experienced an increase in dune area over the last 100–120 years. This pattern is
consistent with a more widely observed trend for net sediment accumulation
within many Welsh estuaries over the same time period (Pye and Saye 2005).
However, at least 27 of the 49 dune systems in Wales are subject to net erosion
(Dargie 1995).
8.3.2 Nitrogen Deposition
The stabilization of dunes is thought to be at least in part attributable to the input
of artificially high levels of nitrogen from atmosphere sources (Jones et al. 2004;
Ketner-Oostra et al. 2006; Kooijman 2004; Remke et al. 2009). Since the onset of
the industrial revolution, the levels of reactive nitrogen in the atmosphere have
increased twofold (Fowler et al. 2004) and this has had a negative impact on many
semi-natural habitats that are adapted to very low levels of nitrogen deposition
(Bobbink et al. 1998). Dune systems are no exception, although empirical evidence of negative effects is sparse in the literature compared with other habitats. In
UK dune systems, Jones et al. (2004) showed that elevated nitrogen deposition was
correlated with increased above ground biomass in early successional and fixed
dune habitats, and with decreased species richness in fixed dune grasslands. Soil
parameters, such as the C:N ratio and available nitrogen, showed significant
correlations with nitrogen deposition and soil seed banks in dune slacks may also
be negatively affected (Plassmann et al. 2008). The increase in biomass has
important consequences in that it increases the supply of organic matter to the soil
and may be one mechanism by which nitrogen deposition can accelerate the early
stages of soil development. In the Netherlands, mesocosm experiments showed
that the nitrophilic grass Calamagrostis epigejos could quickly become the
dominant species with increasing nitrogen deposition (van den Berg et al. 2005).
Other studies suggest that the invasive spread of Brachypodium pinnatum is also
linked to the deposition of atmospheric nitrogen (Bobbink and Willems 1987).
This species has now become problematic on certain dune systems in Wales
(Rhind 1993).
The critical load range for nitrogen on sand dune vegetation had been established at 10–20 kg N ha
-1 year
-1 (Achermann and Bobbink 2003). On the basis of
this, most dune systems in Wales approach threshold levels for atmospheric inputs
alone (Jones et al. 2002a, 2002b). More recently, the potential for relatively small
additional levels of nitrogen above the critical load to affect dune ecosystem
processes has been shown in an experimental ‘‘nitrogen-addition’’ study at Newborough Warren (Plassmann et al. 2009). In fact, significant increases in moss
biomass and ecosystem retention of nitrogen were observed at treatment levels
within the critical load range (total deposition of 18 kg N ha
-1 year
-1 including
background deposition). Recent work in the Baltic shows that negative effects of
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P. Rhind et al.
consistent with a more widely observed trend for net sediment accumulation
within many Welsh estuaries over the same time period (Pye and Saye 2005).
However, at least 27 of the 49 dune systems in Wales are subject to net erosion
(Dargie 1995).
8.3.2 Nitrogen Deposition
The stabilization of dunes is thought to be at least in part attributable to the input
of artificially high levels of nitrogen from atmosphere sources (Jones et al. 2004;
Ketner-Oostra et al. 2006; Kooijman 2004; Remke et al. 2009). Since the onset of
the industrial revolution, the levels of reactive nitrogen in the atmosphere have
increased twofold (Fowler et al. 2004) and this has had a negative impact on many
semi-natural habitats that are adapted to very low levels of nitrogen deposition
(Bobbink et al. 1998). Dune systems are no exception, although empirical evidence of negative effects is sparse in the literature compared with other habitats. In
UK dune systems, Jones et al. (2004) showed that elevated nitrogen deposition was
correlated with increased above ground biomass in early successional and fixed
dune habitats, and with decreased species richness in fixed dune grasslands. Soil
parameters, such as the C:N ratio and available nitrogen, showed significant
correlations with nitrogen deposition and soil seed banks in dune slacks may also
be negatively affected (Plassmann et al. 2008). The increase in biomass has
important consequences in that it increases the supply of organic matter to the soil
and may be one mechanism by which nitrogen deposition can accelerate the early
stages of soil development. In the Netherlands, mesocosm experiments showed
that the nitrophilic grass Calamagrostis epigejos could quickly become the
dominant species with increasing nitrogen deposition (van den Berg et al. 2005).
Other studies suggest that the invasive spread of Brachypodium pinnatum is also
linked to the deposition of atmospheric nitrogen (Bobbink and Willems 1987).
This species has now become problematic on certain dune systems in Wales
(Rhind 1993).
The critical load range for nitrogen on sand dune vegetation had been established at 10–20 kg N ha
-1 year
-1 (Achermann and Bobbink 2003). On the basis of
this, most dune systems in Wales approach threshold levels for atmospheric inputs
alone (Jones et al. 2002a, 2002b). More recently, the potential for relatively small
additional levels of nitrogen above the critical load to affect dune ecosystem
processes has been shown in an experimental ‘‘nitrogen-addition’’ study at Newborough Warren (Plassmann et al. 2009). In fact, significant increases in moss
biomass and ecosystem retention of nitrogen were observed at treatment levels
within the critical load range (total deposition of 18 kg N ha
-1 year
-1 including
background deposition). Recent work in the Baltic shows that negative effects of
132
P. Rhind et al.