Aquatic Health Monitoring System (AHMS) Development
Mentor: Dr. James Bonner
Department: Civil and Environmental Engineering
Eutrophication in lakes, bays and estuaries can be linked to exceedingly high productivity due in part to high levels of nutrients resulting from agricultural and other anthropogenic factors. When combined with stratification, this could result in hypoxic conditions in the hypolimnion. This is a problem of national concern (PNC) and occurs in several of the lakes in the Great Lakes region, Corpus Christi Bay and the Gulf of Mexico, calling for continuous monitoring to determine the effectiveness of management plans instituted for these water bodies. This underscores the importance of ecological studies and environmental modeling to better understand the bio-chemical cycling through quantification of both total and available forms of nitrogen and phosphorous (TN and TP) in the water column. There is a requirement for material balance and flux measurements in turn calling for in situ total nutrient level determination. Our research laboratory has purchased and evaluated commercial-off-the-shelf (COTS) nutrient analyzers costing as much as $80,000 a piece and found serious limitations involving operational logistics, QA/QC and result interpretation. The unit we have is based on colorimetric techniques using continuous flow reaction process to facilitate color development. This approach results in offsets between the data points and the location/timestamp information and aligning through post-processing is the only recourse. However more serious is the long tubing runs required for the process retention time which results in dispersion of the sample and is not accounted for in the algorithm making the results difficult or impossible to interpret. We also developed a prototype four-parameter in situ nutrient analyzer based on absorption spectrophotometry for detection of nitrate, nitrite, bromide and bisulfide. This method is direct, not requiring the use of reagents and lends itself to high sampling frequencies compared to the COTS nutrient analyzers that we evaluated. Although it solves the problem with retention time as discussed, our bench tests reveal that this method works well only with freshwater systems and only at moderate sensitivity. This does not meet our design criteria for an AHMS in terms of portability across different geomorphologies and relatively high sensitivity (~uM). There are two inter-related objectives in this study: Objective 1: Design of an automated thermo-chemical digestion system using acid hydrolysis; bench-testing, process optimization and interfacing to downstream colorimetric (ascorbic acid reduction) module. Objective 2: Using micro-fluidics, automate the process of reagent addition for the colorimetric (ascorbic acid reduction) process; interfacing to a photo-detector module downstream; interfacing upstream to the digestion chamber. Each objective will be addressed individually by two students working together as a team under the supervision of the project PIs. The students will gain understanding of optical probes (fluorescence, absorbance, near-IR, UV-VIS spectroscopy); develop sensing elements and deployment schemes; interface sensing element to analog-digital converter on an MCU with embedded Webserver for configuring instrument and direct data readout to the Internet. Real-time measurements of constituent of interest in a waterbody will be demonstrated on project completion. Students working on this project will have the opportunity to deploy the sensor in the field in our testbed and take in situ measurements, transmitting the data by wireless Ethernet to the Internet, host computer or database.