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  Heat and Oxygen Budgets for Halsted's Bay


The RUSS data from Ice Lake is summarized to show the lake's average heat and oxygen content on each day. These are calculated by averaging the amount of heat and oxygen contained in each 1 meter thick layer of the lake over the course of the day and then adding them up from 0-3 m, 3-8 m and 8 meters to bottom. Therefore, the sum of the values for the 3 layers is the total amount in the whole lake on that day. - Limnologists say that these values are morphometrically, or volume-weighted.

Charts of heat and oxygen content are provided below. These are "stacked-area" charts - showing the contribution of each layer to the total. Below each chart you will find a more detailed description of the calculations involved for determining the heat content and oxygen content. You can also download the Excel spreadsheet (it's about 90 Kbytes) containing this data and the charts for Ice Lake.

These data should be considered "provisional" until otherwise indicated. The data are undergoing several rounds of QA/QC review and some may be modified at a subsequent date. We chose to leave the data hose on full blast whenever possible to familiarize ourselves with the operation and maintenance requirements of the RUSS units and to generate real data for use in developing curricula and lesson plans. Data gaps were associated with various RUSS system upgrades and occasional gremlins.


Click image for a larger version
total heat budget graph

The ability of a body of water to store heat is due primarily to the heat capacity of its water. Water has a specific heat of 1.0 calories per gram per degree Celsius. This means that it takes 1 calorie of heat energy to raise the temperature of a gram of water by 1°C. For example, using the data from Ice Lake on May 29, 1998 at 6 a.m. we can calculate the heat content of the upper layer, where

heat content = mass x specific heat x temperature (m * C * deltaT )

= (grams) x (calories/gram/degree) x (degrees°C)

And since Mass of water = density x volume and density = 1 gram/milliliter which = 1 kg/Liter,

Heat content = volume x density x specific heat x temperature

(m * C * deltaT ) = (liters x kg/Liter) x (calories/gram/degree) x (degrees°C)


(x 105 m3)

(average of layer)

(calories per layer)

0-1 meters      
1-2 meters      
2-3 meters      
Total (0-3 m)      

Large bodies of water can modify the weather in their region by their ability to store heat energy during warm periods and release it during cooler times. For instance in Duluth, Minnesota, the weather forecasts typically say "cooler by the lake" in summer because the average surface temperature of the lake is only about 10°C (50°F) then, and "warmer by the lake" in winter because its average temperature is about 4°C (39°F) which is much warmer than the air.

We can follow trends in the lake's "heat budget" by computing the heat content of its layers relative to their minimum values at 0°C. This is the subject of a specific Studying Heat Budgets Lesson and the Investigating Heat Budgets Lesson. Further discussion of the heat balances of lakes can be found in standard limnology and geosciences texts (e.g. Horne, A.J. and C.R. Goldman 1994. Limnology, 2nd edition. McGraw-hill, Inc.).


Click image for a larger version
total DO graph

We plot the dissolved oxygen content of the top (0-3 m), middle (3-8 m) and bottom (8 m - bottom) layers for use in a number of specific lab lessons and for generating hypotheses to explain changes in these values over time. As for heat, the total amount of oxygen in a layer is calculated as the sum of individual layer volumes multiplied by their respective dissolved oxygen concentrations. This yields a mass of oxygen. Using the data set again taken from 6 a.m. on May 29, 1998:

Note: remember that 1 mg/L = 1 g/m3

(x 105 m3)
Dissolved O2
(mg/L average for layer)
Total O2 mass
0-1 meters      
1-2 meters      
2-3 meters      
Total (0-3 m)      

That's more than 4 metric tons of oxygen gas !


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date last updated: Tuesday March 09 2004