Analyzing Dryland Nitrogen Emissions

Introduction

Previous research has indicated that soil wetting and drying cycles can trigger significant pulses of nitrogen emissions in the form of nitric oxide (NO) and nitrous oxide (N₂O). These emissions arise from biological and abiotic processes, with their intensity varying according to the degree of aridity.

Certain dryland regions have exhibited some of the world’s highest NO and N₂O emission pulses. Given the anticipated expansion of dryland areas due to climate change, it becomes imperative to comprehend the mechanisms underlying nitrogen emissions in these ecosystems, enabling a better understanding of their impact on climate and air quality.

In the article “Rapid nitrate reduction produces pulsed NO and N₂O emissions following wetting of dryland soils”, researchers from the University of California Riverside investigated nitrogen emissions at two dryland sites (desert and chaparral) in Southern California.¹ The primary objective of this research was to investigate the factors contributing to NO and N₂O emissions in dryland areas following soil wetting with isotopically enriched nitrate and ammonium solutions.

Furthermore, the study aimed to elucidate how nitrogen availability affects the magnitude of these emissions. Various biological and abiotic processes influence these emissions, including nitrification, denitrification, and chemodenitrification. These processes can occur simultaneously, making it challenging to pinpoint their individual contributions to nitrogen emissions.

Methods

To understand the various factors contributing to the NO and N₂O emissions, the authors introduced ¹⁵N-labeled NO₃⁻ or NH₄⁺ solutions into the dry soils. They utilized an automated chamber system connected to an NO analyzer (based on UV measurement of the depletion of ozone titrated by NO) and to a laser-based ABB Enhanced Performance QC Benchtop Isotopic Nitrous Oxide Analyzer (GLA451-N₂OI2). Additionally, the researchers also quantified NH₃ emissions using passive samplers as a relative index of the amount of NH₃ in soil spore space, which could be accessible to nitrifying organisms.

Results

Large N₂O emission pulses were observed within minutes after wetting. However, rapid reduction of NO₃⁻ produced pulsed N₂O emissions at both sites within 15 minutes of adding water. This was unexpected as denitrification is an anaerobic process and not thought to dominate in well-aerated coarse-textured soils during dry summer months.

This was possibly due to the rapid onset of microbial respiration consumed sufficient O₂ to stimulate N₂O production via denitrification immediately after adding water, or soil aggregates may have sustained a viable denitrifier population within anoxic microsites throughout the hot and dry summer. They also observed that the N₂O emissions were insensitive to the experimentally added nitrogen as the N₂O pulse magnitude did not increase in proportion to the amount of ammonium or nitrate added.

In contrast to N₂O, NO emissions lasted for 24 hours in both types of soils and were governed by nitrogen limitation of multiple N cycling processes, suggesting that N-limited NO production pathways could increase in response to higher rates of atmospheric nitrogen deposition.

This work demonstrates that nitrate can be rapidly reduced within minutes of wetting summer-dry desert soils, producing significant N₂O emission pulses and that multiple processes contribute to prolonged NO emissions. These wetting-induced nitrogen trace gas production pathways are widespread across ecosystems experiencing repeated drying–wetting cycles and are likely to become increasingly important sources of atmospheric NO and N₂O as global precipitation regimes become more variable. These mechanisms represent significant pathways of ecosystem nitrogen loss, contributing to regional air quality and global climate dynamics.

References and Further Reading

1. Krichels, A.H., et al. (2022) Rapid nitrate reduction produces pulsed NO and N₂O emissions following wetting of dryland soils. Biogeochemistry. https://doi.org/10.1007/s10533-022-00896-x

SDGs, Targets, and Indicators

1. Sustainable Development Goal: Goal 13 – Climate Action

• Target 13.2: Integrate climate change measures into national policies, strategies, and planning.
• Indicator 13.2.1: Number of countries that have integrated mitigation, adaptation, impact reduction, and early warning into their national planning.

2. Sustainable Development Goal: Goal 15 – Life on Land

• Target 15.3: By 2030, combat desertification, restore degraded land and soil, including land affected by desertification, drought, and floods, and strive to achieve a land degradation-neutral world.
• Indicator 15.3.1: Proportion of land that is degraded over total land area.

3. Sustainable Development Goal: Goal 17 – Partnerships for the Goals

• Target 17.16: Enhance the Global Partnership for Sustainable Development, complemented by multi-stakeholder partnerships that mobilize and share knowledge, expertise, technology, and financial resources.
• Indicator 17.16.1: Number of countries reporting progress in multi-stakeholder development effectiveness monitoring frameworks that support the achievement of the sustainable development goals.

Analysis:

1. The issues highlighted in the article are connected to Sustainable Development Goals (SDGs) 13 (Climate Action) and 15 (Life on Land). The article discusses the impact of nitrogen emissions on climate and air quality in dryland ecosystems, which aligns with SDG 13’s focus on addressing climate change. Additionally, the article emphasizes the need to understand nitrogen emissions in drylands, which relates to SDG 15’s objective of combating desertification and restoring degraded land.

2. Based on the article’s content, the specific targets under the identified SDGs are:
– Target 13.2: Integrate climate change measures into national policies, strategies, and planning.
– Target 15.3: By 2030, combat desertification, restore degraded land and soil, including land affected by desertification, drought, and floods, and strive to achieve a land degradation-neutral world.

3. The article does not explicitly mention any indicators related to the identified targets. However, the article discusses the use of advanced analytical tools, such as the ABB laser-based Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) Enhanced Performance QC Benchtop Isotopic Nitrous Oxide Analyzer, to measure N2O emissions and isotopic composition. These measurements can be considered as indicators to measure progress towards understanding nitrogen emissions and their impact on climate and air quality in drylands.

Table: SDGs, Targets, and Indicators

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Source: azom.com

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