Shallow Groundwater Conditions Research Articles

A preliminary groundwater investigation using geoelectrical resistivity survey in the Bengkalis Island, Indonesia

Groundwater resources are one of the natural resources that need to be preserved. The main problem of groundwater in coastal areas is the intrusion of seawater into the groundwater aquifer. The problem will be even more complex when the land is covered by peat soil. The purpose of this study was to investigate the potential of groundwater in the western part of Bengkalis Island. Geoelectrical resistivity data was taken with the Schumberger configuration with the increase in the electrode distance being varied to obtain accurate measurements. Groundwater samples were measured to obtain the physical character of the groundwater. The results show that groundwater close to the shoreline has been contaminated by the presence of seawater intrusion. However, in areas that are a bit far from the shoreline, the shallow aquifer groundwater conditions are still not contaminated by seawater. It can be concluded that the presence of seawater in the aquifer is caused by the trapping of seawater in the aquifer during sediment deposition in the past.

Glyphosate and AMPA dynamics during the transition towards conservation agriculture: Drivers under shallow groundwater conditions

The environmental fate of glyphosate and its metabolite AMPA were investigated in buried lysimeters in a factorial combination of two cropping systems (conservation and conventional agriculture) and two water table depths (120 and 60 cm). Glyphosate was applied at a rate of 1.44 kg ha−1 a.i., and pore-water was sampled for 48 non-consecutive days along the soil profile (15, 30 and 60 cm) as well as the groundwater. Glyphosate and AMPA concentration in soil was detected to compare the effect of different soil-crop managements on transformation/dissipation dynamics and a full characterization of the soil profile was performed. Freundlich adsorption coefficients were calculated down to 110 cm depth and correlated to laboratory-estimated soil properties. Clay minerals, soil organic carbon, phosphate content, Al and Fe amount were the driving factors influencing most of the glyphosate sorption, regardless of the crop and water management system that did not differentiate between adsorption dynamics. In contrast, conservation practices differently affected glyphosate concentration in the soil profile, although its adoption was limited to two years. Moreover, the occurrence of a shallow water table influenced glyphosate transport in the vadose zone, and its detection in groundwater supported the hypothesis of fast transport of the molecule as mediated by preferential pathways, compromising groundwater quality, especially in agricultural lands. On the contrary, AMPA has never been detected in the groundwater, giving evidence of a diverse adsorption and transport dynamic compared to glyphosate.

Effects of different shallow and saline groundwater depths on soil salinity, evapotranspiration, grain yield and spike traits of winter wheat

AbstractThe 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 D2and D1compared to D3was 20.9% and 30.7%, respectively, while the decrease for S2, S3and S4compared to S1was 11.8%, 18.0% and 25.1%. The highest evapotranspiration was found in the D3S1treatment (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 D1S4treatment. Thus, a GWD at 80 cm with 0.38 dSm−1GWS 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−3in the first season and from 1.18 to 1.73 kg m−3in 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−1GWS 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−1GWS 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.

Wet Grassland Sites with Shallow Groundwater Conditions: Effects on Local Meteorological Characteristics

Agriculturally used wet grassland sites (WGSs) with shallow water tables are considered to be sites with a special microclimate. Meteorological measurement series, examining the air temperature (Ta) and vapour pressure (VP) in three regions, reveal differences between WGSs and outside the lowland. The results show that the average annual Ta at all three WGSs is significantly lower than in their surrounding area (0.7 to 1.0 K). The differences are minimally larger in the summer half-year than in the winter half-year (1.0 vs. 0.7 K in the Spreewald region, 0.7 vs. 0.6 K in the Havelland region). The differences cannot only be explained by higher evapotranspiration (ET), but are mainly due to the ground heat balance of the sites with shallow water tables and organic soils. The VPs of the WGSs and the surrounding area only differ significantly from each other in the summer months and do not vary as clearly as the Ta. While the VP is higher in the Spreewald wetland than in the surrounding area (+0.05 kPa), it is lower in Paulinenaue than in that surrounding area (−0.04 kPa). The reason for this is different ET due to the different site conditions.

