SOIL AND WATER QUALITY CRITERIA SOIL AND WATER

SOIL AND WATER QUALITY CRITERIA

SOIL AND WATER CRITERIA/REQUIREMENTS FOR AQUACULTURE • Important - site characteristics • Bottom soils - undesirable - Potential acid sulphate soils, saline soils, high organic matter content, excessive porosity etc • Poor quality water - highly acidic, alkaline, turbid, high BOD, rich in nutrients and organic matter, high in suspended solids or polluted with industrial or agricultural chemicals • Higher amount of nutrients and organic matter due to excessive organic menuring and feed wastage - lead to poor water quality and bottom soil condition

WATER QUALITY CRITERIA IN AQUACULTURE • Influence greatly on the growth and survival of aquatic organism. Dissolved oxygen of water • The optimum dissolved oxygen - of 5. 0 mg/l • A fish might survive 0. 5 ppm DO for few hours • An average condition, 3. 0 ppm DO or less regard as hazardous for fish

Temperature of water • Temperature sets the pace of fish metabolism by controlling molecular dynamics (defeasibility, solubility, fluidity) and biochemical reaction rates • The optimum temperature range for several cold water and warm water fishes are 14 -18 o C and 24 o-30 o C respectively Effects of Do levels on fish production DO (ppm) < 1. 0 > 1. 0 – 5. 0 > 5. 0 effects lethal on exposure for more than few hours fish survive but poor growth normal survival and growth

BOD 5 • The biochemical oxygen demand (BOD) - the amount of oxygen required to microorganisms to decompose the organic matter in a water sample under specific condition of the pond management • Has direct bearing on the oxygen balance of water • BOD 5 values in fish ponds varied between 5 – 20 ppm • The optimum BOD 5 value is 10 – 20 ppm for fish ponds

Turbidity of water • Turbidity - due to suspended soil particles, Planktonic organism and humic substances • The optimum Secchi disc visibility of fish ponds is considered to be 40 -60 cm. Ammonia of water • Fish are very sensitive to unionized ammonia (NH 3 -N); optimum range - 0. 020. 05 mg/l Hydrogen sulfide in water • Fresh water fish ponds should be free from hydrogen sulfide • At concentration of 0. 01 mg/litre of hydrogen sulfide fish loose its equilibrium and subjected to sub lethal stress

p. H • p. H - measure of hydrogen ion concentration in water and indicate how much water is acidic or basic • Water p. H - affects metabolism and physiological process of fish • Considerable influence on toxicity of ammonia and hydrogen sulfide as well as solubility of nutrients and thereby water fertility Effect of p. H on fish p. H Effect 4. 0 Acid death point 4 -6 Slow growth 6 -9 Best for growth 9 -11 Slow growth, lethal to fish overlong period of time 11+ Alkaline death

Total alkalinity • The ideal range of total alkalinity for fresh water fish ponds is 60 -300 mg/liter as Ca. CO 3 Total hardness • Total hardness for fresh water fish ponds should be greater than 40 mg/litre as Ca. CO 3 Carbon dioxide • Fresh water fish ponds should contain a low concentration of free CO 2 below 5. 0 mg/litre • In intensive aquaculture free CO 2 level may fluctuate between 5 and 10 ppm with at ill effects on fish

SOIL QUALITY CRITERIA FOR AQUACULTURE • Bottom soil - determines the productivity of a pond • The productivity of ponds - depends on the availability of different nutrients • Bottom soil is - Chemical Laboratory of the Pond

Soil Texture • The nature and its properties of the parent material determine the soil texture • An ideal pond soil - should not be too sandy to allow leaching of the nutrients or should not be too clayey to keep all the nutrients absorbed on to it

Cation exchange capacity • It is the total quality of cations which a soil can adsorb by cation exchange is termed as C E C of the soil • Expressed as milli equivalents / 100 gm soil (meq / 100 gm of soil ) • Higher C E C - more concentration of easily exchangeable • The cations are called exchangeable bases. • Ca++, Mg++, Na+ and K+ ions. – Water holding capacity – capacity of soil to hold water; Clay-silt soils are best for fish ponds – Soil porosity, particle density, bulk density - physical quality’s of pond soils – Help to aeration, filtration, percolation, adsorption of nutrients etc

Soil acidity • The ideal range of soil p. H - 6. 0 -8. 0 • Water passing over acid soil tends to be a acidic with low alkalinity and hardness • High concentration of metal ions particularly aluminum (A 1+++) and Iron (Fe+++) to soil acidity • Acid ponds do not respond well to fertilization

Acid sulphate soils • Acid sulphate soils from mine spills and coastal mangroves contain high levels phyrite (Fe 82 1 -6%) • Sediments containing pyrites on oxidation results in sulfuric acid • Sulfuric acid reduces the p. H of water when pond is filled • Acid sulphate soils usually originate is pond dykes

Bottom soil oxidation • Aeration and water circulation are beneficial in improving bottom soil oxygenation • The surface layer of soil may still become anaerobic in intensive fish culture ponds due to settlement of suspended particulate matter

Soil reaction (p. H) • One of the most important factors for maintaining pond productivity - controls most of the chemical reaction in the pond environment • Near neutral or slightly alkaline p. H - ideal for fish production • If the p. H is too low - strongly acidic - reduce the availability of key nutrients in the water and lower the pond productivity

Organic Carbon Content • Acts as the source of energy for bacteria and other microbes that release nutrients through various biochemical processes • Pond soils with less than 0. 5% Organic carbon - unproductive • 0. 5 -1. 5% and 1. 5 -2. 5% Organic carbon - medium and high productivity respectively • Organic carbon - more than 2. 5% - may not be suitable for fish production

Carbon to nitrogen ratio • C: N ratio of soil influences the activity of soil microbes • Affects the rate of release of nutrients from decomposing organic matter • Nutrient release - very fast - C: N ratio - less than 10 • Nutrient release - medium- C: N ratio - 10 -20 • Nutrient release – More - C: N ratio – more than 20 • Soil C: N ratios between 10 and 15 are considered favorable for aquaculture • Ratio of 20: 1 or narrower gives good results

Nutrients • Nitrogen, phosphorous and potassium - major nutrients required by phytoplankton • Pond soil with 30 ppm, 30 -60 ppm, 60 -120 ppm and more than 120 ppm available phosphate (P 2 O 5) - high productive • Ponds with less than 250 ppm available soil nitrogen - low productivity • Soil nitrogen concentration - 250 to 500 ppm and above 500 ppm - medium and highly productive respectively • Relatively small amounts of potassium are needed in fish ponds

• The best method for preventing soils and water quality problems is aquaculture ponds is to select a site with good soil and an adequate supply of high quality water • If this is done, liming, fertilization and aeration can prevent most soil and water quality imbalances • Proper pond management viz. liming, fertilization, aeration, water exchange and bottom soils drying and oxidation are the keys to improve soil and water quality in ponds

REFERENCES : 1. The nature and properties of soils (7 th edition 1969) by Harry O. Buckman and Nyle C Brady 2. Soils and soil fertility (5 th edition 1993) by Frederick R. Troch and Louis M Thompson 3. Methods in environmental analysis - water, soil and air by P. K. Gupta (2007)