A clear plastic film when spread over a water body, reduces evaporation losses without affecting the growth of aquatic plants. This is a better alternative to coating the water body with a layer of oil / paraffin / organic emulsion.
The run-off water collected in the ponds and ditches are used extensively for both domestic and agricultural activities, especially in the limited water situations. A good amount (nearly 20-25%) of water is lost through evaporation, which, however, is difficult to control. The percolation loss, on the other hand, can be checked effectively by different types of lining. In limited water situations, it is very much essential to reduce the evaporation loss of water from the water bodies for conserving it for a prolonged period to minimize the drudgery of the people. But, it is equally important to find out the method of reducing the water loss without affecting the aquatic eco-system. The project has therefore been proposed to test the best method of checking the loss of water by evaporation from the stored water bodies, without affecting aquatic life.
- 4 number of identical round bottom containers (6-8 cm height and 30-45 cm diameter),
- Four number of pointers (plastic scales can also be used instead),
- Little quantity of oil/paraffin/organic emulsions,
- Aquatic plants,
- Plastic sheet / film
- Fill each container to the same level with water
- Put in some aquatic plants in each container
- Fix a pointer at the center of each container so that the tip of the pointer touches the water level.
- Place the container in an open area, where there are no obstructions.
- Put a layer of oil on top of the water level in one container
- Put a clear plastic film on top of the water level in the second
- Punch some holes in a clear plastic film and put that on top of the water level in the third.
- The fourth container is left as it is. It is used as a control
- Cover all the containers with a net /mesh to protect it from the animals.
- Record the daily mean temperature, wind velocity and relative humidity.
- Record the height of water level either weekly or every fortnightly. The difference of two consecutive heights will give an estimate of the amount of water loss through evaporation. The height can then be converted into volume by multiplying it with the cross sectional area of the container.The volume of water loss can also be measured every time by pouring the amount of water lost with the help of measuring cylinder. Care should be taken while filling the water. It should be poured in such a way that it will just touch the tip of the pointer in every case. From the cylinder itself the volume of water added can be known. By addition of the amount of water added each time will give the total amount of water evaporated in each case.
- Continue this experiment for 3-4 months.
- Note the condition of the aquatic plants every time (do they look healthy?)
- After 4 months, collect water samples for ecological analysis viz. number of micro organisms etc.
- Estimation of loss of water from each of the treatments
- Record of temperature, wind velocity and relative humidity
- To find out the nature of micro organisms under each of the treatments.
- To compare the rate of water loss under different treatments;
- To compare the evaporation loss with climatic parameters;
- To find out the impact on the aquatic ecosystem.
Source: Harness water resources for a better future - Activity Guide for the 13th National Children's Science Congress