1. Mitchell Lake Association 2011 Mark Enochs September 22, 2011

3. “One Water” Resource Management“One Water” Resource Management Citizen Leadership and PriorityCitizen Leadership and Priority Resource SpecificResource Specific Restore and ProtectRestore and Protect Measureable BenefitsMeasureable Benefits

5. 2008 & 2009: SolarBee pilot project for hypolimnetic mixing Result: Ineffective mixing 2008: Sediment Oxygen Demand sampling 2009: Community Sediment Oxygen Demand sampling 2009: Hypolimnetic Oxygenation Pilot. Result: Successful Calcium Peroxide Addition: Result: Positive, but inconclusive District Projects in Mitchell Lake…

6. 2008: Weed Harvesting. 272 tons removed May: Curly leaf pondweed 2009: Weed Harvesting. 732 tons removed May: Curly leaf pondweed July: Eurasian water milfoil 2010: Weed Harvesting. 459 tons removed May: Curly leaf pondweed July: Eurasian water milfoil District Projects in Mitchell Lake… 1,462 tons total Thank you for weed survey input!

7. 2011 Herbicide Treatment 2011 Herbicide Treatment (almost)

8. MLA-initiated. Thank you 2,4-D was to be used MnDNR-classifies Mitchell as Natural Environment Lake Thus, herbicide use by anyone in Mitchell is not permitted, including… –Individual homeowners –City –District –Others MnDNR does allow the use of copper sulfate for algae or snail control, but not for submerged plant control 2011 Herbicide Treatment

9. 2011: Paleolimnology – Record of historic water quality from sediment cores www.also.org www.laccore.org 9

10. Mitchell Lake Sedimentation History 0.10.20.30.40.5 2000 1950 1900 1850 Sediment accumulation, g/cm 2 /year Settlement Farming Urbanization Current Bottom has low oxygen in summer Probable summer TP ~ 40 µg/L Highest sedimentation Big swings in water quality Sedimentation slightly over presettlement Summer TP at 89 µg/L Water quality is legacy of sedimentation

11. Mitchell Lake Lake Reclamation Status 40 µ g/l 60 µ g/l impaired water threshold DISTRICT GOAL CURRENT CONDITIONS STATE GOAL PRESETTLEMENT 89 µ g/l

12. Sedimentation near presettlement value → Stormwater infrastructure is working Sedimentation legacy responsible for current impairment Short term (2012 to 2022): Improve water quality with in-lake methods to counter legacy Long term (2022 - 2072): Incremental adoption of LID in watershed Mitchell Lake Recommendations

13. Current Status

15. Lake Reclamation Alternatives

16. Questions?

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19. Historical record in sediment www.wikimedia.com Pollen: Land use (e.g. farm, prairie, city) Diatoms: Past water quality Midge fly larvae: Bottom oxygen concentration Lead-210: Dating back 150 years (1862-2009 our samples) Rate of sedimentation: how much washes in from watershed

20. Lead-210 dating Radioactive decay: Radium-226 → Radon + lead-210 Half life = 22.3 years Dates back about 150 years (7 half- lives) in core samples Sediment depth