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Too much of a good thing: nutrient cycles

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Nitrogen and phosphorus are vital nutrients and indispensable for the production of food. However, increased nutrient inputs by humans change the nutrient balance and put a strain on ecosystems. We study nutrient cycles in various natural habitats in order to gain an understanding of these effects.

 

One of the most serious environmental issues worldwide is the entry of nutrients such as nitrogen and phosphorus into the environment. In order to produce fertiliser for agriculture, humans extract approximately 120 million tonnes (Mio t) of nitrogen from the atmosphere and 20 Mio t of phosphorus from fossil sources every year – many times the amounts naturally present in the nutrient cycle.

Nitrogen is distributed across the globe in the atmosphere and through precipitation; therefore, it also fertilizes ecosystems which are far removed from industry and agriculture. Phosphorus, on the other hand, is conveyed into streams, lakes and seas by water. Due to over-fertilisation, not only must Swiss lakes such as the Greifensee and Hallwilersee be artificially aerated, but seas such as the Baltic are sometimes positively asphyxiated in parts.

 

Erosion of biodiversity

Nutrient inputs also have consequences on land: biodiversity in meadows is breaking down and, in the forest, the nutrient balance is being thrown out of equilibrium. In particular, nutrient-poor habitats for rare animal and plant species such as moors and dry grasslands are being lost as a result of this involuntary fertilisation.

At WSL, we conduct several research projects to study how changes in nutrient inputs affect the functioning or productivity of terrestrial ecosystems. How is plant diversity and thus the stability of ecosystems affected? Which consequences does this have for the sustainable management of meadows and forests?

 
 
 
 
 

Nutrient Network

Nutrient Network: the global impact of fertilisers on pastures

Within the context of the international research project "Nutrient Network (NutNet)", more than one hundred sites on six continents are being studied with the aim of understanding how fertilisation and herbivorous animals influence natural pasture ecosystems. The WSL "Animal-Plant Interactions" Group is responsible for one of the research areas in Val Müstair. Each research group carries out exactly the same standardised experiments at their location and follows the same protocol for data collection. The data are therefore comparable, and the findings are globally applicable.

They demonstrate that the diversity of plant species in pasture ecosystems is very quickly diminished as a result of fertilisation. The greater the number of different nutrients (for example, nitrogen, phosphorus, potassium) that are used in combination, the faster diversity breaks down. If the herbivorous animals disappear, the extinction process is once again accelerated. Declining biodiversity causes ecosystems to become unstable, which means they can no longer cope well with environmental changes.

 

WSL-Projects: Nutrient Network

Additional Links: Nutrient Network (international research cooperation)

Contact: Anita Risch

 

 

Nutrient cycles in forests

The WSL Long-Term Forest Ecosystem Research (LWF) Programme has been recording the flow of substances in the nutrient cycle at selected forest sites in Switzerland since 1994 (link to experimental plants - LWF). In this research programme, we examine the nutrient inputs that enter the forest ecosystem through the atmosphere and their effects on leaves and needles, soil vegetation, soil solution, tree growth and forest conditions. We also study the effects of other environmental influences, such as temperature and vegetation, on nutrient cycles within the ecosystem.

WSL projects:

Contact: Peter Waldner

 

 

Nutrient inputs in moors and dry grasslands

The «Monitoring the effectiveness of habitat conservation in Switzerland» (project was launched jointly by FOEN and the WSL to study changes to biotopes of national importance (raised bogs and fens, dry grasslands, wetlands, and amphibian breeding sites). Nutrient inputs from the air or from the adjoining farmland play an important role, particularly in nutrient-poor moors and dry grasslands. There, nutrient inputs can lead to significant and, from the point of view of biotope protection, undesirable changes. Consequently, highly competitive plant species displace the predominantly slower growing and often smaller, low-nutrient-adapted typical moors and dry grasslands.

The project does not measure nutrient inputs and nutrient enrichment directly; rather, these are recorded via average indicator values from several thousand vegetation recordings. Initial results from the moors show that nutrient enrichment, which was identified as early as the 2000s, has not yet been stopped.


WSL projects: Monitoring the effectiveness of habitat conservation in Switzerland

Literature:

  • Bergamini A, Ginzler C, Schmidt BR, Küchler M, Holderegger R 2016. Die Wirkungskontrolle Biotopschutz Schweiz (WBS) in der Routinephase. NL Inside 2/2016: 21-24.
  • Klaus G. (Red.) 2007. Zustand und Entwicklung der Moore in der Schweiz. BAFU, Bern.
  • Küchler M., Küchler H., Bergamini A., Bedolla A., Ecker E., Feldmeyer-Christe E., Graf U., Holderegger R. (im Druck). Moore der Schweiz: Zustand, Entwicklung, Regeneration. Bristol-Schriftenreihe, Haupt.

 

Contact: Ariel Bergamini

 

 

Nutrients in water catchment areas

We have been studying how water quality, and particularly nutrient concentrations, of precipitation and runoff in small, wooded catchment areas changes on seasonal and long-term bases in Alpthal (canton of Schwyz) for almost fifty years. Throughout this time, we have observed only insignificant trends in the chemical composition of the effluent. Since 2003, these measurements have been part of the National Long-Term River Monitoring and Survey Programme (NADUF) which is carried out jointly by the FOEN and the EAWAG (Swiss Federal Institute of Aquatic Science and Technology).

WSL projects:

 

Contact: Manfred Stähli

 

 

 

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