This is a proposal to develop an autonomous submersible analyzer to measure ammonium. Ammonium is the most rapidly cycled nitrogen compound in coastal and marine environments. In oceanic waters, ammonium concentrations are normally below 1 mole, but exhibit considerable temporal and spatial variability. An automated, in-situ, and submersible analyzer is the only way to assess the actual environmental variability of ammonium. Not only will the proposed analyzer significantly contribute to biogeochemical and oceanographic research but the novel technical approach used can be applied to other wet chemistry analyses. Moreover the system will have immediate non-research applications given environmental concerns about the effects of ammonium discharge from wastewater-treatment facilities as well as agricultural and industrial inputs in tidal inlets, coastal rivers and estuaries. Such ammonium discharge has become an issue of major significance to both state and federal environmental regulators.
The proposed system is based on a novel fluidic technique called Autonomous Batch Analysis (ABA) in conjunction with a LED photodiode-based fluorescence detector (LPFD) for in-situ underwater measurement of ammonium in natural waters. The analyzer the investigators propose to construct will be mechanically simple (only two moving parts), highly precise, submersible, require only modest power, and have the capability of measuring ammonium at nanomolar levels with a sampling frequency of 15 minutes for periods of a month (or more frequently for shorter deployments). Where necessary, the analyzer can be equipped with back flushed passive filters to enable measurements in turbid, sediment-laden waters. The parts required to assemble such an analyzer will cost under $9000. The proposed instrument will be immediately deployable on moorings or fixed stations but applicability to lowered or towed systems and Autonomous Underwater Vehicles (AUV) will also be explored.
