Predominance of terrestrial organic matter in sediments from a cyanobacteria- blooming hypereutrophic lake

Although an understanding of the quantity and quality of sedimentary organic matter (SOM) pools is necessary to design sound environmental management strategies for lacustrine systems, the characterization of organic matter sources and the assessment of their relative contributions to eutrophic and inland lake sediments remain insufficient. In this study, the contribution of potential organic matter sources to sediments in shallow and hypereutrophic lake Taihu, China was assessed on the molecular level using source-specific fatty acid biomarkers. The results indicated that SOM was composed mainly of terrestrial plants with a maximal contribution of 45.3 ± 2.4% to the total organic carbon, which accounted for approximately 66% among the determined organic matter sources. Evidence suggests the terrestrial plants remained in a fresh state in surface sediments: the correlation (R² = 0.62, p < 0.05) between bacterial and terrestrial plant carbon was strong. On the other hand, aquatic plant and bacterial carbon contributed 5–15% to the total organic carbon, which was followed by the faint contribution (<5% of total organic carbon) of algae-derived organic carbon including cyanobacteria, diatoms, and dinoflagellates. The results provided details of the contributions of SOM sources, illustrating the usefulness of fatty acid biomarkers in discriminating organic matter sources within lake environments. Although organic matter sources of sediments varied in spatial and temporal patterns, the strong correlation between terrestrial plant and total organic carbon (R² = 0.60, p < 0.05) indicates that terrestrial plants were the dominant source in lake sediments.     

The dynamics of experimental arable weed communities under different management practices

Abstract. Weed communities, comprising 12 introduced species at constant starting densities and three species already present in the seed bank, were followed through three years of continuous winter wheat. The wheat and weeds were subjected to two treatments in a split-plot factorial design, organic contrasting with conventional fertilizer, and ploughing plus hand-roguing contrasting with minimum tillage plus herbicide. The minimum tilled plots developed in a uniform manner, and became dominated by very high densities of Anisantha sterilis. Agrostemma githago and Galium aparine also persisted in these plots at lower densities. The ploughed plots had a lower total density but a greater range of species. Stellaria media, Veronica persica and Avena fatua were the most common; other species occurred at lower densities. The major effect of fertilizer treatment was a greater initial increase by G. aparine on the organic, minimum tilled plots compared with the conventionally fertilized, minimum tilled plots. Species associated with minimum tillage were annuals with either no or a short term seed bank and autumn germination and rather predictable dynamics, whereas species that did well under ploughing were either spring germinating or had a persistent seed bank, implying greater annual variation in population size associated with weather conditions. There seemed no clear way to distinguish between those species which were abundant on the ploughed plots and those which were scarce under all conditions using readily accessible data.     

α-Amylase (AmyP) of glycoside hydrolase subfamily GH13_37 is resistant to various toxic compounds

The α-amylase (AmyP) from a marine metagenomic library shows very low sequence similarity with characterized α-amylases and belongs to a new glycoside hydrolase subfamily GH13_37. This amylase retained above 87% residual activity in the presence of metal ions (concentrations <10 mM) tested except Hg²⁺ and was strongly stimulated by 5 mM Cu²⁺. AmyP was active over a wide range of salt concentration (0–3 M) with the optimal concentration at 1 M. The enzyme exhibited 119, 106, 108, 42 and 31% of its activity the presence of 2% Tween 20, Tween 40, Triton X-100, SDS and CTAB, respectively, showing excellent resistance. Oxidizing agents (H₂O₂ and NaClO₃) not strongly inactivated the enzyme. DTT was found to greatly enhance the activity (to 198% of original activity), while 2-mercaptoethanol had no significant effect on the enzyme. Moreover, AmyP retained considerable activity in both hydrophobic solvents and hydrophilic solvents, and n-octanol even increased the amylase activity to 113%. Compared to other α-amylases capable of resisting toxic compounds, AmyP was the first α-amylase with such broad spectrum resistance.     

Immobilization of Lipase from Rhizopus Niveus: A Way to Enhance its Synthetic Activity in Organic Solvent

Lipase (EC 3.1.1.3) from Rhizopus niveus was immobilized by physical adsorption on various carriers, including different types of Celite, Spherosil and Duolite. After the enzyme immobilization, the recovered hydrolytic and synthetic activities on the different carriers were then determined. The results showed that the highest synthetic activity was obtained when Duolite XAD 761 was used as the carrier. However the recovered hydrolytic activity after the immobilization on this resin was relatively low although this carrier showed the best protein loading capacity. The highest recovered hydrolytic activity was observed when the lipase was immobilized on Celite Hyflo-Supercel using an immobilization buffer adjusted to pH 4. The comparison of the free and immobilized lipase specific activities suggest that the immobilization on Celite Hyflo-Supercel, Spherosil XOA 200 and silica has enhanced the lipase hydrolytic activity. On the other hand, the use of the lipase immobilized on Duolite XAD 761 as biocatalyst of synthetic reaction, compared to that of the free enzyme, allows the reaction initial velocity to be increased 12.2-fold. In addition, the synthetic activity of the lipase immobilized on Duolite XAD 761 was shown to be maximum at a water activity in the range of 0.32-0.52.     

