*3.8.1.3 Total phosphorus (TP)*

a. Persulfate Digestion Method: Water samples are digested with persulfate to oxidize all forms of phosphorus to orthophosphate. The resulting orthophosphate is then measured using colorimetric methods like those mentioned for DRP.

*Major procedure involved include:*

	- *Collect a representative water sample in a clean and acid-washed container. For accurate results, ensure proper preservation and storage.*
	- *Prepare a reagent solution by dissolving ammonium persulfate and potassium persulfate in deionized water.*
	- *In a digestion tube or vessel, add a measured volume of the water sample and an appropriate volume of the persulfate reagent.*
	- *Heat the mixture in a digestion block or other appropriate heating apparatus to a high temperature (usually around 120–160°C) for a specified period (often about 1–2 hours).*
	- *The high temperature breaks down the organic and inorganic phosphorus compounds, converting them to orthophosphate.*
	- *Allow the digested sample to cool to room temperature after the digestion period.*
	- *Dilute the digested sample with deionized water to bring it within the working range of the colorimetric method.*
	- *Use a colorimetric method, such as the Molybdate Blue Method or the Ascorbic Acid Method, to measure the concentration of orthophosphate in the digested sample.*
	- *Prepare standard solutions of known phosphate concentration to create a calibration curve for accurate quantification.*
	- *Perform replicate measurements and include a blank solution to ensure accuracy.*
	- *Regularly calibrate the colorimetric instrument using standard solutions.*
	- *Calculate the total phosphorus concentration in the sample based on the measured orthophosphate concentration and any dilution factors used.*

#### **3.9 Monitoring employing remote sensing**

Satellite and aerial imagery can be used to detect changes in water quality associated with phosphorus pollution. Remote sensing allows for the monitoring of algal blooms, turbidity, and other indicators of nutrient enrichment. Remote sensing plays a crucial role in assessing and monitoring phosphorus pollution in aquatic environments. It provides valuable information about water quality, algal blooms, sediment dynamics, and other indicators of nutrient enrichment.

Here are some key applications of remote sensing in the context of phosphorus pollution in aquatic systems:

#### *3.9.1 Algal bloom detection and monitoring*

Remote sensing can identify and track algal blooms, which often result from excessive phosphorus levels. Sensors on satellites and aircraft can detect the unique spectral signatures of chlorophyll-a, a pigment in algae. Monitoring changes in chlorophyll-a concentrations helps in early detection and management of harmful algal blooms.

#### *3.9.2 Water transparency and turbidity*

Phosphorus pollution can lead to reduced water transparency due to suspended particles. Remote sensing measures water turbidity, which is indicative of sediment and nutrient loads. Monitoring turbidity helps understand how phosphorus affects water clarity.
