Nutrient concentrations in surface water from time series station L4 in the western English Channel in 2009@en

Nutrient samples for nitrate, nitrite, silicate and phosphate are taken weekly, when possible, at station L4 of the Plymouth Marine Laboratory Western Channel Observatory long-term hydrographic time series. They are sampled under clean conditions and returned in the cool and dark, and as soon as possible, to the laboratory in Plymouth where triplicate samples are analysed both for filtered (0.2 µm Millipore Fluoropore) and non-filtered water. Samples are not stored or frozen unless there are extenuating circumstances making the live analysis impossible. The analyser is a 5-channel Bran and Luebbe segmented flow system using well tested methodologies, and the same as those used by the PML nutrient group in all their International Research cruises, and research programmes. Quality control procedures are carried out using certified reference materials, and also the group participates in the Quasimeme programme. This has been the protocol since 2007, and prior to that the samples were stored frozen and then analysed in batches.