scholarly journals Bacterial density as an unexpected factor regulating decomposition by soil oligotrophs

2020 ◽  
Author(s):  
Alexandre Coche ◽  
Tristan Babey ◽  
Alain Rapaport ◽  
Laure Vieublé Gonod ◽  
Patricia Garnier ◽  
...  
Keyword(s):  
Transport Model ◽  
Transport Processes ◽  
Bacterial Density ◽  
Strong Interactions ◽  
List Type ◽  
Soil Core ◽  
Dispersive Transport ◽  
Density Regulation ◽  
Metabolic Traits ◽  
Ratio Dependent

AbstractBacterial decomposition of organic matter in soils is generally believed to be mainly controlled by the accessibility of bacteria to their substrate. The influence of bacterial metabolic traits on this control has however received little attention in highly heterogeneous spatial conditions under advective-dispersive transport of bacteria and substrates. Here, we develop a biochemical transport model to screen the interactive impacts of dispersion and metabolic traits on mineralization. We compare the model results with two sets of previously performed cm-scale soil-core experiments in which the mineralization of the pesticide 2,4-D was measured under well-controlled initial distributions and transport conditions. Bacterial dispersion away from the source of substrate induced a significant increase in 2,4-D mineralization, revealing the existence of a control of decomposition by the bacterial density, in addition to the accessibility to the substrate. This regulation of degradation by density becomes dominant for bacteria with an efficient uptake of substrate at low substrate concentrations (i.e. oligotrophs). The model output suggests that the distance between bacteria adapted to oligotrophic environments is a stronger regulator of degradation than the distance between substrate source and these bacteria. Such oligotrophs, commonly found in soils, compete with each other for substrate even under remarkably low population densities. The ratio-dependent Contois growth model, which includes a density regulation in the expression of the uptake efficiency, appears more versatile and accurate than the substrate-dependent Monod model. In view of their strong interactions, biochemical and transport processes cannot be handled independently but should be integrated, in particular when biochemical processes of interest are carried out by oligotrophs.Abstract FigureHighlights–Biodegradation in soils results from strong biochemical and transport couplings–Biodegradation depends on bacterial density, in addition to substrate accessibility–Bacterial density regulation counterbalances substrate accessibility regulation–Density regulation is enhanced for oligotrophic bacteria–The ratio-dependent Contois model is relevant to represent this double regulation

scholarly journals Application of divided convective-dispersive transport model to simulate variability of conservative transport processes inside a planted horizontal subsurface flow constructed wetland

2020 ◽  
Author(s):  
Ernő Dittrich ◽  
Mihály Klincsik ◽  
Dávid Somfai ◽  
Anita Dolgos-Kovács ◽  
Tibor Kiss ◽  
...  
Keyword(s):  
Constructed Wetland ◽  
Dispersion Coefficient ◽  
Transport Model ◽  
Subsurface Flow ◽  
Distribution Functions ◽  
Transport Processes ◽  
Inverse Gaussian ◽  
Dispersive Transport ◽  
Subsurface Flow Constructed Wetland ◽  
Horizontal Subsurface Flow

AbstractThis paper offers a novel application of our model worked out in Maple environment to help understand the very complex transport processes in horizontal subsurface flow constructed wetland with coarse gravel (HSFCW-C). We made tracer measurements: Inside a constructed wetland, we had 9 sample points, and samples were taken from each point at two depths. Our model is a divided convective-dispersive transport (D-CDT) model which makes a fitted response curve from the sum of two separate CDT curves showing the contributions of the main and side streams. Analytical solutions of CDT curves are inverse Gaussian distribution functions. This model was fitted onto inner points of the measurements to demonstrate that the model gives better fitting to the inner points than the commonly used convective-dispersive transport model. The importance of this new application of the model is that it can resemble transport processes in these constructed wetlands more precisely than the regularly used convective-dispersive transport (CDT) model. The model allows for calculations of velocity and dispersion coefficients. The results showed that this model gave differences of 4–99% (of velocity) and 2–474% (of dispersion coefficient) compared with the CDT model and values were closer to actual hydraulic behavior. The results also demonstrated the main flow path in the system.

