共查询到20条相似文献，搜索用时 31 毫秒
1.
D. B. Denisov 《Water Resources》2007,34(6):682-692
Paleoecological studies of small water bodies were carried out in a model subarctic lake-river system. The degree of transformations of aquatic ecosystems under a set of anthropogenic factors is shown to vary depending on the load and individual features of water bodies. Data on the state of aquatic ecosystems before the industrial development of the region are collected. The species composition of diatom algae and their ecological characteristics are examined. 相似文献
2.
Analysis of paleolimnological data on a part of Lake Imandra (Kola Peninsula), polluted by wastewaters discharged from a copper-nickel plant, is used to calculate the vertical profile of toxicity of bottom sediments and determine the response of dominant species of diatomic complex to the growing toxicity. The species are aggregated by the similar responses to the load. The dependence between the population sizes of diatom groups and toxicity is established. The diatom complex is shown to change its structure twice—at the toxicity exceeding the background level by factors of 1.2 and 3.2, respectively. A model is developed to describe variations in the species composition of the community under growing toxicity; the model is shown to be applicable to the analysis of paleolimnological data. General analysis of the model is given, and typical scenarios of variation in the number of species under growing toxic load are described. 相似文献
3.
A model of bacterial culture, utilizing a toxic substrate in continuous flow conditions' is discussed in the present paper. The relative velocity of microorganisms growth is expressed by means of a formula proposed by us, grounded on the analogy of a model of an irreversibly inhibited enzymatic reaction. It is assumed that the integral parameter characterizing the damage of the bacterial cell by a toxic agent may be considered a slow variable in regard to the variation of the biomass and substrate concentrations. An equation for the evolution of this parameter is proposed. A problem of minimum time adaptation of the bacterial population is proposed as a time optimal control problem that is solved on the basis of the Pontryagin maximum principle. This model provides a possibility of studying some regularities in the adaptation mechanism of the microorganisms destroying toxic substances. The same model can also be used to forecast the optimal regimes in cultivation of bacterial cultures that play an essential role in the biological self-purification of various water pools. 相似文献
4.
Urška Kuhar Tatjana Gregorc Miran Ren?elj Nina Šraj-Kr?i? Alenka Gaberš?ik 《Limnologica》2007,37(2):146-154
The distribution and abundance of macrophytes, land-use beyond the riparian zone, characteristics of the riparian zone and selected channel properties have been studied in 9 streams flowing through an agricultural landscape in the north-eastern part of Slovenia. The streams studied supported a rich macrophyte community. Altogether, 53 plant taxa were observed on 93 km of the streams. Canonical correspondence analysis indicated that 10 out of the 11 parameters examined significantly influenced macrophyte distribution. Of these, substrate characteristics and riparian vegetation type were the most influential. Species composition analysis revealed that the majority of species indicated moderate nutrient load while, in the more strongly modified reaches, species indicating eutrophic conditions, i.e. Myriophyllum spicatum and different species of genus Potamogeton, were more abundant. 相似文献
5.
《Limnologica》2015
Submerged macrophyte detritus is a major component of the organic matter entering shallow lakes. Plant litter decomposition is a complex process that is mediated by microorganisms and some invertebrates. However, the role that aquatic organisms play in the decomposition of macrophytes in shallow subtropical lakes is unclear. This study compared the decomposition rates of Potamogeton pectinatus and Chara zeylanica in a shallow lake (southern Brazil) and assessed the fungal biomass and the macroinvertebrate community associated with the detritus. Aliquots of both species were incubated in litter bags and placed in the lake. After 1, 7, 20, 40, 60, and 80 days of incubation, one set of litter bags was removed from the lake. In a laboratory, plant material was washed for the determination of decomposition rates, chemical characterisation, and quantification of microorganisms and invertebrates. After 80 days of incubation, there was no C. zeylanica detritus, with a decomposition that was four times faster than that of P. pectinatus. The chemical composition was also different between the two detritus, with P. pectinatus showing a higher concentration of nitrogen, phosphorus, organic matter, polyphenols, and carbon. The fungal biomass was similar between the two species. In total, 7502 invertebrates belonging to 27 taxa were sampled in this study. The composition and abundance of invertebrates was different between the two species. In conclusion, the chemical structure of the macrophyte species studied was important for the microorganisms’ and invertebrates’ colonisation. In addition, leaching had an important function in the initial degradation process. 相似文献
6.
