Shallow Groundwater Table Research Articles

Geo-spatial technology based study on climate change impact and stewardship for rural India: A pragmatic approach for comprehensive groundwater resource mapping and management

Climate change may influence hydrogeological processes and groundwater resources directly and indirectly in various modes. Therefore, a systematic planning, management and adaption are challenging task. Considering the importance of climate change impact, the study was to identify the sustainable Groundwater (GW) / Drinking Water (DW) resources potential zones, suitable locations for GW harvesting structures, recommendation for GW quality management and GW extraction methods for Dhubri District of Assam, India and also with emphasis on Non-Covered (NC) and Partially-Covered (PC) habitations in the rural area of Dhubri District. The quality and quantity of GW/DW resources potential of the region is under extreme threat due to frequent flood, drought and population pressure. geographic information system (GIS) and Remote sensing (RS) technology along with on-field investigations were used to achieve the goal. GW availability is controlled by the local hydrogeomorphology, geology and geological structures of the area. Based on these controlling factors the GW resource Potential Zone Maps of the study area were prepared. Well inventorisation was also carried out including depth to water level, water level fluctuation, yield range and well-type, etc. It was found that more than half of the area falls under shallow GW table zone. The GW resource potential zones were successfully delineated based on Weightage Value (WV). The entire study area has been classified into various classes that is, excellent, very good, good, moderate and poor. To enhance and manage the GW resources in this area, GW recharge structures such as check-dams, percolation tanks and recharge-pits were suggested. Various types of GW extraction methods such as, Ring Well (RW), Tube Well(TW), Bore Well(BW) were recommended for this region.

Simazine transport in undisturbed soils from a vineyard at the Casablanca valley, Chile

Simazine is a soil-active herbicide that has been applied worldwide in agricultural soils, being the second most commonly detected herbicide in groundwater and surface waters. Although its use has been restricted in many countries of Europe, it is still applied in many locations around the world in orchards, vineyards and forestry. Therefore, it is important to study its fate and transport in the environment. This paper investigates simazine transport in undisturbed bare soils from a vineyard at the Casablanca valley, Chile. In the study site, shallow groundwater tables (<1.0 m depth) and high simazine levels (>15 μg L−1) in the groundwater were observed and thus, there is potential for simazine to be transported further away through the saturated zone. The soils from the study site were characterized and the hydrodynamic transport parameters were determined. Column leaching experiments showed that the two-site chemical non-equilibrium model correctly represented simazine transport. It was found that 36.3% of the adsorption sites achieve instantaneous equilibrium and that the first-order kinetic rate of the non-equilibrium sites was 6.2 × 10−3 h−1. Hydrus 2D was used to predict the transport of simazine in the study site under natural field conditions. Simulation results showed that simazine concentrations at depths shallower than 2.1 m are above the maximum contaminant level of 4 μg L−1 (defined by the U.S. Environmental Protection Agency). The timing of herbicide application was found to be important on simazine leaching and the main processes involved in simazine transport were degradation and adsorption, which accounted for 95.78 and 4.19% of the simulated mass of pesticide, respectively. A qualitative agreement in the timing and magnitude of simazine concentration was obtained between the simulations and the field data. Therefore, the model utilized in this investigation can be used to predict simazine transport and is a valuable tool to assess agricultural practices to minimize environmental impacts of simazine.

Water sources of shrubs grown in the northern Ningxia Plain of China characterized by shal-low groundwater table

Water sources of shrubs grown in the northern Ningxia Plain of China characterized by shal-low groundwater table

Mass-balance modeling of mineral weathering rates and CO2consumption in the forested, metabasaltic Hauver Branch watershed, Catoctin Mountain, Maryland, USA

