Methodology           

OBJECTIVES

Wetlands are currently degraded by both natural and anthropogenic activities, which deteriorate their quality, and push them to the brink of extinction in the process of unplanned development, giving rise to the need for suitable conservation strategies. Unfortunately, over the years, less attention has been given to wetland losses world over, including Bangalore. The degradation of the wetlands has altered their functions, affecting the ecological balance. The objectives of carrying out the physico-chemical and biological analyses of water bodies are as follows: 

1.        Generally, lake functions directly relate to their physical, chemical and biological integrity. Water quality evaluation for wetlands leads to information about their misuse by indicating the pollution status. Gale et al. (1993) define water quality objectives as the overall direction and purpose of the project, and furthermore define goals as milestones to be met during the course of a project. Since the quality of aquatic life depends on the water quality, a thorough assessment of the water quality is an integral part of wetland evaluation. The assessment of the chemical criteria of the waterbody helps in:

·         Evaluating the chemicals that cause toxicity to aquatic life.

·         Studying the long-term effects on the ecosystem.

·         Conducting the status and monitoring of wetland resources by studying their physico-chemical and biological parameters.

2.        Designate uses that protect the structure and function of wetlands for protection of fish, birds, wildlife, and recreation. The baseline values attached to wetlands in terms of designating the viable usage of these water bodies based on established standards protecting their functions is also attempted.

3.        Analyse the qualitative and quantitative aspects of plankton population of the water bodies. The biological integrity of the wetlands is the driving force for their sound ecological functioning. Wetlands that support a vast diversity of fish, birds, mammals, etc., depend directly on it by supporting vast and diverse forms of plankton providing a nutrient base and a complex food-web. In many cases, planktons also act as the biological indicators of pollution being very sensitive to changes in water quality.

 METHODOLOGY

Water is a dynamic medium and its quality varies spatially and temporally. In order to characterise any water body, studies on the major components, hydrology, physico-chemical and biological characteristics, should be carried out.

 Hydrological features

A thorough knowledge of the hydrological properties of the water body must be acquired before an effective water quality monitoring system is established. Each of the inland waterbody is characterised by unique hydrological features such as:

Large variations in the water residence time occur in different types of inland water bodies. The hydrodynamic characteristics of each type of water body are highly dependent on the size of the waterbody, climatic conditions and the drainage pattern associated with it. Ground water greatly depends on the recharge regime i.e. infiltration through unsaturated aquifer zone, that allows renewal of the groundwater.

 Physical, chemical and biological properties

The physical and chemical properties of a freshwater body are characteristic of the climatic, geochemical, geomorphological and pollution conditions (largely) prevailing in the drainage basin and the underlying aquifer. The biota in the surface water is governed entirely by various environmental conditions that determine the selection of species as the physiological performance of the individual organisms. The primary production of organic matter, in the form of phytoplankton and macrophytes is more intense in lakes and reservoirs than in rivers. In contrast to the chemical quality of water bodies, which can be measured by suitable analytical methods, biological quality is a combination of both qualitative and quantitative characterisation. This can be carried out in two levels:

 SAMPLING

The sample collected should be small in volume, enough to accurately represent the whole water body. The water sample tends to modify itself to the new environment. It is necessary to ensure that no significant changes occur in the sample and preserve its integrity till analysed (by retaining the same concentration of all the components as in the water body). The essential objectives of water quality assessment are to:

 Site selection

Sampling sites for the waterbody/lake are selected to represent the water quality at different points and depths. Generally three sampling sites are selected for monitoring.

Generally three types of sampling are adopted for collecting water samples.

The quality of water varies with time in a water body due to various natural and human induced factors. The monitoring has to be done in a way that records all the changes in the quality. The sampling frequencies generally adopted in monitoring are:

Variations in water quality are mainly due to changes in the concentrations of the components of the water flowing into the water body. These variations can be man-made or natural and can either be cyclic or random.

In lakes, the mass of water and good lateral mixing provide inertia against any rapid modifications due to inputs and outputs.

The sampling container should not react with the sample, be of adequate capacity to store the sample and be free from contamination.

Grab sampling was done at the inlet, center and outlet in most of the water bodies studied to assess their physical and chemical qualities at monthly intervals, expect during some seasons when the center of the lake was not accessible due to excessive growth of water hyacinth. The samples were collected in thoroughly cleaned 2.5-litre inert plastic containers, which were rinsed with distilled and lake/tank water before collection.

Note:

Water samples were collected in a sampling bottle avoiding floating materials. The stoppers of the sample containers were closed properly to prevent outside contamination. The container was labelled describing the name of the water body, date, time, sampling-point, and conditions under which it was sampled.

Between the time a sample is collected and analysed in the laboratory, physical, chemical and biochemical reactions may take place in the sample container leading to changes in the intrinsic quality of the sample, making it necessary to prevent or minimize these changes with suitable preservatives such as alcohol and mercuric chloride. Highly unstable parameters such as pH, temperature, transparency, free carbon-di-oxide, dissolved oxygen, etc. are measured at the sampling site.

The preservation procedure includes keeping the samples in the dark, adding chemical preservative, lowering the temperature to retard reactions, or combinations of these.

The preservation methodologies followed are as follows:

(Source: Analytical Methods Manual, Water quality branch, Environment Canada, 1981)

ANALYSES OF PHYSICAL, CHEMICAL AND BIOLOGICAL PARAMETERS

The parameters analysed to assess the water quality are broadly divided into:

Field measurement: The field parameters measured include pH, conductivity, dissolved oxygen, temperature and transparency.

COLOUR

In natural water, colour is due to the presence of humic acids, fulvic acids, metallic ions, suspended matter, plankton, weeds and industrial effluents. Colour is removed to make water suitable for general and industrial applications and is determined by visual comparison of the sample with distilled water.

Visual comparison: About 20ml of the sample and 20ml of distilled water were taken in two separate wide mouthed test tubes. The results were tabulated (as clear, greenish, greyish, brownish, blackish, etc) by comparing the colour of the sample with distilled water.

TEMPERATURE

Impinging solar radiation and atmospheric temperature brings about spatial and temporal changes in temperature, setting up convection currents and thermal stratification. Temperature plays a very important role in wetland dynamism affecting the various parameters such as alkalinity, salinity, dissolved oxygen, electrical conductivity etc. In an aquatic system, these parameters affect the chemical and biological reactions such as solubility of oxygen, carbon-di-oxide-carbonate-bicarbonate equilibrium, increase in metabolic rate and physiological reactions of organisms, etc. Water temperature is important in relation to fish life. The temperature of drinking water has an influence on its taste. 

Apparatus required: Thermometer- 0.1^o C division.

Procedure: Temperature measurement is made by taking a portion of the water sample (about 1litre) and immersing the thermometer into it for a sufficient period of time (till the reading stabilizes) and the reading is taken, expressed as °C.

