Diurnal Water Table Fluctuations Research Articles

Hydrologic evaluation of a poplar phytoextraction system

This paper reports the results of a seven-year study of a phytoremediation system consisting of 349 hybrid poplars (Populous deltoids x Populus nigra ‘DN-21’) that were emplaced to reduce the migration of impacted groundwater toward a nearby stream. For the relatively small tree stand, the achievement of hydraulic containment was challenged by several factors, including topographic constraints on tree placement, spatial heterogeneity in depth-to-groundwater, and lack of controls on surface runoff. However, the interpretation of measured diurnal water table fluctuations indicated substantial and increasing levels of groundwater extraction, consistent with poplar sap flow measurements collected during two growing seasons. The project also provided unique educational experiences for undergraduate and graduate students from multiple academic disciplines who participated in monitoring, site maintenance, and data interpretation. Novelty statement The paper adds to the limited literature on poplar-based phytoextraction of contaminated groundwater by describing a seven-year case study with detailed hydrologic measurements. Novel elements include (1) a very large data set of poplar sap flow measurements that provides insight into potential spatial and temporal variability, and (2) a detailed application of an under-utilized analytical tool (water table fluctuations) to evaluate hydraulic capture.

Quantification of groundwater recharge and evapotranspiration along a semi-arid wetland transect using diurnal water table fluctuations

Quantification of groundwater recharge and evapotranspiration along a semi-arid wetland transect using diurnal water table fluctuations

Modified method for the estimation of groundwater evapotranspiration under very shallow water table conditions based on diurnal water table fluctuations

Groundwater evapotranspiration (ETG) is often estimated using the White method from diurnal water table fluctuations. However, under very shallow water table conditions (<1 m in this study), the groundwater replenishment to ET-induced depleted soils during nighttime is significant, but is ignored in the White method. A variably saturated flow model, HYDRUS-1D, was used to elucidate the impact of this omission on the accuracy of ETG under various soils, depths to the water table, climatic conditions, vegetation coverage, and root distributions. We found that the mean ETG was underestimated by 33–69% by the original White method because of the inaccurate estimation of the water table recovery rate during nighttime. The daily hydrostatic equilibrium recovery (Re) term was introduced to modify the original White method by considering the ET-induced disequilibrium in soil moisture. Using the modified method, the estimated ETG approaches its real value, and the mean difference between them is only approximately 2%. The modified method was applied to estimate ETG in a wetland in NW China, resulting in better agreement with potential evapotranspiration measurements than the original White method.

Estimation of Groundwater Evapotranspiration of Different Dominant Phreatophytes in the Mu Us Sandy Region

Groundwater evapotranspiration (ETG) estimation is an important issue in semiarid areas for groundwater resources management and environmental protection. It is widely estimated by diurnal water table fluctuations. In this study, the ETG at four sites with different plants was estimated using both diurnal water table and soil moisture fluctuations in the northeastern Mu Us sandy region, in order to identify the groundwater utilization strategy by different dominant phreatophytes. Groundwater level was monitored by ventilatory pressure transducers (Solinst LevelVent, Solinst Canada Ltd.; accuracy ±3 mm), while soil moisture was monitored using EM50 loggers (Decagon Devices Inc., Pullman, USA) in K1 and K14 and simulated by Hydrus-1D in other observation wells. A significant spatial variation of ETG was found within a limited area, indicating a poor representativeness of site ETG for regional estimation. The mean values of ETG are 4.01 mm/d, 6.03 mm/d, 8.96 mm/d, and 12.26 mm/d at the Achnatherum splendens site, Carex stenophylla site, Salix psammophila site and Populus alba site, respectively, for the whole growing season. ETG is more sensitive to depth to water table (DWT) in the Carex stenophylla site than in the Achnatherum splendens site for grass-dominated areas and more sensitive to DWT in the Populus alba site than in Salix psammophila site for tree-dominated areas. Groundwater extinction depths are estimated at 4.1 m, 2.4 m, 7.1 m, and 2.9 m in the Achnatherum splendens site, Carex stenophylla site, Salix psammophila site and Populus alba site, respectively.

