (II) EC 3.5.1.1, and L-glutaminase (III) EC 3.5.1.2, were studied in sediment samples taken from a shallow eutrophic freshwater lake.Sediment samples were air dried (ADS) and stored for at least 3 months before being enzymically characterized. The pH optimum of I, II, and III were pH 7.0, 8.4, and 6.5–7.0, respectively, while III in soluble extracts from ADS was most active between pH 8.0 and 9.0. The temperature response of the three enzymes in ADS gave E_a values of 38.9, 41.6, and 35.9 kJmol^–1 for I, II, and III, respectively. K_m and V_max values for ADS I, II, and III were 1.2 mM and 1.9mol NH₃ g^–1h^–1; 0.8 mM and 4.1mol NH₃ g^–1h^–1; and 1.25 mM and 17.4mol NH₃ g^–1h^–1. K_m values for all three enzymes in ADS extracts were at least an order of magnitude greater than those of the ADS. The susceptability of each enzyme to proteolysis was followed in ADS and fresh wet sediment and compared with that of III in an ADS extract. All sediment enzymes were found to be more resistant than the commercial preparation of bacterial L-glutaminase subjected to the same treatment. These results suggested that I, II, and III all exist to some extent as colloid-immobilized enzyme fractions in freshwater sediments and are analogous to the stable enzyme fractions in soils.     

Estimation of methanotroph abundance in a freshwater lake sediment

The numbers of methane-oxidizing bacteria (methanotrophs) in the sediments of Lake Washington were estimated using three culture-independent methods. Quantitative slot-blot hybridizations were performed with type I and type II methanotroph-specific probes. These data were compared to data from quantitative hybridizations using a pmoA-specific probe and a eubacterial probe. From the combined hybridization data, the methanotroph population in Lake Washington was estimated to be 3.6 x 10(8)-7.4 x 10(8) cells/g dry weight. Methanotroph community structure and number were also investigated using polar lipid fatty acid (PLFA) analysis. Analysis of biomarker PLFAs characteristic of both type I (16:1 omega 8) and type II (18:1 omega 8) methanotrophs was used to estimate the abundance of these bacteria in Lake Washington sediments. From the PLFA data, the methanotroph population in Lake Washington was estimated to be 7.1 x 10(8)-9.4 x 10(9) cells/g dry weight. As a third method of quantitation, we calculated the methanotroph population using the total methane oxidation rate for whole cells in Lake Washington sediment to be 1.3 x 10(8)-1.2 x 10(9) cells/g dry weight. The three independent estimates of the number of methanotrophs in Lake Washington sediment agree within a two- to fourfold range. These data suggest that the three techniques used in this study detect the functionally significant population of methanotrophs in Lake Washington. Furthermore, these techniques will be useful for obtaining estimates of methanotroph abundance in additional environments.     

Molecular characterization of methanotrophic isolates from freshwater lake sediment

Profiles of dissolved O(2) and methane with increasing depth were generated for Lake Washington sediment, which suggested the zone of methane oxidation is limited to the top 0.8 cm of the sediment. Methane oxidation potentials were measured for 0.5-cm layers down to 1.5 cm and found to be relatively constant at 270 to 350 micromol/liter of sediment/h. Approximately 65% of the methane was oxidized to cell material or metabolites, a signature suggestive of type I methanotrophs. Eleven methanotroph strains were isolated from the lake sediment and analyzed. Five of these strains classed as type I, while six were classed as type II strains by 16S rRNA gene sequence analysis. Southern hybridization analysis with oligonucleotide probes detected, on average, one to two copies of pmoA and one to three copies of 16S rRNA genes. Only one restriction length polymorphism pattern was shown for pmoA genes in each isolate, and in cases where, sequencing was done, the pmoA copies were found to be almost identical. PCR primers were developed for mmoX which amplified 1.2-kb regions from all six strains that tested positive for cytoplasmic soluble methane mono-oxygenase (sMMO) activity. Phylogenetic analysis of the translated PCR products with published mmoX sequences showed that MmoX falls into two distinct clusters, one containing the orthologs from type I strains and another containing the orthologs from type II strains. The presence of sMMO-containing Methylomonas strains in a pristine freshwater lake environment suggests that these methanotrophs are more widespread than has been previously thought.     