TRANSPARENCY (LIGHT PENETRATION)

Solar radiation is the major source of light energy in an aquatic system, governing the primary productivity. Transparency is a characteristic of water that varies with the combined effect of colour and turbidity. It measures the light penetrating through the water body and is determined using Secchi disc.

Apparatus required: Secchi disc, a metallic disc of 20cm diameter with four quadrats of alternate black and white on the upper surface. The disc with centrally placed weight at the lower surface, is suspended with a graduated cord at the center.

Procedure: Transparency is measured by gradually lowering the Secchi disc at respective sampling points. The depth at which it disappears in the water (X₁) and reappears (X₂) is noted. The transparency of the water body is computed as follows:

                Transparency (Secchi Disc Transparency)     =              (X₁ + X₂ )/2

Where, X₁ = Depth at which Secchi disc disappears

             X₂ = Depth at which Secchi disc reappears

 TURBIDITY

Turbidity is an expression of optical property; wherein light is scattered by suspended particles present in water (Tyndall effect) and is measured using a nephelometer. Suspended and colloidal matter such as clay, silt, finely divided organic and inorganic matter; plankton and other microscopic organisms cause turbidity in water. Turbidity affects light scattering, absorption properties and aesthetic appearance in a water body. Increase in the intensity of scattered light results in higher values of turbidity.

Apparatus required: Nephelometer (It detects scattered light at 90^o to the incident beam of light. It consists of a light source for illuminating the sample. One or more photoelectric detectors with a display unit indicate the intensity of light scattered at 90^o to the path of incident light.), sample cells, lab-glass wares and Monopan balance.

Principle: Nephelometric measurement is based on comparison of the intensity of scattered light of the sample with the intensity of light scattered by a standard reference suspension (Formazin polymer) under similar conditions.

Reagents:

·         Solution 1: 1.0 g Hydrazine sulphate is dissolved in 100ml of distilled water.

·         Solution 2: 10.0g of Hexamethylenetetramine is dissolved in distilled water and made up to 100ml in a volumetric flask.

 Procedure: The nephelometer is calibrated using distilled water (Zero NTU) and a standard turbidity suspension of 40NTU. The thoroughly shaken sample is taken in the nephelometric tube and the value is recorded.

                Turbidity (NTU) = (Nephelometer readings) (Dilution factor*)

* If the turbidity of the sample is more than 40 NTU, then the sample is diluted and the dilution factor is accounted in final calculations.

 pH:

The effect of pH on the chemical and biological properties of liquids makes its determination very important. It is one of the most important parameter in water chemistry and is defined as -log [H⁺], and measured as intensity of acidity or alkalinity on a scale ranging from 0-14. If free H⁺ are more it is expressed acidic (i.e. pH<7), while more OH^- ions is expressed as alkaline (i.e. pH> 7).

 In natural waters pH is governed by the equilibrium between carbon dioxide/bicarbonate/carbonate ions and ranges between 4.5 and 8.5 although mostly basic. It tends to increase during day largely due to the photosynthetic activity (consumption of carbon-di-oxide) and decreases during night due to respiratory activity. Waste water and polluted natural waters have pH values lower or higher than 7 based on the nature of the pollutant.

 * The colorimetric indicator method can be used only for approximate pH values. 

 Apparatus required:

 Procedure:

 ELECTRICAL CONDUCTIVITY

Conductivity (specific conductance) is the numerical expression of the water's ability to conduct an electric current. It is measured in micro Siemens per cm and depends on the total concentration, mobility, valence and the temperature of the solution of ions. Electrolytes in a solution disassociate into positive (cations) and negative (anions) ions and impart conductivity. Most dissolved inorganic substances are in the ionised form in water and contribute to conductance. The conductance of the samples gives rapid and practical estimate of the variation in dissolved mineral content of the water supply. Conductance is defined as the reciprocal of the resistance involved and expressed as mho or Siemen (s).

               1

G =     --------

                 R

G – Conductance (mho or Siemens) and R - Resistance

 Apparatus required: Conductivity meter

 Procedure: The electrode of the conductivity meter is dipped into the sample, and the readings are noted for stable value shown as mS/cm.

 TOTAL SOLIDS:

Total solids is the term applied to the material residue left in the vessel after evaporation of the sample and its subsequent drying in an oven at a temperature of 103-105^oC. Total solids include Total Suspended Solids (TSS) and Total Dissolved Solids (TDS).

 Principle: A known volume (50 ml) of well-mixed sample is evaporated in a pre-weighed dish and dried to constant weight in an oven at 103-105^o C. The increase in weight over that of the empty dish gives the total solids.

 Apparatus: Evaporating dishes-100ml porcelain dish, steam bath, drying oven, desiccator, Monopan balance and measuring jars.

 Procedure: A known volume of the well-mixed sample (50ml) is measured into a pre-weighed dish and evaporated to dryness at 103^o C on a steam bath. The evaporated sample is dried in an oven for about an hour at 103-105^o C and cooled in a desiccator and recorded for constant weight.

 Calculation:

                                            (W₁-W₂) (1000)

Total solids  =                      -------------------

(mg/L)                                  Sample volume (ml)

W₁    = Weight of dried residue + dish

W₂  = Weight of empty dish

 TOTAL DISSOLVED SOLIDS

Dissolved solids are solids that are in dissolved state in solution. Waters with high dissolved solids generally are of inferior palatability and may induce an unfavourable physiological reaction in the transient consumer.

 Principle: The difference in the weight of total solids and the total suspended solids expressed in the same units gives the total dissolved solids.

 Apparatus: Glass-fiber filter disks, membrane filter funnel, filtration apparatus, suction flask and pump, drying oven and Grooch crucible.

 Procedure: The difference in the weights of Total Solids (W₁) and Total Suspended Solids (W₂) expressed in the same units gives Total Dissolved Solids (TDS).

 Calculation:    

                                           (W₁-W₂) X 1000

Total Dissolved Solids  =     -------------------

(mg/L)                                 Sample volume (ml)

W₁    = Weight of total solids + dish

W₂  = Weight of total suspended solids         

TOTAL SUSPENDED SOLIDS

Suspended solids are the portions of solids that are retained on a filter of standard specified size (generally 2.0 µ) under specific conditions. Water with high-suspended solids is unsatisfactory for bathing, industrial and other purposes.

Principle: A well – mixed sample is filtered through a weighed standard glass fibre filter and the residue that is retained on the filter is dried to a constant weight at 103-105 ^o C. The increase in the weight of the filter determines the total suspended solids.

Apparatus: Porcelain dish (100ml capacity), glass fiber filter disk, suction pump and flask, measuring jar, membrane filter funnel, oven and filtration apparatus.

Procedure: The known volume of vigorously shaken sample (50ml) is filtered into a pre-weighed glass fibre filter disk fitted to suction pump, and washed successively with distilled water. The filter is carefully removed from the filtration apparatus and dried for an hour at 103-105 ^o C in an oven, cooled in dessicator and weighed for constant weight.

