Search

Determining the evapotranspiration (ET) of cotton as a water-intensive crop is crucial for effective irrigation planning and water management, especially in regions like Sindh province, Pakistan, where shallow groundwater table depths (WTDs) are prevalent. Despite the importance of cotton, a major cash crop in Sindh, previous studies on ET were conducted decades ago and may no longer be reliable due to ongoing climate change and the introduction of new crop varieties. Thus, we quantified cotton ET across two cropping seasons and at various WTDs (0.45, 0.60, 0.75, 1.50, 2.25, and 2.75 m). The experimental study was based on the data procured from 12 mini lysimeters and 12 large lysimeters for two years (2018 and 2019) and at two soil series. The findings revealed that cotton ET ranged from 1332 to 1437, 1114–1202, 988–1075, 781–821, 690–733, and 637–683 mm at WTDs of 0.45, 0.60, 0.75, 1.50, 2.25, and 2.75 m, respectively. WTDs from 0.45 to 0.75 m fulfilled 94–96 % of cotton ET through groundwater (GW) contribution in Sultanpur soil (silt loam) and 93–97 % in Miani soil (silty clay loam). At 1.50–2.75 m WTDs, irrigation water requirements (excluding rainfall and leaching) were 63–88 % in Sultanpur soil and 67–89 % in Miani soil. The highest yield was observed at a 1.50 m WTD, while the highest water use efficiency was identified at a 2.25 m WTD. However, soil salinity increased by 60–80 %, resulting in a 40–60 % lower cotton yield at 0.45–0.75 m WTD. Therefore, periodic flushing of salts is necessary to utilize shallow WTDs effectively. Considering GW contribution to ET when allocating water for irrigation channels and devising irrigation schedules is crucial. This approach can lead to water savings, prevent land from becoming waterlogged and saline, manage the groundwater table, and reduce the need for drainage channels and labor force for their preparation.

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

There are areas with high saline water and saline irrigation water in Iran that may be used for quinoa cultivation. In these conditions, proper saline irrigation water regimes and nitrogen application should be determined and used. Therefore, the aim of this experiment is to investigate the effect of different saline irrigation water regimes (100, 75 and 50% of full irrigation, FI) and nitrogen application rates (0, 100, 200 and 300 kg ha−1) on growth and yield of quinoa with water table depth of 0.8 m, salinity of irrigation water and water table of 20 dS m−1. The irrigation of 75% FI and 50% FI decreased the applied water by 19 and 38%, respectively. Further, there was no reducing effect of irrigation water regimes in seed and shoot dry matter yield. Furthermore, groundwater contribution (GWC) increased significantly by 8 and 18% in 75%FI and 50%FI compared with that obtained in full irrigation, and resulted in no extreme water stress under high water table depth (0.8 m). Increasing application of nitrogen fertilizer significantly increased the yield components, ETc and GWC. In addition, reducing irrigation water did not show a significant decrease in water use efficiency (WUE) in high water table depth. However, water productivity increased significantly by decreasing irrigation water. It is concluded that under deficit irrigation, high water table depth could be a valuable source of water supply to meet quinoa water requirements. Moreover, application of nitrogen fertilizer at all levels significantly increased water use efficiency and water productivity. [ABSTRACT FROM AUTHOR]

This study was carried out to assess the effects of main and interactive groundwater salinities (GWS) (GWS1:0.38, GWS2: 5.0, and GWS3: 10 dS m−1) and groundwater depths (GWD) (GWD1: 0.30, GWD2: 0.55, and GWD3: 0.80 m) on yield and growth parameters of sweet corn. The canned seed yield in the GWS2 and GWS3 treatments reduced by 21.97% and 54.87%, respectively, as compared to the GWS1. Increasing GWS from 0.38 to 5.0 and 10.0 dS m−1 decreased aboveground fresh biomass by 16.67 and 37.95%, respectively. The groundwater contribution to ET varied from 26.80% to 87.10%, and capillary rise from groundwater to plant root zone decreased significantly with increasing GWD. The results showed that plant growth was not significantly affected under 0.38 dS m−1 GWS conditions at 0.55 m GWD, while the groundwater contribution to ET was about 52%. Stomata and SPAD values increased by 36.36% and 4.34%, respectively, in GWD3 treatment compared to GWD1 treatment. Besides, GWS decreased the leaf's K+, K+/Na+, and Ca2+/Na+ ratios at different depths. In conclusion, it can be suggested that GWD should be at least 0.80 m to achieve high sweet corn production in regions with moderately or highly saline groundwater. [ABSTRACT FROM AUTHOR]

The contribution of groundwater to evapotranspiration in crop irrigation scheduling is gaining importance worldwide. A two consecutive year wheat experiment was conducted in drainable lysimeters to evaluate the response of grain yield and quality, spike traits, water use efficiency, evapotranspiration and thousand kernel weight of wheat plants under twelve different shallow and saline groundwater conditions. The treatments included three groundwater depths (GWD) (D1: 30 cm, D2: 55 cm and D3: 80 cm) and four groundwater salinities (GWS) (S1: 0.38, S2: 2, S3: 4 and S4: 8 dSm−1). The results show that the average decrease in grain yield for D2 and D1 compared to D3 was 20.9% and 30.7%, respectively, while the decrease for S2, S3 and S4 compared to S1 was 11.8%, 18.0% and 25.1%. The highest evapotranspiration was found in the D3S1 treatment (630.1 and 550.1 mm in 2017–2018 and 2018–2019, respectively), which increased by 48.0% and 30.2% in the first and second seasons, respectively, compared to the D1S4 treatment. Thus, a GWD at 80 cm with 0.38 dSm−1 GWS was able to meet 72% of the total water requirement of wheat under loam soil conditions. Water use efficiency values ranged from 1.49 to 1.65 kg m−3 in the first season and from 1.18 to 1.73 kg m−3 in the second season, with the highest water use efficiency values found at 80 cm GWD. Regression analysis showed that GWS had a greater effect on water use efficiency than GWD. On average, thousand kernel and hectolitre weights were highest under D3S1, reaching 49.6 g and 77.8 kg hl−1, respectively. Soil salinity increased steadily with increasing GWS at all GWD conditions, and higher soil salinity values were observed at 30 cm GWD. In addition, controlling a groundwater depth at 80 cm with 8.0 dSm−1 GWS did not significantly increase soil salinity, which did not result in high grain yield losses. Finally, it is recommended to control groundwater at a constant depth of 80 cm with 0.38 dSm−1 GWS after the tillering period of winter wheat to save more irrigation water, control soil salinity and improve yield and grain quality in the region with shallow‐saline groundwater. [ABSTRACT FROM AUTHOR]

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.;

Study region: The Athabasca River Basin (ARB), Canada Study focus: This study investigates the dynamic interactions that occur between surface water and groundwater systems within the Athabasca River Basin (ARB). The integrated surface-subsurface model of the ARB was first calibrated under monthly normal transient flow conditions to observed surface water and groundwater data, after which the model was forced with monthly average transient data to evaluate model performance. From these results, groundwater contribution to the Athabasca River system was calculated using simulated surface water-groundwater exchange fluxes. These estimates are compared to those obtained from an isotope-based balance analysis which also estimated groundwater contribution to the Athabasca River. New hydrological insights for the region: The results from this study suggest that the groundwater system in the basin has a high degree of interaction with the surface water system. Specifically, the groundwater contribution to the surface water system along the Athabasca River ranges from 34% (high flow season) to 63% (low flow season) with an overall average annual groundwater contribution of 45%. These results indicate that the groundwater system needs to be considered when analyzing potential climate change impacts on future water availability and extreme hydroclimatic events.

