Rapid on-site determination of enzymatic activity in water resources: from the technical assessment towards new perspectives in water quality monitoring

Abstract

Health-related water quality research, but also the management, allocation and utilization of water resources could highly benefit from an enhancement of the temporal and spatial resolution of microbial parameters. Recent technological developments have brought automated on-site measurements of enzymatic activity within the reach of real time monitoring and the detection of enzymatic activities has been proposed as a rapid surrogate for the microbiological pollution monitoring of water resources. Such automated enzymatic assays, operated on-site and online have the potential to indicate microbial contamination of waters in near-real time, are therefore of great interest to be implemented into early warning systems and could significantly enhance our understanding of contaminant transport processes and pathways. By proceeding from technically and method oriented science questions towards the applied utilization of a novel on-site monitoring technique, the goals of this thesis are: To test the technical realization of prototypes for the rapid and automated determination of beta-D-glucuronidase (GLUC) activity in sediment sediment laden streams, to disclose the indicator applicability of such assays for culture-based fecal indicator bacteria E. coli. and to use this novel technique within an interdisciplinary framework to improve modern-day water quality research. A long-term and continuous field deployment of measurement equipment is the key to generate time-series data, suitable to capture both event- and seasonal dynamics of crucial parameters, such as GLUC activity. In Chapter 2 an auto-sampler is presented, that was designed to be used as sample pretreatment in order to allow on-site measuring apparatuses to be operated in sediment laden water resources. The device was called SAMP-FIL and delivered automatically a filtered ambient water sample to the connected measurement equipment. Focus has been set on minimal sample alteration as well as on an effective self-cleaning procedure. It was controlled by a RaspberryPi microcomputer. The SAMP-FIL sample pretreatment was tested for over one year for rapid and on-site GLUC determination in sediment-laden stream water. The installation of the SAMP-FIL increased the error-free running time and measurement accuracy of the connected devices and enabled the continuous operation of the measuring devices in a technically challenging environment. Using the development from the previous chapter and having the technical challenges for long-term on-site operation of GLUC measurements disclosed, the next step was composed of testing the method´s robustness and assessing the plausibility of gathered data. GLUC activity values yielded with two different prototype construction designs have been compared and the temporal dynamics of these signals, their variation due to hydrological events and seasons as well as their correlation with microbial standard analyses have been assessed in Chapter 3. Four prototypes for rapid GLUC measurements have been operated at the stream monitoring station at the experimental HOAL catchment for over two years. Field tests, reference sample campaigns and event monitoring were used to highlight the capability and limits of rapid GLUC measurements in surface waters. The experiments suggest very consistent results of the instrument pairs with the same construction design, and somewhat lower consistency for different designs. GLUC activity is less well associated with suspended sediment concentrations than E. coli which is interpreted in terms of indicator applicability. This chapter shows that this rapid assay can yield consistent results over a long period of on-site operation in technically challenging habitats. Different water resources, such as ground- or surface water, constitute fundamentally differing operation environments for rapid enzymatic assays in regards to the range and temporal dynamics of signals as well as the concentration of organic and inorganic matter causing potential interference effects. Chapter 4 evaluates the operation of rapid GLUC measurements in different water resources. It is shown that the evaluated apparatuses for automated enzymatic activity measurements were technically robust for long-term on-site monitoring at diverse sites, ranging from pristine groundwater to sediment-laden stream water. Near real-time automated enzymatic activity measurement can thus be considered to be realized successfully from a technical point of view. The generated near-real-time data on GLUC activity point to habitat-specific differences with regard to their proxy capacities for culture-based fecal pollution detection. While Chapter 3 and Chapter 4 are focused on the temporal dynamics of GLUC activity at definite monitoring stations in different water resources, Chapter 5 assesses the capability of automated enzymatic activity measurements conducted from a mobile research vessel to detect the spatial variability of beta-D-glucuronidase (GLUC) activity on large fresh water bodies. Surveys have been performed on the Columbia River, the Mississippi River and on Lake Mendota covering up to 500 km river course or 50 km2 lake area, respectively. The observations provide for the first time high resolution spatial data of GLUC activity on large water bodies and document its association to hydrological conditions and land use. The ship-borne measurements disclosed effects of precipitation events and urban run-off on the GLUC activity of inland waters, localized point in-lets of potential fecal pollution and showed an increasing GLUC signal along a gradient of urbanization. The results of this thesis point out, that automated on-site methods based on specific enzymatic activity monitoring have great potential to be integrated in early warning systems, use oriented protection of water resources and process control. By determining the potential and constrains of rapid on-site enzymatic methods, the thesis paves the ground for a purposeful integration of such prototypes as a novel complementary parameter into well-established monitoring systems to improve data interpretation and process understanding within the fields of health related water quality and water resource management. Innovative applications of automated enzymatic assays, such as ship-borne measurements of GLUC activity, are described in this thesis for the first time to highlight new perspectives in water quality monitoring.