d15N

Delta-N-15; δ15N

Measure for the enrichment of the stable nitrogen isotope 15N in the food web

Nitrogen exists naturally in the form of two stable isotopes, 14N and 15N, which differ in their atomic mass. By means of mass spectrometry (MS) both isotopes can be analysed separately (isotope ratio MS). In the air, 99.634% of the total nitrogen is 14N whereas 15N contributes only with 0.366%.

In organisms, 15N has a higher retention time, i.e. it is transformed and excreted more slowly and consequently accumulates in the organism. This leads to an increase of 15N relative to 14N. The ratio 15N/14N is expressed in the δ-notation (δ15N).

In the food web δ15N increases: carnivores have higher values than herbivores and herbivores have higher δ15N values than plants. With each trophic level the δ15N value increases by about 3 to 4 per mille (‰). The δ15N value can therefore be used to determine the trophic level of organisms.

When assessing chemical pollution, the trophic position of organisms can help to identify the accumulation of substances and their potential for biomagnification in the food web. This requires the parallel measurement of trophic position and chemical residues in the organism.
However, it must be kept in mind that also environmental conditions and physiological characteristics of organisms affect the δ15N value.

Specimen

Zebra mussel Common mussel species as invasive animal in rivers and lakes with high information level for water pollution
Bream Bioindicator in rivers and lakes
Common bladder wrack Common brown alga of the coastal areas of the North and Baltic Sea
Blue mussel One of the most important edible mussel species common in the North and Baltic Sea
Eelpout As the only viviparous fish in German nearshore waters, it is a bioindicator in nearshore coastal marine ecosystems.
Herring gull Inshore, the herring gull mainly feeds from the sea: upon fish, mussels, and crabs.
Common spruce A major primary producer in semi-natural and anthropogenic affected ecosystems.
Pine A major primary producer in semi-natural and anthropogenic affected ecosystems.
Beech As the most dominant deciduous tree species in Central Europe, it plays a significant role in most nearly natural and also anthropogenically influenced forest ecosystems up to an altitude of 1100 m.
Roe deer, one-year-old The roe deer is the most common of the larger herbivores (first order-consumer) to be found in the wild in Europe.
Feral pigeon A pigeon species home in nearly every city.
Earthworm (Aporrectodea longa) As an organism living at ground level, it is a major driver of the decomposition of organic material (e.g. plant litter).
Earthworm (Lumbricus terrestris) As an organism living at ground level, it is a major driver of the decomposition of organic material (e.g. plant litter).

Sampling area

BR/NP Berchtesgaden The only high mountains national park in Germany and an area of the Limestone Alps with international relevance
Saarländischer Verdichtungsraum Important, old-industrialised conurbation in Germany.
Bornhöveder Seengebiet Main water divide between the North- and Baltic Sea
Rhein Longest river in Germany
NP Bayerischer Wald Germany's first national park
NP Vorpommersche Boddenlandschaft National Park in the largest brackish water (Bodden) habitat of the world.
BR/NP Wattenmeere National park in the world largest connected sand and mud flats.
Elbe Fourth largest river basin in Central Europe
Verdichtungsraum Halle-Leipzig Region in the chemical triangle of Central Germany
NP Harz Germany's largest forest national park
Solling Second highest and largest low mountain range in Northern Germany
BR Pfälzerwald Germany's largest connected forest area in a range of low mountains
Oberbayerisches Tertiärhügelland The Upper Bavarian Tertiary Uplands are a part of the Southern German Molasse Basin
Donau Second largest river in Europe

Sampling period

1993 - 2018