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| Titel |
Regulation of CO2 emissions from temperate streams and reservoirs |
| VerfasserIn |
S. Halbedel, M. Koschorreck |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 11 ; Nr. 10, no. 11 (2013-11-22), S.7539-7551 |
| Datensatznummer |
250085433
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| Publikation (Nr.) |
 copernicus.org/bg-10-7539-2013.pdf |
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| Zusammenfassung |
It has become more and more evident that CO2 emission
(FCO2) from freshwater systems is an important part of the
global carbon cycle. To date, only a few studies have addressed the different
mechanisms that regulate FCO2 in lotic and lentic systems. In
a comparative study we investigated how different biogeochemical and physical
factors can affect FCO2 values in streams and reservoirs. We
examined the seasonal variability in CO2 concentrations and emissions
from four streams and two pre-dams of a large drinking water reservoir
located in the same catchment, and compared them with environmental factors
that were measured concurrently. All the streams were generally
supersaturated with CO2 throughout the year, while both reservoirs
functioned to a small degree as CO2 sinks during summer stratification
and CO2 sources after circulation had set in. FCO2 from
streams ranged from 23 to 355 mmol m−2 d−1 and exceeded the
fluxes recorded for the reservoirs (−8.9 to
161.1 mmol m−2 d−1). Both the generally high piston velocity
(k) and the CO2 oversaturation contributed to the higher
FCO2 from streams in comparison to lakes. In both streams and
reservoirs FCO2 was mainly governed by the CO2
concentration (r = 0.92, p < 0.001 for dams; r = 0.90, p < 0.001 for
streams), which was in turn affected by metabolic processes and nutrients in
both systems and also by lateral inflow in the streams. Besides CO2
concentration, physical factors also influence FCO2 in lakes
and streams. During stratification, FCO2 in both pre-dams was
regulated by primary production in the epilimnion, which led to a decrease of
FCO2. During circulation, when CO2 from the hypolimnion
was mixed with the epilimnion, FCO2 increased on account of
the CO2 input from the hypolimnion. The CO2 from the hypolimnion
originates from the mineralisation of organic matter. FCO2
from streams was mainly influenced by geomorphological and hydrological
factors affecting k, which is less relevant in low-wind lakes. Under
high-wind conditions, however, k regulates FCO2 from lotic
systems as well. We developed a theoretical framework describing the role of
the different regulation mechanisms for FCO2 from streams and
lakes.
In summary, the dominant factor affecting FCO2 is the
concentration of CO2 in the surface water. Lake stratification has a
very important regulatory effect on FCO2 from lakes on account
of its influence on CO2 concentrations and metabolic processes.
Nevertheless, FCO2 values in heterotrophic streams are
generally higher. The higher k values are responsible for the comparatively
high degree of FCO2. On a Central European scale, CO2
emission from streams is probably of greater importance than the CO2
flux from standing waters. |
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