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Behavior of water balance components at sites with shallow groundwater tables: Possibilities and limitations of their simulation using different ways to control weighable groundwater lysimeters
Abstract
The water cycle of sites with shallow groundwater tables is characterized by complex interactions of hydrological and ecological processes. The water balance components, which are subject to diurnal fluctuations, are best measured with groundwater lysimeters. However, the lower boundary condition of such lysimeters affects most of the hydrological variables, particularly when considering short time scales, and has to be defined in such a way as to facilitate realistic simulations. In this paper, different means of controlling the lower boundary condition of groundwater lysimeters were compared with respect to their ability to simulate the behavior of the water balance components properly. Measurements of rain-free periods from a lysimeter station installed in the Spreewald wetland in north-east Germany were evaluated. The most common groundwater lysimeter type is controlled using a Mariotte bottle and sets the groundwater level in the soil monolith to a constant level, which here caused an alteration of the inflow to the lysimeter, with respect to both its value and diurnal behavior. Still, daily evapotranspiration values were realistic and this simple and robust approach may be used for time intervals not shorter than one day. High-resolution measurements can be gained from lysimeters that automatically adjust the groundwater level by a system of pumps and valves on an hourly basis. Still, reliable results were only obtained when the conditions in the lysimeter and the surrounding field, where the target groundwater level was measured, were in accordance. Otherwise (e.g., when the groundwater level differed) an unrealistic inflow behavior evolved. Reasonable results, even for slightly diverging conditions, were gained with a new approach that defined the lower boundary conditions by controlling the inflows and outflows of the lysimeter. This approach further enabled the groundwater level itself to be the study subject, thereby enlarging the field of possible applications of groundwater lysimeters.
... The experimental dataset was obtained from an advanced weighable groundwater lysimeter station equipped with chamber system for gas flux measurements. The station, established in 2009, is located in the Spreewald wetlands of Germany (51 • 52′N, 14 • 02′E, Fig. 1; Dietrich et al., 2016). Four cylindrical soil monoliths, each with a surface area of 1 m 2 , a depth of 2 m, and an existing permanent grassland vegetation cover were placed in the lysimeters in such a way that the soil profile was not disturbed. ...
... Each lysimeter contains a different soil type (Table S1 in the Supplementary Material). The station recorded meteorological conditions (Table S2) including net radiation (CNR 4, Kipp & Zonen), soil heat flux (HFP01SC, Huxeflux), air temperature, relative humidity 2 m above the surface (PC-ME, Galltec + mela), wind speed and wind direction (classic, Thies) (Dietrich et al., 2016). In addition, a precipitation gauge (Hellmann RG 50, Thies) was positioned at a height of 1 m above the ground. ...
... The lysimeters were fenced in to protect against animal incursions, and were not additionally fertilised. A detailed description of the technical equipment at the lysimeter station, the associated weather station, data acquisition and data evaluation can be found in Dietrich et al. (2016). ...
... However, we did not come across any shallow groundwater modeling studies where variable flux conditions were applied based on inflow and outflow measurements at the lower boundary. Collecting such data requires significant effort, particularly when utilizing a weighable groundwater lysimeter (Dietrich et al., 2016). Nevertheless, it's worth noting that the choice of a lower BC can substantially impact the parameterization of SHPs, although this issue was not encountered in studies involving the inverse estimation of SHPs for shallow groundwater table sites. ...
... This setup allowed for precise adjustments of the lysimeter's WT to mimic the surrounding conditions. For a more comprehensive understanding of the lysimeter station's methodology and technology, readers are referred to Dietrich et al. (2016). The Spreewald region in northeast Germany has experienced alluvial sedimentation processes, resulting in the formation of extensive layers comprising clay and organic matter that are interspersed among typical sandy layers. ...
... Schematic diagram of the groundwater lysimeter station, adapted from Dietrich et al. (2016). WTD is water table depth, ET a is actual evapotranspiration, P is precipitation, R in and R out are in and output fluxes at the lysimeter bottom, ΔS is water storage change of the soil monolith, θ is volumetric water content, here measured with a profile soil moisture probe at eight depths, and h is soil water pressure head measured here at three depths. ...
Degraded peatlands release large amounts of greenhouse gases. The development of effective mitigation and management measures requires an understanding of relevant site‐specific biogeochemical and hydraulic processes. However, the simulation of water fluxes and vadose zone state variables of degrading peatlands relies on proper process description, parameterization of hydraulic functions, and representation of the boundary conditions. The objective of this study was to analyze the effects of unimodal versus bimodal soil hydraulic functions and pressure head versus flux‐type lower boundary conditions (LBCs) on the calculated hydraulic characteristics of a degraded peat profile. HYDRUS‐1D was used to study the hydraulic flow dynamics parameterized with data from a weighable groundwater lysimeter for the period from May 1 to December 31, 2019. Simulations comparing uni‐ and bimodal hydraulic functions showed only minor differences. Simulations of soil water pressure at a depth of 30 cm using a flux‐type LBC (RMSE: 27 cm, where RMSE is root mean square error) performed better than simulations using a pressure head LBC (RMSE: 48 cm). The pressure head LBC performed better at simulating volumetric water contents in 30‐cm depth than the flux LBC variant (RMSE: 0.05 vs. 0.09 cm³ cm⁻³). For specific site conditions with a shallow, fluctuating groundwater table and temporary air entrapment, the choice of LBC was important for a more accurate simulation of soil water fluxes and volumetric water content.
... The study area is an extensively agriculturally used wetland area in the Spreewald wet grassland, Germany (51 • 52 ′ N, 14 • 02 ′ E, and 50.5 m above sea level (Figure 1). The lysimeter station (container design) was installed in 2009 [35] and has been in operation since 2010; since then, the system has collected data, with the most recent available data coming from 2020. Since the recorded values for 2010 were only used for calibration purposes, the core data stemmed from spring 2011 to winter 2020 simultaneously from a weather station, a groundwater gauge, and a soil-hydrological measuring unit. ...
... The study area is an extensively agriculturally used wetland area in the Spreewald wet grassland, Germany (51°52′ N, 14°02′ E, and 50.5 m above sea level ( Figure 1). The lysimeter station (container design) was installed in 2009 [35] and has been in operation since 2010; since then, the system has collected data, with the most recent available data coming from 2020. Since the recorded values for 2010 were only used for calibration purposes, the core data stemmed from spring 2011 to winter 2020 simultaneously from a weather station, a groundwater gauge, and a soil-hydrological measuring unit. ...
... Above-ground biomass (AGB) was measured twice per growing season, after ea mowing event [11]. We measured the leaf area index (LAI) approximately every t weeks, using the S1 SunScan Canopy Analysis System [35]. In addition, once a year bef the first cut, we conducted a vegetation composition assessment based on the Braun-Bl Mowing was performed twice per growing season (mid-June, beginning of September). ...
Large-scale assessments of agricultural productivity necessitate integrated simulations of cropland and grassland ecosystems within their spatiotemporal context. However, simultaneous simulations face limitations due to assumptions of uniform species distribution. Grasslands, particularly those with shallow groundwater tables, are highly sensitive to water availability, undergoing rapid species composition changes. We hypothesised that predicting above-ground biomass (AGB) remains challenging due to these dynamic responses. Ten years of data from four lysimeters at a German wet grassland site, with varying water table treatments, was utilised to test this hypothesis. Correlation analysis revealed a strong positive indirect effect of the water regime on AGB, with a one-year time lag (r = 0.97). The MONICA model initially exhibited fair agreement (d = 0.69) in simulating Leaf-Area-Index (LAI) but performed poorly in replicating AGB (d = 0.3). After removing the species composition change effect from the LAI and AGB datasets, the simulation notably improved, with the overall relative root mean square error (rRMSE) of AGB decreasing from 1.55 to 0.90 between the first and second simulations. This demonstrates MONICA’s ability to predict grass growth patterns amidst changing water supply levels for constant species composition. However, it needs a competition model to capture biomass growth changes with varying water supply.
... Principal equation soil surface energy balance R n + H − LE − G = 0 (Turc 1954;Pike 1964; R n = (1 − a l )R s + (R a − εσT 4 s ) Monteith 1965;Allen et al. 1989;Gerrits et al. 2009; LAI=24.h c for clipped grass or LAI=5.5+1.5 ln h c for other crops Soil surface water balance (Dietrich et al. 2016) ...
... • du bilan hydriqueà la surface du sol (Dietrich et al. 2016 Les résultats montrent qu'une température du fluide d'entrée de 50 o C enété (Sto50) augmente fortement la performance du système (13,7à 41,4%) alors que l'amélioration par rapportà un système sans stockage (NSto) est moins significative (0à 4,8%) lorsque la température au cours de l'été correspondà la température ambiante (StoA) ( Figure B.6). Par ailleurs, une perte de chaleur considérable aété observée pendant les saisons de relaxation et de déstockage. L'augmentation de la profondeur d'installation améliore la performanceénergétique mais augmenteégalement les coûts d'installation. ...
In geotechnical engineering, thermal energy storage in embankments can be considered as a new economically efficient, and environmentally friendly structure for space heating. In these structures, horizontal heat exchanger tubes can be installed inside the different layers of compacted soil to store the heat in the medium during the summer, to be extracted in the winter. Seasonally temperature variations caused by heat exchangers can affect Thermo-Hydro-Mechanical (THM) properties of the compacted soil in the embankment. Both the short and long term behavior of this compacted soil should be investigated. The aim of this study was to investigate the effect of temperature variations in the range of 5° to 50 °C, on THM behavior of a compacted sandy lean clay in saturated state. To achieve this, temperature-controlled œdometric and direct shear tests were performed. The results showed that, the effect of the temperature on mechanical properties are more pronounced under a vertical stress higher than the preconsolidation pressure. Heating changed the void ratio during consolidation phase but has a negligible effect on the shear characteristics. The results also showed that the cooling slightly changed the shear parameters.
... Principal equation soil surface energy balance R n + H − LE − G = 0 (Turc 1954;Pike 1964; R n = (1 − a l )R s + (R a − εσT 4 s ) Monteith 1965;Allen et al. 1989;Gerrits et al. 2009; LAI=24.h c for clipped grass or LAI=5.5+1.5 ln h c for other crops Soil surface water balance (Dietrich et al. 2016) ...
... • du bilan hydriqueà la surface du sol (Dietrich et al. 2016 Les résultats montrent qu'une température du fluide d'entrée de 50 o C enété (Sto50) augmente fortement la performance du système (13,7à 41,4%) alors que l'amélioration par rapportà un système sans stockage (NSto) est moins significative (0à 4,8%) lorsque la température au cours de l'été correspondà la température ambiante (StoA) ( Figure B.6). Par ailleurs, une perte de chaleur considérable aété observée pendant les saisons de relaxation et de déstockage. L'augmentation de la profondeur d'installation améliore la performanceénergétique mais augmenteégalement les coûts d'installation. ...
