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Nuisance Cladophora Blooms in Lake Michigan: Possible Causes and Management Options

Nuisance Cladophora Blooms in Lake Michigan: Possible Causes and Management Options Harvey Bootsma Erica Young John Berges. LIGHT. NUTRIENTS. TEMPERATURE. Phosphorus. 13 – 17 o C. HARD SUBSTRATE. The Role of Temperature. Optimum for Cladophora growth.

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Nuisance Cladophora Blooms in Lake Michigan: Possible Causes and Management Options

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

  2. LIGHT NUTRIENTS TEMPERATURE Phosphorus 13 – 17oC HARD SUBSTRATE

  3. The Role of Temperature

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

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

  6. The Role of Light

  7. Irradiance at 10 m, Atwater 7 Growth optimum at > 26 mol m-2 d-1 6 5 +ive growth PAR (mol photons m-2 d-1) 4 3 -ive growth 2 1 0 July Aug Sep Oct 1-Jul-04 31-Jul-04 31-Aug-04 30-Sep-04 31-Oct-04 Date

  8. Mussel invasion Data provided by MMSD

  9. Irradiance at 10 m, Atwater 7 2004 6 5 +ive growth PAR (mol photons m-2 d-1) 4 3 -ive growth 2 1991 1 0 July Aug Sep Oct 1-Jul-04 31-Jul-04 31-Aug-04 30-Sep-04 31-Oct-04 Date

  10. 10 m

  11. The Role of Phosphorus

  12. 0.8 0.6 Net Specific Growth Rate (d-1) 0.4 0.2 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Stored Phosphorus (%P) Influence of P on Cladophora Growth Rate

  13. 1.0 1.7 1.6 Cladophora phosphorus content, September 2004 1.2 1.0 1.2 1 mg mg-1

  14. 20-Year Phosphorus Trend at River Junction TP mg/L SRP 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01

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

  16. Milwaukee R. Menomonee R. Kinnickinnic R. 10 km

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

  18. Milwaukee River discharge 2004 m3 s-1 2006 2005 May June July Aug Sep Oct 3-Year Comparison of Cladophora phosphorus content Lake Michigan Cladophora P content mg P mg-1 2004 P limited growth 2006 2005 June July Aug Sep Oct

  19. River P • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • P • • • • • • • • • • • • • • • • • • 5 m • • • • • • • • • • • • • • • • • • • • • • 1990 8oC

  20. River P • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • P • • • • • • • • • • • • • • • • • • • • • • • • 10 m • • • • • • • • 2005 12oC

  21. 0.8 0.6 Net Specific Growth Rate (d-1) 0.4 0.2 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Stored Phosphorus (%P) Influence of P on Cladophora Growth Rate

  22. 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?

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