Groundwater Table Depth Research Articles

Effects of nitrogen application on winter wheat growth, water use, and yield under different shallow groundwater depths.

Shallow groundwater plays a vital role in physiology morphological attributes, water use, and yield production of winter wheat, but little is known of its interaction with nitrogen (N) application. We aimed to explore the effects of N fertilization rate and shallow groundwater table depth (WTD) on winter wheat growth attributes, yield, and water use. Experiments were carried out in micro-lysimeters at WTD of 0.6, 0.9, 1.2, and 1.5m with 0, 150, 240, and 300 kg/ha N application levels for the winter wheat (Triticum aestivum L.). The results showed that there was an optimum groundwater table depth (Op-wtd), in which the growth attributes, groundwater consumption (GC), yield, and water use efficiency (WUE) under each N application rate were maximum, and the Op-wtd decreased with the increase in N application. The Op-wtd corresponding to the higher velocity of groundwater consumption (Gv) appeared at the late jointing stage, which was significantly higher than other WTD treatments under the same N fertilization. WTD significantly affected the Gv during the seeding to the regreening stage and maturity stage; the interaction of N application, WTD, and N application was significant from the jointing to the filling stage. The GC, leaf area index (LAI), and yield increased with an increase of N application at 0.6-0.9-m depth-for example, the yield and the WUE of the NF300 treatment with 0.6-m depth were significantly higher than those of the NF150-NF240 treatment at 20.51%, and 14.81%, respectively. At 1.2-1.5-m depth, the N application amount exceeding 150-240 kg/ha was not conducive to wheat growth, groundwater use, grain yield, and WUE. The yield and the WUE of 150-kg/ha treatment were 15.02% and 10.67% higher than those of 240-300-kg/ha treatment at 1.2-m depth significantly. The optimum N application rate corresponding to yield indicated a tendency to decrease with the WTD increase. Considering the winter wheat growth attributes, GC, yield, and WUE, application of 150-240 kg/ha N was recommended in our experiment.

Effects of climate anomaly on rainfall, groundwater depth, and soil moisture on peatlands in South Sumatra, Indonesia

Climate anomalies can cause natural disasters such as severe fires and floods on peatlands in South Sumatra. Factors that affect the natural disasters on peatlands include rainfall, groundwater level, and soil moisture. This paper aims to study the effect of the climate anomalies in 2019 and 2020 and effects of these influencing factors on peatlands in South Sumatra. The data used in this study was derived from in-situ measurement at two SESAME’s measurement stations in the study area. The results indicate that in the 2019 dry season, the rainfall was minimal, the lowest groundwater table depth was −1.14 m and the lowest soil moisture was 3.4%. In the 2020 dry season, rainfall was above the monthly average of 100 mm, the lowest groundwater level was −0.44 m, and the lowest soil moisture was 26.64%. There is also a strong correlation between soil moisture and groundwater table depth. The correlation between the two is stronger when there is less rainfall.

Effects of soil particle size and gradation on the transformation between shallow phreatic water and soil water under laboratory freezing-thawing action

