Factors influencing the organic carbon pools in tidal marsh soils of the Elbe estuary (Germany)

  • Allochthonous and autochthonous carbon
  • Elbe estuary
  • Elevation
  • Organic carbon
  • Salinity
  • Tidal marsh soils
  • Purpose Soils of tidal marshes play an important role in re- gional carbon (C) cycles as they are able to store considerable amounts of organic carbon (OC). However, theCdynamics of marsh soils of the Elbe estuary have not been investigated so far. Therefore, the aimof this study was to identify the sources and distribution of soil organic carbon (SOC) and the factors influencing the SOC pools of tidal marshes of the study region. Materials and methods In this study, SOC pools were deter- mined in different salinity zones and elevation classes of the estuarine marshes. The amount of initial allochthonous OC was derived from the OC content in fresh sediments. The difference to the recentOC content in the soils was interpreted as autochthonous accumulation or mineralization by microorganisms. Results and discussion Young, low marshes of the study sites seem to be predominantly influenced by allochthonous OC deposition whereas the older, high marshes show autochtho- nous OC accumulation in the topsoils (0–30 cm) and miner- alization in the subsoils (30–70 cm). SOC pools of the whole profile depth (0–100 cm) did not significantly differ between elevation classes, but decreased significantly with increasing salinity from 28.3 kg m−2 in the most upstream site of the oligohaline zone to 9.7 kg m−2 in the most downstream site of the polyhaline zone. Even though the areal extent of the investigated salinity zones was similar, the SOC mass within 100 cm soil depth decreased from 0.62 Tg (1 Tg = 1012 g) in the oligohaline zone to 0.18 Tg in the polyhaline zone. Conclusions Elevation was found to be one factor influencing the SOCpools of tidal marshes. However, salinity seems to be an even stronger influencing factor reducing the above-ground biomass and, accordingly, the autochthonousOCinput as well as the allochthonous input by enhanced mineralization of OC along the course of the estuary. An upstream shift of the sa- linity zones by sea level rise could, therefore, lead to a reduc- tion of the SOC storage of the estuarine marshes.
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