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LIMNOLOGY (part 1)

LIMNOLOGY (part 1). There are two broad groups of fresh-water systems Lentic systems are standing water ecosystems Lotic systems are flowing water ecosystems. Limnology is the study of fresh-water ecosystems. Lentic ecosystems - Lakes.

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LIMNOLOGY (part 1)

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  1. LIMNOLOGY (part 1)

  2. There are two broad groups of fresh-water systems Lentic systems are standing water ecosystems Lotic systems are flowing water ecosystems Limnology is the study of fresh-water ecosystems

  3. Lentic ecosystems -Lakes What is a lake? It is an inland depression of standing water Size? Can be up to thousands of square miles Depth? Can be a few feet deep, or could be over a mile deep It may have an outlet stream It is temporary…it will fill in over time

  4. The world’s deepest lakes

  5. Temperature cycles in a lakeSpring • 1) Ice melts at the surface • 2) Water temperature rises to 4°C, sinks, colder, less dense water rises (convection current) • 3) Winds mix water to a uniform 4°C • 4) Mixing causes nutrients and oxygen to circulate

  6. Summer • 1) Surface water heats up • 2) A thermal density gradient is created • 3) This creates an epilimnion, metalimnion and hypolimnion

  7. Epilimnion • “Epi-” means “on top of” • The epilimnion is the uppermost layer • It is the warmest layer • Lots of oxygen • Most plankton

  8. Metalimnion • “Meta-” means “middle” • The metalimnion is an area of steep, rapid temperature decline • Contains the thermocline- a narrow plane at which the temperature drops most rapidly (about 1°C per meter) • Plankton are rare below this layer

  9. Hypolimnion • “Hypo-” mean “below or beneath” • This is a deep, cold layer • Little mixing of water occurs

  10. Autumn • Air temperature falls • Surface water cools to 4°C. convection currents form • Air temperature continually cools water at the surface • Eventually, water temp becomes uniform

  11. Winter • Cold air lowers surface temp below 4°C • Ice forms at surface • There is no mixing • Oxygen levels can drop in the water so low that “anoxic” conditions exist. Can result in fish kills

  12. Lentic systems -Ponds • How is a pond different from a lake? • A lot of the answer is in local usage. Ponds are really just small lakes • They too are temporary and may have an outlet stream • Over time, ponds will accumulate nutrients, fostering dense growth of algae and other organisms, the decay of which depletes the shallow waters of oxygen in summer. • This aging and eventual “death” of the pond is called eutrophication

  13. However, we can say… • 1) ponds are shallow enough for aquatic plants to reach the surface across the area of the pond • 2) The area of a pond is insufficient to produce large waves • 3) There is no temperature layering as there is in a lake

  14. What are wetlands? • Those areas that are inundated or saturated by surface or ground water (hydrology) at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation (hydrophytes) typically adapted for life in saturated soil conditions (hydric soils). Wetlands generally include swamps, marshes, bogs, and similar areas

  15. What’s all that mean? • Wetlands are, well, wet, for all of, or for a significant portion of the year • They have vegetation that is dominated by hydrophytes – water loving plants • And the soils are hydric – meaning typically saturated with water. The upper portion of hydric soils take on anoxic (anaerobic) conditions.

  16. Marshes

  17. Marshes • The dominant vegetation of a marsh is characterized by herbaceous stems (not woody-stemmed plants) • Typically, this means reed, sedges, grasses and cattails • Think of them as “wet prairies” • Water depth is usually a few inches to a few feet

  18. Reeds

  19. Cattails

  20. Sedges

  21. The Florida Everglades is the largest marsh in the world

  22. Everglades

  23. Swamps • Swamps are wooded wetlands • Trees dominate a swamp • They can often be a successional stage from marsh to forest • Again, water depth varies from a few inches to several feet

  24. The Atchafalaya is the largest swamp in North America

  25. Bogs • Bogs develop where drainage is blocked • They typically have a cushion-like mat of vegetation • And an accumulation of peat • Decomposition is slow because of low oxygen • They are most abundant in cold northern forests • Semi-floating mats of sphagnum moss characterize many bogs

  26. A Bog Are there any bogs in Cheshire County?

  27. Sphagnum

  28. Estuaries and vernal pools are worth considering • Estuaries are brackish water ecosystems, where fresh (river) water enters the ocean • We’ll leave a discussion of estuaries to the Marine Biology class • Vernal pools deserve their own slide presentation

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