The Free On-line Aquaculture Dictionary

Geological Impacts on Aquaculture

Geological Feature

Effect on aquaculture operations

Acid Sulphate soils The exposure of acid sulphate soils to oxygen, through excavation for ponds, can lead to the acidification of the soil to such an extent that it becomes very difficult to maintain the pH of the pond. Typical areas where acid sulphate soils are found is in mangrove areas where there is no oxygen in the muds. The soil only becomes acidic once exposed to oxygen and the reaction is irreversible, therefore many of the large areas of mangrove that have  been removed cannot be reinstated as the soil will no longer support the plant or animal life of the mangrove.
Clay The percentage of clays in a soil determine itís porosity. Soils with a high clay content are suitable for ponds etc. as the water will not readily leak out of the pond. A rule of thumb test is to gently squeeze some soil in your hand. If it retains itís shape and does not crumble, it probably has a clay content high enough for pond or channel building. Soils with high clay contents also make more stable channels as the sides do not crumble so easily. Areas of high clay content may however give rise to flash floods following rainfall, as the rain does not soak into the ground, and instead runs off directly into the water courses

Limestone, chalk and other and Calcium carbonate deposits

Areas of rocks where there is a significant amount of Calcium carbonate or other types of lime, will cause the water in the area to be well buffered, with an alkaline pH. As limestone and chalk are porous, springs are often found in areas with such rock.

Peat

Areas where peat is found often exhibit waters with an acidic pH. As the water soaks through the peat the humic acids reduce the pH of the rain water. Peat areas also act as a sponge, soaking up the water and slowly releasing it. Such areas are therefore often quite secure sources of water for hatcheries etc.

Porous rocks

Areas of porous rocks and soils give rise to steady, consistent flows of water. As the rain can soak into the ground, flash floods are avoided, and the water held in the rock is released at a more or less constant rate through springs resulting in little variation in summer and winter flow rates.

Non Porous rocks

Unless there is a good covering of soil and vegetation, to soak the rain up, areas of non porous rocks such as granite, may however give rise to flash floods following rainfall, as the rain does not soak into the ground, and instead runs off directly into the water courses.

Metal ores

The presence of metal ores in areas where waters are acidic can cause toxicity problems as the metals leach into the water. This is generally only a problem at pH<6.0