The Water Analysis Trailer for Environmental Research (WATER): Proof-of-concept and process insights from multi-source, high-frequency measurements

To test hypotheses about catchment processes inferred from hydrological and hydrochemical patterns observed at the outlet, measurements are needed at a high temporal frequency from multiple water sources distributed in space. Here we present the Water Analysis Trailer for Environmental Research (WATER), a trailer-based mobile sampling platform capable of autonomously measuring stable water isotopes, nitrate, electrical conductivity, pH and temperature for 72 samples per day, collected from up to 11 sources. As a proof of concept, the WATER was deployed to the Schwingbach Environmental Observatory (1.03 km²) in Hesse, Germany, where six water sources were analysed (2 × stream water, 3 × groundwater, 1 × precipitation) for a period of six months. The multi-source, high-frequency data offered new insights into catchment functioning that had not been revealed by previous, lower-resolution sampling campaigns. For example, rapid vertical movement of incoming precipitation into the soil and a strong linkage between shallow sub-surface flow paths and the stream became apparent during events. In addition, streamflow generation and water quality at the catchment outlet showed likely signs of influence from nearby water sources and arable farming practices. Simulating the reduced sampling frequency associated with connecting additional sources to the WATER indicated that key features of the collected data would likely be preserved if sampling occurred over a period of several months. Overall, the WATER provides a mobile and scalable approach for moving from pattern-based inference to process understanding through multi-source, high-temporal-frequency measurements.