The Distribution of H^S in the Lake of Faro 199 



During this time, the hydrogen sulphide was found in in- 

 creasing quantities from the transition zone towards the bottom. 

 At 10 m it had already reached remarkable values, between 

 54.74 and 66.15 mg/L. The maximum value found was 84.52 

 mg/L at 25 m in March. 



It is to be pointed out that the quantity of H-S contained in 

 the "red water" was between a minimum of 0.78 mg/L, as found 

 on 4 April at 9 m at station A, and a maximum of 49.50 mg/L, 

 as found on the same day at 10 m at station C. 



Quite exceptional values were found in samples collected on 

 4 August. Oxygen at the surface readied 4.08 ml/L, a value 

 which, although low, however is to be considered as possible 

 during that period. Oxygen disappeared almost completely at 2 

 m and was replaced by increasing quantities of H-S. Up to 10 m, 

 HuS appeared in rather reduced limits (14.13 mg/L), while from 

 15 m to the bottom it showed a tendency to reach its normal 

 values (68.26 mg/L). 



In tlie following months, the distribution of the two gases 

 had a tendency to progressively stabilize, according to their 

 normal stratification. Indeed in November and December 1960, 

 oxygen was found down to 10 m in quantities above 3 ml. Notice, 

 however, that hydi'ogen sulphide at a depth of 15 m, which 

 previously had rather high values and slightly less than the 

 noted maximum, now had a tendency to gradually decrease 

 (Fig. 4). On 6 December, the quantity of H2S present was only 

 0.29 mg/L. 



In the last month of the investigation, there took place again, 

 to a less extent and thus with less distrophic effects, the condi- 

 tions encountered in August. On 9 January 1961 at 5 m only 

 1.20 ml of O2 was found, with slightly lower quantities at both 8 

 and 10 m. 



Surface temperature (Fig. 5), was a maximum of 27 C in 

 July, and a minimum of 10.9 C in January, and appeared to 

 follow the changes in the atmospheric temperature. At 20 m, all 

 through the year, there was a regimen of omotermia with 

 temperatures between 15.5 and 16 C. At 10 m, during the early 

 period of investigation, up to July, the temperature followed the 

 changes in the temperature of the deep layers, while in the 

 remaining months, it followed the changes of the surface temper- 



