Increasing Groundwater Depth Research Articles

Study on extinction depth and steady water storage in root zone based on lysimeter experiment and HYDRUS-1D simulation

HYDRUS-1D was combined with lysimeter experiments to study extinction depth and steady water storage in root zone (Ws) of groundwater evaporation (ETgw) under winter wheat and silt soil. The measured soil water contents and daily ETgw with various groundwater depths were used to calibrate and validate the parameters in HYDRUS-1D. In total, 13 groundwater depths ranging from 0.5 to 5.0 m were set up for scenario simulation to determine the extinction depth and Ws. The results showed that HYDRUS-1D had an acceptable performance in simulating the soil water storage in the 0–60 cm layer and the daily ETgw. Moreover, the ETgw decreased linearly with increasing groundwater depth from 0.5 to 2.5 m and decreased as a power function with increasing groundwater depth from 2.5 to 5.0 m. Under the condition of winter wheat and silt soil, the extinction depth of ETgw was about 5.0 m. Ws decreased linearly with increasing groundwater depth from 0.7 to 2.0 m, but was not influenced further by the groundwater at depths beyond 2.0 m.

The effects of oasis ecosystem hydrological processes on soil salinization in the lower reaches of the Tarim River, China

ABSTRACTOn the basis of the characteristics of the oasis hydrological recycling processes in the lower reaches of the Tarim River, the impacts of surface water and groundwater on soil salt content were analyzed to determine how these processes affect soil salinization. The results showed that the relationship between surface water quality and soil salt content in the 0–50 cm layer of soil was significantly positive, with soil salt content declining as groundwater depths increased. However, there was no clear correlation between surface water and salt content in the 50–100 cm layer of soil. When the groundwater depth was <6 m, the soil salt content showed a high‐surface concentration, exhibiting a ‘T’ distribution and decreased with increasing soil depth in the order of 0–20 cm > 20–50 cm > 50–100 cm. However, with increasing groundwater depth (>6 m), soil salt loads were reduced and showed a ‘rhombus’ distribution, mainly accumulating in the middle layer in the order of 20–50 cm > 0–20 cm > 50–100 cm. When groundwater depth was greater than 6 m, the hardness, total dissolved solids (TDS), and conductance of the groundwater underwent a radical change. Thus, the critical threshold groundwater depth for condensing salt content in groundwater and changing soil salt load distributions was deemed to be 6 m. Salt accumulation in the 0–50 cm layer of soil was determined by the TDS volume in the groundwater when groundwater depth was shallow, which accounted for more than 90% of salt accumulation. However, salt accumulation was determined by the volume of TDS in irrigation water when groundwater depth increased. Copyright © 2013 John Wiley & Sons, Ltd.

Characteristics of the clonal propagation of Alhagi sparsifolia Shap. (Fabaceae) under different groundwater depths in Xinjiang, China

Clonal reproduction of plants commonly occurs in arid areas because seedling establishment is rare in such severe environments. The features of clonal architecture differ not only among plant species but also within the same species growing in different environments. The characteristics of clonal propagation of Alhagi sparsifolia Shap. (Fabaceae), growing on the margins of Cele Oasis on the southern rim of the Taklamakan Desert, were investigated in September 2010. The study was conducted on three sites with different groundwater depths (2.5, 4.5, and 11.0 m). The results showed that the root suckering depth and the ability to expand and the biomass of coarse lateral roots of A. sparsifolia significantly increased when the groundwater depth increased. Moreover, the vegetative regeneration capacity of A. sparsifolia significantly declined with increasing groundwater depth, and the canopy cover at the site with a groundwater depth of 2.5 m was significantly greater than at the other two sites. There was no difference in aboveground biomass at the three sites. In such hyper-arid environments with a scarcity of soil nutrients, it was demonstrated that groundwater depth plays an important role in the clonal growth and propagation traits of A. sparsifolia. Increases in the groundwater depth as a result of over-use of oasis water for irrigation could lead to reduced populations of this important species in the interfaces between oases and the surrounding desert.

