EAPSI: Stable nitrogen isotopes as indicators of pollution sources in the Yinchuan Plain, China

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Over the past 150 years, human activities have doubled the concentration of reactive nitrogen (Nr) entering the terrestrial nitrogen cycle. Excess nitrogen in the environment is detrimental to human health and has been linked to soil acidification, eutrophication, and decreases in biodiversity. China's rapid economic development in the last 30 years has made it the world's largest emitter of Nr. As a result, China is currently experiencing some of the worst pollution problems on Earth. Since Nr affects the soil, water, and air, a better understanding of how nitrogen moves between point sources and ecosystem components is necessary in order to develop strong models for predicting the outcomes of mitigation efforts. This project will investigate the feasibility of using the nitrogen isotope signatures of tree rings, foliage, and soil as indicators of changes in pollution sources and nitrogen uptake of plants in the Yinchuan Plain, China. Due to high pollution levels within the study area, the research will serve as a good case study for testing these methods then potentially applying them elsewhere, including the United States, which also experiences the harmful effects of high reactive nitrogen emissions. The research will be conducted in collaboration with Dr. Hui Qian at Chang'an University in Xi'an, China. Differences in the delta15N signature of tree rings, foliage, and soil have been used to infer changes in the cycling of N in the surrounding ecosystem. Tree ring 15N can indicate changes in the source of N deposition. Additionally, stable isotopes of carbon (delta13C) and oxygen (delta18O) as well as dendrochronological methods will be used to determine if there are changes in the physiological functioning and growth rates of forests in the Yinchuan Plain due to increases in Nr emissions within the valley. This NSF EAPSI award is funded in collaboration with the Chinese Ministry of Science and Technology.