1. Environmental control and limnological impacts of a large recurrent spring bloom in Lake Washington, USA.. Arhonditsis 1, M.T.Brett 1, D.E. Schindler 2 and J.Frodge 3 1 Department of Civil and Environmental Engineering, University of Washington, Seattle, USA 2 Department of Zoology, University of Washington, 404 Seattle, Washington, USA 3 King County Department of Metropolitan Services, Seattle, Washington, USA

2. Aims of the study Quantitative assessment of the spatial vs temporal variabilityQuantitative assessment of the spatial vs temporal variability Identification of the best predictors for phytoplankton dynamics over the annual cycleIdentification of the best predictors for phytoplankton dynamics over the annual cycle

3. Land Uses in the Watershed

8. Vol.Wt. Chlorophyll (ug/l) Vol.Wt. Temperature (oC) Temperature Chlorophyll Phyto Growth Time of the year

13. Multivariate Analysis of Variance

14. Time Series Analysis

16. Principal Component Analysis

19. Multiple Regression Models VARIABLESLAGCOEFFICIENTS R 2 partial R2R2 Solar Radiation -20.2497 90.65 % Intercept-0.6579 45.22 %

20. VARIABLESLAGCOEFFICIENTS R 2 partial R2R2 Cladocerans-0.0655 35.98 % 80.17 % Total Phosphorus 0.1442 34.97 % Intercept

21. Bayesian Analysis

22. Conclusions Phosphorus limiting element for primary productionPhosphorus limiting element for primary production Temporal fluctuations 40 % of the total variabilityTemporal fluctuations 40 % of the total variability Spatial heterogeneity 10 % of the total variability Spatial heterogeneity 10 % of the total variability Interactions of space with time 10 % of the total variability Interactions of space with time 10 % of the total variability Basic regulatory factors of spring bloom dynamics:Basic regulatory factors of spring bloom dynamics: 1 st phase Solar radiation 1 st phase Solar radiation 2 nd phase Epilimnion phosphorus stock 2 nd phase Epilimnion phosphorus stock Zooplankton grazing pressure (Daphnia populations) Zooplankton grazing pressure (Daphnia populations)

23. Acknowledgements METRO King County (database 1995-2001)METRO King County (database 1995-2001) A.W Mellon Foundation and Dr. Daniel E. Schindler, Department of Zoology, University of Washington (database 1975-1999)A.W Mellon Foundation and Dr. Daniel E. Schindler, Department of Zoology, University of Washington (database 1975-1999)