Nowadays, thermal energy storage in geostructures like embankments can be possible by installing the horizontal heat exchangers in different layers of compacted soil. In this system, the thermal energy is stored in summer via a fluid, circulating in the heat exchangers, to be extracted in the demand period. When the serviceability of embankment as a medium to store the thermal energy starts, the compacted soil will be subjected to the daily and seasonally temperature variations. These seasonal temperature variations could modify the thermo-hydro-mechanical performance of the compacted soil. Thus, the aim of this study is to investigate the thermal and mechanical performances of a compacted soil when it is subjected to monotonic and cyclic temperature variations. The studied soil is a sandy lean clay that is frequently used in embankment constructions in France. The thermal and mechanical behavior of the soil are investigated at a compaction state corresponding to the optimal thermal properties. However, this compacted soil is unsaturated and the estimation of its thermal properties is complex. In this study, an inverse analytical model is proposed to estimate the thermal properties of the soil using temperature monitoring in the range of 20 to 50 °C in a soil compacted in a large container. The estimated thermal parameters were compared to classical laboratory measurements (transient and steady-state methods). The comparison showed that the estimated values were close to the results obtained in transient laboratory method. Using this method, the thermal efficiency of the compacted soil can be verified in the lifetime of the storage system. To ensure the structure stability, long-term mechanical response of these systems subjected to monotonic and cyclic temperature variations should be investigated. To achieve this aim, using temperature-controlled oedometric and direct shear devices, consolidation and shear parameters of the studied soil at different monotonic (5, 20, and 50 °C) and cyclic (5 to 50 °C) temperatures were investigated. The results of temperature-controlled oedometric tests showed that the effect of the temperature variation is more pronounced under vertical pressures higher than the preconsolidation pressure. The compression and swelling indexes could be considered independent of temperature variations. Therefore, the overall settlement of the embankment due to thermal variation near the heat exchangers could be considered negligible. The results of temperature-controlled direct shear tests showed that the temperature variations (monotonic heating or cooling, or temperature cycles) increased the cohesion which is beneficial for the bearing capacity and slope stability of embankments. These results can be directly used in the design of embankments to store thermal energy exposed to similar thermo-mechanical paths. Finally, the thermal performance of the compacted soil is verified using a numerical simulation considering the soil atmosphere interaction. Different depths installation of heat exchanger loops and different heat storage scenarios were simulated. The results showed that the compacted soil increases 8.5% the systems performance compared to the horizontal loop installation in the local soil. The results of two different scenarios show that an inlet fluid temperature of 50 °C in summer increases highly the system performance (13.7% to 41.4%) while the improvement is less significant (0% to 4.8%) for the ambient inlet temperature. Moreover, a deeper installation of horizontal loops increases the system performance. From the numerical simulation results can be concealed that the embankment is in interaction with the atmosphere from its upper and lateral surfaces, the thermal efficiency of the structure could be affected due to heat losses. Therefore, it is preferable to place the heat exchangers away from the top and side surfaces.
... Applying this procedure, the WT measured at the site can be simulated in the lysimeter with high accuracy [45]. For a more detailed description of the lysimeter station refer to Dietrich, et al. [46]. ...
... The WT of the lysimeter mimicked the reference WT almost perfectly, which is a key precondition to ensure that the lysimeter correctly represents the water balance [46]. During most of the vegetation period, the area of the study site received an inflow (R > 0). ...
Drained wetland sites with shallow water tables cover large parts of Central and Western European lowlands. Their hydrological behaviour is complex and depends on their specific characteristics. In this paper, we analysed how the water budget components of such areas behaved when undergoing rainfall events with amounts greater than 10 mm. All the water budget components were determined using a weighable groundwater lysimeter that was installed in the Spreewald wetland, Germany. On average, 69% of the rainfall was stored in the wetland, while only 8% was discharged and 23% was dissipated by evapotranspiration during the time of the runoff process during and after the rainfall event. More than half of the water that was stored could be attributed to storage within the unsaturated zone, while only a minor part was due to the water storage change under quasi-equilibrium conditions. Hence, the soil moisture depletion in the unsaturated zone in the period before the rainfall had a big influence on the site’s available water storage capacity. The findings show that models and approaches assuming hydrostatic conditions might strongly underestimate the water storage capacity of shallow water table sites and, consequently, overestimate the runoff. Hence, the hydrostatic assumption does not describe the process dynamics of these sites in an appropriate manner.
... Further, it was found that various studies have established root water uptake from the crop rise zone (CRZ) having deep water tables (Kumar et al. , 2015Poddar et al. 2020;Kumar et al. 2021Kumar et al. , 2023Singh et al. 2023;Udom et al. 2024). Studies using Lysimeters to understand the moisture contribution from SGT were also reported (Fahle and Dietrich 2014;Dietrich et al. 2016;Li et al. 2018). However, only a few studies are available in the literature concerning soil moisture dynamics in the root zone, with SGT considering capillary rise. ...
... Shallow GW is present in many fields, mainly in valleys and near river tributaries, and their contribution to the water use of various annual and perennial crops has gained much attention, with studies in controlled environments, that is, laboratories and greenhouses, using weighable (Ayars et al., 2009;Dietrich et al., 2016) or drainage-type (Gul et al., 2024;Nick et al., 2024) lysimeters, and in the field evaluating the water balance (Logsdon et al., 2009;Orellana et al., 2012;X. Wang et al., 2018;Xue et al., 2017) or using stable isotopes (Beyer et al., 2018;Orellana et al., 2012;Y. ...
This study investigates the interplay between shallow groundwater and on‐surface drip irrigation in facilitating water uptake of agricultural crops. Lysimeter experiments utilizing ceramic cups mimicking plant roots provide insights into wetting patterns within the root zone and water balance components. Results reveal that while plants can effectively utilize shallow groundwater even with limited root systems, higher irrigation rates diminish groundwater contribution to water uptake. Conversely, shallow groundwater enhances water uptake from on‐surface irrigation, reducing drainage at low irrigation rates. The findings underscore the potential of groundwater as a supplementary water source for crops, offering practical implications for optimizing supplemental irrigation strategies and sustainable water management in agriculture. When the vertical distance between active roots and the water table exceeds a characteristic length of the soil, it disrupts the continuity of the liquid water phase. As a result, intensive capillary upward water flow, against gravity, cannot be reliably described by Darcy's law. It becomes imperative to formulate a practical continuum theory to more accurately depict capillary rise in such scenarios.
... Despite having several advantages, such as lightweight, flexibility, durability, etc., the usage of plastics has severely polluted the environment. According to reports, 22% and 43% of plastics are disposed of in landfills, which leach toxic or harmful chemicals that pollute groundwater [67]. Using eatable or decomposable components, such as plant fibers, grain powders, and nanomaterials, as an alternative and sustainable approach to food packaging systems can reduce the ecological burden of conventional food packaging [68]. ...
Proper municipal solid waste (MSW) administration and disposal is a crucial environmental and economic issue of the modern world [1, 2]. Currently, 56% of the total world population resides in urban areas and accounts for generating a substantial volume of MSW [3]. In the present scenario, MSW is being generated from various sources, viz. agro-waste, industrial waste, sewage waste, plastic waste, animal waste, and food and vegetable waste [4]. As per a report, the amount of MSW generated on a global scale was 2.02 billion metric tons in 2016 and by 2050, it is expected to observe an annual increment of 70% (3.4 billion metric tons) [5]. Environmental harm is caused by a remarkable increase in waste production, inadequacy in sustainable waste management strategies, and their implementation laws [6]. The World Health Organization (WHO) has drawn attention to the concerns connected with improper solid waste disposal with regard to soil and water quality and related health implications for populations living around the affected areas [7]. It is, therefore, important that waste generation be minimized and the recovery of wastes maximized for environmental and economic sustainability [3]. The proper management and refinement of MSW in the landfills can be a bipolar process to balance the ecosystem in reducing the organic pollution load and creating some value-added products such as enzymes, chemicals, fertilizer, simple sugars, and energy fuels. These products are also very cost-effective, eco-friendly and sustainably an alternative by-product [3].
... The interactions between the atmosphere, GHE and soil are illustrated in Fig. 1. The water cycle between atmosphere and soil is a process of mass conservation and can be expressed as (Dietrich et al., 2016): ...
... Groundwater use is the delivery of phreatic water to the aeration zone (Yang 2008) via evapotranspiration (Yan & Zhou 2002;Wang & Hou 2008), one part of which is used for crop evapotranspiration and another part of which is used for ground evaporation between plants. Groundwater use can be observed using a Mariotte bottle, the groundwater level was set to a constant level (Dietrich et al. 2016), and the groundwater consumption by crops was measured using a flowmeter. Zhu & Wang (2013) obtained crop groundwater use by subtracting the phreatic water evaporation without crops from that with crops, which does not include the ground evaporation between plants. ...
Using groundwater for crop growth plays a key role in the sustainable management of water resources and irrigation and drainage design. Some studies did not consider the influence of different crop growth stages and the non-linear effect of the groundwater depth on groundwater use. In this study, three types of formulae for groundwater use were developed by referencing the phreatic evaporation formula without crops. According to the observation data, groundwater depth and use, and wheat evapotranspiration were fitted using these three non-linear formulae in each crop growth stage. The Accelerated Gene Algorithm (AGA) was used to optimize the parameters, and their performance indices were calculated. We observed that groundwater use increased gradually as the decrease in groundwater depth and the increase in wheat evapotranspiration; the correlation coefficients of wheat evapotranspiration and groundwater use were small (such as 0.539, 0.428) in the seedling stage and mature stage and large (such as 0.631, 0.625) in other stages. The performance of the Aviriyanover formula was the best with a correlation coefficient of 0.686 between the simulation and observation; therefore, this formula was recommended to determine groundwater use.
HIGHLIGHTS
Three groundwater use formulae were developed: the Aviriyanover, Ye Shuiting, and power function.;
Groundwater use increased gradually as groundwater depth decreased increasing wheat evapotranspiration.;
The Aviriyanover formula is recommended for groundwater use as it showed the least error.;
... Typically, the analyses of water use for crop production are based on experimental designs considering different irrigation water inputs, where measurements of xylem potential, sap flow, and micrometeorological techniques (Novák, 2012) are needed to monitor the water use. In spite of their precision, they usually require intensive field campaign with high labor and time costs (Dietrich et al., 2016;Phogat et al., 2017). Also, these methods do not allow for continuous long-term monitoring of the water use variables, limiting their applicability for long term planning. ...
