Insect pests: It is generally thought that the increased infestations of insect pests particularly sucking insects, observed following N addition from the atmosphere or as fertiliser, is a response to increased N content of the plants. While the presence of certain pests may indicate an effect of N deposition, their absence does not indicate the lack of an effect and the introduction of pests in order to observe change is not acceptable.
Soil invertebrates: The composition of soil fauna may reflect the N status of the soil, although the application of high doses of nitrogen has had mixed results.
For insect pests, the infestation of beech aphid Phyllaphis fagi in a N fertilization experiment, increased significantly with increasing N concentration in leaves and N/P ratios respectively (Fluckiger and Braun, 1998). The occurrence of insect damage to pine needles in permanent plots in Scotland was positively correlated with modelled N deposition (range 7-22 kg N ha-1 yr-1). This relationship was associated with a negative relationship between the years of needles retained and modelled N deposition (NEGTAP, 2001).
For soil fauna, the abundance of Nematoda, Oligochaeta and microarthropodes, especially Collembola, had increased in some studies, but decreased in others after fertilizers (>150 kg N ha-1 yr-1) (Abrahamsen and Thompson, 1979; Huhta et al., 1983; Vilkamaa and Huhta, 1986). A one-time application of 100 kg N ha-1 yr-1 (as NH4NO3) in Eastern France, produced an effect on soil microorganisms which was still significant after 23 years (Deleporte and Tillier, 1999). A reduction in the nitrogen deposition in a Pinus sylvestris stand to preindustrial levels increased the species diversity of microarthropods due to a decreased dominance of some species (Boxman et al., 1995). In Sweden, a significant decrease of snails over 14-46 years in areas with N deposition of 15-25 kg N ha-1 yr-1 was observed, while in areas with N deposition of 3-6 kg N ha-1 yr-1 no significant changes were found (Gardenfors et al.,1995).
Suitability to indicate atmospheric concentrations:
Suitability to indicate atmospheric depositions:
There is some evidence to suggest a link between abundance of certain species and N deposition. However the relationship is not robust and further work is needed.
Suitability to indicate environmental impacts:
By definition, changes in invertebrates would represent a biological impact of nitrogen. However, However the relationship is not robust and further work is needed.
Sensitivity to other factors:
There will be sensitivity to many other factors, which affect the growth of the insect pests and their hosts and the competitive growth of soil invertebrates.
No evidence available, likely to be a response over many years.
The method is in principle relevant for most terrestrial ecosystems, but the main concerns are the sensitivity to other factors which limit its practicle application.
Expertise in field:
Agency staff may be trained to check for and monitor insect pests. Surveys of soil fauna require skilled staff to both develop and apply the methods.
Expertise in laboratory:
Identification of soil fauna require skilled staff.
Cost (per unit sample): £unknown
Cost Comment: Insufficient information.