Nitrogen Migration and Transformation Mechanism in the Groundwater Level Fluctuation Zone of Typical Medium

Because of the nitrogen pollution problem in groundwater, the migration conversion mechanism of nitrogen in groundwater level fluctuations was analyzed. Technology and methods through indoor experiments and theoretical analysis were used to study coarse sand, medium sand, and fine sand groundwater level fluctuation in the aeration zone and saturated zone under the situation of nitrogen distribution characteristics, revealing groundwater level fluctuation with the nitrogen migration mechanism. The experimental results showed that the variation range of the nitrate-nitrogen (NO3−−N) concentration with the water level is medium sand > fine sand > coarse sand. The ammonium nitrogen (NH4+−N) concentration showed a downward trend after water level fluctuations, and there were more apparent fluctuations in coarse sand and medium sand. The nitrite nitrogen (NO2−−N) in coarse sand and medium sand first increased the water level and then gradually reached a balance. The sampling points below the water level in fine sand showed a downward trend with fluctuation of the water level, and then gradually reached equilibrium. The results provide a scientific basis for the remediation and treatment of soil and groundwater pollution.

Characterization of Regional Groundwater System Based on Aquifer Response to Recharge–Discharge Phenomenon and Hierarchical Clustering Analysis

The investigations of groundwater hydrograph reasonably reflect the aquifer response to recharge–discharge phenomenon and its characteristics. A better understanding of aquifer characteristics such as regional aquifer classification, recharge and discharge patterns, aquifer geology and flow patterns are the surface indicators that may be more effective and less costly for interpreting basic regional hydrogeological conditions and assessments. This study deals with the application of Hierarchical Clustering Analysis to understand the groundwater spatio-temporal patterns and to visualize/classify the nature of the aquifer in the regional area of Kaohsiung City, Taiwan. Groundwater level fluctuation patterns and slopes of rising and recession limbs are used to identify the pumping effects and classify aquifers. The results of clustering analysis show that the groundwater observation wells in the study area can be divided into five major characteristics along with the upstream to downstream of Kaoping River. The clusters are consistent with basic lithology distribution and age of sedimentary, which represents the characteristics of groundwater level fluctuation. The identified groundwater hydrographs patterns provide newer insights related to aquifer response to recharge–discharge phenomenon, types of aquifers and their behaviors. The knowledge of water level fluctuations in the observation wells provides a piece of prior information about the abstraction of groundwater. The proposed aquifer classification and pumping effect have great potential for applied use in groundwater management e.g., save drilling cost.

High-resolution Data Based Groundwater Recharge Estimations of Aynalem Well Field

Due to the ever-increasing demand for water in Aynalem catchment and its surrounding, there has been an increased pressure on the Aynalem well field putting the sustainability of water supply from the aquifer under continuous threat. Thus, it is vital to understand the water balance of the catchment to ensure sustainable utilization of the groundwater resource. This in turn requires proper quantification of the components of water balance among which recharge estimation is the most important. This paper estimates the groundwater recharge of the Aynalem catchment using high-resolution hydro-meteorological data. Daily precipitation and temperature measurement data for years 2001-2018; groundwater level fluctuation records collected at every 30 minutes; and soil and land use maps were used to make recharge estimations. In the groundwater level fluctuation, three boreholes were monitored, but only two were utilized for the analysis because the third was under operation and does not represent the natural hydrologic condition. Thornthwaite soil moisture balance and groundwater level fluctuation methods were applied to determine the groundwater recharge of the Aynalem catchment. Accordingly, the annual rate of groundwater recharge estimated based on the soil-water balance ranges between 7mm/year and 138.5 mm/year with the weighted average value of 89.04 mm/year. The weighted average value is considered to represent the catchment value because the diverse soil and land use/cover types respond differently to allow the precipitation to recharge the groundwater. On the other hand, the groundwater recharge estimated using the groundwater level fluctuation method showed yearly groundwater recharge of 91 to 93 mm/year. The similarity in the groundwater recharge result obtained from both methods strengthens the acceptability of the estimate. It also points out that the previously reported estimate is much lower (36 to 66 mm/year).

IDENTIFYING THE EFFECT OF TIDES ON GROUNDWATER LEVEL FLUCTUATIONS ON GILI KETAPANG ISLAND, INDONESIA

This research aims to identify the effect of tides on groundwater level fluctuation in Gili Ketapang Island by using a combination of field monitoring and hydrodynamic modeling. Groundwater data were collected from 5 July to 17 August 2018 from two wells monitoring, while the hydrodynamic model was adopted to identify sea-level conditions. The result explains the sea level around the island is similar among extremely strong correlations between the points. The hydrodynamic model proves a standing wave due to tidal amplification in Madura Strait waters. The effect of tides on the groundwater level characterized by decreasing in amplitudes and time lags as increasing the distance from the coast.

Groundwater recharge estimation using groundwater level fluctuation patterns in unconfined aquifer of Yogyakarta City, Indonesia

Water demand in the world increases rapidly every year, especially in urban areas due to population growth and improved economic conditions. The largest freshwater source on earth is groundwater that can be utilized and easily obtained. However, the number of groundwater resources is very dynamic, depending on the recharge and discharge, including groundwater extraction. Increasing groundwater abstraction will cause a decline in groundwater level and seawater intrusion in the coastal area. Groundwater level fluctuation trends can be used to estimate groundwater recharge for optimum utilization. Therefore, this study aims to find the trend of groundwater level fluctuation related to rainfall to estimate the groundwater recharge in Yogyakarta City, Indonesia. The study was carried out by measuring the groundwater level of four monitoring wells that spread evenly in Yogyakarta City from 2011 to 2017 every month and comparing the result to monthly rainfall and annual groundwater abstraction from hotels in Yogyakarta City. The annual trend of rainfall and groundwater level fluctuation analysis using the nonparametric Mann-Kendall test and analyzing the trend's magnitude using the nonparametric Sen’s method. The groundwater recharge was estimated by using the water table fluctuation (WTF) method. The study results showed that the trend of rainfall and groundwater level fluctuation is positive in the city's western and eastern parts. However, the groundwater level fluctuation in the city's central and southern parts is a negative trend due to groundwater over-exploitation by hotels. Groundwater recharge is estimated at around 158 up to 538 mm/year based on the WTF method. Higher groundwater recharge was identified in the city's central and eastern parts due to the high contribution from urban wastewater recharge.