Remediation and management of degraded earthen shrimp ponds in Indonesia and Australia

• Australian National University, Australia
• Research Institute for Coastal Fisheries, Indonesia
• University of Western Sydney, Australia
• Research Institute for Coastal Fisheries, Indonesia
• University of Hassanudin, Indonesia
• Center for Soil and Agroclimate Research, Indonesia
• NSW Department of Primary Industries, Australia
• Assessment Institute for Agricultural Technology, Indonesia
• Central Research Institute for Fisheries, Indonesia

Until recently problems of production in shrimp farms of the Asia Pacific region have been linked to disease and farm management practices. There was little understanding of the effect of acid sulfate soils (ASS) on pond productivity. An earlier ACIAR study in Indonesia, Philippines, India and Australia found a link between ASS and disease in wild and pond-cultured aquatic animals, so severe in some circumstances that shrimp ponds were abandoned.

This has been the case in India and now in Indonesia, where many small farm owners, particularly in rural areas and transmigration zones had turned to shrimp farming in place of traditional agriculture. The failure of shrimp ponds in these systems has led to reduced land value, economic hardship, altered social structure, lower standards of living and long-term environmental degradation. The problems faced on acid sulfate soils in Indonesia were considered so large that urgent research was needed. Research on sediment accumulation and soil erosion were also critical to more effective shrimp farming in Australia, especially in light of the need to comply with strict environmental guidelines in order to gain and retain an aquaculture licence.

The project aimed to develop and assess cost-effective, low technology methods of treating and managing soil acidification associated with the disturbance of ASS. It also tested low-cost technology, settlement ponds and vegetation planting to ameliorate and conserve soils on pond walls and bottoms, and in effluent canals. Another focus was the accumulation of iron in pond sediments and development of strategies to minimise iron leaching from the soil and its deposition in intensive ponds.

The project team assessed various cost-effective, low-technology methods for treating and managing acidification brought about by disturbance to acid sulfate soils. Study sites on soils typically used in shrimp farming in Australia and Indonesia were used for field experiments .The scientists characterised the soils, acid production rates and hydrological conditions in the ponds.

The team tried various low-cost ways of treating the acidity-adding lime, flushing with seawater, laying down a capping material at the bottom of the pond or leaching the soils. The different methods were evaluated both at the ponds and in adjacent groundwater. Treated and untreated ponds were compared.
The main method of reducing soil erosion is through plant growth. Acid-tolerant and salt-tolerant plant varieties were evaluated as stabilising agents. In ponds already abandoned the team tested treatments on accumulated sediments, assessing the potential for using such sediments as topsoil once the acidity was neutralised and salinity reduced.

Finally, the project examined the relationship between sediment composition and the health of shrimps.

The project produced an immense amount of valuable information for the shrimp industry as well as for resource and environmental planning in Indonesia and Australia. Major outcomes included description of the chemical and physical processes leading to ASS problems, and development of methods to identify ASS in the field and laboratory to assist in site selection for shrimp ponds.

Other advances included the development of strategies for dyke construction, lime use and water management for ameliorating and minimising the effects of ASS in shrimp ponds. Alternative farming systems were trialled for ponds severely affected by ASS, including use of net enclosures for juvenile shrimp production, and culture of milkfish and seaweed. Different types of acid- and salt-tolerant vegetation were tested to determine their effectiveness against erosion from rill, splash, wind and wave. The vegetation was found to decrease the likelihood of erosion and reduce the levels of erosion in water and the erodability of pond soils.

Pond construction was investigated, including pond wall stability under different slopes, dyke heights and widths for the common soil types, lining materials and water management to prevent soil erosion. To determine the extent of the ASS and as a guide to future planning of coastal shrimp aquaculture the scientists employed geographic information systems, remote sensing techniques and soil assessment to map and classify ASS across South and Southeast Sulawesi.

Data sharing with other agencies led to the redesign of a large irrigation system based on soil mapping and characteristics. Before the redesign the system was planned to run through a large area of ASS.