Soil & Water Interaction And Its Implications In Aquaculture

Soil and Water Interaction and Its Importance In Aquaculture Dr. Subhendu Datta Sr. Scientist CIFE, Kolkata Centre SALT LAKE CITY, KOLKATA, INDIA

Introduction


Soil is a key factor in aquaculture. Most of the pond is built from from and in soil.




Many dissolved and suspended substances are derived from contact with soil.




Pond soil are store house for many substance that accumulate in the pond ecosystem and chemical and biological process occurring in the surface layer of pond soil influences water quality and aquaculture.




Hence an understanding of soil properties and the reaction and process in soil can be useful in pond aquaculture.

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POND SOIL


Material composing the bottom of streams, lake and ponds are known as sediment, mud or soil.




The pond bottom is originally made of terrestrial’ terrestrial’s soil and when the pond is filled with water the bottom becomes wet.




Mixture of solid materials and with water is called ‘mud’ mud’.




Solids settle from the pond water and cover the pond bottom is ‘sediment’ sediment’.




Basic function of pond soil is an embankment that impound water and forms barrier to seepage so that pond will hold the water.




Substances continually settle from pond water into the pond bottom bottom




For example - suspended solid, particles of soil and organic matter that eroded from pond bottom and insides of levees by water current and and wave action, manure and uneaten feed from management inputs and remains of plants and animals produced with in the pond.




Substances also enter from solid phase of soil from the aqueous phase through ion exchange, adsorption and precipitation.




For example - potassium can be exchanged for other cation on the soil, phosphorus can be adsorbed by soil and CaCO3 may precipitate from solution and become a part of the bottom soil matrix.

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Substances that enter the soil may be stored permanently, or they they may be transformed to other substance by physical, chemical or biological biological means and lost from the pond ecosystem.




For example - phosphorus adsorbed by pond soil can become buried in the sediment and lost from circulation with the pool of available available phosphorus.




Organic matter deposited on the pond bottom is decomposed to inorganic carbon and released to the water as carbon dioxide.




Nitrogen compound may be denitrified by pond soil microorganism and lost to the atmosphere as nitrogen gas.




Bacteria, fungi, algae, higher aquatic plants, small invertebrates invertebrates and other organism know as benthos live in and on the bottom of the soil.




Crustaceans and some species of fishes spend much time on the bottom soil and many fish lay eggs in the nest built in the bottom.




Benthos serves as food for some aquaculture species.




It also involved in gas exchange, primary and secondary productivity, decomposition and nutrient cycling.

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Substances stored in the pond soil can be released to the water through ion exchange, dissolution until equilibrium attained between solid phase and liquid phase.




The equilibrium concentration may be too low for optimal phytoplankton growth or the equilibrium concentration of a heavy metal may be too high enough to cause toxicity to aquatic animal.




Microbial decomposition is extremely important because organic matter is oxidized to CO2 and ammonia and other nutrient element is released.




Carbon dioxide and ammonia are highly soluble and quickly enter the water.

Soil Properties


Soil consists of weathered mineral organic matter. They are a product of interaction among parent material, climate and biological activity.




It is well known that soil differ from place to place on the earth earth surface and beneath a given site the soil profile consists of horizontal layers that change in characteristics with depth given given below the land surface.




The most active fraction of soil is clay particles, because of electric charge and large surface area and the organic matter, of of its biological activity and high chemical reactivity.

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The pore spaces among the mineral fragments and organic matter are filled with air and water.




In flooded water air is completely displaced by water.




This greatly impedes the movement of oxygen into append soil, because the oxygen must move over by diffusion or be carried along with water that seeps through the soil.




Coarse texture soil is better oxygenated than fine.




Pond soil often are fine textured because they usually have at least least 2222-30% clay content will limits seepage and they have higher percentage of organic matter than terrestrial soil.




Pond soil is highly reactive, have oxygen demand and tend to become anaerobic.




In addition to this specific chemical compounds in soil have a pronounced affect on aquaculture.




