Since the mid-20th century, scientists have been warning about the negative effects of excess nitrogen on natural ecosystems.
But a new study suggests that some parts of the world are experiencing a dramatic drop in the availability of nitrogen.
Over the last century, human industry and agriculture have more than doubled the total global supply of reactive nitrogen.
This nitrogen can be concentrated in streams, inland lakes and coastal waters, resulting in an accumulation of nutrients, oxygen-poor dead zones and harmful algae blooms.
However, concomitant increases in carbon dioxide along with other global changes have increased demand for nitrogen from plants and microbes.
In many areas of the world that are not exposed to excessive supply of nitrogen from humans, nitrogen availability is actually declining, with important consequences for plant and animal growth.
“There is both too much nitrogen and too little nitrogen on earth at the same time,” said Rachel Mason, lead author of the study and former postdoctoral fellow at the National Socio-Environmental Synthesis Center.
Nitrogen makes up 79 percent of the Earth’s atmosphere and is an essential element in proteins. As such, availability is crucial for the growth of plants and the animals that eat them
Changes in the nitrogen cycle can be detected by monitoring the nitrogen supply of the ecosystem, the nitrogen cycle of the inland soil, the nitrogen status of the plants and the loss of nitrogen. Models show that nitrogen deposition in Europe declines from a peak in 1980 and stabilizes close to current levels (Figure A)
Nitrogen makes up 79 percent of the Earth’s atmosphere and is an essential element in proteins.
As such, availability is crucial for the growth of plants and the animals that eat them.
Gardens, forests and fisheries are almost all more productive when fertilized with moderate amounts of nitrogen.
If the plants’ nitrogen becomes less available, the plants grow more slowly and their leaves are less nutritious for insects, potentially reducing growth and reproduction – not only of insects, but also of the birds and bats that feed on them.
“When nitrogen is less available, all living things stay on the element for longer, slowing the flow of nitrogen from one organism to another through the food chain,” explained Andrew Elmore, senior author of the paper and professor of landscape ecology at the University of Maryland Center for Environmental Science.
‘That’s why we can say that the nitrogen cycle is getting slower.’
Gardens, forests and fisheries are almost all more productive when fertilized with moderate amounts of nitrogen
Ozone may weaken one of the Earth’s most important cooling mechanisms
Ozone may weaken one of the Earth’s most important cooling mechanisms and heat our planet even more than we realize, warns a new study.
An international team of scientists discovered changes in ozone levels in two layers of the Earth’s atmosphere.
In the troposphere (the lowest layer of the Earth’s atmosphere), ozone has risen, which is bad news because it acts as a greenhouse gas, captures outgoing long-wave radiation and thereby warms the Earth.
Meanwhile, ozone levels in the stratosphere (the next layer up from the troposphere) have dropped, which is also bad news, according to the team.
Both of these changes have weakened a natural cooling mechanism in the southern ocean and in turn contributed to global warming.
Researchers reviewed long-term, global, and regional studies and found evidence of declining nitrogen availability.
For example, grasslands in central North America have experienced declining nitrogen availability for hundreds of years, and cattle grazing these areas have had less protein in their diet over time.
Meanwhile, many forests in North America and Europe have experienced nutritional declines for decades or longer.
These declines are likely to be caused by several environmental changes, one of which is elevated atmospheric carbon dioxide levels.
Atmospheric carbon dioxide has reached its highest level in millions of years, and terrestrial plants are exposed to about 50 percent more of this essential resource than just 150 years ago.
Elevated atmospheric carbon dioxide fertilizes plants, allowing faster growth but diluting the plants’ nitrogen in the process, leading to a cascade of effects that lower the availability of nitrogen.
In addition to rising atmospheric carbon dioxide, warming and disturbances, including wildfires, can also reduce availability over time.
Declining nitrogen availability is also likely to limit the ability of plants to remove carbon dioxide from the atmosphere.
Currently, plant biomass stores almost as much carbon as is contained in the atmosphere, and carbon storage of biomass increases every year as carbon dioxide levels rise.
Declining nitrogen availability, however, jeopardizes the annual increase in plant carbon storage by imposing restrictions on plant growth.
Excess nitrogen can be concentrated in streams, inland lakes and coastal water bodies, resulting in an accumulation of nutrients (eutrophication), oxygen-poor dead zones and harmful algae blooms
Declining nitrogen availability is also likely to limit the ability of plants to remove carbon dioxide from the atmosphere
Therefore, climate change models currently trying to estimate carbon stored in biomass, including trends over time, must take into account nitrogen availability.
“The strong indications of declining nitrogen availability in many places and contexts are another important reason for rapidly reducing our dependence on fossil fuels,” Elmore said.
“Additional management responses that may increase nitrogen availability across large regions are likely to be controversial, but are clearly an important area to be explored.”
The study has been published in the journal Science.
‘We are on the fast track to climate disaster’: Cursing UN report warns that greenhouse gas emissions must peak by 2025 to limit global warming to 2.7 ° F
To achieve the ambitious goal of limiting global warming to 2.7 ° F (1.5 ° C), global greenhouse gas emissions must peak by 2025 at the latest, a new UN report has warned.
The report by the United Nations Intergovernmental Panel on Climate Change (IPCC) claims that there is a “short and fast-closing window of opportunity” to limit global warming by 2100.
Emissions of carbon dioxide (CO2) must be cut by as much as 48 percent by 2030 and reach net zero by 2050 if we are to achieve the goal, according to the report.
Meanwhile, methane emissions must be reduced by a third by 2030 and almost halved by 2050.
As it stands, we are currently heading for a global warming of 5.7 ° F (3.2 ° C) by 2100, with devastating consequences for ‘all living things’, according to the IPCC.
‘We are at a crossroads. The decisions we make now can ensure a viable future. We have the tools and the knowledge required to limit warming, says IPCC President Hoesung Lee.
UN Secretary-General Antonio Guterres described the report as a ‘disgrace’ and warned that we were on the ‘fast track to climate disasters’.