Use of mature willows (Salix nigra) for hydraulic control of landfill-impacted groundwater in a temperate climate

Phreatophytic trees such as willows and poplars have a large capacity for extracting shallow groundwater, as evidenced by diurnal water table fluctuations corresponding to intensified transpiration during the day. As a result, they have been employed for phytoremediation of shallow contaminated groundwater. In this study, the water extraction (i.e. pumping) capacity of mature willows (Salix nigra) to capture shallow polluted groundwater in Belle Park, the site of a former landfill in Kingston, Ontario (Canada), was assessed using continuous field measurements of sap flow and water table levels associated with a single willow tree, combined with a transient numerical model (FEFLOW). On an annual basis, the sapflow averaged 2.3 m3d-1, with 70% of the cumulative sap flow occurring during the active growing season (May to September). The calibration showed a good fit (0.91 < R2<0.97) between measured groundwater levels from three shallow wells installed near the willow and the calculated water table level fluctuations, thus confirming that the water extraction rate based on sap flow data for the willow was appropriate. At stand level, additional modelling suggests that 3.4–4.7 ha of mature willows (i.e. between 7.8% and 10.6% of the Park area), could compensate for the current water volumes extracted by the municipality using a conventional pump and treat system. The results of this study indicate that willows can play a significant role in capturing contaminated groundwater underlying Belle Park, and potentially at other sites where removal of contaminants from shallow aquifers is desired.

Estimating groundwater evapotranspiration by phreatophytes using combined water level and soil moisture observations

AbstractOne of the classical methods for estimating groundwater evapotranspiration (ETg) by phreatophytes is based on diurnal water table fluctuations (WTFs). This method was initially introduced by White in 1932 and has recently been improved. However, vegetation‐induced disequilibrium between groundwater and capillary fringe (CF) water is not considered under White's assumptions. In this study, we propose an approach that considers root‐driven water depletion in the CF using the soil moisture profile (hereafter referred to as the SMP method). The SMP method is demonstrated to perform equally well for both long‐term water table rises and declines. The apparent advantages of the SMP method over traditional WTF‐based methods include its greater effectiveness in revealing physical mechanisms and its omission of specific yield determination. However, appropriately determining the boundary condition, which is related to active root‐zone thickness, is crucial for the SMP method. Further development of the SMP method requires a deeper understanding of the interactions among roots, groundwater, and soil moisture.

Estimating groundwater evapotranspiration by a subtropical pine plantation using diurnal water table fluctuations: Implications from night-time water use

Exotic pine plantations have replaced large areas of the native forests for timber production in the subtropical coastal Australia. To evaluate potential impacts of changes in vegetation on local groundwater discharge, we estimated groundwater evapotranspiration (ETg) by the pine plantation using diurnal water table fluctuations for the dry season of 2012 from August 1st to December 31st. The modified White method was used to estimate the ETg, considering the night-time water use by pine trees (Tn). Depth-dependent specific yields were also determined both experimentally and numerically for estimation of ETg. Night-time water use by pine trees was comprehensively investigated using a combination of groundwater level, sap flow, tree growth, specific yield, soil matric potential and climatic variables measurements. Results reveal a constant average transpiration flux of 0.02mmh−1 at the plot scale from 23:00 to 05:00 during the study period, which verified the presence of night-time water use. The total ETg for the period investigated was 259.0mm with an accumulated Tn of 64.5mm, resulting in an error of 25% on accumulated evapotranspiration from the groundwater if night-time water use was neglected. The results indicate that the development of commercial pine plantations may result in groundwater losses in these areas. It is also recommended that any future application of diurnal water table fluctuation based methods investigate the validity of the zero night-time water use assumption prior to use.

