Inorganic Nutrient

Inorganic nutrients are the dissolved mineral forms of nitrogen, phosphorus, and silicon that phytoplankton take up for growth: nitrate, nitrite, ammonium, phosphate, and silicate. Their supply sets primary production and, when in excess, drives eutrophication. The Redfield ratio of 106 carbon to 16 nitrogen to 1 phosphorus describes the average elemental stoichiometry of marine phytoplankton and frames which nutrient limits a given system. Diatoms additionally require silicate for their frustules, so shifting nitrogen-to-silicon ratios can favor non-siliceous, sometimes harmful, species. Inorganic nutrient concentrations are core monitoring parameters under the EU Water Framework Directive and OSPAR-HELCOM eutrophication assessments, alongside chlorophyll-a and dissolved oxygen.