Our knowledge relating to water contamination from point and diffuse sources has increased in recent
years and there have been many studies undertaken focusing on effluentfrom sewage plants or combined
sewer overflows. However, there is still only a limited amount of microbial data on non-point sources
leading to diffuse pollution of surface waters. In this study, the concentrations of several indicator microorganisms
and pathogens in the upper reaches of a river system were examined over a period of 16
months. In addition to bacteria, diffuse pollution caused by Giardia lamblia and Cryptosporidium spp. was
analysed.
A single land use type predestined to cause high concentrations of all microbial parameters could not
be identified. The influence of different land use types varies between microbial species. The microbial
concentration in river water cannot be explained by stable non-point effluent concentrations from different
land use types. There is variation in the ranking of the potential of different land use types resulting
in surface water contamination with regard to minimum, median and maximum effects. These differences
between median and maximum impact indicate that small-scale events like spreading manure
substantially influence the general contamination potential of a land use type and may cause increasing
micro-organism concentrations in the river water by mobilisation during the next rainfall event.
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