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?
 


 

• Flush lake with nutrient-poor water

Moses and Green Lakes in Washington State. The dilution water was low in nitrogen and phosphorus content relative to the lake. Flushing rates were 10X normal in Moses Lake and 3X in Green Lake. Improvement in quality (nutrients, algae, and transparency) was on the order of 50% in Moses Lake and even greater in Green Lake.

Besides reducing phosphorus concentration,  what other factor might result in phytoplankton decline?

What are the disadvantages?
 
 

• Lake protection from runoff

• In stream treatments
• Detention and retention basins
• Wetlands
  


http://www.co.clark.nv.us/Parks/Wetlands/Wetland's_Erosion_Control.htm
 

What are the disadvantages?
 
 
 

• Phosphorus inactivation

 

aluminum sulfate salts (alum)

---->

insoluble floc of aluminum hydroxide that bounds tightly to P regardless of oxygen concentration

Lafayette Reservoir, California

Sodium aluminate for soft water lakes.  Lime (CaCO₃) may also improve effectiveness in some situations.
   
What are the disadvantages?
    

 

Artificial Circulation/Hypolimnetic aeration

Why might this work?
 
 
 

What are the disadvantages?
 
 
 

• Hypolimnetic withdrawl



Why might this work?
 


What are the disadvantages?
 
 


• Top-down restoration
• Eliminate littoral browsers consuming macrophytes. Why might this work?

 
• Trophic cascade  e.g. Lake Vikvatan
• increased herbivory by zooplankton
• feces of large zooplankton have higher sedimentation rates
• more macrophytes due to increased transparency

Methods include:
• stocking of piscivores
• rough fish removal
• water-level drawdowns
• fish poisons

 
Click here for detailed discussion

• Copper Sulfate poisoning



 


What are the disadvantages?

http://ace.ace.orst.edu/info/extoxnet/pips/coppersu.htm

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

2) SHALLOW WEED CHOKED LAKES

One example of potentially problematic aquatic macrophytes: 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.

 
 
 
 
• Harvesting


http://www.ecy.wa.gov/programs/wq/plants/management/
 


What are the disadvantages?
 
 


• Herbicides




Numerous types

What are the disadvantages?
 
 

•  Biological Controls

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?
 

• Shading and Sediment Covers

Various materials

What are the disadvantages?

Controlling macrophytes have often increased phytoplankton.  Why?

SOLUTIONS THAT MAY ADDRESS BOTH PHYTOPLANKTON AND MACROPHYTE PROBLEMS

Sediment Removal

• deepens lake for macrophyte control
• removes internal P loads
• potentially removes toxic substances

What are the disadvantages?
 
 
 

Watershed protection

• stream buffers
• Best Mananagement Practices (BMP's)
• enforcment of silt fences, septic tank construction and maintence, sewer line maintence

What are the disadvantages?

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