Sulfur Signature of a Mediterranean Wetland: The Case of Soils of the Inundated Floodplain Area at the Tablas de Daimiel National Park

In the Mediterranean region, numerous wetlands co-exist with competitive agricultural systems. Although wetlands’ hydrology (in water volume, source, and residence time terms) plays a major factor in their ecosystem structure, many of these wetlands have been subjected to different degradation processes. One such case is the Tablas de Daimiel National Park (TDNP), which witnesses one of its most environmentally sensitive times. In this context, scarce information is available on the sulfur (S) contents in this wetland. To diagnose this wetland’s degradation status, 43 soil samples were selected and analyzed to investigate S contents in the surface soils (0 to 30 cm) of the inundated floodplain area of the TDNP. They represent different degrees of exposure to pollutants and exposure to flooding. Sulfur determination was carried out by X-ray fluorescence. The S contents in the area range between 1.85 and 37.15 g kg−1, with a mean value of 13.71 g kg−1, which implies marked variability throughout this wetland. The highest values were observed near the wetland entrance via the Gigüela River, while the lowest ones appeared at its exit, with a relatively uniform gradient from the entrance to the exit. The relatively high S concentrations observed at sites other than the wetland entrance can be probably related to the continuous non-point source contamination with P, N, and S fertilizer applications, via runoff agricultural production systems. The results of this study are essential for understanding and predicting total S variability within the TDNP (Spain), which can interfere with soil management practices.