The transformation between shallow phreatic water and soil water during the freezing-thawing period affects the accurate evaluation of water resources and aggravates soil salinization. In laboratory freezing-thawing experiments, constant temperature freezing at − 10, −20, and − 25 °C was conducted for 62 successive days, and natural thawing was conducted for 13 days, with a groundwater table depth of 1.0 m. The variations in the soil temperature, upward migration amount of phreatic water to soil water (UMA), and downward movement amount of soil water to phreatic water (DMA) of soil columns with particle sizes of d50 = 0.3 mm (A1), d50 = 0.75 mm (B1), d50 = 1.25 mm (C1), d50 = 1.75 mm (D1), and d50 = 2.25 mm (E1) and different particle gradations with inhomogeneity coefficients of 3.47 (A2), 4.69 (B2), 8.31 (C2), 14.67 (D2), and 19.08 (E2) were analyzed. The results showed that the soil temperature was more variable and reached stability earlier as the soil particle size or inhomogeneity coefficient increased. The cumulative UMA decreased as the soil particle size increased and the inhomogeneity coefficient decreased during the freezing process. For the constant temperature freezing at − 10, −20, and − 25 °C, the cumulative UMA and average soil particle size were fitted using an exponential function, but the effect of the soil particle size on the UMA gradually weakened as the freezing air temperature decreased. The daily DMA decreased as the soil particle size decreased, and the particle gradation improved during days 0–5 of the thawing stage, while the cumulative DMA increased as the soil particle size decreased and the inhomogeneity coefficient increased after days 9–10 during the thawing stage. The groundwater was in a negative equilibrium under freezing-thawing action, and the consumption of groundwater was greater when the average soil particle size was smaller and the inhomogeneity coefficient was larger during the freezing-thawing process. The results of this study have important significance for soil salinization prevention and the scientific evaluation of water resources.

“Failure envelops for foundation subjected to inclined and eccentric loading considering steady state and transient flow conditions in unsaturated soils”

In this paper, an analytical method and semi-empirical equations are presented for determining the bearing capacity failure envelopes for foundations subjected to inclined or eccentric loads in unsaturated soils considering the influence of steady and transient state flow conditions. Firstly, the analytical method is proposed extending the slip line theory coupled with analytical solutions for different matric suction profiles. The failure envelopes in the V - H (Vertical - Horizontal) and V - M (Vertical - Moment) loading spaces for two fine-grained soils were investigated by conducting parametric studies using the proposed method. The influence of the ground water table depth variation, internal friction angles, surface flux boundary conditions and different infiltration durations were considered. Based on the parametric studies results, semi-empirical equations were proposed for the failure envelopes in the two loading spaces. The validity of the proposed failure envelope equations is examined by providing comparisons with the proposed analytical method and published results from the literature. Good agreement is found between the fitted failure envelopes and that obtained from the analytical method and published studies.

Water table depth effect on growth and yield parameters of hard red spring wheat (Triticum aestivum L.): a lysimeter study

Groundwater is a significant source of plant water use since groundwater consumption of plants reduces the volume of surface irrigation water. In this study, groundwater table effect on hard red spring wheat (Triticum aestivum L.) growth and yield parameters were investigated using a lysimeter technique in a controlled environment. Three different groundwater table depths including 30, 60, and 90 cm and a control treatment with surface irrigation were tested. The results showed that water consumption in the 90 cm water table depth was 11% and 31% lower than the water consumption in the 60 and 30 cm water table depths, respectively. Consequently, the groundwater table depth increased, and crop water consumption decreased. Similarly, with the increasing water table depth from 30 to 90 cm in the lysimeter, the crop water use efficiency and crop yield increased by 79% and 71%, respectively. The 90 cm water table produced the highest crop yield, above-ground biomass, and kernel quality compared to 30 and 60 cm water table depths. Quality analysis of the wheat kernels indicated that the kernels from the 90 cm depth had relatively higher starch content, pasting properties, and gluten proteins compared to the kernels from other water table depths.

Behaviour of Groundwater Table with Rainfall in North-West Region of Bangladesh

Groundwater is the major source of water to meet up the vast domestic and agricultural demand in Bangladesh. Additionally, reduction in reliable surface water resources resulting the increased reliance on groundwater day by day. Therefore, monitoring the groundwater fluctuation over time is crucial to ensure the sustainable use of groundwater resources in future. The present study analyzed historical groundwater data to know the behaviour of groundwater at four locations of two districts Pabna and Rangpur in the North-Eastern part of the country. Historical groundwater level data and monthly rainfall data from 1989 to 2017 were collected from Bangladesh Water Development Board and Bangladesh Meteorological Department, respectively. The annual maximum groundwater table depth (MaxGWT) and minimum groundwater table depth (MinGWT) and its trend was analyzed, and positive and negative recharge years were identified from these values. We found the maximum declining rate at 6.6 cm annually and the maximum 205 cm total depletion in the study area. The number of years of negative recharge is more than that of positive recharge for 32 years. As a result, a declining trend in groundwater table was found at three locations of the study area. The maximum groundwater table remains below suction limit at Ishwardi, causes no shallow tubewell (STW) works during that period. A declining trend in annual rainfall is observed in Pabna district. A linear relationship between rainfall and recharge was found at two locations of the study area. Bangladesh Rice J. 25 (2) : 85-95, 2021