Irrigation effectively guarantees the development of agriculture in arid areas, and groundwater is an essential source of supporting farmland water consumption in shallow groundwater areas. However, it is difficult to accurately quantify the contribution of groundwater to evapotranspiration (ET) on a short time scale, and the influence of different irrigation methods on the hydrological process of farmland are rarely involved. It is significant to understand this process for managing agricultural water use and assessing groundwater resources, especially in arid areas with shallow groundwater. The main purposes of this study were to evaluate the effects of border and drip irrigation on maize ET, and to assess the contribution of groundwater to crop water consumption under shallow groundwater. In this study, eddy covariance system and meteorological station were used to estimate actual ET and potential ET, and the groundwater depth, soil water content in the maize field were monitored. Water balance equation was used to clarify the effective utilization efficiency of irrigation water and water transformation process. The results showed that the total ET of maize growth period under border irrigation and drip irrigation were 490.3 mm and 536.9 mm, and the crop coefficient at the critical growth period were 1.11 and 1.22, respectively. According to the water balance calculation, the effective utilization efficiency of irrigation water under the two irrigation methods were only 0.72 and 0.66. The daily average water flux of groundwater evaporation under border irrigation was around 1.55 mm, which was less than 2.58 mm under drip irrigation over the whole growth period of maize. The contribution rates of groundwater evaporation to crop water consumption of border irrigation at whole growth stage was 26%, which was less than 41% of drip irrigation. These results highlighted the effects of irrigation methods and shallow groundwater on the crop evapotranspiration and field water flux exchange in arid regions, and provided a new perspective for understanding agro-hydrological processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • First time calibration of digital filter with natural tracers in Mediterranean region. • Efficient calibrated digital filter for long-term functional baseflow analysis. • Mountainous Mediterranean rivers are seasonally and interannually baseflow-dominated. • Larger baseflow contribution sustaining Mediterranean rivers during severe droughts. • Baseflow and groundwater can buffer impacts of climate change on the short-term. Baseflow defined as the contribution of groundwater and delayed subsurface flow, is generally described by indices such as the baseflow index (BFI), the long-term ratio of baseflow to streamflow. Characterizing baseflow is challenging because it is not directly accessible, particularly in sensitive areas to climate change like the mountainous Mediterranean regions with hard-rock aquifers. In these areas, little is known about the temporal and spatial contribution of baseflow to streamflow. This study aimed to address this scientific gap by using the first calibrated and validated recursive digital filter with natural tracers for such regions. Two watersheds of Corsica (France), the Tavignanu and the Fiumaltu, were chosen as application models for calibration and validation, respectively, due to their representative characteristics of these regions. Various methods exist for baseflow analysis, including empirical, analytical and physical methods. Empirical and analytical methods, such as digital filters, are easy to use but lack physical significance. Conversely, physical methods using natural tracers, such as isotopes and ions, are more physically representative but are difficult to implement. By calibrating and validating analytical methods with tracers in this specific context, we were able to leverage the strengths of both approaches for effective long-term baseflow analysis. This innovative approach confirmed that baseflow was the main contributor to river flow during dry months, with a contribution of 88–90 % for both watersheds. Notably, baseflow remained a significant contributor during periods of high flow, averaging 54 % for the Tavignanu and 60 % for the Fiumaltu. Over a 25-year period, the mean annual contribution was substantial, at 73 % for the Tavignanu and 77 % for the Fiumaltu. In a particularly dry year, which are expected to become more common with climate change, baseflow contribution was even higher, confirming its origin from deep groundwater and delayed subsurface components. Our results demonstrate that, in the context of climate change, groundwater and delayed subsurface flow will play an increasingly important role in sustaining rivers, connected ecosystems, as well as many human activities in the mountainous Mediterranean regions. [ABSTRACT FROM AUTHOR]

Determining the evapotranspiration (ET) of cotton as a water-intensive crop is crucial for effective irrigation planning and water management, especially in regions like Sindh province, Pakistan, where shallow groundwater table depths (WTDs) are prevalent. Despite the importance of cotton, a major cash crop in Sindh, previous studies on ET were conducted decades ago and may no longer be reliable due to ongoing climate change and the introduction of new crop varieties. Thus, we quantified cotton ET across two cropping seasons and at various WTDs (0.45, 0.60, 0.75, 1.50, 2.25, and 2.75 m). The experimental study was based on the data procured from 12 mini lysimeters and 12 large lysimeters for two years (2018 and 2019) and at two soil series. The findings revealed that cotton ET ranged from 1332 to 1437, 1114–1202, 988–1075, 781–821, 690–733, and 637–683 mm at WTDs of 0.45, 0.60, 0.75, 1.50, 2.25, and 2.75 m, respectively. WTDs from 0.45 to 0.75 m fulfilled 94–96 % of cotton ET through groundwater (GW) contribution in Sultanpur soil (silt loam) and 93–97 % in Miani soil (silty clay loam). At 1.50–2.75 m WTDs, irrigation water requirements (excluding rainfall and leaching) were 63–88 % in Sultanpur soil and 67–89 % in Miani soil. The highest yield was observed at a 1.50 m WTD, while the highest water use efficiency was identified at a 2.25 m WTD. However, soil salinity increased by 60–80 %, resulting in a 40–60 % lower cotton yield at 0.45–0.75 m WTD. Therefore, periodic flushing of salts is necessary to utilize shallow WTDs effectively. Considering GW contribution to ET when allocating water for irrigation channels and devising irrigation schedules is crucial. This approach can lead to water savings, prevent land from becoming waterlogged and saline, manage the groundwater table, and reduce the need for drainage channels and labor force for their preparation. • The cotton evapotranspiration (ET) is highly dependent on water table depth (WTD). • Providing reliable data on cotton ET across various WTDs and soil series. • Identifying optimal WTDs for maximum yield and water use efficiency. [ABSTRACT FROM AUTHOR]

Groundwater contributes to the delivery of phreatic water to crop aeration zones via evapotranspiration, which is important for crop growth in drought-prone regions. Most studies on groundwater contribution have not considered the influence of crop growth stage or daily evapotranspiration. In this study, a neural network based on a genetic algorithm and the Levenberg–Marquardt backpropagation algorithm, as well as formula methods based on an accelerated genetic algorithm, were built to assess soybean groundwater contribution; in addition, a performance comparison was conducted. The results indicated that machine learning had the best performance for fitting errors, with values for relative mean error (RME), root mean square percentage error (RMSPE), and correlation coefficient of 1.088, 2.165, and 0.762, respectively; in addition, for validation errors, it had values for RME, RMSPE, and correlation coefficient of 1.069, 2.136, and 0.735, respectively. The machine learning method is recommended for readers seeking to calculate groundwater contribution. [ABSTRACT FROM AUTHOR]

