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Pond & Lake Zone Identification

Each pond or lake has several different zones that divide the water column from top to bottom and side to side. The zones discussed are the Littoral Zone, Limnetic Zone, Profundal Zone, Euphotic Zone, and Benthic Zone.

The Littoral Zone is the shore area of the lake or pond. The littoral zone consists of the area from the dry land sloping to the open water and can be very narrow or very wide. Typically oligotrophic or young ponds have narrow littoral zones due to their steep sides and eutrophic or old ponds have wide littoral zones due to their gently sloping shoreline and sides. The littoral zone is shallow and gets a lot of nutrients from runoff and non-point source pollution. Therefore, it typically has an abundance of aquatic plant and algae growth. Some other common inhabitants of the littoral zone are cattails, reeds, crawfish, snails, insects, zooplankton, and small fish.

The Limnetic Zone is generally classified as the open water area of the lake or pond. This is a much larger section of water in oligotrophic or younger ponds and lakes than it is in eutrophic or older bodies of water. Within the limnetic zone are two separate sections. The upper portion of the limnetic zone near the surface of the water is the Euphotic Zone or Epilimnion (warm water region). This is the portion of water that receives sunlight. The zone ends where the sunlight fails to penetrate the water. The euphotic zone is where algae and other aquatic plants thrive (along with the littoral zone). Also this is the typical area of dense fish populations because oxygen levels are typically higher due to contact with the air.

Below the euphotic zone is the Profundal Zone or Hypolimnion (cold water region). The profundal zone is located below the thermocline where the sunlight does not penetrate. Again, the size of this zone depends on the age and water clarity of the pond or lake. The profundal zone typically has lower fish populations because of the lack of oxygen during many parts of the year.

The final zone is the Benthic Zone. This is the bottom of the pond or lake and consists of organic sediments and soil. The benthic zone is the pond or lakes digestive system. This is where bacteria decompose organic matter from dead algae, aquatic plants, and fish and animal waste. The more organic matter in the pond, the more decomposition taking place. Decomposition can take place either aerobically (in the presence of oxygen) or anaerobically (without oxygen). It is much better to have aerobic decomposition because it is a faster process and the byproducts are easier to handle. The benthic zone increases as the pond or lake ages.

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