Table grape production requires large amount of water, which can be problematic in semi-arid Mediterranean regions, where climate change projections anticipated reductions in water availability associated to decreases in precipitation and increases in temperature. In this context, this study aims to evaluate the effect of contrasting irrigation strategies and climate change scenarios on key water balance variables using a Chilean Table grape crop as case study. A standard and an improved irrigation management treatments were implemented in situ during the observed growing seasons, respectively. Then, the HYDRUS-1D water transfer model was run to simulate the three observed growing seasons and 27 near future growing seasons (2019/2020-2044/2015) under climate change conditions. Satisfactory calibration and validation results against soil moisture and water storage measurements were obtained within the first and the second observed growing seasons respectively (RRMSE values below 5%). Results during the observed seasons showed that by changing the standard irrigation by the improved irrigation management, the water use efficiency (WUE i) increases from 49.5% to 55.7%. For the near future, the calibrated model shows that under all the tested climate change scenarios, irrigation strategies based on supplying 80% and 50% of the crop evapo-transpiration (ETc) (deficit irrigation scenarios) have larger efficiencies compared to the standard irrigation management (presenting a higher actual basal crop coefficient and lower percolation). Similar results were obtained under future extreme climate change years, defined as the ratio between model-based projections of reference evapotranspiration (ET0) and precipitation, with the deficit irrigation scenarios having larger effi-ciencies than the standard irrigation management. Based on these results, it is concluded that by mid-century, the irrigation management has more relevance than climate change impacts for tables grapes growing under a Mediterranean climate in central Chile.
... At SPW, a weighable groundwater lysimeter station is used to measure ET a . The technical equipment at the lysimeter station and the associated weather station, data acquisition, and data evaluation are described in detail in Dietrich et al. [26]. For the evaluations in the article, the values measured by the station's reference lysimeter are used. ...
In recent years, Germany has experienced an increasing number of extreme wet and dry years. In the North German lowlands, wet grassland sites with shallow water table conditions are widespread landscape elements. They are characterized by a special water and nutrient balance that reacts very sensitively to changes in the hydrological system. Studies on evapotranspiration (ETa) and the development of groundwater levels were carried out at two typical wet grassland sites with shallow water table conditions. A weighable groundwater lysimeter system in the Spreewald wetland (SPW) and an eddy covariance station in Havelländisches Luch (HL) were used to measure ETa. The results show that even these shallow water table sites cannot sufficiently meet the vegetation’s water demands in extreme dry conditions. The groundwater levels drop to values deeper than 1 m below the surface. As a result, water supply to the vegetation is temporarily limited. The mean crop coefficients (Kc) of these wet grassland sites reach values of 1.1 in the vegetation period with a sufficient water supply, but drop to around 0.8 in dry years when the water supply is limited. Areas with small catchment areas, such as HL, are more seriously affected by the dry meteorological conditions than areas with sufficient inflows from larger catchment areas, such as SPW.
... It is assumed that the precipitation (P) is the only water source at the field condition, which is kept balanced with water run off (Wr), actual evaporation (E), and infiltration (Wi) through the ground surface (Dietrich et al., 2016). Therefore: ri P W E W = + + (6.24) ...
Shallow geothermal energy is an energy that can help humanity to reach the goal of sustainable development. Ground-Coupled Heat Pump system is traditionally used to benefit this energy. As a main element of the system, ground heat exchanger performance directly influences its energy efficiency. The shallow ground heat exchangers are normally installed in soils, which show high heterogeneity of hydrothermal properties along the soil profiles. The main objective of this project is identifying how ground heat exchanger behaves in the soil. In summary, the following investigations were conducted: the first is introducing hydrothermal transfer in the numerical modeling of Borehole Heat Exchanger installed at a site in Alsace region (France); the second is identifying the factors influencing the performance of a shallow Borehole Heat Exchanger installed in soils; the third is conducting sensitive analysis of Thermal Response Tests for Borehole Heat Exchanger installed in soils; the fourth is identifying the performance difference of a numerical simulation model with Neumann and Dirichlet boundaries on the ground surface for a Horizontal Ground Heat Exchanger.
... In the event of flooding, the parameters that influence groundwater dynamics need to be quantified as completely as possible so that the water absorption capacity of adjacent floodplains can be predicted more accurately. Because detailed measuring of pedohydrological parameters in the floodplain itself is very difficult, a weighable groundwater lysimeter was developed (Dietrich et al., 2016;Bethge-Steffens et al., 2004). For plane floodplains, rewetting, or shallow water sites, the water balance equation can be specially adapted. ...
A lysimeter is a device to collect drainage water for mass and solute balances and fills the gap between laboratory and field-scale studies. There is a tendency in the international literature that this measuring technique is increasingly used to investigate the effects of climate change on land and water resources. These studies include simple nonweighable lysimeters as well as highly sophisticated weighable lysimeters. The objective of the paper is to demonstrate different lysimeter types and how they can be used to investigate the effects of climate change. On the basis of case studies, the determination of soil water balance parameters such as precipitation, actual evapotranspiration, soil moisture, and the leaching behavior of the environmental relevant nutrient phosphorus will be explained and evaluated regarding sustainable soil management strategies under the conditions of climate change.
... Authors like Wang et al. [64] consider shallow groundwater as an important source of water, which necessitates a deeper understanding of its complex spatial and temporal dynamics driven by hydrological processes, especially in arid environments. Tillage, crop yields and water consumption at lowlands characterized by shallow ground-water levels are affected by the groundwater levels, which therefore influence the potential to use the land for agriculture [68]. ...
The objective of this study is to explore the spatio-temporal nature of groundwater monitoring data using space-time (ST) geostatistics in order to predict water table depths at Bauru Aquifer System (BAS) in a conservation area at São Paulo State, Brazil. The information about the groundwater oscillation process in space and time can be measured in terms of spatial and temporal correlation through the ST variogram. The targets was predict water table depths in a missing date inside the monitoring period and propose a validation of these predictions based on predicted and observed values distribution curves for that specific date. Before modelling the ST empirical variogram, separability between space and time structures was checked. Then, the ST kriging predictions for March 31, 2016 were compared with independent observed dataset. ST kriging was a robust interpolator, turning possible a reasonable reconstructions of a hypothetical missing scenario inside the monitoring period in the BAS study area. The results showed a strong dependence of the temporal mean in the predictions.
... The precipitation (P) is the only water source, which is kept balanced with water run off (W r ), actual evaporation (E), and infiltration (W i ) through the land surface [36]. Therefore: ...
... Unlike conventional groundwater lysimeters with constant groundwater levels as a lower boundary condition (Bethune & Wang, 2004;Noory, Liaghat, Chaichi, & Parsinejad, 2009) or a variable adaptation of the water level at time intervals of several days (Yang, Wan, Deng, & Zhang, 2007), our station used an automatic system to control the lower boundary condition. The automatic control system can regulate the groundwater level on the basis of a measured reference value (Bethge-Steffens, Meissner, & Rupp, 2004;Meissner, Rupp, Seyfarth, & Punzel, 2000) or regulate the inflow/outflow on the basis of a measured inflow/outflow value (Dietrich, Fahle, & Seyfarth, 2016). This control system was an important precondition to study the behaviour of the water table under the influence of different water management targets. ...
The management of shallow water table sites is often the subject of discussion between different interest groups, the most controversial topic being the different target groundwater levels. A good level of knowledge about the effects of the different water levels on the water budget components is a precondition for the development of compromises in well‐balanced water resource management.
We used groundwater lysimeters to investigate the impact of different water level regimes on the water balance. The lysimeters were installed directly within a typical shallow water table site and had a specially designed system to control the lower boundary condition. This enabled us to simulate different management options in a realistic way.
Our results show increasing evapotranspiration with higher water levels but only if the vegetation is adapted to these conditions. Adaptation may take place within a few years of higher water levels. High water levels in spring are linked to increased water storage. This can help to compensate for the higher evapotranspiration for some weeks but not for the entire season. The meteorological conditions have a large short‐term impact on the water budget, which is difficult to compensate for using long‐term water management strategies or slow‐responding vegetation development. Our results underline the complex ecohydrological dependencies in such site conditions and could be an important basis for the development or improvement of ecohydrological models.
... Precipitation was measured using ground-level gauge records. This approach is recommended to evaluate the water balance as the gauges are located at the same height as the lysimeters and are exposed to the same environmental conditions (Dietrich et al., 2016;Gebler et al., 2015;Klammler and Fank, 2014). The weekly volumetric drainage collected from the lysimeters was considered as outgoing water flux. ...
Water balance is an important tool to evaluate water deficit or excess in crop systems. However, few studies have evaluated the water balance of vegetation grown on the residues from potash mining because the high sodium chloride levels of the residues hinder agricultural development. Therefore, this study aims to measure the water balance components in eight non-weighing lysimeters installed on a potash tailings pile in Heringen (Werra), Germany. These lysimeters were filled with different mixtures of household waste incineration slags and coal combustion residues, resulting in 4 different substrates with two repetitions. Manual seeding was performed using 65% perennial ryegrass (Lolium perenne L.), 25% red fescue (Festuca rubra L.) and 10% Kentucky bluegrass (Poa pratensis L.). Environmental conditions were monitored using an automatic weather station; ground-level and 1-m-high rain gauges. Precipitation and drainage were recorded weekly following the initial saturation of the lysimeters. Water balance components were determined for two hydrological years based on the expression: ET (mm)?=?P - D, where ET?=?evapotranspiration, P?=?precipitation and D?=?drainage. In addition, evapotranspiration was studied using the standard FAO Penman-Monteith equation and Haude's method. The lysimeter water balance measured in 2014 revealed an actual evapotranspiration rate of 66.4% for substrate 1, 66.9% for substrate 2, 65.1% for substrate 3 and 64.1% for substrate 4. In 2015, evapotranspiration ranged from 65.7% for substrate 4 to 70.2% for substrate 1. We observed that the FAO Penman-Monteith and Haude's evapotranspiration models generally overestimated the water use of the green coverage by 67% and 23%, respectively. Our study suggests that an evapotranspiration cover for potash tailings piles may decrease brine drainage from these piles and reduce soil and water contamination.
... Similar data were also used to evaluate a water balance model for predicting crop water requirements (Muzikova et al., 2010). In general, applications of sophisticated lysimeter facilities are manifold, including simulations of groundwater fluctuations (Fahle and Dietrich, 2014; Dietrich et al., 2016) or validation of water flow models that focus on processes in the vadose zone (Durner et al., 2008; Schelle et al., 2012). An overview on different lysimeter types and their usage was recently presented by Meissner et al. (2014). ...
