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Significant Process (significant + process)
Selected AbstractsQuantification of in vivo biotransformation of the anionic surfactant C12 -2-linear alkylbenzene sulfonate in fathead minnowsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2000Johannes Tolls Abstract Linear alkylbenzene sulfonate (LAS) is a major surfactant in household detergents and enters the environment via the wastewater. Aquatic organisms are thus exposed to LAS and can bioaccumulate this compound. Even though the extent of bio-accumulation is determined by the organisms' capability of metabolizing LAS, little is known about metabolism of LAS in small aquatic organisms. In the present investigation, we present a novel approach to quantify in vivo biotransformation. Fish (fathead minnows [Pimephales promelas]) were exposed to the LAS constituent 2- n -(p -sulfophenyl)-dodecane (C12 -2-LAS). The parent surfactant and its biotransformation product 3- n -(p -sulfophenyl)-butyric acid (C4 -3-SPC) were determined in fish tissue. On the average, the concentration of C4 -3-SPC in fish was 70 to 80% of that of C12 -2-LAS. The first-order one-compartment model of bioconcentration was extended to include biotransformation as an explicit process. Analysis of the C4 -3-SPC/C12 -2-LASconcentration ratio in fish allowed estimating a rate constant for in vivo biotransformation of C12 -2-LAS in fathead minnows. With the estimates of the biotransformation rate constant (kBT,LAS) ranging between 0.31 and 0.72/d, biotransformation contributes to more than 40% of the elimination of C12 -2-LAS in fathead minnows. This indicates that biotransformation is a significant process in reducing the bioaccumulation potential of LAS. Moreover, the present investigation demonstrates that the combination of measurements of parent compound and metabolite with an extended bioaccumulation model is a viable approach for quantification of biotransformation in small aquatic test animals. [source] Phosphorus and nitrogen in a monomictic freshwater lake: employing cyanobacterial bioreporters to gain new insights into nutrient bioavailabilityFRESHWATER BIOLOGY, Issue 6 2010OSNAT GILLOR Summary 1. It is an uncontested paradigm that an adequate supply of the macronutrients nitrogen (N) and phosphorus (P) is critical for maintaining phytoplankton primary production in aquatic ecosystems; it has also been suggested that there is an optimal total N : total P ratio for this globally significant process. 2. This ratio, normally assessed by chemical determination of the major dissolved N and P species, poses a dilemma: do chemical measurements actually reflect the bioavailable fraction of these nutrient pools? Accurate determination of the various N and P species and their fluxes into phytoplankton cells is notoriously difficult. 3. To provide a possible solution to this difficulty, we engineered strains of the cyanobacterium Synechococcus sp. strain PCC 7942 that ,report' on N and P bioavailability via a bioluminescent signal. These strains were used to quantify, for the first time, bioavailable concentrations of these essential macronutrients in a freshwater lake. 4. Only a small fraction (0.01,1%) of the chemically determined P may actually be bioavailable to this unicellular cyanobacterium and, by inference, to the phytoplankton community in general. In contrast, bioavailable N comprises most of the dissolved N pool. Consequently, bioavailable N : P ratios based on these assays are higher then those based on chemical determinations, indicating that P limitation in Lake Kinneret is more extensive then previously thought. [source] A thermodynamic analysis of the anaerobic oxidation of methane in marine sedimentsGEOBIOLOGY, Issue 5 2008D. E. LAROWE ABSTRACT Anaerobic oxidation of methane (AOM) in anoxic marine sediments is a significant process in the global methane cycle, yet little is known about the role of bulk composition, temperature and pressure on the overall energetics of this process. To better understand the biogeochemistry of AOM, we have calculated and compared the energetics of a number of candidate reactions that microorganisms catalyse during the anaerobic oxidation of methane in (i) a coastal lagoon (Cape Lookout Bight, USA), (ii) the deep Black Sea, and (iii) a deep-sea hydrothermal system (Guaymas basin, Gulf of California). Depending on the metabolic pathway and the environment considered, the amount of energy available to the microorganisms varies from 0 to 184 kJ mol,1. At each site, the reactions in which methane is either oxidized to , acetate or formate are generally only favoured under a narrow range of pressure, temperature and solution composition , particularly under low (10,10 m) hydrogen concentrations. In contrast, the reactions involving sulfate reduction with H2, formate and acetate as electron donors are nearly always thermodynamically favoured. Furthermore, the energetics of ATP synthesis was quantified per mole of methane oxidized. Depending on depth, between 0.4 and 0.6 mol of ATP (mol CH4),1 was produced in the Black Sea sediments. The largest potential productivity of 0.7 mol of ATP (mol CH4),1 was calculated for Guaymas Basin, while the lowest values were predicted at Cape