Exploring the response of shallow groundwater to precipitation in the northern piedmont of the Qinling Mountains, China

Groundwater recharge from precipitation is a complex process that often exhibits strong nonlinearity. This process is influenced by multiple hydrogeological and topographical conditions. This study aims to assess the response of shallow groundwater table to precipitation in the northern piedmont of the Qinling Mountains in China from 2005 to 2015 using a combination of the Mann-Kendall (MK) test, continuous wavelet transform, and cross-wavelet transform. The MK test revealed a slight upward trend of precipitation from 2005 to 2015. In addition, 71% of the shallow groundwater monitoring wells exhibited increasing trends in the groundwater table depth. Continuous wavelet transform demonstrated periodic groundwater responses to precipitation. Both precipitation and groundwater table showed significant monthly oscillation of 9–15 months, while the highest wavelet power was detected at the temporal scale of 12 months. According to the results of the cross wavelet transform, lag times between groundwater level responses and precipitation events were 78, 73, and 99 days for P1-PF1, P2-FT1, and P3-ST1 in pluvial fans, first terraces, and second terraces, respectively. Moreover, the results suggested spatiotemporal variations in the lag time, which might be due to the variation in groundwater levels, aquifer lithology, precipitation intensity, and groundwater exploitation intensity. The current study revealed the spatiotemporal response mechanism of the shallow groundwater to precipitation, providing a scientific basis for assessing the regional water cycle processes and ensuring effective groundwater resource management.

Machine-learning-based downscaling of modelled climate change impacts on groundwater table depth

Abstract. There is an urgent demand for assessments of climate change impacts on the hydrological cycle at high spatial resolutions. In particular, the impacts on shallow groundwater levels, which can lead to both flooding and drought, have major implications for agriculture, adaptation, and urban planning. Predicting such hydrological impacts is typically performed using physically based hydrological models (HMs). However, such models are computationally expensive, especially at high spatial resolutions. This study is based on the Danish national groundwater model, set up as a distributed, integrated surface–subsurface model at a 500 m horizontal resolution. Recently, a version at a higher resolution of 100 m was created, amongst others, to better represent the uppermost groundwater table and to meet end-user demands for water management and climate adaptation. However, the increase in resolution of the hydrological model also increases computational bottleneck. To evaluate climate change impacts, a large ensemble of climate models was run with the 500 m hydrological model, while performing the same ensemble run with the 100 m resolution nationwide model was deemed infeasible. The desired outputs at the 100 m resolution were produced by developing a novel, hybrid downscaling method based on machine learning (ML). Hydrological models for five subcatchments, covering around 9 % of Denmark and selected to represent a range of hydrogeological settings, were run at 100 m resolutions with forcings from a reduced ensemble of climate models. Random forest (RF) algorithms were established using the simulated climate change impacts (future – present) on water table depth at 100 m resolution from those submodels as training data. The trained downscaling algorithms were then applied to create nationwide maps of climate-change-induced impacts on the shallow groundwater table at 100 m resolutions. These downscaled maps were successfully validated against results from a validation submodel at a 100 m resolution excluded from training the algorithms, and compared to the impact signals from the 500 m HM across Denmark. The suggested downscaling algorithm also opens for the spatial downscaling of other model outputs. It has the potential for further applications where, for example, computational limitations inhibit running distributed HMs at fine resolutions.

