The effects of anthropogenic nitrogen inputs on dune grassland at Newborough
National Nature Reserve, in Anglesey, North Wales were investigated using both
field surveys and experimental approaches.
In a survey on the study area conducted at eight transect sites from coastal to
inland sites, total N of vegetation and soil increased from the coastal towards the inland sites, it also differed significantly between sampling years. Effects of grass mowing treatments in a long-term experiment on total N of vegetation were examined and tissue N does not show any significant difference between mowing treatments. However, total N per unit area was significantly different, attributed to the higher biomass obtained from the unmown plots. Nine environmental variables were determined and discussed. Species composition was surveyed at each transect in three-year survey. An analysis using MATCH programme in VESPAN package indicated a vegetation sequence of mobile dune communities to mesotrophic grassland communities from coastal to inland sites. Separation between these two end communities was clearly shown by ordination using DECORANA. The relationships between species and their environmental
variables were determined using Canonical Correspondence Analysis (CCA),
which shows that the relationships between species are positive or negative
depending on their demands on the environmental sources.
Survey of atmospheric nitrogen dioxide using diffusion tubes revealed a small
amount of NO2 deposited to the area. The NO2 concentrations do not differ
between sites but it shows a very highly significant difference between sampling
periods, with greater concentrations during winter months. Annual mean
concentration of 3.26 ppb indicates that atmospheric NO2 is unlikely to contribute much N inputs at Newborough area.
The large poultry farm near Newborough NNR is a point sources of increased
concentration of atmospheric ammonia in the area. The NH3 concentrations
were measured at six distances south-west of the farm across the dune, and at
several other locations near the farm and at a sewage works. In all months, NH3
concentration decreased significantly with distance from the farm. After 1000 m
distance south-west from the farm, no measurable effect could be distinguished.
NH3 concentrations close to the farm are very large with annual mean
concentration of 60.05 μg m-3 compared to background of 0.94 μg m-3. Tissue N
content of ground cover species samples declined with distance from the farm,
and a positive relationship was shown between tissue N and NH3 concentrations
along the dune transect.
In the pot experiments, the responses of models of dune plant communities to
various N inputs revealed that most species were positively responsive to the
gradient of N concentrations, by increasing in dry weight. The Relative
Ecological Performance (REP) based on plant yields, enabled the seven species
to be compared. Faster growing mesotrophic grassland species such as Dactylis
glomerata, Plantago lanceolata and Festuca rubra had higher REPs than dune
species such as Galium verum, Leontodon hispidus, Achillea millefolium and
Centaurea nigra.