Processes and conditions influencing phytoplankton growth and bloom initiation in a macrotidal estuary, Southampton Water

Ali, Elham Mahmoud (2003) Processes and conditions influencing phytoplankton growth and bloom initiation in a macrotidal estuary, Southampton Water. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Southampton Water is known to be a highly dynamic, macrotidal, and hypernutrified estuary and has previously been reported to support large phytoplankton populations during the spring-summer period. However, phytoplankton blooms in the estuary have been shown to be short lived due to rapid changing conditions of irradiance and variable intensity of tidal mixing. The aim of this research was to investigate the coupling between variations in phytoplankton community and bloom development in Southampton Water and changes in environment conditions. This was achieved through using a combination of different field sampling approaches over intensive temporal and spatial scales, as well as experimental incubation experiments.

In 1999 data from a coastal monitor (installed on the dock wall in the upper estuary) provided very frequent measurements of chlorophyll fluorescence (every 10 minutes) together with temperature, salinity and turbidity data to investigate environmental conditions causing the initiation of blooms of diatoms and dinoflagellates in the estuary. The data covered the productive period (from April to September 1999) when water samples were collected adjacent to the sensor package at frequent intervals (5-7 days). The main Spring bloom occurred during spring tides in May 1999 and was coincident with mean water column irradiance values of >100Wh m^-2d^-1), water temperatures of 14°C and some salinity stratification. This combination of conditions provided optimum conditions for the growth of Guinardia delicatula that dominated this bloom. Later secondary blooms were identified during the period of study and these were correlated with the physical, chemical and meterological data collected. The spring diatom bloom appeared to be independent of the spring- neap tidal state, whereas a summer dinoflagellate bloom coincided with both high daily irradiance and reduced mixing during a period of reduced fresh water river flows and neap tides. A transition period dominated by flagellates and ciliates was recorded following the spring diatom bloom collapse.

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