Hetivity : 1. Prepare a Sechhi disc to check/measure the turbidity of water. Do experiment of 'Secchi disk' under the guidance of an adult or a teacher. 2. Identify and label some of the household water purification devices given below. hor's feedback and signature with date :
Answers
Answer:
1.
Applications
Turbidity measurements can be used for water quality analysis in lakes and streams. Generally the more turbid a lake is, the less biota it will be able to support. Turbid waters inhibit light from penetrating deeply into water column and therefore negatively affect primary productivity and dissolved oxygen available to support other organisms.
How To- Making, Using, and Considerations Regarding the Secchi Disk
Secchi disks may be purchased by science equipment suppliers, but they can also be hand-made. Below is a set of instructions on how to make a Secchi disk, how to use it, and a list of considerations when analyzing data.
Making A Secchi Disk:
Secchi disk
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Materials:
a 20cm-diameter, 6mm-thick Plexiglas disk with a hole in the middle (this may be cut from a square sheet of Plexiglas)
metal disk with a hole in the middle (to weigh down Secchi disk)
an eyebolt with nuts and washers to fit it
rope or cord- try to avoid cotton, as it stretches
waterproof black and white paint
Assembly:
Divide the Plexiglas disk into equal quadrants and paint the quadrants alternating black and white. Using masking tape as a guide often helps maintain sharp edges to each quadrant. Let the paint dry fully.
Attach the metal disk to the unpainted side of the Plexiglass disk using the eyebolt, nuts, and washers.
Tie the cord securely to the eyebolt. You may want to mark the cord with a permanent marker in 0.5 or 1 m increments to make measurements easier to read.
Secchi Disk Protocol:
Slowly lower the Secchi disk into the water on the shady side of the boat until it is no longer visible. Record this depth.
Slowly raise the disk until it just becomes visible once again. Record this depth.
Average the depths from steps 1 and 2 to get the Secchi depth.
This may be repeated for a measurement of precision.
Considerations:
Several considerations are involved with Secchi disk measurements:
The quality of Secchi depth data is user-dependent; that is, it varies from person to person as a function of vision.
The depth of visibility for the Secchi disk is dependent on external factors such as sun light intensity and waves. Hence, measurements should be taken at the same general time between 10am and 4pm, in the shade, and in calm waters.
Repeated measurements can aid in resolving precision. In addition, repeated measurements by multiple observers can aid in determining the relative accuracy of the measurement.
Results Analysis
In general, lower turbidity is associated with cleaner, healthier water. Turbidity measurements can vary across different types of environments, so they are especially useful when comparing similar environments or the same water body through time. Some examples of Secchi depths provided by The Great North American Secchi Dip-In Records Website include:
Crater Lake, OR: 44m
Spirit Lake, WA, after Mount Saint Helens Eruption: 1-2cm
Sargasso Sea: 66m
Mediterranean Sea: 53m
Turbidity is a result of sediment load and biomass in a given environment, so while it is generally true that clearer lakes are cleaner, this is not always the case. For example, a glacial stream may have a large suspended sediment load resulting in high turbidity, even if it is clean. However, due to decreased light penetration a highly turbid lake may be relatively unproductive with respect to phytoplankton, since they need light to live. So, when interpreting Secchi disk results, one must consider other aspects such as possible sediment or pollution sources, nutrient loading, etc.
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Explanation:
Secchi Disk is a simple way to measure turbidity. The Secchi disk is lowered into the water until it is no longer visible, and that depth is measured. Secchi depth values that are high indicate clearer water, and low Secchi depths indicate high turbidity.