katrinteubner

geographical location of the large river

Danube delta, near Tulcea, Romania, 2005:
Meadows and woodland are surrounding the lakes in the delta. Danube floodplain, near Vienna, Austria, 2008:
A sign that beavers (Castor fiber) were recently at work here.

The second largest river in Europe, the Danube River, connects a large number of countries along its length: Germany, Austria, Slovakia, Hungary, Croatia, Serbia, Bulgaria, Moldavia, Ukraine and Romania. Other countries connected to the Danube tributaries are Bosnia and Herzegovina, Czech Republic, Slovenia, Montenegro, Switzerland, Italy, Poland, the Republic of Macedonia and Albania. The Danube River, with its tributaries and floodplain systems forms a vital landscape element across many national borders. The Danube River serves as a migration corridor for many plants and animals over long distances in the large Danube River Basin in Europe.

In particular in middle reaches of urban areas, the Danube River or side arms of the Danube River are often canals and, at least in the past, the water quality was further impaired due to high nutrient loads. An example is the side channel "Neue Donau" in Vienna, where the nutrient concentrations measured in year 1988 were much higher than compared with later five-year period from 1992 to 1996 (Dokulil and Teubner, 2000 R). The Neue Donau is located near the Alte Donau (sometimes also named "Old Danube"), a separate arm of the Danube River in the urban floodplain area of Vienna, which now serves as a recreational lake for the Viennese (ALTE DONAU / OLD DANUBE S). For more than two decades, the Alte Donau has undergone a lake restoration (Dokulil et al., 2018 R; Teubner et al., 2018 R; Teubner 2019 R) which shifted the oxbow lake from a nutrient-rich, algal turbid state to a water plant-dominated, clear-water state (Teubner et al., 2022 R) with sustained high water quality of high recreational value and providing many other ecosystem services for a higher quality of city life in Vienna, the capital of Austria (Teubner et al., 2020 R).

The International Associationof Danube research (IAD) is the scientific network about relating to Danube research founded in 1956 (see further about IAD-history, Haidvogl et al., 2023 R). The elecetd IAD-presidium consists of a president, a vice president an a general secretary are elected at an IAD-General Assembly for a 6-year voting period. The mission statment of the newly elected general secretary in 2018, issues on the rapidely changing Danube River ecosystem over recent decades (R). The IAD bulletin Danube News appears twice a year since 1999. The member Country Representatives (IAD-CR) and more than ten Expert Group Leaders who issue on water quality, habitat observation of different biota, nature conservation and sustainable development (IAD-EGL) are building an active network covering the vast majority of Danubian countries joining the IAD for many years. Among other activities as e.g having an observer role in the International Commission for the Protection of the Danube River, (ICPDR, IAD organises every second year an international conference. The IAD-conference missions reflect a still ongoing attempt to enhance our understanding for today's changing environment in the Danube River or Danube River Basin (IAD-conferences).

Studies on algae and other photosynthetic microbes in the Danube River  have a long tradition in the history of IAD conferences since the 1950’s. During recent IAD conferences, about 12-15% of Danube research presentations relate to studies on microbial primary producers IAD conferences 2008-2023). These are photosynthetic organisms that either float freely and are carried along by the flowing water (phytoplankton) or live attached to the river bottom (phytobenthos). These studies describe in detail the abundance distribution of rare and common microbial autotrophic organisms across the Danube and its tributaries. In addition, their interactions with prevailing environmental influences and with other organisms within the benthic and planktonic communities, as well as their use as bioindicators for microhabitat reference conditions were investigated. In recent years, the response of microbial primary producers to current environmental pollution and eutrophication (excessive nutrient accumulation) and to global climate change, biodiversity loss has been studied. This shows that the current Danube has become a completely different habitat than a few decades ago for microorganisms, but also for many other aquatic organisms: see e.g. the opinion letter "No doubt about it - the Danube River Ecosystem is changing" by KT (2018), R. There is, however, a growing awareness for nature protection and sustainable use of both the river and its floodplains by people living along the Danube. The nexus between ecosystems and human activity is a central focus in recent Danube studies, with particular attention given to "Ecosystem Services" and "Water-Energy-Food (security) Nexus" (example for the Danube Delta in Romania, see Balaican et al. in 2024).