Soil that have been highly weathered and contain appreciable quantities of aluminum oxides and hydroxides or acidic and water in contact with acidic soils have low total alkalinity and poorly buffered against pH change.




The presence of iron pyrite in pond soils can results in extreme acidity because sulphuric acid is formed from pyrite oxidation.




Free calcium carbonate in soils leads to high concentration of total alkalinity and total hardness of overlie water.

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The four most important soil features for aquacultural production are





Texture Organic matter pH Presence or absence of particular soluble compound that may have beneficial effect or harmful to water quality.

Some important reaction and processes controlling pondpond-soilsoil-water interaction are

Reactions











Dissociation: CaCO3 + CO2 + H2O = Ca2+ + 2HCO3Precipitation: Al3+ + H2PO4 + 2H2O = Al(OH)2H2PO4 +2H+ Hydrolysis: Al3+ + 3H2O = Al(OH)3 + 3H+ Neutralization: HCO3- + H+ = H2O +CO2 Oxidation: NH4+ 2O2 = NO3- +2H+ + H2O Reduction: SO42+ + 4H2 = S2- +4H2O Complex Formation: Cu2+ + CO32- =CuCO3 Adsorption: adsorption of phosphorus on soil colloids Cation Exchange: K (Soil) = K+ (Water) Hydration: Al2O3 + 3H2O = Al2O3.3H2O

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Processes










Sedimentation: Sedimentation: Soil particles in runoff settle to pond bottom Decomposition: Decomposition: Microorganisms break down soil organic matter. CH2O + O2 → CO2 +H2O Photosynthesis: Photosynthesis: Benthic algae produce organic matter and release oxygen. 6CO2 + 6H2O = C6H6O6 + 6O2 Diffusion: Diffusion: Oxygen diffuses into bottom soil from water above Seepage: Water carrying dissolved substance seeps downward into the pond soil Erosion: Water current in pond erode the bottom soil Suspension: Particulate matter eroded from the bottom is suspended in pond water.

CHEMISTRY OF POND MUD


When pond is flooded with water, the first effect of flooding is to drive out the air from the soil.




Then the aquatic bacteria in the soil become active, decomposing the organic matter in the newly water logged soil and using up the oxygen.




This lead to anaerobic conditions and the pond mud is in a reduced reduced state and the flooded soil comes to contain carbon dioxide (CO2) but no oxygen (O2).




Under such conditions, sulphates are reduced to sulphides (SO4 to S) nitrogenous substances to ammonia (NH3), Iron occurs in the reduced form (Fe2+) and some of the organic matter to methane (CH4).




Because of ammonia, the soil becomes alkaline and because of presence presence of ferrous ion complex, the colour of the soil becomes a more or less intense blue blue--black.




The water overlaying the mud becomes oxygenated partly because the the water dissolve oxygen from the air and partly due to the oxygen (O2) release during the photosynthesisby the aquatic plants presents in the pond phytoplankton, which soon soon develops there.

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CHEMISTRY OF POND MUD (continued… (continued…)


This oxygen will oxidize the surface skin of the pond mud (1 to few mm thick only) and develop on oxidized microzone. microzone.




Where ferrous iron (Fe2+) becomes ferric (Fe3+), sulphides (S) becomes sulphates (SO4) and ammonia (NH3) becomes nitrate and nitrite.




Because of disappearance of ammonia (NH3) and the appearance of acid, this layer becomes acidic and the surface of the pond mud turned from blue – black to yellow to brown in colour due to the presence of ferric compounds compounds (Fe).




This phenomenon can almost always be seen when the mud of a pond pond is exposed, for example when it is drained to take the crop of fish, fish, the foot prints of men working in the mud are deep blue or black, the undisturbed mud mud is yellow.




But almost as one looks, the exposed black reduced soil takes up oxygen from the air and turns yellow.

Mechanism of Release of Nutrients from Soil


The yellow ferric iron compound chiefly the hydroxide at the oxidized oxidized surface layer are usually in a very finely divided or colloidal state and this colloidal ferric hydroxide together with colloidal humic substances make a mud which has highly absorptive properties for both acid and basic radicals.




