HYDROGEOCHEMISTRY OF SEASONAL VARIATION OF URMIA SALT LAKE

Abstract

Urmia Lake has recorded as an intemational park by the United Nations. The lake occupies 4600 k i n 2 of a depression in NW of Iran. Thirteen rivers flow into the lake. Water level has been decreased 3.5 m in the last decade due to shortage of precipitation and progressive dry climate. Geologically it is considered to be a tectonic origin graben. Na, K, Ca and Mg are the main anions in the lake. A causeway crossing the lake is under construction, which may affect the lake's annual geochemistry. Water from surface (0.5 m depth) analyzed for Na, Mg, Ca, Br and Li, averages 87.118, 4.82, 4.54 g/L, 1.19x10 6 and 12.7x10 6 in order. Sodium ranging between 84 to 91.2 g/L shows higher concentrations in the south rather than in the north. This unexpected result may be caused by shallower depth in the south and higher evaporation effect. Calcium ranged between 4.2 to 5 g/L, apparently slightly higher in the north. K is higher in the south due to shallower depth or rivers entering from south possibly carry slightly higher K in solution. In middle samples (0.5-5m) K averaging 1.43 g/L ranged from 140 to 146. At this depth the distribution of K is clearly higher. The south is separated by the causeway under construction. It is not clear whether this is the effect of road construction or partially affected by salty Aji-Chay River and Khoy salt domes in the west of the lake. At depth (5-10 m) K averaging 1.48 g/L and ranging from 1.4 to 1.49 is differing only by second decimal from the average of middle and surface samples. Na, K, Ca and Mg are the main anions in the lake. K and Mg could be other elements worth of production from the lake forming 6.6 and 1.10 g/L in order. Br, F, Li, B and I in the limit of <50x10 s don't look to be in the economical range. Ignoring the small difference between the average of three sample types and the depth, the distribution of K is highly homogenized in the lake water due to its high solubility. Therefore, road construction has not yet strongly affected K distribution or it may be at the starting point. Magnesium concentration ranging from 4.6 to 5 g/L elevated in the south, which is reverse compared to calcium. Lithium apparently in three seasons has not shown any variation and the average of 12x106-13x10 -6 is rather constant in all seasons, only slightly higher in the south. Iodine was bellowing the detection limit.