Detection of enzymatic activities has been proposed as a rapid surrogate for the culture-based microbiological pollution monitoring of water resources. This paper presents the results of tests on four fully automated prototype instruments for the on-site monitoring of beta-d-glucuronidase (GLUC) activity. The tests were performed on sediment-laden stream water in the Hydrological Open Air Laboratory (HOAL) during the period of March 2014 to March 2015. The dominant source of faecal pollution in the stream was swine manure applied to the fields within the catchment. The experiments indicated that instrument pairs with the same construction design yielded highly consistent results (R(2) = 0.96 and R(2) = 0.94), whereas the results between different designs were less consistent (R(2) = 0.71). Correlations between the GLUC activity measured on-site and culture-based Escherichia coli analyses over the entire study period yielded R(2) = 0.52 and R(2) = 0.47 for the two designs, respectively. The correlations tended to be higher at the event scale. The GLUC activity was less correlated with suspended sediment concentrations than with E. coli, which is interpreted in terms of indicator applicability and the time since manure application. The study shows that this rapid assay can yield consistent results over a long period of on-site operation in technically challenging habitats. Although the use of GLUC activity as a proxy for culture-based assays could not be proven for the observed habitat, the study results suggest that this biochemical indicator has high potential for implementation in early warning systems.

Microbiological cultivation methods estimate the number of bacteria in water samples mainly as an amount of Colony Forming Units in 100 ml (CFU/100ml) or as a Most Probable Number of fecal bacteria in 100 ml (MPN/100ml). The growing amount of molecular methods for specific detection of fecal bacteria allows rapid measurement without the need for cultivation. These methods could determine the presence of specific genetic markers of fecal bacteria in water expressed in Genomic Equivalent Units per 100 ml (GEU/100ml) or Target Sequence Copy (TSC) per 100 ml. Analysis of enzymes, such as β-Dglucuronidase in indicator bacteria have been used for many years to quantify feces-associated contamination, but the measurement parameter which allows the comparison of the obtained results is not clearly defined. In this work we are introducing a novel parameter: enzymatic activity of beta-D-glucuronidase expressed in Modified Fishman Units per 100 ml of water sample (MFU/100ml). A fully automated device to detect enzymatic activity above 0.001 MFU/100ml in freshwater without sample pretreatment within less than 60 minutes was developed and subjected to field tests. The instrument measures enzymatic activity by detection of accumulated reaction product. Due to the short measurement time, the technology can be used both for water quality monitoring purposes and for process control applications.