期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：16
页码：5808-5812
DOI：10.1073/pnas.1319441111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Nitrogen stable isotope ratio ({delta}15N) in Greenland snow nitrate and in North American remote lake sediments has decreased gradually beginning as early as [~]1850 Christian Era. This decrease was attributed to increasing atmospheric deposition of anthropogenic nitrate, reflecting an anthropogenic impact on the global nitrogen cycle, and the impact was thought to be amplified [~]1970. However, our subannually resolved ice core records of {delta}15N and major ions (e.g., [IMG]/medium/pnas.1319441111i1.gif" ALT="Formula ">, [IMG]/medium/pnas.1319441111i2.gif" ALT="Formula ">) over the last [~]200 y show that the decrease in {delta}15N is not always associated with increasing [IMG]/medium/pnas.1319441111i3.gif" ALT="Formula "> concentrations, and the decreasing trend actually leveled off [~]1970. Correlation of {delta}15N with H+, [IMG]/medium/pnas.1319441111i4.gif" ALT="Formula ">, and HNO3 concentrations, combined with nitrogen isotope fractionation models, suggests that the {delta}15N decrease from [~]1850-1970 was mainly caused by an anthropogenic-driven increase in atmospheric acidity through alteration of the gas-particle partitioning of atmospheric nitrate. The concentrations of [IMG]/medium/pnas.1319441111i5.gif" ALT="Formula "> and [IMG]/medium/pnas.1319441111i6.gif" ALT="Formula "> also leveled off [~]1970, reflecting the effect of air pollution mitigation strategies in North America on anthropogenic NOx and SO2 emissions. The consequent atmospheric acidity change, as reflected in the ice core record of H+ concentrations, is likely responsible for the leveling off of {delta}15N [~]1970, which, together with the leveling off of [IMG]/medium/pnas.1319441111i7.gif" ALT="Formula "> concentrations, suggests a regional mitigation of anthropogenic impact on the nitrogen cycle. Our results highlight the importance of atmospheric processes in controlling {delta}15N of nitrate and should be considered when using {delta}15N as a source indicator to study atmospheric flux of nitrate to land surface/ecosystems.
