A Comprehensive Monitoring and Assessment Survey on the Danube - page 4

Prioritization of Danube River Basin Specific Pollutants

The analysis of a large amount of organic substances during JDS3 was able to provide suggestions for the update of the Danube river basin-wide list of specific pollutants. The prioritization methodology which was based on the approach developed by the prioritization working group of the NORMAN network (Dulio 2013) produced a list of 22 substances suggested as relevant for the Danube river basin based on the results of the JDS3 target screening of 654 substances in the Danube water samples by 13 laboratories. PNEC values were available for 189 out of 277 JDS3 substances actually determined in the samples. The cut off criteria to include a compound in the list was its exceedance of the ecotoxicological threshold value (PNEC or EQS) at minimum of one JDS3 site. The list contains five WFD priority substances (three PAHs, fluorathene and PFOS) and two EU Watch List candidate compounds (17beta-estradiol, diclofenac). The 'top ten' substances are dominated by (i) the pesticides 2,4- dinitrophenol (exceeding the limit value at all sites), chloroxuron, bromacil, dimefuron and transformation products of widely used atrazine and terbuthylazine, (ii) three polyfluorinated substances (PFOS, PFOA, PFNA) and (iii) the plasticiser bisphenol A determined at 30 sampling sites.

 

Hydromorphology

Two different approaches were used to assess hydromorphology. The first, the 'continuous survey', assessed the entire 2,415 rkm of the Danube River, subdividing it into 241 segments of 10 rkm lengths plus 18 segments for branches in the Danube Delta. All of the data was obtained by using high-resolution image analysis, maps and field observations. This approach used WFD parameters for morphology (e.g. river depth), hydrology (e.g. quantity of water flow) and river continuity (e.g. impacts of dams). The five classes of assessment were: 1 – near natural, 2 – slightly modified, 3 – moderately modified, 4 – extensively modified, and 5 – severely modified. The assessment was further organized according to the main Danube channel, banks and floodplains, as well as the three Danube reaches.

 

Fig06
Figure 6: CEN-Overall assessment.

 

The continuous longitudinal survey in 10 rkm segments brought the following results:

  • Overall Assessment: About 60% of the Danube stretch was found better or equal to class 3, with 21% in class 2 (slightly modified) and 39% in class 3 (moderately modified). However, 40% fell in the two worst classes: class four (26%), and class five (14%). The overall picture is therefore split into one large part with satisfactory conditions and a second part with totally altered reaches (Figure 6). The "poor" assessment in the Upper Danube differs significantly from the comparatively "good" assessment in the Lower. The assessment also confirms the main findings of the JDS2.
  • Danube channel: Many segments fell under classes 2 and 3, especially for the long free-flowing stretches in the Middle and Lower Danube. About 590 km fell to the worst class because of impoundments and severely altered stretches within dense settlements.
  • Banks: Over 25% of the surveyed banks fell into classes 1 and 2, mainly in the Lower Danube. Many fortified banks, belonging to classes 4 and 5, can be found along the Upper Danube, where higher degrees of urbanization and hydropower also cause negative impacts.
  • Floodplains: Very few stretches still host good conditions and space for floodplains. Floodplains have been lost in at least 65%-70% of the river represented by classes 4 and 5 and partially by class 3. Floodplains that do remain often suffer from disconnection with the river, sediment build-up from dams, and poplar plantations substituting for natural floodplain vegetation.

The second approach, performed for the first time on the Danube, consisted of detailed individual site analyses for each of the 68 JDS3 sampling sites. This was especially useful to support the biological assessment under the WFD, for example, to provide detailed physical habitat data (e.g. for fish).

 

The hydromorphological survey confirmed that sustainable restoration actions should be continued to help meet the good ecological status/potential along the entire Danube. Floodplain restoration should be a long-term goal for ecological and flood mitigation planning. The impacts of existing dams should be a matter of further basin-wide investigations. And given the fact that many large European rivers are severely altered, less altered water bodies along the Danube should be carefully managed.


Conclusions

The JDS3 followed up on the past work to determine if the 'status' of waters had improved or deteriorated, as some key measures had already been put in place by ICPDR Member Countries. The findings of JDS3 are supportive to the implementation of EU WFD as they provide an extensive homogeneous dataset production of which was mainly based on WFD compliant methods commonly used by the Danube experts. Even though these data have no ambition of replacing the national data used for the assessment of the ecological and chemical status they are an excellent reference database serving for future efforts of method harmonization in the Danube River Basin, especially concerning the development of a concerted type-specific approach to the status assessment of large rivers, and of the prioritization of the Danube river basin specific pollutants.

The JDS3 helped to raise awareness for water protection and the work of the ICPDR – through active communications, media relations and nine public events during the expedition (visit www.danubesurvey.org).