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 an...

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Water-level fluctuations (WLF) in lakes and rivers, especially their extent, frequency and duration, are dominant forces controlling the functioning of these ecosystems. In particular, WLF play an important role in the lake's littoral and aquatic-terrestrial interface processes. WLF may take place on different spatial and temporal scales under natural conditions but water levels have been artificially modified in regulated lakes, and their impacts are expected to be enhanced within the actual global change scenarios with forthcoming management problems. This article presents an overview on the literature published on this important topic since 1991 by using journals indexed in the ISI Web of Knowledge. The overall objective was to examine temporal and spatial trends in publications on WLF, the specific aspect of WLF concerned and their main effects. Throughout the article we have used case studies to illustrate different effects of WLF on the variety of lake habitats and indicators that have been studied. Overall, the number of papers published on the subject since the 1990s has risen steadily, when less than ten papers were published each year; until 2006 and peaking in 2005. The greatest number of papers on WLF has been carried out in Europe and North America (c. 73%). These data also showed that the effects of WLF have not been studied equally for different groups of organisms. There is a greater interest on macrophytes, which are the most studied group of organisms (18.4% of the papers). Nearly 7% of the papers deal with algae, and zooplankton and invertebrates account for a 7% followed by fish. WLF effects on ecosystems are very complex, and the biological effects in lakes are greatest in shallow water and littoral areas, where even small changes in water levels can result in the conversion of large areas of a standing-water environment in air exposed habitats. Finally, these data might serve to highlight knowledge gaps still existing on this topic and, in particular, some of the approaches that can potentially contribute to solve several of these lacunae are explored.

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