Glossary of Terms

Biological sampling

Animals and plants are collected with specific devices and analysed regarding species composition and individual density. This data gives information about how natural the ecosystem is at a certain sampling site – i.e. how far away the ecosystem is from being in a completely undisturbed state. 

This kind of analysis is done for five specific groups that are also used within the EU-wide monitoring:

  • macrozoobenthos (small animals living on and in the sediments);
  • macrophytes (water plants);
  • phytobenthos (algae living attached to sediment surface);
  • phytoplankton (algae floating in water);
  • and fish.

During JDS4, zooplankton (small animals floating in water, only visible with a microscope) and microorganisms are also analysed.

Chemical sampling

Water, sediment, or organism tissue is collected and analysed for chemical substances. Some of those substances are natural and good for the ecosystem, e.g. nutrients like nitrogen and phosphorus, or a variety of organic substances stemming from biodegradation. These only cause problems when their concentration is above or below certain limits. 

Other chemicals are pollutants, e.g. pesticides, pharmaceuticals or substances from industry. Limits set by the EU or by national laws exist for most of these, and their concentration should be as low as possible. However, nowadays the analytical methods are already extremely effective at detecting even minimal amounts of such substances, and thus a wide variety of them are often detected. During JDS4, water, sediment, and tissue in the Danube are all checked for thousands of chemical substances with modern methods, Searching for substances presenting a risk to both the environment and humans, and also for the information regarding which substances will have to be observed in more detail in the future.


(aka “Environmental DNA”). Animals and plants living in the Danube leave their traces in the water in the form of microscopic particles from their body. The DNA in those particles (eDNA found in the environment in contrast to the “organismic DNA” found directly in the body) can be analysed and compared to “barcodes” in a database. Such a “barcode” is the genetic information for a single species that is necessary for its identification. With this revolutionary method, the presence of animals and plants can be detected in a water sample without catching or collecting them – even without observing them directly! During JDS4, brand new eDNA methods are being tested in comparison to conventional methods of aquatic species identification. In the future, the use of eDNA could revolutionize biological research and biological monitoring for the assessment of ecological quality.


(Also Macroinvertebrates): Small animals without backbones that live on or in the sediments underwater and can be seen without the help of a microscope (i.e. larger than 0.5 mm). A huge variety of aquatic insects, worms, snails, clams, crabs and other animals belong to this group.

Passive Sampling

“Passive sampling” is a technique used to monitor an environment, whereby a medium is collected over time in something, such as a man-made device or biological organism. This is in contrast to “grab sampling”, which involves taking a sample directly from the media of interest at a single point in time. In passive sampling, average chemical concentrations are calculated over a device's deployment time, which avoids the need to visit a sampling site multiple times to collect multiple representative samples.

Currently, passive samplers have been developed and deployed to detect toxic metals, pesticides, pharmaceuticals, radionuclides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and other organic compounds in water. Notably, some passive samplers can be used to detect hazardous substances in the air.