The response of Windermere to external stress factors: analysis of long-term trends

• Main Authors: Maberly, S. C., Thackeray, S. J., Jones, I. D., Winfield, I. J.
• Format: Report
• Language: English
• Published: NERC/Centre for Ecology & Hydrology 2008
• Subjects: Ecology and Environment; Arctic; Arctic charr; Phytoplankton; Zooplankton
• Online Access: http://nora.nerc.ac.uk/id/eprint/3752/; https://nora.nerc.ac.uk/id/eprint/3752/1/The_response_of_Windermere_to_external_stress_factors-final_report.pdf; https://nora.nerc.ac.uk/id/eprint/3752/2/ResponseofWindermereReportplusCover.pdf

1. The motivation for this report was the documented recent deterioration in the water quality in the two basins of Windermere since around 2000. The aim was to analyse the long-term records to assess the likely causes of this deterioration. 2. Records were analysed between 1950 and 2007, where available, including data on lake physics (annual mean water temperature at the surface, water temperature at depth, duration of stratification), nutrient availability (mean winter concentration of total phosphorus, soluble reactive phosphorus and nitrate); responding chemical variables (minimum concentration of nitrate, minimum concentration of silica, maximum pH and minimum oxygen concentration at depth); phytoplankton chlorophyll a (annual mean, spring maximum and summer maximum); zooplankton grazing (spring mean and summer mean abundance); and the fish predation on zooplankton (hydroacoustic data, perch recruitment and Arctic charr abundance, the latter only available in the North Basin). 3. Changes in the period upto around 1991 are largely the result of increasing nutrient load to the lake. This led to increasing winter concentrations of soluble reactive phosphorus, nitrate and total phosphorus (latter significant in South Basin only). This caused increased concentrations of phytoplankton chlorophyll a as an annual mean and as spring and summer maxima in both basins. This in turn caused a greater depletion of silica in the late spring, increased pH in the summer (significant in North Basin only) and reduction in the minimum oxygen concentration at depth. 4. Since around 2000 there has been a significant reduction in water quality in both basins: summer phytoplankton chlorophyll a has increased, as has maximum pH and the minimum concentration of oxygen (only significant in the North Basin). Summer Secchi depth has declined in both basins. 5. Annual phosphorus load from the two wastewater treatment works (WwTWs) that discharge directly to the lake has fallen by about 50% in the period 1993-2007 following tertiary ...