International Journal of Aquatic Science

ISSN: 2008-8019

Vol 2, No 1, 2011

 

 

On the red coloration of Urmia Lake (Northwest Iran 

Fereidun Mohebbi, Reza Ahmadi, Mohsenpour Azari, A., Esmaili, L, Asadpour, Y

 In summer 2010, the Urmia Lake water was changed to a pinkish- purple color in several areas such as two sides of its cause-way. To investigate on the reasons of this color change, we collected water samples for phytoplankton and some physicochemical parameters analyses from six sampling sites on the both sides of the lake cause-way on 18 August 2010.

Phytoplankton samples were immediately fixed by 4% formaldehyde and preserved in cold, dark conditions for laboratory analysis. Phytoplankton counting and identification were made using 5-ml settling chambers with a Nikon TS100 inverted microscope at 400× magnification by Utermöhl (1958) method.

A railroad causeway built in 1959 divided Great Salt Lake into northern and southern sections, leading to dilution of the southern section, and concentration of the northern section to nearly saturating salinity. The red color is the result of a bloom of extreme halophiles, which can reach 108 cells per ml or greater concentration in the north arm (DasSarma, 2006).

Although β-carotene derived from Dunaliella may be the most abundant carotenoid pigment in the hypersaline water, its dense packaging within granules inside the cell’s chloroplast greatly decreases its contribution to the overall light absorbance in the water. As a result, most of the pink-red color of the hypersaline environments is caused by α-bacterioruberin and other bacterioruberin derivatives present in the family of Halobacteriaceae (Fernandez-Castillo et al. 1986).

The North Arm of Great Salt Lake, Utah, with salt concentrations above 300 g l-1 shows similar colors (Post 1977; Baxter et al. 2005).

Solar salt ponds are established all over the world in many tropical and sub-tropical regions to produce salts from seawater. The seawater is evaporated by a step by step process through shallow ponds which have relatively constant salinity, so that each set of ponds contains particular microbial population which adapted to same salt concentration. At the last step of evaporation process, the salt concentration rises to more than 300 gl-1 in crystallization ponds. In this situation, the main microbial communities are as planktonic populations which give a pink- reddish color to water (Javor, 1989).

In fact, α- bacterioroberin and its other 50- carbon derivatives present in Archaea from Halobacteriaceae play the major role in establishing such a pink- reddish color in crystallization ponds. It can be concluded that a similar mechanism contributed in color change of brine water both at natural hypersaline waters and at man-made solar salt ponds. This is a biological process in which Halobacteriaceae with its vast number of genera and a few recently identified bacteria involved in water color shift in NaCl saturated water.