Accessing the effects of the January 2018 storm on blowout activity in grey dunes at ‘De Nederlanden’ at Texel. A comparison with 2017 and historical aerial photograph data

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Accessing the effects of the January 2018 storm on blowout activity

in grey dunes at ‘De Nederlanden’ at Texel. A comparison with 2017

and historical aerial photograph data.

Bachelor thesis

Name: Tobi Diepenmaat

Student number: 11130946

Date: 2-7-2018

Place: Amsterdam

Supervisor: Dr. Kooijman, A.M. Second supervisor: Dr. ir. Van Boxel, J.H. BSc Future Planet Studies, major Earth Sciences

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Abstract

Coastal Grey Dune systems are susceptible to landscape and vegetation change, containing large open areas and low vegetation. The Wadden sea forms a special system in the

Netherlands, which has been added to the Unesco World heritage site in. Grey Dunes form part of the Habitats directive H2130 of the European commission. Safeguarding Eolic processes, including protecting and reactivating blowouts forms part of the directive. This research analyses the effects of the 2018 storm on blowout activity at ‘De Nederlanden’, Texel. This was conducted by comparing the 2018 results with the 2017 research and historical aerial photograph analysis, using the main question ‘What is the impact of the January 2018 storm on the development of the active and stable blowout areas in lime poor Grey Dunes at Texel?’. Some resulting positive influences on blowout activity were found, which could possibly be attributed to the 2018 storm. Higher pH and bulk density values indicate potential increased activity. Contrary, nitrogen and carbon contents suggested little fresh sand influx. The vegetation parameters also indicated little effects of the 2018 storm. Vegetation presence could furthermore reduce natural reactivation processes. Vegetation indicators presume, however, a larger diversity in 2018. Historical storms did not seem to provide any clear relation with bare sand coverage. Microbial processes and rodent activity have potential large influence on the dynamics of Grey dunes as well. Assumed is, that the overall effects of the storm are therefore not severe enough to induce large scale activation.

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Dunes form a large part of the north-western European coast. Coastal Grey Dune systems are susceptible to landscape and vegetation change, containing large open areas and low vegetation (van der Meulen et al., 1996). These processes are distinctive for dynamic coastal dune systems (Provoost et al., 2011). Furthermore, dunes contain close to 70 % of all flora species found in the Netherlands. The Wadden Sea forms a special system in which erosion and sedimentation are largely influenced by tide (Wang et al., 2012). To ensure the

protection of these characteristic systems, the Wadden Sea has been added to the UNESCO World Heritage site in 2009 (Provoost et al., 2011). Furthermore, Grey Dunes form part of the Habitats Directive, which contains protected habitats according to the directive of the European Commission. Blowouts are local depressions in dune hills, which provide fresh sand dispersion at sufficient Aeolian activity (Arens, 2007). Blowout activation and monitoring is incorporated in the directive H2130, of the European Commission.

Future safeguarding of the Wadden dune systems include understanding natural and disrupting processes that occur on these islands. Over the last 150 years, anthropogenic influence on these systems has increased through land use practises and emissions from agricultural-and industrial origin. As a result nitrogen depositions have risen tremendously in the 20th century (Provoost et al., 2011). Since 1980, nitrogen emissions have been reduced in the Netherlands. Especially from 1990 onwards, when strict nitrogen emission regulations were adopted (Erisman et al., 2005). Nonetheless, harmful nitrogen depositions do still occur in the Netherlands (Arens et al., 2013). Open dune systems have, as a result experienced large eutrophication events. The increased nitrogen concentrations also enhanced dune acidification. Both processes have occurred at parts of dune systems in North-West Europe, including coastal dune systems in The Netherlands (van der Meulen et al., 1996; Provoost et al., 2011). These processes resulted in monocultures, containing mostly grasses mosses and shrubs, which cover most of the Wadden islands. These vegetation changes reduced species richness of open coastal Grey Dune ecosystems (Provoost et al., 2011). In term – as a result of increasing vegetation cover – geomorphological processes changed as well, reducing transportation of sediments. These processes were embraced until 25 years ago, when research provided opposing insights, that focuses on the natural dynamic state of these systems (Arens et al., 2013; van Boxel et al., 1997).

Aeolian activity can provide positive effects on the restoring capacity of Grey Dune systems, by reducing and even reversing soil acidification and grass domination (van Boxel et al., 1997; van der Meulen et al. 1996; Kooijman et al. 2005; Aggenbach et al., 2016). In the Netherlands the PAS (Programma Aanpak Stikstof), includes measures to protect and increase resilience of natural ecosystems. Reactivating natural blowout areas is one of the major measures insisted by the PAS programme (Aggenbach et al., 2016). Active blowouts are essential to develop and maintain advanced habitat conditions. Their regenerating role as rejuvenating sand buffers increases natural ecosystem establishment. This in term stimulates ecosystem diversity and therefore resilience.