Knowing the components of a soil water balance—for example, evapotranspiration, soil water content, and precipitation—is the basis for agricultural water management. Weighing lysimeters and soil water sensors are commonly used to quantify these components. Data can be used to validate common models to estimate evapotranspiration based on meteorological data, for instance. As every measurement device has its own characteristics, it is helpful to assess and improve the performance of a system to obtain best possible data. Recent developments in the processing of lysimeter data allow determining both evapotranspiration and precipitation directly from lysimeter data. Resulting datasets are characterized by a proper accuracy, completeness, and a high temporal resolution. Soil water sensors usually measure a physical property that is related to soil water content or matric potential via a specific calibration function. Hence, measurement accuracy depends not only on this calibration but also on basic physical principles and material properties. Knowing the performance of a device is, therefore, essential for the selection of an adequate sensor arrangement and truthful data interpretation. Advanced soil water monitoring sites combine different sensor types that are integrated into a wireless network to enable real-time data availability and provide a basis for large-scale monitoring.
A well-known backfill soil was considered to be used as the backfill substitutive material. The hydrothermal properties of the backfill material were estimated in laboratory and then injected in a numerical framework considering the atmosphere-soil-HGHE interaction. Numerical simulations were performed for a HGHE installed in the compacted backfill soil and the local materials. Two heat storage scenarios at three different installation depths were also investigated. The results show that an inlet fluid temperature of 50°C in summer increases highly the system performance (13.7% to 41.4%) while the improvement is less significant (0% to 4.8%) for the ambient inlet temperature scenario. A deeper installation depth increases also the system performance.
Horizontal ground heat exchanger (HGHE) is a cost effective method to exploit geothermal energy due to its shallow installation depth, which meanwhile causes its performance sensitive to climatic conditions. However, quantitative effects of climatic conditions on the HGHE performance still remain unclear. Influence degrees of key factors on the HGHE performance are not yet studied. Therefore, we do not know which factors should be priorities for the HGHE design. To this end, influence degrees of all key factors, including injection mass flow rate, operation modes, heat storage, subsurface water flow, soil thermal conductivity, installation depth and especially atmospheric conditions (precipitation and air temperature), on the HGHE performance are comprehensively analyzed and compared through numerical simulation and gray correlation analysis. Results indicated that non-consideration of climatic conditions could underestimate HGHE outlet temperature in summer and winter. The intermittent operation mode showed much better performance than continuous one. Increasing installation depth and improving grout thermal conductivity were both beneficial for HGHE performance. The most significant impact factors on the HGHE performance were groundwater flow velocity > circulation flow rate > precipitation > air temperature. Based on simulation results, subsurface water flow, injection mass flow rate and climatic conditions should be priorities for the optimal design of HGHE.
Horizontal ground heat exchanger (HGHE) is a low-cost shallow geothermal exploitation method compared with vertical ones, but it needs more land area. Optimizing geometrical configurations and arrangements of ground heat exchangers is desirable to enhance heat exchange per unit land area. However, a comprehensive study on different HGHE configurations and arrangements considering atmosphere-soil-HGHE interaction is still inadequate. To this end, thermal performances of four configurations, including slinky, spiral, multi-tube with serial connection and tiled tubes, are compared based on a 3D numerical model for HGHE considering atmosphere conditions variation and humidity migration. Effects of main geometrical parameters on HGHE performance and economical efficiency are investigated for these four configurations. Finally, different tube arrangements of multi-tube HGHE are designed and their thermal performances are analyzed. Results indicated that longer HGHE tube length has better thermal performance but lower economical efficiency, thus being not advisable for the HGHE design. Among these four configurations, multi-tube with serial connection shows the best thermal performance. Increasing the tube spacing is beneficial for reducing the tube mutual interference and enhance the heat exchange per unit land area, which is recommendable. Results are expected to provide meaningful suggestions for the HGHE design.
The determination of the volumetric soil water content θv by means of capacitive profile probes is often applied to investigate the soil water storage change ΔS that serves as basis for decisions in agricultural water management. The soil properties have a big effect on the accuracy of the θv measurements. The use of only one calibration function, often provided by the manufacturers of the probes, cannot fulfil the requirements of all site conditions. Therefore, many individual calibration functions have in the past been determined for different soils and sensors. A literature review of existing calibration functions of the capacitive profile probe Diviner 2000 shows the broad range of available functions. The review makes it clear that there is a lack of functions for organic soils. These soils are typical soils of wet sites with shallow groundwater tables. The soil moisture is of big importance for many ecological processes of these sites and therefore an exact determination of θv is important. A Diviner 2000 profile probe was calibrated on such a shallow groundwater site in a classic field calibration procedure and the determined functions were applied to the soil profile of a weighable groundwater lysimeter. The soil water storage change ΔS was estimated with the measured θv values and compared with the measured mass change Δm of the lysimeter. The mean error (bias) between ΔS with the field calibration function and Δm was 7.8 kg and the root mean squared error (RMSE) 19.9 kg. An iterative adaptation of the calibration functions to the measured Δm values of the lysimeter reduced the bias to 0.9 kg and the RMSE to 14.0 kg. The investigations illustrate the problems of a classic field calibration under the conditions of a shallow groundwater site with low θv changes in deeper soil horizons and soils with high Corg contents as well as the inaccuracy in the determination of ΔS based on θv measurements with capacitive profile probes.
The good capacity of the numerical simulations makes possible to bring some further responses on the backfill soil selection and its installation depth in the Horizontal Ground Heat Exchanger (HGHE). Therefore, a well-known backfill soil was considered to be used as substitutive material. The hydrothermal properties of the backfill material were estimated in laboratory and then injected in a numerical framework considering the atmosphere-soil-HGHE interaction. Numerical simulations were performed for a HGHE installed in the compacted backfill soil and the local natural soil. The simulation results showed that the compacted backfill soil improves by 8.5 % the HGHE performance compared to local uncompacted soil. Two heat storage scenarios at three different installation depths were also investigated. The results showed that an inlet fluid temperature of 50 Co in summer increased highly the system performance by 13.7% to 41.4%, while the improvement was less significant (0% to 4.8%) for the ambient inlet temperature scenario. A deeper installation depth of HGHE increased also the system performance, the more energy could be stored and extracted.
In arid agricultural areas with shallow water table depth, water exchange between vadose zone and groundwater is intensive during the freezing-thawing period, and thus has a significant impact on crop growth. This study is aimed to develop a one-dimensional model that couples heat and variably saturated water in seasonally freezing-thawing agricultural areas. To alleviate numerical oscillations occurring during the phase change at zero temperature, a three-level iteration scheme was developed for solving the water and heat coupling model, which improves numerical stability for variably saturated water and heat modeling. The model accuracy was evaluated by comparing the simulation results with those from SHAW under various soil texture and bottom conditions. The square of correlation coefficient (R²) of freezing and thawing depth and soil temperature profiles are above 0.95 and the values of root mean square error (RMSE) of total soil water content are lower than 0.05 cm³/cm³, which suggest the model accuracy. The model was further applied to simulate the hydrothermal conditions in the Yonglian irrigation field of Hetao Irrigation District in Inner Mongolia, China. Model calibration and validation were conducted, and the validated model was used to predict hydrothermal changes under scenarios with different soil surface temperatures and pre-freezing water table depths. The results show that the soil freezing process has great impact on the fluctuation of water table depth when the pre-freezing water table depth is shallower than 180 cm. The maximum freezing depth has a negative relation with the pre-freezing water table depth when it is shallower than 180 cm. An empirical formula was established to estimate the upward flow of groundwater to freezing soils. The soil moisture and thermal conditions were analyzed in the germination and seedling stages after the freezing-thawing period, and the analysis leads to a recommended pre-freezing water table depth of 100 cm, which provides suitable soil moisture and thermal conditions for the crop growth.
One of the most important components of the earth's surface water balance is evapotranspiration, which regulates the exchange of energy between ground and atmosphere. The effects of global warming intensify the water demand and therefore, the potential scarcity of water could affect several landscapes and agricultural systems. Therefore, it is essential to monitor evapotranspiration in order to assess water use efficiency and drought risks. There are a several methods to estimate and monitor evapotranspiration (ET), which differ in accuracy, cost and complexity. In this article, we present a general background of ET concepts, then, direct, empirical and remote sensing‐based methods to estimate it and finally we conclude with some recent ET applications in Chile.
Effective water management is essential to ensure the sustainability of irrigated agriculture. The accurate determination of crop water requirements is the first step in this task. This paper describes the building of a one-tree weighing lysimeter (3 x 3 m and 2.15 m depth) located in an almond (Prunus dulcis cv. Guara) orchard, inside the experimental farm "Alameda del Obispo" in Cordoba, Spain, to measure orchard evapotranspiration (ETc). Following a review on lysimetry, the description of the construction of the weighing lysimeter is provided in detail, including considerations relative to system resolution and wind effects on the measurements. Finally, some preliminary results of the evaporation and transpiration of young almond trees are presented demonstrating that lysimetry in orchards provides accurate ETc values needed to determine irrigation water requirements.
Water movement in unsaturated soils is commonly affected by hysteresis, a phenomenon often ignored as to keep the mathematical description of water flow and solute transport simple. In this study, the importance of hysteresis was quantified at lysimeter scale on two Belgian soils, a loamy and a sandy loam soil. Undisturbed soil monoliths (79 cm diameter by 105 cm height) were collected in each soil and the flow studied for various boundary conditions. Each monolith was equipped with different measuring devices to monitor online soil water content, pressure head, and outlet water fluxes. Four unsaturated steady state flow experiments were conducted on each monolith. Hydraulic properties were obtained by inverting the governing flow equation of Richards, using a global multilevel coordinate search inversion algorithm. Measured soil water contents, pressure heads, and outlet water fluxes were used in the objective function. First soil hydraulic parameters in the retention and hydraulic conductivity functions were estimated neglecting hysteresis and compared with the functions obtained using approaches considering hysteresis in their analysis. Hysteresis was incorporated in the retention curve using the simple empirical model proposed by Scott et al. (1983) and using the universal conceptual model of Mualem (1977). Hysteresis in both soils was characterized by a relative large difference between the main drying and wetting soil water retention curves. However, results showed that the effect of hysteresis was different on various components of water flow in the two studied soils. The Scott's model considerably improved pressure head estimates in the loamy soil and Mualem's model somewhat improved the soil water content estimates in the sandy loam soil. Outlet water fluxes in both soils were less sensitive to hysteresis. In general, the simple hysteretic model of Scott was more successful in studying hysteresis in both studied soils.
A simple method for the installation of groundwater lysimeters in peat soils was developed which reduces both time and financial effort significantly. The method was applied on several sites in the Rhinluch, a fen peat land 60 km northwest of Berlin, Germany. Over a two-year period, upward capillary flow and evapotranspiration rates under grassland with different groundwater levels were measured. The installation of tensiometers and TDR probes additionally allowed the in situ determination of the soil hydraulic properties (water retention and unsaturated hydraulic conductivity). The results of the measurements of the unsaturated hydraulic conductivity demonstrate that more than one single method has to be applied if the whole range of the conductivity function from saturation to highly unsaturated is to be covered. Measuring the unsaturated conductivity can be done only in the lab for an adequately wide range of soil moisture conditions.
