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Associate Professor Ronald L. Siefert

Research

Some of Dr. Siefert's current and past research projects are listed below. More information about Dr. Siefert's research interests can be found by reviewing his publications.
"Lab on a Chip" - The Integration of Organosilicate Materials in a Microfluidic Based Liquid Chromatography System.
This project is investigating the use of organosilicate materials in a microfluidic based liquid chromatography system constructed on a microchip (“laboratory- on-a-chip”). The organosilicate material will be used as the column material for the preconcentration and separation of nitroenergetic chemicals, which include nitroaromatic and nitroamine explosives, and their degradation products. The sample matrix will be seawater and the detection method will include UV absorbance detection. Nitroaromatic and nitramine explosives are an ongoing concern of the U.S. Navy. The ability to detect these analytes at trace levels in seawater is important to both military and environmental threats. Organosilicate materials can be synthesized to have a high binding capacity and selectivity to nitroenergetic chemicals. These properties make the organosilicate material an ideal column material for chromatography. This project will involve the development of a method to synthesis these organosilicate materials on the microchip, and then the characterization of their chromatographic properties.
Atmospheric Deposition of Nutrients: Nitrogen

Loadings of nutrients to estuaries and the coastal oceans have been enhanced by anthropogenic activities. Historically, loadings of nitrogen from the landscape, including overland flow, river and groundwater discharge, and direct discharges, have been considered to be the major sources of this nutrient.

However the role of the atmosphere in transporting ‘new’ nitrogen into coastal waters throughout North America and northern Europe has recently been shown to also be an important pathway. Atmospherically derived nitrogen can represent a significant fraction of the total nitrogen budget in East Coast Estuaries (e.g., 25% of new nitrogen is from atmospheric deposition in the Chesapeake Bay). However, there are still high uncertainties associated with these estimates. Our research is investigating the sources, transport and deposition of nitrogen nutrients in the Chesapeake Bay airshed.

Enzyme Degradation of Colored Dissolved Organic Matter (CDOM)
Colored dissolved organic matter (CDOM) is found in natural aquatic systems. It can be used as a tracer for sources of organic material and also has implications for the interpretation of of remote sensing measurements. The breakdown of CDOM affects its light absorption characteristics. This project is investigating how various enzymes degrade CDOM, their effect on the light absorption characteristic of the CDOM, and their use as a possible new analytical technique for measuring CDOM in natural aquatic systems.
Atmospheric Deposition of Nutrients: Iron

Atmospheric aerosols provide a pathway for the delivery of chemical species to surface waters. This atmospheric source of chemical species is believed to control primary productivity in various oceanic regions. For example, iron is an important rate limiting micro nutrient in high nutrient low chlorophyll (HNLC) regions of the oceans, and the dominant source of iron to these regions is from atmospheric deposition.

Primary productivity in oligotrophic (nutrient deficient) regions of the oceans is also hypothesized to be controlled by atmospheric deposition. In these oligotrophic regions, nitrogen fixing microorganisms provide a source of "new" nitrogen for primary productivity. These microorganisms use a nitrogenase enzyme that has a high iron requirement to fix the nitrogen. Therefore the ability of these microorganisms to fix nitrogen is believed to be dependent on the availability of iron.

The dominant source of iron to these oligotrophic regions is also from atmospheric deposition however the chemical speciation of iron in the remote atmosphere is not well characterized, This chemical speciation is critical to assessing the ability of marine microorganisms to utilize this micronutrient. Several factors may control this labile fraction of iron in the atmosphere including different terrestrial sources (e.g., wind blow dust, anthropogenic emissions) and the chemical processing of aerosol iron as it is transported through the atmosphere.

This processing includes photochemical reductive dissolution mechanisms occurring in deliquesced aerosol or cloudwater systems. Dr. Siefert's research is investigating the temporal and spatial distribution of labile iron over the remote oceans and the factors that control the chemical speciation of iron.

Organic Phosphorus in Soils
Phytic acid is a common organic phosphorus molecule that is common in agriculture. It is produced by crops and also used in the feed for livestock. The degradation of phytic acid results in the release of phosphate which can contribute to eutrophication in estuaries and lakes through infiltration of groundwater. Dr. Siefert has been involved with projects investigating the factors that control this degradation of phytic acid in soils.
Atmospheric Processing of Aerosols

Understanding the chemical composition and speciation in atmospheric aerosols is critical to understanding their behavior after deposition, and begins with understanding the aerosol sources (e.g., windblown dust, sea salt, combustion). However, chemical processing (e.g., cloud processing) in the atmosphere can alter the composition and speciation of atmospheric aerosols as they are transported through the atmosphere.

For example, iron is known to undergo various aqueous (photo)redox reactions in the atmosphere. Therefore iron speciation and oxidation state are expected to change as aerosol particles are processed in clouds. Ultimately, it is important to understand these processes since the bioavailable fraction of iron is directly related to its chemical speciation and oxidation state.

Atmospheric processing is also important to nitrogen species. For example, ammonia exists both in the gas-phase and aerosol-phase in the atmosphere and the deposition rate of ammonia is dependent on its phase. Again, atmospheric processing can alter the fraction of ammonia in each phase and therefore effect its deposition rate.

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