Part 2: Disturbances in the nitrogen cycle
Translation by Marc Siepman. Original title: ‘Stikstof: essentieel maar lastig – deel 2: verstoringen in de stikstofkringloop‘. Editor: Frederique Hijink.
Part 1 can be found here.
Nitrogen has always been ubiquitous as a gas, but nevertheless it causes a massive destruction throughout the world. Nitrogen adds to the massive dying of forests, the unprecedented loss of biodiversity, dead zones in the oceans … For most people however, the real causes are rarely visible. Nitrogen can be described as a sniper: it kills without being seen – but in this second part the killer gets caught in the act.
In the first part of this article, you could read how bacteria make sure that nitrogen is made available to plants, while making sure no excess nitrogen is produced. Man’s hubris however has caused the amount of excess available nitrogen to double. In this article I cover the causes and the chain reactions it has set in motion.
What complicates things
Nitrogen can be found in different forms (nitrogen gas, ammonium, nitrates, ammonia, nitrogen oxides) in different places (soil, atmosphere, water) and moves between these places in biotic and abiotic processes (volatilisation, oxidation, deposition, fixation).
The disturbances caused by mankind have led to acidification and eutrophication, which both have a variety of ill effects. Please bear in mind that the processes in this article are by no means linear, and that it’s hard to capture their complexity in a linear story. I have left out many aspects of problems nitrogen causes.
Sources of reactive nitrogen: fixation and oxidation
There are two unnatural ways in which extra reactive nitrogen is added to the soil: industrial nitrogen fixation and the burning of fossil fuels.
Industrial nitrogen fixation
In 1913 the first artificial fertiliser factory was opened, and using the Haber-Bosch process nitrogen gas (N2) was converted to ammonia (NH3). Since 1915 we have been producing nitrogen on a industrial scale. This is done at high temperatures (basically, lightning is mimicked), which is very energy intensive. The required hydrogen atoms (H+) are taken from natural gas: The Netherlands uses about 4 or 5 percent of their reserves solely for this purpose.
The burning of fossil fuels
The purpose of industrial nitrogen fixation is to add more nitrogen to the soil. Since the advent of the industrial revolution (in The Netherlands circa 1850) we have burned more and more fossil fuels, which inadvertently also adds nitrogen dioxide (NO2) to the atmosphere. In Europe, The Netherlands is the number two nitrogen dioxide emitter, but even globally The Netherlands and Belgium top the charts.
In contrast with what the agricultural industry wants us to believe, 70% of all people are fed by small-scale farmers. Industrial agriculture, which is based on the use of artificial fertiliser and pesticides, predominantly produces animal fodder and biofuels.
Still, the extra nitrogen has led to an unprecedented growth of human populations. In natural systems, the availability of nitrogen has always been low. Therefore, it has historically been a limiting factor in the production of food for humans: the human population could only grow to a certain extent. The human population was about 1.8 billion in 1915. Thanks to the industrial production of ammonia for artificial fertilisers, the global population has witnessed an explosive growth: we already passed the 7.5 billion mark – over four times as many in just over a century. It may come as no surprise to you now that almost 80 percent of the nitrogen in the human body originates from artificial fertiliser.
More domesticated animals
About three quarters of the agricultural land in The Netherlands is used, directly or indirectly, to feed domesticated animals. Still, we need to import about 9 million tons of nitrogen-rich animal fodder from the Amazonian area. The import of this genetically modified soy and maize makes the impossible possible: we rear and slaughter about 650 million animals a year in this tiny country. Due to the way manure is handled, we emit a lot of ammonia: The Netherlands are number one in Europe. Factory farming is responsible for 90 percent of the Dutch emissions.
Greenhouse gases cause more greenhouse gases
Due to the use of artificial fertiliser, agriculture is responsible for about a third of all dinitrogen oxide (N2O) emissions. Dinitrogen oxide is a greenhouse gas, that is over three hundred times more potent than carbon dioxide (CO2), and possibly degrades the ozone layer.
Dinitrogen oxide is released when using (artificial) fertiliser and when burning fossil fuels. The fast melting permafrost of the arctic tundra holds approximately 67 billion tonnes of dinitrogen oxide, which can be released over a very short period. This is on top of the 1400 billion tonnes of methane (CH4) that is stored there. The latter is not only a problem due to its capabilities as a greenhouse gas. When released into the atmosphere, it oxidises within ten years or so into carbon dioxide (CO2) and water (H2O). Which leaves us with a lot of greenhouse gases and a whole lot less oxygen. I think it would be a good idea to try to prevent that from happening.
Gaseous nitrogen, nitrogen gas excluded, is eventually deposited somewhere, this causes acidification and eutrophication.
Acidification caused by nitrogen deposition
Factory farmed animals are reared mostly on grilles, allowing the droppings and urine to mix in a slurry pit below. Due to the anaerobic conditions (without oxygen), the nitrogen is released into the atmosphere as ammonia, which is generally deposited within 10 kilometres or so. Some say ammonia can not cause acidification, because it’s an alkaline molecule. The latter is true and in the atmosphere ammonia indeed neutralises acids. But in the soil, it can be converted to nitric acid. In the atmosphere, ammonia and nitrogen oxides can be converted to acids like nitric or sulphuric acid.
Nitrogen oxides can travel over a 1000 kilometre before they’re deposited. Dissolved in water they form nitric acid which causes acid rain.
