Catchment-scale non-linear groundwater-surface water interactions in densely drained lowland catchments

Freely discharging lowland catchments are characterized by a strongly seasonal contracting and expanding system of discharging streams and ditches. Due to this rapidly changing active channel network, discharge and solute transport cannot be modeled by a single characteristic travel path, travel time distribution, unit hydrograph, or linear reservoir. We propose a systematic spatial averaging approach to derive catchment-scale storage and discharge from point-scale water balances. The effects of spatial heterogeneity in soil properties, vegetation, and drainage network are lumped and described by a relation between groundwater storage and the spatial probability distribution of groundwater depths with measurable parameters. The model describes how, in lowland catchments, the catchment-scale flux from groundwater to surface water via various flow routes is affected by a changing active channel network, the unsaturated zone and surface ponding. We used observations of groundwater levels and catchment discharge of a 6.6 km2 Dutch watershed in combination with a high-resolution spatially distributed hydrological model to test the model approach. Good results were obtained when modeling hourly discharges for a period of eight years. The validity of the underlying assumptions still needs to be tested under different conditions and for catchments of various sizes. Nevertheless, at this stage the model can already improve monitoring efficiency of groundwater-surface water interaction

Pressure head distribution during unstable flow in relation to the formation and dissipation of fingers

Wetting front instability creates a shallow induction zone from which fingers emerge that rapidly transport water and solutes downwards. How the induction zone affects finger location and spacing is unknown. In the moist subsoil, fingers may well dissipate because the finger tips no longer have to overcome the water entry value. Both flow regions were investigated in a two-dimensional chamber with a fine-over-coarse glass bead porous medium. A capillary fringe was created by upward wetting through capillary rise. Upon ponding with dye-coloured water, fingers emerged, propagated downward and diverged when reaching the capillary fringe. Microtensiometers were installed in the induction zone, the fingers, and in the capillary fringe. In the induction zone, a lateral sinusoidal pressure head developed within minutes. Only in one of two experiments could the observed pressure head pattern be satisfactorily reproduced by a steady-state model assuming uniform induction zone properties and uniform infiltration. Later, fingers emerged below the pressure head minima. The induction zone did not affect finger properties. The pressure head in the induction zone was determined by the depth of the finger tips. The water requirement of the fingers dictated the lateral pressure head gradients. The pressure heads in the capillary fringe supported the hypothesis that the flow stabilised and dissipated there

The diverse and unanticipated roles of Histone deacetylase 9 in coordinating plant development and environmental acclimation

Plants tightly control gene transcription to adapt to environmental conditions and steer growth and development. Different types of epigenetic modifications are instrumental in this. In recent years, an important role for the chromatin modifying RPD3/HDA1 class I HDAC HISTONE DEACETYLASE 9 (HDA9) emerged in the regulation of a multitude of plant traits and responses. HDACs are widely considered transcriptional repressors and are typically part of multiprotein complexes containing co-repressors, DNA and histone binding proteins. By catalyzing the removal of acetyl groups from lysine residues of histone protein tails, HDA9 indeed negatively controls gene expression in many cases, in concert with interacting proteins such as POWERDRESS (PWR), HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 15 (HOS15), WRKY53, ELONGATED HYPOCOTYL 5 (HY5), ABA INSENSITIVE 4 (ABI4) and EARLY FLOWERING 3 (ELF3). However, HDA9 activity has also been directly linked to transcriptional activation. In addition, following the recent breakthrough discovery of mutual negative feedback regulation between HDA9 and its interacting WRKY-domain transcription factor WRKY53, swift progress in gaining understanding of HDA9 biology is expected. In this review, we summarize knowledge on this intriguing versatile – and long underrated – protein and propose novel leads to further unravel HDA9-governed molecular networks underlying plant development and environmental biology

Measuring very negative water potentials with polymer tensiometers: principles, performance and applications

In recent years, a polymer tensiometer (POT) was developed and tested to directly measure matric potentials in dry soils. By extending the measurement range to wilting point (a 20-fold increase compared to conventional, water-filled tensiometers), a myriad of previously unapproachable research questions are now open to experimental exploration. Furthermore, the instrument may well allow the development of more water-efficient irrigation strategies by recording water potential rather than soil water content. The principle of the sensor is to fill it with a polymer solution instead of water, thereby building up osmotic pressure inside the sensor. A high-quality ceramic allows the exchange of water with the soil while retaining the polymer. The ceramic has pores sufficiently small to remain saturated even under very negative matric potentials. Installing the sensor in an unsaturated soil causes the high pressure of the polymer solution to drop as the water potentials in the soil and in the POT equilibrate. As long as the pressure inside the polymer chamber remains sufficiently large to prevent cavitation, the sensor will function properly. If the osmotic potential in the polymer chamber can produce a pressure of approximately 2.0 MPa when the sensor is placed in water, proper readings down to wilting point are secured. Various tests in disturbed soil, including an experiment with root water uptake, demonstrate the operation and performance of the new polymer tensiometer and illustrate how processes such as root water uptake can be studied in more detail than before. The paper discusses the available data and explores the long term perspectives offered by the instrument

Parameterizing the Leaching Surface by Combining Curve-Fitting for Solute Breakthrough and for Spatial Solute Distribution

Multi-compartment samplers (MCSs) measure unsaturated solute transport in space and time at a given depth. Sorting the breakthrough curves (BTCs) for individual compartments in descending order of total solute amount and plotting in 3D produces the leaching surface. The leaching surface is a useful tool to organize, present, and analyze MCS data. We present a novel method to quantitatively characterize leaching surfaces. We fitted a mean pore-water velocity and a dispersion coefficient to each BTC, and then approximated their values by functions of the rank order of the BTCs. By combining the parameters of these functions with those of the Beta distribution fitted to the spatial distribution of solutes, we described an entire leaching surface by four to eight parameters. This direct characterization method allows trends to be subtracted from the observations, and incorporates the effects of local heterogeneity. The parametric fit creates the possibility to quantify concisely the leaching behavior of a soil in a given climate under given land use, and eases the quantitative comparison of spatio-temporal leaching behavior in different soils and climates

Verbonden door water: van 1984 via het heden naar 2034

Wageningen UR hield in september 2009 een reünie voor oud-studenten, die in 1984 aan hun studie waren begonnen. In dat jaar was de opkomst hoog. Maar liefst 1.200 studenten verschenen aan de start, waarvan ongeveer driekwart de finish haalde. Deze lichting heeft twee hoogleraren voortgebracht en vele promovendi. Beide hoogleraren (Marc Bierkens, Geografische hydrologie aan de Universiteit van Utrecht, en Remko Uijlenhoet, Hydrologie en Kwantitatief waterbeheer aan Wageningen UR) kozen destijds voor dezelfde studierichting Cultuurtechniek, oriëntatie Hydrologie en waterbeheer. Een goed waterjaar, want na 25 jaar blijken ook de andere hydrologen uit 1984 nog steeds geïnspireerd door water en bekleden gevariëerde functies binnen wetenschap, overheid en bedrijfsleven

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo