INTEGRATED GEOPHYSICAL MAPPING OF GROUNDWATER AQUIFER FOR SPATIAL DISTRIBUTION OF GROUNDWATER DEVELOPMENT IN IPERINDO AND ITS ENVIRONS, SOUTHWESTERN NIGERIA

Assessment of groundwater potential of Iperindo area, Southwestern Nigeria was conducted by mapping spatial distribution of groundwater availability within the area and consequently locating areas of groundwater reserve to serve the community and its environs. This was achieved by integrating geophysical techniques involving landsat ETM-7 satellite data, aeromagnetic data, VLF-EM and electrical resistivity methods to delineate subsurface structures, understand the direction of groundwater flow, and detect the depth to groundwater aquifer. The result of landsat and aeromagnetic revealed some lineament intersection approximately NE-SW direction and interpreted to be potential sites for groundwater development. VLF-EM revealed geologic structures of significant hydrogeological importance at depths of 40 m to 200 m. Vertical electrical sounding (VES) confirmed high groundwater prospect in the areas with estimated depth to water table between 30 m and 100 m. The integrated results of the study revealed adequate groundwater spatial distribution for effective groundwater development in the area.

Depth to water table correction for initial carbon-14 activities in groundwater mean residence time estimation

Carbon-14 (14C) is routinely used to determine mean residence times (MRTs) of groundwater. 14C-based MRT calculations typically assume that the unsaturated zone is in equilibrium with the atmosphere, controlling the input 14C activity. However, multiple studies have shown that unsaturated zone 14C activities are lower than atmospheric values. Despite the availability of unsaturated zone 14C data, no attempt has been made to generalise initial 14C activities with depth to the water table. We utilise measurements of unsaturated zone 14C activities from 13 studies to produce a 14C–depth relationship to estimate initial 14C activities. The technique only requires the depth to the water table at the time of sampling or an estimate of depth to water in the recharge zone to determine the input 14C activity, making it straightforward to apply. Applying this new relationship to two Australian datasets (113 14C measurements in groundwater) shows that MRT estimates were up to 9250 years younger when the 14C–depth correction was applied relative to conventional MRTs. These findings may have important implications for groundwater samples that suggest the mixing of young and old waters and the determination of the relative proportions of young and waters, whereby the estimated fraction of older water may be much younger than previously assumed. Owing to the simplicity of the application of the technique, this approach can be easily incorporated into existing correction schemes to assess the sensitivity of unsaturated zone 14C to MRTs derived from 14C data.

Depth to water table correction for initial carbon-14 activities in groundwater mean residence time estimation

Carbon-14 (14C) is routinely used to determine mean residence times (MRTs) of groundwater. 14C-based MRT calculations typically assume that the unsaturated zone is in equilibrium with the atmosphere, controlling the input 14C activity. However, multiple studies have shown that unsaturated zone 14C activities are lower than atmospheric values. Despite the availability of unsaturated zone 14C data, no attempt has been made to generalise initial 14C activities with depth to the water table. We utilise measurements of unsaturated zone 14C activities from 13 studies to produce a 14C-depth relationship to estimate initial 14C activities. The technique only requires the depth to the water table at the time of sampling, or an estimate of depth to water in the recharge zone to determine the input 14C activity, making it straightforward to apply. Applying this new relationship to two Australian datasets (113 14C measurements in groundwater) shows that MRT estimates were up to 9250 years younger when the 14C-depth correction was applied relative to conventional MRTs. These findings may have important implications for groundwater samples that suggest the mixing of young and old waters and the determination of the relative proportions of young and waters, whereby the estimated fraction of older water may be much younger than previously assumed. Owing to the simplicity of the application of the technique, this approach can be easily incorporated into existing correction schemes to assess the sensitivity of 14Cuz to MRTs derived from 14C data.

Functional Performance of Parallel Drain Subsurface System in Waterlogged Paddy Field

Waterlogging induced salinity is a common problem in many command areas of irrigation projects. Subsurface drainage improves the productivity of poorly drained soils by decreasing the water table, providing greater soil aeration, improving root zone soil salinity and enhancing the crop yield. A pilot study has been conducted to explore the functional performance of the parallel drain subsurface system in waterlogged paddy field by considering the lateral drain spacing and drain depth are the factors influences the soil properties. This experiment was carried out in farmers’ field at Sembari village, Lalgudi, Tamil Nadu, India in waterlogged paddy field during October 2020 to February 2021. Treatments of this study consisted the combination of three lateral drains spacing of 7.5 m, 10.0 m and 12.5 m and two drain depths of 60 cm and 80 cm and a control plot. This study investigated the changes in soil properties, depth to water table, drainage coefficient and crop behaviors after installation of the system. Reduction in Soil pH, removal of slats in drain water, lowering the depth to water table and higher drainage coefficient recorded for narrow lateral drain spacing and deeper drain depth treatment has improved the root zone environment for crop growth. Paddy has been established very well in terms of plant height and number of tillers per plant in S1D2 (7.5 m drain spacing and 80 cm drain depth) treatment which was also reflected in grain yield and straw yield over undrained paddy field yield. Based on the results, it is recommended to install parallel drain subsurface system at 7.5 m drain spacing and 80 cm drain depth in the study area.

