Water Quality Parameters PDF

Water Quality Parameters Water quality testing is an important part of environmental monitoring. When water quality is poor, it affects not only aquatic life but the surrounding ecosystem as well. The following are water parameters that need to be monitored during...

Water Quality Parameters Water quality testing is an important part of environmental monitoring. When water quality is poor, it affects not only aquatic life but the surrounding ecosystem as well. The following are water parameters that need to be monitored during culture operations. 1. Temperature Temperature has a profound influence on biological activity which, generally within the range that supports life. All changes to the pond such as fertilization, feeding and fishing must take temperature into account. The growth and activity of the fish depend on its body temperature. A relatively low temperature can adversely affect fish by: 1. Slowing down the development of their eggs 2. Reducing the growth of juveniles and older fish 3. Delaying and even preventing their maturation and spawning 4. Decreasing their food intake 5. Increasing their susceptibility to infections and diseases - It is critical during stocking of fish. Sudden changes in temperature can result to mortality in aquatic animals. Optimum water temperature for Nile tilapia is 28-35˚C. A laboratory thermometer is used to monitor the appropriate water temperature during stocking. Fig. 1. Digital Thermometer Every fish species has an ideal temperature range within which it grows quickly. This is called the optimum temperature range and it means that the fish grows best at temperatures within that range. In a fishpond, the fish should live at their optimum temperature ( 24 - 35oC) to grow well. 2. Hydrogen ion Concentration (pH) - The pH of the water is a measure of the concentration of hydrogen ion in the water. Water may be acid, alkaline or neutral. The measure of the alkalinity and the acidity of the water is expressed by its pH value. pH Meter – instrument used in measuring the acidity/alkalinity.  Fig 2. Digital pH Meter The pH of the water is a measure of the concentration of hydrogen ion in the water. Water may be acid, alkaline or neutral. The measure of the alkalinity and the acidity of the water is expressed by its pH value. The pH value ranges from 0 to 14. A pH of 7 indicates that the water is neutral, values below 7 indicates acidity and above 7 indicates alkalinity. The pH of water can greatly affect fish production. The table below shows the effect of pH to the fish. pH Effect to fish 4 Acid death point 4-5 No reproduction will occur below 6.5 Slow growth 6.5 – 9 Desirable range for fish culture 11 Alkaline death point 3. Dissolved Oxygen - All fishes regardless of species and culture conditions need oxygen for growth and survival. Lack of oxygen results in poor growth and out-break of diseases of mortality. Generally, most warm water species of fish need dissolved oxygen at a level of one part per million (ppm) for survival and  about 3 ppm for comfort. Dissolved oxygen of five part per million ( 5 ppm) is the most ideal for growth and excellent in maintaining fish health. D.O. Meter – instrument used in measuring dissolved oxygen Fig 2. Portable D.O. Meter 4. Salinity - The amount of salt present in the water as expressed in parts per thousand (ppt). It can be measured with the use of hydrometer or refractometer. A hydrometer is simple and inexpensive. Salinity is determined by collecting small amount of pond water where the hydrometer is floated. A refractometer is an expensive device but very useful. With a drop of pond water place on the refractometer, the salinity can be determined through direct reading. Refractometer – instrument used in measuring salinity Fig 4. Refractometer 5. Water Turbidity  - This is a term for the suspended dirt and other particles in water. Suspended particles in the water column determine the nature of turbidity. Turbidity maybe of different kinds as follows: Secchi disk – instrument used in measuring water turbidity and transparency Fig 5. Secchi disk Mineral turbidity is caused by high quantities of silt and/or clay particles which turn the water light brown or reddish depending on the color of the particles. This is common in shallow ponds and lakes where slight wind disturbance stirs up the bottom sediments. Disadvantages: 1. Clay particles prevent fertilizer effects. 2. Inhibit plankton growth by reducing light penetration. 3. High turbidity usually causes acidity; low nutrient levels and reduced primary production. Controlling mineral turbidity A settling basin A water filter Organic matter spread throughout the pond at the rate of 20 kg for every 100 square meter. Plankton turbidity is caused by a high content of phytoplankton and zooplankton in the water, turning it to various shades of green, brown, blue-green or yellow- green depending on the plankton species dominating the area.  Controlling plankton turbidity o Water filter o Adequate liming o Adequate fertilization To measure turbidity, a secchi disc is used. The reading is sometimes called Secchi Disc Transparency. Productive ponds usually have a Secchi Disc Transparency depth between 10 - 30 cm. Measuring Secchi Disc Transparency/Turbidity: 1. Slowly lower the disc into the water. 2. Stop when it just disappears from sight. 3. Note at which point the line breaks the water surface. Mark this point A. 4. After noting at which point along the line the disc just disappears, lower disc a little and then raise it until it just reappears. Mark this point B. 5. Mark point C midway between points A and B. 6. Measure the transparency of the water as equal to the distance from the top of the disk to this point C counting the knots along the line. This value is the Secchi Disc Transparency in cm. 6. Total Hardness - Hardness is a measure of total soluble salts such as calcium and magnesium ions that are dissolved in water. Hardness is related to pH of the water, but unlike the pH, hardness stays constant throughout the day. Hardness should be between 50 and 300 ppm in the pond for best fish growth. Determination of total hardness is done typically with ethylene diamine tetra acetic acid. The principle is that EDTA form a chelated soluble complex when added to a solution of certain metal cat ions. Total hardness test kit – used in measuring total hardness of the water  Fig 6. Total Hardness Test Kit 7. Transparency - A measure of the depth of light penetration into the water. 8. Ammonia - It is an inevitable water quality problem under high biomass loading. It is produced mostly from the decomposition of nitrogenous organic compounds such as feeds, dead fish/shrimps or dead algae. Ammonia occurs in equilibrium as NH3NH+4. This equilibrium is pH and temperature dependent. NH3 is ready absorbed in the body making it toxic while NH +4 in non-toxic. Ammonia Meter – instrument used in determining ammonia content of the water Fig. 7 Portable Ammonia Meter  9. Water Depth - Water in the pond is kept at certain levels for optimal fish growth. In general, a pond water depth of 1 meter is considered best for culture of tilapia, carps, and shrimps; traditional milkfish ponds can do with just 40-60 cm of water. Meter stick – instrument used in measuring water depth Table 1. Water Parameters with corresponding Instruments used and Unit of measurement Water Quality Parameters Instruments Unit of Measurement Centimeter, Meter or Water Depth Meter Stick Foot/Feet Temperature Thermometer Degree Celsius Fahrenheit Transparency/Turbidity Secchi Disc Meter, Feet, cm Dissolved Oxygen D.O. Meter ppm Salinity refractometer ppt pH (hydrogen ion pH Meter pH concentration) Colorimeter/Ethylene Hardness Diamine Tetra acetic ppm Acid (ETDA) Ammonia Ammonia Tester Kit ppm