Microbiological Water Quality of the Danube River: Status Quo and Future Perspectives

Fecal microbial pollution is a major problem throughout the Danube River Basin, posing a threat to various types of water use, including drinking water production from river bank filtrates, water supply for agricultural and industrial use, and the role of the river as a recreational space. Fecal microbial pollution is introduced into the river by point sources, such as discharges of treated or untreated sewage from human sources or livestock, and by nonpoint sources, such as urban and agricultural runoff. In addition, fecal input from wildlife may be of importance in specific regions. Despite huge efforts to improve wastewater management in the past decade, in many sections, the river and its tributaries exhibit very high levels of fecal microbial pollution. To assess microbiological water quality, indicators of fecal pollution are used as surrogates for the potential presence of intestinal pathogens. However, the standard indicators cannot provide any reliable information regarding the origin of fecal pollution, nor can their concentration levels be directly related to human health risks for many types of exposure and situations. The aim of this book chapter is to summarize the historical developments in microbiological water quality research and to reflect the most recent publicly available data on the fecal microbial pollution status of the Danube River. Moreover, the first results on fecal microbial source tracking by molecular biology methods are presented along with their applicability in river water quality monitoring, including the monitoring of riparian wells and alluvial groundwater resources. Finally, a discussion of the general state of water quality and public health is presented concerning (i) the current situation and potential limitations of the Water Framework Directive regarding the microbiological quality elements, (ii) further improvements regarding sampling and monitoring strategies, and (iii) the recently introduced concept of "integrated framework of fecal pollution monitoring and management" and expected further methodological developments in the context of the Danube watershed. Rapid progress in research and development is currently being made in the area of fecal microbial source tracking, pathogen detection, and health risk assessment, and these innovations are also likely to complement basic fecal pollution monitoring programs for river systems such as the Danube in the near future.