Journal article
Spatially resolved groundwater and river nutrient inputs to Baltic Sea coastal waters via radium isotopes
Marine chemistry, Vol.First online, pp.1-38
21/07/2026
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Abstract
Subterranean estuaries modify nutrient transport to coastal waters through submarine groundwater discharge (SGD). In marginal seas with restricted circulation, both surface water and groundwater nutrient inputs may trigger and sustain eutrophication. Here, we use 224Ra to quantify total SGD and related nutrient inputs from beaches across 5 Baltic countries. Groundwater sampled from 17 transects was brackish, hypoxic, and nutrient rich relative to river waters. Nutrient and radium concentrations were highest at the shoreline and rapidly decreased with distance offshore, indicating a terrestrial nutrient source at the land-ocean interface. Groundwater DIN and DIP concentrations were on average ~4 and ~21 times higher, respectively compared to nearby rivers. Overall, mean nutrient ratios across all river and groundwater samples deviated from the Redfield ratio, with elevated DIN: DIP (>16:1) and DSi:DIP (>15:1) but reduced DIN:DSi (<16:15). An SGD source was not needed to close the 224Ra mass balance in ~50% of the transects. Total SGD inputs could be estimated using 224Ra mass balances in ~50% of sampled transects resulting in mean total SGD of 6 ± 10 m3/day per meter of shoreline across 8 beach-transects. Despite large natural variability and uncertainties, extrapolating beach-scale total SGD-derived fluxes to the 8000 km Baltic shoreline led to total SGD nutrient fluxes comparable to river inputs. Total SGD derived from 224Ra budgets, but not fresh SGD derived from hydrological models, seems to be a relevant but still uncertain component of Baltic coastal nutrient budgets.
Details
- Title
- Spatially resolved groundwater and river nutrient inputs to Baltic Sea coastal waters via radium isotopes
- Creators
- Aprajita S. Tomer - University of GothenburgTristan McKenzie - University of GothenburgClaudia Majtényi-Hill - University of GothenburgCeylena Holloway - Southern Cross UniversityJúlia Rodriguez-Puig - Universitat Autònoma de BarcelonaGloria Reithmaier - University of GothenburgLinnea Henriksson - University of GothenburgBeata Szymczycha - Instytut Oceanologii Polskiej Akademii NaukIsaac R. Santos - University of Gothenburg
- Publication Details
- Marine chemistry, Vol.First online, pp.1-38
- Publisher
- Elsevier B.V.
- Grant note
- Funding was provided by the Knut and Alice Wallenberg Foundation (2022-0096), a Swedish Research Council grant (2020-00457) and a Formas Early Career Researcher grant (2023-01324).
- Identifiers
- 991013389894102368
- Copyright
- © 2026.
- Academic Unit
- National Marine Science Centre; National Centre for Naturopathic Medicine
- Language
- English
- Resource Type
- Journal article