H33C-1615
Dynamic Kinetics of Nitrogen Cycle in Groundwater-Surface Water Interaction Zone at Hanford Site
Wednesday, 16 December 2015
Poster Hall (Moscone South)
Yuanyuan Liu1, Chongxuan Liu2, Yunde Liu3, Fen Xu3, Ailan Yan4, Liang Shi2, John M Zachara2, Yuqian Gao2, Weijun Qian2, William Nelson2, Jim Fredrickson2, Lirong Zhong5 and Christopher Thompson1, (1)Pacific Northwest National Laboratory, Geochemistry, Richland, WA, United States, (2)Pacific Northwest National Laboratory, Richland, WA, United States, (3)China University of Geosciences, School of Environmental Studies, Wuhan, China, (4)Zhejiang University of Water Research and Electric Power, Hangzhou, China, (5)Joint Global Change Research Institute, College Park, MD, United States
Abstract:
Nitrogen cycle carried out by microbes is an important geobiological process that has global implications for carbon and nitrogen cycling and climate change. This presentation describes a study of nitrogen cycle in groundwater-surface water interaction zone (GSIZ) at the US Department of Energy’s Hanford Site. Groundwater at Hanford sites has long been documented with nitrate contamination. Nearby Columbia River stage changes of up to 3 m every day because of daily discharge fluctuation from upstream Priest Rapids Dam; resulting an exchange of groundwater and surface water in a short time period. Yet, nitrogen cycle in the GSIZ at Hanford Site remains unclear. Column studies have been used to identify nitrogen metabolism pathways and investigate kinetics of nitrogen cycle in groundwater saturated zone, surface water saturated zone, and GSIZ. Functional gene and protein abundances were determined by qPCR and PRISM-SRM (high-pressure, high-resolution separations coupled with intelligent selection and multiplexing for sensitive selected reaction monitoring) to identify key enzymatic reactions and metabolic pathways of nitrogen cycle. The results showed that dissimilatory nitrate reduction to ammonium (DNRA) competed with denitrification under anaerobic conditions, reducing 30% of NO3- to NH4+, a cation strongly retained on the sediments. As dissolved oxygen intruded the anaerobic zone with river water, NH4+ was oxidized to NO3-, increasing the mobility of NO3-. Multiplicative Monod models were established to describe nitrogen cycle in columns fed with O2 depleted synthetic groundwater and O2 saturated synthetic river water, respectively. The two models were then coupled to predict the dynamic kinetics of nitrogen cycle in GSIZ.
