To estimate the Net Primary Production (NPP) of an aquatic ecosystem

 

Aim :- 

 To estimate the Net Primary Production (NPP) of an aquatic ecosystem. 

Apparatus :- 

- Light and dark bottles (BOD bottles or similar)

- Water sampler (e.g., Van Dorn sampler)

-  turbidity meter

- pH meter

- Temperature probe

- Dissolved oxygen (DO) meter or oxygen electrodes

- Stopclock or timer

- Calculator or computer with statistical software

Theory :- 

- Net Primary Production (NPP) is the rate at which plants produce organic matter through photosynthesis

- The light and dark bottle method measures the change in dissolved oxygen (DO) levels in the water over time

- The difference in DO levels between the light and dark bottles represents the NPP

Chemicals Used :- 

1. *Sodium thiosulfate (Na2S2O3)*: Used to remove chlorine and chloramines from the water sample, which can interfere with DO measurements.

2. *Manganese sulfate (MnSO4)*: Used as a catalyst to facilitate the oxidation of iodide to iodine in the Winkler method for DO measurement.

3. *Alkaline iodide (KI)*: Used in the Winkler method to measure DO levels.

4. *Sulfuric acid (H2SO4)*: Used to acidify the water sample and stop biological activity in the light and dark bottles.

5. *Sodium hydroxide (NaOH)*: Used to standardize the pH of the water sample.

Reagents Used in Winkler Method :- 

1. *Manganous sulfate (MnSO4) solution*: 1 gm MnSO4 + 100 ml distilled Water. 

2. *Alkaline iodide (KI) solution*: 10 g KI and 10 g NaOH in 100 mL distilled water

3. *Sulfuric acid (H2SO4) solution*: 1:1 (v/v) H2SO4 and distilled water

4. *Sodium thiosulfate (Na2S2O3) solution*: 1 g Na2S2O3 in 100 mL distilled water

Note: The specific chemicals and reagents used may vary depending on the laboratory protocol and the specific requirements of the analysis.

Procedure :- 

1. *Sampling*: Collect water samples from the aquatic ecosystem using a water sampler.

2. *Initial DO Measurement*: Measure the initial DO levels in the water sample using a DO meter or oxygen electrodes.

3. *Light and Dark Bottle Setup*: Fill the light and dark bottles with the water sample, leaving about 1-2 cm of headspace.

4. *Incubation*: Incubate the light and dark bottles in the aquatic ecosystem for a set period (e.g., 2-4 hours).

5. *Final DO Measurement*: Measure the final DO levels in the light and dark bottles using a DO meter or oxygen electrodes.

6. *Calculation*: Calculate the NPP using the following formula:

 

Precaution :- 

- Ensure accurate DO measurements by calibrating the DO meter or oxygen electrodes before use.

- Minimize disturbance to the aquatic ecosystem during sampling and incubation.

- Use identical light and dark bottles to minimize differences in DO levels due to bottle effects.

- Avoid contamination of the water samples during handling and incubation.

Result :- 

- NPP Value

Note: The result will vary depending on the aquatic ecosystem and environmental conditions.