The relationship between groundwater and lakes in Qaidam Basin is often overlooked. Therefore, we employed Landsat satellite images and meteorological data to investigate the causes of lake expansion through model calculation and statistical analysis and then determine groundwater sources through isotope analysis (2H, 3H, and 18O). In the two study periods of 2003–2011 and 2011–present, temperature, precipitation, and runoff increased at a steady rate, whereas the expansion rate of Tuosu Lake increased from 1.22 km2/yearr to 3.38 km2/yearr. This significant increase in the rate of lake expansion reflects the substantial contribution of groundwater to lake expansion. The groundwater contribution to the lake includes not only the glacial meltwater that infiltrates the piedmont plain but also other, more isotopically deleted water sources from other basins. It is speculated that the 2003 Ms 6.4 earthquake in the northwest of the Delingha region was a possible mechanism for lake expansion. Earthquakes can enhance crustal permeability and keep fractures open, which promotes groundwater contribution to lakes and in turn causes rapid lake expansion and an increased groundwater level. This study is important for understanding the sources, circulation, and evolution of groundwater in Qaidam Basin. [ABSTRACT FROM AUTHOR]

Copyright of World Water Policy is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Groundwater contributes to the delivery of phreatic water to crop aeration zones via evapotranspiration, which is important for crop growth in drought-prone regions. Most studies on groundwater contribution have not considered the influence of crop growth stage or daily evapotranspiration. In this study, a neural network based on a genetic algorithm and the Levenberg–Marquardt backpropagation algorithm, as well as formula methods based on an accelerated genetic algorithm, were built to assess soybean groundwater contribution; in addition, a performance comparison was conducted. The results indicated that machine learning had the best performance for fitting errors, with values for relative mean error (RME), root mean square percentage error (RMSPE), and correlation coefficient of 1.088, 2.165, and 0.762, respectively; in addition, for validation errors, it had values for RME, RMSPE, and correlation coefficient of 1.069, 2.136, and 0.735, respectively. The machine learning method is recommended for readers seeking to calculate groundwater contribution.

The San Juan catchment is form up of San Agustín, Cañas and San Juan sub-catchment. The simple balance of San Agustín sub-catchment, with an area of 267 km2, showed that for the hipper-annual balance of 428,6 hm3 to exist, the sub-catchment must have an additional area of about 55 km2, which generates an additional contribution of 30,5 hm3 to runoff from the basin and is considered to correspond to a significant groundwater contribution. To verify this hypothesis, the groundwater component value was computed by different methods concluding that the additional contribution is given by the value of groundwater component, which is generated by the infiltration of rainfall that occurs in the polje area and the karst zone existent in Aguacate catchment at west of San Agustín - Cañas sub-catchment. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The relationship between groundwater and lakes in Qaidam Basin is often overlooked. Therefore, we employed Landsat satellite images and meteorological data to investigate the causes of lake expansion through model calculation and statistical analysis and then determine groundwater sources through isotope analysis (2H, 3H, and 18O). In the two study periods of 2003–2011 and 2011–present, temperature, precipitation, and runoff increased at a steady rate, whereas the expansion rate of Tuosu Lake increased from 1.22 km2/yearr to 3.38 km2/yearr. This significant increase in the rate of lake expansion reflects the substantial contribution of groundwater to lake expansion. The groundwater contribution to the lake includes not only the glacial meltwater that infiltrates the piedmont plain but also other, more isotopically deleted water sources from other basins. It is speculated that the 2003 Ms 6.4 earthquake in the northwest of the Delingha region was a possible mechanism for lake expansion. Earthquakes can enhance crustal permeability and keep fractures open, which promotes groundwater contribution to lakes and in turn causes rapid lake expansion and an increased groundwater level. This study is important for understanding the sources, circulation, and evolution of groundwater in Qaidam Basin.

Groundwater plays an important role in supplying water to vegetation in floodplain wetlands. Exploring the effect of water table depth (WTD) on vegetation transpiration is essential to increasing understanding of interactions among vegetation, soil water, and groundwater. In this study, a HYDRUS-1D model was used to simulate the water uptake of two typical vegetation communities, Artemisia capillaris and Phragmites australis, in a floodplain wetland (Poyang Lake wetland, China). Vegetation transpiration was compared for two distinct hydrological conditions: high water table (2012) and low water table (2013). Results showed that vegetation transpiration in the main growth stage (July–October) was significantly influenced by WTD. Under high water table conditions, transpiration of A. capillaris and P. australis communities in the main growth stage totaled 334 and 735 mm, respectively, accounting for over 90% of the potential transpiration. Under low water table conditions, they decreased to 203 and 510 mm, respectively, due to water stress, accounting for merely 55% of the potential transpiration. Scenario simulations found different linear relationships between WTD and the ratio of groundwater contribution to vegetation transpiration. An increase of 1 m in WTD in the main growth stage may reduce the ratio by approximately 25%.

The crop water requirements of three major crops grown in the Lower Indus Basin namely wheat, cotton and sugarcane were determined at different water-table depths and the groundwater contribution to the total water requirement was quantified. The study was conducted in drainage type lysimeters of size 3.05 m x 3.05 m x 5.18 m constructed at the Drainage Research Centre Tandojam, Pakistan. Three different water-table depths of 1.5, 2.25 and 2.75 m were maintained during the study. The evapotranspiration (ET) was more at shallow water-table depths and it decreased with increase in water-table depths. The maximum wheat yield was obtained at water-table depth of 2.25 m whereas the maximum cotton and sugarcane yields were observed at 1.5 m depth. The groundwater contribution to wheat crop was, 19, 6 and 4%, to cotton crop, 20, 4 and 1% and to sugarcane crop, 21, 5 and 1% at the three water-table depths, respectively. At 1.50 m depth, the water productivity of wheat was 8-22%, cotton 27-30% and sugarcane 34-57% higher than at 2.25 and 2.75 m depths. Therefore, there is a need to exploit the shallow water table to reduce the surface water applications and to improve the water productivity. [ABSTRACT FROM AUTHOR]

Yield and production functions of sunflower (Helianthus annuus) were evaluated under full and deficit irrigation practices with the presence of shallow saline groundwater in a semi-arid region in the Imperial Valley of southern California, USA. A growing degree day (GDD) model was utilized to estimate the various growth stages and schedule irrigation events throughout the growing season. The crop was germinated and established using overhead irrigation prior to the use of a subsurface drip irrigation (SDI) system for the remainder of the growing season. Four irrigation treatments were implemented: full irrigation (100% full sunflower crop evapotranspiration, ETC), two reduced irrigation scenarios (95% ETC and 80% ETC), and a deficit irrigation scenario (65% ETC). The salinity of the irrigation water (EC) (Colorado River water) was nearly constant at 1.13 dS·m−1 during the growing season. The depth to groundwater and groundwater salinity (ECGW) were continuously monitored in five 3 m deep observation wells. Depth to groundwater fluctuated slightly under the full and reduced irrigation treatments, but drastically increased under deficit irrigation, particularly toward the end of the growing season. Estimates of ECGW ranged from 7.34 to 12.62 dS·m−1. The distribution of soil electrical conductivity (ECS) and soil matric potential were monitored within the active root zone (120 cm) at selected locations in each of the four treatments. By the end of the experiment, soil salinity (ECS) across soil depths ranged from 1.80 to 6.18 dS·m−1. The estimated groundwater contribution to crop evapotranspiration was 9.03 cm or approximately 16.3% of the ETC of the fully irrigated crop. The relative yields were 91.8%, 82.4%, and 83.5% for the reduced (95% and 80% ETC) and deficit (65% ETC) treatments, respectively, while the production function using applied irrigation water (IW) was: yield = 0.0188 × (IW)2 − 15.504 × IW + 4856.8. Yield reduction in response to water stress was attributed to a significant reduction in both seed weight and the number of seed produced resulting in overall average yields of 2048.9, 1879.9, 1688.1, and 1710.3 kg·ha−1 for the full, both reduced, and deficit treatments, respectively. The yield response factor, ky, was 0.63 with R2 = 0.745 and the irrigation water use efficiencies (IWUE) were 3.70, 3.57, 3.81, and 4.75 kg·ha−1·mm−1 for the full, reduced, and deficit treatments, respectively. Our results indicate that sunflowers can sustain the implemented 35% deficit irrigation with root water uptake from shallow groundwater in arid regions with a less than 20% reduction in yield.