A Machine Learning Approach to Predict Groundwater Levels in California Reveals Ecosystems at Risk

Groundwater dependent ecosystems (GDEs) are increasingly threatened worldwide, but the shallow groundwater resources that they are reliant upon are seldom monitored. In this study, we used satellite-based remote sensing to predict groundwater levels under groundwater dependent ecosystems across California, USA. Depth to groundwater was modelled for a 35-years period (1985–2019) within all groundwater dependent ecosystems across the state (n = 95,135). Our model was developed within Google Earth Engine using Landsat satellite imagery, climate data, and field-based groundwater data [n = 627 shallow (< 30 m) monitoring wells] as predictors in a Random Forest model. Our findings show that 1) 44% of groundwater dependent ecosystems have experienced a significant long-term (1985–2019) decline in groundwater levels compared to 28% with a significant increase; 2) groundwater level declines have intensified during the most recent two decades, with 39% of groundwater dependent ecosystems experiencing declines in the 2003–2019 period compared to 27% in the 1985–2002 period; and 3) groundwater declines are most prevalent within GDEs existing in areas of the state where sustainable groundwater management is absent. Our results indicate that declining shallow groundwater levels may be adversely impacting California’s groundwater dependent ecosystems. Particularly where groundwater levels have fallen beneath plant roots or streams thereby affecting key life processes, such as forest recruitment/succession, or hydrological processes, such as streamflow that affects aquatic habitat. In the absence of groundwater monitoring well data, our model and findings can be used to help state and local water agencies fill in data gaps of shallow groundwater conditions, evaluate potential effects on GDEs, and improve sustainable groundwater management policy in California.

Investigasi kondisi airtanah dengan geolistrik: studi kasus endapan aluvial di Bengalon Kutai Timur, Provinsi Kalimantan Timur Indonesia

Bengalon is located in East Kutai Regency, East Kalimantan Province. Bengalon is included in the Samarinda-Bontang groundwater basin. The development of agricultural and industrial areas, followed by an increase in residential areas, will cause an increase in the water demand. This study aims to determine the groundwater potential of alluvial areas using the resistivity geoelectric method. The resistivity survey resulted in subsurface lithology, shallow groundwater conditions in the form of depth, thickness, and location of the aquifer as well as the type of groundwater quality. There are 10 locations for geoelectric data collection using the 2D geoelectric method. The results showed that the majority of the aquifers were alluvial deposits consisting of sand and sandy clay. The resistance indicating groundwater is 1 - 4 Ω m, at a depth of 10 – 50 m with a thickness varying from 10 – 20 m which has been dominated by sand. The presence of sea water intrusion in aquifers causes the quality of groundwater to tend to be brackish because the research location is in a swamp area bordering the coast.

Testing the EPIC Richards submodel for simulating soil water dynamics under different bottom boundary conditions

AbstractMost biogeochemical models simulate water dynamics using the tipping bucket approach, which has been often found to be too simplistic to represent vadose zone dynamics adequately under shallow groundwater conditions. Recently, a solution to the Richards equation using the Mualem–van Genuchten model (Rich‐vGM) has been added into the EPIC (Environmental Policy Integrated Climate) model to address this shortfall. Its performance was tested using lysimeters operating under free drainage (FD) and at a shallow water table (60‐ [WT60] and 120‐cm depth [WT120]). Model accuracy was also compared with the upgraded tipping bucket‐based method implemented into EPIC (the variable saturation hydraulic conductivity method [VSHC]). Soil water content (SWC) data were split into calibration and validation subsets. Model evaluation also included annual evapotranspiration (ET), percolation (PRK), and upward water movements to assess underlying soil water balance factors. The submodels provided accurate and similar results upon comparison with SWC measures under FD (Nash–Sutcliffe coefficient [NSE] = 0.26 and 0.61 using VSHC and Rich‐vGM, respectively). The Rich‐vGM model accurately reproduced observed SWC and ET (e.g., NSE = 0.70 and percentage bias [PBIAS] = −3.7% for WT120, respectively) although it slightly overestimated PRK (PBIAS = 47.8%, on average). Instead, VSHC proved unable to correctly simulate shallow groundwater conditions (e.g., NSE = −1.85 for WT60 SWC). Under shallow groundwater conditions, the Rich‐vGM method is recommended, despite the additional data required and the need to define the bottom boundary conditions according to water table fluctuations. In conclusion, the Richards solver introduced and tested in EPIC improved the model's ability to represent complex biophysical and biogeochemical processes in terrestrial ecosystems associated with the hydrological balance.