Past testate amoeba communities in landslide mountain fens (Polish Carpathians): The relationship between shell types and sediment

Landslide mountain fens formed in landslide depressions are dynamic environments as their development is disturbed by a number of factors, for example, landslides, slopewash, and surface run-off. These processes lead to the accumulation of mineral material and wood in peat. Disturbed peatlands are interesting archives of past environmental changes, but they may be challenging for providing biotic proxy-based quantitative reconstructions. Here we investigate long-term changes in testate amoeba communities from two landslide mountain fens – so far an overlooked habitat for testate amoeba investigations. Our results show that abundances of testate amoebae are extremely low in this type of peatlands, therefore not suitable for providing quantitative depth-to-water table reconstructions. However, frequent shifts of dominant testate amoeba species reflect dynamic lithological situation of the studied fens. We observed that high and stable mineral matter input into the peatlands was associated with high abundances of species producing agglutinated (xenosomic) as well as idiosomic shells which prevailed in the testate amoeba communities in both analyzed profiles. This is the first study that explores testate amoebae of landslide mountain fens in such detail, providing novel information about microbial communities of these ecosystems.

Evaluation of land suitability for citrus cultivation in Khana Local Government Area of Rivers State, Southern Nigeria

Soils of Khana Local Government Area of Rivers State, Southern Nigeria were evaluated using semi detailed soil survey for citrus cultivation. The purpose of this research was to evaluate the suitability of soils of the study area for the cultivation of citrus. The total land area covers 49,631.54 ha and was delineated into eight mapping units based on the soil types. One pedon each was dug in each mapping unit and described using the FAO system. The nonparametric method of soil suitability evaluation was used. Four soil orders, majorly Inceptisols/Cambisols, Entosols/Arenosols, Ultisols/Acrisols, and Alfisols/Lixisols, were identified in the area. The results showed that land requirements/characteristics such as climate (mean annual rainfall), wetness (depth to water table) and fertility made the land marginally suitable (S3) to not suitable (N) for citrus cultivation across the eight pedons. The three limitations for citrus cultivation in the area are climate (annual rainfall), wetness (depth to the water table) and fertility (low status of NPK and pH). The land is potentially suitable for citrus cultivation but currently marginally and not suitable due to these three limitations.

Dimensional Analysis of Transmissivity Equations and Comparison of Dependent Variables Using Birnin Gwari Aquifer Characteristics in Northern Nigeria

This study established relationship among three transmissivity equations using dimensional analysis, comparing three dependent variables inherent in the transmissivity equations, and use correlation analysis to examine the nature of interrelationship between drawdown and specific capacity in the Birnin-Gwari local government area of Kaduna State, Nigeria between October 2018 and October 2019. Relationship between three transmissivity equations, namely, Jacob, Logan and Babuskin was determined using dimensional analysis. The equations and the outcome were applied to the hydraulic data obtained from 26 producing boreholes in the study area. Comparison of the dependent variables, namely discharge, drawdown and hydraulic conductivity, was carried out to observe the relationship among them. The Correlation analysis was used to examine the nature of interrelationship between drawdown and specific capacity, while the plots of depth-to-water table and depth-to-basement were made to provide pictorial comparison between positions of water table and the underlying Basement. The results showed that the values computed from the Jacob method are the lowest among the three, while Logan method gave higher values, although they all trend in similar manner. The study revealed an inverse trend in the drawdown versus discharge and hydraulic conductivity. Correlation analysis between drawdown and specific capacity gave a regression coefficient of -0.593 and correlation coefficient of 0.352, indicating a weak relationship between them. The graphical relation of water level versus basement rock surfaces portend a near-parallel trend possibly determined by the underlying geology. Transmissivity values computed from the Babuskin method gave almost average values among the three methods. Both the regression and correlation coefficients gave low to average values between drawdown and specific capacity. The depth-to-basement versus depth-to-water plots showed that water table variations are probably controlled by the type and trend of basement topography.

DRAINMOD – Calibration and Validation for Prediction of Drainage Coefficient and Water Table Depth

DRAINMOD model predicts the effects of drainage and associated water management practices on water table depths and drainage coefficients. It simulates the performance of a given system for a long period of weather record. The field evaluation of this model has been carried out by comparing model predicted drain flow and depth to water table with the observed data collected from water table management system installed at A-block of Eastern Farm, Agricultural Engineering College and Research Institute Kumulur during the year 2015-2016. The comparison between predicted and observed drainage coefficient and depth to water table with treatment of different drain spacing (7.5, 10, 12.5 and 15 m) and drain depth (75 and 60 cm) is made. The statistical measures indicated that, there was a close relationship between predicted and observed drainage coefficient during the calibration and validation period as indicated by average root mean square error value ranges from 12.3 to 15.7 and 19.63 to 26.19 and average Chi-squared test value ranges from 0.010 to 0.725 and 0.01 to 0.28. Similarly for water table depth, the average root mean square value ranges from 7.630 to 17.20 and 16.67 to 21.54 and average Chi-squared test value ranges from 1.19 to 2.365 and 3.90 to 5.02.