The upward movement of water by capillary rise from shallow water-table to the root zone is an important incoming flux. For determining exact amount of irrigation requirement, estimation of capillary flux or upward flux is essential. Simulation model can provide a reliable estimate of upward flux under variable soil and climatic conditions. In this study, the performance of model UPFLOW to estimate upward flux was evaluated. Evaluation of model performance was performed with both graphical display and statistical criteria. In distribution of simulated capillary rise values against observed field data, maximum data points lie around the 1:1 line, which means that the model output is reliable and reasonable. The coefficient of determination between observed and simulated values was 0.806 (r = 0.93), which indicates a good inter-relation between observed and simulated values. The relative error, model efficiency, and index of agreement were found as 27.91%, 85.93% and 0.96, respectively. Considering the graphical display of observed and simulated upward flux and statistical indicators, it can be concluded that the overall performance of the UPFLOW model in simulating actual upward flux from a crop field under variable water-table condition is satisfactory. Thus, the model can be used to estimate capillary rise from shallow water-table for proper estimation of irrigation requirement, which would save valuable water from over-irrigation.

Agricultural water conservation is important in arid and semi-arid areas where water resources are deficient and agriculture irrigation accounts for a high proportion of water use. Thus, efficient deficit irrigation methods, which the supplied water is less than potential evapotranspiration have been developed. In semi-arid areas, groundwater can contribute to crop’s water consumption but less is known about impact of deficit irrigation on the contribution. We conducted, therefore, a two-year field experiments with deficit flood irrigation for maize in an arid district with shallow groundwater in China. Four irrigation practices were tested with water applied at approximately 82.5%, 75%, 67.5% and 60% of the 540 mm potential evapotranspiration (PET) in 2014 and the 500 mm in 2013 over the crop growing season. We found that the upward flux between soil water and groundwater varied from 5 mm with input water of 488 mm to 60 mm with input water of 353 mm. The yield of maize decreased by only 15% from 10.0 to 8.5 t/ha for the WS treatment (irrigated at 60% of PET) compared with the WH treatment (irrigated at 82.5% of PET) due to more groundwater contribution to the crop growing with less irrigation. As a consequence, the water use efficiency (WUE), defined as quotient of the yield and plant evapotranspiration was not significantly different among different irrigation treatments. However, the irrigation water use efficiency (IWUE), which is the yield per unit of water applied, increased significantly with the decreasing amount of water applied due to the contribution of upward fluxes. The implication is that deficit irrigation enhances the contribution of groundwater to crop water use and will not produce an obvious reduction of yield within a stable shallow groundwater level. [ABSTRACT FROM AUTHOR]

Groundwater provides an important source of water for maize cultivation where the water table is shallow in the semi-arid Hailiutu River catchment of the Maowusu Desert on the Erdos Plateau in Northwest China. A HYDRUS-1D model of the unsaturated flow beneath a maize (Zea mays L.) field was calibrated and validated with measured soil water contents at various depths during the maize growing period from 30 April to 1 October 2011, and from 23 May to 27 September 2012, respectively. The model computed the actual maize evapotranspiration (ETa) as 580 mm during the whole growing period from 30 April to 1 October 2011. The groundwater contribution to ETa was calculated to be 220 mm, accounting for 38% of maize water use during the growing season in 2011. When the groundwater level drops below a depth of 157 cm, maize can no longer use groundwater for transpiration. The irrigation water requirement increases with the increase of groundwater table depth. These results are very important for managing crop irrigation in the area. EDITOR D. Koutsoyiannis ASSOCIATE EDITOR L. Ruiz [ABSTRACT FROM AUTHOR]

The Horqin sandy steppe is an ecosystem where groundwater-dependent grasslands are main components. To study the dynamics of soil water and evapotranspiration, and its partition into transpiration and soil evaporation, the SIMDualKc model was applied to two sites in the Agula eco-hydrological study area, Inner Mongolia, China. This model adopts the dual crop coefficient approach to compute daily crop evapotranspiration (ETc) and uses a parametric function to compute capillary rise from a shallow watertable. The application refers to three years of field observations, 2008 with high rainfall and higher watertable, 2009 with low rainfall and lower watertable, and 2011 with average rainfall and watertable conditions. Model calibration and validation were performed comparing simulated against observed soil water content throughout the vegetation seasons, with regression coefficients close to 1.0 and small root mean square errors (RMSE < 0.013 cm3 cm−3). The groundwater contribution represented 41-47% of the actual ETc in the higher rainfall year and 56-59% in the dry year, which clearly shows the role of groundwater in sustaining grasslands in the Horqin steppe. The ratio between transpiration and actual ETc ranged 88 to 94%, which is much higher than observations in other grasslands because capillary rise contributes to extraction by crop roots, not to soil evaporation. Simulations relative to lowering the watertable show that groundwater contribution decreases up to 25% for a dry year with a consequent decrease of transpiration of 24%. Hence, there is the need for developing appropriate groundwater protection measures to preserve the Horqin landscape. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The contribution of groundwater to streamflow in Alpine catchments is still poorly understood, despite the fact that it may heavily impact hydrological balance and stream habitats. This paper presents the results of a field campaign based on experiments with heat tracer methods to assess the hyporheic flow during the low-flow period of a large Alpine river in Italy. These measurements were employed to validate a distributed hydrological model that can be used to asses river-groundwater interaction in both low-flow and high-flow conditions. The results show that groundwater may have a relevant role during low-flow periods, by increasing river discharge and during floods, by subtracting direct run-off that is stored in river banks. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A number of lysimetric experiments were carried out from 2010 to 2011 to determine total water use, shallow groundwater contribution percentage and the effects of different shallow water table levels in the presence of supplementary surface irrigation on water requirements, wet yield production, and water use efficiencies of different edible green vegetables including Solanum pseudoca psicum , Ocimum basilicum and Lepidium sativum . These experiments were performed in a randomized complete block factorial experimental design with three replicates at the Lysimetric Research Station of Razi University, Kermanshah, Iran. Three treatments were applied to each experiment by maintaining groundwater with EC 2 dS m −1 and different water table levels of 0.6, 0.80 and 1.10 m, respectively. Supplementary surface irrigation with quality of 1 dS m −1 was used during the experiments. The average total values of water use, surface water use, surface water saving percentages, groundwater uses and groundwater contribution percentages were found to be as 436 mm, (208, 292, 324 mm equal to 51, 32 and 24%) and (218, 134, 102 mm equal to 49, 34 and 27%) for S. pseudoca psicum ; 417 mm (201, 279, 305 mm equal to 52, 34 and 27%) and (206, 129, 102 mm equal to 50, 31 and 25%) for O. basilicum and 415 mm, (197, 299, 315 mm equal to 53, 26 and 25%) and (209, 107 and 91 mm equal to 51, 26 and 22%) for L. sativum , respectively. Generally, the results showed a higher wet weights and water use efficiencies for lower water table depths considering wet weights due to lower and higher surface water and groundwater uses, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This research was conducted to determine the yield and water-use efficiency of maize under fixed and variable alternate furrow irrigation (fixed AFI, variable AFI) and every furrow irrigation (EFI) at different irrigation intervals in areas with shallow and deep groundwater. In variable AFI, water was applied to the furrow, which was dry in the previous irrigation cycle. The results indicated that even at 4-day irrigation intervals the water needs of maize on a fine textured soil in both areas (with deep and shallow water table) are not met by AFI. The decrease in grain yield due to water stress was mainly due to the decrease in the number of grains per cob and to a lesser extent to the decrease in 1000-grain weight. At the Kooshkak site with shallow groundwater (between 1.31 and 1.67 m), grain yields in AFI at 4- and 7-day intervals were comparable to those obtained in EFI at 7- and 10-day intervals, respectively. This might be due to the contribution of groundwater to the water use of the plant (about 5-10%). In the Badjgah area, with deep water depth, grain yield in AFI at 7-day intervals was statistically lower than that obtained in EFI at 10-day interval. In AFI, a shorter irrigation interval (4-day) may alleviate the water stress and result in no yield reduction compared with that in EFI at 7-day intervals even though water application was reduced. Furthermore, in the area with a shallow water table, AFI at 7-day intervals may be superior to EFI at 10-day irrigation intervals. When seasonal irrigation water is less than 700 mm, it may be preferable to use AFI at 10-day intervals to increase water-use efficiency, especially in areas with shallow groundwater. In general, when water was insufficient for full irrigation, the relative grain yield (yield per unit water applied) of maize under AFI was higher than those under EFI.