Calculation:

                                           (W₁-W₂) (1000)

Total Suspended Solids  =   ------------------

(mg/L)                                 Sample volume (ml)

W₁    = Weight of dried glass fibre filter + residue

W₂  = Weight of glass fibre filter disk before filtering  

TOTAL HARDNESS

Hardness is predominantly caused by divalent cations such as calcium, magnesium, alkaline earth metal such as iron, manganese, strontium, etc. The total hardness is defined as the sum of calcium and magnesium concentrations, both expressed as CaCO₃ in mg/L. Carbonates and bicarbonates of calcium and magnesium cause temporary hardness. Sulphates and chlorides cause permanent hardness.

Hardness Chart (for drinking water):

Principle: In alkaline conditions EDTA (Ethylene-diamine tetra acetic acid) and its sodium salts react with cations forming a soluble chelated complex when added to a solution. If a small amount of dye such as Eriochrome black-T is added to an aqueous solution containing calcium and magnesium ions at alkaline pH of 10.0 ± 0.1, it forms wine red colour. When EDTA is added as a titrant, all the calcium and magnesium ions in the solution get complexed resulting in a sharp colour change from wine red to blue, marking the end point of the titration. Hardness of water prevents lather formation with soap rendering the water unsuitable for bathing and washing. It forms scales in boilers, making it unsuitable for industrial usage. At higher pH>12.0, Mg⁺⁺ ion precipitates with only Ca⁺⁺ in solution. At this pH, murexide indicator forms a pink color with Ca⁺⁺ ion. When EDTA is added Ca⁺⁺ gets complexed resulting in a change from pink to purple indicating end point of the reaction.

Apparatus required: Lab glassware-burette, pipette, conical flask, beakers etc.

Reagents:

Procedure: Exactly 50ml of the well-mixed sample is pipetted into a conical flask, to which 1ml of ammonium buffer and 2-3 drops of Eriochrome black -T indicator is added. The mixture is titrated against standard 0.01M EDTA until the wine red colour of the solution turns pale blue at the end point.

Calculation:

                                                               (T) (1000)

                                Total hardness =  ---------------

                                   (mg/L)                   V

Where, T = Volume of titrant

V = Volume of sample

 CALCIUM HARDNESS

The presence of calcium (fifth most abundant) in water results from passage through or over deposits of limestone, dolomite, gypsum and such other calcium bearing rocks. Calcium contributes to the total hardness of water and is an important micro-nutrient in aquatic environment and is especially needed in large quantities by molluscs and vertebrates. It is measured by EDTA titrimetric method. Small concentration of calcium carbonate prevents corrosion of metal pipes by laying down a protective coating. But increased amount of calcium precipitates on heating to form harmful scales in boilers, pipes and utensils.

 Principle: When EDTA (Ethylene-diamine tetra acetic acid) is added to the water containing calcium and magnesium, it combines first with calcium. Calcium can be determined directly with EDTA when pH is made sufficiently high such that the magnesium is largely precipitated as hydroxyl compound (by adding NaOH and iso-propyl alcohol). When murexide indicator is added to the solution containing calcium, all the calcium gets complexed by the EDTA at pH 12-13. The end point is indicated from a colour change from pink to purple.

 Apparatus required: Burettes, pipette, conical flask, beakers and droppers.

 Reagents:

 Procedure: A known volume (50ml) of the sample is pipetted into a clean conical flask, to which 1ml of sodium hydroxide and 1ml of iso-propyl alcohol is added. A pinch of murexide indicator is added to this mixture and titrated against EDTA until the pink color turns purple.

 Calculation:

                                                                T  X  400.5  X  1.05

                                Calcium as Ca  =      ----------------------           

                                      (mg/L)                 Sample taken, ml

Where, T= volume of titrant, ml

                                     T  X 1000 X 1.05

 Calcium hardness  =     -------------------                                                                                            

 (mg/L as CaCO₃)         Sample taken, ml

MAGNESIUM HARDNESS

Magnesium is a relatively abundant element in the earth's crust, ranking eighth in abundance among the elements. It is found in all natural waters and its source lies in rocks, generally present in lower concentration than calcium. It is also an important element contributing to hardness and a necessary constituent of chlorophyll. Its concentration greater than 125 mg/L can influence cathartic and diuretic actions.

 Principle: Magnesium hardness can be calculated from the determined total hardness and calcium hardness.

 Calculation:

                Magnesium  =  (T - C) x 0.243

                 (as mg/L)

 where, T = Total hardness mg\L (as CaCO₃) 

            C = Calcium hardness mg\L (as CaCO₃)

 High concentration of magnesium proves to be diuretic and laxative, and reduces the utility of water for domestic use while a concentration above 500 mg/L imparts an unpleasant taste to water and renders it unfit for drinking. Chemical softening, reverse osmosis and electro dialysis or ion exchange reduces the magnesium hardness to acceptable levels.

 NITRATES

Nitrates are the most oxidized forms of nitrogen and the end product of the aerobic decomposition of organic nitrogenous matter. The significant sources of nitrates are chemical fertilizers from cultivated lands, drainage from livestock feeds, as well as domestic and industrial sources. Natural waters in their unpolluted state contain only minute quantities of nitrates. The stimulation of plant growth by nitrates may result in eutrophication, especially due to algae. The subsequent death and decay of plants produces secondary pollution. Nitrates are most important for biological oxidation of nitrogenous organic matter. Certain nitrogen fixing bacteria and algae have the capacity to fix molecular nitrogen in nitrates. The main source of polluting nitrates is domestic sewage. Nitrates may find their way into ground water through leaching from soil and at times by contamination. They can be measured by the phenoldisulphonic method.

 Principle: Nitrates react with phenoldisulphonic acid and produce a nitrate derivative, which in alkaline solution develops yellow colour due to rearrangement of its structure. The colour produced is directly proportional to the concentration of nitrates present in the sample.

 Apparatus required:  Nessler's tube, pipettes, beakers, spectrophotometer, cuvettes, measuring jar and hot water bath.

 Reagents:

·         Stock nitrate solution: 721.8 mg (0.722g) of AR potassium nitrate is dissolved in distilled water and made up to 100ml for stock solution.

·         Standard nitrate solution: Standard nitrate solution is prepared by evaporating 50ml of the stock solution to dryness in the water bath. The obtained residue is dissolved in 2ml of phenol disulfonic acid and diluted to 500ml, to give 1ml = 10 mg. The solution of various strengths ranging from 0.0 (blank) to 1.0 mg/L at the intervals of 0.2 mg/L is prepared by diluting stock solution with distilled water.

