‘Ferry-Boxes’ and data stations for improved monitoring and resolution of eutrophication-related processes: application in Southampton Water UK, a temperate latitude hypernutrified estuary

Abstract

To provide detailed observations of algal bloom development in Southampton Water which is a hypernutrified, macro-tidal estuary (mean tidal range 3.2 m, low suspended load <100 g m−3), a ferry running between Southampton and Cowes on the Isle of Wight, was fitted with an instrument package (‘Ferry-Box’). Measurements were made of temperature, conductivity, turbidity, and chlorophyll-fluorescence at a data rate of 1Hz. For comparison a data station which measured the same variables was operated at a fixed site in the estuary. In 1999 the Ferry-Box achieved reliable operation with a data return over 95%, for the fixed data station the return was 92%. From this data spatial and temporal variations in chlorophyll a concentrations have been mapped. The maps show the development of blooms in different areas of the estuary, through the spring and summer, in relation to tidal and weather conditions. In 1999 conditions were such that the spring bloom increased in intensity through a spring tide (maximum chlorophyll a 55 mg m−3), which coincided with calm weather with high light levels (irradiance). This was followed by a sequence of seven blooms, the development of which can be related to changes in the tidal energy, irradiance and nutrient supply.