An improved estimation of soil water and salt dynamics by considering soil bulk density changes under freeze/thaw conditions in arid areas with shallow groundwater tables

Soil bulk density (BD) is a parameter dependent on soil texture, compositions of soil minerals and organic matter and the extent of soil compaction. Seasonal freeze/thaw in arid areas with shallow groundwater tables (AASGT) may significantly change BD and hence soil hydrothermal properties and water holding capacity. Therefore, quantifying soil bulk density changes (BDC) under freeze/thaw conditions can improve estimates of soil water-salt dynamics in AASGT. In this study, we conducted field experiments to investigate the soil water-salt dynamics under freeze/thaw conditions from three typical land-use types (i.e., farmland, woodland, and natural land) in the upper Yellow River basin, China. We proposed a method to estimate BDC, which can better describe the soil water-salt dynamics during the freeze/thaw period. Our results showed marked BDC occurred in all layers within the 0–100 cm profile in natural land, while mainly at the 20–80 cm profile in farmland. During the freezing period, BD in farmland and natural land first decreased rapidly and then remained relatively stable until the thawing period started. After that, BD gradually increased during the thawing period. The largest BDC in farmland and natural land were 0.48 g cm−3 (occurring at the 30–40 cm layer) and 0.43 g cm−3 (occurring at the 80–90 cm layer), respectively, close to 30 % of their initial values. The differences in BDC between the three land-use types were mainly owing to their differences in groundwater table depth, initial soil salt concentration, soil texture, and surface coverage conditions. Moreover, in farmland and natural land, ignoring BDC resulted in different degrees of overestimation or underestimation in soil water content, water fluxes, and soil hydrothermal properties in the selected soil layers. This study demonstrates that considering BDC can improve the accuracy of soil water-salt dynamics estimation in AASGT under freeze/thaw conditions.

GIS-Based Simulation for Landfill Site Selection in Mekong Delta: A Specific Application in Ben Tre Province

The aim of this research is to develop a GIS-based simulation for selecting the most suitable site of solid waste landfill which could help to minimize harmful impacts to the environment and society in the extreme sensitive and complex delta by an integration of geographic information system (GIS) and analysis hierarchy process (AHP) and nine criteria (distance from surface water; depth of ground water table; distance from residential area, land use, distance from main roads, geo-environmental and geotechnical characteristics, distance from historical and tourism sites, and distance from industrial zones). Different from most of the previous studies on the landfill site selection, geology-related criteria including soil types/lithology, soil permeability, and soil depth/soil thickness (soil-structure), which are called geo-environmental and geotechnical characteristics in this research, will be carefully considered, integrated, and evaluated. The AHP was employed to determine the weight of each criterion based on pair weight comparison and its matrix, while a land suitability index (LSI) score was calculated to determine the most suitable site. Moreover, the suitability map was also created which indicated very advantageous, advantageous, rather advantageous, and disadvantageous areas in the study area for landfill siting. Finally, the developed model could be used for supporting planners, managers, policy makers, and local government to make decisions on suitable and effective planning strategies for landfill site selection and could be applied anywhere and especially in other deltas around the world.

Modeling the topographic influence on aboveground biomass using a coupled model of hillslope hydrology and ecosystem dynamics