scholarly journals MODELING ESTUARIAL COHESIVE SEDIMENT TRANSPORT

1984 ◽  
Vol 1 (19) ◽  
pp. 199
Author(s):  
E.J. Hayter ◽  
A.J. Mehta
Keyword(s):  
Sediment Transport ◽  
Transport Model ◽  
Cohesive Sediment ◽  
Transport Processes ◽  
Weighted Residual Method ◽  
Dispersive Transport ◽  
Time Step ◽  
Advection Dispersion ◽  
Cohesive Sediment Transport ◽  
Suspended Sediment Concentrations

Cohesive sediment related problems in estuaries include shoaling in navigable waterways and water pollution. A two-dimensional, depth averaged, finite element cohesive sediment transport model, CSTM-H, has been developed and may be used to assist in predicting the fate of sorbed pollutants and the frequency and quantity of dredging required to maintain navigable depths. Algorithms which describe the transport processes of redispersion, resuspenslon, dispersive transport, settling, deposition, bed formation and bed consolidation are incorporated in CSTM-H. The Galerkin weighted residual method is used to solve the advection-dispersion equation with appropriate source/sink terms at each time step for the nodal suspended sediment concentrations. The model yields stable and converging solutions. Verification was carried out against a series of erosion-deposition experiments in the laboratory using kaolinite and a natural mud as sediment. A model application under prototype conditions is described.

Influence of the Distribution of Tail States in a-Si:H on the Field Dependence of Carrier Drift Mobilities

2004 ◽  
Vol 808 ◽  
Author(s):  
Monica Brinza ◽  
Evguenia V. Emelianova ◽  
André Stesmans ◽  
Guy J. Adriaenssens
Keyword(s):  
Field Dependence ◽  
Carrier Mobility ◽  
Transport Model ◽  
Chemical Vapor ◽  
Gaussian Component ◽  
Dispersive Transport ◽  
Exponential Distributions ◽  
Band Tail ◽  
Multiple Trapping ◽  
Gaussian Density

ABSTRACTExponential distributions of tail states have been able, within the framework of a multiple-trapping transport model, to account rather well for the time-of-flight photoconductivity transients that are measured with ‘standard’ a-Si:H, i.e. material prepared by plasma-enhanced chemical vapor deposition at ∼250°C. A field-dependent carrier mobility in the dispersive transport regime is part of the observations. However, samples prepared in an expanding thermal plasma, although still exhibiting the dispersive transients, fail to show this field dependence. The presence of a Gaussian component in the density of valence-band tail states can account for such behavior for the hole transients. Nanoscale ordered inclusions in the amorphous matrix are thought to be responsible for the Gaussian density of states contribution.

scholarly journals Sediment transport modelling in a distributed physically based hydrological catchment model

2010 ◽  
Vol 7 (5) ◽  
pp. 7591-7631 ◽  
Author(s):  
M. Konz ◽  
M. Chiari ◽  
S. Rimkus ◽  
J. M. Turowski ◽  
P. Molnar ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Hydrological Model ◽  
Transport Model ◽  
Water Cycle ◽  
Transport Processes ◽  
Distributed Hydrological Model ◽  
Water Fluxes ◽  
Transport Modelling ◽  
Erosion Processes ◽  
Grid Level

Abstract. Sediment transport and erosion processes in channels are important components of water induced natural hazards in alpine environments. A distributed hydrological model, TOPKAPI, has been developed to support continuous simulations of river bed erosion and deposition processes. The hydrological model simulates all relevant components of the water cycle and non-linear reservoir methods are applied for water fluxes in the soil, on the surface and in the channel. The sediment transport simulations are performed on a sub-grid level, which allows for a better discretization of the channel geometry, whereas water fluxes are calculated on the grid level in order to be CPU efficient. Flow resistance due to macro roughness is considered in the simulation of sediment transport processes. Several transport equations as well as the effects of armour layers on the transport threshold discharge are considered. The advantage of this approach is the integrated simulation of the entire water balance combined with hillslope-channel coupled erosion and transport simulation. The comparison with the modelling tool SETRAC and with LiDAR based reconstructed sediment transport rates demonstrates the reliability of the modelling concept. The modelling method is very fast and of comparable accuracy to the more specialised sediment transport model SETRAC.

scholarly journals Numerical evaluation of the performance of a single-well groundwater source heat pump system in Beijing, China

