| Popis: |
Streams can carry and spread numerous pathogen species, either free floating or attached to the surface of fine particles. These pathogens can pose serious threats to human health in places where untreated water is directly consumed or by contact with the water when using for recreation, washing or irrigation purposes. The most important sources of pathogens to streams in urbanized catchments are wastewater treatment plants that continuously release wastewater effluent, which is still infectious. Moreover, untreated wastewater is also discharged to streams through combined sewer overflows during heavy rain events, resulting in the release of high loads of pathogens. Once pathogens are introduced to a stream from these sources, their fate is controlled not only by transport in surface water but also by exchange with streambed sediments. Within streambeds, pathogens are subject to a complex array of processes that include seepage transport, sorption to sediment surface, and decay, with some pathogens being eventually released back to surface water. Recently, a model for stream transport of pathogens has been developed that is based on the Continuous Time Random Walk (CTRW) framework. This model describes the stream corridor as the interaction of a mobile and immobile zones, and a few applications to pathogen transport have been discussed in the literature. This contribution will present an application of this model approach to predict the fate of pathogens in an urban stream in Vienna. The model application will be tailored to work with the uncertainty that typically affects the information that is available in these situations. Thus, stochastic boundary conditions will be applied to consider the variability of pathogen loads to the stream, and model parameters will be calibrated on available concentrations of C. perfringens spores (used as conservative microbial tracer for municipal sewage) and the human genetic fecal marker HF183/BacR287, and eventually validated based on concentrations of the reference pathogens Cryptosporidium and Giardia, observed at the catchment outlet. |
