Rethinking tracer-based (Ra, Rn, salinity) approaches to estimate point-source submarine groundwater discharge (SGD) into coastal systems

JOURNAL OF HYDROLOGY

卷:598

Article

Savatier, Maxime¹  Rocha, Carlos¹ 

[1] Trinity Coll Dublin, Sch Nat Sci, Biogeochem Res Grp, Dublin 2, Ireland

关键词: Submarine groundwater discharge;    Karst;    Radon;    Radium;    Modelling;    Salinity;    Ireland;   

DOI  :  10.1016/j.jhydrol.2021.126247

来源: Elsevier

【 摘 要 】

Submarine groundwater discharge (SGD) has been shown to potentially be a more important source of solutes to the global ocean than river flow. As a result, the accuracy of predictions of the magnitude and seasonal variability of SGD to the sea is critical for the management of coastal marine ecosystems. For a model site (Kinvarra Bay, Ireland) dominated by point source SGD inputs, we show that the difference between estimates provided by different marine tracer-based methods can be large, depending on the way water residence time within the system and water exchange across its boundaries are described. For example, results from tidal-prism and freshwater fraction models, the most widely used approaches to quantify freshwater fluxes into marine areas of restricted exchange, vary by one order of magnitude depending on the way the water exchange across the outer system boundaries is considered and whether Lagrangian or Eulerian data is used. We show that SGD estimates based on single point time series (Eulerian) outside of a retention area can lead to consistently lower estimates than when using transect data (Langrangian). Moreover, the outcome of radon (Rn-222) based SGD estimates is dependent on the way the effect of water age variability on radon decay and degassing is accounted for. We provide a solution to this conceptual problem by developing a correction to Rn-222 budgetary approaches to estimate SGD, based on the spatial variation of water ages estimated from radium isotopes (Ra-223, Ra-224) in solution. We use new data to compare the different sets of approaches while examining the validity of their underlying assumptions to verify internal consistency and use the substantial range of published data on Kinvarra bay to assess the quality of results produced with the new method.

【 授权许可】

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