Transdisciplinary approach to the characterisation and current status of Spanish karstic lakes on gypsum

Abstract

Karstic lakes on gypsum are a very peculiar type of ecosystem declared as a Habitat Type of Community Interest (Type 3190) by the European Habitats Directive. They are usually small lakes but often displaying a high relative depth, located in active gypsum karst areas, with a high saturation of Ca2+ and SO42− in its waters. These lakes can usually stratify from spring to early autumn when the depth is high enough, then a sulphide-rich anoxic hypolimnion can develop in deep layers. So far, neither a comprehensive scientific definition of their ecological characteristics nor an exhaustive catalogue of their occurrence in a particular territory are available. This paper delves on their biotic and abiotic features needed for their identification as an ecosystem type. A proper methodology was also designed and applied for the evaluation of their conservation status, with the definition of reference values and assessment methods following the criteria of the Habitats Directive. The Spanish karstic lakes on gypsum (THCI 3190) were here identified, statistically representative sites were selected, and spatial GIS methods and multimetric indices were applied to assess the range, area, structure and function, and future prospects of this Habitat Type, as requested for the reporting according to Article 17 of the Habitats Directive. Results showed a favourable conservation status of this habitat type in the Alpine and Atlantic regions of Spain, but unfavourable-inadequate status in the Mediterranean, due to the pressures and impacts acting on some specific sites. A critical analysis of the methodologies and the values obtained for its conservation status was carried out.