WHAT ARE LAKES? Lakes are inland depressions containing standing water.
WHERE ARE LAKES FOUND? All over the world Lakes are not evenly distributed on the earths surface; most are located in high latitudes and mountainous regions. Canada alone contains 50% of the world’s lakes
HOW ARE LAKES FORMED? 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.
EXAMPLE: GREAT LAKESGlaciers are responsible for the large basin that holds most of the GreatLakes. The Great Lakes consist of Lake Superior, Lake Huron, LakeMichigan, Lake Erie, and Lake Ontario.
Shifts in earth’s crustEXAMPLE: LAKE TITICACA IN SOUTH AMERICAThe highest large lake in the world is Lake Titicaca in South America. It was formed bymelted ice and snow. The melted ice and snow filled a basin in the Andes Mountains thatwas formed by the folding of the mountains that caused cracks or faults in the earth’scrust.
Craters of some extinct volcanoEXAMPLE: TAAL LAKE
LandslidesEXAMPLE: ALABAD LAKElake in the Hunza valley of northern Pakistan created in January 2010 bya massive landslide.
PHYSICAL CHARACTERISTICS OF LAKES 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.
3 LAYERS IN LAKE STRATIFICATIONIntense 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.
WHAT IS AN OVERTURN? Overturn is a circulation which recharges oxygen and nutrients through the basin.
LAKE OVERTURN 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
LAKE OVERTURN IN A TEMPERATE LAKE
1. LITTORAL ZONE 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
2. LIMNETIC ZONE 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.
3. PROFUNDAL ZONE 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.
4. BENTHIC ZONE 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.
NUTRIENT STATUS Eutrophic Systems Oligotrophic Systems Dystrophic Systems
EUTROPHIC 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
OLIGOTROPHIC SYSTEM Water is clear and appears blue to blue green in the sunlight The nutrien