 Procedure: A known volume (50ml) of the sample is pipetted into a porcelain dish and evaporated to dryness on a hot water bath. 2ml of phenol disulphonic acid is added to dissolve the residue by constant stirring with a glass rod. Concentrated solution of sodium hydroxide or conc. ammonium hydroxide and distilled water is added with stirring to make it alkaline. This is filtered into a Nessler's tube and made up to 50ml with distilled water. The absorbance is read at 410nm using a spectrophotometer after the development of colour. The standard graph is plotted by taking concentration along X-axis and the spectrophotometric readings (absorbance) along Y-axis. The value of nitrate is found by comparing absorbance of sample with the standard curve and expressed in mg/L.

Calculation:

                      Absorbance of sample  X  Conc. of Std  X 1000

Nitrates =     ---------------------------------------------------

(as mg/L)       Absorbance of Std. X Sample taken

The high concentration of nitrate in water is indicative of pollution.

PHOSPHATES

Phosphates occur in natural or wastewaters as orthophosphates, condensed phosphates and naturally found phosphates. Their presence in water is due to detergents, used boiler waters, fertilizers and biological processes. They occur in solution in particles or as detritus. They are essential for the growth of organisms and a nutrient that limits the primary productivity of the water body. Inorganic phosphorus plays a dynamic role in aquatic ecosystems; when present in low concentration is one of the most important nutrients, but in excess along with nitrates and potassium, causes algal blooms. It is calculated by the stannous chloride method.

Principle: In acidic conditions orthophosphate reacts with ammonium molybdate forming Molybdophosphoric acid, reduced further to molybdenum blue by stannous chloride. The intensity of the blue colour is directly proportional to the concentration of phosphate. The absorbance is noted at 690nm using spectrophotometer.

Apparatus required: Spectrophotometer, lab glassware, hot plate and Nessler's tube.

Reagents:

Procedure: To 50ml of the filtered sample, 4ml of ammonium molybdate reagent and about 4-5 drops of stannous chloride reagent is added. After about 10 min but before 12 min, the colour developed is measured photometrically at 690nm and calibration curve is prepared. A reagent blank is always run with same treatment with distilled water as sample. The value of phosphate is obtained by comparing absorbance of sample with the standard curve and expressed as mg/L.

Calculation:

                               Absorbance of sample  X  Conc. of Std  X 1000

Phosphates    =       --------------------------------------------------       

(as mg/L)                 Absorbance of Std. X Sample taken

 High phosphorus content causes increased algal growth till nitrogen becomes limiting, although blue green algae continues to dominate because of its ability to utilize molecular nitrogen. Besides sedimentation, high uptake by phytoplankton is one of the reasons for fast depletion of phosphorus in water.

 SULPHATES

Sulphates are found appreciably in all natural waters, particularly those with high salt content. Besides industrial pollution and domestic sewage, biological oxidation of reduced sulphur species also add to sulphate content. Soluble in water, it imparts hardness with other cations. Sulphate causes scaling in industrial water supplies, and odour and corrosion problems due to its reduction to hydrogen sulphide. It can be calculated by turbidometric method.

 Principle: Sulphate ions are precipitated in acetic acid medium with barium chloride to form barium sulphate crystals of uniform size. The scattering of light by the precipitated suspension (barium sulphate) is measured by a Nephelometer and the concentration is recorded.

 Apparatus required: Nephelometer, magnetic stirrer, Nessler's tubes and lab glassware.

 Reagents:

·         Conditioning reagent: 50 ml of glycerol was mixed in a solution containing 30 ml of conc. hydro chloric acid, 300ml distilled water (10% HCl), 100 ml of 95% ethyl alcohol or isopropyl alcohol and 75g NaCl.

·         Barium Chloride

·         Standard sulphate solution: 147.9mg of AR grade sodium sulphate was dissolved in distilled water and made up to 1000ml, to give 1ml = 100mg sulphate.

 Procedure: 100ml of the sample is filtered into a Nessler's tube containing 5ml of conditioning reagent. About 0.2g of barium chloride crystals is added with continued stirring. A working standard is prepared by taking 1ml of the standard, 5ml of conditioning reagent and made up to 100ml, to give 100 NTU. The turbidity developed by the sample and the standards are measured using a Nephelometer and the results are tabulated.

 Calculation:

Sulphate                =   (Nephlometric reading) (0.4) (Dilution Factor)

(as mg/L)

CHLORIDES

The presence of chlorides in natural waters can mainly be attributed to dissolution of salt deposits in the form of ions (Cl^-). Otherwise, high concentrations may indicate pollution by sewage, industrial wastes, intrusion of seawater or other saline water. It is the major form of inorganic anions in water for aquatic life. High chloride content has a deleterious effect on metallic pipes and structures, as well as agricultural plants. They are calculated by Argentometric method.                

Principle: In alkaline or neutral solution, potassium chromate indicates the endpoint of the silver nitrate titration of chlorides. Silver chloride is quantitatively precipitated before the red silver chromate is formed.

 Apparatus required:  Lab glassware.

 Reagents:

·         Potassium chromate indicator solution: 50g of potassium chromate is dissolved in minimum amount of distilled water and silver nitrate is added drop wise till a red precipitate is formed. The mixture is allowed to stand for about 12 hours and diluted to 1000ml with distilled water.

·         Silver nitrate solution (0.014N): 2.395g of silver nitrate is dissolved in distilled water and made up to 1000ml.

 Procedure: A known volume of filtered sample (50ml) is taken in a conical flask, to which about 0.5ml of potassium chromate indicator is added and titrated against standard silver nitrate till silver dichromate (AgCrO₄) starts precipitating.

 Calculation:

                                     (A-B) (N) (35.45)

  Chlorides (Cl^-) =         ----------------------                     

                                      Sample taken in ml

Where,

A - Volume of silver nitrate consumed by the sample

B - Volume of silver nitrate consumed by the blank

N - Normality of silver nitrate  (Standard methods, APHA, 16th edn, pp 286-88)

DISSOLVED OXYGEN

Oxygen dissolved in water is a very important parameter in water analysis as it serves as an indicator of the physical, chemical and biological activities of the water body. The two main sources of dissolved oxygen are diffusion of oxygen from the air and photosynthetic activity. Diffusion of oxygen from the air into water depends on the solubility of oxygen, and is influenced by many other factors like water movement, temperature, salinity, etc. Photosynthesis, a biological phenomenon carried out by the autotrophs, depends on the plankton population, light condition, gases, etc. Oxygen is considered to be the major limiting factor in water bodies with organic materials. Dissolved oxygen is calculated by many methods.

 Method 1: Membrane electrode method

 Principle: The membrane electrode has a sensing element protected by an oxygen-permeable plastic membrane that serves as a diffusion barrier against impurities. Under steady conditions the electric current read is directly proportional to the D.O concentrations (electric current is directly proportional to the activity of molecular oxygen).

 Apparatus required: Oxygen-sensitive membrane electrode and lab glassware.

 Procedure: The calibrations are carried out following the manufacturer’s calibration procedure. The electrode is dipped into the sample, and the reading noted.

