Spatial and Temporal Variations in the Hydrochemistry and Isotopic Compositions of the Groundwater and Surface Runoff in the Jordan Rift Valley (Case Study for Ramallah Jerusalem Sub-basin)
Zusammenfassung der Projektergebnisse
The spatial and temporal changes of the composition of the groundwater from the springs along Wadi Qilt stream in the Jerusalem–Ramallah Mountain slope area and in the Jericho Plain, Palestine, was studied for the hydrological year 2006/2007. The residence time as well as the intensity of recharge plays the important role in controlling the changes in the chemical composition of spring water within one hydrological year, and is mainly affected by the distance from the main recharge area. A very important factor is the oxidation of organics derived from sewage and garbage resulting in variable dissolved CO2. High CO2 yields lower pH values and thus undersaturation with respect to calcite (and dolomite). Low CO2 concentrations result in over-saturation, thus the beginning and at the end of the rainy season calcite saturation is achieved. The degradation of dissolved organic matter is a major source for increase the water hardness and mineralization. A detailed analysis of dissolved species reveals that besides dissolution of carbonates, nitrate, chloride and sulfate are leached from soil and the aquifer rocks together with small amounts of Mg. Thus, Mg not only originates from carbonates but also from Mg-Cl saline waters included in the rocks. This effect is particularly high at the beginning of the winter season and lowest at its end. Therefore special mitigation procedures should be taken in suitable time of the year to prevent more deterioration for the infiltrated ground water in the aquifer, and further studies for the amount and quality of waste discharge to the wadi should be done. Two zones of recharge are distinguishable. Zone 1 represented by Ein Fara and Ein Qilt is fed directly through the infiltration of meteoric water and surface runoff from the mountains along the eastern mountain slopes with less groundwater residence time and high flow rate. The second zone is near the western border of Jericho at the foothills, which is mainly fed by the underground water flow from the eastern slopes with low surface infiltration rate. This zone shows higher groundwater residence time and slow flow rate than zone 1. Both zones have varied isotopic signatures where the later zone shows more enriched deuterium values in the early season which confirmed the long residence of the groundwater that flushed out later and replaced by the new replenished groundwater with more depleted values. The main factors affected the groundwater residence time and flow rate are the geological structure of the aquifer, the amount of active recharge to the aquifer, and the recharge mechanism. The results thus might be very useful for more efficient freshwater exploitation in the region, as pre-cautions should be take place for the replenished water, and the runoff water should not be freely infiltrated along the Wadi as the last has a bad infiltration zone in one of its parts (zone 2) and thus much more water could be lost by evaporation.