Mineral weathering rates and a forest macronutrient uptake stoichiometry were determined for the forested, metabasaltic Hauver Branch watershed in north-central Maryland, USA. Previous studies of Hauver Branch have had an insufficient number of analytes to permit determination of rates of all the minerals involved in chemical weathering, including biomass. More equations in the mass-balance matrix were added using existing mineralogic information. The stoichiometry of a deciduous biomass term was determined using multi-year weekly to biweekly stream-water chemistry for a nearby watershed, which drains relatively unreactive quartzite bedrock. At Hauver Branch, calcite hosts ~38 mol% of the calcium ion (Ca2+) contained in weathering minerals, but its weathering provides ~90% of the stream water Ca2+. This occurs in a landscape with a regolith residence time of more than several Ka (kiloannum). Previous studies indicate that such old regolith does not typically contain dissolving calcite that affects stream Ca2+/Na+ ratios. The relatively high calcite dissolution rate likely reflects dissolution of calcite in fractures of the deep critical zone. Of the carbon dioxide (CO2) consumed by mineral weathering, calcite is responsible for approximately 27%, with the silicate weathering consumption rate far exceeding that of the global average. The chemical weathering of mafic terrains in decaying orogens thus may be capable of influencing global geochemical cycles, and therefore, climate, on geological timescales. Based on carbon-balance calculations, atmospheric-derived sulfuric acid is responsible for approximately 22% of the mineral weathering occurring in the watershed. Our results suggest that rising air temperatures, driven by global warming and resulting in higher precipitation, will cause the rate of chemical weathering in the Hauver Branch watershed to increase until a threshold temperature is reached. Beyond the threshold temperature, increased recharge would produce a shallower groundwater table and reduced chemical weathering rates. Copyright © 2013 John Wiley & Sons, Ltd.

Effect of Shallow Groundwater Table on the Moisture Depletion Pattern in Crop Root Zone

Effect of Shallow Groundwater Table on the Moisture Depletion Pattern in Crop Root Zone

Net Recharge vs. Depth to Groundwater Relationship in the Platte River Valley of Nebraska, United States

One-km resolution MODIS-based mean annual evapotranspiration (ET) estimates in combination with PRISM precipitation rates were correlated with depth to groundwater (d) values in the wide alluvial valley of the Platte River in Nebraska for obtaining a net recharge (Rn) vs. d relationship. MODIS cells with irrigation were excluded, yielding a mixture of predominantly range, pasture, grass, and riparian forest covers on sandy soils with a shallow groundwater table. The transition depth (dt ) between negative and positive values of the net groundwater recharge was found to be at about 2 (±1) m. Within 1 (±1) m of the surface and at a depth larger than about 7 to 8 (±1) m, the mean annual net recharge became independent of d at a level of about -4 (±12)% and 13 (±10)%, respectively, of the mean annual precipitation rate. The obtained Rn(d) relationship is based on a calibration-free ET estimation method and may help in obtaining the net recharge in shallow groundwater areas of negligible surface runoff where sufficient groundwater-depth data exist.

Coupled GSI-SVAT Model with Groundwater-Surface Water Interaction in the Riparian Zone of Tarim River

AbstractThe Tarim River is located in the arid areas of northwestern China, where groundwater (GW) and surface water (SW) in different landscape units have undergone regular and duplicate transformation processes, greatly improving the utilization of water resources. Investigation of the interaction between groundwater and surface water is critical to determine proper water resources planning and management in the Tarim River region. A new approach of coupling the soil-vegetation-atmosphere transport model (SVAT) with the groundwater-surface water interaction model (GSI) is presented in this paper. Usually, the surface water recharges to groundwater and groundwater-soil water exchange are not considered in the SVAT model. However, in reality, the soil water content profiles and soil heat profiles are intensely affected by shallow groundwater table, especially in arid riparian zones where groundwater levels fluctuate substantially. A new method linking the SVAT model with the GSI model is proposed in this ...

Runoff formation from experimental plot, field, to small catchment scales in agricultural North Huaihe River Plain, China

Abstract. Runoff formation at an experimental plot (1600 m2), a field (0.06 km2), and a small catchment (1.36 km2) with a shallow groundwater table and a dense drainage system in the agricultural North Huaihe River Plain (China) was analysed based on the observed rainfall, runoff, and groundwater table data of 30 storm events that occurred during the 1997 to 2008 flood seasons. The surface runoff was collected and measured at the outlet of the furrow of the experimental plot, whereas the total runoff was collected and measured at the outlets of the drainage ditches of the field and the small catchment. The present study showed that the relatively narrow range of rainfall amounts resulted in significantly different runoff amounts at the 3 scales. When the groundwater is close to the surface, the runoff amount is a large percentage of the total rainfall. The difference in rainfall and runoff amounts was regressed against changes in the groundwater table, and a significant linear relationship was determined. Significant rainfall-runoff relationships were indicated for the events divided into 3 groups according to the initial groundwater table depths (as indicators of the antecedent moisture conditions): less than 0.5 m, more than 2.1 m, or between 0.5 m and 2.1 m. These findings suggest that saturation excess surface flow dominated the runoff response, particularly when the groundwater table was shallow. For almost all events, the groundwater table rose above the bottom of the drainage ditch. The total runoff amounts were larger both at the field and at the catchment than at the plot with only the surface runoff collected, which shows a considerable contribution of subsurface flow. Groundwater table depth, which indicates antecedent moisture conditions and influences lateral sub-surface flow to the drainage ditches, is an important parameter that influences runoff formation in catchments, including the study area with a shallow groundwater table and a dense drainage system.

