Biodiversity Step 2 / Correction Factor Determination Form
Because each sampling station located along the study system will utilize slightly different sampling methods, it is necessary to determine the correction factor for your sampling device. Therefore, ALL biodiversity data needs to reflect the estimated number of species and organisms found within a standardized unit of water (i.e. 1.0 m3).
The process of standardizing data or formulating a correction factor is important so that each individual school participating in the project will be able to interpret, utilize, and compare each other's river monitoring data. NOTE: Correction factors need only be computed once for each sampling station and technique unless the sampling device or volume of water sampled is changed.
DETERMINING THE DESIRED VOLUME
- Using the information from your BIODIVERSITY MONITORING FORM, determine the area of your sampling device. Since both the kick net and seine are both rectangles (when fully submerged in the water), the formula will be:
Width of net * Height of net = Area of net
- Using the information from your BIODIVERSITY MONITORING FORM, determine the volume of water sampled through the sampling device. The formula will be:
Area of net * Distance net was pull through water = Volume of water sampled
- Now that the volume of water filtered through either the seine or the kick net has been determined, a correction factor must be calculated in order that an estimated average of how many organisms found in your samples are expected to be found in 1.0 m3 of water.
Since we know that 1.0 m3 of water contains 100 cm (width)* 100 cm (height) *100 cm (depth), we know that there are 1,000,000 cm3 in 1.0 m3. THIS IS OUR DESIRED VOLUME
DETERMINING THE ACTUAL VOLUME SAMPLED
- From our sample BIODIVERSITY MONITORING FORM, we recorded our net dimensions as:
.25 m * .45 m or converting to cm = 25 cm * 45 cm = 1,125.00 cm2
- From our sample BIODIVERSITY MONITORING FORM we recorded our length of pull as 3.0 m. In order to obtain the ACTUAL VOLUME FOR ONE REPLICATE of water filtered we multiply by 300 cm to get the number of cm3. The resulting equation is:
1,125.00 cm2 * 300 cm = 337,500 cm3
- From our sample BIODIVERSITY MONITORING FORM we recorded that we had three replicates. We must now multiply our results by three to get the ACTUAL VOLUME FOR ALL REPLICATES.
337,500.00 cm3 * 3 = 101,250.00 cm3
THIS IS OUR ACTUAL VOLUME FOR ALL REPLICATES
(Note: This number will change for each sampling technique used.)
DETERMINING THE CORRECTION FACTOR
In order to determine the correction factor for converting the number of organisms found in 1,012,500 cm3 to the number of organisms you would expect to find in 1,000,000 cm3, we divide the DESIRED VOLUME by the ACTUAL VOLUME FOR ALL REPLICATES.
1,000,000 cm3 / 1,012,500. cm3 = .9877
The correction factor for this sampling technique is: