The Great Lakes

Introduction

The 5 Great Lakes

• Huron• Ontario• Michigan• Erie• Superior

An Important Coastline

• 1/10th of the population of the USA

• 1/4th of the Canadian population

• 25% of the Canadian Agriculture and 7% of the USA

Lake Superior

• Largest volume• Deepest and

coldest• Fewest people

living on it• Least amount of

pollution• Forested basin

Lake Michigan

• 2nd Largest • only Great Lake entirely in

the USA• Northern = less populated,

fishing industry, and paper mills

• Southern = densely populated (8 mill.) with Chicago and Milwaukee

Lake Huron

• 3rd Largest by volume• vacation location on

Georgian Bay and Northern Michigan

• high population in the Saginaw River Basin

• Fishing in the Saginaw Bay

Lake Erie

• Smallest in Volume• Warm and Shallow• Freezes in winter• Land around it is

farmland = lots of pollution

• 17 urban centers of over 50,000 people

Lake Ontario

• Smaller in area than Lake Erie, but deeper

• Canadian Shore = densely populated (Toronto) and used for industry and farming

• US Shore = mostly unused; one large city (Rochester), some farming and industry

Great Lake Exploitation

• The Great Lakes were heavily used from the point European settlers moved in– killing fur-bearing

animals– clear-cut forests for

agriculture and logging– over-fishing

Industrialization of the Great Lakes

• Early Settlement Times = untreated waste released into rivers (bacteria and disease)

• 1920’s = PCB’s = carcinogen in plastic and fertilizers

• 1940’s = DDT = bio-magnifying pesticide

Great Lakes Water Quality Agreement (1972)

• Growing concern for deteriorating water quality in the Great Lakes

• included the US and Canada• agreement limited the

amount of pollutants that were discharged into the Lakes

Toxic Contaminates

• Accumulate up the food chain– egg thinning in bird fish-eating

bird eggs– Cormorants, Ospreys, Herring

Gulls

• Human health risks – mercury contamination– PCB’s– Birth defects, reproductive

health, immune system

Great Lakes Water Quality Agreement Revisions

(1978)• Manage Lakes with an

ecosystem approach• Actions Plans (RAPs) for

Areas of Concerns (AOCs)

• health of lakes determined by ecological indicators (specific bird and fish populations)

The Problem of Management

• Several Governments control the lakes and make individual decisions on them– 2 Sovereign Nations (US and

Canada)– 1 Province (Ontario)– 8 States (MN, WI, IL, IN, PA,

MI, OH, NY)– Thousands of local

governments

Great Lakes Formation

• 3 Billion yrs ago = volcanic activity and folding creates the Great Lakes basin

• 600 million yrs ago = most of N. America covered by a salt water sea (salt deposits, petosky stones)

Great Lakes Formation

• 1 million yrs ago = continental glaciers up to 6,500 ft thick advanced over Michigan– leveled hills– altered ecosystems– created large rivers that

became the lakes

Great Lakes Formation

• 14,000 – 10,000 years ago = climate warms up and continental glaciers shrink– sand, silt, clay, and boulders deposited

by glacier– meltwater fills in the depression left

from the weight of the glacier– uplift occurs and shapes the current

great lakesLink

The Great Lakes

Natural Processes

Climate

• Summer– North = cool, dry air

from Canada– South = tropical air

from the Gulf of Mexico

– Areas directly near the lakes have cooler temperatures because the lakes cool the air

Climate

• Winter– cool arctic air flows

over the Great Lakes and picks up moisture, then drops it on the land

– Lake-effect snow creates snowbelts on the Eastern side of all the lakes

Global Warming Effects

• More evaporation from lakes = lower lake levels

• increased weather disturbances

• changes in crops and food production

• problems with shipping

Lake Levels

• Day-to-Day Changes = caused by winds

• Annual = winter (low levels) and summer (high levels)

• Long-term cycles = cyclic changes caused by changes in climate

Lake Stratification

• Layering of lake water based on temperature differences

• caused by density differences

• cold water = more dense = sinks to bottom

Lake Layers• Epilimnion = warm

layer on surface and near shore, most life lives here, sunlight

• Thermocline = thin middle layer separating warm and cold layers

• Hypolimnion = cool, dense lower layer, not much sunlight, not much life

Fall Turnover

1. Cold fall air cools the surface of the water2. Cold, dense surface water drops to the

bottom of the lake3. Entire lake mixes as water drops

Spring Turnover

• 1. Ice freezes over the surface in the winter

• 2. Ice melts and cools the water near the surface

• 3. Water at surface is cooler than on the bottom

• 4. Water from the bottom rises and mixes the lake

Importance of Turnover

• Mixes oxygen through all layers so life can exist in most of the lake

• mixes and dilutes pollutants

• fishing industry

Great Lake Invertebrates

• Phytoplankton = sun-catching plankton, (algae, euglena)

• Zooplankton = eat other types of plankton (copepod, spiny water flea, daphnia)

Great Lake Fishes

• Smallmouth and largemouth bass

• northern pike• lake trout• lake herring• whitefish• salmon

Great Lakes Birds

• Eagle = population is on the come back after their habitat was destroyed and DDT affected their reproduction

• Herring Gull = often know as sea gulls, eat fish, mice, garbage, and anything else they can find

• Cormorant = eat large amounts of fish and are not liked by fishermen