Geophysical assessment of open dumpsite nearby Khamis Mushait industrial zone, Southwestern Saudi Arabia

Vertical electrical soundings, seismic refraction tomography, and ground magnetic measurements were taken or conducted close to an open dumpsite near Khamis Mushait, southwestern Saudi Arabia, which is characterized by shallow groundwater conditions. Structurally, intersected series of north- to northwest-trending faults affect the area. A new urban expansion and the Khamis Mushait industrial zone are close to the open dumpsite. This study evaluates the potential for leachate intrusion into groundwater aquifers. The results of electrical soundings reveal four geoelectric units: the topsoil, weathered layer, partly weathered/fractured basement, and fresh basement bedrock. At the dumpsite, relatively low resistivity values that are less than 30 Ωm characterize the topsoil, weathered layer, and partly weathered/fractured basement because of conductive leachate from the dumpsite. Besides, the results of ground magnetic data indicate that the deformation of varying intensities affects the dumpsite area, resulting in fractures developing in the N–S, NE–SW, NW–SE, and, to a lesser extent, E–W directions. Moreover, geoseismic tomographic models illustrate a low P-wave velocity zone corresponding to a low resistivity zone, and a NE–SW fault was identified from geoseismic cross-sections. Finally, these fractures and faults could become contaminant pathways for shallow aquifers around the dumpsite. To minimize the impact of such leachate, from a dumpsite, on groundwater quality and the environment in general, the dumpsite must be properly designed, constructed, and managed using engineering principles.

Modelling the Impacts of Climate Change on Shallow Groundwater Conditions in Hungary

The purpose of the present study was to develop a methodology for the evaluation of direct climate impacts on shallow groundwater resources and its country-scale application in Hungary. A modular methodology was applied. It comprised the definition of climate zones and recharge zones, recharge calculation by hydrological models, and the numerical modelling of the groundwater table. Projections of regional climate models for three different time intervals were applied for the simulation of predictive scenarios. The investigated regional climate model projections predict rising annual average temperature and generally dropping annual rainfall rates throughout the following decades. Based on predictive modelling, recharge rates and groundwater levels are expected to drop in elevated geographic areas such as the Alpokalja, the Eastern parts of the Transdanubian Mountains, the Mecsek, and Northern Mountain Ranges. Less significant groundwater level drops are predicted in foothill areas, and across the Western part of the Tiszántúl, the Duna-Tisza Interfluve, and the Szigetköz areas. Slightly increasing recharge and groundwater levels are predicted in the Transdanubian Hills and the Western part of the Transdanubian Mountains. Simulation results represent groundwater conditions at the country scale. However, the applied methodology is suitable for simulating climate change impacts at various scales.

