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Freshwater Sediments (freshwater + sediment)
Selected AbstractsMicrobial response to salinity change in Lake Chaka, a hypersaline lake on Tibetan plateauENVIRONMENTAL MICROBIOLOGY, Issue 10 2007Hongchen Jiang Summary Previous investigations of the salinity effects on the microbial community composition have largely been limited to dynamic estuaries and coastal solar salterns. In this study, the effects of salinity and mineralogy on microbial community composition was studied by using a 900-cm sediment core collected from a stable, inland hypersaline lake, Lake Chaka, on the Tibetan Plateau, north-western China. This core, spanning a time of 17 000 years, was unique in that it possessed an entire range of salinity from freshwater clays and silty sands at the bottom to gypsum and glauberite in the middle, to halite at the top. Bacterial and archaeal communities were studied along the length of this core using an integrated approach combining mineralogy and geochemistry, molecular microbiology (16S rRNA gene analysis and quantitative polymerase chain reaction), cultivation and lipid biomarker analyses. Systematic changes in microbial community composition were correlated with the salinity gradient, but not with mineralogy. Bacterial community was dominated by the Firmicutes -related environmental sequences and known species (including sulfate-reducing bacteria) in the freshwater sediments at the bottom, but by halophilic and halotolerant Betaproteobacteria and Bacteroidetes in the hypersaline sediments at the top. Succession of proteobacterial groups along the salinity gradient, typically observed in free-living bacterial communities, was not observed in the sediment-associated community. Among Archaea, the Crenarchaeota were predominant in the bottom freshwater sediments, but the halophilic Halobacteriales of the Euryarchaeota was the most important group in the hypersaline sediments. Multiple isolates were obtained along the whole length of the core, and their salinity tolerance was consistent with the geochemical conditions. Iron-reducing bacteria were isolated in the freshwater sediments, which were capable of reducing structural Fe(III) in the Fe(III)-rich clay minerals predominant in the source sediment. These data have important implications for understanding how microorganisms respond to increased salinity in stable, inland water bodies. [source] Hydrogen ,leakage' during methanogenesis from methanol and methylamine: implications for anaerobic carbon degradation pathways in aquatic sedimentsENVIRONMENTAL MICROBIOLOGY, Issue 4 2007Niko Finke Summary The effect of variations in H2 concentrations on methanogenesis from the non-competitive substrates methanol and methylamine (used by methanogens but not by sulfate reducers) was investigated in methanogenic marine sediments. Imposed variations in sulfate concentration and temperature were used to drive systematic variations in pore water H2 concentrations. Specifically, increasing sulfate concentrations and decreasing temperatures both resulted in decreasing H2 concentrations. The ratio of CO2 and CH4 produced from 14C-labelled methylamine and methanol showed a direct correlation with the H2 concentration, independent of the treatment, with lower H2 concentrations resulting in a shift towards CO2. We conclude that this correlation is driven by production of H2 by methylotrophic methanogens, followed by loss to the environment with a magnitude dependent on the extracellular H2 concentrations maintained by hydrogenotrophic methanogens (in the case of the temperature experiment) or sulfate reducers (in the case of the sulfate experiment). Under sulfate-free conditions, the loss of reducing power as H2 flux out of the cell represents a loss of energy for the methylotrophic methanogens while, in the presence of sulfate, it results in a favourable free energy yield. Thus, hydrogen leakage might conceivably be beneficial for methanogens in marine sediments dominated by sulfate reduction. In low-sulfate systems such as methanogenic marine or freshwater sediments it is clearly detrimental , an adverse consequence of possessing a hydrogenase that is subject to externally imposed control by pore water H2 concentrations. H2 leakage in methanogens may explain the apparent exclusion of acetoclastic methanogenesis in sediments dominated by sulfate reduction. [source] Anaerobic redox cycling of iron by freshwater sediment microorganismsENVIRONMENTAL MICROBIOLOGY, Issue 1 2006Karrie A. Weber Summary The potential for microbially mediated anaerobic redox cycling of iron (Fe) was examined in a first-generation enrichment culture of freshwater wetland sediment microorganisms. Most probable number enumerations revealed the presence of significant populations of Fe(III)-reducing (approximately 108 cells ml,1) and Fe(II)-oxidizing, nitrate-reducing organisms (approximately 105 cells ml,1) in the freshwater sediment used to inoculate the enrichment cultures. Nitrate reduction commenced immediately following inoculation of acetate-containing (approximately 1 mM) medium with a small quantity (1% v/v) of wetland sediment, and resulted in the transient accumulation of NO2, and production of a mixture of gaseous end-products (N2O and N2) and NH4+. Fe(III) oxide (high surface area goethite) reduction took place after NO3, was depleted and continued until all the acetate was utilized. Addition of NO3, after Fe(III) reduction ceased resulted in the immediate oxidation of Fe(II) coupled to reduction of NO3, to NH4+. No significant NO2, accumulation was observed during nitrate-dependent Fe(II) oxidation. No Fe(II) oxidation occurred in pasteurized controls. Microbial community structure in the enrichment was monitored by denaturing gradient gel electrophoresis analysis of polymerase chain reaction-amplified 16S rDNA and reverse transcription polymerase chain reaction-amplified 16S rRNA, as well as by construction of 16S rDNA clone libraries for four different time points during the experiment. Strong similarities in dominant members of the microbial community were observed in the Fe(III) reduction and nitrate-dependent Fe(II) oxidation phases of the experiment, specifically the common presence of organisms closely related (, 95% sequence similarity) to the genera Geobacter and Dechloromonas. These results indicate that the wetland sediments contained organisms such as Geobacter sp. which are capable of both dissimilatory Fe(III) reduction and oxidation of Fe(II) with reduction of NO3, to NH4+. Our findings suggest that microbially catalysed nitrate-dependent Fe(II) oxidation has the potential to contribute to a dynamic anaerobic Fe redox cycle in freshwater sediments. [source] Toxicity assessment of reference and natural freshwater sediments with the LuminoTox assayENVIRONMENTAL TOXICOLOGY, Issue 4 2006P. M. Dellamatrice Abstract We examined the possibility of adapting the LuminoTox, a recently-commercialized bioanalytical testing procedure initially developed for aqueous samples, to assess the toxic potential of sediments. This portable fluorescent biosensor uses photosynthetic enzyme complexes (PECs) to rapidly measure photosynthetic efficiency. LuminoTox testing of 14 CRM (Certified Reference Material) sediments was first undertaken with (1) a "solid phase assay" (Lum-SPA) in which PECs are in intimate contact with sediment slurries for a 15 min exposure period and (2) an elutriate assay (Lum-ELU) in which PECs are exposed for 15 min to sediment water elutriates. CRM sediment toxicity data were then compared with those generated with the Microtox Solid Phase Assay (Mic-SPA). A significant correlation (P < 0.05) was shown to exist between Lum-SPA and Mic-SPA, indicating that both tests display a similar toxicity response pattern for CRM sediments having differing contaminant profiles. The sediment elutriate Lum-ELU assay displayed toxicity responses (i.e. measurable IC20s) for eight of the 14 CRM sediments, suggesting that it is capable of determining the presence of sediment contaminants that are readily soluble in an aqueous elutriate. Lum-SPA and Mic-SPA bioassays were further conducted on 12 natural freshwater sediments and their toxicity responses were more weakly, yet significantly, correlated. Finally, Lum-SPA testing undertaken with increasing mixtures of kaolin clay confirmed that its toxicity responses, in a manner similar to those reported for the Mic-SPA assay, are also subject to the influence of grain size. While further studies will be required to more fully understand the relationship between Lum-SPA assay responses and the physicochemical makeup of sediments (e.g., grain size, combined presence of natural and anthropogenic contaminants), these preliminary results suggest that LuminoTox testing could be a useful screen to assess the toxic potential of solid media. © 2006 Wiley Periodicals, Inc. Environ Toxicol 21: 395,402, 2006. [source] Cyst-based toxicity tests XIII,Development of a short chronic sediment toxicity test with the ostracod crustacean Heterocypris incongruens: Methodology and precisionENVIRONMENTAL TOXICOLOGY, Issue 6 2002Belgis Chial Abstract Experiments were carried out with neonates of the freshwater ostracod Heterocypris incongruens to verify and complete previous choices of test parameters for a new culture/maintenance-free solid-phase microbiotest for freshwater sediments. From trials with increasing volumes of reference sediment, it was concluded that 300 ,L was the most appropriate amount of substrate to be put in 12-cup multiwell plates with 2 mL of standard freshwater. Tests in 3,9 replicates eventually showed