Real-Time Underway Mapping of Nutrient Concentrations of Surface Seawater Using an Autonomous Flow Analyzer

Abstract

High-frequency field nutrient analyzers offer a promising technology to solve time-consuming and laborious sampling problems in dynamic and complex river−estuarine− coastal ecosystems. However, few studies on the simultaneous underway analysis of five key nutrients (ammonium, nitrite, nitrate, phosphate, and silicate) in seawaters are available because of the limitations of the technique. In this study, a state-of-the-art autonomous portable analyzer for the shipboard analysis of nutrients in the environment of varied salinities and concentration ranges was reported. The analyzer consisted of compact hardware that was well suited for shipboard deployment with minimal maintenance. Moreover, a novel LabVIEW-based software program was developed, containing additional functions such as automated calibration curve generation, autodilution of high-concentration samples, and a user-friendly interface for multiparameter analysis using a single instrument. After the optimization of chemical reactions and work flow chart, the analyzer exhibited low limits of detection, a large linear range with automated dilution, and relative standard deviations of less than 2% (n = 11). Compared to other flow-based techniques, this analyzer is more portable and consumes less reagent with an autonomous data processing function and applicability within a broad salinity range (0−35). The analyzer was successfully applied for real-time analysis in the Jiulong River Estuary−Xiamen Bay with excellent on-site accuracy and applicability. The relationship between high spatial resolution nutrient concentrations and salinities showed very different patterns in estuarine and coastal areas, indicating the benefit of using an underway automated analyzer for chemical mapping in a dynamic environment.

Programmable flow injection: a versatile technique for benchtop and autonomous analysis of phosphate and silicate in seawater

“…The detection limits, defined as three times the standard deviation of LNSW or MQ samples (n=6), were 0.06 µmol L -1 for phosphate and 0.2 µmol L -1 for silicate. These values are comparable to those reported for other portable flowbased nutrient analyzers capable of multi analyte determinations (Thouron et al, 2003;Deng et al, 2020;Zhu and Ma, 2020;Fang et al, 2022a, Fang et al, 2022b. Sample throughput for simultaneous analysis of phosphate and silicate on the same sample is approximately 11 hr -1 , with a precision (RSD) < 6% for both analytes across their working range.…”

“…While emerging phosphate and silicate electrochemical sensors could mirror the success of UV nitrate sensors due to their reagentfree nature and low power requirements, they remain at the research and development stage and their suitability for longterm operation has yet to be demonstrated (Barus et al, 2017, Barus et al, 2018Chen Legrand et al, 2021;Chen et al, 2023). As such, the primary approach for autonomous phosphate and silicate monitoring involves adapting established wet chemical colorimetric assays to various flow-based instruments (Vuillemin et al, 2009;Grand et al, 2017;Altahan et al, 2022;Fang et al, 2022a, Fang et al, 2022b. For in situ deployments, whether stationary or on mobile platforms, Lab-On-Chip analyzers stand out for their robustness, low-power consumption, and ability to operate in diverse environments, including the deep-sea (Grand et al, 2017;Birchill et al, 2021;Beaton et al, 2022).…”

“…However, LOC sensors are limited to single nutrient measurements, work best when submerged and hardware components are not readily serviceable by the user. For benchtop tasks, fixed location monitoring, or shipboard underway applications, several syringe-based analyzers offer multi-nutrient determinations capabilities (Altahan et al, 2022;Fang et al, 2022a, Fang et al, 2022b. Notably, the iSEA-II analyzer is well suited for discrete sample analysis and underway monitoring of P and Si, with analytical performance comparable to state-of-the-art benchtop systems (Fang et al, 2022a).…”

“…Notably, the iSEA-II analyzer is well suited for discrete sample analysis and underway monitoring of P and Si, with analytical performance comparable to state-of-the-art benchtop systems (Fang et al, 2022a). However, iSEA-II is not commercially available, and its potential for long-term unattended deployments awaits validation (Fang et al, 2022a, Fang et al, 2022b.…”

StimulatedProrocentrum donghaiensecell growth byin-situmariculture dissolved organic matter

“…A 15mL sample was removed from each culture and filtered through a GF/F membrane, and the filtrate was used to measure DIN (sum of nitrate, nitrite, and ammonium) and DIP concentration using the autonomous portable analyzer— i SEA-II (Xiamen university, China) (Fang et al, 2022).…”