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 O 2 in lower depths Summertime depletion of O 2 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 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 0-100 Alternative 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.