Synthetic fragrances perfume lake sediments.
Explore the source record for details and available documents.
Fatty Acids, Monounsaturated↗
SEARCH · Search PubMed
Results for “Geologic Sediments”
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Temporal and spatial variation of perchlorate in streambed sediments: results from in-situ dialysis samplers.
The fate of perchlorate (ClO4-) in streambed sediments is becoming a concern due to the increasing number of groundwater and surface water contamination sites in the United States. Dialysis samplers were deployed at three sites over a period of 1 year to determine the vertical distribution of ClO4- in sediment pore water. Results indicated that the spatial and temporal ClO4- penetration into sediments could be affected by numerous factors, such as temperature, microbial degradation, ClO4- surface water concentration, and sediment physico-geological properties. In general, maximum ClO4- penetration into sediments at the studied sites was 30 cm below the sediment-water surface. The vertical sequential depletion of electron acceptors in sediments suggested that microbial reduction was responsible for ClO4- depletion in stream sediments. Biodegradation of ClO4- occurred over a seasonally variable active depth zone of 1-10 cm. Results implied that there was a rapid natural attenuation potential of perchlorate in saturated near-surface sediments.
Dialysis↗
Relevance of mangroves for the production and deposition of organic matter along tropical continental margins.
Mangroves are highly complex ecosystems occupying a major part of tropical coastlines. High primary productivity, efficient biological nutrient recyling and a permanent exchange with terrestrial and marine ecosystems are their common features. Despite the high production and export rates of leaf litter, mangrove detritus has been reported to be of minor importance in sustaining marine food webs. The geographical distribution of mangrove-derived organic matter (OM) in marine sediments is found to be restricted to the vicinity of its source. Dissolved nutrient inputs from mangroves and rivers may fuel the production of marine OM. In this paper we assess the relevance of mangroves for the production and sedimentation of OM in the tropical coastal ocean based on data available from the literature and our own research results. We estimate the rates of carbon accumulation in mangrove sediments and of carbon export to the coastal seas. From the rates of litter fall and export we calculate carbon accumulating in mangrove sediments to be in the order of 23x10(12) g C per year and mangrove carbon introduced into the coastal ocean to be in the order of 46x10(12) g C per year. They account for about 11% of the total input of terrestrial carbon into the ocean and 15% of the total carbon accumulating in modern marine sediments.
Ecosystem↗
Interpolation and approximation of water quality time series and process identification.
Data records with equidistant time intervals are fundamental prerequisites for the development of water quality simulation models. Usually long-term water quality data time series contain missing data or data with different sampling intervals. In such cases "artificial" data have to be added to obtain records based on a regular time grid. Generally, this can be done by interpolation, approximation or filtering of data sets. In contrast to approximation by an analytical function, interpolation methods estimate missing data by means of measured concentration values. In this paper, methods of interpolation and approximation are applied to long-term water quality data sets with daily sampling intervals. Using such data for the water temperature and phosphate phosphorus in some shallow lakes, it was possible to identify the process of phosphate remobilisation from sediment.
Berlin↗
Heavy metal distribution in marine sediments from the southwest coast of Spain.
The latest version (1999) of the BCR-sequential extraction technique was used to determine the distribution of metals (Cu, Zn, Cd, Pb, Fe, Ni, Cr, and Mn) with major sedimentary phases (acid-soluble, reducible, oxidisable and residual) in samples from the southwest coast of Spain. The total metal content was also determined. The results showed that an extensive area along the coast (35 km long), near the joint mouth of the Tinto and Odiel Rivers, contains sediments with high concentrations of metals, with maximums of 649 mg/kg of Zn, 336 mg/kg of Cu, 197 mg/kg of Pb and 2.5 mg/kg of Cd. The values found for Cr, Ni and Mn are comparable to those in unpolluted areas. Based on the chemical distribution of metals, we found that Zn is the most mobile (i.e., it can pass easily into the water under changing environmental conditions). This metal showed the highest percentages in the acid-soluble fraction (the most labile), especially in the central coastal area, where the samples contained over 50% of this element associated with this fraction. This area close to the Tinto and Odiel river mouths also shows a significant increase in the mobility of Cd and Cu. In both cases the amount present in the residual fraction is lower, and the acid-soluble fraction is increased for Cd and the oxidisable fraction for Cu. However, the highest percentages of Fe, Cr and Ni are found in the residual fraction (84%, 89% and 75%, respectively), which implies that these metals are strongly bound to the sediments.
