Springs of the Alps – Sensitive Ecosystems to Environmental Change: From Biodiversity Assessments to Long-term Studies

The main aim of the present review is to synthesise the present level of knowledge on the hydrobiology of springs in the Alps. Springs are usually small, but complex and taxa rich. They have a mosaic structure, a high degree of individuality and an azonal character, due to the peculiar physicochemical stability. Springs are ecotones linking an aquifer to the uppermost section of a surface running water system. Due to adaptations, of which stenothermy is the most frequent, representatives of many groups of plants and animals have in springs their exclusive (crenobionts) or favourite (crenophiles) habitat. This leads to a peculiar longitudinal distribution of organisms. In spite of this complexity, springs (in particular high elevation springs of the Alps) have received much less attention than other types of inland waters. They are endangered habitats, being menaced by a series of direct impacts (primarily water abstractions) and indirect impacts. The classical Steinmann–Thienemann ecomorphological types are still used with differences in the physical and chemical characteristics and in the biota. In the Alps rheocrene springs (where current velocity is one of the most relevant factors and the importance of the fringing semi-aquatic habitats is reduced) are the most frequent. However, in nature, most springs are transition types among the three traditional ones and these can now be assessed thanks to procedures considering mainly the substrate particle size. The physicochemistry of springs is characterised by limited seasonal fluctuations and determined by the characteristics of the aquifer and by indirect (especially airborne contaminants) and direct impacts. Many groups of organisms are well represented and include indicators of the trophic and acid–base status, of hydrogeology, hydrological stability and biological integrity. The groups with the highest proportions of specialised taxa are mosses, water mites, dipterans, hydrobioid snails and caddisflies. Attempts are being made to add to the traditional spring types hydrochemistry and vegetation and to the regional faunistic types, diatom-based types, to combine different approaches and to consider also functional ones, such as the distinction between POM and mosses’ springs. Given the high proportion of spring-specific taxa, we propose to use the zoobenthos, especially water mites, for an evaluation of the biological integrity of springs, whilst autotrophs, and in particular diatoms, which are the most widespread and taxa-rich group, can provide excellent indicators of eutrophication, acidification and ionic strength. This would require the calibration of the most promising diatom-based procedures to the spring environment and improvement of the knowledge on the taxonomy and distribution of key zoobenthos groups in the Alps. Other areas where further research is required are the definition of integrated spring-types, the potential for recovery of autotrophs in restored springs, functional aspects, the applicability of paleolimnological techniques to springs and the link between impacts on the drainage basin and spring environmental quality. Only once the importance of springs can be understood and effective conservation measures are undertaken, will it be possible to use these peculiar environments characterised by stability and by integration in time and space of direct and indirect impacts as ideal study sites for long-term ecological research.