Air pollutants not only affect human health, they can also cause harm to plants, habitats and ecosystems. Nitrogen is an essential nutrient for plant growth. However, inputs of excess nitrogen into an ecosystem can result in detrimental effects. For example, excess nitrogen can cause a bloom of fast growing plants so that other plants are starved of nutrients and light and eventually die. The heathland habitat within the SAC requires a low nitrogen input to maintain the species of interest at Ashdown Forest.
While there are many sources contributing to nitrogen, an important one is air pollution. Nitrogen in the atmosphere comes from many different sources, both local and more distant. However, road traffic is the most important local source where road transport emits nitrogen from fuel combustion.
Measurements will be made of a number of nitrogen species in the atmosphere. This will include the gases: nitrogen dioxide, nitrogen oxides, ammonia and nitric acid, as well as nitrogen associated with airborne particles, in particular ammonium nitrate. These gases and pollutants are either deposited directly to the surface of vegetation or converted to other less common nitrogen compounds in the atmosphere which are also then deposited.
There is an automatic monitor in an air conditioned housing measuring nitrogen dioxide, nitrogen oxides and ammonia. There are samplers that pump air through tubes that absorb ammonia, nitric acid, and ammonium nitrate particles. Finally there are diffusion samplers used to measure nitrogen dioxide and ammonia. These are small plastic tubes that are fixed to posts. The bottom of the tube is open, while a specially coated grid under the plastic cap at the top of the tube absorbs the pollutant. The tubes are replaced regularly and returned to the laboratory for analysis.
The first monitors were put out in August 2014. All of the other monitors were installed in October and November 2014.
The air quality monitoring will be the responsibility of Air Quality Consultants Ltd. Regular visits will be made to the sites by WeCare4Air Ltd. to change the samplers. The automatic monitors will be serviced by Enviro Technology Services plc, and independently checked twice a year by Ricardo-AEA.
Nitrogen deposition is increasingly recognised as being one of the most significant threats to biodiversity in Europe. The consequences of nitrogen deposition can have detrimental effects on certain plant species such as those present at Ashdown Forest. The ability for species to withstand the effects caused by nitrogen may differ from place to place and may depend on a range of different factors. For this reason, it is important to monitor the vegetation and species at Ashdown Forest to learn about the condition of the protected species and whether the health of the heathland habitat is changing over time. The purpose of vegetation monitoring is to therefore assess the effects and potential effects of nitrogen on the protected heathland species.
A small number of transects will be set up throughout Ashdown forest, stretching from a road into the heathland, with a number of quadrats (an area of ground of 2 x 2m) selected along each transect. A survey of the vegetation within each quadrat will be undertaken on a yearly basis. The most intrusive aspect will be installing small ground markers to mark the quadrats, to ensure that the same locations are surveyed each year. Ground markers comprise metal pegs that are set into the ground, at or just below ground level. Two corners of each quadrat will be marked with pegs. This is a standard survey technique and approved by the Conservators of Ashdown Forest and Natural England. Survey work will require a small team of surveyors on the ground for up to four weeks each year.
In addition to transect monitoring, vegetation and soil samples will be taken for chemical analysis to determine the level of nitrogen present. Soil and vegetation sampling will be undertaken every year for the first three years of the study.
The only permanent ecological monitoring equipment left on site will be the ground markers to identify the quadrat locations and these will not be visible to the public due to the height of the vegetation.
Experienced ecologists from Ecus Ltd will be undertaking the vegetation survey work.
To provide reliable data it will be necessary to carry out the monitoring for a number of years. The initial programme of monitoring and assessment runs for four years. A decision will then be taken as to whether it should be continued.
The monitoring began in the summer of 2014. It is necessary to monitor for at least a year to obtain reliable data. The first air pollution data should be available after the summer of 2015. However, it will be longer before a full understanding of the effects on vegetation can be determined and several years of monitoring may be required before any conclusion can be made. A report will be provided to the Council following 3 years of monitoring.
A large number of scientific research studies have shown that, once aircraft reach altitudes of more than a few hundred metres, which usually happens within a few hundred metres from the airport boundary, their effect on ground level air pollution concentrations becomes negligible. This is because the pollution which is emitted becomes dispersed and diluted into high-altitude air, rather than being brought down to the ground. Emissions at height will have an incremental effect on general background pollution levels, but no measurable effect on ground level concentrations or deposition rates.