Options for the remediation of Windermere: PROTECH modelling of the effects of different management scenarios

Maberly, S.C.; Elliott, J.A.. 2009 Options for the remediation of Windermere: PROTECH modelling of the effects of different management scenarios. NERC/Centre for Ecology and Hydrology, 28pp. (CEH Report Ref: LA/C03623/2)

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1. The purpose of this report was to establish the effect of reduced nutrient loading from the two wastewater treatment works (WwTW) at Ambleside and Tower Wood on the amount and types of phytoplankton in the two basins of Windermere. A secondary objective was to assess the likely impact of reduced grazing pressure by zooplankton on phytoplankton amount. 2. The nutrient loads from the catchment and the WwTWs were estimated in previous reports for the whole lake (Maberly 2008, 2009) but basin-specific loads were calculated here. The modelling work was carried out using the algal lake model PROTECH based on the year 1998. The model produced a good representation of the seasonal changes in phytoplankton chlorophyll a and also successfully simulated the types of algae present. 3. The mean contribution of direct discharge of SRP from WwTW between 1997 and 2007 was 30% of the total load in the North Basin but 52% of the total load in the South Basin of Windermere. In 1998, the year used for the modelling exercise, this difference was even greater at 15% and 62% for the North and South Basin respectively. 4. The differential contribution of the WwTWs to their respective basin translated across to the responsiveness of each basin to reductions in SRP loading from the WwTW. In the North Basin, even complete removal of the SRP load from the WwTW at Ambleside only caused an 11% decrease in annual mean phytoplankton chlorophyll a. In contrast, in the South Basin complete removal of the SRP load from the Windermere WwTW would cause a 54% decrease in annual mean phytoplankton chlorophyll a. However, these differences are consistent with the observed minimal reduction in winter concentrations of SRP and TP in the North Basin following tertiary treatment in 1992, while substantial reductions have been recorded in the South Basin. 5. Further removal of SRP from the Ambleside WwTW, while beneficial, will not be sufficient to cause a marked further improvement in water quality in the North Basin. More effort will be needed to tackle other sources of phosphorus including smaller point sources and diffuse sources from the catchment. In contrast, severely reducing the SRP load from WwTW discharging to the South Basin should have a further benefit in reducing phytoplankton. 6. The limited modelling of the effect of zooplankton grazing on phytoplankton did not show a large effect but a more sophisticated zooplankton grazing module is needed (and is currently being developed) before we can be confident about the magnitude of this effect. Further work addressing the effect of climate change will also need to be included in future models and the forecasts could be made more robust by modelling additional years.

Item Type: Publication - Report (UNSPECIFIED)
Programmes: CEH Topics & Objectives 2009 onwards > Water > WA Topic 2 - Ecohydrological Processes > WA - 2.3 - Assess the responses of river, lake and wetland ecosystems to ecohydrological drivers
CEH Sections: Parr
Funders/Sponsors: Environment Agency
NORA Subject Terms: Ecology and Environment
Related URLs:
Date made live: 10 Jun 2009 15:27

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