Thursday, July 18, 2024

Introduction to Limnology

All organisms depend on water for their survival. Limnology evolved into a distinct science only in the past century, integrating physical, chemical and biological disciplines in order to describe and manage freshwaters ecosystems.

Although inland water bodies are well below the oceans size, they are complex systems and they can’t be fully understood if studied without taking into account the complex interrelations between physical, chemical and biological aspects.

The study is vital because productivity and production are both dependent on the relative interaction of physical, biological, and chemical features operating within a given system.


Keep all field equipment clean, dry, and fully charged. An important note to remember is that battery power is dependent on temperature because an instrument runs well a t20 C does not mean it will function properly at 0 C.

Calibrations should be conducted at each sampling station to insure the accuracy of the measurements. Label all bottles and complete the inventory forms prior to sending them to the laboratory.

Field Measurements

Introduction to Limnology

Temperature: Before taking temperature measurements, calibrate the thermometer by placing the probe in a mixture of ice and water. The ice-water mixture is 0C.

Record the temperature to the nearest 0.5 C at 1 meter intervals when the lake is stratified by lowering a 50-m cabled probe through the water column, and at every other meter when the lake is isothermal.

Dissolved Oxygen: Calibrate the meter lower the probe while agitating if the probe is not equipped with an automatic stirrer, and record D.O. concentrations (mg-1L) and temperatures.

Salinity: 1) Prepare a salinity standard by dissolving 31.77 g of reagent grade NaCl in 1000 ml of DI water. This solution has a chlorinity of 19.4%% and a salinity of 35%%. 2) Measure the conductivity of the standard and the sample.

Rinse the probe with DI water following the standard measurement before continuing to the sample. Solutions should be 15 C, and the meter’s temperature compensator turned off.

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Alkalinity: Calibrate the pH meter, Pour 100 ml of sample into a beaker and place on a magnetic stirrer. Immerse the pH probe in the sample. Using the buret slowly add titrant (0.02 N H2S04) to a pH of4.5.

Record the volume (ml) of titrant. Rinse the probe with DI water before continuing to the next sample.

Turbidity: Calibrate the turbidimeter with a reference standard according to the manufacturer’s instructions. Invert an unfiltered sample several times and pour into a cuvette.

Introduction to Limnology

After all air bubbles have dissipated, record the NTU reading from the appropriate scale.

Dissolved Gases: Collect the sample in a 300-ml BOD bottle without trapping air bubbles in the bottle.

Add in order 2 ml each of solutions I and 11. Invert several times to mix.

Allow the floc or precipitate to settle, mix again, and allow to re-settle.

Add 2 ml of sulfuric acid and mix until the floc is completely dissolved. The sample is now fixed and can be analyzed later ( < 8 hr) if kept in the dark.

Pour 101 ml of the fixed sample into a 250-ml erlenmeyer flask,

Using an automatic buret, titrate the sample with 0.025 N sodium thiosulfate to a pale straw color.

Add 1-2 ml of the starch solution and complete the titration until the blue-black color turns clear. Record the volume (ml) of titrant used.

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Nitrogen, Ammonium, Nitrate and Nitrite: Pour 50 ml of sample or standard into a 50-ml stoppered cylinder.

Add 2 ml and invert to mix.

Add 2 ml of phenol and invert to mix.

Add 2 ml of potassium ferrocyanide and invert to mix.

Add 5 ml of the hypochlorite solution, invert twice to after 15 minutes invert again.

Allow 2 hours for full color development, and measure the absorbance at 640 nm against a DI water blank.

In summary, limnology is a subject that should interest anybody who is concerned about the quality of life the freshwater environment either in Nigeria or any Third world Country of Africa and Asia.

The practical application has therefore, been designed to help you understand the most complex problems of managing both the lotic and lentic water systems. You must apply concepts to understand limnology.

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Benadine Nonye is an agricultural consultant and a writer with several years of professional experience in the agriculture industry. - National Diploma in Agricultural Technology - Bachelor's Degree in Agricultural Science - Master's Degree in Science Education - PhD Student in Agricultural Economics and Environmental Policy... Visit My Websites On: 1. - Your Comprehensive Practical Agricultural Knowledge and Farmer’s Guide Website! 2. - For Effective Environmental Management through Proper Waste Management and Recycling Practices! Join Me On: Twitter: @benadinenonye - Instagram: benadinenonye - LinkedIn: benadinenonye - YouTube: Agric4Profits TV and WealthInWastes TV - Pinterest: BenadineNonye4u - Facebook: BenadineNonye

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