Lookout Bight. The approach used in this study leads to a better understanding of the environmental controls on the energetics of AOM. [source] Gully position, characteristics and geomorphic thresholds in an undisturbed catchment in Northern AustraliaHYDROLOGICAL PROCESSES, Issue 14 2006Dr G. R. Hancock Abstract Gullying is a significant process in the long-term dynamics and evolution of both natural and rehabilitated (i.e. post-mining) landscapes. From a landscape management perspective it is important that we understand gully initiation and development, as it is well recognized that catchment disturbance can result in the development of gullies that can be very difficult to rehabilitate. This study examines gully position using geomorphic statistics relating to features such as depth, width and length in a catchment undisturbed by European activity in the Northern Territory, Australia. The results demonstrate that gullying occurs throughout the catchment and that a slope,area threshold does not exist and that gully position broadly follows the catchment area,slope relationship. Simple relationships relating catchment area and slope to gully depth, width and length provide poor results, despite these relationships having been found to apply for ephemeral gullies in cropland. The results suggest that gully initiation thresholds are low as a result of an enhanced fire regime. A threshold model for gully position that uses catchment area and slope to switch between gully and hillslope was evaluated and found broadly to capture gully position. Copyright © 2006 John Wiley & Sons, Ltd. [source] Modelling approaches to compare sorption and degradation of metsulfuron-methyl in laboratory micro-lysimeter and batch experimentsPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 12 2003Maik Heistermann Abstract Results of laboratory batch studies often differ from those of outdoor lysimeter or field plot experiments,with respect to degradation as well as sorption. Laboratory micro-lysimeters are a useful device for closing the gap between laboratory and field by both including relevant transport processes in undisturbed soil columns and allowing controlled boundary conditions. In this study, sorption and degradation of the herbicide metsulfuron-methyl in a loamy silt soil were investigated by applying inverse modelling techniques to data sets from different experimental approaches under laboratory conditions at a temperature of 10 °C: first, batch-degradation studies and, second, column experiments with undisturbed soil cores (28 cm length × 21 cm diameter). The column experiments included leachate and soil profile analysis at two different run times. A sequential extraction method was applied in both study parts in order to determine different binding states of the test item within the soil. Data were modelled using ModelMaker and Hydrus-1D/2D. Metsulfuron-methyl half-life in the batch-experiments (t1/2 = 66 days) was shown to be about four times higher than in the micro-lysimeter studies (t1/2 about 17 days). Kinetic sorption was found to be a significant process both in batch and column experiments. Applying the one-rate-two-site kinetic sorption model to the sequential extraction data, it was possible to associate the stronger bonded fraction of metsulfuron-methyl with its kinetically sorbed fraction in the model. Although the columns exhibited strong significance of multi-domain flow (soil heterogeneity), the comparison between bromide and metsulfuron-methyl leaching and profile data showed clear evidence for kinetic sorption effects. The use of soil profile data had significant impact on parameter estimates concerning sorption and degradation. The simulated leaching of metsulfuron-methyl as it resulted from parameter estimation was shown to decrease when soil profile data were considered in the parameter estimation procedure. Moreover, it was shown that the significance of kinetic sorption can only be demonstrated by the additional use of soil profile data in parameter estimation. Thus, the exclusive use of efflux data from leaching experiments at any scale can lead to fundamental misunderstandings of the underlying processes. Copyright © 2003 Society of Chemical Industry [source] Towards natural polyploid model organismsMOLECULAR ECOLOGY, Issue 8 2008RICHARD J. A. BUGGS Abstract Populations of natural allopolyploids with available and well-developed genomic resources are currently hard to come by. These are needed because whole genome duplication and hybridization , both combined in allopolyploids , are significant processes in evolution, especially the evolution of plants. The new characterization of a naturally occurring allopolyploid in the genus Mimulus by Sweigart et al. in this issue of Molecular Ecology is therefore to be welcomed. Mimulus is rapidly emerging as a model system for evolutionary functional genomics. Sequences of the whole genome and 200 000 expressed sequence tags of diploid M. guttatus, a putative parent of the polyploid described in this issue, will soon be available. These will facilitate investigation of the fates of genes duplicated by whole genome duplication, and their effects on morphology, mating system and ecology in natural populations. [source] | ||||||||||