The roles of hydrographic and biogeochemical processes in the distribution of dissolved inorganic nutrients in a Scottish sea-loch system

Watts, Louisa Jane (1994) The roles of hydrographic and biogeochemical processes in the distribution of dissolved inorganic nutrients in a Scottish sea-loch system. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Fjords, like other estuaries form an important transition zone through which land-derived nutrients must pass before reaching the oceans. They possess topographic features which result in a unique type of circulation whereby water of marine origin may be retained and the flushing time of the system extended. These factors facilitate the study of nutrient distributions in the deeper waters of the basin because temporary or permanent isolation potentially enables these processes to be distinguished from hydrodynamic processes.

Work has been carried out over two field-seasons which spanned the spring months of March to May 1991 and February to April 1992, in the upper basin of Loch Linnhe, a sea-loch system based on the west coast of Scotland. Concentrations of nutrients (NO₃^-, PO₄^3-, dissolved Si) were measured, together with hydrographic and biological parameters, on samples from stations along the longitudinal axis of the upper basin.

Water in the upper basin of Loch Linnhe is vertically stratified. Water temperature plays a negligible role in determining the density structure of the water column. Water in the upper basin is essentially horizontally uniform in terms of its salinity and density properties although a slight gradient was present due to the freshwater input at the head of the loch. During both field-seasons a deep-water renewal event has been observed in which the system is flushed by incoming saline water. The timing of this event has been linked to a wind-driven upwelling event seaward of the sill, allowing high salinity water to enter the system. These flushing events occur on or close to large spring tides thus allowing relatively high volumes of saline water to enter the basin on a flood tide. In 1992 a temperature inversion was also observed throughout the water column prior to the renewal thus favouring its occurrence.

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