Phytoplankton and nutrient analysis of a nuclear fuel-storage pond at Sellafield

Summary •The aim of the project was to identify and enumerate phytoplankton cells and analyse phosphate and nitrate concentrations in samples from a nuclear fuel-storage pond from Sellafield. The samples were taken in five different bays, at two depths and at two time points. •All samples contained large numbers of phytoplankton cells. •The dominant species in bays B1 to B4 was a filamentous cyanobacterium, Oscillatoria limnetica. Bay B5 was dominated by small single cells of the chlorophyte, Stichococcus bacillaris. Other species in significant numbers that were found in nearly all samples were Haematococcus pluvialis, Chlamydomonas sp. and Chlorella sp. (all Chlorophyceae) and the cyanobacterium Synechococcus. The numbers of other species that were identified were neglectable. •There was no clear difference in species composition and numbers between the samples taken at different depths. •There was no significant difference in the species composition between the samples taken in June and July 2007, even when the July samples showed a slightly higher diversity. The difference between the two sampling time points was more of a quantitative nature; the number of O. limnetica was reduced in July compared to June, but the number of small phytoplankton species, especially S. bacillaris, increased in July. •The chemical analysis revealed only low concentrations of phosphate and nitrate that were mainly below the detection limit of our detection method. Only the July sample contained detectable amounts of nitrogen.