Reading: Nutrient Cycling in Lakes
In the News: Bubbles as a remedy for ocean acidification?
Homework: Due 4/25/2017
Consider a lake of infinite horizontal dimension, a depth of 20 meters, and a thermocline at 10 meters. The epilimnetic temperature is 25 oC. The hypolimnetic temperature is 6oC. Both layers are well mixed vertically. The alkalinity of the lake is 0.10 mM. The hypolimnion volume is 10% of the epilimnetic volume. Draw a sketch of the lake and use it to answer the questions below.
1) Calculate the equilibrium concentration of oxygen at depths of 5 and 15 meters in units of ppm and moles/liter.
2) Lakes in Maine tend to bloom when the dissolved phosphorus in the springtime is above 12 ppb (as P). Assume that all of 12 ppb P is converted to biomass in the epilimnion. What fraction of the epilimnetic biomass is required to reduce the oxygen in the deep water to below 1 ppm?
3) If bacterial oxidation of the deep biomass is complete, what is the phosphourus concentration in the deep water just before the fall overturn?
4) Qualitatively, will the pH of the deep water increase or decrease over the course of the summer?
Overview of Water Properties – Look UP – Ice Floats
Homework: We are beginning a series of homework assignments calculating the physical and chemical properties of water. Please create ONE Workbook with multple worksheets, one for each assignment. You will be able to use your workbook for the next exam. This week you will create two worksheets.
1) Calculate the density of water as a function to temperature and salinity. Plot the density as a function of temperature for four different salinities (0 to 35 o/oo). At what salinity will cold water no longer have a density maximum? Assume that you have two 1 meter cube blocks of water sitting on top of each other. The top block is 25 0C and the bottom block is 15 oC. How much mechanical energy would be required to mix the water in both blocks? This is the Strength of Stratification.
2) Calculate the solubility of oxygen in mg/L and micro mole/L as a function of temperature and salinity. Plot the solubility of oxygen as a function of temperature for four different salinities (3 to 35 o/00).
Hand in each worksheet printed on a single page of paper. Due 4/13/2017
http://pubs.acs.org/doi/pdf/10.1021/es040686l – Surface Water Trends
Reading: Jacobs: Chapter 11 and 12.
Homework: Due: 3/30/2017. In May 2015 I purchased a VW Golf Diesel Wagon due to the excellent performance and fuel economy (50 mph at highway speeds). In September 2015 VW acknowledged that they cheated on the emissions test: Everything You Need to Know About the VW Diesel Emissions Scandal. My car is producing more NOx than is allowed by EPA emission limits. It is also producing a lot less CO2 than most other cars. VW is required to provide a fix for the car, but everyone expects this will come with decreased mileage and performance. What are the environmental tradeoffs for a 2015 Turbo Diesel Golf Sportwagon assuming that I drive the car in Waterville? Is the NOx or CO2 a greater environmental concern?
Parameters for the Model:
We will focus on ozone and CO2 as the primary pollutants of concern. How much will ozone increase in Waterville on a warm summer day, with no appreciable wind, if everyone drove a VW diesel? Outline your calculation and assumptions in detail. How does this compare to the environmental impact of less CO2?
Reading: Chapters 18, 19, 20, IPCC Reports
Homework: 1) Calculate the average global temperature of the earth if it were 20% closer and 20% further away from the sun. 2) How would this average global temperature change with increasing CO2? 3) How would doubling the volume of the deep ocean impact atmospheric CO2 concentrations? 4) Why is the global warming potential of some gases many times higher than the GWP of CO2? – due 3/16/2017.
Resources: Global Warming Potentials
Reading: Jacobs 10: Oxone Hole
Homework: due – 3/7/2017
Reading: Chapter 15 and 16
Homework: (due 2/28) Consider the following global phosphorus cycle:
Calculate the evolution of atmospheric oxygen assuming zero oxygen in the atmosphere at time zero. Assume that the flux of oxygen TO the atmosphere is 138 times (mole/mole) the flux of P from the surface to deep ocean and the flux of oxygen FROM the atmosphere is 138 times the flux of P from the deep to surface ocean. Modeling the figure above using simple finite difference approximations is tricky because the surface box needs short time steps (<100 years) and the evolution of oxygen in the atmosphere takes at least 0.6 billion years. It would be a very long spreadsheet indeed!
