Eutrophication - Dissolved inorganic nitrogen (salinity normalised) 2012-2019

Since 2001 surface water samples have been collected from Scottish coastal and offshore waters during January, and have been analysed for nutrients (nitrate, phosphate, silicate and ammonia) with the aim of establishing regional background nutrient concentrations and contributing towards an assessment of the eutrophication status of Scottish coastal and offshore waters.

Surface water samples were collected at 15 minute intervals from the non-toxic water supply of FRV Scotia IV, during the MSS CSEMP cruise. The input for the non-toxic water supply is situated on the hull of the ship at a depth of ~ 4.5 m. Water samples were analysed at sea within 10 hours of collection (where possible) using a Bran & Luebbe QuAAtro continuous flow autoanalyser. The method for analysis of nutrients in seawater is accredited to ISO17025 standards by the United Kingdom Accreditation Service.

Nutrient data can be assessed against assessment criteria established by OSPAR as indicators of nutrient enrichment (OSPAR 2005). Background levels (or concentrations) and assessment levels (50% above background levels) are used to assess nutrient concentrations; concentrations above the assessment level may lead, in time, to an undesirable disturbance to the marine ecosystem.

Dissolved inorganic nitrogen (DIN) is the sum of the concentration of total oxidised nitrogen (TOxN) and ammonia. Ammonia contributes only about 5% to the DIN concentration in Scottish regions