1. Nuisance Cladophora Blooms in Lake Michigan: Possible Causes and Management Options Harvey Bootsma Erica Young John Berges

4. HARD SUBSTRATE NUTRIENTS Phosphorus LIGHT 13 – 17 o C TEMPERATURE

6. The Role of Temperature

7. J J A S O N D J F M A M J J A S O 2003 2004 Optimum for Cladophora growth

8. Temperature at the Linnwood Intake (15 m) Optimum for Cladophora growth No growth

9. The Role of Light

10. 0 1 2 3 4 5 6 7 1-Jul-0431-Jul-0431-Aug-0430-Sep-0431-Oct-04 +ive growth Growth optimum at > 26 mol m -2 d -1 -ive growth July Aug Sep Oct PAR (mol photons m -2 d -1 ) Date Irradiance at 10 m, Atwater

11. Data provided by MMSD Mussel invasion

12. 0 1 2 3 4 5 6 7 1-Jul-0431-Jul-0431-Aug-0430-Sep-0431-Oct-04 +ive growth -ive growth July Aug Sep Oct PAR (mol photons m -2 d -1 ) Date Irradiance at 10 m, Atwater 2004 1991

13. 10 m

14. The Role of Phosphorus

15. Influence of P on Cladophora Growth Rate Net Specific Growth Rate (d -1 ) 0.6 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.4 0.2 Stored Phosphorus (%P) 0.8

16. 1  g mg -1 1.2 1.0 1.2 1.0 1.7 1.6 Cladophora phosphorus content, September 2004

17. mg/L SRP TP 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 20-Year Phosphorus Trend at River Junction

18. Is there enough phosphorus coming in from rivers to support the Cladophora growth that we observe?

19. 10 km Milwaukee R. Kinnickinnic R. Menomonee R.

21. Milwaukee River = 250 kg/day P Sources in the nearshore zone (0 – 10 m) Mussel recycling = 1,700 kg/day gg Cladophora demand ~ 2,000 kg/day

22. June July Aug Sep Oct m 3 s -1 May June July Aug Sep Oct 2004 2005 2006 Milwaukee River discharge 3-Year Comparison of Cladophora phosphorus content Lake Michigan Cladophora P content  g P mg -1 2004 2005 2006 P limited growth

23. 8oC8oC River P P 1990 5 m

24. 12 o C River P P 2005 10 m

25. Net Specific Growth Rate (d -1 ) 0.6 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.4 0.2 Stored Phosphorus (%P) 0.8 Influence of P on Cladophora Growth Rate

26. Conclusions The recent increase in Cladophora growth is likely due to: - Increased water clarity (more light at lake bottom) - Warmer water temperatures in summer - increased phosphorus inputs Although P input from rivers has increased, there must also be an internal source of P in the lake that is promoting Cladophora growth. We suspect dreissenid mussels. Future work must focus on the fate of river-borne phosphorus, and the importance of mussels as a phosphorus source. An important question to answer: If we lower P input from rivers, will there be less Cladophora?