Monday, April 18, 2016

18/04/2016: Decomposition and accumulation of organic matter in ponds - Proper management prevents problems
Image: Sarah Joy
The major sources of organic matter in aquaculture ponds are organic fertilizer, remains of microorganisms — phytoplankton, zooplankton, and benthos — produced within the pond, faeces of the culture animals, and uneaten feed, writes Claude E Boyd, PhD in the Global Aquaculture Advocate.

A relatively small proportion of the total organic matter input to ponds (usually less than 10 percent) is recovered in the form of harvested fish, shrimp or other culture animals. The rest of the organic matter is converted to carbon dioxide and water by respiration of the culture species and other pond biota, discharged in pond effluent, or it accumulates in the sediment.

Many producers believe that a large amount of organic matter in pond bottoms negatively impacts sediment condition and water quality during future crops. Although this opinion is true, organic matter decomposes quickly, and its accumulation is not usually as great as often believed. More importantly, with proper management, problems associated with organic matter accumulation in ponds can be avoided.

Factors controlling decomposition
The process of microbial decomposition of organic matter is controlled by several factors to include water temperature, pH, dissolved oxygen concentration, and the chemical composition of the organic matter itself. Bacteria and other organisms of decay decompose organic matter fastest at temperatures of 30 to 35 degrees-C — doubling the temperature in the range of 0 to 35 degrees-C usually will double the rate of decomposition.

Bacteria function best in the pH range of 7 to 8.5. When the pH is lower, decomposition by fungi is favoured over that by bacteria — especially at pH less than 6. Fungi are not as efficient as bacteria in decomposing organic matter because they convert more of the organic matter to their own biomass than do bacteria.

Read the full article in the Global Aquaculture Advocate HERE

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