Evidence for eutrophication of the Irish Sea over four decades

The Irish Sea is showing early signs of eutrophication extending offshore, beyond localized inshore effects, according to an unusually long time serie s of measurements taken in the central Irish Sea. Background levels of diss olved inorganic forms of nitrogen and phosphorus have risen substantially o ver the last 30 to 40 years. This rise has coincided with a significant ris e in phytoplankton biomass, measured as chlorophyll 4 during the late sprin g bloom. Contrary to trends in other coastal seas, the increase in N and P was not accompanied by a decline in silicate; in fact, a small but signific ant increase in Si was noted in autumn and winter. This may be related to t he well-mixed conditions over much of the Irish Sea. However, the common as sumption that there are no anthropogenic sources of dissolved Si may not be valid in this area and requires further consideration.