Design measures to mitigate the impact of shallow groundwater on hydrologic performance of permeable pavements

AbstractPermeable pavements (PPs) are widely implemented in urban areas to mimic natural hydrologic processes through enhancing infiltration, and reducing, delaying, and retaining surface runoff. However, its performance can be affected by shallow groundwater since high soil moisture may inhibit its infiltration and exfiltration. This study built a numerical model, which was calibrated and validated based on laboratory experiment data, to evaluate the water balance and retention of PP in shallow groundwater conditions. It assessed the impacts of shallow groundwater and the hydrologic effectiveness of different PP design measures (i.e., building a PP with a smaller storage depth, implementing an underdrain at different elevations, and installing an impermeable liner) on relieving the impacts. Shallower groundwater led to larger amounts of surface runoff and underdrain flow, and a higher chance of saturating the PP reservoir. The three design measures had both benefits and drawbacks in mimicking natural hydrologic cycle and retaining the performance of PP under extreme conditions (e.g., areas of very shallow groundwater tables and/or extreme rainfalls). A PP with a smaller storage depth resulted in less underdrain flow but was prone to saturation. It is, thus, more recommended for PP with more‐permeable subsoils, which can avoid frequent pavement saturation. Although a shallower PP corresponds to a smaller storage volume and shorter hydraulic retention time, it can increase the applicability of PP to shallow groundwater areas, which is beneficial to the regional hydrologic environment. Installing an underdrain generated underdrain flow, which is a burden to the downstream drainage system. However, it significantly reduced the surface runoff and the chance of saturating the PP reservoir, which, thus, is more recommended for PP with less‐permeable subsoils. Comparatively, elevating the underdrain is recommended in areas of shallow groundwater because it can reduce the frequency and amount of groundwater‐induced underdrain flow. In addition, a higher underdrain together with an impermeable liner can create a storage depth, increase the retention duration, enhance exfiltration and evaporation without increasing the saturation risk.

A field-validated surrogate crop model for predicting root-zone moisture and salt content in regions with shallow groundwater

Abstract. Optimum management of irrigated crops in regions with shallow saline groundwater requires a careful balance between application of irrigation water and upward movement of salinity from the groundwater. Few field-validated surrogate models are available to aid in the management of irrigation water under shallow groundwater conditions. The objective of this research is to develop a model that can aid in the management using a minimum of input data that are field validated. In this paper a 2-year field experiment was carried out in the Hetao irrigation district in Inner Mongolia, China, and a physically based integrated surrogate model for arid irrigated areas with shallow groundwater was developed and validated with the collected field data. The integrated model that links crop growth with available water and salinity in the vadose zone is called Evaluation of the Performance of Irrigated Crops and Soils (EPICS). EPICS recognizes that field capacity is reached when the matric potential is equal to the height above the groundwater table and thus not by a limiting hydraulic conductivity. In the field experiment, soil moisture contents and soil salt conductivity at five depths in the top 100 cm, groundwater depth, crop height, and leaf area index were measured in 2017 and 2018. The field results were used for calibration and validation of EPICS. Simulated and observed data fitted generally well during both calibration and validation. The EPICS model that can predict crop growth, soil water, groundwater depth, and soil salinity can aid in optimizing water management in irrigation districts with shallow aquifers.

Short and Long-Term Field Performances and Optimal Timing of Chip Seal in Hot and Humid Climates

Chip seal is a preventive maintenance technique typically applied on relatively low traffic roads to reduce pavement deterioration rate and to defer the need for costly rehabilitation activities. This study aims to address the common challenges with chip seal application in hot and humid climates such as Louisiana to ensure the maximum benefits are achieved. Specifically, this study evaluated the short and long-term field performances and optimal timing of chip seal by analyzing the cracking, roughness, and overall pavement conditions of 47 flexible and composite pavement sections in Louisiana. Furthermore, potential moisture damage in asphalt concrete after chip seal application was assessed. Results indicated that chip seal extended pavement service life by 4–17 years based on the pre-treatment pavement conditions and pavement type (flexible or composite). Based on the cost benefit analysis, it is recommended to use alternating cycles of asphalt overlay and chip seal on low volume roads (less than 5,300 vehicles per day) with chip seal applied when the pavement condition index (PCI) of the pavement drops to a value between 70 and 74. In this case, significant monetary savings could be achieved when compared with adding chip seals at different time periods (outside the recommended range of PCI between 70 and 74). Results also showed that the application of chip seal does not seem to contribute to moisture damage. Instead, shallow groundwater conditions present in the State seem to contribute to moisture damage in asphalt pavements owing to moisture entrapment underneath the asphalt layer.

