The quality of the Forth estuary

The introduction indicates the legal position relative to the control of discharges to the Forth estuary. Details are given of the volumes of the known sources of pollution, in 1958; chemical, bacteriological and biological data then follow relative to a survey carried out in August and September of that year. The conclusions, drawn from the 1958 Survey, emphasised the gross pollution existing at that time, and suggested methods whereby the pollution might be reduced. Section 4 of the paper discusses the results of chemical, biological, bacteriological and hydrographical surveys carried out since 1962. The results stress the deterioration in conditions in the estuary compared with the earlier survey, and in particular, the lower dissolved oxygen concentration in inshore waters and the increase in the Coliform and Escherichia coli counts in certain areas. Isolation of Salmonella species implies the possible health hazards existing at the present time. Work so far carried out in respect of the determination of heavy metal concentrations in core samples taken in the intertidal zone along the shore has indicated relatively high concentrations of certain metals and their effect on the ecology of the estuary has yet to be fully assessed. Float tests made over a period emphasise the tendency for the sewage discharges to be confined to inshore waters, resulting in the gross pollution of certain beaches. Present information stresses the need for the continuance of the monitoring programme.

The quality of the Forth estuary

The Forth Estuary is divided into two parts, the narrow part to the west of Queensferry which is wholly within the area of the Forth River Purification Board and in which there is a substantial tidal variation in salinity, and the broader part to the east of Queensferry which is divided between the Forth and Lothians Boards and is virtually open sea.

There is no record of extensive biological appraisal of the narrow part of the Forth and the quality is assessed largely by general physical and chemical observations. The quality is largely determined by discharge of degradable organic matter in the form of sewage, sewage effluents and trade effluents, the bacterial oxidation of which deoxygenates the water, more or less, according to the combination of fresh water flow, meteorological conditions and the monthly tide cycle. The condition may be aggravated by thermal waste discharge.

In the broader part of the estuary on the north shore, pollution problems are limited to the littoral zone. In a number of places there is local beach pollution from sewage solids but mining pollution in the form of washery slurry pit redd and ferruginous pit waters has extensively affected conditions over a six mile stretch of shore.