Abstract. Topographic heterogeneity and lateral subsurface flow at the hillslope scale of ≤1 km may have outsized impacts on tropical forest through their impacts on water available to plants under water-stressed conditions. However, vegetation dynamics and finer-scale hydrologic processes are not concurrently represented in Earth system models. In this study, we integrate the Energy Exascale Earth System Model (E3SM) land model (ELM) that includes the Functionally Assembled Terrestrial Ecosystem Simulator (FATES), with a three-dimensional hydrology model (ParFlow) to explicitly resolve hillslope topography and subsurface flow and perform numerical experiments to understand how hillslope-scale hydrologic processes modulate vegetation along water availability gradients at Barro Colorado Island (BCI), Panama. Our simulations show that groundwater table depth (WTD) can play a large role in governing aboveground biomass (AGB) when drought-induced tree mortality is triggered by hydraulic failure. Analyzing the simulations using random forest (RF) models, we find that the domain-wide simulated AGB and WTD can be well predicted by static topographic attributes, including surface elevation, slope, and convexity, and adding soil moisture or groundwater table depth as predictors further improves the RF models. Different model representations of mortality due to hydraulic failure can change the dominant topographic driver for the simulated AGB. Contrary to the simulations, the observed AGB in the well-drained 50 ha forest census plot within BCI cannot be well predicted by the RF models using topographic attributes and observed soil moisture as predictors, suggesting other factors such as nutrient status may have a larger influence on the observed AGB. The new coupled model may be useful for understanding the diverse impact of local heterogeneity by isolating the water availability and nutrient availability from the other external and internal factors in ecosystem modeling.

Effects of Artificial Water Withdrawal on the Terrestrial Water Cycle in the Yangtze River Basin

Clarifying the response of the terrestrial water cycle to the influence of climate change and human activities and accurately grasping the variations in the water cycle and water resources under the changing environment are the scientific basis for achieving the sustainable development of the Yangtze River Economic Belt. In this paper, a dataset of rasterized water consumption in the Yangtze River Basin was constructed, and an artificial water withdrawal module considering the process of water intake, water consumption and drainage was designed, which was coupled with the land surface model CLM4.5. Based on the multi-scale validation in the Yangtze River Basin, two numerical simulation experiments were carried out to reveal the impact of artificial water withdrawal on the water cycle process in the Yangtze River Basin. The results indicate that artificial water withdrawal leads to an 0.1–0.3 m increase in groundwater table depth in most areas of the basin, and agricultural irrigation leads to a 0–0.03 mm3/mm3 increase in soil moisture in most areas. Climate change dominates the variation of discharge in the Yangtze River basin and leads to an increase in discharge at most stations.

Variation of Moisture and Soil Water Retention in a Lowland Area of Central Poland—Solec Site Case Study

Soil moisture monitoring is crucial for a variety of activities involving soil water regime estimation. Different phenomena such as drought, exhibit impacts of a variable extent in the soil profile, requiring moisture content monitoring as well as reliable analyses of the soil properties. In the village of Solec, located in central Poland, monitoring of the moisture content was attempted for a sandy soil in order to estimate soil moisture distributions for two dry years (2015, 2016) and a wet one (2017). Simple and easily obtainable drought indices, such as dry spells, climatic water balance, groundwater table depth, soil water content and potential were estimated and related with spatiotemporal evolution of soil water conditions. Soil layers subject to drought were found to be different either from a moisture (15–45 cm) or soil water potential (10–25 cm), showing diverse physical properties and relations with the ground water table. The coherence of the analysed drought indices was proven for a light, sandy soil, which has national significance for the state, drought monitoring network. Knowledge obtained during previous studies, which omitted soil water conditions for this type of the soil was supplemented. Based on its own water content, the profile of the analysed soil (Stagnic Folic Gleysols–Arenic) exhibits a negative climatic water balance and requires irrigation practices to mitigate drought effects.

Space-time dynamics of soil moisture and groundwater in an agriculture-dominated critical zone observatory (CZO) in the Ganga basin, India

