Related Experiment Video
Updated: May 11, 2026
08:05
Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O
Published on: October 7, 2020
The global nitrogen cycle in the twenty-first century
David Fowler1, Mhairi Coyle, Ute Skiba
1NERC Centre for Ecology and Hydrology, Penicuik, UK. dfo@ceh.ac.uk
Summary
Human activities contribute half of the global reactive nitrogen (Nr) fixed annually. Agricultural fertilizer use and emissions lead to nitrogen pollution in air and water, impacting ecosystems and potentially long-term climate feedbacks.
Area of Science:
- Environmental Chemistry
- Biogeochemistry
- Atmospheric Science
Background:
- Global nitrogen fixation supplies essential reactive nitrogen (Nr) to ecosystems.
- Anthropogenic activities now account for approximately half of the annual global Nr fixation.
Observation:
- Agricultural fertilizer use is a primary source of anthropogenic Nr on land.
- Nitrogen compounds like ammonia (NH3) and nitrogen oxides (NOx) are emitted into the atmosphere.
- Nitrate (NO3(-)) leaches from agricultural land into waterways and oceans.
Findings:
- Atmospheric Nr transforms into secondary pollutants such as ozone and aerosols.
- Oceanic Nr processing is significantly influenced by land-based Nr inputs and atmospheric deposition.
- Terrestrial ecosystems have shorter Nr lifetimes (decades) compared to potentially longer oceanic lifetimes.
Implications:
- Understanding Nr cycling is crucial for managing nitrogen pollution.
- Longer oceanic Nr lifetimes suggest slow responses to emission control measures.
- Reactive nitrogen's atmospheric processing contributes to air quality issues and climate-relevant compounds.
Related Concept Videos
01:49The Nitrogen Cycle
Nitrogen atoms, present in all proteins and DNA, are recycled between abiotic and biotic components of the ecosystem. However, the primary form of nitrogen on Earth is nitrogen gas, which cannot be used by most animals and plants. Thus, nitrogen gas must first be converted into a usable form by nitrogen-fixing bacteria before it can be cycled through other living organisms. The use of nitrogen-containing fertilizers and animal waste products in human agriculture has greatly influenced the...
01:20Overview of Nitrogen Metabolism
Nitrogen is a very important element for life because it is a major constituent of proteins and nucleic acids. It is a macronutrient, and in nature, it is recycled from organic compounds and stored in the form of ammonia, ammonium ions, nitrate, nitrite, or nitrogen gas by many metabolic processes. Many of these metabolic processes are carried out only by prokaryotes.
The largest pool of nitrogen available in the terrestrial ecosystem is gaseous nitrogen (N2) from the air, but this nitrogen...
The largest pool of nitrogen available in the terrestrial ecosystem is gaseous nitrogen (N2) from the air, but this nitrogen...
01:22Inorganic Nitrogen Assimilation
Nitrogen is an essential element in biological systems, forming a crucial component of proteins, nucleic acids, and other cellular constituents. Many bacteria and archaea acquire nitrogen in the form of nitrate (NO₃⁻) or ammonia (NH₃), which are then assimilated into biomolecules through specific enzymatic pathways.Assimilatory Nitrate ReductionWhen nitrate enters the cell, it undergoes a two-step reduction process known as assimilatory nitrate reduction. Initially, the enzyme nitrate reductase...
00:54What are Biogeochemical Cycles?
The most common elements in organic molecules, carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus, are only available in the ecosystem in limited amounts. Therefore, these nutrients must be recycled through both biotic and abiotic components of the ecosystem, in processes generally called biogeochemical cycles.
01:14The Carbon Cycle
Carbon is the basis of all organic matter on Earth, and is recycled through the ecosystem in two primary processes: one in which carbon is exchanged among living organisms, and one in which carbon is cycled over long periods of time through fossilized organic remains, weathering of rocks, and volcanic activity. Human activities, including increased agricultural practices and the burning of fossil fuels, has greatly affected the balance of the natural carbon cycle.
01:21The Phosphorus Cycle
Unlike carbon, water, and nitrogen, phosphorus is not present in the atmosphere as a gas. Instead, most phosphorus in the ecosystem exists as compounds, such as phosphate ions (PO43-), found in soil, water, sediment and rocks. Phosphorus is often a limiting nutrient (i.e., in short supply). Consequently, phosphorus is added to most agricultural fertilizers, which can cause environmental problems related to runoff in aquatic ecosystems.