Acid sulphate soils in aquaculture.

Hello everyone:

Have you heard about this? 
Sudden death of fish at overnight after rain. It happened in many places. It is due to presence of acid sulphate soils. The toxicity which is produced under aerobic condition and diffusion from soil to water then cause sudden death of fish. 


Acid sulphate soils:
       These types of soils present in the regions of wetlands. Excess accumulation of organic sediments in bottom soil causes pyrite formation. Mostly occurs in mangrove areas and other wetlands. The root system in mangroves accumulates more organic matter. 
    It also formed in the area with more anaerobic condition. 


Before that, we have to know about different forms of iron. 
Iron generally present in Ferrous iron in anaerobic condition, when it is oxidized then changed into ferric iron and precipitates as a ferric hydroxides. 

In acid sulphate soils, sulphate gets reduced to sulphide and oxidation of sulphide to sulphur. 

What is present in acid -  sulphate soil? 
     The different components which gives rise to formation of acid-sulphate soils are Sulphate, iron, excess organic matter and anaerobic condition. 
    This is called as pyrite. 

Oxidation of pyrite:
 When the soil gets aerated then this process will happens. 
               Pyrite oxidation
                Acidic condition
                 Ferrous iron
        At low pH get oxidized to 
                    Ferric iron
            Reacts with sulphate
                 Ferric sulphate

Sulphuric acid also formed from the oxidation of element sulphur. 
This causes soil more acidic and not suitable for aquaculture and causes toxicity to animals. 

Iron, aluminium ions in the soils causes various toxicity. These ions make unavailable of essential minerals which is required for primary production in pond. 

Measures to take for treating acid-sulphate soils:
1. Try to avoid the site which have acid sulphate soils
2. Removal of subsoils with certain depth to reduce organic load in pond bottom. 
3. Application of minerals like calcium carbonate to neutralize the acidity. 
4. Drying and drain the ponds at regular intervals. 
5. Gets completely in oxidized zone. 

In this soil can be easily identified by testing soil pH and presence of yellow or reddish colour in the surface soils. 

Thank you.. 

Contact for more info.... 

P. Dhivagar BFSc, 
+91 9384346193

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