Spatial and temporal variability in nutrient concentrations in Liverpool Bay, a temperate latitude region of freshwater influence

Abstract

This paper presents data for the temporal and spatial distribution of nutrients in Liverpool Bay between 2003 and 2009 and an analysis of inputs of nutrients from the major rivers. The spatial distribution of winter nutrient concentrations are controlled by the region of freshwater influence (ROFI) in Liverpool Bay through the mixing of riverine freshwater and Irish Sea water, with strong linear relationships between nutrient concentration and salinity between December and February. The location of highest spring and summer phytoplankton biomass reflects the nutrient distributions as controlled by the ROFI. Analysis of 7 years of data showed that the seasonal cycle of winter maximum nutrient concentrations in February and drawdown in April/May is a recurrent feature of this location, with the timing of the drawdown varying by several weeks between years. A comparison of observed nutrient concentrations in Liverpool Bay with those predicted from inputs from rivers has been presented. Nutrient concentrations in the rivers flowing into Liverpool Bay were highly variable and there was reasonable agreement between predicted freshwater nutrient concentrations using data from this study and riverine nutrient concentrations weighted on the basis of river flow, although the exact nature of mixing between the rivers could not be determined. Predicted Irish Sea nutrient concentrations in the winter were lower than those reported for the input waters of the North Atlantic, supporting findings from previous work that nitrogen is lost through denitrification in the Irish Sea.