ODYSSEA Trophic state index


TRIX is a trophic state index used to explain the eutrophication state at sea, covering a wide range of trophic conditions from oligotrophy to eutrophy (Vollenweider et al. 1998). According to TRIX scaling, values < 4 refer to oligotrophic waters with good water column transparency; values 4 to 5 refer to moderate productive waters with occasional incidents of hypoxia; values 5 to 6 refer to mesotrophic waters of limited water transparency and hypoxia to occasional anoxic events, and values >6 refer to eutrophic waters with high benthic mortality risk and persistent hypoxic/anoxic incidents.  

TRIX has been applied to several coastal marine systems, as the Adriatic (Giovanardi & Vollenweider, 2004), the Black Sea (Dyatlov et al., 2010) and the eastern Mediterranean Sea (Tugrul et al., 2011). TRIX index is based on four state variables directly related to productivity: chlorophyll-a (Chl, mg m−3), dissolved oxygen as the absolute percentage deviation from oxygen saturation (DO, %), dissolved inorganic nitrogen (DIN, mg m−3) and total phosphorus (TP, mg m−3).  

For the development and integration of the TRIX index in ODYSSEA platform, several assumptions were made in order to use the data available through CMEMS. 

  1. Nitrates are the main nitrogen species contribution to the total DIN, due to the lack of ammonia data. In open sea, ammonia and nitrites are of relative low concentration and at the sea surface ammonia rapidly oxidises to nitrates. (When ODYSSEA models are in place, ammonia concentration will be available and the algorithm will be changed slightly to include it especially in areas where wastewater treatment plants outfall).
  2. Orthophosphates are the main component of total phosphorus. This is true for the inorganic component, perhaps not true for the organic one, but it is very hard to find data on organic phosphorus (particulate and dissolved) and this is a commonly made assumption.

For the computation of deviation of current DO level from saturation a step-by-step procedure was provided in the deliverable 13.2.

Finally, the coefficients of TRIX calculation are based on data from the Adriatic, general applicability to other areas might not be guaranteed. This means that a rescaling will be needed at a later stage.    


The algorithm code was initially industrialized in collaboration between Thales and GTD. The work consisted in adding configuration support, integrating automatic source data download from CMEMS,  adding error handling & console logging, and generating NetCDF compliant output files.


Later, the industrialized algorithm was taken by GTD, and wrapped into a Docker image based on the  WPS 2.0 framework developed by CLS. This is the image that has been finally integrated into ODYSSEA platform in order to launch the product automatically.



Geographical coverage
Temporal coverage   
2020-03-26 00:00:00 / TODAY + 3

Latitude = 30.1875/45.97; Longitude =-5.54/36.29

Vertical coverage

Spatial resolution
1/25 degree

Update frequency