Lithology‐controlled evolution of stream bed sediment and basin‐scale sediment yields in adjacent mountain watersheds,Idaho, USA 
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下载免费PDF全文 The composition, grain‐size, and flux of stream sediment evolve downstream in response to variations in basin‐scale sediment delivery, channel network structure, and diminution during transport. Here, we document downstream changes in lithology and grain size within two adjacent ~300 km2 catchments in the northern Rocky Mountains, USA, which drain differing mixtures of soft and resistant rock types, and where measured sediment yields differ two‐fold. We use a simple erosion–abrasion mass balance model to predict the downstream evolution of sediment flux and composition using a Monte Carlo approach constrained by measured sediment flux. Results show that the downstream evolution of the bed sediment composition is predictably related to changes in underlying geology, influencing the proportion of sediment carried as bedload or suspended load. In the Big Wood basin, particle abrasion reduces the proportion of fine‐grained sedimentary and volcanic rocks, depressing bedload in favor of suspended load. Reduced bedload transport leads to stronger bed armoring, and coarse granitic rocks are concentrated in the stream bed. By contrast, in the North Fork Big Lost basin, bedload yields are three times higher, the stream bed is less armored, and bed sediment becomes dominated by durable quartzitic sandstones. For both basins, the geology‐based mass balance model can reproduce within ~5% root‐mean‐square error the composition of the bed substrate using realistic erosion and abrasion parameters. As bed sediment evolves downstream, bedload fluxes increase and decrease as a function of the abrasion parameter and the frequency and size of tributary junctions, while suspended load increases steadily. Variable erosion and abrasion rates produce conditions of variable bed‐material transport rates that are sensitive to the distribution of lithologies and channel network structure, and, provided sufficient diversity in bedrock geology, measurements of bed sediment composition allow for an assessment of sediment source areas and yield using a simple modeling approach. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
7.
Several models explaining species composition of aquatic bryophytes are available for specific regions. However, a more general, conceptual model applicable to a broader range of regions is lacking.We present a conceptual model ranking environmental factors determining submerged bryophyte communities in small mountain streams. It was tested on a dataset of 54 stream sections after removing the effect of stream size and altitude. Species responses were modeled with pH as predictor variable based on 97 stream sites covering six mountain regions all over Germany. Multiple regressions revealed the importance of primary growth factors (light, Ep(CO2)) and substrate for the total submerged bryophyte coverage.The known distinction of hard- and softwater bryoflora was clearly supported. The floristic composition of headwaters was predominantly determined by the bicarbonate/ionic strength complex. Species response to pH values supported this result and thus our conceptual model. The primary growth resources light, Ep(CO2) and availability of coarse streambed material explained one third (Radjusted2 = 0.34) of total submerged bryophyte cover. Disturbances, predominantly spates, reduce biomass but do not affect the basic floristic structure.In conclusion, conceptual models and monitoring methods focusing on aquatic bryophytes need to clearly distinguish “aquatic” from “submersed by chance”. All “aquatic bryophytes” found in Germany can also occur at least temporarily at non-submerged sites. Therefore, a distinction between primary growth factors and additional resources is recommended to disentangle factors determining aquatic bryophyte communities. 相似文献
8.
The redistribution of stable isotopes allows specifying the pathway of substrate utilization and identifying the relevant kinetic parameters. To describe degradation kinetics and identify predominant metabolic pathway for microbial substrate transformation, new basic equations, which take into account the dynamics of heavier isotope in the substrate, intermediates, and products were added to the common model of microbial substrate transformation, which did consider isotope differences at any step of substrate transformation. Using the unified approach, we showed that the dynamic changes of isotope fractionation depend on the kinetic coefficients, the initial conditions, and the microorganisms participating in the reactions during microbial denitrification, anaerobic oxidation of methane by sulphate and nitrite, aerobic oxidation of methane gas, and anaerobic digestion of cellulose. 相似文献
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10.