 Method 2: Winkler’s method

 Principle: Oxygen present in the sample oxidizes the dispersed divalent manganous hydroxide to the higher valency to precipitate as a brown hydrated oxide after addition of potassium iodide and sodium hydroxide. Upon acidification, manganese reverts to its divalent state and liberates iodine from potassium iodide, equivalent to the original dissolved oxygen content of the sample. The liberated iodine is titrated against N/80 sodium thiosulphate using fresh iodine as an indicator.

 Apparatus required: BOD bottles-300ml capacity, sampling devices, lab glassware - measuring cylinder, conical flasks, etc., and Bunsen burner.

Reagents:

·         Manganese sulphate: 480g of manganous sulphate tetrahydrate is dissolved and made up to 1000ml with distilled water (Discarded if it changes colour with starch).

·         Alkaline iodide-azide reagent: 500g of sodium hydroxide and 150g of potassium iodide along with 10g of sodium azide (NaN₃) is dissolved and made up to 1000ml with distilled water.

·         Conc. sulphuric acid

·         Starch indicator: 0.5g of starch is dissolved in distilled water and boiled for few minutes.

·         Stock sodium thiosulphate: 24.82g of sodium thiosulphate pentahydrate (Na₂S₂0₂. 5H₂O) is dissolved in distilled water and made up to 1000ml.

·         Standard sodium thiosulphate (0.025N): 250ml of the stock sodium thiosulphate pentahydrate is made up to 1000ml with distilled water to give 0.025N.

Procedure: The samples are collected in BOD bottles, to which 2ml of manganous sulphate and 2ml of potassium iodide are added and sealed. This is mixed well and the precipitate allowed to settle down. At this stage 2ml of conc. sulphuric acid is added, and mixed well until all the precipitate dissolves. 203ml of the sample is measured into the conical flask and titrated against 0.025N sodium thiosulphate using starch as an indicator. The end point is the change of colour from blue to colourless.

Calculations:

                203ml because (200) (300)/ (200-4) = 203ml.

                1ml of 0.025N Sodium thiosulphate  =  0.2mg of Oxygen

                                                        (0.2) (1000 ml of Sodium thiosulphate)

                Dissolved              =       ------------------------------------------

                Oxygen(as mg/L)                                      200

(Water analysis, APHA, 16th edn., pp 423-17)      

BIOLOGICAL OXYGEN DEMAND

Biological Oxygen Demand (BOD) is the amount of oxygen required by microorganisms for stabilizing biologically decomposable organic matter (carbonaceous) in water under aerobic conditions. The test is used to determine the pollution load of wastewater, the degree of pollution and the efficiency of wastewater treatment methods. 5-Day BOD test being a bioassay procedure (involving measurement of oxygen consumed by bacteria for degrading the organic matter under aerobic conditions) requires the addition of nutrients and maintaining the standard conditions of pH and temperature and absence of microbial growth inhibiting substances.

 Principle: The method consists of filling the samples in airtight bottles of specified size and incubating them at specified temperature (20 ^oC) for 5 days. The difference in the dissolved oxygen measured initially and after incubation gives the BOD of the sample.

 Apparatus required: BOD bottles - 300ml capacity, air incubator - to be controlled at 20 ^oC -\+ 1 ^oC, oximeter and magnetic stirrer.

 Reagents:

·         Preparation of dilution water: To 1000ml of water, 1ml each of phosphate buffer, magnesium sulphate, calcium chloride and ferric chloride solution is added, before bringing it to 20 ^oC and aerating it thoroughly. 

 Procedure: The sample having a pH of 7 is determined for first day DO. Various dilutions (at least 3) are prepared to obtain about 50% depletion of D.O. using sample and dilution water. The samples are incubated at 20 ^oC for 5 days and the 5^th day D.O is noted using the oximeter. A reagent blank is also prepared in a similar manner.

 Calculation:  

                                                        (D₁ - D₂) - (B₁ - B₂) X f

                BOD                         =     --------------------------

                (in mg/L)                                         p                                    

D₁  - 1^st day D.O of diluted sample

D₂  - 5^th day D.O of diluted sample

P - decimal volumetric fraction of sample used.

B₁  - 1^st day D.O of control

B₂  - 5^th day D.O of control

 (Water analysis, APHA, 16th edn)

 CHEMICAL OXYGEN DEMAND

Chemical oxygen demand (COD) is the measure of oxygen equivalent to the organic content of the sample that is susceptible to oxidation by a strong chemical oxidant. The intrinsic limitation of the test lies in its ability to differentiate between the biologically oxidisable and inert material. It is measured by the open reflux method.

 Principle: The organic matter in the sample gets oxidized completely by strong oxidizing agents such as potassium dichromate in the presence of conc. sulphuric acid to produce carbon-di-oxide and water. The excess potassium dichromate remaining after the reaction is titrated with Ferrous Ammonium Sulphate (FAS) using ferroin indicator to determine the COD. The dichromate consumed gives the oxygen required for the oxidation of the organic matter.

 Apparatus required: Reflux apparatus, Nessler’s tube, Erlenmeyer flasks, hot plate and lab glassware.

 Reagents:

·         Standard potassium dichromate solution (0.250M): 12.25g of potassium dichromate dried at 103  ^oC for about 2 hours is dissolved in distilled water and made up to 1000ml.

·         Standard ferrous ammonium sulphate (FAS) 0.25N: 98g of FAS is dissolved in minimum distilled water to which 20ml of conc. sulphuric acid is added and made up to 1000ml using distilled water to give 0.25N of ferrous ammonium sulphate.

·         Ferroin indicator: 1.485g of 1,10-Phenanthroline monohydrate and 695mg of ferrous sulphate is dissolved in 100ml of distilled water.

·         Conc. sulphuric acid

·         Silver sulphate crystals

·         Mercuric sulphate crystals

 Procedure: 15ml of conc. sulphuric acid with 0.3g of mercuric sulphate and a pinch of silver sulphate along with 5ml of 0.025M potassium dichromate is taken into a Nessler's tube. 10ml of sample (thoroughly shaken) is pipetted out into this mixture and kept for about 90 minutes on the hot plate for digestion. 40ml of distilled water is added to the cooled mixture (to make up to 50ml) and titrated against 0.25M FAS using ferroin indicator, till the colour turns from blue green to wine red indicating the end point. A reagent blank is also carried out using 10ml of distilled water.

 Calculation:

                                                        (Blank reading - Sample reading) X N X F X 1000

                                COD    =            ------------------------------------------------------

                                (mg/L)                                    Sample taken, ml

To calculate F,

                                 10000  

                F     =        ----------------------        

                                Titrant value of blank.