The storage capacity of a soil profile (soil water storage capacity [SWSC]) is the depth of water required to raise a shallow water table to the land surface. The concept of SWSC is fundamental to many hydrological processes, including surface runoff by saturation excess, expansion, and contraction of wetlands, and estimation of the length of an overland flow plane. A model is introduced and tested to estimate SWSC using simultaneous observations of shallow water table fluctuations and soil moisture in a shallow, sandy soil (hyperthermic Aeric Alaquods). The water table at the selected site fluctuated between a shallow depth and the land surface during the summer, allowing frequent observation of surface inundation and profile storage. An equation of the form SWSC = AdB + Cd + D adequately described the variability of SWSC with d, depth to the water table. It is shown that parameters A, B, C, and D are easily derived from basic physical properties of the soil horizons, including porosity and water retention. The SWSC can be significantly limited by the capillary fringe above the water table, encapsulated air (the volume of air trapped under positive pressure beneath the water table), or the presence of a clay pan at shallow soil depths. The capillary fringe had some influence on SWSC in this sandy soil, but encapsulated air as high as 11.0% of the soil volume was observed at the site. Encapsulated air reduced the available soil storage and resulted in a rapid rise in water table. Ignoring encapsulated air significantly overestimated profile storage. Storage results including and excluding air encapsulation were compared as a function of water table depth.
Water demand for irrigated agriculture is increasing against limited availability of fresh water resources in the lower reaches of the Amu Darya River e.g., Khorezm region of Uzbekistan. Future scenarios predict that Khorezm region will receive fewer water supplies due to climate change, transboundary conflicts and hence farmers have to achieve their yield targets with less water. We conducted a study and used AquaCrop model to develop the optimum and deficit irrigation schedule under shallow groundwater conditions (1.0–1.2 m) in the study region. Cotton being a strategic crop in the region was used for simulations. Capillary rise substantially contributes to crop-water requirements and is the key characteristic of the regional soils. However, AquaCrop does not simulate capillary rise contribution, thereby HYDRUS-1D model was used in this study for the quantification of capillary rise contribution. Alongside optimal irrigation schedule for cotton, deficit strategies were also derived in two ways: proportional reduction from each irrigation event (scenario-A) throughout the growth period as well as reduced water supply at specific crop growth stages (scenario-B). For scenario-A, 20, 40, 50 and 60 % of optimal water was deducted from each irrigation quota whereas for scenario-B irrigation events were knocked out at different crop growth stages (stage 1(emergence), stage 2 (vegetative), stage 3 (flowering) and stage 4 (yield formation and ripening)). For scenario-A, 0, 14, 30 and 48 % of yield reduction was observed respectively. During stress at the late crop development stage, a reduced water supply of 12 % resulted in a yield increase of 8 %. Conversely, during stress at the earlier crop development stage, yield loss was 17–18 %. During water stress at the late ripening stage, no yield loss was observed. Results of this study provide guidelines for policy makers to adopt irrigation schedule depending upon availability of irrigation water.
In many regions around the world, groundwater is the key source of water for some vegetation species, and its availability and dynamics can define vegetation composition and distribution. In recent years the interaction between groundwater and vegetation has seen a renewed attention because of the impact of groundwater extraction on natural ecosystems’ health and increasing interest in the restoration of riparian zones and wetlands. The literature provides studies that approach this problem from very different angles.
Information on the vegetation species that are likely to depend on groundwater and the physical characteristics of such species can be found in a large body of literature in ecology and plant physiology. Environmental engineers, hydrologists, and geoscientists are more focused on ecosystem restoration
and the estimation of a catchment’s water balance, for which the groundwater transpired by vegetation might be an important component. Here we join together these different bodies of literature with the aim of providing the state of knowledge on groundwater-dependent vegetation. We describe the physiological features that characterize groundwater-dependent vegetation, review different methods to study vegetation water use in the field, discuss recent advances in the understanding of how groundwater levels
might determine vegetation composition, and present a summary of the available mathematical models that include the interaction between groundwater levels and vegetative water use. Several future research directions are identified, such as the quantification and modeling of the partitioning of transpiration between unsaturated and saturated zones and the development of integrated models able to link hydrology, ecology, and geomorphology.
In shallow unconfined aquifers, the response of the water table (WT) to input and output water fluxes is controlled by two distinct storage parameters, drainable and fillable porosity, which are applicable for WT drawdown and rise, respectively. However, only the drainable porosity estimated from the hydrostatic soil moisture profile is in common use. In this study, we show that under conditions of evapotranspiration and/or recharge from or to a shallow water table, drainable and fillable porosity have different values. Separate analytical expressions are developed for drainable and fillable porosity accounting for dynamic soil moisture conditions through the assumption of successive steady state fluxes in the unsaturated zone. The equations are expressed in terms of soil hydraulic parameters and matric suction at the soil surface. Parametric evapotranspiration and recharge functions are used to estimate the suction at the soil surface. The final expressions are independent of evapotranspiration or rec
The surface renewal method was used to estimate evapotranspiration (ET) for a restored marsh on Twitchell Island in the Sacramento–San Joaquin Delta, California, USA. ET estimates for the marsh, together with reference ET measurements from a nearby climate station, were used to determine crop coefficients over a 3-year period during the growing season. The mean ET rate for the study period was 6 mm day−1, which is high compared with other marshes with similar vegetation. High ET rates at the marsh may be due to the windy, semi-arid Mediterranean climate of the region, and the permanently flooded nature of the marsh, which results in very low surface resistance of the vegetation. Crop coefficient (Kc) values for the marsh ranged from 0·73 to 1·18. The mean Kc value over the entire study period was 0·95. The daily Kc values for any given month varied from year to year, and the standard deviation of daily Kc values varied between months. Although several climate variables were undoubtedly responsible for this variation, our analysis revealed that wind direction and the temperature of standing water in the wetland were of particular importance in determining ET rates and Kc values. Published in 2007 by John Wiley & Sons, Ltd.
1] Groundwater consumption by phreatophytes is a difficult-to-measure but important component of the water budget in many arid and semiarid environments. Over the past 70 years the consumptive use of groundwater by phreatophytes has been estimated using a method that analyzes diurnal trends in hydrographs from wells that are screened across the water table (White, 1932). The reliability of estimates obtained with this approach has never been rigorously evaluated using saturated-unsaturated flow simulation. We present such an evaluation for common flow geometries and a range of hydraulic properties. Results indicate that the major source of error in the White method is the uncertainty in the estimate of specific yield. Evapotranspirative consumption of groundwater will often be significantly overpredicted with the White method if the effects of drainage time and the depth to the water table on specific yield are ignored. We utilize the concept of readily available specific yield as the basis for estimation of the specific yield value appropriate for use with the White method. Guidelines are defined for estimating readily available specific yield based on sediment texture. Use of these guidelines with the White method should enable the evapotranspirative consumption of groundwater to be more accurately quantified.
Natural peat soils serve as important sinks for nutrients, organic components, and water. Peat soils can pose major environmental problems when they are drained for agricultural production, which may change their role in the landscape from a sink to a source. To successfully restore and conserve peat soils, it is important to understand the soil-moisture dynamics and water demand of drained peat soils for different climate and groundwater conditions. For this purpose, we conducted a series of lysimeter experiments with peat soils subject to different groundwater levels. Evapotranspiration (ET) rates and upward capillary fluxes in peat soils under grass were measured, while TDR probes and tensiometers were used to monitor the soil-water dynamics in the lysimeter during the growing season. The lysimeter data were simulated using an extended version of HYDRUS-1D to enable ET calculations using the Penman-Monteith equation. A physically based approach was tested to predict the canopy resistance as a function of the average pressure head of the soil root zone. The numerical simulations closely followed the observed soil-moisture dynamics in the lysimeter and were consistent with measured differences in ET rates for different groundwater levels. Besides average climate conditions, the effects of extreme dry and wet weather conditions on ET and groundwater recharge during the growing season were evaluated using the calibrated numerical model for different groundwater levels. Evapotranspiration rates during dry years depended very much on upward capillary flow from the water table and hence on the soil hydraulic properties. During wet years, however, ET was controlled mostly by the evaporative demand of the atmosphere, and much less by the soil hydraulic properties.
Recent community based actions to ensure the sustainability of irrigation and protection of associated ecosystems in the Murrumbidgee Irrigation Area (MIA) of Australia has seen the implementation of a regional Land and Water Management Plan. This aims to improve land and water management within the irrigation area and minimise downstream impacts associated with irrigation. One of the plan objectives is to decrease current salt loads generated from subsurface drainage in perennial horticulture within the area from 20 000 tonnes/year to 17 000 tonnes/year. In order to meet such objectives Controlled Water table Management (CWM) is being investigated as a possible ‘Best Management Practice’, to reduce drainage volumes and salt loads.
During 2000–2002 a trial was conducted on a 15 ha subsurface drained vineyard. This compared a traditional unmanaged subsurface drainage system with a controlled drainage system utilizing weirs to maintain water tables and changes in irrigation scheduling to maximize the potential crop use of a shallow water table. Drainage volumes, salt loads and water table elevations throughout the field were monitored to investigate the effects of controlled drainage on drain flows and salt loads.
Results from the experiment showed that controlled drainage significantly reduced drainage volumes and salt loads compared to unmanaged systems. However, there were marked increases in soil salinity which will need to be carefully monitored and managed.
Shallow ground water is a resource that is routinely overlooked when water management alternatives are being considered in
irrigated agriculture. Even though it has the potential to provide significant quantities of water for crop use under the
proper conditions and management. Crop water use from shallow groundwater is affected by soil water flux, crop rooting characteristics,
crop salt tolerance, presence of a drainage system, and irrigation system type and management. This paper reviews these factors
in detail and presents data quantifying crop use from shallow ground, and describes the existing state of the art with regard
to crop management in the presence of shallow ground water. The existing data are used to determine whether in-situ crop water
use from shallow ground water is suitable for a given situation. The suggested methodology uses ratios of ground water electrical
conductivity to the Maas–Hoffman yield loss threshold values, the day to plant maturity relative to plant growth period, and
the maximum rooting depth relative to the nearly saturated zone. The review demonstrates that for in-situ use to be feasible
there has to be good quality ground water relative to crop salt tolerance available for an extended period of time. Shallow
ground water availability is one area that can be managed to some extent. Crop selection will be the primary determinant in
the other ratios.
