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The response of Windermere to external stress factors: phosphorus load from wastewater treatment works

Maberly, S. C.. 2008 The response of Windermere to external stress factors: phosphorus load from wastewater treatment works. NERC/Centre for Ecology and Hydrology, 14pp. (CEH Report Ref: LA/C03468/1)

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Abstract/Summary

1. The input from the wastewater treatment works (WwTW) that discharge directly into Windermere at Ambleside and Tower Wood contribute a large amount of the total phosphorus load to the lake. In 1992 this load was reduced by establishment of tertiary treatment at each works. This elicited a rapid improvement in water quality but this started to deteriorate subsequently. This report analyses the output phosphorus loads from the two WwTW to establish to what extent the deterioration might be caused by any increases from the WwTW. 2. Data were available from 1978 with, on average, weekly sampling or better from the two WwTW. Before 1987 there were infrequent measurements of P-load. Since 1995 there have been one or two load measurements per week from each plant. 3. The average seasonal pattern of flow is relatively even, but higher values in winter suggest input from non-domestic sources. There are large seasonal changes in the concentration of phosphorus leaving the WwTWs, with highest concentrations in summer, possibly as a result of higher tourist numbers and slightly lower flow. The load of phosphorus also varies seasonally: monthly load is highest in summer. 4. In 1991 the average concentration of phosphorus leaving the WwTW was 3.2 and 3.8 mg L-1 at Ambleside and Windermere Tower Wood respectively. There was a step-reduction in the concentration of phosphorus leaving the two WwTW in 1992 and no evidence for a return to the higher values of pre 1992, apart from transiently higher values at Ambleside in 1999 and 2000 (around 2.5 mg L-1). Between 1993 and 2007 the annual average concentration of phosphorus leaving the WwTWs was 1.48 mg L-1 and 1.26 mg L-1 for Ambleside and Windermere Tower Wood respectively. 5. Annual phosphorus load has fallen by about 50% in 1993-2007 compared to 1978-1991 at both WwTWs. At Ambleside it has fallen from 2.2 to 1.09 Mg y-1 and at Windermere Tower Wood it has fallen from 5.85 to 2.82 Mg y-1. Loads from storm overflows are not included in these estimates since no data appear to exist. 6. It is difficult to estimate catchment loads of phosphorus, nevertheless the data suggest that the WwTW contribute about 37% of the total phosphorus and 66% of the soluble reactive phosphorus load to the lake. The percentages for the North Basin are slightly lower, and the percentages for the South Basin are slightly higher, than this average. The WwTW are still the largest source of available phosphorus to the lake. 7. Any more recent deterioration in water quality in the two basins of Windermere are unlikely to be cause by increased phosphorus loads from the two WwTWs.

Item Type: Publication - Report (UNSPECIFIED)
Programmes: CEH Programmes pre-2009 publications > Water > WA02 Quantifying processes that link water quality and quantity, biota and physical environment > WA02.2 Hydrochemical and sediment processes
CEH Sections: Parr
Funders/Sponsors: Environment Agency
NORA Subject Terms: Ecology and Environment
Date made live: 23 Apr 2008 14:58
URI: http://nora.nerc.ac.uk/id/eprint/2607

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