Conference Proceedings - IAD

Connectivity
39th IAD Conference, August 2012, Szentendre, Hungary
Connectivity is primarily seen as longitudinal connectivity, which is e.g.
interrupted by hydro-electric power installations (Vannote et al. 1980, Ward,
Stanford 1995). Of course, connectivity is overlapping with the phenomenon of
water flow impact (Janauer et al. 2010), but several studies have pointed out an
intrinsic component of lateral river channel connections, which are more often
easier to assess than to cope with the high variability of water flow in a selected
environment. Hydrobotanists pointed out as early as 1991 that lateral
connectivity is a prime driver for macrophyte distribution in floodplain water
bodies (Bornette, Amoros 1991). The ‘Connectivity Concept’ (Petts, Amoros
1996) then formed a fundamental theory, which covers main river channel and
floodplain water characteristics, relating habitat types with the “strength, duration
and frequency of their connectivity [with the] river channel” (Petts, Amoros, p.6).
Those authors also defined that “…biota are seen to be distributed according to
predictable environmental gradients…”. Later Herny et al. (1996) and Bornette et
al. (2009) reported on flood disturbance and recolonization thereafter, and about
succession processes in former river channels. Chovanec et al. (2005) based
their “Floodplain Index” of oxbow-related fauna on the connectivity type of
floodplain water bodies. With relation to the aquatic macrophyte vegetation of the
eastern reach of the Austrian Danube Janauer et al. (2012) reported the highest
species number for floodplain waters directly connected with the main river
channel during only 5 days per year, at average (Fig. 1).
Figure 1. Total species number (TSpN) and number of Indicator Species in the eastern
reach of the Austrian Danube. Floodplain Habitat Types, average connectivity with the
main channel: HT-1: Cd > 330 days; HT-2: Cd < 330 days; HT-3: Cd < 120days; HT-4:
Cd < 5 days; HT-5: temporary waters. Indicative species of HT-4 (statistically significant):
Nuphar lutea (L.) Sm., Myriophyllum verticillatum L., Sagittaria sagittifolia L., Hippuris vulgaris L.,
Najas marina L., Carex elata All., Potamogeton lucens L., Nymphaea alba L., Utricularia vulgaris
L., Ranunculus x glueckii A.Félix nom. nud., Rumex sp., Sparganium erectum L., Schoenoplectus
lacustris (L.) Palla, Potamogeton pusillus L., Lythrum salicaria L., Mentha aquatica L., Riccia
fluitans L. emend Lorb., Potamogeton nodosus Poir., Sparganium emersum Rehmann, Veronica
anagallis-aquatica L. (order according to indicator strength).
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