Lake Restoration and Applied Limnology
(A rare opportunity for ecologist to study whole system manipulations)
 
 
 
 
 
 
 

1) DEEP LAKES WITH HIGH PHYTOPLANKTON PRODUCTIVITY
What are the negative effects associated with eutrophication?

What factors effect the levels of phytoplankton in lakes?


 
 
 
 
 

  • Divert or treat nutrient-laden wastewater or storm water

  •  

     
     
     

    Lake Washington (Seattle) - wastewater divervision
    stats
     
    Sewage from Seattle during first half of 1900's resulted in algal blooms by the mid 1950's  (Oscillatoria rubescens).   Sewage effluent diverted to  Pugeut Sound (Pacific Ocean) eliminated  99% of nutrient inflow to the lake resulting in decline of phosphorus levels in the lake (from 70 to 16 µg/L), and increased water clarity , and declines in algal biomass  (from 35 to 4 µg/L).
     
     

    Lake Shagawa (MN)   Wastewater treatment

     Reduction in wastewater phosphorus did not result in major changes in chlorophyll levels. Why?

     

    INTERNAL  versus EXTERNAL LOADING
    Can be estimated by calculating a phosphorus budget

    What are the disadvantages?
     
     
     
  • Artificial Circulation/Hypolimnetic aeration

  • Why might this work?
     
     
     

    What are the disadvantages?
     
     
     
     
     
     

    Other chemical and biocides and selectively adapted strains of bacteria also used to reduce phytoplankton directly.

     
     
     
     
     
     

    2) SHALLOW WEED CHOKED LAKES

    One example: Eurasian watermilfoil (Myriophyllum spicatum)
     
     

    Nutrient reduction does not necessily lead to macrophyte reduction and sometimes increases macrophytes. Why?
     
     

    Sedimentation causing increased littoral zone may be the driving force in small lake eutrophication.

    Addition of tripliod grass carp.

    What are the disadvantages?
     
     
     
     

  • Lake Level Drawdown

  • Expose rooted plants to hot or freezing. Results variable

     

    What are the disadvantages?
     


     
     
     

    Controlling macrophytes have often increased phytoplankton.  Why?

     
    Many solutions to macrophytes create phytoplankton problems and vice-versa
     
     
     

    SOLUTIONS THAT MAY ADDRESS BOTH PHYTOPLANKTON AND MACROPHYTE PROBLEMS

  • Sediment Removal

  • What are the disadvantages?
     
     
     

  • Watershed protection

  • What are the disadvantages?

    Conclusions:

    Effectiveness depends on funds available, risks willing to be taken, goals, and the lake system.
    (from Soil & Water Conservation Society of Metro Halifax at http://www.chebucto.ns.ca/Science/SWCS/lakerest.html)
     

    Overall problems complex.  Every lake is different and must understand the basic limnology to evalute the effectiveness of a possible treatment.

    Lake Allatoona

    Lake Acworth