Homework Set III --CE 310. Fall 2017 Due Oct. 18 B.A. DeVantier

Transcription

1 Homework Set III --CE 310 Fall 2017 Due Oct. 18 B.A. DeVantier Problem 1 Combination class text End of Chapter Problem 5-1&2. 5-1: A population of purple rabbits lives on the island Zulatop. The rabbits have a net growth rate of 0.09 yr -1. At the present time there are 176 rabbits on the island. What is the predicted number of rabbits 5, 10, and 20 years from now? Use the simple exponential growth equation to calculate the number of rabbits. 5-2: Recalculate the number of purple rabbits if the carrying capacity is 386 and you use the logistic equation. Assume the same number of rabbits at the present and use the same intervals. Problem 2 Like Class text End of Chapter Problem The concentration of dioxin has been measured to be 18.5 g/l in a California lake. The measured dioxin level in fish tissue is 300 mg/kg. What is the bioconcentration factor for dioxin in units of L/kg? Problem 3 Describe the interactions between 1) the hydrologic and nitrogen cycles 2) earth energy balance and the carbon/oxygen cycle 1) The main interactions between the hydrologic cycle and the nitrogen cycle have to do with transport by flowing water or groundwater seepage of dissolved forms of nitrogen (ammonia/ammonium, nitrate, and nitrite) and transport of suspended living matter (containing both amino acids, proteins, and many other nitrogen bearing organics) in the form of suspended solids. Students should cite at least two. 2) The earth s energy balance interacts with the carbon and oxygen cycles primarily through trophic transformations (plants store solar energy in chemical bonds between the four major elements C - O - H - N though converting carbon dioxide to organic matter, energy is passed on between organisms in the form of organic chemical bonds). Another connection to the energy balance is through the chemical reactions with organic matter to produce heat (to keep warm blooded animals alive or as a direct result of biochemical decomposition reactions both giving off carbon dioxide). Carbon storage in plants and trees interacts with the energy balance in moderating the amount of carbon dioxide in the atmosphere and reducing the atmospheric warming effect of the increasing atmospheric carbon dioxide. Students should cite at least one, but for both 1) and 2) the interactions stated here are not all the of significant possibilities. Problem 4 From the temperature profile of Campus Lake measured in the springtime more than twenty years ago, shown as a function of water depth below, determine the epilimnion in whole number of feet (0 to N), the thermocline (N to M), and the hypolimnion (M to 15). Determine the arithmetic average epilimnion and hyprolimnion tempertures to estimate

2 the density difference density difference between them using Table A-1 in the back of the class text in units of kg/m 3. Note that you should use linear interpolated values for density, not the value at the nearest tabulated temperature. Depth Temp (ft) ( o C) The values of M and N are not clear because there is temperature drop with depth or rise with elevation in both the epilimnion and hypolimnion. I will present a numerical approach that calculates ΔT/Δz between elevation levels. The change is less than 1 /ft for 0 to -9 ft and greater than 1 /ft for -9 to -12 ft. Thus, I take M = 9ft and N = 12 ft. The negative values for elevation were chosen for later plotting the elevation as the dependent variable and temperature as the independent variable to make the vertical oriented in the same direction as in the lake. This allows a visual assessment of temperature slope if one remembers the dt/dz is the inverse of the plot dy/dx slope. Again the 9 to 12 ft region is my estimate of the thermocline. Temp ( o C) Vert. elev. z (ft) ΔT/Δz Epilim Average T <-- M <-- N Hypo Average T

3 Elevation from water surface (ft) Temperature ( C) Problem 5 Like Class text End of Chapter Discussion Question 6-4. A hazard quotient of 0.01 implies (a) risk = 10-2, (b) the probability of hazard is 0.01, (c) the RfD is small compared to CDI, or (d) there is little concern for potential health effects? Also explain what is wrong with the incorrect choices. A hazard quotient (HQ= dose / RfD) of 1.0 means the threshold of measurable toxicity is being approached. This means that the correct choice is (d), because HI = 0.01 implies that the dose is well below the reference dose (RfD). The other choices are not correct for the reasons: (a) risk is not estimated by HQ, (b) - risk is the probability of hazard, so again risk is not estimated by HQ, (c) CDI is the dose, so (CDI) / (RfD) = 1 / (HQ) = 100 and CDI then is not comparatively small with respect to RfD. Problem 6 Like Class text End of Chapter Problem 6-10.Characterize the hazard index for a chronic daily exposure by the water pathway (oral) of 3 x 10-2 mg/(kg-day) of xylenes, 6 x 10-4 mg/(kg-day) of Cadmium, and 0.3 mg/(kg-day) of toluene. Also determine the drinking water concentrations for a generic adult weighing 70 kg and consuming water at the EPA adult rate.

4 Problem 7 Like Class text Examples 6-2&3. Characterize the risk of a chronic daily exposure over a lifetime by water containing chloroform at one half the regulated level (40 ppb). You may assume that the two main risk pathways are through drinking the water and breathing the chloroform vapors in the shower with an assumed concentration of 4 µg/m 3. Use the 50 th percentile shower time given in Class text Table 6-7. Since sex is not specified, students must choose. Both solutions are presented as well as a generic adult representing both sexes. EPA has used BW = 70 kg for generic adult, but the text does not state it.

5