Transcript Slide 1

Trophic Classification of
Lakes
Created 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 Minnows
Lots 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 Chlorophyll
in 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
Total Phosphorus (mg/m3) Average
Range
8
3 .0 - 17.7
Mesotrophic
Eutrophic
26.7
84.4
10.9 - 95.6
16 –
386
Chlorophyll a (mg/m3)
Average
Range
Secchi Disk Depth (m)
Average
Range
1.7
0.3 - 4.5
9.9
5.4 - 28.3
4.7
14.3
3 – 11
3 – 78
4.2
2.45
1.5 – 8.1
7.0
Table I – Data from Wetzel, 1983
0.8 –
Carlson, Robert
TSI 0-100
Alternative Definitions
Trophic states use by DEP
TSI
< 30
Trophic state
Oligotrophic
Attributes
Aquatic life
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
Notes: Table from USEPA, 1999, p.4-2.
Dense algae and macrophytes
Noticeable Odor
Fish Kills Possible
Research Data: Field Limn
Relationship of chlorophyl a with Transparancy
100
Adj R2=0.98
p=0.0008
-1
Chl a (g L )
York
10
MP
BP SP
1
RP
1
10
Secchi Disk (m)
Research Data: Field Limn
1.2
NS
Turbidity (NTU)
BP
1.0
p= 0.325
0.8
R2 = 0.183
0.6
0.4
0.2
SP MP
0.0
RP
-0.2
-0.4
2
4
6
8
Secchi Disk (m)
10
12
14
THE END
Please fill out your evaluations
Thank You