1) Describe lake or pond stratification and how it changes the vertical profile
ID: 52111 • Letter: 1
Question
1) Describe lake or pond stratification and how it changes the vertical profile of physical, chemical, and biological characteristics of lake or pond ecosystems. What are the names of the different strata or zones, and what environmental factor determines the stratification? What physical properties drive this stratification and turnover (change from stratified to uniform profile)? Describe how these profiles change in a northern latitude lake or pond in the summer, fall, and winter? Where is primary productivity highest, respiration highest, and dissolved oxygen greatest in a northern latitude lake in the summer vs fall? Explain why.Explanation / Answer
Lake stratification:
There are 3 layers:
Epilimnion - top of the lake
Metalimnion - Middle layer
Hypolimnion - Bottom layer
The top layer will be less dense as cold water is denser than warm water. In summer, a clear temperature and density difference is seen in the two layers. The nutrients at the bottom of the lake are not available to the organisms in the top layer. Bacteria in the top layer consume dead organisms and the debris falls to the hypolimnion. The oxygen supply to the hypolimnion is low due to lack of photosynthesis. The hypolimnion finally becomes anoxic. This leads to death of fish in the hypolimnion.
In winter, the top layer is convered with ice which prevents the entry of sunlight and oxygen. If the ice is thin, fish and other marine organisms survive. If the is thick, the oxygen gets depleted slowly. IF the oxygen is entirely depleted, the fish gets killed.
In autumn and spring the lake experiences mixing of both the layers.
In northern altitude lakes, the temperature changes are not very great. Hence, a marked difference is seen only during summer where the top layer is warm water. during fall, the temperature remains chilly and so the top layer also has cold water.
The highest primary productivity is seen where there is penetration of sunlight and the presence of nutrients. Hence, the top layer shows the highest productivity in summer. During fall, the middle layer shows the highest productivity since sunlight penetrates to the middle layer. The top layer becomes cold due to the fall weather.
Respiration is highest in the top layer in the summer and highest in the middle layer in the winter. This relates to the productivity.
Dissolved oxygen is highest in the top layer. The wind moving across the top of the water allows more oxygen molecules to enter the water. In the fall, the oxygen is equal in all layers due to turnover.
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