Two Contrasting Soil and Vegetation Catenas in the Saline Wetlands of Monegros, Spain.

Surveys of vascular flora conducted between 2004 and 2010, historical aerial photographs, and topographic information were used to produce a map of the 149 saline wetlands that occur in karstic depressions in the semiarid region of Monegros, NE Spain. Playa-lakes and other saline depressions are expressions of solution dolines which largely reflect groundwater dynamics and whose formation is favored by the limestone and gypsum substrate in the region. The distribution of vegetation in the Monegros saline wetlands reflects gradations in flooding frequency and soil salinity, and provides insights into hydrologic connections.

We studied two catenas of soils in Rollico, RLL, and Amarga Alta, AMA, two wetlands representing the westernmost and easternmost sectors of the area. Gypsum is the dominant substrate in the western area (mean elevation = 333 m a.s.l.) and limestone in the eastern area (mean elevation = 350 m a.s.l.). Both wetlands are playa-lakes, with a mean temporal water occurrence of 45% and persistent water-saturation of soils, even in summer. Salt crusts and algal mats are common.

Halophytes covered about 40% of the surface of both wetlands. At RLL, hypersaline habitats covered 91% of the wetland, including four habitats of communitarian interest (HCI), of which two (1510 and 1520) qualified as priority habitats (Directive 92/43/CEE). At AMA, hypersaline habitats covered 42% of the wetland, including six HCI’s of which one (1510) qualified as a priority habitat.

The mean soil gypsum content was 46% at RLL and 55% at AMA, and the highest and lowest contents were recorded for soils with Suaedetum (82%) and Salsolo-Artemisietum (7%). Soil salinity at RLL was highest in the bare soil (112 dS m^-1) and in the Suaedetum soils at AMA (84.1 dS m^-1). The mean Mg/Ca ratio in the halophyte habitats at AMA (13.4) was about three times higher than at RLL (4.9).