Spatiotemporal patterns of water table fluctuations and evapotranspiration induced by riparian vegetation in a semiarid area

AbstractGroundwater evapotranspiration (ETg) links various ecohydrological processes and is an important component in regional water budgets. In this study, an extensive monitoring network was established in a semiarid riparian area to investigate various controls on the spatiotemporal pattern of water table fluctuations (WTFs) and ETg induced by riparian vegetation. Along a vegetation gradient (∼1200 m), diurnal WTFs were observed during a growing season in areas covered by woody species (Populus sect. Aigeiros and Juniperus virginiana) and wet slough vegetation (Panicum virgatum and Bromus inermis) with deeper root systems; whereas, no diurnal WTFs were found in the middle section with shallower‐rooted grasses (Poa pratensis and Carex sp.). The occurrence of diurnal WTFs was related to temperature‐controlled plant phenology at seasonal scales and to radiation at subdaily scales. Daily ETg in the mid‐growing season was calculated using the White method. The results revealed that depth to water table (DTWT) was the dominant control on ETg, followed by potential evapotranspiration (ETp). By combining the effects of DTWT and ETp, it was found that at shallower depths, ETg was more responsive to changes in ETp, due to the closer linkage of land surface processes with shallower groundwater. Finally, exponential relationships between ETg/ETp and DTWT were obtained at the study site, although those relationships varied considerably across the sites. This study demonstrates the complex interactions of WTFs and ETg with surrounding environmental variables and provides further insight into modeling ETg over different time scales and riparian vegetation.

Responses of shelterbelt stand transpiration to drought and groundwater variations in an arid inland river basin of Northwest China

Plant water use characteristics and transpiration responses under dry conditions are considered essential for effective and sustainable ecosystem management in arid areas. This study was conducted to evaluate the response of shelterbelt stand transpiration to precipitation, soil drought and groundwater variations in an oasis-desert ecotone in the middle of the Heihe River Basin, China. Sap flow was measured in eight Gansu Poplar trees (Populus Gansuensis) with different diameter at breast height over three consecutive growing seasons (2012-2014). The groundwater evapotranspiration via plant use was estimated by the White method with diurnal water table fluctuations. The results showed that precipitation increased the stand transpiration but not statistically significant (paired t-test, p > 0.05). The recharge of soil water by irrigation caused stand transpiration acceleration significantly (t-test, p < 0.05). Stand transpiration and canopy conductance increased by 27% and 31%, respectively, when soil water conditions changed from dry to wet. Canopy conductance decreased logarithmically with vapor pressure deficit, while there was no apparent relationship between canopy conductance and solar radiation. The sensitivity of canopy conductance to vapor pressure deficit decreased under dry soil conditions. Groundwater evapotranspiration (0.6-7.1 mm day(-1)) was linearly correlated with stand transpiration (1.1-6.5 mm day(-1)) (R-2 = 0.71), and these two variables had similar variability. During the drought period, approximately 80% of total stand transpiration came from groundwater evapotranspiration. This study highlighted the critical role of irrigation and groundwater for shelterbelt, and might provide the basis for the development of water requirement schemes for shelterbelt growth in arid inland river basins. (C) 2015 Elsevier B.V. All rights reserved.

Evapotranspiration Estimation from Diurnal Water Table Fluctuations: Implementing Drainable and Fillable Porosity in the White Method

