High spatial and seasonal heterogeneity of pCO2 and CO2 emissions in a karst groundwater-stream continuum, southern China
Accurate quantification of the emission of CO 2 from streams and rivers is one of the primary challenges in determining the global carbon budget because our knowledge of the spatial and seasonal heterogeneity on these CO 2 emissions is limited. In karst areas, the groundwater-stream continuum is lik...
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Veröffentlicht in: | Environmental science and pollution research international 2019-09, Vol.26 (25), p.25733-25748 |
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Sprache: | eng |
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Zusammenfassung: | Accurate quantification of the emission of CO
2
from streams and rivers is one of the primary challenges in determining the global carbon budget because our knowledge of the spatial and seasonal heterogeneity on these CO
2
emissions is limited. In karst areas, the groundwater-stream continuum is likely ubiquitous because the carbon-rich groundwater discharges into some of the streams through springs or subterranean streams, which results in more complex spatial and seasonal variations in the CO
2
emissions. To address this issue, the spatial and seasonal characteristics of partial pressure of CO
2
(
p
CO
2
), the δ
13
C
DIC
, and the CO
2
emission flux of the Guancun surface stream (GSS) karst groundwater-stream continuum in southern China were investigated from the stream head (groundwater outlet) to the downstream mouth during the 2014–2017 period. Our results reveal that the
p
CO
2
and CO
2
emissions exhibit high spatial and seasonal heterogeneities over ~ 1300 m in the GSS. Spatially, the
p
CO
2
and CO
2
emissions decrease sharply from the stream head (mean 8818.4 μatm for
p
CO
2
and mean 423.4 mg m
−2
h
−1
for CO
2
emission) to the site farthest downstream (mean 2752.7 μatm for
p
CO
2
and 257.0 mg m
−2
h
−1
for CO
2
emission). Except for the dates when extreme rainfall occurred, the
p
CO
2
and CO
2
emission values were higher in the rainy season than in the dry season. This suggests that in a groundwater-stream continuum, CO
2
emission occurs very soon after the water is transferred from the karst groundwater to the surface water. We estimate that the total amount of CO
2
released to the atmosphere from the GSS is 21.75 t CO
2
/year, which is only 1.71–5.62% of the dissolved inorganic carbon loss flux in the GSS during the study period. It is important to note that the measured CO
2
emission and
p
CO
2
levels decrease farther downstream, so carbon loss is underestimated when it is calculated using downstream sampling points. Therefore, accurate assessments of the CO
2
emission flux need to take into consideration the high spatio-temporal heterogeneity in order to reduce the bias of the entire CO
2
emission flux. |
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ISSN: | 0944-1344 1614-7499 |
DOI: | 10.1007/s11356-019-05820-9 |