Aggregation of vertical flow in the vadose zone with auto- and cross-correlated hydraulic properties

International audienceQuantifying water flow across larger areas of the vadose zone has applications in water resources management and climate modeling. The nonlinearity of unsaturated flow and the variability of vadose zone parameters make it difficult, if not impossible, to accurately simulate near-surface water content and flux with large-scale models. Monte Carlo simulations of one-dimensional infiltration and evaporation were conducted with the Richards equation to simulate moisture content and flux in a heterogeneous field according to the streamtube concept. A set of 126 retention curves and saturated hydraulic conductivities from the UNSODA database was used to generate random fields of hydraulic parameters with pre-defined auto- and cross-correlation. Two stochastic parameters were used: the retention shape factor, ln mn, and either the retention scale parameter θs or ln hG or the saturated hydraulic conductivity, ln Ks. Infiltration is mostly governed by ln Ks. The evaporative flux is strongly determined by the “structural” parameter ln hG and also by the “textural” parameter ln mn. The water content in the upper part of the soil depends mostly on ln mn and somewhat on θs. Cross-correlations all resulted in clusters with consistently low or high water contents and moisture fluxes. Aggregation to obtain results at larger scales was done by a posteriori averaging of local results. This procedure is a convenient benchmark for large-scale modeling approaches. In an example of a priori aggregation, effective retention parameters were optimized to synthetic retention curves for the larger pixel scale and subsequently used in the Richards equation. The amount of infiltrated water was overestimated by up to 40%, large parts of the upper profile were erroneously predicted to be saturated. Although effective hydraulic properties have been used successfully in evaporation studies, considerable errors, which increased with pixel size, also occurred for evaporation. The stream tube modeling offers a convenient and accurate, albeit mundane, approach to elucidate the role of hydraulic properties and to obtain large-scale hydrological data

Soil Water Retention : II. Derivation and Application of Shape Index

International audienceThe concept of a shape index was introduced in Part I to characterize the water retention curve. A potential problem with the parameterization of retention data is the interdependency of parameter values and their conversion to other parametric models. In this Part II the shape index is used to derive formulae for the conversion between: (i) hydraulic parameters of the Brooks-Corey (BC) and van Genuchten (vG) equations, (ii) parameter sets with and without the constraint that the residual water content r = 0, and (iii) vG-shape parameters with different constraints. The dependency of hydraulic parameters on the optimization strategy and the applicability of conversion equations were investigated with 660 retention curves from the GRIZZLY database. The BC-shape parameter and the vG-shape factor mn are poorly correlated for larger and mn (overall r2 = 0.96 for r = 0). Instead of the commonly used equality = mn, conversion based on the shape indices PBC and PvG is more accurate (r2 = 0.99). The shape index is also convenient to accurately predict shape parameters for different constraining scenarios involving r and m = 1 – k/n. The values for r and the shape parameters and mn are not unique. They are positively correlated to maintain the same soil water capacity for a particular soil. For the optimization of parameters, we recommend constraining r. Accurate optimization of retention data, in particular the shape parameters, is possible by constraining r to a non-zero value inferred from the shape index

Soil Water Retention : I. Introduction of a Shape Index

International audienceKnowledge of soil water retention is fundamental to quantify the flow of water and dissolved substances in the subsurface. Water retention is often quantified with models fitted to observed retention points. Interpretation and conversion of parameters from different models is subjective and prone to error. We examined 461 retention curves from the UNSODA database and 660 from the GRIZZLY database. Parameters of the Brooks-Corey (BC) and van Genuchten (vG) equations were fitted to the retention data. The shape parameters in these functions (, m, and n) are closely correlated to soil texture and may be predicted with so-called pedotransfer functions (PTFs). Among the scale parameters, the saturated water content s proved to be a robust fitting parameter regardless of parameterization. Reliable optimization of the residual water content r is more difficult; without any constraint it was negative for 54.4% of the GRIZZLY samples, and its value was strongly correlated to the shape parameters. The BC- and vG-shape parameters are often converted assuming = mn, which is incorrect when or mn is large (e.g., > 0.8). To facilitate the interpretation, conversion, and optimization of retention parameters, we introduce a water retention shape index P. This index constitutes an integral measure of the slope of the retention curve and characterizes the retention behavior of a particular soil with a single number. A value for the index can be estimated directly from retention data. For the majority of the samples P ranged between 0 and 0.4; rarely did P exceed 3, which is the maximum expected for fractal behavior. The value for P was related to soil texture: fine-textured soils tend to have smaller values than coarse-textured soils. The shape index provides a benchmark for conversion and comparison of parameters