Spruce roots under heavy machinery loading in two different soil types

We studied the influence of soil compaction by heavy machinery (two-wheeled trailer with 0.2MPa pressure) on spruce roots at two sites in the Moravian Highlands with different soil properties to determine whether soil compaction by loading affects root water uptake. We also analysed the effects of the soil type and water-holding capacity with regards to root structure development. Site Jedovnice has a loamy to sandy–loamy soil texture with a shallow groundwater table at approximately 1m in depth. The roots are mostly distributed in deeper layers. Site Mraveniště has shallow, sandy–loamy soil overlying a granodiorite. This site has no access to groundwater and a higher proportion of shallow roots. To evaluate the effect of soil compaction, we installed heat-field-deformation sap flow sensors in the superficial roots and stem bases of trees close to machinery trails. Our results showed that loading mainly affected soils with a high proportion of shallow roots (33% of shallow roots at site Mraveniště; 22% at site Jedovnice). The number of roots treated by loading, verified after root opening with an air spade, depended on root positioning in soil. Acropetal sap flow occurred in roots in soil layers with sufficient available soil water. Some of the sampled trees exhibited decreased daytime sap flow after loading. In the shallower site Mraveniště the root responses to loading were also accompanied by water redistribution among the roots and between the roots and soil. Basipetal (reverse) flow was recorded in roots in dryer soil layers. Soil compaction due to loading substantially increased the magnitude and duration of redistributed flow between soil layers with different water contents. Determining the soil type and soil water content is recommended before choosing the machinery type for a given forest because the predicted tree root structure can be used to assess possible damage due to loading.

High resolution satellite imagery analysis for inferring surface–subsurface water relationships in unstable slopes

We investigate the instability of slopes in a 15.6km2 catchment area in the Southern Apennine mountains (Italy) traversed by a mid-slope road and characterized by predominance of clay-rich flysch units. High resolution multispectral satellite imagery is used to identify active landslides, to investigate their close association with seasonally wet zones (areas covered by free surface-water including ponds, migrating surface-water, seeps), as well as to guide subsurface hydrogeological investigations. By combining the remotely sensed surface information and the extensive subsurface dataset from over 40 monitoring piezometer boreholes we demonstrate that many wet zones initially mapped from the IKONOS imagery are indicative of sites with seasonally persistent very high groundwater levels within landslide-prone slopes and on intermittently active landslides. Where such surface–subsurface water linkage can be established, the appearance of the wet zones (fully saturated ground/soil) resulting from groundwater discharge or seepage can be used as a forewarning signal of the increased susceptibility to landsliding, since the hillslopes with shallow groundwater tables are generally more prone to failure. The information about changing surface-water conditions retrieved from high resolution satellite data timely acquired during rainy seasons can thus provide crucial input for temporal and spatial landslide hazard assessments. We anticipate that in the near future high resolution optical space-borne remote sensing will become a commonly used tool for monitoring landslide activity and for providing temporal series of spatial data necessary to improve our understanding of causative and triggering processes leading to slope failures.

Groundwater recharge under compacted agriculturalsoils, pineand prairie in Central Wisconsin, USA

