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| Titel |
Accounting for Dispersion and time-dependent Input Signals during Gas Tracer Tests and their Effect on the Estimation of Reaeration, Respiration and Photosynthesis in Streams |
| VerfasserIn |
Julia Knapp, Karsten Osenbrück, Olaf Cirpka |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250113097
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| Publikation (Nr.) |
 EGU/EGU2015-13294.pdf |
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| Zusammenfassung |
| The variation of dissolved oxygen (DO) in streams, are caused by a number of processes, of
which respiration and primary production are considered to be the most important ones
(Odum, 1956; Staehr et al., 2012).
Measuring respiration and photosynthesis rates in streams based on recorded time series
of DO requires good knowledge on the reaeration fluxes at the given locations. For this,
gas tracer tests can be conducted, and reaeration coefficients determined from the
observed decrease in gas concentration along the stretch (Genereux and Hemond,
1990):
( )
–-1– -cup-
k2 = t2 - t1 ln Rcdown
(1)
with the gas concentrations measured at an upstream location, cup[ML-3], and a
downstream location, cdown. t1[T] andt2 [T] denote the measurement times at the two
locations and R [-] represents the recovery rate which can also be obtained from conservative
tracer data.
The typical procedure for analysis, however, contains a number of assumptions, as it
neglects dispersion and does not take into account possible fluctuations of the input signal.
We derive the influence of these aspects mathematically and illustrate them on the basis of
field data obtained from a propane gas tracer test. For this, we compare the reaeration
coefficients obtained from approaches with dispersion and/or a time-dependent input signals
to the standard approach. Travel times and travel time distributions between the different
measurement stations are obtained from a simultaneously performed conservative tracer test
with fluorescein.
In order to show the carry-over effect to metabolic rates, we furthermore estimate
respiration and photosynthesis rates from the calculated reaeration coefficients and measured
oxygen data.
This way, we are able to show that neglecting dispersion significantly underestimates
reaeration, and the impact of the time-dependent input concentration cannot be disregarded
either. When estimated reaeration rates are used to calculate respiration and photosynthesis
from measured oxygen data, these effects carry over, leading to higher respiration rates for
higher reaeration.
References:
Genereux, D. P., & Hemond, H. F. (1990). Naturally-Occurring Rn-222 as a Tracer for
Streamflow Generation - Steady-State Methodology and Field Example. Water Resources
Research, 26(12), 3065-3075. doi: Doi 10.1029/Wr026i012p03065
Odum, H. T. (1956). Primary production in flowing waters. Limnol. Oceanogr, 1(2),
102-117.
Staehr, P. A., Testa, J. M., Kemp, W. M., Cole, J. J., Sand-Jensen, K., & Smith, S. V.
(2012). The metabolism of aquatic ecosystems: history, applications, and future
challenges. Aquatic Sciences, 74(1), 15-29. doi: DOI 10.1007/s00027-011-0199-2 |
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