Skip to main content


Title: Phosphate in the cut-off channel
Author: National Rivers Authority Anglian Region
Document Type: Monograph
Annotation: EA additional title info: phosphate in the cut-off channel
This report considers only the impact on the Cut off Channel of phosphate removal from STWs serving more than the equivalent of 10,000 people, i.e. UWWT Directive Qualifying Discharges. The additional impact of other eutrophication control measures is not assessed. Phosphate removal at qualifying discharges is likely to reduce mean concentrations of phosphate in the Cut off Channel by about 24 per cent. In some locations the reduction could be up to 62 per cent. Phosphate removal at Bury St Edmunds and RAF Lakenheath STWs would have the biggest impact on the level of eutrophication in the Cut off Channel, particularly in the stretch to the south of Blackdyke, to the River Lark. The degree of reduction will depend on the average concentration of phosphate achieved in the effluent of qualifying discharges. Even if we went further than required by the Directive, and phosphate was completely removed from all effluents entering the system, it is likely that the phosphate concentration in the Cut off Channel, although significantly reduced, would still exceed 0.1 mg per l along much of its length. The biological response to a reduction in phosphate concentration would depend on the size of the reduction, and also on the length of time for which the reduced levels could be maintained. However, if phosphate were removed from Bury St Edmunds and RAF Lakenheath STWs then it is likely that the Cut off Channel between Blackdyke and the River Lark would show a reduction in the incidence of filamentous algae such as Cladophora, and would move toward a dominance of higher plants. Invertebrate diversity would also be expected to improve. Experience from systems where nutrient removal has been carried out for several years suggests that nutrient removal should be seen as only one of a series of eutrophication control measures for a watercourse. Since the modelling predicts that nutrient removal at Bury St Edmunds and RAF Lakenheath STWs will have the largest effect on nutrient concentrations in the Cut off Channel between Blackdyke and the River Lark, and this stretch is physically distinct from the rest, we suggest that P removal should he introduced initially at Bury St Edmunds and RAF Lakenheath STWs. The situation should be re evaluated at the second review of Designations, in the light of future phosphate concentrations, the effect of any P removal at Bury St Edmunds and RAF Lakenheath STWs, and the interaction with other eutrophication control measures.
Publisher: National Rivers Authority
Publication Date: 1996
Publication Place: Peterborough
Subject Keywords: PhosphorusDirectives (European Union)EutrophicationWater qualityChannels (geography)EffluentsModelling
Geographic Keywords: Cam and Ely Ouse catchment
Extent: 18; + appendices
Total file downloads: 309

Download PDF    Display PDF in separate tab