The water table in Wisconsin Central Sand Plain (CSP) dropped 1.8 m between 2002 and 2010, and several lakes in the area suffer from low water levels. The lower groundwater level has been attributed to agricultural cropping practices, specifically irrigation, and a reduction in ground-water recharge. Dominant soils in this area are sands (Udipsamments). The objective of our research was to quantify groundwater recharge under (i) irrigated agricultural crops, (ii) prairie, and (iii) a 50-year old pine tree plantation in the CSP. Equipment was installed at five sites to monitor water table elevation, soil water content, and precipitation at 15-minute intervals. It was found that, when the soil was at field moisture capacity, precipitation during the growing season resulted in 1.4 cm more water table rise under a prairie than under irrigated agricultural fields. Agricultural crops used groundwater through irrigation, but natural vegetation relied on soil available water, and capillary rise of water from the shallow groundwater table (1 to 2 m to water table), for daily transpiration. After snowmelt, prairie vegetation yielded greater rise, up to 16 cm, in the water table than agricultural fields. Lack of crop residue on the soil surface of agricultural fields resulted in a continuous layer of frost in the soil profile that extended to about a meter depth. This thick, frozen layer was enhanced by greater soil compaction under irrigated crops compared to limited or no compaction in prairie areas. The key finding was that this deep frost in the soil profile inhibited snowmelt water from infiltrating and recharging the groundwater. Thus, compacted-irrigated agricultural soils in the CSP alter groundwater recharge characteristics during frozen and non-frozen ground periods. Increased crop residues on the surface of agricultural fields might enhance groundwater recharge during winter snow melt periods.

Geoseismological investigation of the January 26, 2001 Bhuj earthquake in western peninsular India

Of the intraplate seismic events, the January 26, 2001 Bhuj earthquake (Mw 7.7) would be remembered as one of the deadliest, in which 13,805 human lives were lost, 0.177 million injured and a total of 1,205,198 houses were fully or partly damaged in 16 districts of Gujarat state with an estimated overall loss of Rs. 284, 23 million. The brunt of the calamity was borne by five districts, namely Kachchh, Ahmadabad, Rajkot, Jamnagar and Surendranagar, where 99 % of the total casualties and damage occurred. In the neighbouring parts of Sindhh Province of Pakistan, 40 human casualties were reported, and some buildings cracked in the Karachi city as well. In the Kachchh district of Gujarat state, the telecommunication links and power supply were totally disrupted, road and rail links partially impaired and water supply snapped at many places. The Bhuj airbase had to be closed for some time due to damage to the infrastructure. The macroseismic survey carried out by the Geological Survey of India in an area as large as 1.2 million sq km indicated an epicentral intensity as high as X on the MSK scale in an area of 780 sq km in the central part of Kachchh rift basin. Apart from damages to civil structures, the January 26 earthquake induced conspicuous terrain deformation in the form of liquefaction features, structural ground deformation and low-order slope failures that were mainly prevalent within the higher intensity isoseists. Liquefaction occurred in an area of about 50,000 sq km. The extensive plains of Rann of Kachchh, the marshy tracts of the Little Rann and the shallow groundwater table zones of Banni Land provided the most conducive geotechnical environments for the development of seismites. The liquefaction activity was profuse in seismic intensity zones X and IX, widespread in intensity VIII, subdued in intensity VII and stray in intensity VI. The common forms of liquefaction were sand blows/boils, ground fissures, craters, lateral spreading and slumping. Ground deformation of tectonic origin was witnessed in the epicentral tract. Such features, though much less subdued in comparison with the 1819 large earthquake (Mw 7.8) in region, occurred along the Kachchh Mainland fault (KMF) and along a transverse lineament, referred to as Manfara–Kharoi fault. The manifestations were in the form of fractures, displacement of strata, linear subsidence, upheaval, formation of micro-basins/micro-ridges, ripping off of rock surface, and at places violent forms of liquefaction. The localities where coseismic deformations were observed include Bodhormora, Sikra, Vondh, Chobari, Manfara and Kharoi. The 2001 event has demonstrated the role of local geology in influencing the ground motion characteristics and, therefore, the hazard estimation.

Groundwater recharge under compacted agriculturalsoils, pineand prairie in Central Wisconsin, USA

The water table in Wisconsin Central Sand Plain (CSP) dropped 1.8 m between 2002 and 2010, and several lakes in the area suffer from low water levels. The lower groundwater level has been attributed to agricultural cropping practices, specifically irrigation, and a reduction in ground-water recharge. Dominant soils in this area are sands (Udipsamments). The objective of our research was to quantify groundwater recharge under (i) irrigated agricultural crops, (ii) prairie, and (iii) a 50-year old pine tree plantation in the CSP. Equipment was installed at five sites to monitor water table elevation, soil water content, and precipitation at 15-minute intervals. It was found that, when the soil was at field moisture capacity, precipitation during the growing season resulted in 1.4 cm more water table rise under a prairie than under irrigated agricultural fields. Agricultural crops used groundwater through irrigation, but natural vegetation relied on soil available water, and capillary rise of water from the shallow groundwater table (1 to 2 m to water table), for daily transpiration. After snowmelt, prairie vegetation yielded greater rise, up to 16 cm, in the water table than agricultural fields. Lack of crop residue on the soil surface of agricultural fields resulted in a continuous layer of frost in the soil profile that extended to about a meter depth. This thick, frozen layer was enhanced by greater soil compaction under irrigated crops compared to limited or no compaction in prairie areas. The key finding was that this deep frost in the soil profile inhibited snowmelt water from infiltrating and recharging the groundwater. Thus, compacted-irrigated agricultural soils in the CSP alter groundwater recharge characteristics during frozen and non-frozen ground periods. Increased crop residues on the surface of agricultural fields might enhance groundwater recharge during winter snow melt periods.

