Dissolved Oxygen Probe System for Real-time, In-situ Subsurface Monitoring

Environmental sensor networks capable of taking data quickly enough to capture minutescale fluctuations and durable enough to capture these data for entire seasons provide essential information for studying the seasonal and annual effects of microbial activity across complete ecosystems. Distributed sensors for subsurface dissolved oxygen (DO) concentration measurement are of particular interest because of the outsized role DO plays in catalyzing a diversity of environmentally important biogeochemical reactions. Commercially available DO sensors cannot provide the desired spatial and temporal density for resolving data over extended periods at the ecosystem level The overall goal of this proposed body of research is to develop a monitoring technology that provides insight into spatial and temporal variations in dissolved oxygen as a result of hydrological factors, such as seasonal infiltration events and excursions groundwater elevation. To accomplish this goal, a cost competitive DO sensor that can operate for months (or longer) in an uncontrolled, outdoor environment without the need for human intervention and/or recalibration will be developed. The sensor design will allow having multiple sensing sites within a single sensor probe. This will enable data acquisition from multiple probes to generate fourdimensional (space and time resolved) maps of oxygen concentration by importing the timetagged data from the sensors into commercially available geographic information system (GIS) systems. Opti O2 improved the design of its single point DO sensor in order to reduce costs and improve manufacturability. We also changed our electronics approach, with the new approach being based on a proprietary timedomain spectrometer to monitor the emission from the sensing film, for which a provisional patent has been filed. We built and calibrated four of these sensors and demonstrated a signaltonoise ratio of greater than 100 over a period of one month of continuous, interventionless operation. We also completed the detailed design of a segmented/modular sensorprobe. The Phase II project has three overarching objectives. First is to build, calibrate, and qualify a number of multisegment sensor probes, including a base module capable of direct communication to a cloudbased data storage system. Second is to develop a GISenabled program that can gather, analyze, and display 4D (time/space) dissolved oxygen data. Third is to deploy sensor systems at three distinct field sites of scientific interest both to have disinterested thirdparties validate our claims of technical superiority as compared to existing one and to gather DO data of unprecedented accuracy and temporal/spatial density that shall be used by the scientific community to better understand these sites. Commercial Applications and Other Benefits: Recent USGS studies have shown that dissolved oxygen is a proxy for detecting a broad array of chemicals which would otherwise require an extensive suite of sensors to identify. Since the use of a single sensing modality device greatly reduces deployed, thereby providing realtime environmental assessment. The data gathered from an ecosystem wide network of DO probes will provide water system operators with the information they need to proactively respond to changes in the environment, thereby ensuring the publics access to safe drinking water.