Lakes are inland depressions containing standing water.

All over the world Lakes are not evenly distributed on

the earth's surface; most are located in high latitudes and mountainous regions. Canada alone contains 50% of the world’s lakes

Glacial erosion and deposition Shifts in earth’s crust Craters of some extinct volcano Land slides

 Glaciers formed lake basins by gouging holes in loose soil or soft bedrock, depositing material across stream beds, or leaving buried chunks of ice that later melted to leave lake basins. When these natural depressions or impoundments filled with water, they became lakes.

Glaciers are responsible for the large basin that holds most of the Great Lakes. The Great Lakes consist of Lake Superior, Lake Huron, Lake Michigan, Lake Erie, and Lake Ontario.

The highest large lake in the world is Lake Titicaca in South America. It was formed by melted ice and snow. The melted ice and snow filled a basin in the Andes Mountains that was formed by the folding of the mountains that caused cracks or faults in the earth’s crust.

Shifts in earth’s crust

Craters of some extinct volcano

 lake in the Hunza valley of northern Pakistan created in January 2010 by a massive landslide.

Landslides

Light influenced by silt and other materials carried into the lake and by the growth of phytoplankton.

Temperature temperature varies

seasonally and with depth.

Density Water is most dense at

4°C and becomes less dense at both higher and lower temperatures. Because of this density-temperature relationship, many lakes in temperate climates tend to stratify, that is, they separate into distinct layers.

Intense heating of the surface waters of the lake help create a strong stratification of lake waters.Epilimnion-  an upper layer of circulating warm water, usually no more than 6 m (20 ft) deep, where dissolved oxygen concentrations are moderate to high. Metalimnion or thermocline-  a layer of rapid temperature and oxygen decrease with depth, often quite thin, separating the upper and lower layers. Hypolimnion – a cold, deep-water, non-circulating layer in which oxygen is low or absent.

Overturn is a circulation which recharges oxygen and nutrients through the basin.

In temperate lakes, the changing of the seasons help move water in the lake. 

Tropical lakes often stay stratified because warm water always stays on the top. 

In temperate lakes the winter months chill the surface water so that it gets colder than the water underneath, causing it to sink.  This happens in the spring and fall

Shallow-water zone Light reaches the bottom Stimulates the growth of rooted plants the area near the shore at the top of

the lake that receives sunlight

is the sunlight part at the top of the lake, similar to the littoral zone.

However, the limnetic zone is the open area away from the shore.

Most photosynthesis occurs in this part of the lake. 

is the deep open water, where it is too dark for photosynthesis to occur.

Its beginning is marked by the compensation level of light, the point at which respiration balances photosynthesis

For the profundal and benthic zones, low levels of photosynthesis result in low levels of dissolved oxygen.

the very bottom of the lake Organisms here tend to tolerate cooler

temperatures well.  Place where decomposition takes place. For the profundal and benthic zones,

low levels of photosynthesis result in low levels of dissolved oxygen.

Eutrophic Systems Oligotrophic Systems Dystrophic Systems

Lakes type with high production associated with high nitrogen and

phosphorus increase in growth of algae and

other aquatic plants. May experience oxygen depletion

Water is clear and appears blue to blue green in the sunlight

The nutrient content in the water is low; and although nitrogen is abundant, phosphorus is highly limited

Low production of organic mater, particularly phytoplankton

Oxygen concentration remains high

Lakes that receive large amounts of organic matter from surrounding lands particularly in the form of humic materials that stain the water brown

Low only in planktonic vegetation but have generally high productive littoral zones

Littoral vegetation dominates the metabolism of the lake, providing a source of both dissolved and particulate organic matter.

THOSE THAT GO WHERE THEY CHOOSE

FISH AMPHIBIANSTURTLES

LARGER ZOOPLANKTONINSECTS

THOSE THAT GO WHERE THE WATER TAKES THEM

LIVING THINGS = PLANKTON   animals - zooplankton   algae - phytoplankton   bacteria - bacterioplankton

DEAD MATERIAL = DETRITUS internal - produced within lake external - washed in from watershed

THOSE THAT LIVE ON THE LAKE BOTTOM

BENTHOS = ANIMALS   aquatic insects   molluscs - clams, snails   other invertebrates -       worms, crayfish

PLANTS   higher plants - macrophytes   attached algae - periphyton 

BACTERIA & FUNGI   sewage sludge   aufwuchs - mixture       of algae, fungi       and bacteria

Zonation of emergent, floating, and submerged vegetation at the edge of a lake or a pond as a response of water depth

Spike rushes and small sedges

ADAPTATION: Roots are

anchored in the bottom bud.

Bulrushes, reeds, and cattails

ADAPTATION:Narrow, tubular,

linear leaves and have broad leaves

Pond lily (Nuphar spp.) and Pond weed (Potamegaton)

ADAPTATION:Poorly developed root system but highly developed aerating system

Certain pond weed species (Chara muskgrass)

ADAPTATION:Lacks cuticles. These plants absorb nutrients and gases directly from the water through thin and finely dissected or ribbon like leaves,

Fishes lack strong lateral muscles characteristics of fish living in swift water such as sunfish.

ADAPTATION:Have compressed bodies that permit them to move with ease through the masses of acquatic plants.

Diving insects such as water boatman and Diving beetles

ADAPTATION:Carry a bubble of air with them when they go under water in search of prey.

The shore line is parceled into lots, residences spring up, nutrient seep in the septic tanks and pesticides find their way into the lake. Before long the structure of the lake changes.

Motorboats discharge an oily mixture that can lower oxygen levels and adversely affect the growth and longetivity of fish.

Wake created by motor boating disturbs littoral vegetation.

Overfishing, pollution and introduction of exotic species accidentally or on purpose

Human activities like road construction, logging, mining, agriculture add another heavy loads of silts and nutrients, especially nitrogen, phosphorus and organic matter.