Groundwater change forecasts widespread forest dieback across an extensive floodplain system

1. Regulation of rivers for human demands has led to extensive forest dieback on many floodplains. If these important ecosystems are to be maintained under future drier climates, we need accurate tools for predicting forest dieback. In the absence of spatially explicit flooding histories for many floodplains, changes in groundwater conditions may be a good indicator of water availability and, therefore, an important environmental indicator. 2. Eucalyptus camaldulensis forests of Australia are an acute example of forest dieback, with 70% of the Victorian Murray River floodplain dying back. We quantified the relationship between forest dieback and ground water across this extensive floodplain (c. 100 000 ha of forest over 1500 km of river length). 3. A combination of extensive ground surveys, remotely sensed data and modelling methods was used to predict forest dieback at the time of the survey and in the past. This approach provides a valuable tool for accurately monitoring forest condition over large spatial scales. Forest dieback was estimated to have increased from 45 to 70% of the floodplain between 1990 and 2006. 4. Accurate groundwater data (depth and salinity) over a 20-year period were obtained for 289 bores and summarised using nonlinear regression. Groundwater depth and salinity were strong predictors of stand condition. This suggests that changes in groundwater conditions could be used to signal areas vulnerable to forest dieback and prioritise the limited water available for managed flooding. 5. In the upper Murray, where ground water is predominantly fresh (<15 mS cm−2), dieback increased with increasing groundwater depth. In contrast, the condition of stands in the lower Murray improved with increases in groundwater depth due its high salinity (>30 mS cm−2). These regional differences in response of the same tree species to groundwater conditions show that our understanding of the drivers of forest dieback is best achieved at spatial and temporal scales representative of the problem.

Effect Of Water Resource On Soil Salinization Of Oasis In The Lower Reaches Of Tarim River, China

The development of oasis in the lower reaches of the Tarim River has been impeded due to serious soil salinization and water resource shortage. To examine the effect of water resource on soil salinization, we analyzed the effects of surface water resource, groundwater depths and quantity on soil salt content based on the field monitoring. The results showed that the relationship between quality of surface water and soil salt content in 0-50 cm was significantly positive, but not to the salt content of the 50-100 cm layers. The soil salt content also closely related to the groundwater depth, of which 0-50 cm layers surface soil salt content declined with the increasing groundwater depth, and the change of 0-20 cm soil salt content was biggest. When the groundwater depth was shallower, the soil salt content was high with high surface concentration, which showed a “T” distribution, and soil salt content decreased with the increasing soil depth, in the order 0-20cm>20-50cm>50-100 cm. With the groundwater depth increasing, soil salt loads reduced and showed a “rhombus” distribution, which mainly accumulated in the middle layer, in the order 20-50 cm > 0-20 cm > 50-100 cm. When the groundwater depth was more than 6m, the hardness, total dissolved solids (TDS) and conductance of the groundwater as well as the soil salt loads distribution appeared sharply changes. So, the critical groundwater depth for condensing salt content in groundwater and changing the soil salt loads distribution was 6 m.

Photosynthesis of Populus euphratica in relation to groundwater depths and high temperature in arid environment, northwest China

The photosynthetic characterization of Populus euphratica and their response to increasing groundwater depth and temperature were analyzed based on net photosynthetic rate (P N), stomatal conductance (g s), intercellular CO2 concentration (C i), transpiration rate (E), water use efficiency (WUE) and stomatal limitation (Ls) measured by a portable gas-exchange system (LI-6400) in the lower reaches of the Tarim River. Light-response curves were constructed to obtain light-compensation and light-saturation points (LCP and LSP), maximum photosynthetic rates (P max), quantum yields (AQY), and dark respiration rates (R D). The growth condition of P. euphratica, soil moisture, and groundwater depth in the plots were analyzed by field investigation. The results showed that the growth condition and photosynthetic characterization of P. euphratica were closely related to groundwater depth. The rational groundwater depth for the normal growth and photosynthesis was 3-5 m, the stress groundwater depth for mild drought was more than 5 m, for moderate drought was more than 6 m, for severe drought was more than 7 m. However, P. euphratica could keep normal growth through a strong drought resistance depended on the stomatal limitation and osmotic adjustment when it faced mild or moderate drought stress, respectively, at a normal temperature (25°C). High temperature (40°C) significantly reduced P N and drought stress exacerbated the damage of high temperature to the photosynthesis. Moreover, P. euphratica would prioritize the resistance of high temperature when it encountered the interaction between heat shock and water deficit through the stomata open unequally to improve the transpiration of leaves to dissipate overheating at the cost of low WUE, and then resist water stress through the osmotic adjustment or the stomatal limitation.