AGU hydrology days 2003

Includes bibliographical references.23rd annual AGU hydrology days was held on March 31 - April 2, 2003 at Colorado State University.Accurate knowledge of water fluxes in the vadose zone of watersheds is important for applications such as water resources management and climate forecasting. Most, if not all, largescale studies follow a pragmatic approach where simplifying assumptions have to be made regarding problem formulation and estimation of hydraulic properties. This study investigates simplifications in both regards to predict infiltration and evaporation fluxes near or at the surface for a generic, rectangular watershed consisting of sand and silt loam columns. The two-dimensional flow problem (reference scenario) as well as simplifying 1-D problems are solved with the finite-element method (FEM) for 1, 10, 100, and 1000 m widths of the flow domain and different proportions of the sand and silt loam soils. The hydraulic functions are estimated from soil texture. In the simplifying scenarios, the flow domain is either represented as an equivalent soil using a weighted particle-size distribution as previously applied in physico-empirical predictions of hydraulic properties (a priori aggregation) or as two parallel stream tubes with area-weighted contributions to the total flux (a posteriori aggregation). Substantial differences were found between the fluxes based on the "equivalent" and reference scenarios even though our approach was based on a most favorable situation where only a limited number of texturedependent hydraulic parameters were different. The "stream tube" scenario typically provided a good description of the flux according to the reference scenario except for infiltration in case of domains less than 10 m wide. No pronounced textural differences are likely to occur over such small distances and the stream tube model appears to be a viable method to describe near-surface fluxes in catchments with a spatially variable soil texture

Dexamethasone exposure of neonatal rats modulates biliary lipid secretion and hepatic expression of genes controlling bile acid metabolism in adulthood without interfering with primary bile acid kinetics

Literature suggests that glucocorticoid (GC) exposure during early life may have long-term consequences into adult life. GCs are known to influence hepatic bile acid synthesis and their transport within the enterohepatic circulation. This study addresses effects of early postnatal exposure to GC on hepatic expression of key genes in bile acid metabolism and bile acid kinetics in adult rats. Male rats were treated with either dexamethasone (DEX) or saline at days 1-3 d after birth. Liver tissue and blood were collected from 2 d to 50 wk of age. Bile acid kinetics were determined at week 8. DEX acutely induced hepatic mRNA levels of cholesterol 7 alpha-hydroxylase (Cyp7a1), cholesterol 27-hydroxylase (Cyp27), and in particular sterol 12 alpha-hydroxylase (Cyp8b1), whereas expression of the bile acid transporters bile salt export pump (Bsep) and sodium taurocholate cotransporting polypeptide (Ntcp) was moderately affected. Neonatal DEX administration led to increased bilary lipid secretion, decreased Cyp8B1 mRNA expression and a 3-fold higher Cyp7a1/Cyp8b1 mRNA ratio in rats at week 8 compared with age-matched controls without alterations in bile acid kinetics. Therefore, neonatal DEX administration causes altered gene expressions later in life that are not translated into quantitative changes in bile acid kinetics

Overexpression of carnitine palmitoyltransferase I in skeletal muscle in vivo increases fatty acid oxidation and reduces triacylglycerol esterification

A key regulatory point in the control of fatty acid (FA) oxidation is thought to be transport of FAs across the mitochondrial membrane by carnitine palmitoyltransferase I (CPT I). To investigate the role of CPT I in FA metabolism, we used in vivo electrotransfer (IVE) to locally overexpress CPT I in muscle of rodents. A vector expressing the human muscle isoform of CPT I was electrotransferred into the right lateral muscles of the distal hindlimb [tibialis cranialis (TC) and extensor digitorum longus (EDL)] of rats, and a control vector expressing GFP was electrotransferred into the left muscles. Initial studies showed that CPT I protein expression peaked 7 days after IVE (+104%, P < 0.01). This was associated with an increase in maximal CPT I activity (+30%, P < 0.001) and a similar increase in palmitoyl-CoA oxidation (+24%; P < 0.001) in isolated mitochondria from the TC. Importantly, oxidation of the medium-chain FA octanoyl-CoA and CPT I sensitivity to inhibition by malonyl-CoA were not altered by CPT I overexpression. FA oxidation in isolated EDL muscle strips was increased with CPT I overexpression (+28%, P < 0.01), whereas FA incorporation into the muscle triacylglycerol (TAG) pool was reduced (−17%, P < 0.01). As a result, intramyocellular TAG content was decreased with CPT I overexpression in both the TC (−25%, P < 0.05) and the EDL (−45%, P < 0.05). These studies demonstrate that acute overexpression of CPT I in muscle leads to a repartitioning of FAs away from esterification and toward oxidation and highlight the importance of CPT I in regulating muscle FA metabolism