As long as the iron compound on the surface layer of the mud were were in ferric state, the surface was strongly adsorptive of positive ions, such as ammonia, ammonia, calcium, manganese and of negative ions such as phosphates and silicates. But nitrate and nitrite were not adsorbed.




During temporary cutting of oxygen from the surface layer of the mud (which may be caused by excessive respiration at night, or by lack of circulation circulation of water or it may be, in deep ponds, a longer term phenomenon due to layering of water), the adsorbed ions are released into the water often in considerable quantities.




The reduced iron has no power to hold, then diffuse up into the pond water and are taken up by plants and then by fish.

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REDOX POTENTIAL (Rh)


When the oxidation taking place in surface of the mud and reduction at lower levels, the electrical charges on the molecule molecule of electrolytes and ions in these two soil layers are responsible for for differences in potential i.e. Redox potential.




Reducing conditions prevails when potential is below millivolts and above it, oxidising conditions occur.




Therefore, the values of redox potential in the pond mud will give an idea about binding or releasing the ions of nutrient materials from pond mud.

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FATE OF ADDED FERTILIZERS


The binding and releasing by adsorption on the pond mud applies not only to the nutrients naturally occuring in the soil, but also to fertilizer added to the pond.




The phosphate in the fish pond remained in the soil, adsorbed on the oxidising layer of the mud on colloidal ferric hydroxide and in absence of the oxygen (O2).




Ferric ion is reduced to ferrous ion and phosphorus is released in soluble form in the water.




Phosphate is also incorporated in the bodies of micro– micro–organisms. These two factors account for the residual effect of phosphatic fertilizers and subsequent release under suitable condition even after 4 years of application.

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H2S TOXICITY


The hydrogen sulphide gas which is frequently detected in the mud during the construction of the ponds could poison the fish.




But so long, as the surface layer of the mud is oxidizing, this very poisonous gas, deadly to fish, could not possibly diffuse into the water, for the sulphide could soon be oxidized to harmless sulphate. sulphate.




If a free circulation of the pond water is impeded, as for example by dense vegetation, then the smell of the gas appears. Clearance of vegetation will minimize the chance of H2S toxicity in this case.




Due to all these fact described above the pond mud has been described as the “Chemical laboratory’ laboratory’ of pond” pond”.




Relationship between pond soil and aquatic animal production is mostly indirect.




Soil affects nutrient concentration in the water, which in turn influence plant productivity.




In pond where aquaculture species depends on natural food for their growth & development, fertility of soil is key factor regulating the fish production.




In pond where feeding of fish comes from the feed; fertility of soil is not as important, but in that condition also soil condition condition is extremely important in determining the water quality and the survival and growth of fish

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Importance of pond bottom soil in fertilized pond


The mineral composition of pond water is to a large degree is reflection reflection of mineral compositions of the soil.




the colloidal fraction of soil consisting of humic substance, hydroxide gel and clay is a powerful absorbent of soluble mineral nutrient and governs their availability




The pond soil is the medium is which live microorganism responsible responsible for decomposition of organic matter and transformation of chemical elements.




The pond soil is the source of food organism for fish.





At the same time pond soil can indirectly effect the aquaculture production through Pond soil can be source of toxic metabolites that can enter water water and harm aquatic animal health




Sedimentation can smother aquatic organism and can destroy fish nesting sites




Sub optimal soil texture and ph may limit production of benthos, which is the food of many aquatic animals.

Effect of aquatic animal on the pond soil


Fish stir the bottom by producing the water current when they swim, swim, and many species make shallow depression for nesting and some species stir bottom when capturing the prey.




Stirring pond bottom can reused sediment. Pond stocked with gold fish, common carp or other bottom feeding fish often are turbid with soil particles suspend.




organism which borrow in the bottom loosen the soil and make it more susceptible to erosion by water current, and burrowing activity activity mixes the sediment and also enhances the aeration of the upper soil soil by facilitating the exchange of pore water with pond water.




