Assessment of the ecological status of Danubian floodplains at Tulln (Lower Austria) based on the Odonata Habitat Index (OHI)

The ecological status of waterbodies situated in a Danubian floodplain section at Tulln (Lower Austria) was assessed by a dragonfly survey using the "Odonata Habitat Index" (OHI) approach suggested by CHOVANEC & WARINGER (2001, Regulated Riv. Res. Mngmt 17: 493-507). The investigation was carried out at 28 standing water bodies and 2 reference sites situated directly at the Danube. Stretches of 100 m shorelength were mapped and the "Representative Spectrum of Odonata Species" (SCHMIDT, 1985, Odonatologica 14: 127-133) was recorded. Only autochthonous spp. were used for the assessment procedure. A total of 11 Zygoptera and 20 Anisoptera spp. was recorded, 29 of them autochthonous. Site-specific Odonata Habitat Indices ranged from 1.72 to 3.67. The OHI of the only reference site where Odonata were detected directly at the Danube was 1.38. The mean OHI for the whole floodplain section was 2.79. These figures indicate a relatively high level of habitat diversity. By comparing this status quo with reference conditions derived from the overall habitat situation before the regulation and from old species inventories dating back to the 19th century, the status of the Tulln floodplain section was ranked as class II ("good ecological status") in a 5-tiered classification scheme.