that six parallels were needed to have good assay precision (repeatability). Application of the final test protocol to oil-contaminated sediments from the St. Lawrence River in Canada revealed that the 6-day chronic ostracod microbiotest had less variation in repeated tests than did the 10-day contact assay with Hyalella azteca and hence can be considered more precise. Based on the 95% confidence intervals for mortality and growth of the ostracods in the controls (reference sediment) of the 56 tests carried out for the Canadian project, a validity threshold of 20% for mortality was eventually selected, in analogy with the acceptability limits applied in many chronic bioassays. A minimum length of 600 ,m in the control sediment after 6 days' exposure was also taken as the threshold for good health of the test organisms and for reliable test conditions. The new microbiotest has been tailored in a handy and user-friendly new toxkit, the Ostracodtoxkit, which is particularly suited for cost-effective routine monitoring. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 528,532, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10086 [source] Experimental and modeling investigation of metal release from metal-spiked sedimentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2005Richard F. Carbonaro Abstract In sediments that contain iron monosulfide, cadmium, nickel, lead, zinc, and silver(I) form insoluble metal sulfides that lower the metal ion activity in the sediment,pore water system, thereby reducing toxicity. However, metal sulfides are susceptible to oxidation by molecular oxygen resulting in metal solubilization. To better understand the sources and sinks of metal sulfides in sediments, iron monsulfide,rich freshwater sediments were spiked with cadmium, nickel, lead, zinc, or silver(I) and placed into cylindrical cores with an overlying layer of oxygen-saturated water. Measurements of the dissolved metal concentration in the overlying water were made as a function of time and the vertical profiles of acid-volatile sulfide (AVS) and simultaneously extracted metal (SEM) were measured after 150 d. A one-dimensional reactive and transport model has been employed to help elucidate processes controlling the fate of metals in sediments. The model incorporates metal-sulfide formation, metal-sulfide oxidation, and metal partitioning onto sediment organic carbon and iron oxyhydroxide to simulate the vertical transport of metals throughout the sediment core. [source] Development and evaluation of consensus-based sediment effect concentrations for polychlorinated biphenyls,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2000Donald D. MacDonald Abstract Sediment-quality guidelines (SQGs) have been published for polychlorinated biphenyls (PCBs) using both empirical and theoretical approaches. Empirically based guidelines have been developed using the screening-level concentration, effects range, effects level, and apparent effects threshold approaches. Theoretically based guidelines have been developed using the equilibrium-partitioning approach. Empirically-based guidelines were classified into three general categories, in accordance with their original narrative intents, and used to develop three consensus-based sediment effect concentrations (SECs) for total PCBs (tPCBs), including a threshold effect concentration, a midrange effect concentration, and an extreme effect concentration. Consensus-based SECs were derived because they estimate the central tendency of the published SQGs and, thus, reconcile the guidance values that have been derived using various approaches. Initially, consensus-based SECs for tPCBs were developed separately for freshwater sediments and for marine and estuarine sediments. Because the respective SECs were statistically similar, the underlying SQGs were subsequently merged and used to formulate more generally applicable SECs. The three consensus-based SECs were then evaluated for reliability using matching sediment chemistry and toxicity data from field studies, dose-response data from spiked-sediment toxicity tests, and SQGs derived from the equilibrium-partitioning approach. The results of this evaluation demonstrated that the consensus-based SECs can accurately predict both the presence and absence of toxicity in field-collected sediments. Importantly, the incidence of toxicity increases incrementally with increasing concentrations of tPCBs. Moreover, the consensus-based SECs are comparable to the chronic toxicity thresholds that have been estimated from dose-response data and equilibrium-partitioning models. Therefore, consensus-based SECs provide a unifying synthesis of existing SQGs, reflect causal rather than correlative effects, and accurately predict sediment toxicity in PCB-contaminated sediments. [source] | ||||||||||