Water quality in the Forth Estuary
Synoptic surveys of the Forth Estuary between Crombie to the
tidal limit at Stirling have been carried out by SEPA (formerly
Forth River Purification Board) for the past 20 years. The surveys
have provided information on the development of a dissolved oxygen
sag in the upper estuary during summer months (June to August)
and the distribution of nutrients within the estuary. Inputs of
carbon and nitrogen from point source discharges have also been
evaluated to determine the load of organic wastes to the estuary.
Over the years the discharge of organic waste to the estuary has
reduced. Water quality data have been periodically reviewed
(Griffiths 1987, Griffiths 1995, Balls et al 1996) to determine the
effects of the reduction in loading from point source discharges on
dissolved oxygen consumption.
The synoptic surveys only provide a limited snapshot of water
quality therefore a continuous remote monitoring system was
deployed in the estuary in 1988 to give a continuous record of
changes in water quality through changes in river flows and tidal
cycle. This continues to provide data collected at 15 minute
intervals from April to September, which is the period during which
the dissolved oxygen sag develops. The water quality monitoring
buoy is deployed 20km downstream of the tidal limit at Alloa. It
collects information on salinity, dissolved oxygen, turbidity and
temperature.