Journal of Groundwater Science and Engineering

Evaluation of groundwater resource potential by using water balance model: A case of Upper Gilgel Gibe Watershed, Ethiopia

Wondmagegn Taye Abebe

2022, 10(3): 209-222. doi: 10.19637/j.cnki.2305-7068.2022.03.001

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Abstract:
Groundwater resource potential is the nation’s primary freshwater reserve and accounts for a large portion of potential future water supply. This study focused on quantifying the groundwater resource potential of the Upper Gilgel Gibe watershed using the water balance method. This study began by defining the project area’s boundary, reviewing previous works, and collecting valuable primary and secondary data. The analysis and interpretation of data were supported by the application of different software like ArcGIS 10.4.1. Soil water characteristics of SPAW (Soil-plant-air-water) computer model, base flow index (BFI+3.0), and the water balance model. Estimation of the areal depth of precipitation and actual evapotranspiration was carried out through the use of the isohyetal method and the water balance model and found to be 1 664.5 mm/a and 911.6 mm/a, respectively. A total water volume of 875 829 800 m³/a is estimated to recharge the aquifer system. The present annual groundwater abstraction is estimated as 10 150 000 m³/a. The estimated specific yield, exploitable groundwater reserve, and safe yield of the catchment are 5.9%, 520 557 000 m³/a, and 522 768 349 m³/a respectively. The total groundwater abstraction is much less than the recharge and the safe yield of the aquifer. The results show that there is a sufficient amount of groundwater in the study area, and the groundwater resources of the area are considered underdeveloped.

Transformation of ammonium nitrogen and response characteristics of nitrifying functional genes in tannery sludge contaminated soil

Xiang-ke Kong, Zi-xuan Zhang, Ping Wang, Yan-yan Wang, Zhao-ji Zhang, Zhan-tao Han, Li-sha Ma

2022, 10(3): 223-232. doi: 10.19637/j.cnki.2305-7068.2022.03.002

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Abstract:
High concentrations of ammonium nitrogen released from tannery sludge during storage in open air may cause nitrogen pollution to soil and groundwater. To study the transformation mechanism of NH₄⁺-N by nitrifying functional bacteria in tannery sludge contaminated soils, a series of contaminated soil culture experiments were conducted in this study. The contents of ammonium nitrogen (as NH₄⁺-N), nitrite nitrogen (as NO₂⁻-N) and nitrate nitrogen (as NO₃⁻-N) were analyzed during the culture period under different conditions of pollution load, soil particle and redox environment. Sigmodial equation was used to interpret the change of NO₃⁻-N with time in contaminated soils. The abundance variations of nitrifying functional genes (amoA and nxrA) were also detected using the real-time quantitative fluorescence PCR method. The results show that the nitrification of NH₄⁺-N was aggravated in the contaminated silt soil and fine sand under the condition of lower pollution load, finer particle size and more oxidizing environment. The sigmodial equation well fitted the dynamic accumulation curve of the NO₃⁻-N content in the tannery sludge contaminated soils. The Cr(III) content increased with increasing pollution load, which inhibited the reproduction and activity of nitrifying bacteria in the soils, especially in coarse-grained soil. The accumulation of NO₂⁻-N contents became more obvious with the increase of pollution load in the fine sand, and only 41.5% of the NH₄⁺-N was transformed to NO₃⁻-N. The redox environment was the main factor affecting nitrification process in the soil. Compared to the aerobic soil environment, the transformation of NH₄⁺-N was significantly inhibited under anaerobic incubation condition, and the NO₃⁻-N contents decreased by 37.2%, 61.9% and 91.9% under low, medium and high pollution loads, respectively. Nitrification was stronger in the silt soil since its copy number of amoA and nxrA genes was two times larger than that of fine sand. Moreover, the copy numbers of amoA and nxrA genes in the silt soil under the aerobic environment were 2.7 times and 2.2 times larger than those in the anaerobic environment. The abundance changes of the amoA and nxrA functional genes have a positive correlation with the nitrification intensity in the tannery sludge-contaminated soil.

Multivariate analysis and geochemical investigations of groundwater in a semi-arid region, case of superficial aquifer in Ghriss Basin, Northwest Algeria