Space-time variability of soil moisture (SM) and ground water plays a fundamental role in shaping hydrology of terrestrial ecosystem, best represented as the Critical Zone (CZ), which extends from top of vegetation canopy to the bottom of groundwater table. In several parts of the world, a network of instrumented sites, known as Critical Zone Observatories (CZOs), have been set up to understand the hydrodynamics of soil–water system in particular reference to natural and anthropogenic forcings. Here, we employed the empirical orthogonal function (EOF), random combination, and temporal stability approach to understand the in-situ space–time dynamics of SM and depth to groundwater table (DTGT) over an agriculture-dominated CZO in the Ganga basin. Our results showed that both the components exhibit a constant temporal coefficient of variation, suggesting a consistent seasonal changing pattern. Around 91 % of the observed DTGT spatial variation are explained by first two spatial EOFs while the first five EOFs explain only 67 % of the total SM variability. On an annual basis, the spatial patterns of SM and DTGT are driven by topography and soil texture (% clay) while monsoon rainfall and post-monsoon crop cycle appear to be the leading factors for temporal variability of both components. Furthermore, we have demonstrated that randomly selected four sampling locations and three monitoring wells within the CZO could capture the mean spatial variability of SM (RMSE = 3 % vol/vol) and DTGT (RMSE = 0.7 mgbl) respectively. In addition, temporal stability analysis indicates that four representative sites and a single monitoring well can provide robust catchment mean with an absolute error of ±2 % vol/vol and 0.36 mgbl respectively. Overall, this study provides an insight to the hydrodynamics and controls of SM and groundwater in an agricultural landscape with significant implications for upscaling and efficient water resource management in such regions.

Spatiotemporal Patterns and Key Driving Factors of Soil Salinity in Dry and Wet Years in an Arid Agricultural Area with Shallow Groundwater Table

Soil salinization is a major eco-environmental problem in irrigated agro-ecosystems. Understanding regional soil salinity spatial patterns and seasonal dynamics and their driving factors under changing environments is beneficial to managing soil salinity to maintain agricultural production in arid agricultural areas. To better investigate this topic, soil salinity was measured, ranging from topsoil to the depth of 1.8 m in an irrigation district with 68 sampling sites before and after the crop growing seasons of the dry year of 2017 and wet year of 2018. Soil texture, groundwater table depth, groundwater salinity, and crop type were monitored. The results indicated that an increase in soil salinity in the root zone (0–0.6 m) was accompanied by a decrease in soil salinity in the deep soil (0.6–1.8 m) through the crop growing season due to water movement from the deep layer to shallow layer, whereas the opposite trend was observed during the fallow seasons. During the dry year, the area with soil desalted was measured to be 19.89%, 14.42%, and 2.78% lower at depths of 0–0.6 m, 0.6–1.2 m, and 1.2–1.8 m than that during the wet year. The groundwater table depth in the crop growing season had the least impact on the change in root zone soil salinity (p > 0.05). Interactions between crop types and groundwater table depth had a significant effect on the change of soil salinity in the root zone during the growing season of the dry year, but were insignificant during the wet year. Crop types, groundwater table depth, and climate conditions determined the contribution of shallow groundwater to crop water consumption and, to a greater extent, soil salinity. Regression tree analysis showed that groundwater salinity and soil texture had a greater influence on soil salinity than groundwater table depth and land elevation. The effect of groundwater on soil salinity is strongly related to soil texture, and the salinity of fine-textured soil was 36–54% greater than that of coarse-textured soil due to large capillary action. Therefore, we suggest strengthening groundwater management in areas with fine-textured soil to relieve soil salinization, particularly during dry years.

Variations of leachate CO2 and N2O concentrations on typical cultivated and natural hillslopes in southeastern hilly area of China