Water scarcity and salinity are two important limitations for agricultural production. Interaction effects of deficit irrigation and shallow groundwater on crop water use could increase water productivity in arid and semi-arid areas. Quinoa is a traditional Andean seed crop that has been introduced all around the world. However, response of quinoa as a salinity and drought tolerant crop to shallow saline groundwater under deficit irrigation has not been studied. Therefore, the aim of this study was to investigate the influence of saline groundwater depths, GD (0.3, 0.55, and 0.80 m) and deficit irrigation, DI (80, 55 and 30% of full irrigation, FI) on growth, yield and water productivity of quinoa and groundwater contribution (GWC) to its water use in lysimeters under greenhouse conditions. Results indicated that 70% reduction of the full irrigation water resulted in only 36% reduction in seed yield (SY) as compared with maximum SY (2.1 Mg ha −1 at 0.80 m GD with 0.80FI), whereas water productivity based on SY (WUEI seed ) increased 12%. Shoot dry matter (SDM) is not sensitive to water deficit and reducing the irrigation volume from 0.80FI to 0.30FI resulted in only 8% decrease in SDM in presence of shallow groundwater. It is concluded that at moderate deficit irrigation (0.80FI) shallow groundwater should be maintained at 0.55 m or higher to obtained maximum SY; however, in places with shallow groundwater (0.30 m), deficit irrigation should be applied in order to achieve higher SY. On average, 27% and 41% reduction in GWC was observed by increasing GD from 0.30 to 0.55 m and 0.30 to 0.80 m, respectively. GWC/ET ranged from 0.40 to 0.72 for 0.80FI, 0.46 to 0.75 for 0.55FI and 0.51 to 0.80 for 0.30FI. Finally, contour plot was developed to show the combined effect of DI and GD on GWC/ET. The boundary for groundwater contribution to quinoa ET is GD = 0.55 SWD + 1.22 (SWD is the soil water depletion fraction of total available water). Results indicated that 210 mm of ET is required to initiate SY production for quinoa in greenhouse conditions and transpiration efficiency (the ratio of SDM to the seasonal transpiration) for quinoa dry matter production is 0.028 Mg ha −1 mm −1 . Seed and dry matter yield response factor to water stress indicated that SY is more sensitive to water stress, followed by root dry matter (RDM) and SDM. [ABSTRACT FROM AUTHOR]

Lysimetric experiments were conducted in order to investigate the effects of saline shallow groundwater on water requirements and other parameters of coriander plant in a semiarid climate. The plants were grown in 27 columns each with a diameter of 0.40 m and packed with silty clay soil. The experiments were carried out with three replicates using a randomized complete block design with different treatment combinations. Nine treatments were applied in each experiment by maintaining groundwater with an EC of 1, 2 and 4 dSm-1, at three different water table levels of 0.60, 0.80, and 1.10 m. The supplementary irrigation requirements for each treatment were applied by adding surface water with EC of 1 dSm-1. The results of experiments showed that for groundwater qualities 1, 2 and 4 dSm-1; and water table depths 0.60, 0.80, and 1.10 m, the average percentage of groundwater contributions were to be 66.6, 55.3, and 46.3%; 59.2, 50.8, and 40.3%; and 49.3, 37.3, and 27.3% of the average annual coriander water requirements, respectively. The results indicated that coriander is a medicinal plant that is sensitive to salinity. [ABSTRACT FROM AUTHOR]

This study aimed at assessing the soil water balance, groundwater contribution, crop transpiration and soil evaporation of a rainfed maize crop in Horqin sandy area, north-eastern Inner Mongolia, China. Two years of field data from the Agula site were used, 2008 with relatively high rainfall (363 mm) and high water table, and 2009 with low rainfall (125 mm) and lower water table. The SIMDualKc water balance model was calibrated with observed soil water content data of 2008 and validated with data of 2009. The model uses the dual crop coefficient approach for evapotranspiration (ET) partitioning, and parametric functions for computing capillary rise. The respective modelling results show that the groundwater contribution represented ca. 50% of crop ET in both years. Estimation errors are small, with root mean square errors of 0.007 and 0.008 cm 3 cm −3 respectively in 2008 and 2009. The Nash and Sutcliffe modelling efficiency were high, 0.93 in both years, which indicates a low variance of residuals. The calibrated basal crop coefficient K cb mid = 0.95 denotes a low density of the crop because it is much lower than common potential values. Soil evaporation was relatively low, 23% of ET in the wet year and 17% in the dry year, because capillary rise does not contribute to soil evaporation but to roots extraction only. Results show that capillary rise plays a main role in supplying the vegetation throughout the season, hence a strong dependence of vegetation upon groundwater. [ABSTRACT FROM AUTHOR]

