First report of a novel multiplexer pumping system coupled to a water quality probe to collect high temporal frequency in situ water chemistry measurements at multiple sites

The increasing availability and use of high-frequency water quality sensors has enabled unprecedented observations of temporal variability in water chemistry in aquatic ecosystems. However, we remain limited by the prohibitive costs of these probes to explore spatial variability in natural systems. To overcome this challenge, we have developed a novel auto-sampler system that sequentially pumps water from up to 12 different sites located within a 12 m radius to a single water quality probe. This system is able to generate high temporal frequency in situ water chemistry data from multiple replicated units during experiments as well as multiple sites and depths within natural aquatic ecosystems. Thus, with one water quality probe, we are able to observe rapid changes in water chemistry concentrations over time and space. Here, we describe the coupled multiplexer-probe system and its performance in two case studies: a mesocosm experiment examining the effects of water current velocity on nitrogen dynamics in constructed wetland sediment cores and a whole-ecosystem manipulation of redox conditions in a reservoir. In both lotic and lentic case studies, we observed minute-scale changes in nutrient concentrations, which provide new insight on the variability of biogeochemical processes. Moreover, in the reservoir, we were able to measure rapid changes in metal concentrations, in addition to those of nutrients, in response to changes in redox. Consequently, we believe that this coupled system holds great promise for measuring biogeochemical fluxes in a diverse suite of aquatic ecosystems and experiments.