An excess of nitrogen in the soil. How does it occur?
marine: “There are two processes: eutrophication and acidification. Fertilization means adding nitrogen to the ecosystem. Think of exhaust fumes from cars, which release nitrogen oxide into the air and ammonia from livestock released from manure. The two substances are spread through the air. and eventually end up in the soil again. In addition to eutrophication, precipitation of these substances also leads to acidification of the soil. “
Joost: “In almost three quarters of the areas, the nitrogen standard has been exceeded and in many cases very markedly. With the programmatic approach to nitrogen (PAS), the government assumed that nitrogen emissions would decrease and that we would eventually reach the standard of thirty “In the meantime, we were still able to provide some space for new nitrogen emitters, but the problem is: everything that is added now causes further deterioration of habitat quality. For this reason, PAS was declared invalid in 2019 by the Council of State.”
marine: “In addition, nitrogen precipitation has not fallen properly over the past ten years and has even increased somewhat around some sensitive nature reserves.”
How do we see it reflected in our landscape?
Joost: “Nitrogen is a nutrient that ensures that plants that can process much of it grow faster. Grasses are the best known example. In open areas like heathlands and dunes, grass grows up quickly and herbs disappear.”
marine: “More grass creates a cooler and more humid microclimate, which makes life difficult for insects. Many insects need bare soil and drought to survive.”
Joost: “Ammonia has even more influence. Plants absorb it from the soil. This process causes the soil to acidify faster and the soil minerals are depleted faster. In very poor soils, it eventually leads to internal soil poisoning, which means that sensitive herbs can no longer “This is a major problem in dry sandy soils. The food quality of the plants is also declining as a result. As a result, the biomass and richness of insect life is also declining. This is leading to the feeding of birds.”
Name one species that suffers from this.
Joost: Take the red-backed thorn. During the breeding season it depends on different types of large insects. They have become quite rare in the heathlands because there are no longer enough prey there. You can only see them there if the soil is still a bit in order. , such as at Doornspijk on the Veluwe. “
marine: “Tons are seen increasing in nature reserves with richer soils, such as watercourse valleys and the edge zones of nature reserves, where nature development takes place. Grazing takes place, and the soil is often less poor and somewhat moist.”
Such areas compensate for the misery on the moor for Red-backed Shrikes. Are there species that are clearly in a pinch due to nitrogen?
Joost: “For the grouse, nitrogen deposition is the last blow. At Sallandse Heuvelrug, where the last grouse are located, I have for years tried the chemistry in soil and heather. We also pull the trawl through the heath to check the row of larvae. Too much nitrogen, which means that there are few larvae.They are vital for the cultivation of grouse.They literally die of starvation.It is also due to the fact that heather germinates earlier in the spring.It is often due to climate change However, it is less known that the increase in nitrogen also larvae seem to be able to move with this advancement of the season, but the grouse can not keep up very well. where the grouse is still on the eggs. “
It is a different situation than in the dunes. In the areas where Wheatears are still breeding, there seems to be enough food for their young. However, there is also the nitrogen problem.
marine: “The problem with the dunes is that rabbits have largely disappeared and the grass is growing fast due to eutrophication. Wheat veins run after insects, which is simply not possible in tall grass. In densely growing dunes, they can no longer hunt their prey, even if they is there. still be. “
Joost: “Ryres do not move away from their native soil all their lives. And most wheat species return each year to the exact same piece of dry soil. That kind of process seems to have the most obvious impact on such base-resistant species. I at least we can do the best there too. It’s much harder to see what role nitrogen plays in their system in birds that have a chance of relapse. “
marine: “I think Natjarren is a good example of this. One would think: fewer insects in the heathland, so a problem. But Natskjolden covers a large hunting area and likes to fly into a forest or a river valley. During prey research with Sovon we saw in 2005 that they mainly benefit from a few species of moths that have increased recently, which in turn are likely to benefit from the warming climate. “
Joost: “There is no clear connection with nitrogen for Natjaren. It is very different from bird species and area whether it is sensitive, so you have to look so subtle. Never throw everything away.”
So specialist work. Can you see some clues to help with this kind of research?
Joost: “In forests on poor soils, there is too little lime in the soil due to acidification. As a result, prey with the lime skeleton drops sharply. We know from a very poor part of Veluwe that it causes calcium deficiency in the skeleton. Of great tit. With the generalist great tit. present, one may not immediately see this problem in numbers and breeding success, but zoom in on permanent tits in coniferous forests: Black Tit and Top Tit. Do they suffer more from it? “
marine: “You could look in nest boxes of these species in different forests. You might be able to see on the breeding success where the acidification has the strongest effect.”
This interview appeared in Sovon News magazine in 2019. As a result of recent government decisions, we are taking it up again and we have supplemented it for NatureToday’s readers.
Living Planet Report 2020 ‘Connected nature and agriculture’ (pdf; 13 MB) published by the World Wide Fund for Nature contains an exploratory analysis of the development of birds, butterflies and reptiles in heaths and forests on sandy soils, based on census series from Sovon, Butterfly Foundation and Ravon. Areas with a very high nitrogen deposition were compared with areas with a high nitrogen deposition (areas with a low nitrogen deposition no longer exist). Characteristic animal populations performed worse on average in both forest and heath with very high nitrogen deposition.
Sovon, Bargerveen Foundation and BioSfeer are currently researching insectivorous birds within the framework of the Knowledge Network for Development and Management of Natural Quality (OBN). Among other things, we want to know which properties make the birds most vulnerable to nitrogen influences. Think of species that forage on open ground and suffer from grass growth. Or on species with a strong food specialization of non-calcareous prey that suffer from acidification.
Text: Albert de Jong, Sovon Bird Research Netherlands
Photos: Harvey van Diek (main photo: Gray Shrike); province of Gelderland; Jan Sleurink; Sovon