THE ARAL SEA 655 



intermediate type between the hydrocarbonate calcium waters of the land 

 and the sodium chloride waters of the ocean . . . although as regards their 

 salt-forming ions the waters of the Aral Sea are closer to typical mainland 

 waters than those of the Caspian. The salt system of the waters of the ocean 

 and of the Caspian Sea is Cl-Na-SO, and that of the Aral Sea is Na-Cl-Mg.'* 



Oxygen content 



In summer time the waters of the Aral Sea are, as a rule, supersaturated with 

 oxygen (at times up to 130 per cent saturation) even over the areas of black 

 mud smelling of hydrogen sulphide. The great transparency of the water at 

 comparatively shallow depths causes an abundant development of sea-weeds 

 on the bottom of the Aral Sea, even at considerable depths, and the peculiar 

 distribution of oxygen, which increases with depth, is also a direct result. 

 Oxygen content below 81 per cent has never been observed in the Aral Sea. 

 The presence of hydrogen sulphide has never been recorded, neither in the 

 deepest parts and near the sea-floor, nor even where the sea-bed was known to 

 contain hydrogen sulphide in its soil (mainly in the western basin). 



The concentration of hydrogen ions 



As regards the concentration of hydrogen ions the Aral waters differ from 

 those of other big lakes ; the pH index is comparatively small (7-2 to 7-8). 



Plant nutrients 



The distribution of plant nutrients in the waters of the Aral Sea has some 

 peculiar characteristics. There is a normal active reaction, which on the 

 average gives only small seasonal fluctuations (8-20 to 8-34) throughout the 

 whole Sea. 



These waters are very poor in phosphates. Their average content (P mg/m 3 ) 

 in certain years (L. Blinov, 1956) varied within the limits 10 to 4-2 mg/m 3 . 

 Over a period of years the largest amount of phosphates, recorded in August 

 1949, was 231 P mg/m 3 . In contrast with other Seas the quantity of phos- 

 phates here decreases with depth, often down to zero (10 to 20 m), and there 

 is no accumulation of phosphorus in the depths. In the near-bottom layer 

 phosphates are rapidly used up by vegetation. The average phosphate con- 

 tent in the upper layer of the Sea is given in Table 280 (L. Blinov). 



The nitrate content is also very low; it was found to be no more than 5 

 mg/m 3 in individual samples. Some increase was recorded only in the estuar- 

 ine zones. There is more nitrogen in ammonium salts in the Aral Sea waters, 

 its content reaching 80 mg/m 3 . However, ammonium nitrogen is apparently 

 of very little use. L. Blinov (1956) points out that it would hardly be possible 

 to find another place affording a more monotonous picture of an 'analytical 

 zero' of phosphorus and nitrogen than the Aral Sea. The content of silicic 

 acid in the Aral Sea is considerably lower than in other seas; however, 



* L. Blinov (1956) has investigated the chlorine number of the Aral Sea waters and has 

 worked out the following formula for the determination of the salinity of total salts in 

 terms of chlorine: 



5% = 0-264+2-791 d% 