Geologic Sediments↗
Calculation of the mercury accumulation in the Idrijca River alluvial plain sediments.
From the historic literature on the Idrija mercury mine, it is evident that part of the smelting and mining waste was dumped into the Idrijca River. This waste was transported downstream during floods. The amount of mercury which has accumulated in the alluvial sediments of the Idrijca River until the present was studied. Mapping of Holocene river terraces of the Idrijca River was performed in order to estimate the volume of the alluvial sediment. For the purpose of the assessment of the mercury concentration, we sampled the alluvial sediments on different levels and performed an analysis of variance. The greatest variability is between the floodplain and terraces inside the same alluvial plain. Considering this fact, which determined the methodology employed for calculation, we estimated that about 2029 tons of mercury is stored in the Idrijca River alluvial sediments.
Environmental Monitoring↗
Heavy metal deposition and variation in sedimentation rate within a sedimentary basin in Central Gulf of Finland.
In studies dealing with the chemical distribution of elements in marine soft sediments, variations in sedimentation rate within a basin can bias the interpretation of the data. A basin in the central part of the Gulf of Finland was sampled at nine sampling sites along a transect, 1.2 nautical miles long. Gravity cores of the topmost recent sediment were analysed for nitric acid leachable concentrations of heavy metals. Almost without exceptions the metal concentrations were lower in the surface sediment, indicating a decrease in pollution load during the last decade. The sedimentation rates within the basin differed substantially, from 2.5 mm a-1 to some 15 mm a-1. Without dating of the sediments, the comparison of different cores is almost impossible. Dating is essential, as is thorough investigation of the basins used in sediment monitoring.
Environmental Monitoring↗
New model calculations of pH-depending tributyltin adsorption onto montmorillonite surface and montmorillonite-rich sediment.
Interactions of the pollutant tributyltin (TBT) with mineral surfaces affects its distribution and transport in aqueous systems. In the present work, model calculations are reported that quantify TBT adsorption onto pure-phase montmorillonite (sample SWy) under various pH and salinity conditions that are important from an environmental perspective. The pH level in the system is of substantial interest because it affects the speciation of TBT in solution as well as the surface properties of the solid phase, which are both important for adsorption reactions. The model is based on the generalized diffused layer model that includes >X- sites in order to account for the cation exchange effects of TBT attraction. The presence of >AIOH and >SiOH sites atthe mineral surface was not considered separately during calculation. Instead, nonselective sites (>SOH) versus selective sites (>SsOH) were distinguished with respect to the sorptive sites on montmorillonite. The latter are characterized by a high affinity of TBT bonding. Both sorptive sites exhibit the same protolysis constants but different TBT binding constants [logK(TBT/2) = -1.18 for (>SOH), logK(TBT/1) = 3.98 for (>SsOH)]. LogK(X/TBT) for the cation exchange reaction was determined as between 3.05 and 4.14. The results indicate that the inclusion of selective sites during calculations is essential for quantifying pH-dependent TBT adsorption successfully. The parameters determined for the TBT adsorption onto pure-phase montmorillonite were subsequently used to calculate pH-dependent TBT adsorption onto a natural montmorillonite-rich sediment.
Adsorption↗
Organic material: the primary control on mercury methylation and ambient methyl mercury concentrations in estuarine sediments.
