Ecological validity of river-floodplain system assessment by planktonic crustacean survey (Branchiata: Branchiopoda)

Changes in species composition of water insects during 25-year monitoring of the Danube floodplains affected by the Gabčíkovo waterworks

This study was based on the complex environmental monitoring of the Danube River in Slovakia. Out of 23 monitored sites, three were chosen for the aim of this study. The three sites were sampled regularly three times per year during a 25-year period, which started in 1990, 2 years before the Gabčíkovo waterworks became operational. Each site represented one of the main potamal types, which we recognised according to the habitat characteristics as eupotamal, parapotamal and plesiopotamal. In order to assess changes which occurred during the 25 years, we studied taxocoenoses of Ephemeroptera, Plecoptera and Trichoptera, which sensitively reflect anthropogenic impacts. The changes caused by the Gabčíkovo waterworks manifested in a decrease of the species diversity in eupotamal because of the disappearance of rheophilous taxa. In the parapotamal and plesiopotamal sites, the initial decrease was followed by a partial recovery of biodiversity due to the artificial floodings. After they were stopped, the decrease occurred again and until 2015, the insect taxa became rare. Conversely, in the eupotamal site, there was an increasing trend in biodiversity since 2011 until 2015. Overall increase in the floodplain index values indicated a loss of connectivity between the floodplain habitats and their fauna with the main channel during the last 25 years. In this paper, we also extended the floodplain index with data on habitat values and indication weight for several stonefly species.

Sedimentary-vegetation response to the channel by-pass: A case study of the Danube river

The Gabčíkovo-Nagymaros waterworks construction on Danube river in Slovakia (1977−1992) was followed with major ecological consequences. The water level and flow velocity was decreased in the original by-passed channel in order to keep high water level for shipping in the bypass canal. The decrease in discharge and lowering flow velocity resulted in the channel narrowing and increase in the vertical accretion magnitude in new floodplain pockets along both sides of by-passed channel. What is more, anthropic intervention in form of groynes structures built for channel adjustment before 1992 dramatically accelerated this process. Vegetation colonisation took place on the new floodplain. In this paper, we analysed land cover changes - vegetation succession using aerial photographs taken in 1986, 1996, 2004 and 2013 as well as field surveys. After the flood in 2013, the area of the new floodplain reached 57% (310 ha) of the original channel area.