Hello Dear Anand, 

Trophic Level Index is calculated from the four water quality measurements:  Total Nitrogen, Total Phosphorous, Water Clarity and Chlorophyll-a.  These four measurements are combined into one number which is the Trophic Level Index. Lesser the TLI , the water body can be assigned as Microtrophic. 

I can suggest two of the papers for references. 

Regards

ANILA AJAYAN

Thank you Anila Mam

Hi Anand,

I am not sure if you mean a specific TLI index formulation, which I am not familiar with.  The trophic index with which I am most familiar is a dated one, but still valid, as long as your lakes are P-limited -- it is Carlson's Trophic State Index, or TSI, originally published in 1977 on Limnology and Oceanography.  You can find it at Dr. Bob Carlson's ResearchGate profile page.

This article showed how TSI calculated on TP concentration, chlorophyll-a concentration, or Secchi depth were interrelated -- so you can actually obtain a single TSI value from any of these three parameters.

Of course the TSI has its limitations, having being based only on temperate lakes (albeit on a large number of them) from North America, and having been formulated at the time when P was the major contaminant.  Now that many of the P-derived problems have been (partly) solved, the paradigm is shifting to N as a major eutrophication factor, so the original TSI may not be as widely applicable as before.  I believe that Dr. Carlson has indeed been trying to address this problem.  My suggestion is then to visit Dr. Calson's profile at https://www.researchgate.net/profile/Robert_Carlson7  -- you might find an answer to your question and the relevant literature there.

Good luck!

-Paola

 Trophic Level Index (TLI) characterization was calculated to water transparency TLI(WT) in meters, total phosphorous – TLI(TP) and Trophic Level Index to chlo-rophyll-a – TLI(Cl). With the results, it was possible to evaluate the Trophic level Index as Ultraoligotrophic (

Other index can be used - the TRIX index (Vollenweider et al., 1998) is very helpful to apply for assessment for water quality and coastal waters.

see more in articles:

Giovanardi, F. and Vollenweider, R.A., 2004. Trophic conditions of marine coastal waters: experience in applying the trophic index TRIX to two areas of the Adriatic and Tyrrhenian seas. Journal of Limnology, 63(2): 199-218

Ioannis Primpas. Michael Karydis, 2011. Scaling the trophic index (TRIX) in oligotrophic marine environments. Environ Monit Assess. Page 257–269

Hello Anand, it seems to me that all the answers you received deal with the calculation of trophic condition indexes (all reliable with the proper premises) in lakes or marine coastal water, but you asked about their application to a river, isn't it? In this case, no one of the suggested indexes properly fits to your requirements. Could you give us more information about the ecosystem type you're studying and the goals of your research? 

A lot of thanks to all of you.

ok, Hoang Trung Du sir,

i will try as per you.

You could also use ITS index

please see here

https://www.researchgate.net/publication/272161108_Towards_methodological_problems_of_trophic_state_assessment_of_running_waters

Article Towards Methodological Problems of Trophic State Assessment ...

Thank you Zbigniew Kowalewski sir for your valuable comment.

The article by Kowalewski et al is interesting. Here is another recent article that proposes to add dissolved oxygen measurements in trophic state indexing:

https://www.researchgate.net/publication/283546408_Determination_of_Trophic_State_Changes_with_Diel_Dissolved_Oxygen_A_Case_Study_in_a_Shallow_Lake

Article Determination of Trophic State Changes with Diel Dissolved O...

We looked at both Burns and Carlson and went with Carlson. But, one would encounter a lot of questions with respect to the data analysis in data gaps, values below the level of detection (particularly for phosphorus) and anomalies. Considering the standard long-term data, I would not go beyond Carlson and Burns. 

A lot of Thanks

Hoang Trung Du sir can  you send me that articles about TRIX because i am unable to search out. i want to include TRIX in my research article.