Presentation Title

Effects of the Oxidation/Reduction Potential on Sediment Ammonia Release in Surface Waters

Location

Nessmith-Lane Atrium

Session Format

Poster Presentation

Research Area Topic:

Engineering and Material Sciences - Civil

Abstract

In recent years, rapid urbanization and agricultural intensification have led to widespread nutrient enrichment of surface waters. From this nutrients, ammonia, a common nitrogen species, is of great concern because it exacerbates the proliferation of nuisance aquatic plants and algae, increases oxygen demand, function as disinfection by-product precursor, and is toxic to aquatic biota under certain conditions. Once ammonia enter surface waters, it is quickly oxidized to nitrate (provided enough dissolved oxygen), consumed by aquatic biota, or it may directly sorb into the sediment surface. Nonetheless, under certain conditions (e.g. anaerobic environments, or low nitrifiers activity) ammonia can be released from the sediments increasing its concentration in the water column. Preliminary results showed that sediment ammonia release occurs in both aerobic and anaerobic environment. However the mechanisms controlling ammonia release remain unclear. The objective of this study is to determine the mechanisms and conditions that stimulate ammonia desorption from the sediments.

Laboratory experiments revealed that ammonia concentrations in microcosm setups seeded with sediments from the Occoquan Reservoir (Virginia) and Ogeechee River (Georgia) increased to values as high as 3 mg/L-N in the absence of oxygen. Additionally, cation exchange analyses performed on the sediments revealed that ammonia extracted from the sediments can reach values higher than 15 mg-N/L, demonstrating the high capacity for the sediment to continuously produce and sorb ammonia. Results further showed that the sediment sorption capacity for ammonia varied when transitioning from an oxidized to a reduced environment at the sediment-water interface. These results suggest that sediments may lose their sorption capacity in anaerobic environments, which are common conditions in bottom waters of productive surface water systems, releasing high amounts of ammonia into the water column. Advanced characterization techniques (i.e. X-ray Photo Electron Spectroscopy) will be used to further study the mechanisms affecting the sediment ammonia sorption capacity in both oxidized and reduced environments. It is expected that results from this study will help to better understand the mechanisms controlling ammonia cycling in surface waters contributing to the overall knowledge of the nitrogen cycle.

Presentation Type and Release Option

Presentation (Open Access)

Start Date

4-16-2016 2:45 PM

End Date

4-16-2016 4:00 PM

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Apr 16th, 2:45 PM Apr 16th, 4:00 PM

Effects of the Oxidation/Reduction Potential on Sediment Ammonia Release in Surface Waters

Nessmith-Lane Atrium

In recent years, rapid urbanization and agricultural intensification have led to widespread nutrient enrichment of surface waters. From this nutrients, ammonia, a common nitrogen species, is of great concern because it exacerbates the proliferation of nuisance aquatic plants and algae, increases oxygen demand, function as disinfection by-product precursor, and is toxic to aquatic biota under certain conditions. Once ammonia enter surface waters, it is quickly oxidized to nitrate (provided enough dissolved oxygen), consumed by aquatic biota, or it may directly sorb into the sediment surface. Nonetheless, under certain conditions (e.g. anaerobic environments, or low nitrifiers activity) ammonia can be released from the sediments increasing its concentration in the water column. Preliminary results showed that sediment ammonia release occurs in both aerobic and anaerobic environment. However the mechanisms controlling ammonia release remain unclear. The objective of this study is to determine the mechanisms and conditions that stimulate ammonia desorption from the sediments.

Laboratory experiments revealed that ammonia concentrations in microcosm setups seeded with sediments from the Occoquan Reservoir (Virginia) and Ogeechee River (Georgia) increased to values as high as 3 mg/L-N in the absence of oxygen. Additionally, cation exchange analyses performed on the sediments revealed that ammonia extracted from the sediments can reach values higher than 15 mg-N/L, demonstrating the high capacity for the sediment to continuously produce and sorb ammonia. Results further showed that the sediment sorption capacity for ammonia varied when transitioning from an oxidized to a reduced environment at the sediment-water interface. These results suggest that sediments may lose their sorption capacity in anaerobic environments, which are common conditions in bottom waters of productive surface water systems, releasing high amounts of ammonia into the water column. Advanced characterization techniques (i.e. X-ray Photo Electron Spectroscopy) will be used to further study the mechanisms affecting the sediment ammonia sorption capacity in both oxidized and reduced environments. It is expected that results from this study will help to better understand the mechanisms controlling ammonia cycling in surface waters contributing to the overall knowledge of the nitrogen cycle.