Recommendations for practice

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species. Also there are two types of lakes, and these are Oligotropic lake and eutrophic lake.

3.1.1 The Four Major Zones of a Lake

a) Littoral Zone includes the shore and the shallow, nutrient rich water were the shore, in which sunlight penetrates to the lake bottom. It contains a variety of free-floating producers, rooted aquatic plants and other form of aquatic life such as frogs, snails and snakes.

b) Limnetic Zone: This is the second zone of the lake.This zone, which is open-water surface layer, get enough sunlight for photosynthesis. It contains varying amount of floating phytoplankton, plant-eating zooplankton, and fish depending on the supply of plant nutrients.

c) Profundal Zone: This is the deep, open water where it is dark for photosynthesis. Fish adapted to its cooler darker water inhabits it.

d) Benthic Zone: This is the bottom of the lake and mostly large members of decomposers, detritus - feeding clams, and worm like insect larvae, inhabit it. The herbivores feed on dead plant debris, animal okmaisis and animal wastes that descent from above.

3.1.2 Types of Freshwater Lakes

a) Oligotropic Lakes: These lakes have small supply of nutrients.

The lake is deep; water is crystal clear while the temperature is ranged between cool-cold. It contains small population of phytoplankton and fish.

b) Eutrophic Lake: This is the opposite of oligotropic lakes. These types of lakes have large supply of nutrients. Depth of lake is shallow; water is cloudy, while temperature is warm. It contains large population of phytoplankton, zooplankton as well as diverse population of fish and carp.

3.2 Reservoirs

There are large deep, human-made bodies of standing fresh-water.

Reservoirs are built behind dams to collect water running down from mountains in stream and rivers. It is built to store water and the stored water is released in a controlled manner. Released water may be used for hydropower generation as in Kainji Dam. It can be used for irrigation purposes to grow crops on dry land as in Goronyo dam in Sokoto. It can

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be stored and released, slowly to prevent flooding as in the case of Ogun-Osun River Basin Project. It can also be used for water supply to cities as in the case of Asejire dam in Oyo State. Other purposes to which a reservoir is put are recreation such as swimming, fishing and boating.

3.3 Freshwater Streams

When rainfalls, the rainwater that does not infiltrate into the land or evaporate into the atmosphere are left on ground surface as surface water. This type of water becomes run-off flows into streams and eventually downhill into oceans for reuse in the hydrologic cycle.

As the water move downhill they become powerful shapers of land. The channel of a stream may be though of as a long, narrow path, shaped by the forces of flowing water to be most effective in moving the quantities of water and sediment supplied from the drainage basin or watershed.

Freshwater is a basic natural resource essential to man in his varied and intense agricultural and industrial activities. Runoff held in reservoirs behind dams provides water supplied for great urban centers. It also provides irrigation water for highly productive lowlands in lands.

3.4 Inland Wetlands

They are also known as freshwater wetlands. The RAMSAR convention (the treaty for the protection of global wetlands) defines wetlands as areas of marsh, fen, Pearland or water, whether natural or artificial permanent on temporary with water that is static, flowing fresh, brackish, or slat, including areas of marine water the depth of which at low tide does not exceed six metres.

Wetlands are characterized by the presence of water at the surface or in the root zone, unique soil conditions and hydrophytes (water loving plants). Wetlands are after marginal habitats between truly aquatic and terrestrial systems. Sizes can vary from small panels to huge regional expenses.

3.4.1 Importance of Wetlands

Wetlands throughout the world support their own unique wildlife. The astonishing variety of benefits local to global provided by wetlands is outlined as follows:

a) Consumptive - Wetlands yield fish, shellfish and prawns.

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b) Non-consumptive - Tourism and recreation rely on the wetland landscape.

c) Storage - Wetlands acts as major water stores, allowing ground water recharge as water slowly seeps into deep aquifers and also discharge.

d) Buffering: Buffering is the ability to slow compensate and ameliorate against change. Wetlands buffer many potentially destructive environmental processes reducing both the size and rate of change.

e) Cleaning - Wetlands are effective filters, particularly between rivers and their surrounding catchments.

f) Pathways - The waterways ramifying throughout many wetlands provide pathways for natural fluxes such as nutrient cycling and alluvial deposition, increasing fertility. Open water also provides literal routes for movement of animal and humans.

Case study:

Role of Wetlands.

4.0 CONCLUSION

This has exposed you to the freshwater ecosystems as well as the various types of freshwater ecosystem. In this unit you have also learned the various uses to which the various types of freshwater ecosystem can be put to.

5.0 SUMMARY

What you have learned in this Unit are the various types of freshwater ecosystems. This Unit also gave the importance of each type of freshwater ecosystem.

6.0 REFERENCES/FURTHER READING

Jefferies M.J. (1997) Biodiversity and Conservation. New York:

Routledge Books

Miller G.T. (1991). Environmental Science: Sustaining the Earth.

Belmont: Wadsworth Publishing Company.

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Strahler A.N. (1982) Physical Geography. 4th Edition: New York:

Wiley Books.

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