Greenhouse gases dissolved in the soil water and transported through subsurface flow were poorly understood in comparison to their emissions at the soil-atmosphere interface. In this study, leachate CO2 and N2O concentrations were monitored on a tea garden (TG) hillslope (cultivated) and a bamboo forest (BF) hillslope (naturally vegetated) from September 2019 to February 2022 in the south-eastern hilly area of China. Leachate CO2 and N2O concentrations ranged from 1.07 to 9.83 mg C L−1 and from 0.32 to 11.74 μg N L−1, respectively, on the TG hillslope, while they ranged from 0.64 to 25.95 mg C L−1 and from 0.23 to 5.68 μg N L−1, respectively, on the BF hillslope. On both hillslopes, leachate CO2 concentrations were the greatest in summer, while they were the lowest in winter. On the TG hillslope, the highest and the lowest leachate N2O concentrations were observed in spring and summer, respectively, while on the BF hillslope, they were observed in autumn and winter, respectively. On both hillslopes, soil temperature, precipitation during the previous 15 days, and matrix potential were positively related to the leachate CO2 concentrations but not related to the leachate N2O concentrations. Soil water content was positively related to both leachate CO2 and N2O concentrations, while such relationships with groundwater table depth were negative. Leachate total inorganic nitrogen and soil total inorganic nitrogen concentrations were positively related to the leachate N2O concentration on the TG hillslope, while such relationships were not observed on the BF hillslope. Spatial variations of leachate CO2 and N2O concentrations were mainly influenced by land covers, terrain attributes (slope, elevation), soil particle size distribution, bulk density and soil organic matter content. The findings of this study supplemented the knowledge of soil water dissolved CO2 and N2O in the cultivated and naturally vegetated land covers. Further researches are needed to quantify the CO2 and N2O losses through subsurface flow and their contributions to the total soil CO2 and N2O losses.

Vegetation analysis and environmental indicators of an arid tropical forest ecosystem of Pakistan

Vegetation composition and/or plant species co-existence is influenced by the environmental variations in any region. The ecological knowledge and order of importance of selected environmental variations is important in conservation and management of plant resources. Based on relevant knowledge gap, the study area of district Jhelum, Pakistan lying in an arid-tropical zone was selected to explore the vegetation types and their driving environmental factors by using latest multivariate statistical approaches. For this, the entire district was ecologically explored to collect the natural wild vegetation and environmental data from January 2018 to December 2020. The study area was partitioned into 171 grids (5 × 5 km2). In each grid, three sites were randomly selected (i.e. 513 samples), and subsequently-nine plots were laid at each sampling site (i.e. 1539 plots). Different statistical tests including Monte Carlo permutation test, Indicator Species Analysis (ISA), hierarchical classification, ordination, and variation partitioning were applied to seek the potential number of vegetation types, plant species composition, classification of the studied samples, order of importance of the considered predictors and groups of environmental variables respectively. The findings of this study indicated that all the documented 291 plant species belong to five statistically significant (p < 0.05) plant communities. Out of thirty (30) considered environmental variables, canonical correspondence analysis suggested the significant role of distance from the river, altitude, latitude, slope, temperature, rainfall, distance from the cropland, grazing and deforestation pressure, and soil pollutants including chromium, arsenic and nickel concentrations. Similarly, plant diversity patterns were found strongly associated with the selected local environmental conditions. This study concluded that distance from the river (a potential leading proxy of ground water table depth) is relatively more important than the rainfall variability in this tropical arid area. Hence, the relative proportion of xerophytic plant species was found higher in the western parts compared to eastern parts adjoining the river Jhelum. Anthropogenic disturbances and potentially toxic metals were found disrupting the normal ecosystem functioning at the local scale in this arid tropical region, and need immediate attention to save the valuable local biodiversity.

The Unabated Atmospheric Carbon Losses in a Drowning Wetland Forest of North Carolina: A Point of No Return?

