Supplementary Information

for:

Impact of Seasonal Changes in Stream Metabolism on Nitrate Concentrations in an Urban

Stream

Sarah H. Ledford1*, Laura K. Lautz2, Philippe G. Vidon3, and John C. Stella3

1Department of Earth and Environmental Science, Temple University, 1301 N. 13th St.,

Philadelphia, PA 19122

2Department of Earth Sciences, Syracuse University, 333 Heroy Geology Laboratory, Syracuse,

NY 13244

3Department of Forest and Natural Resources Management, State University of New York

Environmental Science and Forestry, 1 Forestry Dr., Syracuse, NY 13210

* Corresponding Author: sarah.ledford@temple.edu, (215) 204-7171

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Supplementary Information

Background nitrate and bromide concentrations observed at each site were subtracted

from concentrations observed during the tests to correct for background. Corrected nitrate

concentrations were then normalized to the conservative tracer concentrations, either RWT or

Br-. The natural log of normalized nitrate concentrations (CN) were plotted against distance, and

the longitudinal uptake rate was calculated as described by the Stream Solute Workshop (1990)

and Webster and Valett (2006):

Eq. 1: ln(CN)=ln(CN0)-kwx

where kw is the uptake rate (m-1). Uptake length (Sw) is the inverse of the uptake rate (in m)

(Stream Solute Workshop 1990):

Sw=1/kw

This method does not test if the uptake length is significant when considering analytical

instrument error, so we created a Matlab code to run Monte Carlo simulations of our injections

for 1,000 iterations. For each injection experiment, a random number generator was used to

select a normalized non-conservative tracer concentration from a normal distribution with a

mean equal to the measured concentration and a standard deviation equal to the instrument error.

The same process was replicated for the conservative tracer, and the ratios of each gave us a

range of CN values (Figures S1 and S2, second column). These CN values were then used to

calculate a distribution of slopes (kw, Figures S1 and S2, first column). A t-test was completed

(=0.05) to test if the distribution of slopes (kw) came from a population with a mean less than

zero, and thus a mean uptake length greater than zero. One injection (Oct. 10, 2013) failed to

reject the null hypothesis, and thus did not have a population of slopes with a mean that was

significantly less than zero, and it was removed from further analysis. The other four injections

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came from populations with negative slopes, and thus we considered their uptake lengths to be

significant and continued to use them in our analysis.

For sites where Monte Carlo analysis indicated significant uptake lengths, further uptake

characteristics were calculated (Table 1). The uptake velocity (vf) was calculated to look at the

uptake efficiency relative to nitrate availability and can be thought of as the downward velocity

at which nitrate is removed from the water column into the benthos (Mullholland et al 2008;

Stream Solute Workshop 1990). Hall et al (2009) show the calculation (in mm min-1) as:

Eq. 2: vf = Q/(Sw*w)

where Q is the average discharge (mm3 min-1) and w is the average wetted width of the stream

channel (in mm) and Sw is in mm (Stream Solute Workshop 1990). The uptake velocity

normalizes to stream size, allowing for inter-site comparison (Arango et al 2008). The areal rate

of uptake (U), or the mass of nitrate removed from the stream per unit of streambed per time (mg

m-2 d-1), was calculated as:

Eq. 3: U = vf*[NO3-]

where [NO3-] is the average nitrate concentration along the reach before the injection in mg m-3

and vf is the uptake velocity in m d-1 (Hall et al 2009; Stream Solute Workshop 1990). This can

also be thought of as the areal flux of nutrients into the streambed; U reflects the balance

between permanent removal (denitrification), temporary storage (assimilatory uptake), and

nitrification of NH4+ in the water column (Arango et al 2008). Turnover time (kc

-1) is the average

time a nitrate ion spends being transported in the water column before being removed and was

calculated as

Eq. 4: kc-1 = Sw/u

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where u is the average water velocity in m min-1 and Sw is the uptake length in m (Lautz and

Siegel 2007; Stream Solute Workshop 1990; Valett et al 1996).

References

Arango CP, Tank JL, Johnson LT and SK Hamilton 2008. Assimilatory uptake rather than

nitrification and denitrification determines nitrogen removal patterns in streams of varying land

use. Limnology and Oceanography 53(6): 2558-2572.

Hall RO, Tank JL, Sobota DJ, Mulholland PJ, O’Brien JM, Dodds WK, Webster JR, Valett HM,

Poole GC, Peterson BJ, Meyer JL, McDowell WH, Johnson SL, Hamilton SK, Grimm NB,

Gregory SV, Dahm CN, Cooper LW, Ashkenas LR, Thomas SM, Sheibley RW, Potter JD,

Niederlehner BR, Johnson LT, Helton AM, Crenshaw CM, Burgin AJ, Bernot MJ, Beaulieu JJ

and CP Arango. 2009. Nitrate removal in stream ecosystems measured by 15N addition

experiments: total uptake. Limnology and Oceanography 54(3): 653-665.