A lysimeter experiment was conducted to investigate the effect of water table management (WTM) on distribution of soil salinity
and annual alfalfa (Medicago scutellata) yield. Subirrigations with three levels of water table namely, 0.5 (WT0.5), 0.7 (WT0.7), and 1.0m (WT1.0) and a free drainage
(FD) conventional irrigation treatment were selected for this study. All treatments were arranged in a complete randomized
block design with three replicates. The results of this study indicated that the average soil electrical conductivity of the
saturated extract (ECe) in the root zone gradually increased and exceeded the designated crop threshold value (4dS/m) after
the first forage harvest in subirrigated lysimeters. A higher salt accumulation was observed at the WT0.5 treatment. The average
dry matter yield of annual alfalfa in WT0.5 and WT0.7 treatments was found to be 52 and 73% higher compared with the control
treatment, respectively.
In Europe, the use of direct methods using lysimeters for measuring water and solute flow in soils increased in recent years.
Large weighable lysimeters are best suitable for obtaining reliable data about seepage water quantity and quality. Field lysimeters
– lysimeters built in directly in agriculturally used areas – of high technical standard allow a precise determination of
the influence of different cropping systems on groundwater quality. They combine the advantages of true field conditions and
laboratory possibilities of varying parameters, handling and maintenance. Due to the specific needs of each application the
instrumentation varies. Based on general remarks on the advantages of precise weighing lysimeters four standardized lysimeter
configurations are presented. Beside the specific needs of design and setup of lysimeter stations, there is need to define
general requirements to enable comparable results based on standardized basic design and to reduce individual mistakes.
The stochastic nature of long-term dynamics of soil moisture, water table, and vegetation in wetland ecosystems driven by precipitation are investigated through this modeling study. A simple model is presented here to couple the hydrologic and vegetation dynamics via transpiration and ecosystem carrying capacity. The simulation results portray possible competition outcomes between plant species having different survival strategies in response to the fluctuating soil moisture and water tables under different rainfall conditions. Long-range correlations in the dynamics were detected in several of the key variables of wetland ecosystems, as the result of their dependence on the long- memory structure of the water table. The statistical structure of the modeled water table fluctuations is found to be similar to that obtained from a real case study, validating the ability of the model in capturing water table dynamics and suggesting its potential toward the quantification of the long-term dynamics of wetland vegetation.
In situ use of ground water by plants is one option being considered to reduce discharge of subsurface drainage water from irrigated agriculture. Laboratory, lysimeter, and field studies have demonstrated that crops can use significant quantities of water from shallow ground water. However, most studies lack the data needed to include the crop water use into an integrated irrigation and drainage water management system. This paper describes previous studies which demonstrated the potential use of ground water to support plant growth and the associated limitations. Included are results from three field studies which demonstrated some of the management techniques needed to develop an integrated system. The field studies demonstrated that approximately 40 to 45% of the water requirement for cotton can be derived from shallow saline ground water. That regulation of the outflow will result in increasing use. Implementation of integrated management of irrigation and subsurface drainage systems is a viable and sustainable alternative in the management of subsurface drainage water from arid and semi-arid areas only if soil salinity can be managed and if the system is profitable.
Weighing lysimeters are accurate instruments to measure crop evapotranspiration. Three weighing lysimeters, consisting of undisturbed 1.5- x2.0-m surface area by 2.5-m depth cores of soil, were constructed and installed at the Texas Agricultural Experiment Station in Uvalde, Texas. Two lysimeters, each weighing approximately 14 Mg, were located beneath a linear irrigation sprinkler system and used in the field production of several crops commonly grown in the area. The third lysimeter was constructed and is used to measure reference ET from a well-watered, grass (ETos) located adjacent to the field lysimeters. Design construction, installation, engineering details and other considerations to ensure acceptable performance of the lysimeters are discussed. The lysimeter facility was developed to accurately assess crop water requirements of vegetables as well as other field crops grown in the Winter Garden region of Texas. Preliminary detection capability of the scale system is also reported.
Blanket peat catchments exhibit flashy regimes but little is known about the exact nature of runoff production processes within these catchments. Catchment, hillslope and plot-scale monitoring results are presented from the blanket peats of the northern Pennines, UK. Catchment efficiency for three study catchments with areas of 11.4 km(2), 0.83km(2) and 0.44 km(2) were 72 %, 77 % and 82 % respectively. Mean rainfall peak to discharge peak lag times were 2.7 hours, 2.1 hours and 3.2 hours respectively. Runoff from hillslopes in the catchments was gauged using runoff troughs. Mean hillslope lag times ranged from 0.6 to 2.2 hours and despite large differences in the scale of study there was little difference in response time. This indicates that slopes and channels are strongly hydrologically coupled in these peat systems. Saturation-excess overland flow dominates hillslope runoff, particularly on more gentle slopes, and on footslopes where overland flow occurs most frequently. Overall 81.5 % of the total overland flow and matrix throughflow collected by runoff troughs occurred at the peat surface, with 17.7 % between the surface and 5 cm depth, 0.7 % between 5 and 10 cm depth, and less than 0.1 % from below 10 cm depth, despite the thickness of the peat deposit. Most stormflow is produced as saturation-excess overland flow, whereas most low flow is produced by throughflow from 1 to 5 cm depth. Topography and preferential flow paths are important controls on the spatial pattern of runoff even on low-gradient peat. On steeper midslope regions, more flow occurs within the upper 10 cm of peat rather than at the surface. Preferential flow paths are identified at both the hillslope and plot-scale. Discharge deep within the peat is only produced from small macropore and pipe outlets that are well-connected to the peat surface. Response to rainfall from these macropore networks is rapid and they generate around 10 % of streamflow.
The experiments were conducted to quantify the effects of shallow water tables on the water use and yield of winter wheat under rain-fed condition through lysimeter. The result showed that, under rain-fed condition, the seasonal groundwater contribution met more than 65% of the potential evapotranspiration of winter wheat with precipitation together as water table depth was within 0-150 cm. As water table was not deeper than 110 cm from ground, the water table contribution nearly met the entire water requirement of winter wheat with the total precipitation in winter wheat season. It was found that 150 cm was a desired depth for yield formation due to the full development of root and the high spike numbers when water table depth was not more than 150 cm. The water use efficiency and ground water use efficiency increased with the increase of water table depth, varying from 1.27 to 2.09 kg m -3 and from 1.45 to 2.95 kg m -3, respectively. The water table contribution should be recognized as the predominant source of evapotranspiration when water table was very shallow (≤ 150 cm), and the irrigation and drainage system should be managed to maximize the WUE and yield of winter wheat by controlling water table at desired depth. This study helps to raise the yield of winter wheat and control shallow water tables.
In wetlands or riparian areas water withdrawal by plants with access to groundwater or the capillary fringe often causes diurnal groundwater fluctuations. Various approaches use the characteristics of these fluctuations for estimation of daily groundwater evapotranspiration rates. The objective of this paper was to review the available methods, compare them with measured evapotranspiration and assess their recharge assumptions. For this purpose, we employed data of 85 rain-free days of a weighable groundwater lysimeter situated at a grassland site in the Spreewald wetland in north-east Germany. Measurements of hourly recharge and daily evapotranspiration rates were used to assess the different approaches. Our results showed that a maximum of 50\% of the day to day variance of the daily evapotranspiration rates could be explained by the approaches based on groundwater fluctuations. Simple and more complex methods performed similarly. For some of the approaches there were indications that erroneous assumptions compensated each other (e.g. when overestimated recharge counteracted underestimated storage change). We found that the usage of longer time spans resulted in improved estimates of the daily recharge rates and that the estimates were further enhanced by including two night averages. When derived from fitting estimates of recharge or evapotranspiration with according measurements the specific yield, needed to convert changes in water level to water volumes, differed considerably among the methods (from 0.022 to 0.064). Thus, the specific yield can be seen as “correction factor” that compensates for inadequate process descriptions.
Transitions between aquatic and terrestrial ecosystems represent zones
where soil moisture is a dominant factor influencing vegetation
composition. Niche models based on hydrological and vegetation
observations can be powerful tools for guiding management of these
zones, especially when they are linked with physically based
hydrological models. Floodplain restoration represents a unique
opportunity to utilize such a predictive vegetation tool when a site's
hydrology is altered to create a wetter environment. A variably
saturated groundwater flow model was developed and used to simulate the
soil moisture regime across a floodplain in Wisconsin where
post-settlement alluvium was removed with the intent of increasing
regionally threatened wetland plant species. Hydrological niche models
based on simultaneous observations of vegetation composition and surface
effective saturation were used to predict probability of presence for
two plant species (Carex vulpinoidea (fox sedge) and Elymus
canadensis(Canada wildrye)) and wetland indicator score (a composite
indicator of relative frequency of species in five habitat categories)
based on simulated surface effective saturation. The vegetation
predictions following restoration are more wetland-species dominant
overall. However, zones of the study site where a confining layer is
present that decouples groundwater from the near-surface soil zone tend
to be drier following restoration due to restricted upward groundwater
flow and less soil water storage above the confining layer. As reflected
by an increase in the interquartile range in the predicted wetland
indicator score, this restoration technique may increase the site-scale
spatial diversity of plant community types while simultaneously
accomplishing the goal of increasing wetland plant species occurrence.
Riparian vegetation typically has a great influence on groundwater level and groundwater-sustained stream baseflow. By modifying the well-known method by White [White, W.N., 1932. Method of estimating groundwater supplies based on discharge by plants and evaporation from soil – results of investigation in Escalante Valley, Utah – US Geological Survey. Water Supply Paper 659-A, 1–105] an empirical and hydraulic version of a new technique were developed to calculate evapotranspiration (ET) from groundwater level readings in the riparian zone. The method was tested with hydrometeorological data from the Hidegvíz Valley experimental catchment, located in the Sopron Hills region at the western border of Hungary. ET rates of the proposed method lag behind those of the Penman–Monteith method but otherwise the two estimates compare favorably for the day. At nights, the new technique yields more realistic values than the Penman–Monteith equation. On a daily basis the newly-derived ET rates are typically 50% higher than the ones obtainable with the original White method. Sensitivity analysis showed that the more reliable hydraulic version of our ET estimation technique is most sensitive (i.e., linearly) to the laboratory- and/or slug-test derived values of the saturated hydraulic conductivity and specific yield taken from the riparian zone.
A lysimeter experiment was conducted in southeastern Australia to quantify the deep percolation response under irrigated pasture to different soil types, water table depths, and ponding times during surface irrigation. Deep percolation was governed by the final infiltration rate of the subsoil, the ponding time, the water table depth, and the amount of water stored in the rootzone between saturation and field capacity. These key variables were used to characterize both steady- and nonsteady-state percolation in a conceptual model of deep percolation. The conceptual model was found to provide an effective representation of deep percolation for both the lysimeter and field-scale water balance data. Steady-state percolation during irrigation was the dominant process contributing to deep percolation on most of the studied soils. Nonsteady-state percolation (redistribution) was very important for the sandiest soil type. The conceptual model provided better prediction of deep percolation than both data-based model (artificial neural network) and process-based modeling approach (1-D Richards' equation model).