 FLUORIDE

Fluorides have dual significance in water supplies. High concentration causes dental fluorosis and lower concentration (<0.8 mg/L) causes dental caries. A fluoride concentration of approximately 1mg/L in drinking water is recommended. They are frequently found in certain industrial processes resulting in fluoride rich wastewaters. Significant sources of fluoride are found in coke, glass and ceramic, electronics, pesticide and fertiliser manufacturing, steel and aluminium processing and electroplating industries. It is calculated by SPADNS method.

 Principle: The colorimetric method of estimating fluoride is based on the reaction of fluorides (HF) with zirconium SPADNS solution and the 'lake' (colour of SPADNS reagent), which is greatly influenced by the acidity of the reaction mixture. Fluoride reacts with the dye ‘lake’, dissociating (bleaching) the dye into a colourless complex anion (ZrF₆ ^2-). As the amount of fluoride increases, the colour produced becomes progressively higher or of different hue.

 Apparatus required: Spectrophotometer and lab glassware.

 Reagents:

·         Standard fluoride solution.

^·          Stock: 221.0mg of AR grade sodium fluoride was dissolved in distilled water and made up to 1000ml to give 1ml = 100 m g of F^-

·         Working Standard: 100ml of the stock fluoride was diluted to 1000ml to give 1ml = 10 mg of flouride.

·         SPADNS Solution: 958mg of SPADNS is dissolved in 500ml of distilled water.[1]

·         Zirconyl-acid reagent: 133mg Zirconyl chloride octahydrate (ZrOCl₂ .8H₂O) was dissolved in about 25ml of distilled water. 350ml of conc. HCl was added and diluted to 500ml with distilled water.

·         Zirconyl acid-SPADNS reagent: Equal volume of SPADNS and zirconyl acid reagent was mixed.

Procedure: A standard graph is prepared by using fluoride concentrations ranging from 0.005 mg/L to 0.150 mg/L at 570nm. A reference solution is prepared by adding 4ml of acid zirconyl-SPADNS reagent to 21ml of distilled water. A known volume of filtered sample (21ml) is taken in a test tube, 4ml of acid zirconyl-SPADNS reagent is added to the sample along with a reference solution. The mixture is left for about 30 min for complete colour development and the optical density is read at 570nm.

Calculation:

                                           (O.D sample) (Conc. of the Standard) (1000)         

                F^- mg/L      =      ------------------------------------------------     

                                            (O.D Standard)  (sample taken)                     

   FREE CARBON-DI-OXIDE

The important source of free carbon-di-oxide in surface water bodies is mainly from respiration and decomposition by aquatic organisms. It reacts with water partly to form calcium bicarbonate and in the absence of bicarbonates gets converted to carbonates releasing carbon-di-oxide.

 Principle: Free carbon-di-oxide reacts with sodium carbonate or sodium hydroxide to form sodium bicarbonate. The completion of the reaction is indicated by the development of pink colour, characteristic of phenolpthalein indicator at an equivalent pH of 8.3

 Apparatus required: Lab glassware - measuring jar, pipette, conical flask etc.

 Reagents:

·         Sodium hydroxide solution (0.22N): 1g of sodium hydroxide was dissolved in 100ml of distilled water and made up to 1000ml to give 0.22N.

·         Phenolpthalein indicator

 Procedure: A known volume (50ml) of the sample is measured into a conical flask. 2-3 drops of phenolpthalein indicator is added and titrated against 0.22N sodium hydroxide till the pink colour persists indicating the end point.

 Calculation:

                                                     (Vt) (1000)  

                                 Free CO₂   =  ------------

                              (mg/L)                 Vs

 Where,  Vt - volume of titrant (ml)

             Vs - volume of the sample taken (ml)

Potassium ranks seventh among the elements in order of abundance, behaves similar to sodium and remains low. Though found in small quantities (<20mg/L) it plays a vital role in the metabolism.

  Principle: Trace amount of potassium can be determined by direct reading of flame photometer at a specific wavelength of 766.5nm by spraying the sample into the flame. The desired spectral lines are then isolated by the use of interference filters or suitable slit arrangements. The intensity of light is measured by the phototube.

  Working principle of Flame photometer: The emission of characteristic radiations by alkali and alkaline earth metals and the correlation of the emission intensity with the concentration of the element form the basis of flame photometry. The principle of the flame photometer depends on the "Emission Spectroscopy" in which the electrons of the metals after absorbing energy get excited from ground state to higher energy level and return back to the ground state with emission of light. The sample under test is introduced into flame in solution by means of atomizer. The radiation from the flame enters a dispersing device and isolates it (radiation) from the flame to the desired region of the spectrum. The phototube measures the intensity of isolated radiation, which is proportional to the concentration of the element present in the sample. 

  Apparatus required: Flame photometer, lab glassware and Whattman filter paper.

  Reagents:

  Procedure: The filter of the flame photometer is set at 766.5nm (marked for Potassium, K) the flame is adjusted for blue colour. The scale is set to zero and maximum using the highest standard value. A standard curve of different concentration is prepared by feeding the standard solutions. The sample is filtered through the filter paper and fed into the flame photometer. The concentration is found from the standard curve or as direct reading.

  SODIUM

Sodium is one of the most abundant elements and is a common constituent of natural waters. The sodium concentration of water is of concern primarily when considering their solubility for agricultural uses or boiler feed water. The concentration ranges from very low in the surface waters and relatively high in deep ground waters and highest in the marine waters. It is calculated by flame photometric method.

  Reagents:

  Procedure: The filter of the flame photometer is set to 589nm (marked for Sodium, Na). By feeding distilled water the scale is set to zero and maximum using the standard of highest value. A standard curve between concentration and emission is prepared by feeding the standard solutions. The sample is filtered through filter paper and fed into the flame photometer and the concentration is found from graph or by direct readings.

  Heavy metals

  Heavy metals are elements (properties of metals satisfied) of high atomic numbers. They have high utilities in industrial applications from papers to automobiles, by their very characteristic properties. They are found in the deep bowels of the earth as ores (complexes of mixtures). The metals are segregated from these ores, leaving behind the tailings that find their way into the environment as toxic pollutants. They get into the water bodies directly from point sources as sewage, and non-point sources as runoff and more insidiously as atmospheric deposition that are transported from long distances. Heavy metals affect every level of the food web, from producers in the trophic levels to the highest order carnivore by residing in the system and magnifying at every trophic status.

  Atomic absorption spectrophotometer (AAS)

  Working principle: Atomic absorption spectrometer's working principle is based on the sample being aspirated into the flame and atomized when the AAS's light beam is directed through the flame into the monochromator, and onto the detector that measures the amount of light absorbed by the atomized element in the flame. Since metals have their own characteristic absorption wavelength, a source lamp composed of that element is used, making the method relatively free from spectral or radiational interferences. The amount of energy of the characteristic wavelength absorbed in the flame is proportional to the concentration of the element in the sample.

   Procedure: The sample is thoroughly mixed by shaking, and 100ml of it is transferred into a glass beaker of 250ml volume, to which 5ml of conc. nitric acid is added and heated to boil till the volume is reduced to about 15-20ml, by adding conc. nitric acid in increments of 5ml till all the residue is completely dissolved. The mixture is cooled, transferred and made up to 100ml using metal free distilled water.

