The abstracts of papers are given below,

• Junu Shrestha, Jean Christophe Clement, Joan G. Ehrenfeld, Peter R Jaffe. “Effects of Vegetation Removal and Urea Application on Iron and Nitrogen Redox Chemistry in Riparian Forested Soils.” Water, Air and Soil Pollution, (To Appear)
• Abstract: Riparian wetlands are subject to nitrogen enrichment from upgradient agricultural and urban land uses, and also from flooding by nitrogen (N)-enriched surface waters. The effects of this N enrichment on wetland soil biogeochemistry may be mediated by both the presence of plants and the presence of redox-active compounds, specifically iron (Fe) oxides, in the soil. We propose that plants and Fe compounds can exert competing controls on N forms and quantities in riparian wetland soils. Despite the extensive research on wetland N cycling, the relative importance of these two factors on nitrogen is poorly known, especially for forested wetlands. This study evaluates the responses of the N and the Fe cycles to N enrichment in a riparian forested wetland, contrasting vegetated field plots with plots where the vegetation was removed to test the role of plants. Furthermore, in vitro anaerobic incubations of the experimental soils were performed to track Fe chemical changes over time under anoxic or flooded conditions. Wetland soils treated with N in form of urea, as expected had significantly higher amounts inorganic nitrogen. In the soils where vegetation was also removed, in addition to inorganic nitrogen pool, increase in organic nitrogen pool was also observed. The results demonstrate the role of vegetation in limiting the effects excess urea has on different soil nitrogen pools. Results from anaerobic incubation of the experimental soils demonstrated the effects of N-enrichment on the wetland Fe cycle. The effects of excess nitrogen and the role of vegetation on the Fe cycle in riparian wetland soil became more evident during anaerobic incubation experiments. At the end of the field experiment, Fe concentrations in the soils under the treatments were not significantly different from the control soils at the 5% confidence level. However, during the anaerobic incubation experiment of soils collected at the end of the experiment from these plots, the N-enriched soils and the unvegetated soils maintained significantly elevated concentrations of reducible Fe(III) for the initial two week period of incubation, and the soils collected from the plots with boththe treatments had the highest Fe(III) concentrations. After 20 days of incubation, however, the Fe(III) concentrations decreased to the similar concentrations in all the incubated soils. The study clarifies the roles vegetation play in mediating the effects of N enrichment and also demonstrates that N enrichment does affect wetland redox cycle, which has strong implications on ecosystem services such as water quality improvement.
• J. Shrestha, J. Rich, P. Jaffe and J. Ehrenfeld. “Oxidation of Ammonium to Nitrite under Iron Reducing Conditions in Wetland Soils: Laboratory Demonstration and Field Push Pull Tests.” Soil Science, March 2009.
• Abstract: Nitrite (NO₂^-) in soils has been observed under a variety of field conditions. The formation of NO₂^- in soils is possible during nitrification or denitrification depending on the soil conditions. This study presents a series of experiments performed at different scales that demonstrate the production of NO₂^- under iron-reducing conditions, in the absence of an initial nitrate pool. These experiments were performed either in a riparian wetland in New Jersey or in laboratory experiments using soils from the same location. The rates of use of NO₂^- and ammonium (NH₄⁺) determined in situ by performing push-pull experiments were of the same magnitude, supporting the observation of a steady-state NO₂^- pool under such anaerobic conditions. An isotope experiment performed with ¹⁵NH₄⁺ conclusively showed an existence of a pathway linking NH₄⁺ to dinitrogen gas under anaerobic iron-reducing conditions, in the absence of initial nitrate or NO₂^- . Such observations indicate a possibility for the complete removal of NH₄⁺ from wetland soils under anaerobic conditions that develop when soils are water saturated.
• J. C. Clement, J. Shrestha, J. Ehrenfeld and P. Jaffe. “Ammonium Oxidation Coupled to Dissimilatory Reduction of Iron Under Anaerobic Conditions in Wetland Soils.” Soil Biology and Biochemistry, May 2005.
• Abstract: In exploring the dynamics of iron and nitrogen cycling in sediments from riparian forests we have observed a redox reaction that has not been previously described. During incubations of soil slurries under strictly anaerobic conditions, we repeatedly measured an unexpected production of both nitrite (NO₂^-) and ferrous iron [Fe(II)]. Using this indirect evidence we hypothesize that, under anaerobic conditions, there is a biological process that uses ferric iron [Fe(III)] as an electron acceptor while oxidizing ammonium (NH₄⁺) to NO₂^- for energy production. This NH₄⁺ oxidation under iron reducing anaerobic conditions is thermodynamically feasible and is potentially a critical component of the N cycle in saturated sediments.