A lysimeter study was conducted in the field in Karaj, Iran to investigate the effects of water table management on water quality of subsurface drainage effluents. Drain volumes, nitrate-N concentration, phosphorus concentration, and electrical conductivity of drain effluents were monitored during the growing seasons of alfalfa (Medicago scutellata). Totally 12 lysimeters consisted of four treatments were used in this study, of which nine of them were equipped with subirrigation (SI) and the other three with free drainage (FD) systems. Annual alfalfa (Medicago scutellata) was planted in all lysimeters. Water table levels were kept at 30 cm (SI30), 50 cm (SI50), and 70 cm (SI70) below the soil surface in SI-lysimeters and more than 100 cm below the soil surface in FD-lysimeters. The results of this 2-year study showed a significant reduction in nitrate-N concentrations in SI-lysimeters compared to FD-lysimeters. In 2005, the mean nitrate-N concentrations in drainage effluent were reduced by 84% in the SI30 and by 82% in the SI50, relative to FD. Similarly, in 2006, drain water depth and nitrate-N concentrations were significantly reduced relative to FD. The forage dry matter production from SI30 and SI50 were significantly higher than those from FD in both years. In 2006, the average of dry matter production was increased by 69 and 89% by the SI30 and SI50, respectively, relative to FD. The average electrical conductivity of drainage water was reduced in SI lysimeters compared to FD lysimeters that meet Iranian standard level (3 dS/m). There are no statistically significant differences in phosphorous concentration in drainage water of different treatments. Finally, the results of this 2-year study indicate that the water table management practices are economically and environmentally feasible in Iran in order to have a sustainable agriculture.
Meadow vegetation is controlled by cascading hydrologic processes
Estimation in spite of measurement is the common approach to acquire ET data for most applications. Selection of a method for a specific application requires evaluation of methods with respect to the accuracy needed, available input data, and cost of data generation. Methods vary by complexity and input data requirement. In cases where simple methods provide reasonable estimates, adaptation of such methods could be a cost-effective way of acquiring ET data. In this chapter, several open water evaporation and ET estimation methods are provided with application to a region. Methods are organized from the simplest to the most complex with evaluation of input data requirements. Measured, derived, and estimated input parameters for the application of the Penman–Monteith method are presented in detail with experimental measurements of resistance terms.
A lysimeter was designed and installed in a cattail marsh as part of the Everglades Nutrient Removal project in South Florida (26° 38' N, 9O° 25' W) to measure evapotranspiration (ET) of cattails (Typha domingensis). The fully automated lysimeter with a surface area of 9.8 m2 was located inside the marsh to measure cattail ET in a marsh environment with sufficient fetch and minimum oasis effect on the lysimeter. The average measured ET rate was 3.9 mm per day for the period of 12 February to 19 December 1993. The Penman-Monteith equation was applied to estimate daily ET using physically based resistance parameter estimates and high resolution weather data. Also, average albedo (0.17) was computed for the vegetation for possible future computation of net radiation from solar radiation data. The Penman combination model was applied with new wind function coefficients developed for the study site and the Priestley-Taylor model was applied with an estimated average coefficient (α) value of 1.18. Seven-day mean of measured and estimated data were compared. The Penman-Monteith method had the least error of estimation of 0.39 mm day-1 with an r2 value of 0.89 while the Penman combination equation had an error of estimation of 0.57 mm day-1 with r2 value of 0.86 and a least intercept of 0.03 mm. The Priestley-Taylor method with an α value of 1.18 had standard error of estimate 0.53 mm day-1 with an r2 value of 0.79. The Priestley-Taylor method has the potential to estimate ET in south Florida when climatic data is limited. More data is needed to evaluate each equation to estimate ET of wetland features in humid areas such as south Florida.
A large weighing lysimeter was installed at Yucheng Comprehensive Experimental Station, north China, for evapotranspiration and soil-water–groundwater exchange studies. Features of the lysimeter include the following: (i) mass resolution equivalent to 0·016 mm of water to accurately and simultaneously determine hourly evapotranspiration, surface evaporation and groundwater recharge; (ii) a surface area of 3·14 m2 and a soil profile depth of 5·0 m to permit normal plant development, soil-water extraction, soil-water–groundwater exchanges, and fluctuations of groundwater level; (iii) a special supply–drainage system to simulate field conditions of groundwater within the lysimeter; (iv) a soil mass of about 30 Mg, including both unsaturated and saturated loam. The soil consists mainly of mealy sand and light loam. Monitoring the vegetated lysimeter during the growing period of winter wheat, from October 1998 through to June 1999, indicated that during the period groundwater evaporation contributed 16·6% of total evapotranspiration for a water-table depth from 1·6 m to 2·4 m below ground surface. Too much irrigation reduced the amount of upward water flow from the groundwater table, and caused deep percolation to the groundwater. Data from neutron probe and tensiometers suggest that soil-water-content profiles and soil-water-potential profiles were strongly affected by shallow groundwater. Copyright © 2000 John Wiley & Sons, Ltd.
Accurate estimates of evapotranspiration from areas dominated by wetland vegetation are needed in the water budget of the Upper St. Johns River Basin. However, local data on evapotranspiration rates, especially in wetland environments, were lacking in the project area. In response to this need, the St. Johns River Water Management District collected evapotranspiration field data in Fort Drum Marsh Conservation Area over the period 1996 through 1999. Three large lysimeters were installed to measure the evapotranspiration from different wetland environments: sawgrass (Cladium jamaicense), cattail (Typha domingensis), and open water. In addition, pan evaporation was measured with a standard class “A” pan. Concurrently, meteorological data including rainfall, solar radiation, wind speed, relative humidity, air temperature, and atmospheric pressure were collected. By comparing computed evapotranspiration rates with those measured in the lysimeters, parameters in the Penman-Monteith, the Priestley-Taylor, and Reference-ET methods, and evaporation pan coefficients were estimated for monthly and seasonal cycles. The results from the data collected in this study show that mean monthly evapotranspiration rates, computed by the different methods, are relatively close. From a practical point of view, results indicate that the evaporation pan can be used equally well as the more complex and data-intensive methods. This paper presents the measured evapotranspiration rates, evaporation pan coefficients, and the estimated parameter values for three different methods to compute evapotranspiration in the project area. Since local data on evaporation are often scarce or lacking, this information may be useful to watershed hydrologists for practical application in other project regions.
Presently, the soil water balance of flood-influenced soils in fluvial plains is insufficiently described. The new development of a weighable groundwater lysimeter is the basis for recording the water-balance components precipitation, evapotranspiration, groundwater recharge, capillary rise, and interaction with the water course. Soil-hydrologic measuring setups at two floodplain sites of the Elbe river serve for direct comparability of lysimeter measurements with data obtained on site. A groundwater control was designed for lysimeters that automatically adjusts the current groundwater level at the floodplain measuring setups and quantifies inflow into or outflow from the lysimeter. It turned out that the lysimeter developed is capable of identifying the individual water-balance quantities at high accuracy. Contrary to previous assumptions, it was possible to prove groundwater recharge for the floodplain sites.
Capillary upflow from and deep percolation to a water table may be important in crop water supply in irrigated areas of the lower Yellow River flood plain, north China. These fluxes at the water table and the variations of the capillary upflow in relation to crop evapotranspiration need to be investigated to quantify the effect of a water table on soil water balance and to improve agricultural water management. A large weighing lysimeter was used to determine daily crop evapotranspiration, daily capillary upflow from and daily percolation to a fluctuating water table during a rotation period with wheat growing in a dry season and maize in a rainy season. The water table depth varied in the range 0·7–2·3 m during the maize growth period and 1·6–2·4 m during the wheat growth period. Experimental results showed that the capillary upflow and the percolation were significant components of the soil water balance. Three distinctly different phases for the water fluxes at the water table were observed through the rotation period: water downward period, the period of no or small water fluxes, and water upward period. It implied that the temporal pattern of these water fluxes at the water table was intimately associated with the temporal distribution of rainfall through the rotation period. An empirical equation was determined to estimate the capillary upflow in relation to wheat evapotranspiration and root zone soil water content for local irrigation scheduling. Coupled with the FAO-Penman–Monteith equation, the equation offers a fast and low cost solution to assess the effect of capillary upflow from a water table on wheat water use. Copyright © 2007 John Wiley & Sons, Ltd.
1] Areas with a relatively shallow water table are environments where the groundwater plays a key role on the ecosystem function, and important interactions exist between hydrology and ecosystem processes. We propose here an analytical model to study the interactions between rainfall, water table, and vegetation in groundwater-dependent ecosystems. The water table dynamics are studied as a random process stochastically driven by a marked Poisson noise representing rainfall events. Infiltration, root water uptake, water flow to/from an external water body, and capillary rise are accounted for in a probabilistic description of water table fluctuations. We obtain analytical expressions for the steady state probability distribution of water table depth, which allows us to investigate the long-term behavior of water table dynamics, and their sensitivity to changes in climate, vegetation cover, and water management.
1] In groundwater-dependent ecosystems, interactions between rainfall, water table fluctuations, and vegetation are exerted through the soil water content. The dynamics of soil moisture, in fact, are strongly coupled to fluctuations of the water table and, together, they control the overall ecosystem dynamics. We propose here a simple process-based stochastic model for the study of soil moisture dynamics at a generic depth, to complement the stochastic model of water table depth presented in the companion paper. The model presented here is based on a local and depth-dependent water balance driven by stochastic rainfall (marked Poisson noise) and accounting for processes such as rainfall infiltration, root water uptake, and capillary rise. We obtain a semianalytical formulation of the stationary probability distribution of soil water content at different depths, which is studied for different values of soil, climate, and vegetation parameters. The probability distributions are used to investigate the ecohydrology of groundwater-dependent ecosystems, including the quantitative description of the vegetation–water table–soil moisture interplay and the probabilistic analysis of root water uptake.
More and more evapotranspiration models, evapotranspiration crop coefficients and associated measurements of evapotranspiration (ET) are being reported in the literature and used to develop, calibrate and test important ET process models. ET data are derived from a range of measurement systems including lysimeters, eddy covariance, Bowen ratio, water balance (gravimetric, neutron meter, other soil water sensing), sap flow, scintillometry and even satellite-based remote sensing and direct modeling. All of these measurement techniques require substantial experimental care and are prone to substantial biases in reported results. Reporting of data containing measurement biases causes substantial confusion and impedance to the advancement of ET models and in the establishment of irrigation water requirements, and translates into substantial economic losses caused by misinformed water management.