Comparison of indirect nitrous oxide emission through lysimeter drainage between an Andosol upland field and a Fluvisol paddy field

Indirect emission of nitrous oxide (N2O) due to nitrogen (N) leaching and runoff from agricultural soils is a major source of atmospheric N2O. To evaluate the effect of agricultural land use in combination with soil type on indirect N2O emission through groundwater, we compared the indirect N2O emission between an upland field of Andosol and a paddy field of Fluvisol in a 1-year lysimeter experiment. We established a shallow groundwater table during the non-flooded fallow period in the Fluvisol paddy field to simulate moisture conditions in a lowland soil. Drainage was 795 mm yr−1 (median, n = 6) in the Andosol upland field, versus 1583 mm yr−1 in the Fluvisol paddy field due to flooding during part of the year. The total leached nitrate in the Andosol upland field (4.24 g N m−2 yr−1) was comparable to that in the Fluvisol paddy field (5.57 g N m−2 yr−1). The total indirect N2O emission in the Fluvisol paddy field (88.6 mg N m−2 yr−1) was 55 times that in the Andosol upland field (1.62 mg N m−2 yr−1). The daily indirect N2O emission during the flooded period (0.239 mg N m−2 d−1) was comparable to that in the non-flooded period (0.156 mg N m−2 d−1) in the Fluvisol paddy field. The decrease in dissolved N2O concentration due to the flooding was offset by the increase in the drainage volume. The groundwater emission factors (EF5g) were 0.0003 in the Andosol upland field and 0.0160 in the Fluvisol paddy field versus the IPCC default value of 0.0025. Although the lysimeters had some limitations to simulate actual field conditions, the results indicate that agricultural land use in combination with soil type can strongly affect indirect N2O emission through groundwater.

EFFECT OF GROUNDWATER LEVEL DEPTH AND IRRIGATION AMOUNT ON WATER FLUXES AT THE GROUNDWATER TABLE AND WATER USE OF WHEAT

ABSTRACTThree irrigation water regimes (90.0, 67.5, and 45.0 mm) and five groundwater table depths (1.5, 2.0, 2.5, 3.0, and 3.5 m) were considered in a lysimeter experiment to investigate the effect of groundwater level and irrigation amount on water fluxes at the groundwater table and water use of wheat. Results show that deep percolation (irrigation of 16–23%) occurred to a considerable extent in the present irrigation level at a shallow groundwater table of 1.5–2.0 m. Capillary rise comprised 29% of the water use of wheat, within the period from regreening to harvest, at 1.5 m groundwater table depth, and was reduced with an increase in table depth. A relationship between groundwater contribution and groundwater table depth was also found. In the present irrigation conditions, the water productivity (WPb) of wheat was enhanced from 3.59 kg m‐3 at a shallower groundwater level depth of 1.5 m, to 4.58 kg m‐3 at a deeper groundwater level depth of 3.5 m. WPb can be higher if deficit irrigation is enforced and can reach 3.93–6.03 kg m‐3. Similarly, a relationship between WPb and groundwater table depth was found. Hence, the irrigation amount per time for local wheat can be reduced to 45.0–67.5 mm, depending on the groundwater level depth, in order to use water resources effectively. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Hierarchical controls on runoff generation: Topographically driven hydrologic connectivity, geology, and vegetation

