Nitrogen inputs are recorded on the Level II sites using deposition collectors. These collectors are placed within the forest stand and in an adjacent open field. They continuously capture precipitation at several evenly distributed points.

A subsample of the collected precipitation is analyzed in the laboratory every two weeks for a variety of environmentally relevant substances, including nitrogen compounds. The determination of reduced and oxidized inorganic as well as organic nitrogen allows conclusions on the origin of the nitrogen inputs. Different forms of nitrogen also affect the ecosystem in different ways. The nitrogen concentrations, together with the precipitation amounts, can be used to estimate the amount of nitrogen that enters the forest ecosystem.

Comparing the deposition within the forest stand and on the open field allows to determine the significance of the canopy for substance input. Due to the filtering effect of the tree canopy, not only the dissolved form in precipitation but also gaseous and particulate nitrogen enters the ecosystem. As a result, the input of nitrogen into the forest is greater than into the open field.

In a forest stand, precipitation comprises throughfall and stemflow. For smooth-barked tree species such as beech, stemflow accounts for a significant proportion of the precipitation in the stand.  On the Level II sites, stem flow is measured separately.

The term throughfall refers to the precipitation that falls through the canopy. During this process, exchange processes occur with the leaves and needles: nitrogen is absorbed by the tree canopy. Therefore, the values measured within the stand often underestimate nitrogen input into the forest. To correct for this effect, various methods to calculate and model total nitrogen inputs, known as canopy budget models, are used.

At this time, the app is only available in German.

The app makes it possible to visualize and compare different target values. A target value can be selected via the menu on the left, which is displayed in blue. Some of the values depend on the vegetation. Therefore, the app allows the separate display of coniferous and deciduous forest.

By selecting “Compare target values/ Zielgrößen vergleichen ”, a second target value is displayed in green. For example, the measurements in the stand can be compared with the measurements in the open area or measurements in the coniferous forest with measurements in the deciduous forest.

The magnitudes of the measured values differ greatly. For example, organic nitrogen occurs in smaller quantities than inorganic nitrogen. The slider allows the displayed value range to be adjusted if necessary.

The following target values are determined or calculated:

Inorganic nitrogen in the stand (canopy budget model) corresponds to the mean value of two calculation models (Ulrich (1994) and de Vries et al. (2001)). The range between the results of the two models can be displayed with “Uncertainty interval of the median”. These values are used to evaluate critical deposition rates.

N-NO₃ in the stand is the sum of the nitrogen input with throughfall and stemflow.

N-NH₄ in the stand is the sum of the nitrogen input with throughfall and stemflow.

Total nitrogen input in the stand (canopy budget model) is the sum of inorganic nitrogen input in the stand and organic nitrogen in the open field.

N-NO₃ on open fields in the forest is calculated from the amount of precipitation and concentration.

N-NH₄ on open fields in the forest is calculated from the amount of precipitation and concentration.

Organic nitrogen on open fields in the forest is calculated as the difference between total nitrogen and the sum of N-NO₃ and N-NH₄.

Total nitrogen on open fields in the forest is calculated from the amount of precipitation and concentration.