The effects of acidification
Acidification has a lot of ramifications, for example:
Acidification causes soils to age at an unprecedented rate: in The Netherlands weathering is about a hundred times faster than natural. This causes essential nutrients to leach from the soil.
This causes plants and trees to lose their vitality over the years. As a result, plant pathogens, like the tinder fungus and the giant polypore take advantage of the weakened tree. Bear in mind that the pathogens are not the cause of the disease, they are merely the symptom. They cannot kill a healthy tree. Forests are dying en masse, but the causes are mostly anthropogenic.
Leaching of calcium
Acidification has ramifications for animals, too. It has been shown that calcium leaches from the soil more readily due to acidification, causing it to be out of reach for plant roots. Eggshells are becoming thinner, because the birds’ food is deficient in calcium. A third of their eggs dry out because of this, which means no chick will hatch from those eggs. And even if they do hatch, their bones contain so little calcium that their legs often break while they are still in the nest. They die as a result of that.
Some elements that are poisonous to plants are becoming more available due to acidification – aluminum, for instance. As the pH drops further below 5.2, aluminum becomes more soluble. Clay soils are packed with aluminum silicates; due to acidification, the aluminum can enter the plant. This clogs up the vascular tissues of the plant so less nutrients can be taken up.
Disruption of symbiosis
If a soil’s pH becomes too low or if there’s too much nitrogen or soluble aluminum in it, mycorrhizal fungi cannot function.
Besides acidification, nitrogen also contributes to an excess amount of nitrogen in the soil. I’ll name a couple of problems caused by that.
Leaching and eutrophication
Nitrate is a negatively charged molecule. Most soil particles are also negatively charged, which means the nitrates easily leach from the soil (this is true for artificial fertiliser and animal manure, not for the organic nitrogen in soil life, most importantly bacteria). Nitrates end up in a soil layer where they can stay for decades. They will continue to leach all that time, even if we stop using fertilisers today.
The nitrogen eventually ends up in lakes and rivers, where it causes eutrophication: the water becomes so rich in nutrients, that algae grow explosively. When the algae die, they sink to the bottom where they are decayed by bacteria that use up the oxygen in the water. This causes the life in the water to die – all but the jellyfish. Throughout the world’s oceans there are over four hundred dead zones. The causes are either artificial fertiliser or intensive animal rearing (which is made possible by artificial fertiliser).
Up untill about a hundred years ago, eighty percent of the bacteria in the chernozem, the fertile soils in Ukraine, was Azotobacter (a free living nitrogen-fixing bacterium). This allowed farmers to produce maize for decades, without adding nitrogen. Since the introduction of artificial fertiliser, the soils have become utterly dependent of the external input, because these bacteria have disappeared. Even when you use animal manure, compost or nitrogen-rich mulch, you can make the soil bacteria lazy, as they stop fixing nitrogen if enough of it is available in the soil.
Loss of biodiversity
The growth of the human and domesticated animal populations is at the expense of wildlife habitat. But even in the few patches of nature that are left, the loss of biodiversity is shocking. Partly due to nitrogen, The Netherlands has lost 85% of its biodiversity in the past 150 years.
Many plants are intolerant of nitrogen. An excess of nitrogen in the soil allows other plants, that do like nitrogen, to compete more successfully. Plants like stinging nettle and bramble. These two are becoming more and more obtrusive in the Dutch landscape. Although prickly plants can help protect young trees like European oak against grazing animals, the high nitrogen levels of the soil inhibit the symbiosis with mycorrhizal fungi. Our endemic oaks may become extinct within ten years. What makes matters worse is that they are of great ecological importance: over four hundred species of fungi, algae, mosses, lichens, insects, birds and bats live in and around a fully grown oak. The American oak, an invasive species in The Netherlands, only has a few relations with endemic species.
Just like acidification, eutrophication adds to the loss of insects. Although pesticides play an important role, nitrogen can not be dismissed either. The leaves eaten by caterpillars contain less and less minerals, because these are displaced by nitrogen. On top of that, minerals are leaching from the soil due to the acidification which is also caused by nitrogen. The leaves become so deficient in nutrients that the caterpillars die of malnutrition after a few days. Butterfly numbers are dropping dramatically.
This, in turn, has ill effects on insect-eating birds. After all, just one pair of great tits feeds their nest of young with almost ten thousand spiders, caterpillars and insects.
Carbon dioxide emission
Adding nitrogen to the soil without also adding carbon disturbs the carbon-nitrogen ratio in the soil. This makes the bacteria overly active. They use up what is left of the soil carbon for their metabolism, and emit carbon dioxide into the atmosphere. According to the EU, European soils are emitting ten times more carbon dioxide into the atmosphere than the entire industry in Europe.
Is there a solution?
The only true solution is to simply quit producing artificial fertilisers and stop burning fossil fuels. This asks for a complete rethink of our agriculture, we need systems that have a different goal: producing the highest quality food possible. The current goal is to produce as many tonnes of plants or animals per hectare as possible. It is, therefore, as much an economical as an ecological question. Efficiency should be about how much health and biodiversity we can get from a hectare. We need to base our meat consumption on its availability. Things go awry if we produce to meet demand. Also, we’ll need to make more use of perennials.
There is no golden bullet: every person, every piece of land, every (micro) climate, every plant or tree needs its own unique solution. Plant your food forest where the soil is degraded. Graze animals in a way they can restore the soil. Close nutrient cycles. Eat local. But above all: don’t go at it alone. Learn from each other, share the joy of producing, preparing, processing and consuming food. There’s enough for everybody!