The zoning in the lake:
For a general overview and a better understanding of individual phenomena such as eutrophication or material cycles in the lake, it is first of all important to make a survey of the individual zones in the ecosystem of Lake:
Open water area (Pelagial)The Pelagial covers the whole area of the water: from the shore area to the middle of the lake.
Ground area (Benthal): The bottom area of a lake consists of the visible (above the water) and non-visible area (below the water) on the lake and can be divided into two regions:
Shore region (Littoral) : Usually with plant-covered bank area. The littoral crosses into the profundial. The criterion for distinguishing both regions is the light: The transmitted ground zone belongs to the littoral.
Deep region (Profundal) : Transmitted ground zone, from the end of the Benthal to the bottom of the lake. Photosynthesis is not possible here for organisms.
Nutrient layer, thermocline and extra layer
Nutrient layer (Epilimnion): The surface water is the most affected by temperature fluctuations. In summer, the layer is heated by solar radiation and frozen in winter. All year long, oxygen diffuses from the air into the surface water. In addition, phytoplankton is best at photosynthesis because of the high light intensity, which is why the oxygen content (mainly in summer) is very high and decreases with decreasing light intensity. The term nutrient layer (or trophic zone) comes from the fact that in this layer more oxygen is produced by photosynthetic organisms than is consumed by cellular respiration of aerobic organisms. All in all, the photosynthesis of the producers (phytoplankton, water plants) leads to the production of biomass.
Thermocline (metalimnion): The metalimnion separates the epilimnion from the hypolimnion and is characterized by a sudden drop in temperature. The balance of oxygen production and oxygen consumption is somewhat similar.
Zehrschicht (Hypolimnion): The temperature here is constant 4 ° C because of the density anomaly of the water. At 4 ° C have H2O molecules have the highest density: they are heavier than thermally colder water and sink to the bottom of the lake. Even in winter, such a constant temperature prevails in the deep layer, causing e.g. Fishing a survival is only possible. If hypolimnion in winter would be cold as epilimnion, all living things at the bottom of a lake would freeze. In the Zehrschicht, or tropholytic zone, more oxygen is consumed than could be produced by photosynthesis. As a rule, however, no oxygen is produced due to the lack of light. Accordingly, no biomass production takes place, but only consumption of the declining biomass from the nutrient layer (it is only 'consumed').