Site Selection of Aquifer Thermal Energy Storage Systems in Shallow Groundwater Conditions

: Underground thermal energy storage (UTES) systems are well known applications around the world, due to their relation to heating ventilation and air conditioning (HVAC) applications. There are six kinds of UTES systems, they are tank, pit, aquifer, cavern, tubes, and borehole. Apart from the tank, all other kinds are site condition dependent (hydro-geologically and geologically). The aquifer thermal energy storage (ATES) system is a widespread and desirable system, due to its thermal features and feasibility. In spite of all the advantages which it possesses, it has not been adopted in very shallow groundwater (less than 2 m depth) regions, till now, due to the susceptibility of the storage efficiency of these systems to the in-site parameters. This paper aims to find a reliable method that can be used to find the best location to install ATES systems. The concept of the suggested method is based on integrating three methods. They are, the analytical hierarchy process (AHP), the DRASTIC index method, and ArcMap/GIS software. The results from this method include a criterion that summarizes the best location to install an ATES system. This criterion is depicted by ArcMap/GIS software, producing raster maps that specify the best location for the storage system. The suggested method can be used to find the best location to install the thermal storage, especially in susceptible aquifers.

Modeling shallow groundwater nitrate concentrations by direct coupling of the vadose and the saturated zone

In many aquifers in plains and valley basins, water movement and solute fate in the vadose zone is described without considering the actual depth of the groundwater table. However, for shallow groundwater conditions (i.e., when the water table is few meters below the ground surface), there is a feedback from the groundwater table on the soil moisture content which influences plant growth and evapotranspiration. Thus, an interactive coupling between vadose zone and groundwater processes is needed. In this research the implementation of a time step-based (direct) coupling between the soil water movement and nitrogen fate model SIMWASER/STOTRASIM and the groundwater flow and solute transport model FEFLOW is shown and applied to a part of an aquifer in southeast Austria. At the aquifer scale, areas with time step-based coupling are combined with areas of sequential coupling to account for shallow groundwater levels. To speed up the computation of vadose zone processes, a clustering approach is developed by grouping elements of similar groundwater level and nitrate concentrations time series together. Through the comparison between direct and sequential coupling results, it is demonstrated that including the feedback in the coupling reduces simulated nitrate concentrations by about 10%. Thus, if shallow groundwater conditions exist, the time step-based approach allows considering the interaction between vadose and saturated processes, which may lead to improved compromises between agricultural land use and groundwater protection.

Improving Irrigation Scheduling of Wheat to Increase Water Productivity in Shallow Groundwater Conditions Using Aquacrop

AbstractIrrigation scheduling plays a key role in increasing crop production and controlling soil salinity in arid and semi‐arid regions. Inappropriate irrigation scheduling is considered an effective factor in low water productivity and soil salinization in central and southern parts of Khuzestan. Therefore, the aim of this research was to improve irrigation scheduling in order to increase water productivity and maintain the water and salt balance in a district in central Khuzestan. AquaCrop was selected as the research model, and the effects of the scenarios on wheat grain yield, water productivity, salt and water content in an effective root zone, and salt content moved upward from the groundwater table by capillary rise were compared with each other. Various scenarios of irrigation scheduling were simulated for a 12‐year period (2003–2014). To collect the required data for calibration and validation of the model, a field experiment was carried out during the wheat growing season (2014–2015). The results of the model evaluation indicated that it was an appropriate one for simulating the water and salt balance in the soil and wheat grain yield under different irrigation scheduling scenarios in experimental conditions. Finally, the recommended irrigation scheduling for wheat was seven times of irrigation with 550 mm water consumption. © 2018 John Wiley & Sons, Ltd.

