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Rachel Brockamp, Canada

Coupled Iron Reduction-Ammonium Oxidation (Feammox) in Alkaline Soils Polluted With Nitrogen.

Applying nitrogen (N) fertilizers to N-limited soils can stimulate plant and microbe growth, increasing yield. However, applying excess N fertilizer can cause adverse side effects such as groundwater and surface water pollution, greenhouse gas production, soil acidification, and health issues among humans and wildlife. Common N fertilizers can include ammonium (NH4+), nitrite (NO2-), and nitrate (NO3-). The average soil N input and NH3 emissions have increased in Canada over the past 40 years, and the consequences are becoming apparent. Excess wastewater and groundwater N is typically treated via wastewater treatment plants and permeable reactive barriers. These technologies stimulate two N-removal pathways, denitrification and anaerobic ammonium oxidation (Anammox), which consume NO3- and/or NO2- and/or NH4+ and generate inert nitrogen gas (N2). However, a promising alternative N-removal pathway may improve bioremediation, but has not been explored in Canadian soils. In this iron ammonium oxidation (Feammox) pathway, ferric iron (Fe) is reduced to ferrous iron and NH4+ is oxidized to NO2- or N2.

I explored Feammox activity in alkaline soils from a N-polluted site in Alberta. I prepared oxygen-free (anaerobic) soil slurries and applied treatment combinations of ferric citrate, ferrihydrite, and NH4Cl in a 118-day anaerobic incubation. My purpose was to discover which amendment combinations stimulated the greatest NH4+-N loss via four biostimulation experiments during the incubation. I found that adding ferric citrate and NH4Cl concurrently simulated the greatest dissolved NH4+-N loss, with 49 ± 6.7% and 58 ± 20.8% dissolved NH4+-N loss in two of the biostimulation experiments. Furthermore, evidence of Fe reduction was apparent in the first of those biostimulation experiments. Although ferrihydrite successfully stimulated Feammox in previous work that involved acidic soils, ferrihydrite did not stimulate significant NH4+-N loss in my incubation. These results imply that ferric citrate is more bioavailable and stimulated greater dissolved NH4+ loss than ferrihydrite in near-neutral to alkaline pH conditions, which is important for future bioremediation research.

Lola Visschers, Australia

Tracing wetland responses to saltwater intrusion along the coast of Amapá state, Brazil.

Coastal wetlands in the state of Amapá contribute significant ecosystem services to the environmental, social and economic sectors of the region. Climate change, however, threatens these coastal wetlands by changing local hydrological regimes. In this study, GIS and remote sensing techniques were used to survey mangroves as an indicator of saltwater intrusion to understand the historical coastal dynamics of the Amapá region over a period of 35 years. There was a significant gain of mangrove area over the study period, with the main gains occurring inland. Notably, mangroves appeared to grow alongside extending rivers and channels, indicating the presence of saltwater intrusion. Sea level rise was identified as a significant predictor of mangrove area while coastal erosion was not a significant predictor. It is necessary to understand historical coastal wetland dynamics in order to anticipate future trends. The ability to predict future threats is important in designing effective management strategies and adaptation plans that will protect coastal societies and ecosystems against saltwater intrusion.