Pedological features of a sustainable halophyte wetland: El Hito saline pond (Central Spain)

Abstract

In semi-arid Mediterranean regions, particularly in some wetland soils, salinity is thought to be an indicator of low-quality soils. In this study, a characterization is presented of the soils surrounding El Hito saline pond (Castilla La Mancha, Central Spain), an ecological halophyte niche within a natural semi-arid steppe land. The main aim is to classify the salt-affected soils and their morphology, genesis, and physico-chemical properties. Four soil profiles were opened with a backhoe machine for sampling and subsequent description on the basis of their pedogenetic morphology. Systematic surface sampling was also performed. Standard methods were followed to measure the soil properties of 27 samples. Overall electrical conductivity (EC) and pH levels of the wetland were mapped (using ArcGIS 3.1.3). Soil salinity at elevated levels was detected, inhibiting plant uptake of water and nutrients. Distinct sub-areas of extreme elevated surface salinity providing specialized plant habitats and poor soil structure were observed, as well as a mainly whitened-yellowish-greenish soil colour due to salt accumulation and poor drainage. The soils also showed alkaline pH values. In most samples, the pH was over 8.5, and EC was higher than 4 (dS m⁻¹), and in several samples higher than 20 (dS m⁻¹). A low sodium (Na) content was detected in the saturation extract where magnesium (Mg⁺) was the dominant soluble cation, followed by both calcium (Ca⁺) and sodium (Na⁺), and then potassium (K⁺), present in lower proportions. Sulphate (SO₄²⁻) and then chloride (Cl⁻) anions were dominant, although carbon trioxide, (CO₃⁻) and carbonate (CO₃²⁻) anions were also present. The percentages of organic carbon (C) were very low, while total nitrogen (TN) and available phosphorus (P) were higher in the upper horizons, suggesting a degree of eutrophication. The present work will increase the existing knowledge about the role of El Hito saline pond, that play a vital ecological role in the broader biosphere, providing new suggestions to readers on how this knowledge can be used to improve these types of ecosystems. In particular, the agricultural pesticides and fertilizers continuously damage the soil fertility as evidenced by the high content of soluble phosphorus found in some points of the Hito saline pond.