Vegetation composition and soil microbial community structural changes along a wetland hydrological gradient

Abstract. Fluctuations in wetland hydrology create an interplay between aerobic and anaerobic conditions, controlling vegetation composition and microbial community structure and activity in wetland soils. In this study, we investigated the vegetation composition and microbial community structural and functional changes along a wetland hydrological gradient. Two different vegetation communities were distinguished along the hydrological gradient; Caricetum gracilis at the wet depression and Arrhenatheretum elatioris at the drier upper site. Microbial community structural changes were studied by a combined in situ 13CO2 pulse labeling and phospholipid fatty acid (PLFA) based stable isotope probing approach, which identifies the microbial groups actively involved in assimilation of newly photosynthesized, root-derived C in the rhizosphere soils. Gram negative bacterial communities were relatively more abundant in the surface soils of the drier upper site than in the surface soils of the wetter lower site, while the lower site and the deeper soil layers were relatively more inhabited by gram positive bacterial communities. Despite their large abundance, the metabolically active proportion of gram positive bacterial and actinomycetes communities was much smaller at both sites, compared to that of the gram negative bacterial and fungal communities. This suggests much slower assimilation of root-derived C by gram positive and actinomycetes communities than by gram negative bacteria and fungi at both sites. Ground water depth showed a significant effect on the relative abundance of several microbial communities. Relative abundance of gram negative bacteria significantly decreased with increasing ground water depth while the relative abundance of gram positive bacteria and actinomycetes at the surface layer increased with increasing ground water depth.

Riparian ecohydrology: regulation of water flux from the ground to the atmosphere in the Middle Rio Grande, New Mexico

AbstractDuring the previous decade, the south‐western United States has faced declining water resources and escalating forest fires due to long‐term regional drought. Competing demands for water resources require a careful accounting of the basin water budget. Water lost to the atmosphere through riparian evapotranspiration (ET) is believed to rank in the top third of water budget depletions. To better manage depletions in a large river system, patterns of riparian ET must be better understood. This paper provides a general overview of the ecological, hydrological, and atmospheric issues surrounding riparian ET in the Middle Rio Grande (MRG) of New Mexico. Long‐term measurements of ET, water table depth, and micro‐meteorological conditions have been made at sites dominated by native cottonwood (Populus deltoides) forests and non‐native saltcedar (Tamarix chinensis) thickets along the MRG. Over periods longer than one week, groundwater and leaf area index (LAI) dynamics relate well with ET rates. Evapotranspiration from P. deltoides forests was unaffected by annual drought conditions in much of the MRG where the water table is maintained within 3 m of the surface. Evapotranspiration from a dense Tamarix chinensis thicket did not decline with increasing groundwater depth; instead, ET increased by 50%, from 6 mm/day to 9 mm/day, as the water table receded at nearly 7 cm/day. Leaf area index of the T. chinensis thicket, likewise, increased during groundwater decline. Leaf area index can be manipulated as well following removal of non‐native species. When T. chinensis and non‐native Russian olive (Elaeagnus angustifolia) were removed from a P. deltoides understory, water salvaged through reduced ET was 26 cm/yr in relation to ET measured at reference sites. To investigate correlates to short‐term variations in ET, stepwise multiple linear regression was used to evaluate atmospheric conditions under which ET is elevated or depressed. At the P. deltoides‐dominated sites, ET anomalies were positively correlated to net radiation (Rn) and negatively correlated to sensible heat flux (H), cross‐corridor wind speed (v), and along‐corridor wind speed (u) (r2 = 0·54). At the T. chinensis‐dominated sites, ET anomalies were positively correlated with Rn, u, the friction coefficient (u*), and vapour pressure deficit (VPD) and were negatively correlated to surface humidity scale (q*), daily high and low temperature, H, and precipitation (r2 = 0·66). Both Tamarix and Populus can transpire prodigious quantities of water when conditions are favourable. In the MRG, T. chinensis is preferentially found where summer flooding and cold air drainage occurs, and P. deltoides is preferentially located in areas with shallow groundwater within 2 m of the surface. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Responses of distribution pattern of desert riparian forests to hydrologic process in Ejina oasis

By using the theories and methods of landscape ecology and the technology of GIS and RS, a study has been carried out on the responses of distribution pattern of desert riparian forest to hydrologic process on the basis of the hydrologic data from 1990 to 2000 and the TM image of 2001 year. The results showed that: (1) there appears an even distribution pattern for the relative forest area in oasis, however, the degenerated forest diaplays an increasing tendency from west to east; (2) the desert riparian forest in Ejina is in completely degenerated process at the patch scale; (3) the number of patch is influenced not only by hydrologic process, but also by agricultural activity such as cultivation. The severe deterioration of the degraded vegetation in whole oasis initiates from lower reaches, and gradually impels to upstream; the fragmentation of landscape in the terminal site is more obvious, which is influenced by river shape and decreasing flux of water. It is found that the influence of surface hydrologic process to the ground hydrologic process of desert riparian forest in Ejina oasis is little for the recent ten years. The relative area of the degenerated forest increased with increasing ground water depth in the direction of parallel to river channel. On the contrary, in the direction perpendicular to river channel, there is a decreasing tendency for the average patch area of the forest and the degenerated forest with increasing ground water depth.