Understanding the relative influence of catchment structure (topography and topology), underlying geology, and vegetation on runoff response is key to interpreting catchment hydrology. Hillslope‐riparian‐stream (HRS) water table connectivity serves as the hydrologic linkage between a catchment's uplands and the channel network and facilitates the transmission of water and solutes to streams. While there has been tremendous interest in the concept of hydrological connectivity to characterize catchments, few studies have quantified hydrologic connectivity at the stream network and catchment scales with observational data. Here we examine how catchment topography, vegetation, and geology influenced patterns of stream network HRS connectivity and runoff dynamics across 11 nested headwater catchments in the Tenderfoot Creek Experimental Forest (TCEF), MT. This study builds on the empirical findings ofJencso et al.(2009) who found a strong linear relationship (r2= 0.91) between the upslope accumulated area (UAA) and the annual duration of shallow groundwater table connectivity observed across 24 HRS transects (146 groundwater recording wells). We applied this relationship to the entire stream network across 11 nested catchments to quantify the frequency distribution of stream network connectivity through time, and quantify its relationship to catchment‐scale runoff dynamics. Each catchment's hydrologic connectivity duration curve (CDC) was highly related to its flow duration curve (FDC) and the slope of the relationship varied across catchments. The slope represents the streamflow yield per unit connectivity (Conyield). We analyzed the slope of each catchment's CDC‐FDC relationship or Conyield(annual, peak, transition, and base flow periods) in multiple linear regression models with common terrain, land cover vegetation, and geology explanatory variables. Significant predictors (p&lt; 0.05) across 11 catchments included the ratio of flow path distances and gradients to the creek (DFC/GTC), geology, and a vegetation index. The order and strength of these predictors changed seasonally and highlight the hierarchical controls on headwater catchment runoff generation. Our results highlight direct and quantifiable linkages between catchment topography, vegetation, geology, their topology, and hydrologic dynamics.

Total evaporation estimates from a Renosterveld and dryland wheat/fallow surface at the Voëlvlei Nature Reserve (South Africa)

Accurate quantification of the water balance, in particular evapotranspiration, is fundamental in managing water resources, especially in semi-arid areas. The objective of this study was to compare evaporation from endemic vegetation &ndash; Renosterveld &ndash; and a dryland wheat/fallow cropping system. The study was carried out in the mid-reaches of the Berg River catchment (South Africa), characterised by dryland salinity. Measurements of total evaporation from these 2 land uses were carried out with large aperture scintillometers during window periods from 2005 to 2007. Total evaporation was measured to be higher in Renosterveld than in wheat during the rainy winter season. In the dry summer season, total evaporation from Renosterveld was limited by soil water supply, and vegetation was under water stress. Spatial variability of total evaporation from both wheat/fallow land and Renosterveld was estimated using the Surface Energy Balance Algorithm for Land (SEBAL) model for 3 climatically different years. The scintillometer measurements were used to determine basal crop coefficients for long-term (20 years) simulations with the HYDRUS-1D model to assess temporal variability in total evaporation. Long-term simulations indicated that well-established, deep-rooted Renosterveld uses 39% more water than the shallowrooted wheat/fallow system. A change in land use from Renosterveld to dryland annual crops could therefore affect the soil water balance, cause shallow saline groundwater tables and degradation of soil and water resources.Keywords: evapotranspiration; large aperture scintillometer; Renosterveld; soil water balance; Surface Energy Balance Algorithm for Land (SEBAL); wheat/fallow system

A Comparison of Nitrate Distribution in Shallow Groundwater of Two Agricultural Areas in Sri Lanka and in Japan

This paper compares the effects of adding fertilizer in nitrate pollution of groundwater in the Udunuwara area in Sri Lanka and the Shiroishi Plain in Japan. Excessive application of nitrogen fertilizers to soils contributes to contamination of groundwater by nitrates. As nitrate is one of the most identified contaminant in groundwater several environmental protection agencies maximum contamination level for nitrate is 10 mg/l as NO3-N. The problem becomes severe in rural areas where people depend entirely on dug wells in the shallow groundwater table for their drinking water supply. Several locations were selected from the Udunuwara area of Sri Lanka for the detailed study. Nineteen shallow dug wells and 4 deep tube wells were selected for water sampling beginning of January to March 1998.Shiroishi Plain in Japan reclaimed from the Ariake Sea has a soil layer consisting of Ariake clay. The total 82 drug wells of average depth 1.5 m had been drilled around the area. Sample were collected in December 2000 and continued for one year around. Nitrate concentration in groundwater was measured by Cadmium reduction method.The results showed a varying nitrate distribution pattern compared to that the Udunuwara area. The effect of fertilizer application on groundwater depends on soil type, fertilizer type and amount used, crop type and climatic condition. The highly permeable soil around Udunuwara area showed that shallow groundwater is highly vulnerable for nitrate than the poorly drained soil of the Shiroishi Plain in Japan. As the people living in Shiroishi Plain use deep groundwater for domestic purposes, drinking water is safe (less than Maximum Contaminated Level for nitrate in drinking water for Japan-10 mg/l as NO3-N) as far as the nitrate contamination is concerned. The results of these studies suggest that applying the correct rate of N fertilizer at the optimum time would have a substantial effect on reducing nitrate-N losses. Key Words: Nitate Contamination; Groundwater; Land Reclamation; Fertilizer DOI: http://dx.doi.org/10.4038/suslj.v9i1.3736 Sabaramuwa University Journal, Volume 9 Number 1; December 2010, pp 81-95

