International Symposium on
Drylands Ecology and Human Security
The Role of Geological Factors
A. Tahmasebi1 & V. Jafarian2
1Senior Expert of UNCCD National Focal Point Office
2Senior Expert of Deputy of Range and Soil Affairs, Forest Range and Watershed Organization, Tehran, Iran
The processes that lead to desertification are a combination of different factors, which fall in to categories: environmental and human factors. One of these processes is the salinization, which occurs extensively in the arid and semi arid regions of the world.
Desertification through salinization is due to accumulation of soluble salts in the soil. In the extreme cases, the ground may be covered with a white salt crust. Both the natural and man-made (secondary) salinization processes affected to the appearance and to the extension of desertification. Previous studies showed that during the two decade from 1955 to 1975 the low quality of Rood Shoor River water and inappropriate drainage system was the main cause of secondary salinization and leading to 138 percent increase in salt effected land of Qazvin plain. In this study the role of geological factors in surface water quality were investigated through analyzing the long term water quality data in Hydrometric Stations(HS) as well as taking numerous water sample from drainage of salt resources: evaprotic marl formations, salt dome and gypsum-salt mine. In the first step, the base map illustrating the position of salt resources beside the drainage system has been produced through overlying the geology map and hydrologic drainage system map of study area in a geographic information system (GIS). Then its accuracy were controlled through filed visits using Global Position System (GPS). In the second stage, the variation of water quality along the main river were surveyed through sampling in a certain flood as well as analyzing the long term water quality data HS. Thus the drainages affecting to the salinity of Rood Shoor river were prioritized. In the third stage, according to the results gained in previous stages, numerous samples were collected along the drainages before and after the salt resources and were analyzed. The Semi logarithmic diagram was used for illustrating the changes in Density and Reaction Quality Percentage (RQP) of ions.
Results show that the water quality of khar Rood branch are more affected by geological factors and annually about 116356.8 ton solutes are carried by 103.2 million m3 water from Abe Garm HS to Gazvin Plain. Despite to our expectation, the point salt resources; salt domes and gypsum mines, are supplying only 3.5 percentage of this solutes and the evaprotic marl formation; upper red formations, has the mine role in this regards. The evaporation also playing important role in this process, for instant, the EC in Rahim Abad was 1320 Micromohs and reach to 1730 Micromohs in Pole Shah Abbasi station, its ionic formula also has changed from Cl>Hco3>So4,Na>Ca>Mg to Cl>So4>Hco3,Na>Mg>Ca relatively. Since the RQP of Carbonates has decreased and the RQP of sulfate and chlorides symmetrically increased and the ratio of rso4/rcl were about 0.7 in both stations, it could be conclude that increasing the evaporation of water in this section because of specific topography led to escapement of carbon dioxide and deposition of calcium carbonate. So the change in ionic formula could be result of evaporation in this section.
Keywords: Water quality, Surface water, Geological Formation, secondary Salinization