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Although 16.6 million metric tons of carbon are annually buried in aquaculture ponds, estimated carbon emissions for culture species have approached several metric tons of carbon per metric ton of aquaculture product.
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Various studies suggest that maintaining minimum daily dissolved oxygen concentrations above 3 mg/L in channel catfish and penaeid shrimp ponds assures better feed consumption and growth.
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The oxygen demand of feed represents the dissolved oxygen removed by the respiration of culture animals, microbial decomposition of uneaten feed and feces, and oxidation of ammonia nitrogen by nitrifying bacteria.
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Carbon-nitrogen (C:N) ratio is an important variable related to soil fertility. Intensive ponds have lower C:N ratios, while higher ratios are found in extensive ponds and those constructed in organic soil.
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Excessive concentrations of trace metals, especially copper, are toxic to phytoplankton and other aquatic plants. The ionic forms of trace metals are toxic to fish and other aquatic animals, but soluble, chelated trace metals are relatively non-toxic.
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In calculating chemical treatments to apply to ponds, one must adjust for the percentage of the active ingredients in products. Adjustments for both active ingredient content and specific gravity must be made for liquid products.
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Ponds constructed on sandy or permeable soils are most likely to have high seepage rates. Ponds built in any soil can seep if improperlty constructed.
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Aquaculture ponds typically have ideal conditions for the growth of various species of phytoplankton. Green algae are considered most desirable in freshwater ponds.
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Ponds should be fertilized a few days after chlorine application to encourage the regrowth of natural food organisms before introducing postlarvae.
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Limit pond soil analyses to soil particle size for use in pond construction decisions, initial analysis of total sulfur, occasional analyses of total nitrogen, and routine analyses of pH and soil organic carbon.
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The direct energy input values for aquaculture include energy used in constructing facilities, producing seedstock and feed, powering mechanical aerators, applying feed and harvesting and processing culture animals.
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Carbon dioxide is both a nutrient and a waste product in aquaculture. Some pond managers feel that application of organic matter to provide additional carbon dioxide can reduce pH and control blue-green algae.
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Iron supplementation of pond fertilizers can improve their effectiveness in promoting phytoplankton growth. Ferrous iron in bottom sediment precipitates hydrogen sulfide gas produced by microbial activity.
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Improved feeds and feeding practices increase the proportion of nitrogen recovered in fish and shrimp and lessen the amount of ammonia excreted by the culture animals.
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Management of dissolved oxygen in ponds with static water is difficult, so managers of non-aerated ponds usually limit stocking and feeding rates.
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Ponds constructed where soils contain sulfides can have problems with low pH in culture water. Liming can be an effective emergency measure.