Different Layers of Biological Zones
A lake is a large inland body of salty or freshwater. It is differentiated from the bodies of water, such as gulfs, bays and some seas that have an exchange with the ocean and are prone to tides. Lake basins are created by continuous geologic processes like buckling of stratified rock into big folds, interchanging of large masses of rock by faults and the blocking of valleys by erosions and landslides.
The lake is also formed by glaciations. In this process, glaciers create large basins by scooping up bedrock and redistributing movable materials. The water in lakes comes from atmospheric precipitation that reaches the lake explicitly and by means of rivers, springs and brooks. Lakes may disappear and form over the course of multiple and different lengths of geologic time. Water in lakes may evaporate due to the excessive increasein temperature and some lakes are filled up with sediments that leave a bog or swamp in the some parts of the lake.
In dry regions where precipitation is slight and evaporation is great, the levels of lakes may rise and fall with the season and sometimes got arid for long periods. Some lakes become concentrated because of the dissolve substances and stratification.
The primary mineral constituent lakes are:
- Salt lakes contain common salt
- Alkali lakes contain carbonates
- Borax lakes contain borates
Lakes are bound throughout the world at all forms andattitudes. And almost ½ of the world’s lake are in Canada. However, lakes are more abundant in high altitudes specifically in mountain regions that subject to glacial action. The lakes are also significant commercially as a source of fish and minerals, vacation resorts and shipping arteries.
Lakes have different zones of biological activity that largely determined by the availability of light and oxygen. The most important biological zones are the euphotic, limnetic, littoral and benthic zones.
This is where photosynthesis occurs basically the layer of open water. In limnetic zone, life is abundant where the floating organism (plankton) and actively plunging organism. Plankton algae is the producers in this zone and zooplankton such as crustaceans and rotifers are the primary consumers while swimming insects and fishes are the second highest consumer.
Euphotic zone is the upper layer of water where sunlight can still penetrate. In this region, producers such as plants produce more oxygen through the process of photosynthesis than they remove by respiration. Below the euphotic zone is the zone called “profundal zone” which is the transition between the two zones is called light compensation point, which match up roughly to the depth at which the amount of carbon dioxide being converted to sugar by photosynthesis is the same to that being released during the process respiration.
Littoral Zone is the shallow water near the shore in which rooted emergent plants also called macrophytesgrow. Littoral zone rely on the slope of the bottom of the lake and the depth of the euphotic zone. It cannot also extend deeper than the euphotic zone.
Benthic zone constitutes the bottom sediment, in this zone bacteria and fungi and even attached algae are always present. When an organism dies in overlying water their bodies settle to the bottom and get decomposed by the organism (decomposes) living in the benthic zone. In this zone, life such as worms, aquatic insect, mollusk and crustaceans depends on the availability of oxygen.
Lake productivity is the measure of the ability of lake to sustain and support aquatic life and is always determined by measuring the amount of algal growth that can be supported by the available nutrients.
Productivity is controlled by the limiting factor, which may be the concentration of nitrogen or phosphorus or the light intensity, this phenomenon is known as Liebig’s law of the minimum. It has been estimated that the phosphorus concentration should be below 0.010-0.015 mg. L-1 to limit algae bloom.
Types of Lakes
Oligotrophic Lakes - This type of lake has a low level of productivity due to a severely limited supply of nutrients to support algal growth. As a result, the water is pure that the bottom can be seen at considerable depths. Oligotrophic lakes have less substance in the water that makes it clear enough.
Eutrophic Zone - Eutrophic lakes are lakes that have high productivity because of an abundant supply of nutrients on it. Highly Eutrophic lakes may also have large mats of floating algae that typically impart unpleasant tastes and odor to the water.
Mesotrophic Lakes - Mesotrophic lakes are lakes intermediate between Oligotrophic and Eutrophic. The level of productivity is higher than that of an oligotrophic lake but not quite that of a Mesotrophic lake.
Dystrophic Lakes - These are lakes that obtain large quantities of organic materials from outside the lake and have low productivity due to low nutrient concentrations.Dystrophic lakes are surrounded by conifer forest and small in size, which the composition of fallen needles-like leaves that leads in a significant input of acid to the lake. A dystrophic lake is typically yellowish brown in color, moderately clear, contains high levels of dissolved organic matter and tannin concentrations and is acidic.
Hypereutrophic Lakes - Lakes are severely Eutrophic with a high algal productivity level and intense algal bloom that is often relatively shallow lakes with higher accumulated organic sediment. They have extensive, dense weed beds and often accumulations of filamentous algae. Hypereutrophic lakes are often subject to “winter kill” and even “summer kill” during which the depletion of oxygen results in an extensive kill of fish and sometimes other organisms.
Senescent Lakes - Senescent lakes are very old, shallow lakes in advanced stages of Eutrophication. Senescent lakes have thick organic sediments formed from accumulated aquatic vegetation and dead plant material. These lakes are nearing extinction as a productive lake environment and eventually become marshes.