Soil alkalinization and salinization in the djajerud Basin,Iran

The Djajerud Basin is located on the southern slopes of the Elburz Mountains, to the east of Tehran. Near its source, as the River is fed mainly by the melting of the winter snow and flows over tuffs and schists, its carbonate-enriched water can induce soil alkalinization. The Djajerud River runs from its source across a gypsum and marl piedmont. Gypsum is dissolved and modifies the chemical quality of the waters, which lose their alkaline character and get more salty. These sulphate-rich flows are less damaging because soil degradation hazards in the region are related more to salinization than to alkalinization. The Djajerud River waters next seep deep into a permeable deposition fan and feed water-tables which merge into the groundwaters of the Varamin Plain (which are also fed by chloride-rich waters from other sources). The chemical character of the Djajerud-River changes in this section, developing a marked sodium chloride salinity. The soils in this part of the Basin, due to the high groundwater salinity, have poor drainage which prevents any agriculture. The River eventually flows into the highly saline endorrheic Daryachehnamak Lake. The concept of residual alkalinity is used to examine the chemical composition of the Djajerud River along its course and affords the determination of the soil degradation hazard in the various parts of the Basin.