Trophic Classification of LakesCreated by Diane Gravel

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

Oligotrophic

• Low concentrations of nutrients required for plant growth.

• Productivity is low

• Small populations: zoop and phytoplankton

• Many species, low populations

Organic Matter in Oligotrophic

• Low amounts of organic matter• Small populations of bacteria• Small numbers of plankton, low

oxygen consumption in deep H2O

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

More Characteristics: Oligotrophic

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

Where are Oligotrophic Lakes Found?

• Seldom in populated areas, tends to shift the classification

• Seldom in agricultural areas

• Michigan - upper peninsula

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

Zoop and MinnowsLots of food for all

• High numbers of zooplankton and small fish

• Growth of larger fish

Organic Matter in Eutrophic

• Considerable depth of organic matter

In the bottom of the lake

• Provides Food for high numbers of bacteria.

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)

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

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

Great Fishing for Humans

• Good growth rates of fish

• Due to high production of plankton and benthic (bottom dwelling) organisms

Where are Eutrophic Lakes Found? Hyptothesis…..

• Lower 2/3 of Michigan’s 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.

Transition in Classification: Mesotrophic

• “little beyond oligtrophic”

• “not quite eutrophic”

• 1000’s of years from oligotrophic lakes aging to eutrophic.

• Intermediate stage

Cultural Eutrophication

• Can occur in one human generation

• Chemical enrichment by human activity in drainage basin

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

Weeds and Fishing: Mesotrophic

• Scattered weed beds, sparse

• Fishing is reasonably good

• Lake cannot handle great amounts of fishing pressure as in Eutrophic Lakes.

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

Carlson, Robert TSI 0-100Alternative Definitions

Trophic states use by DEP

TSI Trophic state Attributes Aquatic life

< 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

> 70 Hypereutrophic Dense algae and macrophytes Noticeable Odor Fish Kills Possible

• Notes: Table from USEPA, 1999, p.4-2.

Research Data: Field Limn

Relationship of chlorophyl a with Transparancy

Secchi Disk (m)

1 10

Chl

a ( g

L-1

)

1

10

100

BPMP

RP

SP

York

p=0.0008

Adj R2=0.98

Research Data: Field Limn

THE END

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