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Proceedings - Balai Penelitian Tanah

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157<br />

Sammut et al.<br />

Tarunamulia, 2006; Tarunamulia, 2008). The mapping has also<br />

shown that many ponds are excavated in sandy-textured soils,<br />

including sediments that are also classified as ASS due to the<br />

presence of pyrite. Sandy ASS are a significant challenge to the<br />

reconstruction effort because these sediments have both acid and<br />

engineering problems (Sammut and Tarunamulia, 2006).<br />

Soil sampling and mapping sub-programs have been conducted along<br />

the north east coast where most farms are concentrated. A soil<br />

texture model was developed by Tarunamulia (2008) to identify areas<br />

according to their dominant soil texture and associated engineering<br />

constraints. An existing soil model from ACIAR project FIS/97/22 in<br />

South Sulawesi was adapted to map ASS in Aceh. The latter model is<br />

based on information on the association between ASS formation and<br />

distribution with local geology, geomorphology, elevation, vegetation<br />

type and hydrology. Soil models and maps have been extensively<br />

ground-truthed along the north east coast, but west coast mapping of<br />

ASS is currently entirely based on remote sensing, GIS modelling and<br />

past soil data sets (Tarunamulia, 2008).<br />

Acid sulfate soils present a threat to shrimp and fish production in<br />

several ways. Firstly, the acid produced by these soils mobilise metals<br />

which are toxic to shrimp and fish (Sammut, 2000). Aluminium and<br />

iron can cause severe gill damage in shrimp and fish, stunt growth<br />

and reduce beneficial algal blooms. Mass mortalities of stock may<br />

also occur due to osmoregulatory stress through acid and aluminiuminduced<br />

gill lesions (Callinan et al., 2005; Sammut, 2000). Aluminium<br />

also flocculates clays leading to shrinkage and cracking of dyke soils<br />

(Sammut, 2000). Under severely acidic soil conditions, aluminium may<br />

occur as pearly-white aluminium floccules in the less acidic pond<br />

waters. Suspended iron floccules can precipitate or form on pond<br />

walls where they coat benthic algae used in milkfish production or<br />

smother shrimp gills. Iron and aluminium readily strip phosphate from<br />

the water column and consequently reduce the concentration of<br />

beneficial algal blooms (Sammut, 2000). Affected ponds require<br />

higher than normal lime and fertiliser application to neutralise acidity<br />

and maintain sufficient concentrations of phosphate for phytoplankton<br />

blooms (Mustafa and Sammut, 2007; Sammut, 2000). At high<br />

concentrations, iron also coats shrimp and renders them unsaleable<br />

due to the discoloration of the carapace. Iron oxides and jarosite are<br />

commonly formed on the walls of canals and dykes. The presence of<br />

these minerals is a good indicator of advanced pyrite oxidation in soils<br />

(Dent, 1986; Sammut et al., 1996). High concentrations of metals in<br />

ASS are also a bioaccumulation risk in shrimp, fish and seaweed<br />

culture (Gosavi et al., 2004).<br />

International Workshop on Post Tsunami Soil Management, 1-2 July 2008 in Bogor, Indonesia

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