Measuring of Time-Series Concentrations of Nutrients in Surface Waters Using Osmotic Sampler with Air Bubble Segmentation and Preservative Addition.

The analysis of time-series concentrations (C-TS) is of great importance when investigating the biogeochemical processes of nutrients in aquatic environments. However, obtaining C-TS of nutrients remains a challenge using current sampling techniques. In this study, a novel in situ sampler was constructed using reverse osmosis membrane (ROM) osmotic pumps (OP) (ROM-OP sampler), and was used to obtain the C-TS of nutrients in surface waters. The sampler consisted of a sampling OP, sample storing coil, filter, bubble injection module, and preservative adding module. When deployed, the sampling OP continuously draws ambient water through the filter into the sample storing coil, while simultaneously the preservative adding module continuously delivers preservative (H2SO4 solution) into the water flow. The bubble injection module periodically injects air bubbles into the sample storing coil, to segment the sample and create time stamp indicators that allow the sample age to be defined. Upon retrieval, the sample segments in the coil are sequentially pumped out of the sample storing coil and transferred into different vials for further analysis. The sampler was applied to measure the C-TS of various nutrients, including dissolved total nitrogen, dissolved total phosphorus, dissolved reactive phosphorus, and nitrate in a river over a 20 day period and in municipal sewage treatment plant effluent for a 36 h period. Results showed that the ROM-OP sampler successfully obtained C-TS of nutrients, capturing nutrient variations at a high temporal resolution. This sampler is relatively low-cost (similar to USD 300), small in size, lightweight, robust and does not require an external power source, showing high promise as an effective and efficient tool for monitoring nutrient C-TS in aquatic environments. (C) 2020 Elsevier B.V. All rights reserved.