Coastal wetlands provide the unique biogeochemical functions of storing a large fraction of the terrestrial carbon (C) pool and being among the most productive ecosystems in the world. However, coastal wetlands face numerous natural and anthropogenic disturbances that threaten their ecological integrity and C storage potential. To monitor the C balance of a coastal forested wetland, we established an eddy covariance flux tower in a natural undrained bottomland hardwood forest in eastern North Carolina, USA. We examined the long-term trends (2009–2019) in gross primary productivity (GPP), ecosystem respiration (RE), and the net ecosystem C exchange (NEE) seasonally and inter-annually. We analyzed the response of C fluxes and balance to climatic and hydrologic forcings and examined the possible effects of rising sea levels on the inland groundwater dynamics. Our results show that in 2009, a higher annual GPP (1922 g C m−2 yr−1) was observed than annual RE (1554 g C m−2 yr−1), resulting in a net C sink (NEE = −368 g C m−2 yr−1). However, the annual C balance switched to a net C source in 2010 and onwards, varying from 87 g C m−2 yr−1 to 759 g C m−2 yr−1. The multiple effects of air temperature (Tair), net radiation (Rn), groundwater table (GWT) depth, and precipitation (p) explained 66%, 71%, and 29% of the variation in GPP, RE, and NEE, respectively (p &lt; 0.0001). The lowering of GWT (−0.01 cm to −14.26 cm) enhanced GPP and RE by 35% and 28%, respectively. We also observed a significant positive correlation between mean sea level and GWT (R2 = 0.11), but not between GWT and p (R2 = 0.02). Cumulative fluxes from 2009 to 2019 showed continuing C losses owing to a higher rate of increase of RE than GPP. This study contributes to carbon balance accounting to improve ecosystem models, relating C dynamics to temporal trends in under-represented coastal forested wetlands.

Modeling response of spring wheat yield to soil water and salt contents and its application in scheduling brackish water irrigation

Fresh water shortage and soil salinization are two key factors restricting agricultural development in arid areas. Brackish water is a possible alternative resource for crop irrigation, but brackish water irrigation should be properly scheduled to balance crop yield increment and soil salinization control. To determine suitable water amounts for crop irrigation under different water salinities, an agro-hydrological model, LAWSTAC, was used to simulate soil water and salt dynamics and crop growth in salinized croplands in an arid region of Northwest China. Model calibration and validation results of soil water content, salt concentration, groundwater table depth, leaf area index, biomass, and crop yield agreed well with the field measurements of spring wheat (Triticum aestivum L.) under both fresh and brackish water irrigations with the Nash and Sutcliffe efficiency of 0.50–0.96 and the coefficient of determination of 0.55–0.98. The model was further used to simulate crop yields for 432 combinations of six irrigation levels, six irrigation water salinity levels, four initial groundwater table depths, and three initial soil salt concentrations. Based on the simulation results, a function of relative crop yield response to soil water content and salt concentration was developed, which is expressed as the product of a hyperbolic function for water stress and a sigmoid function for salt stress. For known initial soil water content and salt concentration, a procedure was proposed to determine suitable water amounts applied to the cropland under different irrigation water salinities for expected crop yields using the developed crop-water-salinity production function. With the procedure, the minimum amount of applied water with known salinity can be obtained for an expected relative crop yield. The results are helpful to the amount control in fresh or brackish water irrigations for sustainable crop production in salinized croplands.

Cyclicities in the Regime of Groundwater and of Meteorological Factors in the Basin of the Southern Bug River

The data of observations since 1951 in the upper part of the Southern Bug River basin in the west of Ukraine are analyzed. The results indicate that the climate change occurring on Earth disrupts the regular cyclicity of groundwater flow indicators. The identified 7–8-year groundwater level and flow to the river cyclicity correlates well with the air temperature, precipitation and river runoff cyclicity. The noted groundwater cyclicity appears with some delay after the establishment of the 8-year air temperature cyclicity observed since 1969. The manifestation of a 7–8-year cycle depends on the groundwater table (GWT) depth. For shallow groundwater (1.0–2.5 m), such rhythms have been observed since 1975, and for deeper levels, since 1989, which is recognized as the year of the beginning of the climate changes. Moreover, 7–8-year rhythms in the fluctuation of groundwater parameters are characteristic of mainly high-water periods of their multiyear regime, and during the low-flow phase is significantly weakened. During 2011–2014, the groundwater levels abnormally decreased and the 8-year cycles were replaced with 5-year ones. The influence of air temperature on the groundwater regime exceeds the role of other factors. Wavelet analysis was used as the main method of periodicity observation. Gaussian and Morlet wavelets provide the visualization of pronounced periodicities of data. Using multiple correlation analysis, it was confirmed that temperature has become the dominant impact factor on the groundwater (GWT 1.5–4.0 m) regime in recent decades.