2019 ◽  
Vol 38 (1) ◽  
pp. 201-221 ◽  
Author(s):  
Tianfu Xu ◽  
Fengyu Li ◽  
Bo Feng ◽  
Guanhong Feng ◽  
Zhenjiao Jiang
Keyword(s):  
Heat Transport ◽  
Heat Pump ◽  
Transport Model ◽  
Heat Pumps ◽  
Transport Processes ◽  
Pump System ◽  
Heat Pump System ◽  
Single Well ◽  
Groundwater Source ◽  
Beijing China

Shallow geothermal energy is stable and clean. Using a heat pump to produce groundwater and realize heating and cooling can effectively prevent haze and reduce energy consumption. To reduce engineering costs, many buildings in Beijing, China, plan to utilize single-well groundwater source heat pumps. Numerical modeling is an effective way to gain an understanding of thermal transport processes. However, wellbore-reservoir coupling and the uncertainty of productivity due to geological parameters make simulation difficult. A wellbore-reservoir-integrated fluid and heat transport model is defined by T2Well simulator to predict the productivity of a typical single-well system, with consideration of complex geological factors. The model is validated by the analytical model developed in Beijing, China. The fluid processes in the wellbore are described by 1 D non-Darcy flow, and the reservoir 3 D fluid and heat transport processes are calculated. Six crucial factors satisfying a random distribution are used, and for a single well that can supply heat for an area of 9000 m2, the output temperature during the heating season ranges from 11°C to 15°C.

Modelling of the Transport of Chlorinated Hydrocarbon Solvents in Groundwater: A Case Study

1985 ◽  
Vol 17 (9) ◽  
pp. 13-21 ◽  
Author(s):  
W K. H. Kinzelbach
Keyword(s):  
Transport Model ◽  
Model Parameters ◽  
Dispersive Transport ◽  
Transport Models ◽  
Chlorinated Hydrocarbon ◽  
First Order ◽  
Hydrocarbon Solvents ◽  
Simplifying Assumptions ◽  
Environmental Engineer

At present chlorinated hydrocarbon solvents rank among the major pollutants found in groundwater. In the interpretation of field data and the planning of decontamination measures numerical transport models may be a valuable tool of the environmental engineer. The applicability of one such model is tested on a case of groundwater pollution by 1,1,1,-trichloroethane. The model is composed of a horizontally 2-D flow model and a 3-D ‘random-walk' transport model. It takes into account convective and dispersive transport as well as linear adsorption and a first order decay reaction. Under certain simplifying assumptions the model allows an adequate reproduction of observed concentrations. Due to uncertainty in data and limited comparabili ty of simulated and measured concentrations the model parameters can only be estimated within bounds. The decay rate of 1,1,1-trichloroethane is estimated to lie between 0 and 0.0005 l/d.

The Effects of Scaling and Model Complexity in Simulating the Transport of Inorganic Micropollutants in a Lowland River Reach

2006 ◽  
Vol 41 (1) ◽  
pp. 24-36 ◽  
Author(s):  
Karl-Erich Lindenschmidt ◽  
René Wodrich ◽  
Cornelia Hesse
Keyword(s):  
Large Scale ◽  
Transport Model ◽  
Transport Processes ◽  
Model Complexity ◽  
Scale Model ◽  
Small Scale ◽  
Quality Model ◽  
Large Scale Model ◽  
Iron And Zinc ◽  
Physical And Chemical

Abstract A hypothesis stating that more complex descriptions of processes in models simulate reality better (less error) but with more unreliable predictability (more sensitivity) is tested using a river water quality model. This hypothesis was extended stating that applying the model on a domain of smaller scale requires greater complexity to capture the same accuracy as in large-scale model applications which, however, leads to increased model sensitivity. The sediment and pollutant transport model TOXI, a module in the WASP5 package, was applied to two case studies of different scale: a 90-km course of the 5th order (sensu Strahler 1952) lower Saale river, Germany (large scale), and the lock-and-weir system at Calbe (small scale) situated on the same river course. A sensitivity analysis of several parameters relating to the physical and chemical transport processes of suspended solids, chloride, arsenic, iron and zinc shows that the coefficient, which partitions the total heavy metal mass into its dissolved and sorbed fraction, is a very sensitive parameter. Hence, the complexity of the sorptive process was varied to test the hypotheses.

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