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
Hauptverfasser: Pu, Junbing, Li, Jianhong, Zhang, Tao, Xiong, Xiaofeng, Yuan, Daoxian
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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.
ISSN:0944-1344
1614-7499
DOI:10.1007/s11356-019-05820-9