1. David Burger, David Hamilton 1, Conrad Pilditch 1, Julie Hall 2 & Max Gibbs 2 Nutrient dynamics in Lake Rotorua 1 Department of Biological Sciences, University of Waikato, Hamilton, New Zealand 3 National Institute of Water and Atmosphere Research, Hamilton, New Zealand Research Summary

2. Study Objectives 1.Lake hydrodynamics: Thermal stratification Deoxygenation

3. 1. Lake Hydrodynamics Temperature/ Lake mixing Stratification/ Deoxygenation Climate Epilimnion Hypolimnion Sediment Thermocline Cool, dense, isolated layer. Warm, well mixed layer

4. Julain Day 15161819202123 Temperature (°C) 325350 10 35 60 85110135 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 Depth (m) Lake Stratification Lake Rotorua Temperature Sep 02-June 03

5. Oxygen at 19m (mg/l) Lake Deoxygenation Julain Day 15161819202123 Temperature (°C) 325350 10 35 60 85110135 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 Depth (m) Lake Rotorua Oxygen Sep 02-June 03

6. Study Objectives 1.Lake hydrodynamics: Thermal stratification Deoxygenation 2.Water column nutrient dynamics: Nutrient release rates during stratification Internal lake nutrient model

7. 2. Lake Nutrient Budget & Nutrient Release Sediment nutrient release Temperature/ Lake mixing Stratification/ Deoxygenation Water column nutrients Algae Climate Epilimnion Hypolimnion Sediment

8. 2.2m 6.2m 12.2m 15.4m 19m TP O2 (19m) TN O2 (19m) Temperature Total P Total N

9. Total P Total N

10. Nutrient release rates

11. Study Objectives 1.Lake hydrodynamics: Thermal stratification Deoxygenation 2.Water column nutrient dynamics: Nutrient release rates during stratification Internal lake nutrient model 3.Sediment nutrient release and sedimentation: Sediment nutrient release rates Sedimentation rates Whole lake nutrient budget

12. 3. Nutrient Release & Sedimentation Rates Inflows/ Outflows Sediment nutrient release Temperature/ Lake mixing Stratification/ Deoxygenation Water column nutrients Algae Nutrient sedimentation Decomposition Sediment nutrients Sediment Climate

13. Acknowledgments Environment Bay of Plenty Andrew Lang, Rotorua Harbourmaster Gerald Inskeep & Rob Pitkethley, Eastern Region Fish and Game Eloise Ryan & Dudley Bell, University of Waikato