An alternative is to assume that the entire ocean rapidly reaches steady state between the surface and deep reservoirs.
The net rate of oxygen production is F2-F3, where F2 is a small fraction of the total phosphorus added to the ocean via weathering. Over time, net photosynthesis will increase atmospheric oxygen with 138 O2 produced per mole of P consumed. A problem is that the ocean can’t hold enough organic material [(CH2O)106(NH3)16PO4] to produce significant amounts of oxygen. Significant amounts of organic material must be buried through subduction or precipitation (Prec. Flux).
Using the attached model as a guide, global oxygen flux V2, please answer the following questions:
Reading: Chapter 7 and 9
Homework: (due 2/21) 1) Using the density and depth profiles of the earth shown in figure 7-2, calculate the mass of the Earths inner core, outer core, lower mantle,upper mantle, and crust.
2) Now using data in table 7-2 on the composition of the bulk Earth, compute the total mass of the 10 most abundant elements on the earth.
3) Compare the element masses to the mass of each layer of the Earth, what does this tell us about the possible distribution of elements. (For example, can the crust be made of iron?)
4) Compute the mass of hydrogen in the earth. What is the maximum fraction of oxygen that could be in the form of water?
Atmospheric Chemistry Text: Jacob, Introduction to Atmospheric Chemistry
Reading: Langmuir and Broeker, Chapter 1. Earth and Life as Natural Systems
Chapter 2. The Big Bang
1) Ch142 Final 2000: due 2/9/2017
2) Predicting the water level in a bathtub – an example of Steady State systems: due 2/14/2017.
Consider a simple bathtub with a faucet that adds water to the tub at a constant rate and a drain where water flows out at a rate proportional to the height of the water level. In this exercise you will calculate the water level in the tub as a function of time, determine the steady state water level, and calculate the residence time of water in the tub. This bathtub model is a good analogy for many dynamic environmental systems typical of the atmosphere, ocean, lakes, and living organisms. Assume that water is added to the tub from a faucet with a constant flow rate of 10 liters/minute. The inflow rate expression is a simple zero-order process where the inflow is constant and independent of water level.
The outflow is proportional to the height of the water in the tub. This is a first-order process where the higher the water level the greater the outflow rate.
Notice that the sign of the change in volume with time (dV/dt) is negative since water is leaving the tub. The rate constant k will have units of (liters/minute cm) so that the product of the rate constant and water height is outflow rate (liters/minute). From geometry we also know that the height of the water in the tub is the volume of the tub divided by the area of the tub.
When you start filling a tub the initial volume is usually zero. Adding water increases the volume and outflow decreases the volume.
Volume = initial volume + water added – water lost down the drain (3)
Equation 3 describes the conservation of mass (water) for the tub. We will write similar conservation equations for may environmental systems.
If the amount of water added is greater than the water lost then the volume will increase. As the volume increases the depth of the water in the tub will increase which will increase the outflow rate. Eventually the outflow rate will equal the inflow rate and the bathtub fill level will reach steady state.
Steady State is reached when INFLOW = OUTFLOW. Notice that you can set equation 1 equal to equation 2 to calculate the water height at steady state. It is interesting to think about what steady state means. For the bathtub, steady state water level is only “steady” when the water is running constantly into the tub. Adding water is like adding energy to the system. Steady state systems need energy inputs to maintain their positions. This can be compared to the equilibrium water level of the tub which will be zero after the faucet is turned off.
The residence time of the water is the average time that a water molecule will spend in the tub. This can be defined as the volume of water in the tub divided by the inflow or outflow rate when the system is at steady state (volume/(volume/time) = residence time).
Water inflow rate = 10 l/minute
Water outflow rate constant (k) = 1 (l/min cm)
Area of the tub = 10,000 cm^2
Starting water volume in tub = 0 liters
time step for the model = 0.5 minutes
1) Build and Excel model of bathtub levels as a function of time. Use the attached YouTube video as a model for your program.
2) Try running the model with an initial volume of 0 liters, 100, and 200 liters. How do the simulations compare? What does this tell you about Steady State conditions?
3) Manipulate equations one and two to calculate the expected Steady State level of the bathtub and compare to the results obtained in question two.
4) Calculate the residence time of water in the bathtub at steady state.
Turn in the answers to the questions 1-4 on one piece of paper showing your model on the front of the page and your results on the back side of the page. Don’t waste paper!