At present the development together with an intensification of anaerobic processes calls for methods of observation and control. It is very important to know intermediate metabolites of anaerobic microorganisms and the activity of methanogenic ones. Presented analytical methods are GLC analyses of lower fatty acids, alcohols, aldehydes and ketones and components of biogas. The chromatography using steam as a mobile phase is also mentioned. The method of determining the fluorescent coenzyme F420 was tested and modified. This coenzyme is specific for methanogenic microorganisms and is closely linked with their activity. The determination of the total activity of the hydrogenase system of anaerobic microorganisms by means of the rate of the consumption and evolution of molecular hydrogen was also presented. The applicability and effectivenes of these methods were verified on natural samples. All the methods mentioned above give satisfactory results with available equipment, materials and techniques. 相似文献
11.
Abstract The application of a data-driven adaptive neuro-fuzzy modelling technique for predicting bed load and total bed-material load for the River Rhine is summarized. Four main parameters affecting sediment transport are used to construct the model, using 560 and 510 measured bed load and total bed-material load data, respectively. Two-thirds of the available data sets are used for training and one third for testing. The initial fuzzy model is obtained by grid partitioning of the input variables. The optimization of the model is performed by data-driven tuning of the fuzzy model parameters using the adaptive neuro-fuzzy inference system, so that the model output is able to reproduce the measured value. A sensitivity analysis for the combination of input parameters, as well as the number and type of membership functions, is also performed. The model results show that the data-driven adaptive neuro-fuzzy modelling approach can be a powerful alternative technique for estimating both bed load and total bed-material load. Editor D. Koutsoyiannis Citation Wieprecht, S., Tolossa, H.G., and Yang, C.T., 2013. A neuro-fuzzy-based modelling approach for sediment transport computation. Hydrological Sciences Journal, 58 (3), 587–599. 相似文献
12.
Gaetano Guida Vincenzo Palmeri Luca Settanni Raimondo Gaglio Marco Tolone Vito Ferro 《国际泥沙研究》2022,37(4):493-504
Calanchi(plural of calanco) are typical Italian badlands created by a combination of morphogenetic processes(rill and interrill erosion, gullying, piping, and mass movements) mainly originated by the effect of water. Calanchi are characterized by the sparse and patchy distribution of vegetation, and, in interplant areas, the soil surface is colonized by an association of organisms known as biological soil crust(BSC). A morphometric analysis of 45 basins in the studied calanchi area, based on a h... 相似文献
13.
The accuracy of a series spring model to predict the peak displacement and displacement history of Triple Pendulum? (TP) bearings in a strongly shaken, full‐scale building is evaluated in this paper. The series spring model was implemented as a self‐contained three‐dimensional TP bearing element in OpenSees and is now available for general use. The TP bearing element contains the option for constant friction or a generalized friction model that accounts for the effect of instantaneous velocity and compression load on the friction coefficient. Comparison between numerical simulation and experimental data of a five‐story steel moment frame building shows that the peak displacement of isolation system can generally be predicted with confidence using a constant friction coefficient model. The friction coefficient model accounting for the effect of axial load and velocity leads to minor improvement over the constant friction coefficient models in some cases. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
14.
Two very similar species of freshwater snails,Lymnaea auricularia andL. peregra coexist in Lake Zürich. We examined their diets to determine possible differences. Microscopic analysis of stomach and hind gut contents revealed no marked differences between the diets of the two snail species collected from the same substrate. However, in both species we found significant differences between the composition of the substrate and that of the stomach contents, using discriminant analysis. We conclude that both species of snails feed preferentially on patches of favourable food supply and that their diets overlap almost totally. The coexistence of the two species under these conditions suggests that food does not limit their density in the area studied. 相似文献
15.
The state of the marine environment (the temperature, light intensity, transparency, biogenic load) in Tatar Strait was assessed
based on mean annual data from literary sources and with the use of GIS “Sakhalin Shelf.” The entire strait was divided into
three regions (northern, southwestern, and southeastern), and water exchange between them for each month was estimated by
using Bergen Oceanic Model. The information about the state of the marine environment and water exchange characteristics was
used as input data for a hydroecological model, which enabled the assessment of annual variations of biogenic substance concentrations
and biomasses of microorganisms (heterotrophic bacteria, three groups of phytoplankton, and two groups of zooplankton) in
the strait regions chosen. The development conditions of microorganism biomasses within the year can be characterized by their
activity indices (specific growth rates), the values of internal fluxes of biogenic substances, and calculated bioproductivity
values. The calculated biogenic substance concentrations and phytoplankton bioproductivity values showed good agreement with
the estimates for the Sea of Japan and Tatar Strait available from the literature. 相似文献
16.