Laouni Benadela, Belkacem Bekkoussa, Laouni Gaidi

2022, 10(3): 233-249. doi: 10.19637/j.cnki.2305-7068.2022.03.003

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Abstract:
This study aims to investigate the hydrochemical characteristics of shallow aquifer in a semi-arid region situated in northwest Algeria, and to understand the major factors governing groundwater quality. The study area is suffering from recurring droughts, groundwater resource over-exploitation and groundwater quality degradation. The approach used is a combination of traditional hydrochemical analysis methods of multivariate statistical techniques, principal component analysis (PCA), and ratios of major ions, based on the data derived from 33 groundwater samples collected in February 2014. Results show that groundwater in the study area are highly mineralized and collectively has a high concentration of chloride (as Cl⁻). The dominant water types are Na-Cl (27%), Mg-HCO₃ (24%) and Mg-Cl (24%). According to the (PCA) approach, salinization is the main process that controls the hydrochemical variability. The PCA analysis reveal the impact of anthropogenic factor especially the agricultural activities on the groundwater quality. The PCA highlighted two types of recharge: Superficial recharge from effective rainfall and excess irrigation water distinguished by the presence of nitrate and lateral recharge or vertical leakage from carbonate formations marked by the omnipresence of HCO₃⁻. Additionally, three categories of samples were identified: (1) samples characterized by good water quality and receiving notable recharge from carbonate formations; (2) samples impacted by the natural salinization process; and (3) samples contaminated by anthropogenic activities. The major natural processes influencing water chemistry are the weathering of carbonate and silicate rocks, dissolution of evaporite as halite, evaporation and cation exchange. The study results can provide the basis for local decision makers to ensure the sustainable management of groundwater and the safety of drinking water.

Carbon, nitrogen and phosphorus coupling relationships and their influencing factors in the critical zone of Dongting Lake wetlands, China

Yan-hao Wu, Nian-qing Zhou, Zi-jun Wu, Shuai-shuai Lu, Yi Cai

2022, 10(3): 250-266. doi: 10.19637/j.cnki.2305-7068.2022.03.004

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Wetland is a transition zone between terrestrial and aquatic ecosystems, and is the source and sink of various biogenic elements in the earth’s epipelagic zone. In order to investigate the driving force and coupling mechanism of carbon (C), nitrogen (N) and phosphorus (P) migration in the critical zone of lake wetland, this paper studies the natural wetland of Dongting Lake area, through measuring and analysing the C, N and P contents in the wetland soil and groundwater. Methods of Pearson correlation, non-linear regression and machine learning were employed to analyse the influencing factors, and to explore the coupling patterns of the C, N and P in both soils and groundwater, with data derived from soil and water samples collected from the wetland critical zone. The results show that the mean values of organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in groundwater are 1.59 mg/L, 4.19 mg/L and 0.5 mg/L, respectively, while the mean values of C, N and P in the soils are 18.05 g/kg, 0.86 g/kg and 0.52 g/kg. The results also show that the TOC, TN and TP in the groundwater are driven by a variety of environmental factors. However, the concentrations of C, N and P in the soils are mainly related to vegetation abundance and species which influence each other. In addition, the fitted curves of wetland soil C-N and C-P appear to follow the power function and S-shaped curve, respectively. In order to establish a multivariate regression model, the soil N and P contents were used as the input parameters and the soil C content used as the output one. By comparing the prediction effects of machine learning and nonlinear regression modelling, the results show that coupled relationship equation for the C, N and P contents is highly reliable. Future modelling of the coupled soil and groundwater elemental cycles needs to consider the complexity of hydrogeological conditions and to explore the quantitative relationships among the influencing factors and chemical constituents.

Temporal variations of reference evapotranspiration and controlling factors: Implications for climatic drought in karst areas

Xiao-jiao Guo, Wen-zhong Wang, Cheng-xi Li, Wei Wang, Jian-sheng Shi, Ying Miao, Xing-bo Hao, Dao-xian Yuan

2022, 10(3): 267-284. doi: 10.19637/j.cnki.2305-7068.2022.03.005

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Variations in reference evapotranspiration (ET₀) and drought characteristics play a key role in the effect of climate change on water cycle and associated ecohydrological patterns. The accurate estimation of ET₀ is still a challenge due to the lack of meteorological data and the heterogeneity of hydrological system. Although there is an increasing trend in extreme drought events with global climate change, the relationship between ET₀ and aridity index in karst areas has been poorly studied. In this study, we used the Penman–Monteith method based on a long time series of meteorological data from 1951 to 2015 to calculate ET₀ in a typical karst area, Guilin, Southwest China. The temporal variations in climate variables, ET₀ and aridity index (AI) were analyzed with the Mann–Kendall trend test and linear regression to determine the climatic characteristics, associated controlling factors of ET₀ variations, and further to estimate the relationship between ET₀ and AI. We found that the mean, maximum and minimum temperatures had increased significantly during the 65-year study period, while sunshine duration, wind speed and relative humidity exhibited significant decreasing trends. The annual ET₀ showed a significant decreasing trend at the rate of −8.02 mm/10a. However, significant increase in air temperature should have contributed to the enhancement of ET₀, indicating an “evaporation paradox”. In comparison, AI showed a slightly declining trend of −0.0005/a during 1951–2015. The change in sunshine duration was the major factor causing the decrease in ET₀, followed by wind speed. AI had a higher correlation with precipitation amount, indicating that the variations of AI was more dependent on precipitation, but not substantially dependent on the ET₀. Although AI was not directly related to ET₀, ET₀ had a major contribution to seasonal AI changes. The seasonal variations of ET₀ played a critical role in dryness/wetness changes to regulate water and energy supply, which can lead to seasonal droughts or water shortages in karst areas. Overall, these findings provide an important reference for the management of agricultural production and water resources, and have an important implication for drought in karst regions of China.

