Spatial and temporal variation of chironomid assemblages in high altitude streams of the Hohe Tauern Nationalpark
Niedrist Georg, University of Innsbruck (AT)
Freshwater biodiversity is worldwide under threat, with climate change being a significant contributor. One obvious impact of climate change is the rapid shrinking of glaciers, leading to a reduction of glacial meltwater contribution to river flow in most glacierized catchments. These changes are expected to affect the biodiversity of specialized glacier-fed river communities. Within the pilot activities for the ‘River-Monitoring Program NP Hohe Tauern' (2009 - 2012) selected river reaches (nonglacial, glacial) in four glaciated catchments were investigated in order to i) characterize the abiotic conditions and biotic patterns of the individual systems, ii) elucidate important variables being responsible for species occurrence, richness, diversity and abundance, and iii) to define appropriate indicators showing environmental conditions and change. For this part of the project the chironomid assemblages were used as these organisms are ubiquitous in alpine river systems and are known to react sensitively to environmental gradients. Species of this high diverse dipteran family seem to be stenoecious, thus the occurrence of selected chironomid species could be used as a tool to observe changing environments. Chironomid assemblages showed different temporal and spatial patterns when non-glacial and glacial rivers as well as reaches above and below the tree line were compared, both in terms of structure and functional organization respectively. In general, water temperature, benthic organic material and inorganic sediment load were the main factors influencing the chironomid distribution pattern. Different habitats could be described by their special chironomid communities, demonstrating the potential to indicate different conditions of running waters. We were able to identify indicator species for pristine glacial and non-glacial rivers as a tool for future monitoring of glacial retreat and climatic changes. Our results showed that the presence of certain chironomid species can be unequivocally associated with specific river types: Whereas glacial influenced headwaters are represented by cold-stenothermal species tolerant to high inorganic sediment load (Diamesa steinboecki, Diamesa Gr. latitarsis), spring-fed rivers of the same altitude are indicated by a high abundance and occurrence of cold-stenothermal species restricted to clear water (Pseudokiefferiella parva and Diamesa Gr. cinerella/zernyi). Fundamental premises are however, a robust taxonomy and a comprehensive set of physico-chemical data to characterize specific ecological demands.