Journal article
Porewater exchange as a driver of carbon dynamics across a terrestrial-marine transect: Insights from coupled 222Rn and pCO2 observations in the German Wadden Sea
Marine chemistry, Vol.171, pp.10-20
01/04/2015
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Abstract
We investigate whether radon (222Rn) can be used as a tracer of porewater exchange in the Wadden Sea, and whether porewater exchange may drive carbon dioxide, dissolved organic carbon (DOC), total dissolved nitrogen (TDN) and alkalinity dynamics in surface waters. High temporal resolution, automated radon and pCO2 observations were made for about 24h in five stations along a coastal transect covering upstream brackish water creeks, an enclosed shallow harbour receiving freshwater inputs from the catchment (Neuharlingersiel), and the German Wadden Sea (Spiekeroog Basin). The results revealed clear tidal trends indicative of porewater exchange in the two Wadden Sea stations. All the investigated waterways were a net source of CO2 to the atmosphere with average pCO2 ranging from about 3600μatm in upstream creeks to about 600μatm in the Wadden Sea. The input of upstream creek water could be detected only in the small enclosed harbour, but not in the open Wadden Sea. A radon mass balance required porewater exchange rates of about 12cmday−1 (equivalent to 1.1% of the tidal prism volume) in the Wadden Sea. Average alkalinity, TDN, DOC, and pCO2 values in porewater were 4.5, 18.8, 1.3, and 9.7 fold higher than in Wadden Sea surface waters. Those enrichments translated into estimated porewater-derived fluxes of 1216–1811, 34–139, 34–71, and 6–57mmolm−2day−1, respectively, depending on assumptions about porewater endmember concentrations. The porewater derived free CO2 fluxes were comparable to the CO2 outgassing rates estimated for the Wadden Sea (7 to 20mmolm−2day−1). These estimates as well as significant correlations between radon and pCO2 suggest that porewater exchange was a major driver of CO2 outgassing from the Wadden Sea to the atmosphere. Radon can be a useful porewater (or groundwater) tracer in the Wadden Sea in spite of strong winds and well-mixed surface water conditions.
•Clear radon and pCO2 tidal trends were indicative of porewater exchange.•Creeks and the Wadden Sea were a net source of CO2 to the atmosphere.•Radon-based porewater exchange rates were equivalent to 1% of the tidal prism.•Porewater derived free CO2 fluxes were comparable to CO2 outgassing rates.•Radon was a useful tracer in spite of strong winds and well mixed surface waters.
Details
- Title
- Porewater exchange as a driver of carbon dynamics across a terrestrial-marine transect: Insights from coupled 222Rn and pCO2 observations in the German Wadden Sea
- Creators
- Isaac R. Santos - Southern Cross University, Faculty of Science and EngineeringMelanie Beck - Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl-von-Ossietzky University Oldenburg, D-26111 Oldenburg, GermanyHans-Jürgen Brumsack - Carl von Ossietzky Universität OldenburgDamien T. Maher - Southern Cross University, Faculty of Science and EngineeringThorsten Dittmar - Carl von Ossietzky Universität OldenburgHannelore Waska - University of OldenburgBernhard Schnetger - Carl von Ossietzky Universität Oldenburg
- Publication Details
- Marine chemistry, Vol.171, pp.10-20
- Publisher
- Elsevier B.V
- Identifiers
- 991012820731302368
- Academic Unit
- Centre for Coastal Biogeochemistry; Faculty of Science and Engineering; National Marine Science Centre; School of Environment, Science and Engineering; Science
- Language
- English
- Resource Type
- Journal article