  Operations for analysing heavy metals:

·         Lamp selection:

·         Lamp for the element to be detected is selected.

·         Operating current is suitably adjusted.

·         The lamp is aligned for the visible beam to fall on the slit of the monochromator

·         Wave length selection and slit adjustment:

·         Appropriate wavelength for the element to be detected is selected. The wavelength controller is moved clockwise or anti-clockwise slowly to get maximum percentage of transmittance.

·         The slits are adjusted to get closest to the required wavelength and avoid excess stray light.

·         Flame adjustment:

·         On selecting suitable wavelength, the acetylene-air mixture is lit at the recommended pressure.

·         The burner level is so adjusted that the beam from the cathode crosses 1cm from the top of the burner and the beam is stabilized.

·         Analysis:

·         A calibration graph is obtained by feeding the standard solutions of suitable concentration.

·         The samples are aspirated by feeding them through the capillary and the readings are noted. (Distilled water is aspirated between samples).

  Apparatus required: AAS and lab glassware.

  Reagents:

·         Air-Acetylene flame

·         Metal free water

·         Standard metal solutions

  LEAD

Lead is relatively a minor element in the earth's crust but is widely distributed in low concentrations in uncontaminated soils and rocks. Lead concentration in freshwater is generally much higher. High concentration of lead results from atmospheric input of lead originating from its use in the leaded gasoline or from smelting processes. Industrial processes such as printing and dyeing, paint manufacturing, explosives, photography and mine or smelter operations may contain relatively high values in lead. Lead is toxic to aquatic organisms.

  Principle: Lead can be determined at a wavelength of 283.3 nm by AAS with aspiration of the sample into the oxidising air-acetylene flame. When the aqueous sample is aspirated, the sensitivity for 1% absorption is 0.5 mg/L and the detection limit is 0.05 mg/L.

  Standard lead solution: 1.598g of lead nitrate is dissolved in about 200ml of water containing 1.5ml of conc. nitric acid and diluted to 1000ml of metal free water to give 1ml = 1mg lead. A series of standards ranging from 1mg to 5mg were prepared from the stock and a standard graph was made.                             

  COPPER

Copper is a widely distributed trace element because most copper minerals are relatively insoluble and is sorbed to solid phases, hence only low concentrations are normally present in natural waters. Because of the presence of sulphide, copper would be expected to be even less soluble in anoxic systems. The presence of higher concentrations of copper can usually be attributed to corrosion of copper pipes, industrial wastes or particularly in reservoirs, which uses copper as algaecides. Copper is an essential trace element in the nutrition of plants and animals including man. It is required for the function of several enzymes and is necessary in the biosynthesis of chlorophyll. High levels are toxic to organisms but the response varies greatly with species.

   Principle:

Copper can be determined at a wavelength at 324.7 nm by AAS with aspiration of the sample into an oxidising air-acetylene flame. When the aqueous sample is aspirated, the sensitivity for 1% absorption is 0.1 mg/L and the detection limit is 0.01 mg/L.

  Standard copper solution: 1g of copper salt is dissolved in 15ml of 1+1 nitric acid and diluted to 1000ml to give 1ml = 1mg copper. A series of standards ranging from 1mg to 5mg are prepared from the stock and a standard graph prepared.

  NICKEL

Standard nickel solution: 1.273g of nickel oxide is dissolved in a minimum quantity of 10% HCl and diluted to 1000ml with distilled water to give 1ml = 1mg of nickel. A series of standards ranging from 1mg to 5mg are prepared from the stock and analyzed.     

The write up seems inadequate??

   IRON

Iron is an abundant element in the earth's crust, but exists generally in minor concentrations in natural water systems. Iron is found in the +2 (ferrous) and +3 (ferric) states depending on the oxidation-reduction potentials of the water. The ferric state of iron imparts orange strain to any settling surfaces, including laundry articles, cooking and eating utensils, and plumbing fixtures.               

  Principle:

Iron can be determined at a wavelength of 248.3 nm by AAS with aspiration of the sample into an oxidising air-acetylene flame. Under standard conditions, iron produces 1% absorption at 0.12 mg/L and a linear response up to about 5 mg/L.

   Standard iron solution: 1g of iron is dissolved in 50ml of 1+1 nitric acid and diluted to 1000ml with distilled water to give 1ml = 1mg of iron. A series of standards ranging from 1mg to 5mg are prepared from the stock and analysed. 

   CHROMIUM

The concentration of chromium in natural waters is usually very low. Elevated concentrations of chromium can result from mining and industrial processes. Chromate compounds are routinely used in cooling waters to control erosion. Chromium in water supplies is generally found in the hexavalent form. 

  Principle:

Total chromium can be determined at a wavelength of 357.9 nm by atomic absorption with aspiration of sample into a reducing air-acetylene flame. Under standard concentrations, chromium produces 1 % absorption at 0.25 mg/L and is detectable down to 0.003 mg/L.

  Standard chromium solution: 2.828g of AR grade potassium dichromate is dissolved in about 200ml of distilled water, with 1.5ml of conc. nitric acid and made up to 1000ml with the same to give 1ml = 1mg of chromium. A series of standards ranging from 1mg to 5mg are prepared from the stock and analysed.

  CADMIUM

Cadmium is largely found in nature in the form of sulphide, and as an impurity of zinc - lead ores. The abundance of cadmium is much less than that of zinc. Cadmium may enter the surface waters as a consequence of mining, electroplating plants, pigment works, textile and chemical industries, and is toxic to man. There is evidence that cadmium affects reproductive organs in humans and is also a potential carcinogen. A specific disease called "itai-itai" has been absorbed in Japan due to excess cadmium. In addition, due to bioaccumulation, certain edible organisms may become hazardous to the ultimate consumer. 

   Principle: Cadmium can be determined at a wavelength of 228.8 nm by atomic absorption with aspiration of sample into an oxidising air-acetylene flame. When the aqueous sample is aspirated, the sensitivity for 1 % absorption is 25 mg/L and the detection limit is 2 mg/L.  

  Standard cadmium solution: 1.000 g of cadmium metal is dissolved in minimum volume of 1+1 HCl and  made up to 1000ml with distilled water to give 1ml = 1mg of cadmium. A series of standards ranging from 1mg to 5mg are prepared from the stock and analysed.

  ZINC

Zinc is an abundant element in rocks and ores and is present in natural waters only as a minor constituent. The main industrial use of zinc is in galvanizing and may enter the drinking waters from galvanized pipes. Another important use is in the preparation of alloys, including brass and bronze. It is an essential element in human nutrition. Food provides the main source of zinc to the body. Zinc may be toxic to aquatic organisms but the degree of toxicity varies greatly depending on water quality characteristics as well as the species being considered.