Estuarine environments that have no direct sources of mercury (Hg) pollution may have sediment concentrations of methylmercury (MeHg) as high as those of polluted marine environments. In this study we examined the biogeochemical factors affecting net methylation and sediment MeHg concentrations in an unpolluted estuarine environment, the Ore River estuary, which discharges into the Bothnian Bay (20-120 ng total Hg g(-1) dry sediment, salinity 3-5% per hundred). We analyzed the spatial and temporal differences in surface sediment profiles of MeHg concentration, Hg methylation, MeHg demethylation, and concentrations of sulfide and oxygen between accumulation and erosion type bottoms. The main difference between the bottoms studied was in the proportion of organic material (OM) in the sediment, ranging between 0.8% and 10.8%. The pore water sulfide concentration profiles also differed considerably between sites and seasons, from 0 to 20 microM, with 100 microM as the extreme maximum. The sediment MeHg concentration profiles (0-10 cm) mostly varied between 0.1 and 7 ng g(-1) dry weight (dw, as Hg). The MeHg demethylation rates were relatively low and the depth profiles of the rates were relatively constant over season, site, and depth. In contrast, both rates and depths of maximum Hg methylation differed between the bottoms. The results indicate that the amount of OM accumulated at the bottoms was the main factor affecting net MeHg production, while the total amount of Hg had little or no influence on the amount of MeHg in the sediment.
Environmental Monitoring↗
Metabolism of uniconazole-P in water-sediment systems under illumination.
Aerobic soil metabolism of uniconazole-P ([S]-E-1-[4-chlorophenyl]-4,4-dimethyl-2-[1,2,4-triazole-1-yl]-penten-3-ol) and the effect of illumination on metabolic profiles were studied in the water-sediment system when spiked to water. Uniconazole-P was gradually partitioned to the sediment with an aquatic half-life of 6.9 d in darkness with formation of bound residues. Illumination of the system from a xenon lamp (>290 nm) greatly accelerated the degradation of uniconazole-P via photoinduced isomerization between E- and Z-isomers with a subsequent intramolecular cyclization, and its aquatic half-life was greatly reduced to 0.6 d. Kinetic analysis based on compartment models suggested the possible contribution of photodegradation at the water-sediment interface, leading to more formation of the cyclized derivative in the sediment.
Geologic Sediments↗
Dissipation of beta-cyfluthrin in water as affected by sediment, pH, and temperature.
Explore the source record for details and available documents.
Geologic Sediments↗
Monocorophium insidiosum (Crustacea, Amphipoda) as a candidate species in sediment toxicity testing.
Explore the source record for details and available documents.
Amphipoda↗
Palaeobiology: sea change in sediments.
Explore the source record for details and available documents.
Australia↗
Predicting the fate of sediment and pollutants in river floodplains.
Geological processes such as erosion and sedimentation redistribute toxic pollutants introduced to the landscape by mining, agriculture, weapons development, and other human activities. A significant portion of these contaminants is insoluble, adsorbing to soils and sediments after being released. Geologists have long understood that much of this sediment is stored in river floodplains, which are increasingly recognized as important nonpoint sources of pollution in rivers. However, the fate of contaminated sediment has generally been analyzed using hydrodynamic models of in-channel processes, ignoring particle exchange with the floodplain. Here, we present a stochastic theory of sediment redistribution in alluvial valley floors that tracks particle-bound pollutants and explicitly considers sediment storage within floodplains. We use the theory to model the future redistribution and radioactive decay of 137Cs currently stored on sediment in floodplains at the Los Alamos National Laboratory (LANL) in New Mexico. Model results indicate that floodplain storage significantly reduces the rate of sediment delivery from upper Los Alamos Canyon, allowing 50% of the 137Cs currently residing in the valley floor to decay radioactively before leaving LANL. A sensitivity analysis shows that the rate of sediment overturn in the valley (and hence, the total amount of radioactive 137Cs predicted to leave LANL) is significantly controlled by the rate of sediment exchange with the floodplain. Our results emphasize that flood plain sedimentation and erosion processes can strongly influence the redistribution of anthropogenic pollutants in fluvial environments. We introduce a new theoretical framework for examining this interaction, which can provide a scientific basis for decision-making in a wide range of river basin management scenarios.
Adsorption↗
Sorptive behavior of chlorophenols on river volcanic sediment.
Explore the source record for details and available documents.
