A New Generation of Ammonia Sensor for Deployment in Oceanic, Coastal and Estuarine Waters.

Ammonia is an important part of the oceanic nitrogen cycle and is involved in a number of the key processes, it is also the form of nitrogen that is most easily consumed by microorganisms. Being able to reliably analyse/detect ammonium is therefore crucial in understanding both ocean and coastal ecosystems. The analysis of ammonium by classical analytical techniques (colorimetric and fluorimetric) is extremely prone to contamination during the sampling and storing, and data quality is generally poor unless analysis is carried out on fresh samples. An in situ sensor system for the detection of ammonia would negate many of these issues and bring greater consistency and reliability. The majority of current nutrient sensors are actually small, micro analysers where the ‘sensing’ is carried out by colour forming chemical reactions, similar to those used in land based labs. Even though some of these systems are based on a very small reaction module, in order to deploy them they require housings for chemicals, waste, batteries, and relatively large and high power consumption pump and valve systems to control the reaction dynamics of the units. Once combined these units become relatively heavy and large to be deployed in gliders, buoys etc.

The ideal future scenario is for a simple probe sensor using innovative technology and without any chemicals or needing large battery power.

We report here preliminary results for such an ammonia sensor that can be deployed as a hand-held unit, or within a continuous monitoring system for marine, estuarine or freshwater situations.

We show results of comparisons to analysis of identical samples by a laboratory nutrient autoanalyser, showing acceptable limits of detection and calibration slopes for the new sensor.

A simple sensor system like this will be an important step forward for field deployments and monitoring of the marine and coastal environments.