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LAKES

LAKES. Lakes vs. ponds. In lakes light doesn’t reach the whole way to the bottom No photosynthesis = no O 2 produced Many organisms on or near the bottom require oxygen. How does it get there?. Overturn.

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LAKES

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  1. LAKES

  2. Lakes vs. ponds • In lakes light doesn’t reach the whole way to the bottom • No photosynthesis = no O2 produced • Many organisms on or near the bottom require oxygen. How does it get there?

  3. Overturn • Overturn is the process by which currents circulate the water in a lake or pond resulting in a movement of oxygen and nutrients

  4. Spring Overturn • Mixing of water in the springtime • Caused by melting and the cold water sinking to the bottom • The water is then mixed easily by wind • Temperature is the same throughout • Same temperature = same density • Same density allows for easier mixing • Brings nutrients up from bottom to the top

  5. Spring Overturn

  6. Spring Overturn

  7. Summer Stagnation • In summer the sun heats the top layer faster than the wind can circulate it. • 3 layers result • Different densities = 3 different levels • These layers don’t mix well

  8. Summer Stagnation

  9. Summer Stagnation

  10. Epilimnion • Upper layer warmer • Water circulates freely • Hypolimnion • Cool layer • Does not circulate • No oxygen from the top • Thermocline or metalimnion • Middle layer • Transition from warm to cold

  11. Fall Overturn • Epilimnion (top layer) cools • The fall winds cause another mixing • The entire lake becomes a uniform temperature again

  12. Fall Overturn

  13. Fall Overturn

  14. Fall Overturn

  15. Winter Stagnation • The upper layer (epilimnion) cools further and sinks • Increased cooling = increased density • Now the thermocline is reversed. The water on the bottom is near 4ºC and the water at the top is 0ºC (cold to warm) • Top layer freezes • Result = 3 layers • Epilimnion is ice • Hypolimnion is above or at 4°C

  16. Winter Stagnation

  17. Winter Stagnation

  18. ZONES OF A LAKE

  19. Trophogenic Zone • Upper layer where most oxygen is produced • Organisms here produce food through photosynthesis

  20. Tropholytic Zone • Lower part of the hypolimnion with high CO₂ and a low O₂ • Organisms feed on decomposing matter

  21. Compensation depth • Zone between trophogenic and tropholytic zones • Oxygen production and use are equal

  22. Limnetic zone • Subzone of trophogenic zone • Part of open water where light penetrates the water • Phytoplankton are the main producers

  23. Littoral zone • Subzone of trophogenic zone • Region where light reaches the bottom (near shore)

  24. AGING OF A LAKE

  25. Eutrophication • The process of aging • The increasing productivity of a lake • Means “adequate food” • Nutrient rich • Accumulations of nutrients from runoff, sewage waste

  26. Comparing new and old lakes

  27. Eutrophic • Adequate food or nutrient rich • Oxygen levels decrease greatly at the bottom

  28. Eutrophic

  29. Oligotrophic • “Lacking food” • Nutrient poor • Oxygen decreases only slightly with depth • Young biological lake • Bedrock of limestone or dolomite (basic) • The pH normally drops as a lake ages • Decay releases acids into the water (carbonic acid) • Carbonic acid forms when the carbon dioxide from respiration reacts with the water

  30. Oligotrophic

  31. Mesotrophic • Middle stage of lake life • More acidic • The pH usually rises and becomes more basic

  32. GEOPHYSICAL PROPERTIES OF LAKES Temperature Nature of the bottom Color Turbidity Transparency

  33. Temperature • Each species of organism has its own optimum or preferred temperature • Some can stand a variation in temperature • But if it goes too far in a range = Death or move elsewhere • Increase of 5 ̊C can be lethal • Fish kills • Oxygen demand exceeds the available oxygen • Death occurs • TLM – Tolerance Limit Median - based on time to get out of a bad situation • High temperatures will increase the toxic effects of chemical pollutants in the water

  34. Nature of the Bottom • Detritus • Submerged Plants

  35. Color • Suspended material • Water is green = phytoplankton • Water is yellow or brown = dead algae, runoff

  36. Turbidity • Suspension of solids • Phytoplankton and zooplankton • Dead wastes sewage • Inorganic clay and silt • Secchi Disk

  37. Transparency • How well light passes through water • Suspended solids in water • Secchi Disk • Low reading (1m) = high level suspended matter • High reading (8m) = quite clear • Based on compensation depth

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