nitrogen can be observed on acidic sites at deposition levels as low as 8 kg N ha
-1
year
-1 (Remke et al. 2009), suggesting that critical load ranges may have to be
modified downward for dune habitats. Under current revisions of the critical loads
for nutrient nitrogen in European habitats, a new critical load range of 8–15 kg N
ha
-1 year
-1 is proposed for fixed dune grassland, with the lower end of the range
applied to acidic sites (UNECE 2010).
In addition, background nitrogen deposition at the lower end of the critical load
makes a site very vulnerable to other local sources of nitrogen, e.g., local atmospheric point sources such as poultry farms (Jones 2010), or from ground water
(Jones et al. 2006; van Dijk 1989; van der Meulen et al. 2004). Additional nitrate
inputs from ground water at Merthyr Mawr in South Wales, where the atmospheric
inputs of nitrogen are 10.1 kg N ha
-1 year
-1 , just within the lower end of the
established critical load range (Jones et al. 2005), have the potential to push parts
of this site well above the critical load. In one area, nitrogen inputs in surface
flooding caused by upwelling of ground water input amounted to 51.9 kg N per
day. On this basis just 1 day’s supply of nutrients in the ground water, if added to
the annual atmospheric loading, could cause potential exceedance over an area of
4 ha. These levels of nutrient input are likely to drastically enhance rates of soil
development and to accelerate vegetation succession (e.g., Ketner-Oostra 2006).
8.3.3 Sea-Level Rise
Sea level rise is an important issue in sand dune management not least because of
the flood defense role it plays. Pye and Saye (2005), using an assumed sea level
rise of 0.41 m by 2100 [the median value based on Intergovernmental Panel on
Climate Change (IPCC) predictions at the time], have predicted that several sites
in Wales are likely to experience a significant net loss of dune area/habitat over the
course of the next century. However, in the light of recently revised estimates for
sea level rise produced by the UK Department of the Environment, Farming, and
Rural Affairs (Defra), the values used by Pye and Saye may underestimate medium- to long-term changes, suggesting even higher levels of habitat loss in the
longer term. In fact, rates of sea level rise are predicted to increase to values
approximating to 1.4 cm per year by 2100. Such rates have not been experienced
on the Welsh coastline for some 6,000 years or so. It is therefore difficult to predict
exactly how the coast will respond, but a key aim is to try and conserve the body of
sand. In other words, to allow it to translate landward, but this process will be
fraught with difficulties and may potentially be controversial since assets, such as
golf courses, housing, farmland, and caravan parks, are often located to the rear of
dune systems. On the other hand, the sea level rise will tend to increase the
erosional state of the dunes and this may lead to an increase in mobile dunes over
time (Carter 1991; Davidson-Arnott 2005).
8 The Impact of Dune Stabilization
133
-1
year
-1 (Remke et al. 2009), suggesting that critical load ranges may have to be
modified downward for dune habitats. Under current revisions of the critical loads
for nutrient nitrogen in European habitats, a new critical load range of 8–15 kg N
ha
-1 year
-1 is proposed for fixed dune grassland, with the lower end of the range
applied to acidic sites (UNECE 2010).
In addition, background nitrogen deposition at the lower end of the critical load
makes a site very vulnerable to other local sources of nitrogen, e.g., local atmospheric point sources such as poultry farms (Jones 2010), or from ground water
(Jones et al. 2006; van Dijk 1989; van der Meulen et al. 2004). Additional nitrate
inputs from ground water at Merthyr Mawr in South Wales, where the atmospheric
inputs of nitrogen are 10.1 kg N ha
-1 year
-1 , just within the lower end of the
established critical load range (Jones et al. 2005), have the potential to push parts
of this site well above the critical load. In one area, nitrogen inputs in surface
flooding caused by upwelling of ground water input amounted to 51.9 kg N per
day. On this basis just 1 day’s supply of nutrients in the ground water, if added to
the annual atmospheric loading, could cause potential exceedance over an area of
4 ha. These levels of nutrient input are likely to drastically enhance rates of soil
development and to accelerate vegetation succession (e.g., Ketner-Oostra 2006).
8.3.3 Sea-Level Rise
Sea level rise is an important issue in sand dune management not least because of
the flood defense role it plays. Pye and Saye (2005), using an assumed sea level
rise of 0.41 m by 2100 [the median value based on Intergovernmental Panel on
Climate Change (IPCC) predictions at the time], have predicted that several sites
in Wales are likely to experience a significant net loss of dune area/habitat over the
course of the next century. However, in the light of recently revised estimates for
sea level rise produced by the UK Department of the Environment, Farming, and
Rural Affairs (Defra), the values used by Pye and Saye may underestimate medium- to long-term changes, suggesting even higher levels of habitat loss in the
longer term. In fact, rates of sea level rise are predicted to increase to values
approximating to 1.4 cm per year by 2100. Such rates have not been experienced
on the Welsh coastline for some 6,000 years or so. It is therefore difficult to predict
exactly how the coast will respond, but a key aim is to try and conserve the body of
sand. In other words, to allow it to translate landward, but this process will be
fraught with difficulties and may potentially be controversial since assets, such as
golf courses, housing, farmland, and caravan parks, are often located to the rear of
dune systems. On the other hand, the sea level rise will tend to increase the
erosional state of the dunes and this may lead to an increase in mobile dunes over
time (Carter 1991; Davidson-Arnott 2005).
8 The Impact of Dune Stabilization
133