Mean winter (jan-feb-march) surface (0-10m depth) concentration of nitrate (nitrate + nitrite), expressed in µmol per litre in coastal (less than 20kilometres distance from the coastline) waters, in any given year.
Calculation :
Mean winter (jan-feb-march) surface (0-10m depth) concentration of nitrate (nitrate + nitrite) in µmol/litre in coastal (< than 20km from the coast) waters.