الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 188 |  |  |
| | | from | 188 | | |
Abstract
Heavy metal-polluted soil is a serious concern, especially as brackish water is widely used for irrigation purposes in water-scarce countries. Heavy metals (HMs) accumulation in soil and plants can occur when water contaminated with HMs is used as an irrigation source. In this thesis, the effect of watering the potato crop in sand soil from a polluted water source (El-Salam Canal, Egypt) under surface drip irrigation (DI), sprinkler irrigation (SI), and flood irrigation (FI) on the transport of the HMs in the root zone was experimentally investigated. The transport of copper (Cu), manganese (Mn), lead (Pb), and zinc (Zn) were tracked during the field experiments.
HMs concentrations in potato crop were also determined. The field experiments were conducted in a completely randomized block with three replicates for each irrigation method using nine field lysimeters. Soil and plant samples were collected at the end of the growing season to determine their HMs content.
After that, the HYDRUS-2D model was used to simulate HMs (i.e., Cu, Pb, and Zn) movement through the soil profile. Firstly, the ability of HYDRUS-2D to simulate water flow was validated using the data collected from the lysimeter experiment irrigated by surface drip irrigation. Secondly, the model was calibrated for solute transport parameters.
After that, different simulation scenarios were executed to explore the potential groundwater contamination risk under the DI, SI, and FI methods. Three soil types, namely, silty clay loam, sandy loam, and sand soil, and two irrigation schemes, irrigation every two days (i.e., scheme A) and irrigation every four days (i.e., scheme B), were considered during the simulations.
The results of the lysimeter experiment showed that regardless of irrigation method, irrigation with HMs-contaminated water raised HMs concentrations in both soil and potato plants. DI produced the highest concentrations of most HMs (Cu, Mn, and Pb) in the upper soil layer (0–40 cm) and highest Cu, Pb, and Zn concentrations in plant tubers as well. Maximum Zn concentration in the upper soil layer and maximum Mn concentration in plant tubers occurred under the SI. The maximum concentrations of Cu, Mn, Pb, and Zn in both the upper soil layer and plant tubers were 12.0, 140.0, 11.6, and 67.9 mg/kg and 6.3, 9.4, 2.3, and 23.9 mg/kg, respectively. However, FI produced the highest concentrations in the deep soil layer (40–60 cm) and the least concentration of HMs in plant tubers. These concentrations were 18.8, 203.8, 13.3, and 70 mg/kg and 4.0, 6.0, 0.6, and 17.1 mg/kg in soil and plant tubers for Cu, Mn, Pb, and Zn, respectively. The maximum concentrations of HMs in soil and potato plants were lower than the maximum permissible limits. Therefore, El-Salam Canal water appears not to be harmful in the short term.
The simulation results showed that HYDRUS-2D effectively simulated water flow. Moreover, a good agreement between the simulations and experimental results of HMs concentrations under the calibrated solute parameters was obtained with R2 values of 0.99, 0.91, and 0.71 for Cu, Pb, and Zn concentrations, respectively. Additionally, HMs distribution in the soil profile is considerably influenced by the HMs’ adsorption isotherm. The results of the investigated scenarios revealed that soil texture has a great impact on HMs concentrations in the simulation domain and on the potential contamination risk of the groundwater.
Under both irrigation schemes, lower HMs concentrations were observed in sand, while higher values were observed in silty clay loam for the DI, SI, and FI methods. Subsequently, for the three irrigation methods, the potential shallow groundwater contamination risk is greater when cultivating potatoes in sand, as higher HMs concentrations were found in drainage water compared to those in the two other investigated soils, regardless of the irrigation scheme. The cumulative Cu, Pb, and Zn concentrations in drainage water corresponding to scheme A for silty clay loam and sandy loam were 1.65, 1.67, and 1.67 and 1.15, 1.14, and 1.15 times higher than scheme B under the DI method, respectively.
To safeguard the sustainability of groundwater and agricultural lands irrigated with water contaminated by HMs, it is recommended to adopt an irrigation frequency of once every four days in soils with silty clay loam and sandy loam textures when irrigated with the DI method. For FI and SI methods, the HMs concentrations in scheme B were higher than those in scheme A for nearly all observation nodes at the three investigated soils. Therefore, it could be recommended to use schema A when using FI and SI in all investigated soils. For the DI method, irrigation schemes have a slight effect on HMs concentration in the soil and on potential groundwater contamination risk, and their impact is more pronounced if it is linked to soil texture. Therefore, the effect of irrigation schemes on HMs distribution in the soil profile is affected by the irrigation method.
On the other hand, the highest concentrations of Cu, Pb, and Zn at the end of the simulation period were found in DI, followed by SI, and then FI for most observation nodes for the three investigated soils. The cumulative free drainage flux of HMs at the end of the growing season in the FI method was much greater than in the DI and SI methods for silty clay loam and sandy loam soil, but for sand soil, the ratio decreased. Based on the results, it is recommended to use DI method with scheme B for silty clay loam soil and sandy loam soil to reduce metal migration to the groundwater. However, the DI, SI, or FI method could be utilized with schemes A or B for sand soil.