Biological response to lake remediation by phosphate stripping: control of Cladophora

Authors


Correspodence: Stephen C. Maberly, Institute of Freshwater Ecology, NERC Centre for Ecology and Hydrology, Far Sawrey, Ambleside, Cumbria LA22 0LP, U.K. E-mail: scm@ceh.ac.uk

Summary

  • 1The North and South Basins of Windermere, Cumbria, have experienced a large increase in concentrations of nutrients, particularly phosphate, since 1945 when detailed measurements began. Over-winter concentrations have increased from 1 to 3 mg PO4-P m-3 in the 1940s, up to 30 mg PO4-P m-3 in the South Basin of Windermere in the early 1990s where nutrient enrichment has been most marked. A visible manifestation of this ‘eutrophication’ in recent years has been the production of a large biomass by the green filamentous macroalga, Cladophora.
  • 2Since April 1992, tertiary chemical stripping of phosphate at the two sewage treatment plants on Windermere has reduced direct sources of phosphate to both basins. In the South Basin, over-winter concentrations of phosphate have fallen to values similar to those in the early 1970s.
  • 3The biomass of Cladophora has declined markedly in response to the reduced phosphate availability. Significant relationships were found between the annual maximum biomass of Cladophora and two measures of phosphate availability: the over-winter concentration and, more strongly, the day of year when the concentration fell below 1 mg m-3.
  • 4The annual biomass maxima of Cladophora since 1945, estimated from the regressions, showed a gradual increased potential for biomass production after 1965 as phosphate concentrations increased, followed by a striking and rapid biological response to lake remediation by phosphate stripping.

Ancillary