Trophic Classification of Lakes

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Trophic Classification of Lakes

• Created by Diane Gravel

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The Trophic Concept

• Nutrient richness of lakes is the basis of
  classification.
• Super clear lakes to poor water clarity
• Oligotrophic lakes to Eutrophic
• Place limits along continuum
• Classic Definitions Forsberg, Ryding

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Oligotrophic

• Low concentrations of nutrients required for
  plant growth.
• Productivity is low
• Small populations zoop and phytoplankton
• Many species, low populations

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Organic Matter in Oligotrophic

• Low amounts of organic matter
• Small populations of bacteria
• Small numbers of plankton, low oxygen consumption
  in deep H2O

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Water Transparency

• Secci Disk 10 meters depth
• Few suspended algae.
• Low chlorophyll readings 1.7 mg m-3
• Low nutrients
• Low phosphorous 8.0 mg m-3

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More Characteristics Oligotrophic

• Nice clean water
• Bottoms are sandy and rocky
• No weed problems
• Poor fishing
• Deep and cold water
• Seldom in populated areas

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Where are Oligotrophic Lakes Found?

• Seldom in populated areas, tends to shift the
  classification
• Seldom in agricultural areas
• Michigan - upper peninsula

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Eutrophic Classification

• In Contrast to the oligotrophic lakes the other
  end of the continuum.
• Rich in plant nutrients
• Productivity is high
• high numbers of phytoplanton (suspended algae),
  cloud H2O
• Poor Secchi disk readings of 2.5 meters

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Zoop and MinnowsLots of food for all

• High numbers of zooplankton and small fish
• Growth of larger fish

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Organic Matter in Eutrophic

• Considerable depth of organic matter
• In the bottom of the lake
• Provides Food for high numbers of bacteria.

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Oxygen in the Lower Waters

• Decending plankton and bacteria use O2 in lower
  depths
• Summertime depletion of O2 below the thermocline
  (below 5.5 meters)

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Phosporus and Chlorophyllin Eutrophic Lakes

• High phytoplankton produced
• Resulting in high chlorphyll concentrations, 14
  mg m-3 or higher
• Phosphorous averages 80 mg m-3

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Weeds and Depth of Eutrophic

• Weed beds grow due to available nutients
• Light penetrates shallow depths
• Organic matter in the bottom makes great soil for
  their roots

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Great Fishing for Humans

• Good growth rates of fish
• Due to high production of plankton and benthic
  (bottom dwelling) organisms

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Where are Eutrophic Lakes Found? Hyptothesis..

• Lower 2/3 of Michigans lower Penninsula in study
• Drawing comparisons to Russell Pond in northern
  NH to Barbados and Stonehouse Pond in southern,
  NH
• More north, the more oligotrophic lakes found.

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Transition in Classification Mesotrophic

• little beyond oligtrophic
• not quite eutrophic
• 1000s of years from oligotrophic lakes aging to
  eutrophic.
• Intermediate stage

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Cultural Eutrophication

• Can occur in one human generation
• Chemical enrichment by human activity in drainage
  basin

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Mesotropic Classification

• Plankton is intermediate
• Some organic sediment
• Some loss of O2, usually in lower depths
• Water is moderately clear with Secchi Depths
• Chlorophyll and Phosphorus concentrations between
  Oligotrophic and Eutropic lakes

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Weeds and Fishing Mesotrophic

• Scattered weed beds, sparse
• Fishing is reasonably good
• Lake cannot handle great amounts of fishing
  pressure as in Eutrophic Lakes.

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PHOSPHORUS AND CHLOROPHYLL CONCENTRATIONS AND
SECCHI DISK DEPTHS CHARACTERISTIC OF THE TROPHIC
CLASSIFICATION OF LAKES

• MEASURED PARAMETER Oligotrophic
  Mesotrophic Eutrophic
• Total Phosphorus (mg/m3)   Average 8
  26.7 84.4
•                                                
  Range 3 .0 - 17.7 10.9 - 95.6
  16 386
• Chlorophyll a  (mg/m3)        Average
  1.7 4.7 14.3
•                                               
  Range 0.3 - 4.5 3 11
  3 78
• Secchi Disk Depth (m)          Average
  9.9 4.2
  2.45
•                                               
  Range 5.4 - 28.3 1.5 8.1
  0.8 7.0
•                                                   
        Table I Data from Wetzel, 1983

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Carlson, Robert TSI 0-100Alternative
Definitions

• Trophic states use by DEP
• TSI Trophic state
  Attributes
  Aquatic life
• lt 30 Oligotrophic
  Clear water Trout
  possible in
• 
  Oxygenated hypolimnion in deep
  waters
• 
    Low Production
•  30 50 Mesotrophic
  Moderately clear water  Warm water
  fishery
•  
  Possible Anoxia in summer
•  50 70 Eutrophic
  Low transparency Warm water
  fishery
• 
  Anoxic hypolimnion in summer
• gt 70 Hypereutrophic
  Dense algae and macrophytes
• 
  Noticeable Odor
• 
  Fish Kills Possible

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Research Data Field Limn
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Research Data Field Limn
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