Development and application of autonomous nutrient analysers for natural waters

摘要

The warming of the oceans and consequent enhanced stratification will have significant consequences for ecosystem functioning and carbon sequestration. Nutrient supply will reduce as a result of a strengthening in the stratification, with consequences for microbial ecosystems. Oligotrophic ocean regions are therefore predicted to increase in size as a consequence of global warming. This strengthens the requirement for analytical techniques with low limits of detection for nitrate and phosphate as conventional methods are unable to detect the nanomolar nutrient concentrations in surface waters in these regions. In recent years, sensitive techniques have been developed for shipboard nutrient analysis at nanomolar level with a high sample throughput. An analyser coupled with liquid waveguide capillary cells was deployed in the Atlantic. These techniques are however not suitable for autonomous deployment in oceans for long-term observations. Therefore, I have been working on the miniaturisation of nanomolar nutrient techniques using novel Lab-on-a-chip devices. The aim is to develop systems that are small, low-cost and low-power, and can be used autonomously and remotely to provide in situ real-time data on processes with high temporal and spatial resolution. Microfluidic technology is being used as it enables minimization of reagent and power consumption for in situ deployment of wet-chemical methods which provide accurate results with low limits of detection and high spatial and temporal resolution. In the 3rd chapter, we describe the development of an autonomous analyser for the determination of dissolved reactive phosphorus based on the vanadomolybdate method which allows long-term deployments thanks to the stability of the reagents. It has been deployed off the coast in Plymouth and during D361 (Atlantic). Then in the 4th chapter, a microfluidic platform to measure phosphate with the molybdenum blue method is characterised with optimised parameters and applied to marine waters.