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Description of a Lake Ecosystem

Lakes are a major source of the world's fresh water. While the vast majority -- up to 99 percent -- of the planet's freshwater resources are locked away in glaciers or buried below the earth's surface, lakes can support a variety of life, including fish, crustaceans, amphibians and mammals. Lakes have their own ecosystems, creating a delicate balance that is easily disrupted.

Producers
- Shoreline plants like cattails can provide safe breeding grounds for many lake-dwelling animals.
  
  The producers of the lake are the organisms that make life possible. These organisms take nutrients from the water or soil on the lake's floor and combine it with sunlight to both create oxygen and supply themselves with enough fuel to survive. Without oxygen in the water, larger organisms couldn't survive -- and many of these same organisms feed on producers.
  
  Algae is one of the largest producers of a lake ecosystem. These microscopic organisms work in conjunction with larger plants called macrophytes, distinguished by the fact that they are multi-celled organisms with each cell having a specific, single function. These plants can be submerged and rooted in the lake bed, floating on the surface of the water or rooted along the shoreline, partially submerged. These plants often also provide shelter for young fish and crustaceans.
Primary Consumers
- Most primary consumers are found in the lake's surface zone.
  
  The primary consumers of the lake are those that survive by eating the producers. While all other non-producers in the lake consume the byproducts of photosynthesis in the processes of breathing, primary consumers are those that directly consume algae and plants as food.
  
  Zooplankton are microscopic organisms that feed on algae, and are some of the smallest of the primary consumers. Tiny crustaceans, they are typically found in the limentic zone; this is the lake zone where there is enough sunlight penetrating the water to support photosynthesis. Another type of primary consumer are young fish that feed on the plants of their surroundings as they develop.
Secondary and Tertiary Consumers
- Those outside of the lake play an important role in the ecosystem.
  
  Secondary consumers are those creatures that feed on the primary consumers, and tertiary consumers feed on the secondary. The zooplankton that make up a large portion of the primary consumers of the lake ecosystem are one of the main food sources for small fish -- the secondary consumers. These small fish are in turn eaten by larger fish, birds or even people -- each of which are a tertiary consumer. Because not all tertiary consumers live within the confines of the lake, a lake ecosystem can reach far beyond its shores. Ducks and other fish-eating birds may make their nests on the shore, away from the water's edge.
Decomposers
- When organisms -- both plant and animal -- die in the lake, the decomposers work to restore the nutrients within the body to the ecosystem. Bacteria and fungi live not only in the water but in the soil at the bottom of the lake, and turn waste products as well as dead and decaying tissues into fuel for themselves. The waste products of these processes, nutrients in their raw forms, are returned to the water and to the soil where they are then consumed by the primary consumers and turned back into organic material.
  
  The bottom-dwelling organisms that feed on dead and decaying organisms are called detritivores. While bottom-feeders such as shrimp and crabs help to break down the dead material, tiny microorganisms are ultimately responsible for the final breakdown of material.

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