Diurnal water table fluctuations (DWTFs), normally observed in shallow unconfined aquifers, are commonly used to estimate groundwater evapotranspiration (ETg) by applying the soil water balance pioneered by W.N. White in 1932. A key element of White‐based methods is the drainable porosity (or specific yield), a soil water storage parameter that significantly depends on both the vadose‐zone soil moisture fluxes and water table (WT) elevation. However, it has traditionally been treated as either a constant or a function of the WT under hydrostatic soil moisture conditions. Recent research has shown that, at any given shallow WT position, vadose zone fluxes cause the drainable porosity to behave hysteretically, hence requiring estimation of two distinct parameters, drainable (λd) and fillable porosity (λf), during ETg estimation from DWTFs. We present a White‐based method to estimate ETg that implements separate λd and λf parameters and hence accounts for both WT elevation and unsaturated zone moisture fluxes. The modified method not only improves the ETg estimates but also extend the applicability of the White method to periods during rainfall, unlike most previous implementations, which have been limited to omitting such periods. The modified method is demonstrated here for estimation of ETg from two crop fields in Northeast Florida for two growing seasons, each approximately 50 d, in 2010 and 2011, and the ETg estimates are compared with the standard Penman–Monteith method. The modified method significantly improved ETg estimates compared with the hydrostatic λd based method, reducing the root mean square error by 94 and 96% at hourly and daily resolutions, respectively.

Field observation of diurnal dissolved oxygen fluctuations in shallow groundwater.

Dissolved oxygen (DO) concentrations influence many biogeochemical processes in groundwater systems but studies of temporal variability in DO are lacking. In this study, we used an optical DO probe to measure rapid changes in concentration due to plant-groundwater interaction at an alluvial aquifer field site in Iowa. Diurnal DO concentrations were observed during mid- to late-summer when soil conditions were dry, fluctuating approximately 0.2 to 0.3 mg/L on a daily basis. DO fluctuations in groundwater were out-of-phase with diurnal water table fluctuations, increasing during the day and decreasing at night. DO consumption at night is likely due to increased soil autotrophic and heterotrophic respiration linked with patterns of carbon supply derived from daytime photosynthetic activity, and consistent with available literature on diurnal soil respiration patterns. Although more work is needed to quantify specific processes, our results indicate the potential usefulness of the new optical DO technology to reveal insights regarding many ecohydrological processes.

Estimation of groundwater evaportranspiration using diurnal water table fluctuations in the Mu Us Desert, northern China

Summary Groundwater evapotranspiration (ETg) is a significant component of water balance analysis in desert areas. Estimation of ETg using diurnal water table fluctuations, i.e. the White method, is considered simple and straightforward, but it was seldom applied in desert areas. In this study, long-term and high-resolution groundwater level data were used to estimate ETg rate at two sites covered by typical desert plants Salix psammophila and Artemisia ordosica, respectively, in the Mu Us Desert in northern China. The specific yield (Sy) was derived from a drainage experiment in laboratory. The results showed that the water demand of S. psammophila could result in a weak but identifiable diurnal fluctuation of water table that was 2.35 m below the land surface, reasonable estimates of ETg could be derived from the White method, and the level of the ETg corresponded with the plant growth stages. However, the water table data from the area covered by A. ordosica did not show diurnal fluctuation during the growing season. The White method is good for the desert areas where groundwater use by other processes is negligible, and evapotranspiration is the main process for groundwater consumption. In addition, the information about diurnal water table fluctuations is useful for identification of groundwater-dependence of vegetation. A. ordosica is groundwater-independent, whereas S. psammophila is groundwater-dependent.

On evapotranspiration and shallow groundwater fluctuations: A Fourier‐based improvement to the White method

Evapotranspiration (ET) is a significant component of the water and energy balance in wetlands and riparian zones, yet it is also one of the most challenging components to estimate. Diurnal water table fluctuations can be used to directly measure groundwater consumption by phreatophytes, which are often important contributors to the total ET in riparian systems. Although such methods are cost effective, significant uncertainties usually exist, and more accurate techniques continue to be developed. In this study we present a new “Fourier method” for calculating daily (and longer) groundwater ET consumption using a moving, multiday sine function to capture robust, diurnal water table fluctuations. The technique is tested and calibrated in Tamarix chinensis and Populus deltoids‐dominated riparian areas in the Middle Rio Grande region of New Mexico and in a Phragmites australis‐dominated riparian wetland in south‐central Nebraska (using independent, energy balance estimates of ET). The results show that—at both field sites—the new Fourier technique performs significantly better than the commonly used White method, regardless of the length of the moving window that is employed. The Fourier method presented here provides a step toward increasing the accuracy of ET estimates from diurnal water table fluctuations. Guidelines are defined for applying the new and improved method in the most accurate fashion, based on groundwater hydrographs and solar radiation data (or theoretical clear‐sky estimates).