Water scarcity and water salinity are major constrains for agricultural production in arid and semi-arid regions of Iran. Salt tolerant and high nutritious crop, quinoa, has been introduced all around the world. However, little documented investigations are presented about the effect of different saline groundwater depths and irrigation water salinities on plant growth, yield and water use of quinoa. Therefore, the aim of this study was to investigate the influence of saline groundwater depths, SGD (0.3, 0.55 and 0.80 m) with salinity equivalent to irrigation water and irrigation water salinity, WS (10, 20, 30 and 40 dS m −1 ) on growth and yield of quinoa and groundwater contribution to its water use in cylindrical lysimeters in greenhouse conditions. Results indicated that increasing in WS caused significant decrease in seed yield (SY) and shoot dry matter (SDM) and at all SGDs . However, root dry matter (RDM), harvest index (HI), protein content, 1000-seed weight (SW), number of panicle per plant (NP) and plant height (PH) are reduced by WS higher than 20 dS m −1 . Furthermore, at all WSs increasing in SGD resulted in significant increase in SY, SDM, RDM and ET. Results indicated that quinoa is able to extract water (groundwater contribution to evapotranspiration ratio, GWC/ET as 18 to 66%) from saline groundwater, even at no deficit irrigation conditions. Contour plot was developed to show the combined effect of WS and SGD on GWC/ET. It is indicated that non-saline groundwater depth lower than 1.62 m could contribute to quinoa water use. In presence of saline groundwater (SGD as m), the salinity should be considered by the equation SGD = 1.62 − 0.013 WS .Yield-salinity functions indicated that maximum threshold EC e for SY (20.7 dS m −1 ) occurred at 0.80 m SGD and seed yield reduction coefficient (b) was on average, 7.7% per unit soil salinity increase. Also, increasing in SGD resulted in significant decrease in RDM reduction coefficient. Minimum RDM reduction coefficient was 5.5% per unit soil salinity increase. It showed that quinoa root is more tolerant to salinity than shoots. [ABSTRACT FROM AUTHOR]

As a free water resource, groundwater is extensively used for agricultural purposes. This is sometimes referred to as underground irrigation. Two-year lysimetric experiments from 2009 to 2011 were conducted in order to determine the effects of different shallow water table levels without any supplementary irrigation on water requirements, yield production and water-use efficiencies of three wheat cultivars namely W33g, Cross Alborz and Bahar. The experiments were carried out in a randomized complete block factorial experiment design with three replicates at the Razi University Lysimetric Research Station, Iran. Nine treatments were applied to each experiment by maintaining groundwater EC of 5 dS m−1, with different water table levels of 0.6, 0.80 and 1.10 m, respectively. The results showed the highest and lowest groundwater uses by wheat for water table depths of 0.6 m and 1.10 m, during the experimental years, respectively. For all wheat cultivars, the average groundwater contributions were found to be 70.90% (5 mm day−1), 67.85% (4.3 mm day−1) and 63.4% (3.6 mm day−1) for water table levels of 0.60, 0.80 and 1.10 m, respectively. Finally, the results showed the highest yield production and groundwater-use efficiency under water table levels of 0.80 m for all the three wheat cultivars. [ABSTRACT FROM AUTHOR]

Highlights: [•] Groundwater contribution by Black cumin was studied under different saline and water table conditions. [•] Increasing groundwater salinity and WT depth resulted in a significant reduction in groundwater contribution. [•] Surface irrigation can be managed to increase crop water requirement from shallow groundwater. [•] The planting of Black cumin under shallow water table depth and low salinity condition is recommended. [Copyright &y& Elsevier]

In Iran, rice is grown in areas where the groundwater depth (GD) is low. Therefore, water-saving irrigation (WSI) can be used instead of continuous flood irrigation (CFI) in order to use the groundwater. The objectives of this study were to investigate the interaction effects of irrigation regimes and GDs on growth and yield of rice and groundwater contribution (GC) to crop evapotranspiration (ET) in cylindrical greenhouse lysimeters. Irrigation regimes were CFI and intermittent flood irrigation (IFI) with 4- and 8-day intervals (IFI-4 and IFI-8, respectively), and GDs were 0.3, 0.45, and 0.60 m. Results indicated that in a climate condition similar to experimental environment in greenhouse, using IFI-4 at a GD of 0.3 m produced grain yield and straw and root dry matter (DM) similar to those obtained when using CFI, with 53% reduction in irrigation water use. However, straw and root DM increased in CFI with increasing soil column length. Maximum GC/ET (41%) was observed when using IFI-4 at a GD of 0.3 m. A multiple regression equation was presented to estimate GC/ET as a function of GD and soil moisture deficit (SMD). This equation indicates that at a given GD with extension of irrigation intervals and increased SMD GC/ET reached a maximum value followed by a decrease afterwards. Maximum values of GC/ET were obtained at SMD values of 0.47, 0.40, and 0.33 at GDs of 0.3, 0.45, and 0.6 m, respectively. [ABSTRACT FROM PUBLISHER]

In the Huaibei Plain basin, China, soybean is a main crop. During the soybean growth period, rainfall can vary largely and depth to watertable can also vary largely. The amount of water supplied to the soybean rootzone by groundwater affects soybean growth and yield. Accurate simulation of groundwater contributions to soybean rootzone soil moisture (groundwater contribution) can be important for determining irrigation to and drainage from soybean fields. Based on field observations and local weather data of 2005, HYDRUS-1D was validated by comparing simulated and measured rootzone soil water contents. The validated model was used to estimate the daily groundwater contributions for three different soybean hydrological growing seasons, i.e., an average year (1997), a wet year (2005), and a dry year (2004) with soybean growth at its optimal state. The main results were: (1) seasonal groundwater contribution was 157 mm in the experimental field, and the estimated groundwater contributions were 158, 222, and 387 mm in the wet, average, and dry seasons, respectively; (2) the groundwater contribution was about 63% of the total seasonal transpiration in the experimental field, and those were about 142, 80, and 66% of the total seasonal transpiration in dry, average, and wet seasons, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A number of column experiments were conducted in order to determine groundwater contributions by safflower (Carthamus tinctorius L.) under different saline shallow groundwater (Gw), surface water (Sw) and deficit irrigation schemes. The plants were grown in 16 columns with 0.40m diameter and were packed with silty clay soil. The four replicate randomized complete block factorial experiments were carried out using different treatment combinations. Four treatments were applied during each experiment by maintaining ground and surface water of EC of 1 or 10dS/m at water table level of 0.8m under deficit irrigation condition (75% crop evapotranspiration). The groundwater contribution was determined as a part of crop evapotranspiration by analyzing daily readings of the water levels in Mariotte tubes. The additional surface irrigation requirements for different treatments were applied by adding water of EC of 1 or 10dS/m. The average percentage of groundwater contribution to different treatments including (Gw=1, Sw=1dS/m), (Gw=1, Sw=10dS/m), (Gw=10, Sw=1dS/m), (Gw=10, Sw=10dS/m) with water table level of 0.8m were found to be 58.5%, 14%, 15% and 3.5% of the average annual safflower water requirement, respectively. [Copyright &y& Elsevier]

