Wetlands as Sinks for Reactive Nitrogen at Continental and Global Scales: A Meta-Analysis

Abstract

Wetlands support physical and ecological functions that result in valuable services to society, including removal of reactive nitrogen (Nr) from surface water and groundwater. We compiled published data from wetland studies worldwide to estimate total Nr removal and to evaluate factors that influence removal rates. Over several orders of magnitude in wetland area and Nr loading rates, there is a positive, near-linear relationship between Nr removal and Nr loading. The linear model (null hypothesis) explains the data better than either a model of declining Nr removal efficiency with increasing Nr loading, or a Michaelis–Menten (saturation) model. We estimate that total Nr removal by major classes of wetlands in the contiguous U.S. is approximately 20–21% of the total anthropogenic load of Nr to the region. Worldwide, Nr removal by wetlands is roughly 17% of anthropogenic Nr inputs. Historical loss of 50% of native wetland area suggests an equivalent loss of Nr removal capacity. Expanded protection and large-scale restoration of wetlands should be considered in strategies to re-balance the global nitrogen cycle and mitigate the negative consequences of excess Nr loading.

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Acknowledgments

We appreciate the preliminary review by Dan Sobota, and helpful suggestions from anonymous reviewers. The views expressed in this article are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency. This is contribution 1392 from the Gulf Ecology Division, and a product of EPA’s Ecosystem Services Research Program.

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Correspondence to Stephen J. Jordan.

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SJ conceived the study, performed final data analysis, and wrote much of the paper; JS performed much of the literature review, compiled data, and contributed to preliminary data analysis and writing; JN wrote portions of the manuscript.

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Jordan, S.J., Stoffer, J. & Nestlerode, J.A. Wetlands as Sinks for Reactive Nitrogen at Continental and Global Scales: A Meta-Analysis. Ecosystems 14, 144–155 (2011). https://doi.org/10.1007/s10021-010-9400-z

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Key words

  • nitrogen
  • reactive nitrogen
  • wetlands
  • denitrification
  • nitrogen removal
  • nitrogen loading