Water uptake and nutrient concentrations under a floodplain oak savanna during a non‐flood period, lower Cedar River, Iowa

AbstractFloodplains during non‐flood periods are less well documented than when flooding occurs, but non‐flood periods offer opportunities to investigate vegetation controls on water and nutrient cycling. In this study, we characterized water uptake and nutrient concentration patterns from 2005 to 2007 under an oak savanna located on the floodplain of the Cedar River in Muscatine County, Iowa. The water table ranged from 0·5 to 2·5 m below ground surface and fluctuated in response to stream stage, plant water demand and rainfall inputs. Applying the White method to diurnal water table fluctuations, daily ET from groundwater averaged more than 3·5 mm/day in June and July and approximately 2 mm/day in May and August. Total annual ET averaged 404 mm for a growing season from mid‐May to mid‐October. Savanna groundwater concentrations of nitrate‐N, ammonium‐N, and phosphate‐P were very low (mean &lt;0·18, &lt;0·14, &lt;0·08 mg/l, respectively), whereas DOC concentrations were high (7·1 mg/l). Low concentrations of N and P were in contrast to high nutrient concentrations in the nearby Cedar River, where N and P averaged 7·5 mg/l and 0·13, respectively. In regions dominated by intensive agriculture, study results document valuable ecosystem services for native floodplain ecosystems in reducing watershed‐scale nutrient losses and providing an oasis for biological complexity. Improved understanding of the environmental conditions of regionally significant habitats, including major controls on water table elevations and water quality, offers promise for better management aimed at preserving the ecology of these important habitats. Copyright © 2009 John Wiley &amp; Sons, Ltd.

A method for estimating subdaily evapotranspiration of shallow groundwater using diurnal water table fluctuations

AbstractDiurnal water table fluctuations are a common feature of well hydrographs recorded in wetlands, riparian areas, and similar environments where shallow groundwater supports phreatophytic vegetation. Historically, this periodic signal has been used to estimate daily groundwater consumption by this vegetation and has shown that this is typically a very large component of the water budget. As interest in ecohydrology grows and the need for finer resolution estimates of groundwater consumption increases, new, cost‐effective measurement methodologies must be developed. Here, a method is proposed that uses the observed rate of water table decline during the day to estimate phreatophytic groundwater consumption while using the nighttime records to account for other groundwater fluxes to/from the vicinity of the well at all times. Variably saturated groundwater flow modeling was used to create a synthetic data set to test the methodology, and results showed that accurate, sub‐daily (15 min) estimates of phreatophytic groundwater consumption were obtained. The method was also applied to a preexisting data set to demonstrate the usefulness of the technique. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Estimating groundwater evapotranspiration rates using diurnal water-table fluctuations in a semi-arid riparian zone

In semi-arid climates, phreatophytes draw on shallow aquifers, and groundwater evapotranspiration (ETG) is a principal component of groundwater budgets. Diurnal water table fluctuations, which often are a product of ETG, were monitored in the riparian zone of Red Canyon Creek, Wyoming, USA. These fluctuations were higher in a riparian wetland (2–36 mm) than a grass-covered meadow (1–6 mm). The onset and cessation of water-table fluctuations correspond to daily temperatures relative to freezing. Spatial differences were due to vegetation type and specific yield, while temporal changes were due to vegetation dormancy. Ratios of ETG to potential evapotranspiration (PET), K c,GW, were similar to ratios of actual evapotranspiration (ET) to PET, K c, in semi-arid rangelands. Before vegetation senescence, K c,GW increased between precipitation events, suggesting phreatophytes pull more water from the saturated zone as soil moisture decreases. In contrast, K c decreases with soil moisture following precipitation events as ET becomes increasingly water-limited. Error in ETG is primarily from estimates of specific yield (S y), which is difficult to quantify in heterogeneous sediments. ETG values may be more reliable because the range of acceptable S y is smaller than K c and S y does not change with vegetation type or soil moisture.