Benthic organism dies and contributes organic matter to the soil hence aquatic animal are contributing to the development of soils. soils.

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Soil properties and pond aquaculture Banerjea studied the relationship between soil properties and fish production. According to him fish production is classified as:- Low <200 kg - Average 200-500 kg - High >500 kg









Parameter\ Parameter\Fish production

Low

Average

High

pH

<5.5&>7.5

5.55.5-6.5& 7.57.5-8.5

6.56.5-7.5

Available phosphorus

<30 ppm

3030-60 ppm

>60 ppm

Available nitrogen

<250 ppm

250250-500 ppm

>500 ppm

Organic carbon

%0.5

0.50.5-1.5 %

1.51.5-2.5 %

Carbon nitrogen ratio

<5 & >15

5-10

1010-15

Exchangeable calcium ion

<100 ppm

100100-200 ppm

200200-300 ppm

And also ideal clay content in pond soil is ranging from 25 % to 50 %

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Classification of soil Particle fraction name

USDA

ISSS

Gravel

>2mm

>2mm

Very coarse sand

1-2mm

Coarse sand

o.5o.5-1mm

Medium sand

0.250.25-0.5mm

Fine sand

0.10.1-0.25mm

Very fine sand

0.050.05-0.1mm

Silt

0.0020.002-0.05mm

0.0020.002-0.02mm

Clay

<0.002mm

<0.002mm

0.20.2-2mm

0.20.2-2mm

Pond bottom management


Soil properties and relationship among pond soil, water quality and aquaculture production has been discussed.




It has been shown that initial soil condition in new pond sometimes unsatisfactory and of soil may deteriorate over time in response to demand imposed on them by aquaculture practices, so little treatment is needed for improvement of soil condition.

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Liming


Soil acidity is management concern because both total alkalinity and total hardness of pond water is closely associated with bottom soil acidity.




The total alkalinity and total hardness should be > 20 mg/L to maintain enough buffering action, pH 66-9.5 and sufficient dissolve inorganic carbon to support good phytoplankton growth.




For crustacean pond it should be >50 mg/L because of importance of carbonate and bicarbonate in moulting. moulting.

Pond with acid sulphate soil


Potential acid sulphate soil is identified by a high total sulphur concentration (>0.75 % or low pH (2(2-3) upon drying for several days.




Effects of this acid sulphate soil are low pH, low alkalinity of water and low aquacultural production.

Ways to deal with acid sulphate soil areare


Drain the soil and wait until natural oxidation and leaching remove remove the acidity.




Dry the bottom soil periodically and then flush it with water to remove acidity




Lime to neutralize the acidity




Prevent the oxidation of iron pyrite so that acidity is not expressed. expressed.

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Bottom soil sterilization


To prevent pathogen from surviving between aquaculture crops and infecting the fish and crustacean stocked.




The most sterilants used are burnt lime, hydrated lime, and chorine compounds.




The first two can raise the pH and kill the pathogen, while chlorine is directly toxic to kill the pathogen.

Probiotics


A number of products are promoted to enhance beneficial chemical and biological processes and to improve soil quality.




These products include cultures of living bacteria, enzyme. Preparations composted or fermented residues, plant extracts, and and other concoctions.




There is no evidence from research that any of these products will will improve soil quality.




Nevertheless, they are not harmful to the culture species, surrounding surrounding environment, workers, or quality of aquaculture products.

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Oxidation of pond bottom


Techniques that enhances dissolved oxygen concentration at the pond bottom, increases the redox potential in the surface layer of soils.




This lessens the possibility of migration of toxic metabolite from deeper, anaerobic soil into the pond water.

During growth period


Low pH can retard decomposition of organic matter and permits its accumulation and cause a high oxygen demand in the surface layer of soil. Low concentration of nitrogen retards the decomposition of organic matter because soil micro organism can use oxygen from nitrate when molecular oxygen depleted.




Nitrogen fertilizer should be applied to static pond at 10 kg N/ha every 2 or 4 weeks.