Lautz LK and DI Siegel. 2007. The effect of transient storage on nitrate uptake lengths in

streams: an inter-site comparison. Hydrological Processes 21(26): 3533-3548.

doi:10.1002/hyp.6569.

Mulholland PJ, Helton AM, Poole GC, Hall Jr. RO, Hamilton SK, Peterson BJ, Tank JL,

Ashkenas LR, Cooper LW, Dahm CN, Dodds WK, Findlay SEG, Gregory SV, Grimm NB,

Johnson SL, McDowell WH, Meyer JL, Valett HM, Webster JR, Arango CP, Beaulieu JJ, Bernot

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MJ, Burgin AJ, Crenshaw CL, Johnson LT, Niederlehner BR, O’Brien JM, Potter JD, Sheibley

RW, Sobota DJ and SM Thomas. 2008. Stream denitrification across biomes and its response to

anthropogenic nitrate loading. Nature 452: 202-206. doi:10.1038/nature06686.

Stream Solute Workshop. 1990. Concepts and methods for assessing solute dynamics in stream

ecosystems. Journal of the North American Benthological Society 9(2): 95-119.

Valett HM, Morrice JA, Dahm CN and ME Campana. 1996. Parent lithology, surface-

groundwater exchange, and nitrate retention in headwater streams. Limnology and

Oceanography 41(2): 333-345.

Webster JR and HM Valett. 2006. “Solute Dynamics.” Methods in Stream Ecology. Eds. FR

Hauer and GA Lamberti. Amsterdam: Elsevier. 2nd Edition. 169-183.

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Supplementary Tables

Table S1. Discharge measurements along the stream collected from 2011 to 2014 through ADV

measurements and injection tests

Date Approximate Stream Kilometer

Method Discharge (L/s)

12-Sep.-2011 0.44 RWT injection 67.812-Sep.-2011 0 RWT injection 95.4

Jun.-2012 0.38 ADV 47.4Jun.-2012 0 ADV 53.8Jun.-2012 0.48 RWT injection 60.3Jun.-2012 0 RWT injection 73.4

23-Jul.-2012 0 ADV 31.923-Jul.-2012 1.56 ADV 11.4

18-Aug.-2012 0.37 ADV 25.129-Aug.-2012 0.37 ADV 28.131-Aug.-2012 0.37 ADV 25.74-Sep.-2012 0.37 ADV 21.6Dec.-2012 0.46 RWT injection 79Dec.-2012 0 RWT injection 90

10-Oct.-2013 0.20 ADV 60.712-Oct.-2013 3.80 ADV 15.910-Jun.-2014 0.37 ADV 85.411-Jun.-2014 0.37 ADV 90.112-Jun.-2014 0.37 ADV 81.67-Jul.-2014 0.37 ADV 86.110-Jul.-2014 3.80 ADV 37.212-Jul.-2014 0 ADV 56.212-Jul.-2014 0.44 ADV 55.28-Nov.-2014 3.80 ADV 9.7

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Supplementary Figures

Fig. S1. Results of a Monte Carlo simulation for each injection in the channelized reach to assess the significance of uptake length

calculations. The first row are results from October 12, 2013 (a-d); the second row are results from July 10, 2014 (e-h); the third row

are results from November 8, 2014 (i-f). The first column (a, e, and i) shows the distribution of slopes (kw). All three dates had slope

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distributions with a mean less than zero (t-test, =0.05), indicating they have a positive uptake length, and thus the uptake lengths are

considered significant. The second column (b, f, and j) shows the CN lines from which the slopes were determined. The third column

(c, g, and k) shows the pre- and post-injection nitrate concentrations with distance. The fourth column (d, h, and l) shows the pre- and

post-injection concentrations of the conservative tracer used in the test. RWT injections do not have a pre-injection concentration

because it is assumed to be zero.

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Fig. S2. Results of a Monte Carlo simulation for each injection in the natural reach to assess the significance of uptake length

calculations. The first row are results from October 10, 2013 (a-d); he second row are results from July 12, 2014 (e-h). The first

column (a and e) shows the distribution of slopes (kw). July 12, 2014 had a slope distribution with a mean less than zero (t-test,

=0.05), indicating it has a positive uptake length, and thus the uptake lengths is considered significant. October 10, 2013 failed the t-

test at =0.05 and was removed from further analysis. The second column (b and f) shows the CN lines from which the slopes were

determined. The third column (c and g) shows the pre- and post-injection nitrate concentrations with distance. The fourth column (d

and h) shows the pre- and post-injection concentrations of the conservative tracer used in the test. RWT injections do not have a pre-

injection concentration because it is assumed to be zero.

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