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<p>Coastal peatlands are important carbon, nutrient, and trace metal stores that have been extensively drained and degraded. Rewetting may restore ecological and hydrological functions but could also enhance the export of solutes through the submarine groundwater discharge (SGD) pathway to adjacent marine environments. We directly measured SGD and its associated solute concentrations in front of a coastal peatland using seepage meters across two shore-perpendicular transects in summer and fall 2021. In addition to SGD, groundwater and porewater samples were analyzed for dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), total dissolved nitrogen (TDN), nutrients, trace metals, and stable water and carbon isotopes to characterize the discharging groundwater. Results indicated a mean SGD rate of 1.3 ± 1.7&#xa0;cm d⁻<sup>1</sup> (max. 3.9&#xa0;cm d⁻<sup>1</sup>) during the summer campaign while recharge conditions prevailed in fall, due to intense landwards winds. Notably, salinity of SGD exceeded that of ambient seawater, and isotope analyses revealed that most SGD originated from the recirculation of brackish seawater. Solute concentrations were significantly higher in SGD than in seawater, but lower than values encountered in porewater and groundwater. The flushed permeable coastal sediments thus serve as a source for carbon, nutrients and trace metals. Summer solute fluxes were substantial (mmol m<sup>−2</sup> d<sup>−1</sup>) – DOC: 10; DIC: 44; TDN: 2.8; NH₄⁺: 1.5, PO₄<sup>3</sup>⁻: 0.13; Fe: 0.23; and Mn: 0.17. However, estimates of solute fluxes might be conservative as land-derived groundwater influence was minor during the sampling campaigns. Our findings suggest that SGD in front of coastal peatlands is significant and could influence local and regional biogeochemical budgets.</p>

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Characterization of Submarine Groundwater Discharge in Front of a Rewetted Coastal Peatland

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年11月1日

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  • Erwin Don Racasa,
  • Anna-Kathrina Jenner,
  • Rhodelyn Saban,
  • Jakob Kienzler,
  • Cheryl Batistel,
  • Simeon Choo,
  • Miaorun Wang,
  • Ulf Gräwe,
  • Michael Ernst Böttcher,
  • Manon Janssen

摘要

Coastal peatlands are important carbon, nutrient, and trace metal stores that have been extensively drained and degraded. Rewetting may restore ecological and hydrological functions but could also enhance the export of solutes through the submarine groundwater discharge (SGD) pathway to adjacent marine environments. We directly measured SGD and its associated solute concentrations in front of a coastal peatland using seepage meters across two shore-perpendicular transects in summer and fall 2021. In addition to SGD, groundwater and porewater samples were analyzed for dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), total dissolved nitrogen (TDN), nutrients, trace metals, and stable water and carbon isotopes to characterize the discharging groundwater. Results indicated a mean SGD rate of 1.3 ± 1.7 cm d⁻1 (max. 3.9 cm d⁻1) during the summer campaign while recharge conditions prevailed in fall, due to intense landwards winds. Notably, salinity of SGD exceeded that of ambient seawater, and isotope analyses revealed that most SGD originated from the recirculation of brackish seawater. Solute concentrations were significantly higher in SGD than in seawater, but lower than values encountered in porewater and groundwater. The flushed permeable coastal sediments thus serve as a source for carbon, nutrients and trace metals. Summer solute fluxes were substantial (mmol m−2 d−1) – DOC: 10; DIC: 44; TDN: 2.8; NH₄⁺: 1.5, PO₄3⁻: 0.13; Fe: 0.23; and Mn: 0.17. However, estimates of solute fluxes might be conservative as land-derived groundwater influence was minor during the sampling campaigns. Our findings suggest that SGD in front of coastal peatlands is significant and could influence local and regional biogeochemical budgets.