Liming and nitrogen fertilizer can be more effective in enhancing the aerobic microbial activity when aeration is used to supplement the oxygen supply.

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Bacterial amendments


Bacteria capable of nitrogen fixing, prevention off flavor, reduction reduction in the properties of blue green algae, less nitrite, nitrate, ammonia and and phosphate ; more dissolve oxygen and more rapid organic matter degradation can can achieved.

Aerators


Different type of aerators is mainly paddle type of aerator, vertical vertical pump aerators, propeller aspirator and diffused air aerators.




The main advantages of adopting aerators are:




Prevent thermal stratification




mixing of pond water and provide better oxygenation




Enhance the decomposition of organic matter and thus preventing anaerobic condition.




In most case aeration should be applied at 22-3 kilo watt/ha to improve the condition at the soil water interface.




Bottom animal disturb bottom soil and improve aeration by encourage movement of oxygenated water with in the soil mass. The process is called as “Bioturbation” Bioturbation”.

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Chemical oxidant


Application of sodium nitrate to eutrophic lake prevents highly reduced condition in sediment since here nitrate is function as an oxidant and poises the oxidation reduction potential. NO3 +2H+ +2e- =NO2 +H2O




Similarly calcium peroxide releases oxygen as follows 2CaCO2 + 2H2O = 2Ca(OH)2 + O2




And also hydrogen peroxide releases oxygen as follows 2H2O2 →2H2O +O2




Among them sodium nitrate is cheaper than peroxide and less hazardous to handle.




Hydrogen sulphide released from anaerobic pond soils can be harmful to shrimp and fish. This can be controlled through application of potassium permanganate to oxidize H2S 4KMnO4 +3H2S → 2K2SO4+ 3MnO2 +3H2O




But treatment cannot be highly successful because KMnO4 is highly soluble.




A possible method for preventing H2S in pond is through Iron application. Where iron reacts with H2S and precipitates it as highly insoluble Ferrous Sulphate Fe +H2S →FeSO4

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DRY PERIOD


During the water – logged period where the pond mud is under anaerobic conditions and alkaline in reaction, oxidation processes of organic organic matter cannot be completed and oxygen (O2) debt is built up of these partially oxidized products of fermentation.




Exposure to air completes this oxidation after resulting in the release of carbon dioxide (CO2) making the soils slightly acidic.




The completion of oxidation releases the contained nutrient materials materials by mineralization and acidic condition cause these materials to remain remain adsorbed in the soil, ready for release when the pond is refilled and the oxidation oxidation – reduction system sets itself up again.




The chief advantage of dry period is the restoration of the fertility fertility of the pond.




Rack the bottom if dewatering is not possible. Repeated netting is useful for this.

During the fallow period….


The rate of soil organic matter decomposition by aerobic process when ponds are drained and their bottom are exposed to air is increased by manifolds. manifolds.




The optimal length of fallow period depends on drying conditions and temperature.




In the dry season pond bottom become so dry after 2 to 4 weeks that that microbial activity is suppressed by lack of moisture.




Unless soil can be irrigated to replenish soil moisture there is a little value in extending the fallow period of moisture depleted soil.




The moisture concentration for processing of organic matter is 10 10 – 40 % for different soil.




Drying of soil rich in iron pyrite can causes extremely low pH. So acidity must be washed out of soil before ponds are filled and restocked.

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Tilling


When the soil contain expandable clay dry, cracks forms in the surface surface and extend to depth of 10 -100 cm into the soil.




Air can penetrate the crack and improve oxygenation but air will not readily penetrate the soil mass comprising of columnar blocks between cracks. cracks.




Surface soil dries quickly when compared to deeper soil because there is better exchange of water vapour with atmosphere. A surface layer acts as as a barrier to evaporation.




Plowing breaks up the surface crusts and columnar blocks that form form during drying and greatly improves conditions for drying and aeration in in deeper layer of soil.




