Hydrogeochemistry of seasonal variation of Urmia Salt Lake, Iran

Abstract

Urmia Lake has been designated as an international park by the United Nations. The lake occupies a 5700 km2 depression in northwestern Iran. Thirteen permanent rivers flow into the lake. Water level in the lake has been decreased 3.5 m in the last decade due to a shortage of precipitation and progressively dry climate. Geologically the lake basin is considered to be a graben of tectonic origin. Na, K, Ca, Li and Mg are the main cations with Cl, SO4, and HCO3 as the main anions. F & Br are the other main elements in the lake. A causeway crossing the lake is under construction, which may affect the lake's annual geochemistry. The main object of this project is mainly to consider the potential of K-mineral production along with ongoing salt production. Seven hundred and four samples were taken and partially analyzed for the main cations and anions. Surface water (0.5 m. depth) was analyzed for Na, K, Mg, Ca, Br and Li, and averaged 87.118 g/lit, 1.48 g/lit, 4.82 g/lit, 4.54 g/lit, 1.19 ppm and 12.7 ppm respectively for the western half of the lake. Sodium ranged between 84 to 91.2 g/lit, and showed higher concentrations in the south than in the north. This unexpected result may be caused by shallower depth in the south and a higher net evaporation effect. Calcium ranged between 4.2 to 5 g/lit, apparently slightly higher in the north. K is higher in the south, possibly due to rivers entering from south that may carry slightly higher K in solution. In the middle-range samples (0.5-5 m.), K averaged 1.43 g/lit and ranged from 1.40 to 1.46 g/lit. At this intermediate depth the distribution of K is clearly higher to the south of the causeway that is currently under construction. It is not clear whether this increase is the effect of the causeway or the effect of the salty Aji-Chay River to the east, and the Khoy salt domes to the north of the lake. At depth (5 m-10 m), K averaged 1.48 g/lit and ranged from 1.4 to 1.49 g/lit, differing only in the second decimal from the average of the middle and surface samples. Ignoring the small difference between the averages of the three sample depths, the distribution of K is highly homogeneous in the lake water due to the mixing process. Therefore causeway construction has not yet strongly affected K distribution, or it may be at the starting point. Magnesium concentration ranged from 4.6 to 5-g/lit, and was elevated in the south. This differs somewhat compared to calcium. Lithium, with an average of 12-13 ppm, is slightly higher in the south, and has not shown any significant variation in all three seasons. Iodine was below the detection limit in the lake. Urmia Lake, geochemically, is highly uniform both to the south and north of the causeway, in both the surface and deep brines. K and Mg, which average 1.48 and 6.6 g/lit in order, could be elements worth production in addition to the NaCl currently being produced from the lake. Br, F, Li and B in the limit of <50 ppm don't look to be in the economical range.

Figure 1

Sampling grids and the rivers flowing into the lake.

Figure 2

Salt harvesting from Urmia Lake.

Figure 3

Comparison of rever debits flowing into Urmia Lake during 1991–2000.

Figure 4

Average rainfall and temperature during 1950–2000.

Figure 5

Osman fist, the smallest island of Urmia Lake (height is 10 meters).

Figure 6

Bathymetric map of western half of Urmia lake.

Figure 7

Geological map of Urmia Lake and the surrounding area.

Figure 8

Mineralogy and sediments in drillings of the lake basin (after Kelts, K. and Shahrabi, M. 1986).

Figure 9

Comparison of potassium in top 0.5 m of Urmia Lake in three seasons.

Figure 10

Comparison of potassium in 0.5 to 5 meters of Urmia Lake in three seasons.

Figure 11

Comparison of potassium in the bottom of Urmia Lake in three seasons.

Figure 12

Sodium concentration in the top 0.5 m of Urmia Lake.

Figure 13

Calcium concentration in the top 0.5 m of Urmia Lake.

Figure 14

Magnesium concentration in the top 0.5 m of Urmia Lake.

Figure 15

Lithium concentration in the top 0.5 m of Urmia Lake in fall.