Simulating the hydrological performance of low impact development in shallow groundwater via a modified SWMM

Low impact development (LID) practices are effective in restoring natural hydrological processes, but they may be affected by groundwater and pose additional risk to groundwater dynamics and contamination in shallow groundwater conditions. Their performance in shallow groundwater is not well understood due to monitoring difficulty and the deficiency of modeling tools. The Storm Water Management Model (SWMM) is an urban hydrology-hydraulic model that has been widely used to evaluate the performance of LID practices. However, it cannot accurately simulate the hydrological processes of LID practices in shallow groundwater. This study presents the development, calibration, validation, and testing of a modified SWMM (SWMM-LID-GW) that incorporates groundwater feedbacks into LID simulations. The hydrological performance of LID practices under different environmental conditions was simulated, based on which the impacts of initial groundwater table depth, rainfall type, and in-situ soil type were evaluated, and a number of general nonlinear multivariate formulas were proposed to predict the hydrologic performance of LID practices in shallow groundwater environment and support the feasibility analysis of LID practices before project implementation. The reduction of exfiltration and increase of groundwater drainage in shallow groundwater accounted for a significant proportion of the water budget of LID practices. The influence of shallow groundwater was greater for shallower groundwater tables, in less permeable in-situ soils, and for events of higher intensities and longer durations. However, due to the dominant role of shallow groundwater, the impacts of both rainfall type and in-situ soil type on the hydrological performance of LID practices in shallow groundwater were minimal in general, in contrast to the impacts on deep groundwater tables. The SWMM-LID-GW outperformed the current SWMM for a wide range of groundwater conditions, particularly for locations in which the groundwater table frequently rises to 1.0 m or less below ground.

Impact of agricultural water-saving practices on regional evapotranspiration: The role of groundwater in sustainable agriculture in arid and semi-arid areas

Evapotranspiration (ET) is an important component of the water budget process and is characterized by complex spatiotemporal changes, especially in irrigated agricultural areas. The impact of various hydrological processes and human activities on ET is still a meaty theme to study and investigate. A typical agricultural irrigation district with shallow groundwater and arid climate conditions was selected as the case study area in this work. The impact of the supplied irrigation water, shallow groundwater, crop planting pattern, and weather conditions on regional ET was determined after the regional ET was estimated by a Surface Energy Balance Algorithm of Land (SEBAL) model with Moderate Resolution Imaging Spectroratiometer (MODIS) data. The results show that the regional ET in Hetao kept declining in the past 15 years. The positive correlation between the water input (water diversion and precipitation) and ET indicated that reduced water diversion controls the declining ET, also causing the drop of groundwater level. Due to capillary forces and root uptake, the shallow groundwater tended to move upward to support the crop water consumption because the soil suffered from a water deficit. Furthermore, we quantified the contribution of shallow groundwater to regional ET and found that the water supplied from shallow groundwater increased from 5% to 15% during the period of water–saving irrigation. However, the long–term decrease of irrigation water supply and groundwater level caused a soil water deficit over the crop growth period, and the variation of crop planting pattern reduced ET as well. Therefore, groundwater plays an important role in sustainable agricultural development in arid and semiarid areas and the contribution of shallow groundwater to regional water consumption cannot be neglected.

Incorporating Influences of Shallow Groundwater Conditions in Curve Number-Based Runoff Estimation Methods

Runoff generation process in any watershed is mainly affected by precipitation, land use and land cover, existing soil moisture conditions and losses. Shallow groundwater table conditions that occur in many regions are known to affect the soil moisture retention capacity, infiltration and ultimately the runoff. A methodology that links soil moisture capacity to the shallow groundwater table or High-Water Table (HWT) using a nonlinear functional relationship within a curve number (CN)-based runoff estimation method, is proposed and investigated using single and continuous event simulation models in this study. The relationship is used to obtain an adjusted CN that incorporates the effect of change in soil moisture conditions due to HWT. The CN defined for average conditions is replaced by this adjusted CN and is used for runoff estimation. A single event model that uses Soil Conservation Service (SCS) CN approach is used for evaluation of variations in runoff depths and peak discharges based on different HWT conditions. A real-life case study from central Florida region in the USA was adopted for application and evaluation of the proposed methodology. Results from the case study application of the models indicate that HWT conditions significantly influence the magnitudes of peak discharge by as much as 43% and runoff depth by 48% as the water table height reaches the land surface. The magnitudes of increases in peak discharges are specific to case study region and are dependent on the functional form of the relationship linking HWT and soil storage capacity. Also, for specific values of HWT, an equivalency between HWT-based CN and wet antecedent moisture condition (AMC)-based CN can be established.

