A lab in the field: real-time measurements of water quality and stable isotopes

Abstract:

Hydrological and bio-geochemical processes in catchments are largely determined by the flow pathways of water through the subsurface. While the properties of the input (precipitation) and the output (streamflow) can be monitored with relatively low expenditure, subsurface flow processes and travel times remain difficult to quantify. A comprehensive understanding of these physical mechanisms is, however, crucial for a sustainable management of water resources.

Natural tracers, such as stable isotopes of water (¹⁸O and ²H), in combination with other water quality parameters allows for studying various hydrological and associated processes in great detail. To follow the dynamics in rapidly changing hydrologic systems, high temporal resolution measurements of water isotopes and other constituents is required.

Here, we present first results from an extensive field experiment in Switzerland where rain- and river water samples are sampled and analyzed directly in the field every 30 minutes. With this, sample degradation during storage and transportation can be minimized. At the same time, errors due to the collection and handling of numerous water samples are avoided.

The fully automated monitoring system is comprised of the newly developed Continuous Water Sampler Module (CoWS), which was coupled to a Picarro L2130-i Cavity Ring-Down Spectrometer (Picarro Inc., USA), to continuously measure ¹⁸O and ²H. Optical and electrochemical sensors together with a spectrometer probe monitor NO₃-, DOC and physico-chemical parameters, such as oxygen content, pH, electrical conductivity (s::can Messtechnik GmbH, Vienna). An ion chromatograph (Metrohm, Switzerland) allows for precise measurements of the major anions and cations. For quality control, additional water samples are taken automatically at the same frequency and analyzed in the laboratory.