Determination of total sulfur in geothermal water by inductively coupled plasma-atomic emission spectrometry

Bing-bing Liu, Mei Han, Jia Liu, Na Jia, Chen-ling Zhang, Lin Zhang

2022, 10(3): 285-291. doi: 10.19637/j.cnki.2305-7068.2022.03.006

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Sulfur speciation and concentration in geothermal water are of great significance for the research and utilization of the water resources. In most situations, it is necessary to determine the total sulfur in geothermal water. In this study, the method was established for the determination of determining total sulfur content — the inductively coupled plasma-atomic emission spectrometry (ICP-AES), with the wavelength of 182.034 nm selected in spectral line of sulfur. It was identified that the optimal working conditions of the ICP-AES instrument were 1 200 W for high frequency generator power 9 mm for vertical observation height, 0.30 MPa atomizer pressure, and 50 r/min analytical pump speed. The matrix interference of the method was eliminated by the matrix matching method. Using this method, sulfur detection limit and minimum quantitative detection limit were 0.028 mg/L and 0.110 mg/L, respectively, whilst the linear range was 0.0–100.0 mg/L. The recovery rate of sample was between 90.67% and 108.7%, and the relative standard deviation (RSD) was between 0.36% and 2.14%. The method was used to analyze the actual samples and the results were basically consistent with the industry standard method. With high analysis efficiency, the method has low detection limit and minimum quantitative detection limit, wide linear range, good precision and accuracy, and provides an important detection method for the determination of total sulfur in geothermal water.

Using time series analysis to assess tidal effect on coastal groundwater level in Southern Laizhou Bay, China

She-ming Chen, Hong-wei Liu, Fu-tian Liu, Jin-jie Miao, Xu Guo, Zhou Zhang, Wan-jun Jiang

2022, 10(3): 292-301. doi: 10.19637/j.cnki.2305-7068.2022.03.007

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Sea water intrusion is an environmental problem cause by the irrational exploitation of coastal groundwater resources and has attracted the attention of many coastal countries. In this study, we used time series monitoring data of groundwater levels and tidal waves to analyze the influence of tide flow on groundwater dynamics in the southern Laizhou Bay. The auto-correlation and cross-correlation coefficients between groundwater level and tidal wave level were calculated specifically to measure the boundary conditions along the coastline. In addition, spectrum analysis was employed to assess the periodicity and hysteresis of various tide and groundwater level fluctuations. The results of time series analysis show that groundwater level fluctuation is noticeably influenced by tides, but the influence is limited to a certain distance and cannot reach the saltwater-freshwater interface in the southern Laizhou Bay. There are three main periodic components of groundwater level in tidal effect range (i.e. 23.804 h, 12.500 h and 12.046 h), the pattern of which is the same as the tides. The affected groundwater level fluctuations lag behind the tides. The dynamic analysis of groundwater indicates that the coastal aquifer has a hydraulic connection with seawater but not in a direct way. Owing to the existence of the groundwater mound between the salty groundwater (brine) and fresh groundwater, the maximum influencing distance of the tide on the groundwater is 8.85 km. Considering that the fresh-saline groundwater interface is about 30 km away from the coastline, modern seawater has a limited contribution to sea-salt water intrusion in Laizhou Bay. The results of this study are expected to provide a reference for the study on sea water intrusion.

Thermodynamic transport mechanism of water freezing-thawing in the vadose zone in the alpine meadow of the Tibet Plateau

Gang Qiao, Feng-dan Yu, Wen-ke Wang, Jun Zhang, Hua-qing Chen

2022, 10(3): 302-310. doi: 10.19637/j.cnki.2305-7068.2022.03.008

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High altitude, cold and dry climate, strong solar radiation, and high evapotranspiration intensity have created an extremely fragile ecological and geological environment on the Tibet Plateau. Since the heat in the vadose zone is primarily generated by the external solar radiation energy, and evapotranspiration is contingent on the consumption of vadose heat, the intensity of evapotranspiration is associated with the intensity of solar radiation and the heat budget in the vadose zone. However, the spatial and temporal variation of heat budget and thermodynamic transfer process of the vadose zone in the frigid region are not clear, which hinders the revelation of the dynamic mechanism of evapotranspiration in the vadose zone in the frigid region. With the moisture content of the vadose zone in the alpine regions being the research object, the paper conducts in-situ geothermal observation tests, takes meteorological characteristics into consideration, and adopts the method of geothermal gradient and numerical computation to analyse the temporal and spatial variation rule of heat budget and thermodynamic transmission process of the vadose zone in the high and cold regions. The results show there is a positive correlation between air temperature, ground temperature, and water content of the vadose zone in both thawing and freezing periods. According to the change law of geothermal gradient, the thermodynamic transfer process of the vadose zone has four stages: slow exothermic heating, fast endothermic melting, slow endothermic cooling, and fast exothermic freezing. From the surface down, the moisture freezing rate of the vadose zone is slightly higher than the melting rate. This is of great significance for understanding the evapotranspiration dynamic process of the vadose zone and protecting and rebuilding the ecological and geological environment in the high and cold regions.

2022 Vol. 10, No. 3

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