Adsorption↗
Bacterial dehalogenation.
Halogenated organic compounds are produced industrially in large quantities and represent an important class of environmental pollutants. However, an abundance of haloorganic compounds is also produced naturally. Bacteria have evolved several strategies for the enzyme-catalyzed dehalogenation and degradation of both haloaliphatic and haloaromatic compounds: (i) Oxidative dehalogenation is the result of mono- or dioxygenase-catalyzed, co-metabolic or metabolic reactions. (ii) In dehydrohalogenase-catalyzed dehalogenation, halide elimination leads to the formation of a double bond. (iii) Substitutive dehalogenation in most cases is a hydrolytic process, catalyzed by halidohydrolases, but there also is a "thiolytic" mechanism with glutathione as cosubstrate. Dehalogenation by halohydrin hydrogen-halide lyases is the result of an intramolecular substitution reaction. (iv) A distinct dechlorination mechanism involves methyl transfer from chloromethane onto tetrahydrofolate. (v) Reductive dehalogenations are co-metabolic processes, or they are specific reactions involved in substrate utilization (carbon metabolism), or reductive dehalogenation is coupled to energy conservation: some anaerobic bacteria use a specific haloorganic compound as electron acceptor of a respiratory process. This review discusses the mechanisms of enzyme-catalyzed dehalogenation reactions, describes some pathways of the bacterial degradation of haloorganic compounds, and indicates some trends in the biological treatment of organohalogen-polluted air, groundwater, soil, and sediments.
Bacteria↗
The water fluxes of the Yellow River to the sea in the past 50 years, in response to climate change and human activities.
Since the 1970s, the water fluxes to the sea of the Yellow River have declined significantly. Based on data of precipitation, air temperature, the measured and "natural" river flow, the water diversion and consumption, and the areas of erosion and sediment control measures over the drainage basin, water fluxes to the sea of the Yellow River are studied in relation with the influences of changing climate and human activities. The Yellow River basin can be divided into different water source areas; multiple regression indicates that the variation in precipitation over different water source areas has different effect on water fluxes to the sea. In the period between 1970 and 1997, averaged air temperature over the whole Yellow River increased by about 1.0 degree C, from 16.5 degrees C to 17.5 degrees C, a factor that is negatively correlated with the water yield of the Yellow River. Water diversion and consumption has sharply increased and resulted in a significant decline in the water fluxes to the sea. Since the 1960s, erosion and sediment control measures have been practiced over the drainage basin. This factor, to a lesser degree, is also responsible for the decrease in water fluxes to the sea. A multiple regression equation has been established to estimate the change in water fluxes to the sea caused by the changes in precipitation, air temperature, water diversion and consumption, erosion, and sediment control measures, indicating that the contribution of water diversion and consumption to the variation in annual water flux to the sea is 41.3%, that of precipitation is 40.8%, that of temperature is 11.4%, and that of erosion and sediment control measures is 6.5%.
China↗
Selective supercritical fluid extraction as a tool for determining the PCB fraction accessible for uptake by chironomid larve in a limnic sediment.
Selective supercritical fluid extraction (SFE) at 40 degrees C, 400 bar and 60 min was used to selectively remove bioavailable PCBs from a naturally contaminated limnic sediment. The extraction decreased the sediment concentrations of the nine studied PCBs by 54% (on average). Chironomid larvae were thereafter cultured in pre-extracted sediment as well as in untreated sediment to study the differences in uptake of PCBs in the two cultures. While the prevailing equilibrium partitioning (EqP) theory predicts a 54% decrease in PCB uptake by the chironomids in the pre-extracted sediment, with a maintained biota-to-sediment accumulation factor (BSAF), a decrease in PCB uptake by 91% was observed. For all investigated PCBs the BSAFs were on average 81% lower in the cultures with pre-extracted sediment than in the untreated systems. The data allowed for a calculation of the bioavailable fraction, which was estimated to 60%. This is very close to the 54% removed by selective SFE, demonstrating the possibility of using SFE as a tool to determine the bioavailable PCB fraction in a polluted sediment.
Algorithms↗