John Pitlick Erich R. Mueller Catalina Segura Robert Cress Margaret Torizzo 《地球表面变化过程与地形》2008,33(8):1192-1209
This study investigates trends in bed surface and substrate grain sizes in relation to reach‐scale hydraulics using data from more than 100 gravel‐bed stream reaches in Colorado and Utah. Collocated measurements of surface and substrate sediment, bankfull channel geometry and channel slope are used to examine relations between reach‐average shear stress and bed sediment grain size. Slopes at the study sites range from 0·0003 to 0·07; bankfull depths range from 0·2 to 5 m and bankfull widths range from 2 to 200 m. The data show that there is much less variation in the median grain size of the substrate, D50s, than there is in the median grain size of the surface, D50; the ratio of D50 to D50s thus decreases from about four in headwater reaches with high shear stress to less than two in downstream reaches with low shear stress. Similar trends are observed in an independent data set obtained from measurements in gravel‐bed streams in Idaho. A conceptual quantitative model is developed on the basis of these observations to track differences in bed load transport through an idealized stream system. The results of the transport model suggest that downstream trends in total bed load flux may vary appreciably, depending on the assumed relation between surface and substrate grain sizes. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
17.
Comparative analysis of the structural organization and functioning of phytoperiphyton in rivers flowing over the territory of the Karelian Republic and subject to anthropogenic load resulting from urbanization is presented. The effect of changes in the hydrological and hydrochemical regimes on the species composition and biomass of periphytic algae is discussed. The possibility of using phytoperiphyton as an indicator of the ecological state of small river ecosystems is analyzed. 相似文献
18.
Eighteen models with different levels of complexity for representing sorption, mass transfer, and biodegradation are used to simulate the biodegradation of toluene (primary substrate) and TCE (cometabolic substrate). The simulations are conducted for hypothetical completely mixed systems of various scenarios with regard to sorbent, microbial composition, and solute concentrations. The purpose of the suite of simulations is to investigate the sensitivity of different modeling approaches in simulating the bio-attenuation of co-existing solutes in sorbent-water systems. The sensitivity of results to the modeling approach depends on the biogeochemical conditions of the system. For example, the results are insensitive to the type of sorption model in systems with low sorption strength and slow biodegradation rates, and insensitive to the biodegradation rate model if mass transfer controlled. Differences among model results are generally greater when evaluated in terms of total mass removal rather than aqueous phase concentration reduction. The fate of the cometabolite is more sensitive to the proper consideration of co-solute effects than is the fate of the primary substrate. For a given system, graphical comparison of a characteristic mass transfer rate coefficient (αmt) versus a characteristic biodegradation rate coefficient (αbio) provides an indication of how sensitivity to the different processes may be expected to change with time and can guide the selection of an appropriate level of model complexity. 相似文献
19.
We examined the influence of algal farming on fish assemblages in two shallow coastal lagoons in Zanzibar, Tanzania. Fish assemblages were visually investigated using a belt transect method and the line-intercept technique was used to examine the substrate composition. 101 species of fish belonging to 31 families were recorded. Algal farming affected the associated fish fauna in terms of abundance, species richness, trophic identity and fish community composition. However, the impact differed between the lagoons. Algal farms in one lagoon hosted a more abundant and diversified fish fauna than controls, whereas farms in the other lagoon exhibited lower fish densities and similar species diversity compared to controls. The discrepancies between lagoons may be an effect of differences in farming intensity and character of the substratum. 相似文献
20.
This paper presents a modified half-sine-squared load model of the jumping impulses for a single person. The model is based on a database of 22,921 experimentally measured single jumping load cycles from 100 test subjects. Threedimensional motion capture technology in conjunction with force plates was employed in the experiment to record jumping loads. The variation range and probability distribution of the controlling parameters for the load model such as the impact factor, jumping frequency and contact ratio, are discussed using the experimental data. Correlation relationships between the three parameters are investigated. The contact ratio and jumping frequency are identified as independent model parameters, and an empirical frequency-dependent function is derived for the impact factor. The feasibility of the proposed load model is established by comparing the simulated load curves with measured ones, and by comparing the acceleration responses of a single-degree-of-freedom system to the simulated and measured jumping loads. The results show that a realistic individual jumping load can be generated by the proposed method. This can then be used to assess the dynamic response of assembly structures. 相似文献