Upward diffusion of nitrous oxide produced by denitrification near shallow groundwater table in the summer: a lysimeter experiment

Movement of nitrous oxide (N2O) produced in subsoil and shallow groundwater is important in determining the direct and indirect N2O emissions from agricultural soils. From the results of our previous study in a lysimeter-contained Gray lowland soil in the summer, we hypothesized that if a large amount of N2O is produced near shallow groundwater table in the summer, it will diffuse upward to the atmosphere. To examine this hypothesis, we conducted a one-year experiment in the same lysimeters for the cultivation of soybean–wheat double cropping (SW) or upland rice (UR). Dissolved N2O concentration in the drainage water in the UR plots exceeded 0.4 mg N L−1 in the summer, whereas that in the SW plots remained <0.1 mg N L−1. Analyses of the concentrations of nitrate and dissolved N2O in the drainage water and their nitrogen and oxygen isotopic compositions (δ15N and δ18O) during the summer revealed that denitrification was the main process for the N2O production near the groundwater table. There was a significant positive correlation between the dissolved N2O concentration and soil-surface N2O flux in the summer. Calculated upward diffusive N2O fluxes at three soil depths by Fick's law also supported our hypothesis. The δ15N values of N2O in the soil-surface flux were similar to those in the shallow groundwater in the UR plots during the summer. Such similarity was not found in the SW plots. We conclude that our hypothesis was confirmed by the above results. Comparison of the monitored data with other seasons indicates that low soil water content was a driving force for the upward N2O diffusion as well as the high dissolved N2O concentration.

Time-lapse processing of 2D seismic profiles with testing of static correction methods at the CO2 injection site Ketzin (Germany)

Abstract The Ketzin project provides an experimental pilot test site for the geological storage of CO2. Seismic monitoring of the Ketzin site comprises 2D and 3D time-lapse experiments with baseline experiments in 2005. The first repeat 2D survey was acquired in 2009 after 22 kt of CO2 had been injected into the Stuttgart Formation at approximately 630 m depth. Main objectives of the 2D seismic surveys were the imaging of geological structures, detection of injected CO2, and comparison with the 3D surveys. Time-lapse processing highlighted the importance of detailed static corrections to account for travel time delays, which are attributed to different near-surface velocities during the survey periods. Compensation for these delays has been performed using both pre-stack static corrections and post-stack static corrections. The pre-stack method decomposes the travel time delays of baseline and repeat datasets in a surface consistent manner, while the latter cross-aligns baseline and repeat stacked sections along a reference horizon. Application of the static corrections improves the S/N ratio of the time-lapse sections significantly. Based on our results, it is recommended to apply a combination of both corrections when time-lapse processing faces considerable near-surface velocity changes. Processing of the datasets demonstrates that the decomposed solution of the pre-stack static corrections can be used for interpretation of changes in near-surface velocities. In particular, the long-wavelength part of the solution indicates an increase in soil moisture or a shallower groundwater table in the repeat survey. Comparison with the processing results of 2D and 3D surveys shows that both image the subsurface, but with local variations which are mainly associated to differences in the acquisition geometry and source types used. Interpretation of baseline and repeat stacks shows that no CO2 related time-lapse signature is observable where the 2D lines allow monitoring of the reservoir. This finding is consistent with the time-lapse results of the 3D surveys, which show an increase in reflection amplitude centered around the injection well. To further investigate any potential CO2 signature, an amplitude versus offset (AVO) analysis was performed. The time-lapse analysis of the AVO does not indicate the presence of CO2, as expected, but shows signs of a pressure response in the repeat data.