The effects of tree establishment on water and salt dynamics in naturally salt-affected grasslands

Plants, by influencing water fluxes across the ecosystem-vadose zone-aquifer continuum, can leave an imprint on salt accumulation and distribution patterns. We explored how the conversion of native grasslands to oak plantations affected the abundance and distribution of salts on soils and groundwater through changes in the water balance in naturally salt-affected landscapes of Hortobagy (Hungary), a region where artificial drainage performed approximately 150 years ago lowered the water table (from -2 to -5 m) decoupling it from the surface ecosystem. Paired soil sampling and detailed soil conductivity transects revealed consistently different salt distribution patterns between grasslands and plantations, with shallow salinity losses and deep salinity gains accompanying tree establishment. Salts accumulated in the upper soil layers during pre-drainage times have remained in drained grasslands but have been flushed away under tree plantations (65 and 83% loss of chloride and sodium, respectively, in the 0 to -0.5 m depth range) as a result of a five- to 25-fold increase in infiltration rates detected under plantations. At greater depth, closer to the current water table level, the salt balance was reversed, with tree plantations gaining 2.5 kg sodium chloride m(-2) down to 6 m depth, resulting from groundwater uptake and salt exclusion by tree roots in the capillary fringe. Diurnal water table fluctuations, detected in a plantation stand but not in the neighbouring grasslands, together with salt mass balances suggest that trees consumed approximately 380 mm groundwater per year, re-establishing the discharge regime and leading to higher salt accumulation rates than those interrupted by regional drainage practices more than a century ago. The strong influences of vegetation changes on water dynamics can have cascading consequences on salt accumulation and distribution, and a broad ecohydrological perspective that explicitly considers vegetation-groundwater links is needed to anticipate and manage them.

A field investigation of phreatophyte‐induced fluctuations in the water table

Hydrographs from shallow wells in vegetated riparian zones frequently display a distinctive pattern of diurnal water table fluctuations produced by variations in plant water use. A multisite investigation assessed the major controls on these fluctuations and the ecohydrologic insights that can be gleaned from them. Spatial and temporal variations in the amplitude of the fluctuations are primarily a function of variations in (1) the meteorological drivers of plant water use, (2) vegetation density, type, and vitality, and (3) the specific yield of sediments in the vicinity of the water table. Past hydrologic conditions experienced by the riparian zone vegetation, either in previous years or earlier within the same growing season, are also an important control. Diurnal water table fluctuations can be considered a diagnostic indicator of groundwater consumption by phreatophytes at most sites, so the information embedded within these fluctuations should be more widely exploited in ecohydrologic studies.

Hydrological consequences of Eucalyptus afforestation in the Argentine Pampas

The impacts of a 40 ha stand of Eucalyptus camaldulensis in the Pampas grasslands of Argentina were explored for 2 years using a novel combination of sap flow, groundwater data, soil moisture measurements, and modeling. Sap flow measurements showed transpiration rates of 2–3.7 mm d−1, lowering groundwater levels by more than 0.5 m with respect to the surrounding grassland. This hydraulic gradient induced flow from the grassland areas into the plantation and resulted in a rising of the plantation water table at night. Groundwater use estimated from diurnal water table fluctuations correlated well with sap flow (p &lt; 0.001, r2 = 0.78). Differences between daily sap flow and the estimates of groundwater use were proportional to changes in surface soil moisture content (p &lt; 0.001, r2 = 0.75). E. camaldulensis therefore used both groundwater and vadose zone moisture sources, depending on soil water availability. Model results suggest that groundwater sources represented ∼67% of total annual water use.

Estimation of groundwater consumption by phreatophytes using diurnal water table fluctuations: A saturated‐unsaturated flow assessment

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.