Details

Autor(en) / Beteiligte

• Atkins, Marnie L.
• Santos, Isaac R.
• Ruiz-Halpern, Sergio
• Maher, Damien T.

Titel

Carbon dioxide dynamics driven by groundwater discharge in a coastal floodplain creek

Ist Teil von

• Journal of hydrology (Amsterdam), 2013-06, Vol.493, p.30-42

Ort / Verlag

Kidlington: Elsevier B.V

Erscheinungsjahr

2013

Quelle

Elsevier ScienceDirect Journals

Beschreibungen/Notizen

• •We performed high resolution measurements of radon and carbon dioxide in a tidal creek.•A radon mass balance revealed that the creek was groundwater dominated.•High CO2 evasion to the atmosphere could be explained by groundwater discharge.•Significant correlations between pCO2 and 222Rn were observed at an upstream station.•Groundwater discharge should be accounted for in CO2 budgets in coastal waters and estuaries. Dissolved carbon dioxide (CO2) may be highly enriched in groundwater. However, the contribution of groundwater discharge as a source of CO2 to rivers, estuaries and coastal waters is poorly understood. We performed high resolution measurements of radon (222Rn, a natural groundwater tracer) and the partial pressure of CO2 (pCO2) in a highly modified tidal creek and estuary (North Creek, Richmond River, New South Wales, Australia) to assess whether CO2 in surface waters was driven by groundwater discharge. A spatial survey revealed increasing 222Rn activities (up to 17.3dpmL−1) and pCO2 (up to 11,151μatm) in the upstream direction. The enrichment occurred in a drained coastal acid sulphate soil wetland upstream of a mangrove forest. Time series experiments (24-h) were performed at two stations upstream and downstream of the pCO2 enrichment area. Upstream measurements demonstrated a significant correlation between pCO2 and 222Rn while downstream values resulted in a significant inverse relationship between pCO2 and dissolved oxygen apparently as a result of respiration in nearby mangroves. Measurements taken 2days after a 245mm precipitation event revealed the highest recorded 222Rn activities (up to 86.1dpmL−1) and high pCO2 (up to 11,217μatm), showing a strong groundwater influence after flooding. These observations imply that groundwater discharge drove CO2 dynamics at the upstream station while multiple complex processes drove CO2 at the downstream station. A 222Rn mass balance model demonstrated that groundwater discharge accounted for about 76% of surface water in this floodplain creek. The CO2 evasion rates (799±225mmolm−2d−1) were driven primarily by currents rather than wind. Groundwater-derived CO2 fluxes into the creek averaged 1622mmolm−2d−1, a value twice as high as atmospheric CO2 evasion and consistent with carbon uptake within the creek and downstream exports. These results demonstrate that groundwater seepage was a major factor driving CO2 evasion to the atmosphere from the creek. Groundwater discharge should be accounted for in CO2 budgets in coastal systems.