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8. For data collected between March 25 to April 4, 1992, Figure 34.B of the USGS report athttps://pubs.usgs.gov/circ/circ1133/nutrients.html gives nutrient data for the Mississippi.Unlike in Figure 34.A. there is a large spike of NH4* (which is essentially total ammonia because NH3 will be negligible at the pH of the river). It looks rather like an exponential decay of an initial spike starting at about river mile 1900. In the accompanying PowerPoint file for this HW, I give you part of this figure plus a transparent exponential function exp(-arg) with -arg varying from 0 to 4, so arg is varying from 0 to -4. At -arg = 1, c/c_o = exp(-1) = 1/e. At -arg = 2, c/c_o = exp(-2) = 1/e², and so on. Overlay the exp function plot on the NH4* peak to get as good a fit as you can. The x axis of the overlay where c/c_o=0 should lie on top of the concentration = 0 line for Figure 34.B. This is where I put it to start. Note that the peak in Figure 34.B is kind of dulled, that's surely because during the cruise they were not able to sample exactly where the peak was, so your overlay should lie above that dulled peak...From your fit, a. pick a value of -arg and read the corresponding number of miles below the front of the spike; b. read the corresponding value of c/c_o. Page 9 of the report https://pubs.usgs.gov/of/1994/0523/report.pdf has incomplete river velocity data for the data collected between March 25 to April 4, 1992. The highest value of river mile for which velocity data are available is 700-954, at 5.7 km/h. c. Lacking anything better, use that velocity to estimate the travel time t to your selected value of -arg.Remember to do any necessary conversions between miles and km. d. Use that t to compute your estimate of the k (h*¹) for decay of NH4* in the Mississippi River during the study.

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