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.
HEAT
CONTENT
Click
image for a larger version
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)
|
Layer |
Volume
(x 105 m3) |
Temperature
(average of layer)
|
Heat
(calories per layer) |
| 0-1
meters |
1.60 |
20.80 |
3.33
x 1012 |
| 1-2
meters |
1.48 |
20.75 |
3.07
x 1012 |
| 2-3
meters |
1.36 |
19.55 |
2.66
x 1012 |
| Total
(0-3 m) |
4.44 |
|
9.06
x 1012 |
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.).
OXYGEN CONTENT
Click
image for a larger version
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
|
Layer
|
Volume
(x 105 m3)
|
Dissolved
O2
(mg/L average for layer)
|
Total
O2 mass
(kilograms)
|
| 0-1
meters |
1.60 |
9.40 |
1504 |
| 1-2
meters |
1.48 |
9.40 |
1391 |
| 2-3
meters |
1.36 |
9.90 |
1346 |
| Total
(0-3 m) |
4.44 |
|
4241 |
That's
more than 4 metric tons of oxygen gas !
|
