Differentiating Nitrate Origins and Fate in a Semi-Arid Basin (Tunisia) via Geostatistical Analyses and Groundwater Modelling

Abstract

Despite efforts to protect the hydrosystems from increasing pollution, nitrate (NO3−) remains a major groundwater pollutant worldwide, and determining its origin is still crucial and challenging. To disentangle the origins and fate of high NO3− (>900 mg/L) in the Sidi Bouzid North basin (Tunisia), a numerical groundwater flow model (MODFLOW-2005) and an advective particle tracking (MODPATH) have been combined with geostatistical analyses on groundwater quality and hydrogeological characterization. Correlations between chemical elements and Principal Component Analysis (PCA) suggested that groundwater quality was primarily controlled by evaporite dissolution and subsequently driven by processes like dedolomitization and ion exchange. PCA indicated that NO3− origin is linked to anthropic (unconfined aquifer) and geogenic (semi-confined aquifer) sources. To suggest the geogenic origin of NO3− in the semi-confined aquifer, the multi-aquifer groundwater flow system and the forward and backward particle tracking was simulated. The observed and calculated hydraulic heads displayed a good correlation (R2 of 0.93). The residence time of groundwater with high NO3− concentrations was more significant than the timespan during which chemical fertilizers were used, and urban settlements expansion began. This confirmed the natural origin of NO3− associated with pre-Triassic embankment landscapes and located on domed geomorphic surfaces with a gypsum, phosphate, or clay cover.

Exploring the Radioactive Nexus: Multidimensional Correlations and Dosimetric Assessment of Elemental Radionuclides

“…Descriptive statistics: This analysis will provide summary measures such as the mean, standard deviation, median, minimum and maximum of radioactivity values in soil and air (Kheli et al 2019;Ncibi et al 2022). It will thus make it possible to characterize the levels of radioactivity and provide quantitative information on the presence of radioactivity in the ground and in the air.…”

Groundwater Quality Evaluation of Fractured Aquifers Using Machine Learning Models and Hydrogeochemical Approaches to Sustainable Water-Irrigation Security in Arid Climate (Central Tunisia)

“…Notably, the recent Quaternary deposits within the study region consist of permeable formations. The variation in the depth of the Mio-Plio-Quaternary sand and gravel accumulations primarily stems from irregularities in bedrock topography [27,[37][38][39][40][41][42]. As one moves eastward within the study area, the depth of the phreatic aquifer increases [27,37], but its spatial extent remains constrained due to the surrounding elevations encompassing the hydrogeological basin.…”

“…As one moves eastward within the study area, the depth of the phreatic aquifer increases [27,37], but its spatial extent remains constrained due to the surrounding elevations encompassing the hydrogeological basin. On average, the depth of this formation measures around 65 m. The shallow aquifer's porosity is estimated at 28% [37,38].…”

“…As one moves eastward within the study area, the depth of th phreatic aquifer increases [27,37], but its spatial extent remains constrained due to th surrounding elevations encompassing the hydrogeological basin. On average, the depth of this formation measures around 65 m. The shallow aquifer's porosity is estimated a 28% [37,38]. In the principal outcrop regions of the hydrogeological Meknassy basin, the fractured formations have undergone secondary porosity development as a result of the fracturing and jointing processes.…”

“…The geological composition is distinguished by the occurrence of sedimentary depos its from the Mio-Plio-Quaternary period that delineate the near-surface aquifer. The fis sured Cretaceous formations encompass the deep aquifer [37,38]. Within the study area groundwater is predominantly found within weathered segments of rocks along joint and fractures, as well as within outcroppings of porous materials.…”