Lakes have numerous features in addition to lake type, such as (but not limited to) drainage basin (also known as catchment area), inflow, and outflow, nutrient content, dissolved oxygen, pollutants, pH, and sedimentation.
The change in level of a lake is controlled by the difference between the sources of inflow and outflow, compared to the total volume of the lake. The significant input sources are precipitation onto the lake; runoff carried by streams and channels from the lake's catchment area; groundwater channels and aquifers; and artificial sources from outside the catchment area. Output sources are evaporation from the lake; surface and groundwater flows; and any extraction of lake water by humans. As climate conditions and human water requirements vary, these will create fluctuations in the lake level.
Lakes can be also categorized on the basis of their richness of nutrients, which typically affects plant growth. Nutrient-poor lakes are said to be oligotrophic and are generally clear, having a low concentration of plant life. Mesotrophic lakes have good clarity and an average level of nutrients. Eutrophic lakes are enriched with nutrients, resulting in good plant growth and possible algal blooms. And hypertrophic lakes are bodies of water that have been excessively enriched with nutrients. These lakes typically have poor clarity and are subject to devastating algal blooms. Lakes typically reach this condition due to human activities, such as heavy use of fertilizers in the lake catchment area. Such lakes are of little use to humans, and have a poor ecosystem due to decreased dissolved oxygen.
Due to the unusual relationship between water's temperature and its density, lakes form layers called thermoclines which are layers of drastically varying temperature relative to depth. Fresh water is most dense at about 4 degrees Celsius (39.2 °F) at sea level. When the temperature of the water at the surface of a lake reaches the same temperature as deeper water (such as during the cooler months in temperate climates), the water in the lake can mix, bringing oxygen starved water up from the depths, and bringing oxygen down to decomposing sediments. Deep temperate lakes can maintain a reservoir of cold water year-round which allows some cities to tap that reservoir for deep lake water cooling.
Lake Billy Chinook, Deschutes National Forest, Oregon.
Since the surface water of deep tropical lakes never reaches the temperature where water reaches its maximum density, there is no process that makes the water mix. The deeper layer becomes oxygen starved, and can become saturated with carbon dioxide, or other gases such as sulfur dioxide if there is even a trace of volcanic activity. Exceptional events, such as earthquakes or landslides, can cause mixing which rapidly brings up the deep layers, and can release a vast cloud of toxic gases which lay trapped at the bottom of the lake. An example of such a release is Lake Nyos in Cameroon. The amount of gas that can be dissolved in water is directly related to pressure. As the previously deep water surfaces, the pressure drops, and a vast amount of gas comes out of solution. Under these circumstances even carbon dioxide is toxic because it is heavier than air and displaces oxygen, so it may flow down the river valley to human or livestock settlements and cause mass asphyxiation.
The material at the bottom of a lake or lake bed may be composed of a wide variety of materials, including inorganics such as silt or sand sediments, and organic material such as decaying plant or animal matter. The composition of the lake bed has a significant impact on the flora and fauna found within the lake's environs by contributing to the amounts and the types of nutrients available.
Tidak ada komentar:
Posting Komentar