Basic principles of ET measuring systems are reviewed and causes of common error and biases endemic to systems are discussed. Recommendations are given for reducing error in ET retrievals. Upper limits on ET measurements and derived crop coefficients are proposed to serve as guidelines. The descriptions of errors common to measurement systems are intended to help practitioners collect better data as well as to assist reviewers of manuscripts and users of data and derived products in assessing quality, integrity, validity and representativeness of reported information. This paper is the first part of a two-part series, where the second part describes recommendations for documentation to be associated with published ET data.
Different methods exist for measuring soil water and solute fluxes in and below the root zone and have been critically reviewed.
Besides indirect methods (e.g. water balance, tensiometer, time domain reflectometry – TDR, frequency domain reflectometry
– FDR, environmental tracer) direct methods (e.g. drainage-type lysimeter, water fluxmeter) have a long tradition and have
been successfully used in seepage research. A large weighable out door lysimeter is the best method for obtaining reliable
data about seepage water quantity and quality, but it involves significant investment and additional expenses for maintenance.
To tackle this problem new methods for the vertical collection of large volume soil monoliths (up to 6m3) as well as for the horizontal collection (up to 6m3) have been developed. For the placement of the lysimeter a container lysimeter unit was constructed, which is cheaper than
a conventional steel or concrete cellar. Furthermore, the technical design of the newly developed lysimeter types as a weighable
gravitation lysimeter, a weighable groundwater lysimeter and a lateral flow lysimeter are presented.
In principle, conventional lysimeters are suitable for the investigation of vertical water and solute fluxes. Lateral fluxes
in water-saturated fen sites are characterized by heterogeneities and abnormities due to anisotropic layering. But due to
lack of adequate monitoring techniques, these fluxes have been insufficiently analyzed. The newly developed large weighable
fen lysimeter (LWFL) overcomes the limitations of conventional lysimetry and enables the measurement of vertical and horizontal
transport processes in undisturbed large volume soil monoliths. The LWFL has a volume of 6m3 (4m length, 1m width and 1.5m depth) and was tested by filling the lysimeter with an undisturbed fen monolith. A special
extraction procedure for the horizontal sliding of the lysimeter vessel through the natural fen was developed. In front of
the vessel a converted cutting tool assisted in carving the soil monolith out of the peat, both vertically and horizontally.
Inlet and outlet of the LWFL was constructed to allow the adjustment of a wide range of hydraulic gradients to depict natural
occurring lateral transport processes. The LWFL including the measurement techniques was tested successfully for 3years.
On the basis of these tests, we conclude that complex physical and biogeochemical research problems involving lateral flows
can be tackled now with multiphase observations and measurements at high spatial and temporal resolution, transdisciplinary
data evaluation and numerical modelling approaches.
Evaporation from small reservoirs, wetlands, and lakes continues to be a theoretical and practical problem in surface hydrology and micrometeorology because atmospheric flows above such systems can rarely be approximated as stationary and planar-homogeneous with no mean subsidence (hereafter referred to as idealized flow state). Here, the turbulence statistics of temperature (T) and water vapor (q) most pertinent to lake evaporation measurements over three water bodies differing in climate, thermal inertia and degree of advective conditions are explored. The three systems included Lac Léman in Switzerland (high thermal inertia, near homogeneous conditions with no appreciable advection due to long upwind fetch), Eshkol reservoir in Israel (intermediate thermal inertia, frequent strong advective conditions) and Tilopozo wetland in Chile (low thermal inertia, frequent but moderate advection). The data analysis focused on how similarity constants for the flux-variance approach, CT/Cq, and relative transport efficiencies RwT/Rwq, are perturbed from unity with increased advection or the active role of temperature. When advection is small and thermal inertia is large, CT/Cq < 1 (or RwT/Rwq > 1) primarily due to the active role of temperature, which is consistent with a large number of studies conducted over bare soil and vegetated surfaces. However, when advection is significantly large, then CT/Cq > 1 (orRwT/Rwq < 1). When advection is moderate and thermal inertia is low, then CT/Cq ∼ 1. This latter equality, while consistent with Monin–Obukhov similarity theory (MOST), is due to the fact that advection tends to increase CT/Cq above unity while the active role of temperature tends to decrease CT/Cq below unity. A simplified scaling analysis derived from the scalar variance budget equation, explained qualitatively how advection could perturb MOST scaling (assumed to represent the idealized flow state).
The study investigated evapotranspiration (ET) and water use efficiency (WUE) on sites of shallow water tables. This contribution was aimed to provide data for soil water modeling and water management planning. Based on a long-term study of groundwater lysimeters in the vicinity of Berlin, Germany, the total ET, the proportion of ground water supply and the water use efficiency of different plants, crops and soils were quantified in the vegetation period from April to October. The climate is characterized by a mean temperature of 8.4°C and an annual precipitation of 500 to 600 mm. ET of groundwater (= subirrigation rate) strongly depended on water table depths, crops and soil texture and showed large variability between different years due to weather conditions. Spring barley consumed 10-60 mm of groundwater, winter wheat 20-250 mm, pasture and meadow grasses 80-300 mm, maize 100-400 nun, reed canary grass (Phalaris arundinacea) 400-900 mm, sedges 600-1000 mm and common reed 700-1400 mm. Plant type associated with appropriate water table depth, fertilization level and soil fertility were crucial factors of WUE. Results showed possible high dry matter yields at all water table levels but increasing WUE with deeper water table. Maize had highest WUE with 4 -6 g dry matter per litre of water, followed by winter wheat, with a WUE of about 3. Wetland plants also produced high amounts of biomass but consumed more water. Common reed and sedges had a WUE of 1.2 and reed canary grass had a WUE of about 1.1.
Understanding of the hydrology of upland blanket peatlands has been limited both by the logistical difficulties of obtaining data from such environments and by technical difficulties with plot scale investigations of peat hydrology. The relative importance of infiltration-excess and percolation-excess as runoff generating mechanisms as opposed to the saturation-excess mechanism remains unclear. This study uses catchment-scale runoff data, in combination with monitoring of water table levels, to identify the relative importance of these mechanisms for an upland peat catchment within the Moor House National Nature Reserve in the UK. Mean runoff coefficients for the catchment are 0.4 and the flood hydrographs are flashy. Monitored water table in the catchment is within 5 cm of the surface (i.e. within the acrotelm) 93% of the time. High stream flows always occur at times of high water table suggesting that overland and near surface runoff is controlled by saturation of the catotelm rather than by infiltration capacity. Depressed rates of water table recovery at the end of a prolonged period of low water table in 1995 suggest possible physical changes once the peat has dried out. The likelihood that such periods of low water table will become more common under global warming scenarios raises concern over the impact of such changes: increased erosion, water discoloration, and increased CO2 flux may result.
Blanket peat catchments exhibit flashy regimes but little is known about the exact nature of runoff production processes within these catchments. Catchment, hillslope and plot-scale monitoring results are presented from the blanket peats of the northern Pennines, UK. Catchment efficiency for three study catchments with areas of 11.4 km(2), 0.83km(2) and 0.44 km(2) were 72 %, 77 % and 82 % respectively. Mean rainfall peak to discharge peak lag times were 2.7 hours, 2.1 hours and 3.2 hours respectively. Runoff from hillslopes in the catchments was gauged using runoff troughs. Mean hillslope lag times ranged from 0.6 to 2.2 hours and despite large differences in the scale of study there was little difference in response time. This indicates that slopes and channels are strongly hydrologically coupled in these peat systems. Saturation-excess overland flow dominates hillslope runoff, particularly on more gentle slopes, and on footslopes where overland flow occurs most frequently. Overall 81.5 % of the total overland flow and matrix throughflow collected by runoff troughs occurred at the peat surface, with 17.7 % between the surface and 5 cm depth, 0.7 % between 5 and 10 cm depth, and less than 0.1 % from below 10 cm depth, despite the thickness of the peat deposit. Most stormflow is produced as saturation-excess overland flow, whereas most low flow is produced by throughflow from 1 to 5 cm depth. Topography and preferential flow paths are important controls on the spatial pattern of runoff even on low-gradient peat. On steeper midslope regions, more flow occurs within the upper 10 cm of peat rather than at the surface. Preferential flow paths are identified at both the hillslope and plot-scale. Discharge deep within the peat is only produced from small macropore and pipe outlets that are well-connected to the peat surface. Response to rainfall from these macropore networks is rapid and they generate around 10 % of streamflow.
There is a long history of drainage of blanket peat but few studies of the long-term hydrological impact of drainage. This paper aims to test differences in runoff production processes between intact and drained blanket peat catchments and determine whether there have been any long-term changes in stream flow since drainage occurred. Hillslope runoff processes and stream discharge were measured in four blanket peat catchments. Two catchments were drained with open-cut ditches in the 1950s. Ditching originally resulted in shorter lag times and flashier storm hydrographs but no change in the annual catchment runoff efficiency. In the period between 2002 and 2004, the hydrographs in the drained catchments, while still flashy, were less sensitive to rainfall than in the 1950s and the runoff efficiency had significantly increased. Drains resulted in a distinctive spatial pattern of runoff production across the slopes. Overland flow was significantly lower in the drained catchments where throughflow was more dominant. In the intact peatlands, matrix throughflow produced by peat layers below 10 cm was rare and produced <1% of the runoff. However, in drained peatlands, matrix throughflow in deeper peat layers was common and provided around 23% of the runoff from gauged plots. Macropore flow, the density of soil piping, and pipeflow were significantly greater in drained peatlands than in intact basins. Gradual changes to peat structure could explain the long-term changes in river flow, which are in addition to those occurring in the immediate aftermath of peatland drainage.
Shallow saline water tables underline large areas of the Riverine Plains of the Murray Basin of southern Australia. It is believed that deep-rooted perennial plants in these areas are able to reduce recharge and use shallow groundwater, thus controlling groundwater levels. Lysimeters represent the best experimental technique for investigating capillary upflow from shallow water tables and the associated processes of salt accumulation, plant water use, and growth response. Techniques involving stable isotopes of water help determine the components of upflow due to vegetation. When combined with models that stimulate salt and water movement in the soil zone and the plant water use and growth, we can thoroughly test our understanding of salinity processes and the ability of plants to control water tables. Results from WAVES simulations of plant growth, evapotranspiration, groundwater uptake, salt accumulation, and the impacts on lucerne growth are compared against measurements made in lysimeters at Griffith, NSW, Australia. With minimal calibration, WAVES was able to reproduce both the daily and seasonal variation in evapotranspiration, upward flux from the groundwater table, plant growth in terms of leaf area development, soil water profiles, soil water salinity, and root water extraction patterns. There was a decline of 36% in transpiration, 42% in leaf area growth, and 67% in upward flux after the salinity of the water table increased from 0.1 to 16dSm−1. Although the upward flux of water was large, lucerne used little of it (< 20%), preferring `fresher' rainfall and irrigation water near the surface. Given the tests presented in this work, we think WAVES is applicable to irrigated agricultural systems.