The baseflow of the Yellow River is vital and important for water resource management and for understanding the hydrological cycle and ecohydrology setting in this arid and semi-arid basin. This study uses a Lyne and Hollick digital filtering technique to investigate the behaviors of the baseflow and the baseflow index in the upper reaches of the Yellow River Basin (China). The observed streamflow discharges along the river were used to analyze the baseflow trend, persistence, and periodic characteristics during the period of 1950-2000. The results show that the average baseflow and BFI in the upper reaches of the Yellow River exhibit a decreasing trend and will continue to decline in the future. Generally, the annual average baseflow and BFI for the most upstream areas of the Yellow River show little difference, while the baseflow and BFI exhibit significant differences for the downstream areas. The filtered annual baseflow varied between 128 × 10 8 m 3 /year and 193 × 10 8 m 3 /year for the Yellow River. The BFI ranged from 0.54 to 0.65, with an average of 0.60. This indicates that on average, 60% of the long-term streamflow is likely controlled by groundwater discharge and shallow subsurface flow. Statistics show that two periodic variations were observed in the baseflow evolution process. The results indicate that on average, the first and second main cycles of baseflow behaviors occur at 28 years and 12-17 years, respectively. Correspondingly, the estimation indicates that the abrupt change points tend to appear in the 1960s, the 1980s, and the 1990s. An improved understanding of baseflow behaviors can help guide future strategies to manage the river regime, its water resources, and water quality.

• Basin-scale anthropogenic effects are quantified with a fully-integrated approach. • Groundwater system over the basin is significantly affected by year-round pumping. • Stream flow and depth are significantly affected by control structure operations. • Fully-integrated approach provides useful insights for water management plans. This study presents a decision support method that can quantify the effects of water management practices on surface water and groundwater systems using a basin-scale fully-integrated model. For improvement to the decision-making process, the integrated model consists of evapotranspiration, surface, and subsurface hydrologic conditions and accounts for anthropogenic water management such as groundwater pumping, and dam and weir operations, which significantly affect the water resources of the Geum River Basin, South Korea. In this study, the fully-integrated model is calibrated based on a step-wise calibration approach. For a reliable decision support model, the calibrated model was further evaluated against five-year monthly transient agricultural pumping and control structure operation data with taking into account the parametric uncertainty of the model. The calibration and evaluation results agree well with various observation datasets including watertable depths, surface flow, reservoir water depths, and dam and weir discharge rates. Simulation results reveal that annual average net precipitation ratio for the simulation period is 0.32 with a range from 0.12 to 0.40, which is a water surplus condition. Within each year, however, negative net precipitation ratios, or water deficit conditions, occur consistently during the dry seasons, indicating that the hydrologic systems in the basin may be vulnerable during the dry seasons. Groundwater pumping within the basin lowers the local groundwater levels an average of 0.52 m over five years. In the downstream area of the basin, groundwater pumping activities affect approximately 30% of the area and result in a reduction of groundwater levels by 0.4 m with an acceptable range of uncertainty. As a decision support method for weir operations, we apply a weir removal scenario to evaluate the changes in surface flow conditions. The simulation results reveal that surface flow rates in weir reservoirs increase by three orders of magnitudes and surface water depths in the reservoirs of the dams and weirs reduce by two to four times compared to a case where all the weirs are in operation. Therefore, appropriate weir removal plans are necessary to minimize the impact on the ecosystem of the Geum River. [ABSTRACT FROM AUTHOR]

The southwestern Adirondack region of New York receives among the highest rates of atmospheric nitrogen (N) deposition in the USA. Atmospheric N deposition to sensitive ecosystems, like the Adirondacks. may increase the acidification of soils through losses of exchangeable nutrient cations, and the acidification of surface waters associated with enhanced mobility of nitrate (NO3-). However, watershed attributes, including surficial terrestrial characteristics, in-lake processing, and geological settings, have been found to complicate the relationships between atmospheric N deposition and N drainage losses. We studied two lake-watersheds in the southwestern Adirondacks. Grass Pond and Constable Pond. which are located in close proximity (∼26 kin) and receive similarly high N deposition, but have contrasting watershed attributes (e.g. wetland area. geological settings). Since the difference in the influence of N deposition was minimal, we were able to examine both within- and between-watershed influences of land cover, the contribution of glacial till groundwater inputs, and in-lake processes on surface water chemistry with particular emphasis on N solutes and dissolved organic carbon (DOC). Monthly samples at seven inlets and one outlet of each lake were collected from May to October in 1999 and 2000. The concentrations of NO3- were high at the Grass Pond inlets, especially at two inlets, and NO3- was the major N solute at the Grass Pond inlets. The concentrations of likely weathering products (i.e. dissolved Si, Ca2+, Mg2+, Na+) as well as acid neutralizing capacity and pH values, were also particularly high at those two Grass Pond inlets, suggesting a large contribution of groundwater inputs. Dissolved organic N (DON) was the major N solute at the Constable Pond inlets. The higher concentrations of DON and DOC at the Constable Pond inlets were attributed to a large wetland area in the watershed. The DOC/DON ratios were also higher at the Constable Pond inlets, possibly due to a larger proportion of coniferous forest area. Although DON and DOC were strongly related, the stronger relationship of the proportion of wetland area with DOC suggests that additional factors regulate DON. The aggregated representation of watershed physical features (i.e. elevation, watershed area. mean topographic index, hygrometric-analysis index) was not clearly related to the lake N and DOC chemistry. Despite distinctive differences in inlet N chemistry, NO3- and DON concentrations at the outlets of the two lakes were similar. The lower DOC/DON ratios tit the lake outlets and at the inlets having upstream ponds suggest the importance of N processing and organic N sources within the lakes. Although an inverse relationship between NO3- and DOC/DON has been suggested to be indicative of a N deposition gradient, the existence of this relationship tor sites that receive similar atmospheric N deposition suggest that the relationship between NO3- and the DOC/DON ratio is derived from environmental and physical factors. Our results suggest that, despite similar wet N deposition at the two watershed sites, N solutes entering lakes were strongly affected by hydrology associated with groundwater contribution and the presence of wetlands, whereas N solutes leaving lakes were strongly influenced by in-lake processing. [ABSTRACT FROM AUTHOR]

This paper describes the role of groundwater contribution to surface flow at the Causse d’Aumelas, a karst system near Montpellier (France), which is traversed by an intermittent river, the Coulazou. A first hydrologic model integrating a digital terrain model shows the inability of a standard rainfall-runoff model to replicate recorded flood hydrographs. While the flood peaks are routed through the karstic system along the Coulazou without a phase lag, the peak magnitude is somewhat modified. These results indicate an initial karst system recharge followed by a significant contribution to surface flow. A hydrodynamic analysis of ground-water flow confirms these results: the karst system first absorbs part of the rainfall, which induces a general water table rise within the aquifer, and then contributes to surface flow in the Coulazou. [ABSTRACT FROM AUTHOR]

