The preferential movement of water and transport of substances play an important role in soil, but they are not yet fully understood, especially in degraded peat soil. In this study, we aimed to deduce changes in flow and transport patterns with titanium dioxide (TiO2) as a dye tracer during the course of soil degradation resulting from peat drainage. The dye tracer experiments were carried out on columns of eight types of differently degraded peat soil from three sites taken in both vertical and horizontal directions. The titanium dioxide suspension (average particle size of 0.3 µm; 10 g l−1) was applied in a pulse of 40 mm to each soil core. The cores were subsequently cut into six slices, photographed and the images were analysed for the extent of dye cover and number of pores. In addition, the saturated hydraulic conductivity (Ks) was determined. Preferential flow occurred in all of the peat types investigated. From the stained soil structural elements, we concluded that undecomposed plant remains are the major preferential flow pathways in less degraded peat. For more strongly degraded peat, bio‐pores, such as root and earthworm channels, operated as the major transport network. Results show that Ks and the effective pore network in less degraded peat soil are anisotropic. With increasing peat degradation, Ks and the cross‐section of effective pores decreased in the predominant direction only and the anisotropy of both properties decreased. The Ks was closely related to the number of macropores and pore continuity. Therefore, we conclude that changes in flow and transport pathways and Ks with increasing peat degradation result from the disintegration of the peat‐forming plant material and the decrease in number and continuity of macropores. Highlights We aimed to deduce changes in flow and transport patterns during peat degradation. TiO2 (dye tracer) was used to visualize the flow and transport patterns in degraded peat soil. The preferential flow paths, Ks and pore structures changed with peat degradation. Changes in flow and transport paths and Ks relate to peat‐forming plant materials and pore structure.
Coastal zones connect terrestrial and marine ecosystems forming a unique environment that is under increasing anthropogenic pressure. Rising sea levels, sinking coasts, and changing precipitation patterns modify hydrodynamic gradients and may enhance sea-land exchange processes in both tidal and non-tidal systems. Furthermore, the removal of flood protection structures as restoration measure contributes locally to the changing coastlines. A detailed understanding of the ecosystem functioning of coastal zones and the interactions between connected terrestrial and marine ecosystems is still lacking. Here, we propose an interdisciplinary approach to the investigation of interactions between land and sea at shallow coasts, and discuss the advantages and the first results provided by this approach as applied by the research training group Baltic TRANSCOAST. A low-lying fen peat site including the offshore shallow sea area on the southern Baltic Sea coast has been chosen as a model system to quantify hydrophysical, biogeochemical, sedimentological, and biological processes across the land-sea interface. Recently introduced rewetting measures might have enhanced submarine groundwater discharge (SGD) as indicated by distinct patterns of salinity gradients in the near shore sediments, making the coastal waters in front of the study site a mixing zone of fresh-and brackish water. High nutrient loadings,
Coastal low-lying areas along the southern Baltic Sea provide good conditions for coastal peatland formation. At the beginning of the Holocene, the Littorina Sea transgression caused coastal flooding, submergence and erosion of ancient coastlines and former terrestrial material. The present Heiligensee and Hütelmoor peat deposits (located near Rostock in Northern Germany) were found to continue more than 90 m in front of the coastline based on on-and offshore sediment cores and geo-acoustic surveys. The seaward areal extent of the coastal peatland is estimated to be around 0.16-0.2 km 2 . The offshore boundary of the former peatland roughly coincides with the offshore limit of a dynamic coast-parallel longshore bar, with peat deposits eroded seawards. While additional organic-rich layers were found further offshore below a small sand ridge system, no connection to the former peatlands can be established based on 14 C age and C/N ratios. The preserved submerged peat deposits with organic carbon contents of 37% in front of the coastal peatland Heiligensee and Hütelmoor was radiocarbondated to 6725 ± 87 and 7024 ± 73 cal yr BP, respectively, indicating an earlier onset of the peatland formation as presently published. The formation time of the peat layers reveals information about the local sea level rise. The local sea level curve derived from our 14 C-dated organic-rich layers is in general agreement to nearby sea level reconstructions (North Rügen and Fischland, Northern Germany), with differences explained by slightly varying local isostatic movements.
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