Biotransformation of quinoline and methylquinolines in anoxic freshwater sediment

Quinoline (Q) and some isomers of methylquinoline (MQ) were transformed to hydroxylated products in freshwater sediment slurries incubated under methanogenic conditions at 25 °C. Methylquinoline transformation was not affected by a methyl group on the C-3 or C-4 carbon atom of the pyridine ring; 2-MQ, however, was not transformed. All isomers of dimethylquinoline (DMQ) tested (2,4-, 2,6-, 2,7-, and 2,8-DMQ) with a methyl group at the number 2 carbon also persisted in sediments after anaerobic incubation for one year at 25 °C.In most experiments, quinoline initially was transformed to 2-hydroxyquinoline (2-OH-Q), which was further metabolized to unidentified products. A second product, 4-CH₃-2-OH-Q, was detected in some experiments. This product accumulated and was not further transformed. 6-, 7-, and 8-Methylquinoline (6-, 7-, 8-MQ) were hydroxylated to form the respective 2-OH-MQ products. These hydroxylated products accumulated and were not further transformed. Hydroxylation of Q and 6-, 7- and 8-MQ at the 2-carbon position was confirmed by GC/FTIR and GC/MS analyses. The transformations of Q and MQs were pH dependent with an optimal pH of 7–8.The results of this study suggest that two pathways may exist for the anaerobic transformation of quinoline; one pathway leads to the formation of a hydroxylated intermediate and the other to a methylated and hydroxylated intermediate. In addition, our results suggest that a methyl substituent on the number 2 carbon inhibits the anaerobic transformation of quinoline derivatives.Abbreviations GC gas chromatography - GC/FTIR gas chromatography/Fourier transform infrared spectrometry - GC/MS gas chromatography/mass spectrometry - HPLC high performance liquid chromatography - MQ methylquinoline - Q quinoline     

流域尺度水土保持生物措施减沙效益研究

1　引　　言黄土高原位于黄河中游 ,流经黄土高原的 9大支流进入河口镇至花园口的中游河段 ,总径流量为 187× 10 8ｍ3 ,输沙量占黄河流域总沙量的 90 % .建国以来以修建梯田坝地、造林种草、建谷坊、调整种植结构为主的水土保持工程、生物治理长年不懈 ,其目的在于减水减沙 ,改善流域生态环境 .但是 ,除部分中小尺度流域进入生态、经济效益良性循环的轨道外 ,大部分地区生态环境仍然十分脆弱 ,部分地区有恶化之势 .因此 ,定量评价水土保持工程、生物措施的治理效益是广为关注的研究课题 ,虽相关的研究成果不少 ,但是绝大部分工作是评价水土…     

Regiospecific dechlorination of pentachlorophenol by dichlorophenol-adapted microorganisms in freshwater, anaerobic sediment slurries.

The reductive dechlorination of pentachlorophenol (PCP) was investigated in anaerobic sediments that contained nonadapted or 2,4- or 3,4-dichlorophenol (DCP)-adapted microbial communities. Adaptation of sediment communities increased the rate of conversion of 2,4- or 3,4-DCP to monochlorophenols (CPs) and eliminated the lag phase before dechlorination was observed. Both 2,4- and 3,4-DCP-adapted sediment communities dechlorinated the six DCP isomers to CPs. The specificity of chlorine removal from the DCP isomers indicated a preference for ortho-chlorine removal by 2,4-DCP-adapted sediment communities and for para-chlorine removal by 3,4-DCP-adapted sediment communities. Sediment slurries containing nonadapted microbial communities either did not dechlorinate PCP or did so following a lag phase of at least 40 days. Sediment communities adapted to dechlorinate 2,4- or 3,4-DCP dechlorinated PCP without an initial lag phase. The 2,4-DCP-adapted communities initially removed the ortho-chlorine from PCP, whereas the 3,4-DCP-adapted communities initially removed the para-chlorine from PCP. A 1:1 mixture of the adapted sediment communities also dechlorinated PCP without a lag phase. Dechlorination by the mixture was regiospecific, following a para greater than ortho greater than meta order of chlorine removal. Intermediate products of degradation, 2,3,5,6-tetrachlorophenol, 2,3,5-trichlorophenol, 3,5-DCP, 3-CP, and phenol, were identified by a combination of cochromatography (high-pressure liquid chromatography) with standards and gas chromatography-mass spectrometry.