Abstract: Due to the increasing demand for food and fiber by its ever-increasing population, the pressure on fresh water resources of Pakistan is increasing. Optimum utilization of surface and groundwater resources has become extremely important to fill the gap between water demand and supply. At Lahore, Pakistan 18 lysimeters, each 3.05m×3.05m×6.1m deep were constructed to investigate the effect of shallow water tables on crop water requirements. The lysimeters were connected to bottles with Marriotte siphons to maintain the water tables at the desired levels and tensiometers were installed to measure soil water potential. The crops studied included wheat, sugarcane, maize, sorghum, berseem and sunflower. The results of these studies showed that the contribution of groundwater in meeting the crop water requirements varied with the water-table depth. With the water table at 0.5m depth, wheat met its entire water requirement from the groundwater and sunflower absorbed more than 80% of its required water from groundwater. Maize and sorghum were found to be waterlogging sensitive crops whose yields were reduced with higher water table. However, maximum sugarcane yield was obtained with the water table at or below 2.0m depth. Generally, the water-table depth of 1.5–2.0m was found to be optimum for all the crops studied. In areas where the water table is shallow, the present system of irrigation supplies and water allowance needs adjustments to avoid over irrigation and in-efficient use of water. [Copyright &y& Elsevier]

• The effect of climate change on groundwater contributions to winter wheat are investigated. • The exchanges between soil water and groundwater will increase in the future. • Climate change alters groundwater contributions to the root zone of winter wheat during each growth period, especially in the wet season. • Groundwater contributions remove the need for irrigation under RCP 4.5 in wet and normal growing seasons. Winter wheat is the predominant crop in the Huaibei Plain of Anhui Province, China. The Huaibei Plain has a transitional climate and a shallow water table. As global warming accelerates, climate change in the area may impact agricultural production. In shallow groundwater regions, capillary rise can be large, and it can act as an important water resource for crop use. However, it is not clear how climate change will impact groundwater depths and crops. Based on local weather data from 1960 to 2010, a general circulation model, HadGEM2-AO, which performed best in simulating precipitation in the study area, and three Representative Concentration Pathways (RCPs, RCP 2.6, RCP 4.5 and RCP 8.5), the validated numerical model HYDRUS-1D was used to estimate the daily groundwater contribution to the crop root zone in 2011–2100 of different hydrological growing seasons. The largest groundwater contribution and deep drainage occurred at a water table depth of 1.5 m. The groundwater contribution to crop root zones was largest for RCP 2.6, and the deep drainage was largest for RCP 8.5. The results indicated that climate change could alter the distribution of the groundwater contribution in each growing period. Meanwhile, the phenophases of winter wheat for RCP 2.6 were delayed while they were advanced for RCP 4.5 and RCP 8.5. In wet and normal seasons, there was no need for irrigation for RCP 4.5 during the whole growing season. However, in a dry season, a small amount of irrigation was still needed during the maturity stage for RCP 2.6. In general, the total irrigation amounts needed for winter wheat growth were reduced for all hydrological conditions with the three RCPs. [ABSTRACT FROM AUTHOR]

• For seasonal and diurnal variations, LE accounted for the highest proportion of R n. • Energy fluxes and ET a were affected by maize LAI with a threshold around 4 m2 m-2. • Irrigation and the decreasing WTD from about 2.2 to 1.2 m increased LE/R n or LE. • The inter-seasonal variation of ET a was more dependent on water conditions than ET 0. • Average WTD of 1.52 and 1.76 m contributed to 36.3 % and 26.2 % ET a in 2017 and 2018. Precise estimations of energy fluxes and evapotranspiration for cropland in arid areas with shallow groundwater are necessary but limited. There is also a need to better understand the contribution of groundwater for meeting crop water consumptive use. In this study, considering the environmental conditions, such as meteorological variables, crop growth and water regimes, energy fluxes and actual evapotranspiration (ET a) in an irrigated maize field with shallow groundwater were examined using eddy covariance system during two growing seasons. Due to the energy imbalance of the eddy covariance method, latent heat (LE) was adjusted using the Bowen ratio preservation of energy principle and subsequently very close (R2 = 0.94) to that measured by the Bowen-ratio-energy-balance system. For seasonal and diurnal variations, LE accounted for the highest proportion of net radiation (R n) from the jointing stage. While LE / R n was a little lower in 2018 than that in 2017 which may be because of the deeper groundwater table depth (WTD) in 2018. The negative sensible heat in the afternoon implied the occurrence of heat advection in the irrigated cropland. Energy fluxes and ET a were significantly affected by crop development when leaf area index was less than about 4 m2 m-2. Moreover, the increasing WTD from 1.2 to 2.2 m decreased LE by about 70 % and increased daily average Bowen ratio. From the jointing stage, total ET a was 522.1 and 453.8 mm in 2017 and 2018, respectively. The inter-seasonal variation in ET a was more dependent on water conditions than the potential evaporative demand. The water balance result showed that average WTD of 1.52 and 1.76 m for the growing period contributed to 36.3 % and 26.2 % ET a in 2017 and 2018, respectively. Besides, daily groundwater contribution between two seasons was different because of the differences in irrigation allocation and WTD. These results highlight the key effect of shallow groundwater to energy fluxes and water exchange of agroecosystem in arid areas. [ABSTRACT FROM AUTHOR]

Yield and production functions of sunflower (Helianthus annuus) were evaluated under full and deficit irrigation practices with the presence of shallow saline groundwater in a semi-arid region in the Imperial Valley of southern California, USA. A growing degree day (GDD) model was utilized to estimate the various growth stages and schedule irrigation events throughout the growing season. The crop was germinated and established using overhead irrigation prior to the use of a subsurface drip irrigation (SDI) system for the remainder of the growing season. Four irrigation treatments were implemented: full irrigation (100% full sunflower crop evapotranspiration, ETC), two reduced irrigation scenarios (95% ETC and 80% ETC), and a deficit irrigation scenario (65% ETC). The salinity of the irrigation water (EC) (Colorado River water) was nearly constant at 1.13 dS·m−1 during the growing season. The depth to groundwater and groundwater salinity (ECGW) were continuously monitored in five 3 m deep observation wells. Depth to groundwater fluctuated slightly under the full and reduced irrigation treatments, but drastically increased under deficit irrigation, particularly toward the end of the growing season. Estimates of ECGW ranged from 7.34 to 12.62 dS·m−1. The distribution of soil electrical conductivity (ECS) and soil matric potential were monitored within the active root zone (120 cm) at selected locations in each of the four treatments. By the end of the experiment, soil salinity (ECS) across soil depths ranged from 1.80 to 6.18 dS·m−1. The estimated groundwater contribution to crop evapotranspiration was 9.03 cm or approximately 16.3% of the ETC of the fully irrigated crop. The relative yields were 91.8%, 82.4%, and 83.5% for the reduced (95% and 80% ETC) and deficit (65% ETC) treatments, respectively, while the production function using applied irrigation water (IW) was: yield = 0.0188 × (IW)2 − 15.504 × IW + 4856.8. Yield reduction in response to water stress was attributed to a significant reduction in both seed weight and the number of seed produced resulting in overall average yields of 2048.9, 1879.9, 1688.1, and 1710.3 kg·ha−1 for the full, both reduced, and deficit treatments, respectively. The yield response factor, ky, was 0.63 with R2 = 0.745 and the irrigation water use efficiencies (IWUE) were 3.70, 3.57, 3.81, and 4.75 kg·ha−1·mm−1 for the full, reduced, and deficit treatments, respectively. Our results indicate that sunflowers can sustain the implemented 35% deficit irrigation with root water uptake from shallow groundwater in arid regions with a less than 20% reduction in yield. [ABSTRACT FROM AUTHOR]