Monitoring soil salinization and waterlogging in the northeastern Nile Delta linked to shallow saline groundwater and irrigation water quality

Abstract

Soil salinization and waterlogging are critical environmental issues affecting agricultural productivity and cultural heritage preservation, particularly in arid regions. This study investigated soil degradation processes in the archaeologically and agriculturally significant northeastern Nile Delta of Egypt. The objective was to assess the severity of soil degradation and identify key drivers related to water resources and soil characteristics to aid in the development of management strategies. The research employed a multi-faceted approach, including hydrochemical analyses (of groundwater, irrigation water, and soil), water quality indices calculations, statistical analyses, and satellite data. The results revealed high levels of soil salinization in the northern and central areas, with 64% of soil samples classified as strongly and very strongly saline. Soil chemistry indicated salinization sources linked to sodium chloride dominance. Satellite data from Sentinel-2 images and SRTM digital elevation data showed widespread severe waterlogging in the northern lowlands. The Irrigation Water Quality Index (IWQI) values indicated that 87.5% of irrigation water samples posed severe restrictions due to high salinity and sodium hazards, which were mismatched with the low soil permeability observed in 81% of the collected samples exhibiting clay texture and covering most of the study area. Furthermore, shallow groundwater at depths of 0.5-3 m with high salinity was detected, where total dissolved solids exceeded 20,000 mg/L, and Na-Cl water types prevailed, indicating saltwater intrusion. A strong positive correlation (r > 0.83) was found between shallow saline groundwater and soil salinity. The combination of poor irrigation water quality, shallow saline groundwater tables, and low-permeability soils created a synergistic effect that severely compromised soil health and agricultural productivity. It also posed severe risks to the structural integrity of archaeological sites and buried artifacts through accelerated physical and chemical weathering processes. This necessitates an urgent mitigation strategy to combat soil degradation in this critical area.

Keywords: Archaeological site deterioration; Correlation analysis; Irrigation water quality; Kriging interpolation; Soil degradation; Spectral water indices; Water quality indices.

Fig. 1

(a) Location of the study area within the Nile Delta depicted via satellite imagery (Esri base-map); (b) Distribution of archaeological tells and irrigation canals/drains network across the study area; (c) Location of Tell San El-Hager (Tanis); (d) Location of Tell Mahgar. These maps were created using ArcGIS software version 10.7.1 [https://desktop.arcgis.com].

Fig. 2

(a) Map showing locations of collected surface water, groundwater, and soil samples created using ArcGIS software version 10.7.1 [https://desktop.arcgis.com]. (b–d) Field photographs depicting soil degradation in the study area due to waterlogging and salinization: (b,c) Waterlogged urban land with salt crusting on soil surface; (d) Abandoned cropland due to salinity.

Fig. 3

(a) Map showing distribution of waterlogged soils based on Water Index (WI) applied to Sentinel-2 A satellite imagery acquired on August 6, 2023. Spatial distribution maps of measured soil chemical parameters: (b) Electrical conductivity (EC); (c) Sodium (Na⁺); (d) Chloride (Cl⁻); (e) Calcium (Ca²⁺); (f) Magnesium (Mg²⁺). These maps were created using ArcGIS software version 10.7.1 [https://desktop.arcgis.com].

Fig. 4

Spatial distribution of mechanical properties of collected soil samples: (a) Clay content (%); (b) Silt content (%); (c) Sand content (%); (d,e) Soil texture and permeability based on USDA classification.

Fig. 5

(a) Map showing depth to water table (DTWT) in meters below ground level; (b) Digital elevation model (DEM) showing land surface elevation in meters above sea level derived from SRTM data. These maps were created using ArcGIS software version 10.7.1 [https://desktop.arcgis.com].

Fig. 6

Spatial distribution maps of groundwater chemical parameters and hydrochemical facies: (a) Total dissolved solids (TDS); (b) Sodium (Na⁺); (c) Potassium (K⁺); (d) Magnesium (Mg²⁺); (e) Calcium (Ca²⁺); (f) Chloride (Cl⁻); (g) Sulfate (SO₄²⁻); (h) Hydrochemical facies. These maps were created using ArcGIS software version 10.7.1 [https://desktop.arcgis.com].

Fig. 7

Correlation matrix showing the relationship between soil (s) and groundwater (g) chemical parameters. Strong positive correlations (> 0.83) are observed between electrical conductivity (EC), TDS, sodium (Na⁺), and chloride (Cl⁻) concentrations in soil versus groundwater.

Fig. 8

Theoretical relationship between capillary rise velocity and depth to groundwater table for different soil textures  (adapted from). The clay soils and shallow groundwater depths found in the study area (0.5–3 m) suggest maximum capillary flow velocities are likely. This confirms the significant contribution of shallow saline groundwater as a continual source of salts to the soil in the northeastern Nile Delta. .