Nitrogen loss by anaerobic ammonium oxidation in unconfined aquifer soils

Shanyun Wang,Siyan Zhao,Dirk Radny,Mike S M Jetten,Shuangbing Huang,Michael Berg,Guibing Zhu,Linjie Zhuang

doi:10.1038/srep40173

Abstract

Anaerobic ammonium oxidation (anammox) is recognized as an important process for nitrogen cycling, yet little is known about its role in the subsurface biosphere. In this study, we investigated the presence, abundance, and role of anammox bacteria in upland soil cores from Tianjin, China (20 m depth) and Basel, Switzerland (10 m depth), using isotope-tracing techniques, (q)PCR assays, and 16 S rRNA & hzsB gene clone libraries, along with nutrient profiles of soil core samples. Anammox in the phreatic (water-saturated) zone contributed to 37.5–67.6% of the N-loss (up to 0.675 gN m−2d−1), with anammox activities of 0.005–0.74 nmolN g−1soil h−1, which were even higher than the denitrification rates. By contrast, no significant anammox was measured in the vadose zone. Higher anammox bacterial cell densities were observed (0.75–1.4 × 107copies g−1soil) in the phreatic zone, where ammonia-oxidizing bacteria (AOB) maybe the major source of nitrite for anammox bacteria. The anammox bacterial cells in soils of the vadose zone were all <103copies g−1soil. We suggest that the subsurface provides a favorable niche for anammox bacteria whose contribution to N cycling and groundwater nitrate removal seems considerably larger than previously known.

Highlights

Was first observed in Massachusetts, USA using isotope tracers[24]
The presence of anammox bacteria was established by amplification of the hydrazine synthase β-subunit (hzsB) and 16 S rRNA gene using primers specific for anammox
The positive Polymerase chain reaction (PCR) products of anammox bacterial gene were only obtained in aquifer soils

Summary

Introduction

Anammox in groundwater was investigated at several sites, such as Mansfield, UK25, Waterloo, Canada[26], and in an in situ experiment at Cape Cod, MA, USA27 where the activity and contribution of anammox varied significantly due to groundwater mobility and allochthonous pollution. Prior studies have not determined whether anammox occurs only in fluent groundwater or whether it occurs in local aquifer soils, where the mechanism of anammox N loss appears different because of the interacting forms. The aim of the present study was to investigate the distribution, activity, contribution and microbial mechanism of anammox in soil profiles that represent both the vadose water-unsaturated zone and the phreatic zone of two unconfined aquifers in China and in Switzerland, in order to determine whether anammox is significant in subsurface environments. The term “aquifer” is defined as the phreatic water-saturated zone below the groundwater table of an unconfined aquifer, while the term “non-aquifer” is used to describe the vadose water-unsaturated zone above the groundwater table

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Conclusion