Understanding Lake Stratification And Climate Change Impacts

Response to Instruction K

Referring to the data from figure 1a and 1b we can understand there had been an exponential decrease in the temperature in the initial phase of heating. The reason behind this decrease in temperature is only because the difference in densities that is existent in warm and cold water. Warm water is less dense than cold water and tends to float above the colder water. The initial warming phase warms the surface of the water but the heat cannot penetrate beyond a limit (2 meters in larger water bodies). The temperature therefore drops exponentially making the lowest layer the densest of the all.

The application of heats creates the conditions for tripartite structure but is the not the only factor that affects the formation of this stratification. The external heat can only increase the temperature of the water for few meters depending upon the size of the lake and is generally restricted to 2-7 meters or around 50 centimeters. The wind creates a most important effect known as the rolling barrel effect which makes the mixing of the water possible. Given the size of the water body, a huge amount of water is required to create the mixing of the water. The wind adds to the tripartite stratification over the water to greater depths.

Comparing the figures and graphs of (a) and (b), it can be very well understood that these have a similarity in terms of their trend. The only difference we find is in the effect of wind with heat with relation to the figures. the figure 2A is a simulated condition where the wind factor had a greater impact for the time whereas real time conditions greatly vary since factors such as wind speed, direction and intensity can make the difference along with the perceived heat.

Table: 1b

What is the density of water at temperatures of 5, 15, 20 and 25 °C? Report your answer to five decimal places.

The density of Water at the various temperatures can be observed from the table below;

 The densities were analyzed form the given calculation

Therefore, density at 15 C will be

1-{15+288.9414/508929.2∗ (15+68.12963)} ∗ (15−3.9863)²

= 1-(303.914/ 42307096.09)*121.3015877

= 1-0.000871

= 0.999128627

Therefore, the density at 15 C is 0.999128627 g/ml

1. The temperate lake has a greater difference in temperature between epilimnetic and hypolimnetic zones.
2. The temperate lake has the greatest density difference between epilimnetic and hypolimnetic layers’ more stable stratification and
3. The temperate lake would exhibit more stable layers being more resistant to mixing owing to its high temperature difference (Horne,  & Goldman, 1994).

During an extended summer, the lake stratification the lake will see lowering of the thermocline which will increase the primary productivity in the sub surface layers resulting in depleting of the dissolved oxygen faster than normal. This will eventually deprive the hypolimnion of oxygen and therefore harming the benthic habitat. We cannot control the stratification of the lake, but we can reduce the impact of global warming by cutting down on green house gases and afforestation might help reduce the impact (Kraemer, et al., 2015) 

Calculation of Volume

Absorbed Heat

The total amount of heat absorbed by the Lake was 230179 joules, between late winter and summer.

378000 joules were applied by the Lamp to reach the maximum temperature over a period of 21 minutes.

Around 60.89% of the applied heat was absorbed by the Lake. The reason behind non absorption of the total heat is due to several external factors that radiated the amount of the heat. The wind applied transferred some amount of heat along with the simulated lake was not in a vacuum and the some amount of heat was dissipated in the environment of the room. The absorption of heat by the water was also affected by the addition of ice which reduced some of the heat absorbed.

References:

Horne, A. J., & Goldman, C. R. (1994). Lake ecology overview. Limnology. McGraw-Hill Co, New York, USA.

Kraemer, B. M., Anneville, O., Chandra, S., Dix, M., Kuusisto, E., Livingstone, D. M., … & Tamatamah, R. (2015). Morphometry and average temperature affect lake stratification responses to climate change. Geophysical Research Letters, 42(12), 4981-4988.

Nürnberg, G. K. (1988). A simple model for predicting the date of fall turnover in thermally stratified lakes. Limnology and Oceanography, 33(5), 1190-1195.

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