The most efficient device for plowing soil - tractor powered rototifer

Liming


Objective of fallow period is to aerate soil and encourage oxidation oxidation of organic matter. The pH range for organic matter decomposition is 7.5 – 8.5. pH 4.54.5-5.0 5.05.0-5.5 6.06.0-7.0

Agricultural limestone (Kg /ha) 4000 2000 1000




Agriculture limestone should be evenly spread over the soil surface, surface, but uniform application is less critical than when spreading burnt or hydrated hydrated lime for soil sterilization.




Agriculture limestone should be incorporated into the upper 55-10 cm soil layer by tilling. Limestone will not dissolve unless soil contains plenty of moisture. moisture.




Burnt or hydrated lime is not recommended as a routine soil treatment treatment between crops.




These materials cause an initial high pH that kills microorganism microorganism and retard the decomposition rate. Agriculture lime is safer to apply and will not cause soil pH to rise above 8.

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Fertilization


The C: N ratio is between 5&10 in most pond soils and organic residues readily decompose if other factor affecting soil respiration is favorable.




The C: N is wide in organic soil and fertilization to increase nitrogen availability accelerates decomposition.




A rate of 100mg N/Kg was necessary to significantly enhance the decomposition of soil organic matter.




Any common nitrogen fertilizer can be used, but sodium nitrates appear to be most effective.

Sediment


Pond should be managed to avoid sediment problem. Vegetative cover cover on watershed will minimize erosion by rainfall and runoff.




Where wave action causes serious erosion of levees, trees or shrubs shrubs are planted to make wind breaks and riprap can be placed on vulnerable expense of levees.




Excessive aeration should not be applied and in aerated ponds, bottom bottom should be hardened in areas with higher water velocities. Tilling pond bottom bottom is aid to drying and organic matter decomposition but it encourages erosion in aerated aerated pond.




It is well known in commercial pond aquaculture that maintenance of water quality with adequate range for optimal aquatic animal production becomes becomes more difficult as pond ages.




The accumulation of sediment enriched with nutrient and organic matter is thought to be a major factor causing the intensification of management problems problems in old ponds.




So the techniques for removing sediment from old ponds should be evaluated Dredges might be a valuable tool for use in aquaculture.

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The following actions should be considered by pond managers who wish to maintain good soil condition in the bottoms of aquaculture ponds: ponds:


Avoid highly intensive aquaculture operation. High nutrient and organic matter inputs to the ponds lead to soil deterioration.




Use conservative fertilization, manuring and feeding techniques. Excessive inputs of nutrients and organic matters are wasteful and harmful to ecosystem.




Reduce external sediment load by maintaining good vegetative cover cover on watersheds and using sediment ponds where the water supply is contaminated contaminated with suspended solids.




Moderate mechanical aeration and waters circulation enhance dissolved dissolved oxygen concentration in bottom water and in surface layer of soil.




Reduce internal sediment load by protecting banks from wave erosion erosion and avoiding excessive aeration and water circulation.




Prevent infestation on rooted aquatic macrophytes by maintaining water depts. greater than 0.5mt in all areas of pond.




encourage plankton growth so that visibility in to the water is not more than 303054 cm. do not allow infestation emergent macrophytes along levees and in shallow water area or mats of floating macrophytes. macrophytes.




An aggressive liming program in acidic water will maintain Ph total total alkalinity and total hardness in desirable ranges.




Identify areas with potential acid sulphate soils. Use pond construction and management techniques that minimize exposure of potential acid sulphate to the air.




Where possible allow a fallow period to dry soils between aqua cultural cultural crops.




Tilling, liming and fertilization enhance organic matter decomposition decomposition between crops in some ponds. Compact tilled soils before refilling ponds to reduce aeration in aerated ponds.

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Pond soil can be sterilized to destroy fish pathogens. Application of brunt or hydrated is probably more reliable than chlorination.




Future research is needed to determine if chemical oxidants can be effective in maintaining aerobic condition in surface layers of bottom soils.




Positive benefits of bacterial and enzyme amendments have to be demonstrated.




Pond should be renovated periodically with removal of sediments from deep areas to reshape bottoms and levees.

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