Distribution of Nutrients and Chlorophyll in the Waters off Plymouth

Mohammed I. Orif

September 2000

Department of Environmental Sciences, University of Plymouth, Plymouth, U.K.

The current study attempts to define and discuss the physical and chemical features of the coastal waters located off Plymouth Sound. The waters off Plymouth typically feature a frontal system during the summer. The Plymouth front is a shallow-sea front separating mixed inshore water with stratified offshore Atlantic water. Sharp horizontal changes in temperature (around 20°C) occur across the front accompanied by other changes in water properties such as salinity, nutrients and chlorophyll concentrations. In the present study, regular (bimonthly in June-September 1999) measurements of nutrients (nitrate and nitrite, phosphate and silicate) and chlorophyll in the coastal waters off Plymouth were made. Validation of chlorophyll concentrations derived from satellite (SeaWiFS) images with "sea truth" measurements are presented.

Chapter One gives an introduction of the factors influencing the distribution and transport of nutrients and chlorophyll describes the role of fronts as fertile areas for primary production and presents a general overview of the analytical methods used for nutrient and chlorophyll determinations. Chapter Two describes in more detail the methods used for nutrient determinations using a segmented flow analyser and chlorophyll determinations fluorimetryc. Optimisation of the segmented flow analyser methods and analytical performance for nutrients and chlorophyll are given in Chapter Three. The limits of detection are 0.027 mM PO43-, 0.012 mM NO3-, 0.096 mM SiO2 and 0.002 mg l-1 Chl a. Results and discussion of field surveys are described in Chapter Four. Field data from waters off Plymouth show a general trend of increasing concentrations from off-shore waters towards Plymouth Sound. Nitrogen to phosphorus ratios showed values close to unity, indicating strong N uptake. Chlorophyll data obtained from satellite images were compared with chlorophyll measurements and showed a better agreement in the stratified off shore waters compared with the in-shore stations. Chapter Five is devoted to conclusions and suggestions for future work.

© 2000 by Mohammed I. Orif. All Rights Reserved

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