The assessment of total phosphorus in open sea areas is made as the average of total phosphorus concentration in the upper (0-10 m) water layer throughout the year. In some coastal areas, annual averages are used as well (Key message figure 1), while in Sweden, Finland, Estonia, Lithuania and Poland the summer average is used to assess total phosphorus in coastal areas (as in Key message figure 1).
Assessment protocol table 1. Specifications of the indicator 'Total phosphorus'.
The indicator is assessed within the geographical HELCOM assessment unit scale 4: open sea sub-basin areas and coastal waters WFD coastal types and bodies.
The assessment units are defined in the HELCOM Monitoring and Assessment Strategy Annex 4.