How shallow water table conditions affect N2O emissions and associated microbial abundances under different nitrogen fertilisations

Globally, agriculture is the largest source of nitrous oxide (N2O), a potent greenhouse gas (GHG). A recognised tool to prevent its loss from agricultural soils is the presence of a shallow water table. A four-year lysimeter experiment (2011–2014) was conducted in northeast Italy to investigate how water table levels affect N2O emissions after different N fertilisation techniques. Soil surface flux and groundwater-dissolved N2O were studied under free drainage and at two shallow water table levels (60 cm and 120 cm) and at two levels of N input (250 and 368 kg N ha−1 y−1), using dry manure in 2011 and 2012 and fresh manure in 2013 and 2014. DNA was extracted from soils and quantitative PCR (qPCR) was used to assess the size of nitrifying, denitrifying and N2-fixing bacterial communities. at three soil depths. The day after pre-seeding fertiliser incorporation, N2O emission started to be detected and continued for two-three weeks; brief measurable emissions also followed top–dressing fertilisation events. Cumulative N2O emission measured between 0.97 and 2.33 kg N2O-N ha−1 y−1, corresponding to emission factors from 0.4% to 1.1%. Manure fertilisation significantly affected the N dose only when applied as fresh manure. Water-filled pore space (WFPS) affected daily N2O emissions with a significant interaction with fertilisation level. The two N input levels showed differences only when WFPS was >40%, which revealed N availability as key to increased N2O emissions at high water content, supposedly by fostering anaerobic denitrification. No significant relationships were observed between peak N2O emissions and the values of the temperature or irrigation variables recorded during the experimental observation period. Groundwater dissolved N2O-N concentrations measured about 1.7 μg L−1 with some peak variability from nitrate leaching. Quantitative PCR assays demonstrated that shifts in microbial population that can be involved in oxidation processes and heterotrophic denitrification occurred in the soil, even though the contributions of the different N pathways on N2O emissions were indistinguishable. Indeed, both nitrifying and denitrifying genes were simultaneously promoted by the high fertilisation input and hindered by the high water table level. Shallow groundwater conditions appeared to reduce N2O emissions probably by favouring complete denitrification. These results suggest that in the Po Plain, regulated by the Nitrate Directive, shallow groundwater conditions, with a balanced N input, may mitigate air and water pollution.

The characteristic and influence factors of extinction depth of shallow groundwater on the high-latitude region: a case study on the Sanjiang Plain, northeast China.

Accurate estimation of extinction depth of shallow groundwater (EDSG) and identification of its influence factors are important for sustainable management of groundwater resources, ecological protection, and human health in intensively irrigated region. In this study, the ratio of actual groundwater depth and EDSG (RAE) method was used to understand the spatial variability of EDSG in the Sanjiang Plain, one of China's largest grain production bases and China's largest inland freshwater wetland region. The study showed a large spatial variation of EDSG in the region. Spatially, the sites, which were in the northeast and center had the deepest and the shallowest EDSG, whereby, indicate that it has higher and lower pumping potential capacity. Many factors including climate, soil parameters, vegetation and topography affected the EDSG. We also identified an area of 3.86 × 1010m2, which accounting for 35.3% of the entire Sanjiang Plain, has exceeded the ESGD by over exploited for years. Knowledge of the variation and influence factors of EDSG for a certain plant system and the current shallow groundwater condition in the higher latitude region can be a key to the development of preventive actions for large quantity pumping groundwater and protection regional and sustainable development of irrigated agriculture.