## (Solved) ESM 321 HW #2 Please complete the following problems (engineering paper is recommended, although not required). You may submit a print-out from Excel...

Below you are given the average monthly streamflow from the Saltzmann Creek watershed in Forest Park. If phosphate (PO43-) concentration in the streamflow was found to average 0.155 mg/L throughout the year, estimate (a) the total volume of water (in L) and (b) the total mass of streamwater-exported PO43- (in kg of PO43-) leaving the watershed in an average year.

Month Mean Q [cfs] Month Mean Q [cfs] Oct 0.493 Apr 2.486 Nov 1.669 May 1.358 Dec 2.348 Jun 0.500 Jan 2.631 Jul 0.333 Feb 2.349 Aug 0.199 Mar 2.014 Sep 0.191

ESM 321 HW #2 Please complete the following problems (engineering paper is recommended, although not required).
You may submit a print-out from Excel that clearly shows all the work and is properly annotated with comments
describing your process. If I canâ€™t easily trace your steps, I wonâ€™t be able to assign partial credit.
Date due: Tues, Feb 28, 2017 in class. No submissions by email. (60 pts available) Concepts to consider:
â€¢
â€¢
â€¢
â€¢ Mass = concentration x volume
Net flux = inputs â€“ outputs
Wet vs. dry deposition
Calculate volume of rain given rainfall
depth and area of watershed â€¢ Residence time = standing stock / flux
â€¢ Use metric units
into or out of pool
â€¢ Molar masses of P vs. PO43- are different
â€¢ New growth = flux into pool of live
â€¢ Average flux = (Total inputs + Total
biomass
outputs)/2 Questions 1-3 relate to one ecosystem, and questions 4-5 relate to another one. You may find it helpful to start out by drawing a box
model that shows inputs, outputs, and storage in each system, to or
1. (10 points) Below you are given the average monthly streamflow from the Saltzmann Creek watershed in Forest Park. If phosphate
(PO43-) concentration in the streamflow was found to average 0.155 mg/L throughout the year, estimate (a) the total volume of water
(in L) and (b) the total mass of streamwater-exported PO43- (in kg of PO43-) leaving the watershed in an average year.
Month
Oct
Nov
Dec
Jan
Feb
Mar Mean Q [cfs]
0.493
1.669
2.348
2.631
2.349
2.014 Month
Apr
May
Jun
Jul
Aug
Sep Mean Q [cfs]
2.486
1.358
0.500
0.333
0.199
0.191 2. (10 points) Suppose that precipitation for an average year in the Saltzmann Creek watershed in Forest Park was 39.5 inches and
that average P concentration in rainfall was 6.4x10-2 mg P/L. Further, suppose that an average of dryfall P deposition rate was found to
be 1.60x10-5 kg P ha-1 hr-1. Suppose that in an average year it rains for a total of 1060 hours. Assume the drainage area of the
watershed is 2.50x102 ha. What is the total mass of atmospheric P input to the watershed in a year?
3. (10 points) (a) If rock weathering represents 83% of P inputs and atmospheric P represents 17% of total inputs, how much P enters
the watershed annually from rock weathering? (b) Based on your computations in problems 1 and 2, compute the net flux of P to/from
the watershed on an annual basis. (c) State what percentage of total P inputs are retained (you can assume that PO43- is the dominant
form of P being exported in stream water)
4. (15 points) The values in the table were found in a mature forest in central Oregon (Sollins et al. 1980. Ecol. Monog. 50:261-285).
Assume these values are representative of conditions at the Saltzmann Creek watershed. What is the total mass of P in (a) the top
meter of soil, (b) live biomass, (c) dead biomass, and (d) the entire watershed?
Ecosystem Component
Foliage
Aboveground live wood
Roots
Conifer leaf litter
Woody litter
Soil (1m depth) Mass (Mg/ha)
1.39 x 101
7.05 x 102
1.53 x 102
1.86
0.48
1.12
1.50 x 104 P%
0.22
0.008
0.01
0.16
0.088
0.045
0.0057 5. (15 points) Assume that live root growth represents 10.0% of total root biomass and new foliage represents 25.0% of total foliage
each year. Assume that the system is roughly in equilibrium with respect to P flux. Assume that PO43- represents the dominant form
of P in the stream and atmospheric inputs. Estimate the residence times of P for (a) living biomass and (b) the entire watershed.
(c) Briefly discuss the relative importance of the soil vs. the live biomass in maintaining P in this watershed ecosystem.

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