A Comprehensive Monitoring and Assessment Survey on the Danube - page 01

The Survey

The survey was carried out using three ships provided by Romania (Istros), Serbia (Argus) and Austria (Wien). The Argus was used for sampling and on-board laboratory analyses, while the Istros provided accommodation for the Core Team and National Team members as well as storage facilities. Three small boats from the ships were used for parallel biological and chemical on-shore sampling. The fish team on Wien followed a separate sampling schedule using additional two electrofishing boats. An additional ship (Meßschiff IV) offered by viadonau (Vienna, Austria) has been used to support the fish survey in the Austrian reach of the Danube.


A total of 68 sites were sampled, with one or two sites visited daily on average (Figure 1). Many samples were tested on-board the ships while others were sent to participating laboratories throughout Europe, within and beyond ICPDR Member Countries. Sampling at JDS3 stations could include up to five different 'sample types' – water, sediment, biology, suspended particulate matter (SPM) and biota (fish). The experts conducted numerous tests, looking for animals and plants, from larger shellfish to microscopic bacteria, and chemical and hazardous substances. The hydromorphological study included activities such as sediment testing, photography, and listing harbors and sand bars. 32 sites were chosen for monitoring fish. Non-lethal 'electro-fishing' stunned fish for collection. The river bottom was sampled with an 'electrified bottom trawler net'.


Figure 1: JDS3 sampling sites.


Results of Biological Monitoring


Multi-Habitat-Sampling - the standardized WFD compliant method for ecological status assessment (AQEM Consortium, 2002) was used as the main sampling approach. Samples were taken at 55 sites along the Danube stretch. Overall, 460 macroinvertebrate taxa (groups of one or more populations of organisms) were identified. Insects dominated with 319 taxa. Diptera were the richest insect order with 222 taxa – 200 species belong to the family Chironomidae. In terms of abundance, Amphipoda were the dominant group in all Danube reaches and increased downstream. Diptera play an essential role in the Upper Reach and decreased downstream. Oligochaeta and Mollusca were found in increasing numbers in the Middle and Lower reaches, with the invasive Asian clam, Corbicula fluminea, occurring in high densities.

Regarding water quality, in total, 73% of the 55 sampled sites can be classified as having an 'indication of good ecological status', 15% with an 'indication of moderate ecological status', and 4% with 'high ecological status', according to the WFD. This proportion is similar to that for the JDS2. Serious organic pollution was identified upstream Novi-Sad. Poor status was indicated at these sites: Jochenstein, upstream Drava, downstream Velika Morava, and at Vrbica/Simjan in the Iron Gate reservoir. Natural (organic) habitats were found to have a higher diversity of animals compared than inorganic habitats, especially artificial ones such as rip-rap where invasive crustaceans are widespread (Figure 2). Furthermore, it was found that the occurrence of species is determined mainly by habitat – information that is important for habitat restoration efforts.


Sampling of macrophytes and other bank vegetation was conducted from a small boat on six survey units of one kilometer length at each sampling site. Three survey units were sampled on the left and three on the right side of the river.


Abundance of plants was estimated according to the Kohler 5-level scale (Kohler, 1978). A total of 198 taxa (182 species divided among 16 genera) were identified. These included bryophytes (35 taxa), ferns (4 taxa), angiosperms (150 taxa), charophytes (1 taxon) and other macroalgae (8 taxa). Across all of the three JDSs to date, the total number of identified taxa is 249.


For phytobenthos sampling and chlorophyll-a measurements, a river segment with a suitable substrate had to be chosen, along with stones in the current. Stones were measured in-situ for chlorophyll-a concentrations using special equipment that take 'fluorescence fingerprints'. Three algal groups were investigated: diatoms, green algae and cyanobacteria. In addition, material from a small area on each stone was brushed into containers for later lab analyses of species composition. The highest level of chlorophyll-a was detected in the Upper Danube down to station JDS10 (rkm 1895) and then again at sites downstream from JDS40 (rkm 1107). The results indicate increasing downstream pressures on, and thus general degradation of, the aquatic environment. The ecological status of the Upper Danube varied between high to good, while sites downstream from Budapest appeared consistently below the good/moderate boundary. However, the results of this assessment method are only indicative.


Chlorophyll-a concentrations were measured to assess water quality. Most concentrations in the Danube belonged to water quality class I (high). Moderate values of class II were observed at three sites from rkm 1367 (downstream Drava) to rkm 1262 (upstream of Novi Sad). When applied to river sections, the results indicated high to good status (water quality class 1–2) in most of the Upper and Lower Danube (Figure 3). Moderate status was assigned to the river section from rkm 1384 (upstream Drava) to rkm 1216 (upstream Tisa). The 15 investigated tributaries are in high to good status except for two tributaries (Figure 3).


Figure 2: Significant indicator species per substrate type.


Figure 3: Chlorophyll-a concentrations in the River Danube and selected tributaries obtained during JDS3, August/September 2013 related to WFD criteria proposed by Mischke and Oppitz (2005).