  Principle: Zinc can be determined at a wavelength of 213.9 nm by AAS aspiration of the sample into an oxidizing air-acetylene flame. When the aqueous sample is aspirated, the sensitivity for 1% absorption is 20 mg/L and the detection limit is 5 mg/L.

  Standard zinc solution: 1.000g of zinc metal is dissolved in 20ml of 1+1 HCl and diluted to 1000ml in distilled water, to give 1ml = 1mg of zinc. A series of standards ranging from 1mg to 5mg are prepared from the stock and analysed.

PLANKTON ANALYSIS:

The physical and chemical characteristics of water affect the abundance, species composition, stability and productivity of the indigenous populations of aquatic organisms. The biological methods used for assessing water quality includes collection, counting and identification of aquatic organisms; biomass measurements; measurements of metabolic activity rates; toxicity tests; bioaccumulation; biomagnification of pollutants; and processing and interpretation of biological data. The work involving plankton analysis would help in:

1.        Explaining the cause of colour and turbidity and the presence of objectionable odour, tastes and visible particles in waters.

2.        The interpretation of chemical analyses.

3.        Identifying the nature, extent and biological effects of pollution.

4.        Providing data on the status of an aquatic system on a regular basis.

Plankton: A microscopic community of plants (phytoplankton) and animals (zooplankton), found usually free floating, swimming with little or no resistance to water currents, suspended in water, nonmotile or insufficiently motile to overcome transport by currents, are called "Plankton". 

Phytoplankton (microscopic algae) usually occurs as unicellular, colonial or filamentous forms and is mostly photosynthetic and is grazed upon by the zooplankton and other organisms occurring in the same environment. Zooplankton principally comprise of microscopic protozoans, rotifers, cladocerans and copepods. The species assemblage of zooplankton also may be useful in assessing water quality.

The structure of photosynthetic populations in the aquatic ecosystems is dynamic and constantly changing in species composition and biomass distribution. An understanding of the community structure is dependent on the ability to understand the temporal distribution of the different species. Changes in species composition and biomass may affect photosynthetic rates, assimilation efficiencies, rates of nutrient utilization, grazing, etc.

  Plankton, particularly phytoplankton, has long been used as indicators of water quality. Because of their short life spans, planktons respond quickly to environmental changes. They flourish both in highly eutrophic waters while a few others are very sensitive to organic and/or chemical wastes. Some species have also been associated with noxious blooms causing toxic conditions apart from the tastes and odour problems.

  Plankton net: The plankton net is a field-equipment used to trap plankton. It has a polyethylene filter of a defined mesh size and a graduated measuring jar attached to the other end. A handle holds the net. The mesh size of the net determines the size range of the plankton trapped. The mesh number 30 of size 60 mm was used for collecting samples.

  Sampling Procedure: The manner in which sampling is done should conform to the objectives of the study. The “surface samples” (samples collected from the surface) are collected as close to the water surface as possible, mostly towards the center of the lake at regular monthly intervals. A known volume of the sample, 5L to 50 L is filtered and planktons are filtered and preserved for further analysis

Labels: The sample label has the date, time of sampling, study area-lake name and the volume measured and pasted on the containers of 50ml capacity.

Preservation: The samples collected into the 100ml polyethylene vials were preserved by adding suitable amounts of 1ml chloroform to act as the narcotizing agent and 2ml of 2% formalin for preservation and analyses.

Concentration technique: The plankton nets are used to collect samples for the qualitative and quantitative estimation of the plankton, by filtering a known volume of water (5-50 liters) through the net depending on the plankton density of the tanks. 

Qualitative and quantitative evaluation of plankton: Detailed analyses of phytoplanktonic populations are done by estimating the numbers in each species. The phytoplankton consisting of individual cells, filaments and colonies are counted as individual cells. When colonies of species are counted, the average number of cells per colony is counted, and in filamentous algae, the average length of the filament has to be determined.

Sedimentation and enumeration by microscope: Preserved samples in bottles are mixed uniformly by gentle inversion and then exactly 1ml of the sample is pipetted out into the S-C cell for analysis.

Microscope:

Compound microscope:

A monocular compound microscope is used in the counting of plankton with different eyepieces such as 10X, 15X and 20X. The microscope is calibrated using plankton-counting squares.

Counting:

Counting cell- Sedgwick-Rafter (S-R) cell:

The Sedgwick-Rafter cell is a devise used for plankton counting and is about 50mm long by 20mm wide and 1mm deep. The cell is covered by a relatively thick cover slip and is calibrated to contain exactly 1.0 ml.  

Method:

Filling the cell:

The cover slip is placed diagonally across the S-R cell and filled with the sample carefully without air bubbles with a large bore pipette. The sample is allowed to settle for about 5 minutes before the actual counting begins.

  Note: Since the configuration of the S-R cell does not allow the use of high power microscope objectives, the identification of organisms smaller than 10 – 15 mm is difficult or impossible, limiting the usage to only larger forms of relatively dense populations.

  Strip counting:

A "strip" is the length of the cell that constitutes a volume approximately 50 mm long, 1-mm deep accounting to the volume of 25mm³ or 1/40 (2.5%) of the total cell volume. By moving the mechanical stage from left to right, the organisms can be examined in a systematic manner. By knowing the surface area of the portion counted in relation to that of the total, a factor is determined to expand the average counts of the plankton to the total area of the counting surface. This total area represents the number of organisms present per given volume of the sample. This volume expanded to an appropriate factor yields the organisms per litre of water for the lake.

  The total number of planktons in the S-R cell is obtained by multiplying actual count in the strip by the number (enumeration factor) representing the portion of the S-R cell counted. The number of the strips counted is a function of the precision desired and the number of units (cells, colonies) for the strips measured. In this study, 500 cells were counted for estimation. 

The plankton count in the S-R cell is got from the following,

                           C X 1000 mm    

Number/ml =      ----------------

                          L X D X W X S

Where

                                C = Number of organisms counted

                                L = Length of each strip (S-R cell length) mm

                                D = Depth of a strip (S-R cell depth) mm

                                W = Width of a strip in mm

                                S = Number of strips counted

          V₁   = (50)(1)(W)

                 =  mm³       

 The plankton counts per strip are then determined by multiplying the actual count by the factor representing the counted portion of the whole S-R cell volume.

    Number/ml = (C) (1000 mm³) / (L) (D) (W) (S)

  Where

                C = Number of organisms counted.

                L = Length of each strip in mm (of S-R cell)

                D = Depth of the strip in mm (S-R cell)

              W = Width of the strip in mm (Whipple grid image width)

                S = Number of strips counted.

Phytoplankton Counting Units: Some plankton are unicellular while others are multicellular (colonial), posing a problem for enumeration. For analysis, a colony of plankton is accounted as a single count. The large forms that cross two or more boundaries of the grid are counted separately at lower magnification and their number included in the total count.