Nationalparks Austria NPA
Eintrag Nr. 34260
Effects of gravel mining on the surface-active arthropod fauna of ephemeral gravel-bed stream valleys in the National Park Gesäuse (Styria, Austria)
Fachbereich Naturschutz und Naturraum
Zulka, Klaus Peter
SN HT 015.2
In the National Park Gesäuse (Austria, Styria), several tributaries of the Enns river are ephemeral streams that have accumulated large amounts of gravel in the broadened stretches of their valleys. In two of these valleys, gravel mining has been performed until recently. With the establishment of the National Park, these activities have been terminated and the gravel fields have been restored. It remains unclear, however, whether gravel mining has affected the surface arthropod assemblages and whether the restoration measures have re-established a natural arthropod community in those valleys. A randomised, replicated, controlled study was performed between 4 May 2012 and 30 September 2012. In a BACI-type design, ten samplings areas were compared, with sites from impacted valleys and control valleys above, within and below the gravel extraction areas. Each sampling site was visited seven times; during each visit, arthropods were collected by hand catch for the duration of one hour. Additionally, environmental variables were recorded. The sampling visits were randomly allotted to the sampling areas; within the sampling areas, transect positions perpendicular to the stream channel were also located randomly. Detrended Correspondence Analysis and Nonmetric Multidimensional Scaling showed a clear differentiation between the ephemeral gravel valleys and typical riverbanks of Johnsbach and Enns in the region. The gravel valleys showed an arthropod fauna impoverished in species numbers and dominated by a single species, the wolf spider Pardosa saturatior. Gravel valleys impacted by gravel mining showed a more diverse fauna with a higher proportion of trivial species and with assemblages that were more closely related to assemblages of banks and shores of perennial rivers. While the assemblages of the upstream areas were rather similar between impacted and control valleys, the lower valley stretches differed increasingly in their species composition towards the mouth of these valleys. Comparison of a quality index calculated for the sampling areas showed lower values for the impacted areas, but the differences were not significant (ANOVA). It may be concluded that gravel mining has affected the assemblages of surface-active arthropods, but the changes are relatively small. Most of the typical species are still present in the valleys affected by gravel mining, which offers good prospects for the further restoration of these valleys. In summary, alpine gravel valleys with ephemeral streams appear to be a conspicuous yet poorly researched mountain habitat type with a distinct fauna of highly specialised species that are able to tolerate the harsh conditions between catastrophic inundation and dryness.