Evaluation and indirect estimation of nitrate losses from the agricultural microbasin Rybárik

The long-term trends of mean monthly nitrate concentrations in stream and drainage runoff were evaluated in the experimental microbasin Rybárik (0.119 km²) at the Institute of Hydrology, Slovak Academy of Sciences, during the period 1987–2005. The results of analyses indicate a decreasing trend of nitrate concentration after the year 1989, but with relatively high losses in some years and relatively low losses in other years. This decreasing trend is mainly caused by a decrease in the use of nitrogen fertilizers. The nitrate concentration in surface runoff strongly correlates with runoff and fertilization. Based on measured data, an empirical relation was found describing the dependence of annual nitrate transport in the stream on annual runoff depth and on the annual amount of applied nitrogen fertilizers. Presented at the International Conference on Bioclimatology and Natural Hazards, Poľana nad Detvou, Slovakia, 17–20 September 2007.     

Tidal effects on the organic carbon mineralization rate under aerobic conditions in sediments of an intertidal estuary

Laboratory experiments and field measurements were conducted to examine the effect of tide on the organic carbon mineralization rate in sediments under aerobic conditions of an intertidal estuary. Core samples of surface sediments were collected from an intertidal estuary of the Kurose River, Hiroshima, Japan. To mimic low and high tide in the intertidal estuary, organic carbon mineralization rates in the samples were measured in the laboratory under both air-exposed and submerged conditions. Mineralization rates under air-exposed conditions were two to five times higher than those under submerged conditions. Field measurements of the rate of CO₂ emission from the sediment surface revealed a rapid increase in the rate as the sea level fell during ebb tide. The estimated amount of daily organic carbon mineralization assuming a constantly submerged condition was 30% less than that estimated when considering the semi-diurnal fluctuation in sea level. These results indicate that tide has a marked impact on the organic carbon mineralization rate in sediments under aerobic conditions on an intertidal estuary, and tidal effects need to be considered when the amount of mineralized organic carbon is estimated.     

Molecular Modelling of The Mechanism of Action of Organic Clay-Swelling Inhibitors

Abstract

It is well known that the sodium smectite class of clays swells macroscopically in contact with water, whereas under normal conditions the potassium form does not. In recent work using molecular simulation methods, we have provided a quantitative explanation both for the swelling behaviour of sodium smectite clays and the lack of swelling of potassium smectites [1]. In the present paper, we apply similar modelling methods to study the mechanism of inhibition of clay-swelling by a range of organic molecules.

Experimentally, it is known that polyalkylene glycols (polyethers) of intermediate to high relative molecular mass are effective inhibitors of smectite clay swelling. We use a range of atomistic simulation techniques, including Monte Carlo and molecular dynamics, to investigate the interactions between a selection of these compounds, water, and a model smectite clay mineral. These interactions occur by means of organised intercalation of water and organic molecules within the galleries between individual clay layers.

The atomic interaction potentials deployed in this work are not as highly optimised as those used in our clay-cation-water work [1]. Nevertheless, our simulations yield trends and results that are in qualitative and sometimes semi-quantitative agreement with experimental findings on similiar (but not identical) systems. The internal energy of adsorption of simple polyethers per unit mass on the model clay is not significantly different from that for water adsorption; our Monte Carlo studies indicate that entropy is the driving force for the sorption of the simpler organic molecules inside the clay layers: a single long chain polyethylene glycol can displace a large number of water molecules, each of whose translational entropy is greatly enhanced when outside the clay. Hydrophobically modified polyalkylene glycols also enjoy significant van der Waals interactions within the layers which they form within the clay galleries.

In conjunction with experimental studies, our work furnishes valuable insights into the relative effectiveness of the compounds considered and reveals the generic features that high performance clay-swelling inhibitors should possess. For optimal inhibitory activity, these compounds should be reasonably long chain linear organic molecules with localised hydrophobic and hydrophilic regions along the chain. On intercalation of these molecules within the clay layers, the hydrophobic regions provide an effective seal against ingress of water, while the hydrophilic ones enhance the binding of the sodium cations to the clay surface, preventing their hydration and the ensuing clay swelling.     

Meaning in Nature: Organic Manufacture?

The paper examines Marcello Barbieri’s (2007) Introduction to Biosemiotics. Highlighting debate within the biosemiotic community, it focuses on what the volume offers to those who explain human intellect in relation to what Turing called our ‘physical powers.’ In scrutinising the basis of world-modelling, parallels and contrasts are drawn with other work on embodied-embedded cognition. Models dominate biology. Is this a qualitative fact or does it point to biomechanisms? In evaluating the 18 contributions, it is suggested that the answers will shape the field. First, they will decide if biochemistry and explanatory reduction can be synergised by biosemantics. Second, they will show if our intellectual powers arise from biology. Does thinking use—not a language faculty—but what Marko? and colleagues call semiosis by the living? Resolution of such issues, it is suggested, can change how we view cognition. Above all, if the biomechanists win the day, cultural models can be regarded as extending natural meaning. On such a view, biomechanisms prompt us to act and perceive as we model our own natural models. This fits Craik’s vision: intellect gives us the alphanumerical ‘symbols’ that allow thoughts to have objective validity. For the biomechanist, this is explained—not by brains alone—but, rather, by acting under the constraints of historically extended sensoria.     

Ultraviolet radiation, toxic chemicals and amphibian population declines

Abstract. As part of an overall ‘biodiversity crisis’, many amphibian populations are in decline throughout the world. Numerous factors have contributed to these declines, including habitat destruction, pathogens, increasing ultraviolet (UV) radiation, introduced non‐native species and contaminants. In this paper we review the contribution of increasing UV radiation and environmental contamination to the global decline of amphibian populations. Both UV radiation and environmental contaminants can affect amphibians at all life stages. Exposure to UV radiation and to certain contaminants can kill amphibians and induce sublethal affects in embryos, larvae and adults. Moreover, UV radiation and contaminants may interact with one another synergistically. Synergistic interactions of UV radiation with contaminants can enhance the detrimental effects of the contaminant and UV radiation.