Suggested Papers For Class Discussion

Eisenreich, S. J., B. B. Looney, and J. D. Thornton. Airborne organic contaminants in the Great Lakes ecosystem. Environ. Sci. Technol. 15(1), 30-38 (1981).

Holloway, T., A. Feore, and M. G. Hastings. Intercontinental transport of air pollution: Will emerging science lead to a new hemispheric treaty? Environ. Sci. Technol. 37(20), 4535-4542 (2003).

Engstrom, D. R., E. B. Swain, T. A. Henning, M. E. Brigham, and P. L. Brezonik. Atmospheric mercury deposition to lakes and watersheds: A quantitative reconstruction from multiple sediment cores, In: Environmental Chemistry of Lakes and Reservoirs, Advances in Chemistry Series 237, Baker, L. A. ed., American Chemical Society, Washington, DC, Chapter 2, pp. 33-66, 1994.

Concepts:

1. List the major lake formation processes.

2. Give three examples of point sources of pollutants to lakes.

3. Give three examples of non-point sources of pollutants to lakes.

4. Draw a basic diagram showing a stratified lake in summer. Label each portion of the lake.

5. List the order of terminal electron acceptors from increasing to decreasing EH values.

6. Draw a basic concentration versus time diagram for a pulse input to a lake.

7. Draw a basic concentration versus time diagram for a step input to a lake.

Exercises

1. Sitting along the shore of a lake is a leaking storage tank of gasoline. The tank is releasing xylenes (found in gasoline) into the lake at a rate of 5 cubic inches per day. Since xylene is very volatile and moderately biodegradable, assume that it has a half-life of 18 hours when leaked into water. Create a plot by hand (but using Fate® to check your calculations) of concentration of the pollutant in the lake over a period of time. Determine how long it will take the lake to reach an equilibrium concentration of the pollutant.

Volume: 313,348,796m3

Lake detention time: 10 years

Lake outlet flow rates: 44,650,012m3/year

2. A lake is surrounded by agricultural fields. The pesticide malathion, used on these crops, has a chemical degradation half-life of 6.5 days. As a result of its location, the lake receives high doses of malathion after aerial spraying of pesticides (by crop-dusting airplanes). If the initial concentration of malathion in the lake is 13 mg/L, find the amount of malathion in the lake one year after the contamination has ended, using the following parameters (check your answers with Fate®)

Retention time: 5.75 years Flow Rate: 3.65 x 103m3/yr Lake Volume: 2.08 x 104m3

Perform a sensitivity analysis using half-lifes of twice and half as long.

3. Lake Ontario receives an average of 140kg DDT every year, or 0.384kg/day, from the atmosphere. The pollutant enters as a step input and is derived from a chemical factories in South America. The volume of Lake Ontario is 1638 km3, and the outflow into the St. Lawrence River, the effluent of the lake, is 7990m3/yr. The half-life of DDT is 31.3 years. Calculate the concentration of DDT in the lake after six months. Calculate and plot the time versus concentration graph for a time interval from 0.00 to 1.5 years. Check your answers using Fate®.

4. A chrome plating plant on a lake has been operating for years without trouble, but one year fishermen notice their catch becoming scarce. Wildlife biologists doing a survey of regional trout populations find that there are significant amounts of chromium ion (Cr3+) in the fish bones, and conclude that the holding tank for the plant must be leaking. If this is true, what concentration of chromium ion species would you expect to find in the lake water if the tank started leaking 10 months ago? Use the data from the chart below to do the necessary calculations and use Fate® to check your results.

Lake volume = 6.70 x 106 m3 Outlet flow = 8.9 x 106m3/yr Cr3+ input per day = 0.150 kg/day

Note: Chromium does not have a rate constant for loss as it does not degrade. Thus, you will need to use a very high half-life value to graph this in Fate® (suggested value: 1,000,000).

5. Mining activity was common in western Montana, along the Rocky Mountains and nearby ranges during the twentieth century. For the majority of the century, the major constituent used for the extraction of gold was cyanide. Assume that at one site a few barrels of HCN spilled into a nearby lake. The initial concentration of HCN in the lake was 17.5mg/L. The outlet flow from the lake was 2.92 x 107m3/year. The lake volume was 4.00 x 106m3 of water. The half-life for HCN is 334 days. Calculate the concentration of HCN in the lake water after 1.00 and 5.00 years. Use Fate® to check your answers.

6. A frozen railroad track causes a train carrying radioactive cesium to wreck. Unfortunately, the track segment is located on a bridge over a lake, and cesium is released into the water, resulting in a uniform concentration of 6.00 |mg/L in the lake water. The lake has a detention time of 5.56 years. Assuming complete mixing and a pulse release, calculate the concentration of cesium after 20.0 years. Cesium has a half life of 30.17 years. At what point in time does the cesium concentration become undetectable? (The best technologies can detect cesium at a concentration of 10-12M.)

Spreadsheet Exercise

Create a spreadsheet that performs the same calculations as Fate® for both the step and pulse equation. Construct your spreadsheet so that it is interactive (so you can change numeric values for parameters and the plot automatically updates itself).

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