Nutrient Loading

Nutrient loading is the input of nitrogen, phosphorus, or silica to a water body, expressed as a mass flux such as tonnes of nitrogen per year. Sources split into point inputs (sewage and industrial effluent) and diffuse inputs (agricultural runoff, atmospheric deposition, urban stormwater). Loading that exceeds the assimilative capacity of the receiving water drives eutrophication: excess nutrients fuel algal blooms whose decay depletes oxygen. OSPAR and HELCOM set quantified nutrient-reduction targets for the North Sea and Baltic to cut riverine and airborne loads, and the EU treats nutrient enrichment under Water Framework Directive status and Marine Strategy Framework Directive Descriptor 5. Loads are estimated from flow times concentration.