june2.html

Steady state vs. targetted management

A. TMDL approach

• reduction of nutrient input
• will work over the longer time scale
• underlying hypothesis - reduce blooms by reducing algal growth

B. Reducing targetted species - such as HABs

• redirect productivity (rather than suppress it)
• change timing, "flashiness" or species composition
• using tools such as:
  • trophic manipulation
  • mixing regimes
  • aeration to manage sediment water interface

C. Examples

1. humic acid algistatic

• avoid severe blooms and resulting crashes by dampening the bloom
• slower initial growth allows zooplankton to keep up
• link - afa-daphnia-model.html

 

2. Biomanipulation - i.e. adding fish

• current system has
  • many small fish, fewer zooplankton, lots of algae
• add big hungry fish
  • big fish, fewer small fish, more zooplankton, less algae

 

3. Biomanipulation - paying attention to the stoichiometry of C:N:P

• add pike leads to increase in Daphni
• zooplankton community had lower N:P
  • i.e. more P into zooplankton
• increased grazing leads to lower residence time of nutrients in the water, especially P
• management implications
• reference - Elser et al 2000

 

4. Mixing

• sinking rates and buoyancy rates favor different species
• can manipulate mixing
  • aeration - bubblers
  • Solar Bee - epilimnion
• link - ukl-algae-competition.html
• reference - Huisman-etal-1999.pdf

 

5. Micronutrient cycling

• iron is required for N2-fixation metabolism
  • extra Fe in nitrogenase complex
  • extra Fe in all the photosynthesis to handle the extra energy requirement
• iron can come from Fe3+/Fe2+ cycling or siderophores
  • Fe3+ has low solubility, but under reducing conditions can form Fe2+
  • siderophores bind to Fe3+ and transport them to cyanobacteria and eubacteria
  • repressible synthesis of siderophores
  • higher cyano populations can "share" production of siderophores which otherwise diffuse into lake
• bloom formation model - see reference to Molot et al 2014
  • P determines biomass
  • Fe regulates whether it can be N2 fixing or not
    • Fe is made available by anoxic sediments if conditions are stable
    • buoyancy, vertical movement is important
  • model can be used to improve success
    • sulfate availability can lead to tying up Fe as FeS
    • basin morphology
    • sewage treatment should reduce Fe as well
    • hypolimnetic oxygenation could block Fe recycling

D. Management implications summary

• large amount of money being spent on lake restoration
  • much of it focused on P reduction
• other models for cyanobacteria dominance exist that are combinations of:
  • trophic effects
  • nutrient stoichiometry (N&P, C:N:P)
  • trace element
  • mixing
  • need one good model to use scientific adaptive management and to push policy
    • multiple models are not the responsibility of US SAM = "best available research"
    • multiple models are distracting to democratic process
• Sorting this out in our current situation should be a priority
  • more effective management
  • reduction of HABs for human health and water quality utility functions
• Climate change uncertainty exacerbates this issue
  • Paerl reference - start on page about climate change
• What are the research priorities?