Evidence for eutrophication of the Irish Sea over four decades

Abstract

The Irish Sea is showing early signs of eutrophication extending offshore, beyond localized inshore effects, according to an unusually long time series of measurements taken in the central Irish Sea. Background levels of dissolved inorganic forms of nitrogen and phosphorus have risen substantially over the last 30 to 40 years. This rise has coincided with a significant rise in phytoplankton biomass, measured as chlorophyll a, during the late spring 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 significant increase in Si was noted in autumn and winter. This may be related to the well-mixed conditions over much of the Irish Sea. However, the common assumption that there are no anthropogenic sources of dissolved Si may not be valid in this area and requires further consideration.