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To assess the dynamics of Grey Dune systems in the Netherlands, the Wadden Island of Texel was chosen. The presence of a relevant blowout area at Texel enhances research on natural dune dynamics. At this location Aeolian activity varies along time at an annual base (Aggenbach et al., 2016). Following a relatively stable period, instability can occur through disrupting events. Extreme events can influence overall dynamics of these sensitive dune systems (Arens et al., 2013). The storm of January 2018 is such an event, where peak wind gusts could have transported large amounts of sand. Therefore, previous conditions as observed in 2017 will be compared with current conditions at Texel.

This research will elaborate on the effects of the January 2018 storm on blowout areas at Texel. The area – de Nederlanden – North of De Koog, Texel, The Netherlands, with both an active and a stable blowout area, was selected. This area is from large interest, because of the natural occurrence of activated areas in lime poor Grey dunes. Accordingly, the main question ‘What is the impact of the January 2018 storm on the development of the active and stable blowout areas in lime poor Grey Dunes at Texel?’ has been composed. Furthermore, three sub questions have been defined: ‘What is the effect of the 2018 storm on soil and vegetation characteristics?’ What is the effect of the 2018 storm on bare sand coverage in relation to previous years ? How do the 2017 and 2018 data compare on soil and vegetation characteristics? To answer these sub questions systematically, soil and vegetation characteristics as well as aerial photographs have been be analysed. These properties fulfil the requirements needed to thoroughly asses the influence of the January 2018 storm on blowout areas at Texel.

Theoretical framework

Nitrogen (N) is a crucial element in the biosphere, as it is one of the main building blocks of life on earth. Therefore, it has been widely used as an artificial fertilizer to enhance plant growth. Currently, fertilizers containing nitrogen are still applied to crops at large scale to fulfil the worlds food demand (Robertson & Vitousek, 2009). The resulting high soil N concentrations (NH3), together with internal combustion emissions (NOx) are the main causes of nitrogen pollution (Holland et al., 2005; Hicks et al., 2011). Especially during the last century nitrogen concentrations have risen tremendously, peaking at the period 1980-90 (Provoost et al., 2011; Erisman et al., 2005). Despite the gradual decline of overall nitrogen depositions, nitrogen is still excessively deposited in the Netherlands. (Arens et al., 2013; Erisman et al., 2005). Although the nitrogen cycle is complex to understand, especially at a larger scale, the effects of increased nitrogen emissions have been known to disrupt

ecosystems (Robertson & Vitousek, 2009; Veer, 1997). Hypoxia occurs at coasts as a result of nutrient rich water inflow. This process has taken place at the coast of the Waddenzee (Janssen, 1993). The atmosphere furthermore contains nitrogen in the form of NO3 and NH4+, which is deposited over land (Robertson & Vitousek, 2009). These depositions result in eutrophication, which subsequently alters competition changes. Nitrogen depositions are known to be exceeded by 25 % at Dutch dunes. In dunes with non-calcareous soils, nitrogen

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values are exceeded by 40 %. These values are presumably too low, when taking into account uncertainties about exact nitrogen deposition values, critical values and the resilience of habitats (Kooijman et al., 2009). At the Wadden islands, these changes have caused a rise of thriving monocultures in dune ecosystems. Grass abundance has as a result increased, acidifying the soil, and reducing open dune areas (Provoost et al., 2011; Veer & Kooijman, 1997).

At the research area north of the Koog, previous research indicated high Eolic activity. Furthermore, no lime is present until a depth of 0.40 meters, indicating decalcified conditions. In addition, sand samples from soil profiles contain no Iron (Aggenbach et al., 2016). Buffers mitigate natural soil pH fluctuations, increasing ecosystem resilience. A low buffer capacity reduces soil pH. Subsequently, both increased biomass production and reduced organic matter decomposition could result in a higher soil organic matter content. As a result of increased soil organic matter, nitrogen content in the soil increases. Calcium-carbonate forms the most important buffer in the Netherlands. The low lime content of the present soil, reduces buffer forming possibilities. As described above non-calcareous dunes contain larger nitrogen concentrations (Kooijman et al., 2005). Moreover, as a result of nitrogen led acidification, buffer depletion creates toxic aluminium concentrations (Bowman et al., 2008). The soil characteristics at the research area lead to reduced pioneering

capacities, as acid and nutrient tolerant vegetation outcompetes pioneering species (van Boxel et al., 1997).

The research area, North of the Koog contains active and non-activated blowout (figure 1). At this location – 500 meters inland – the dunes consist of both younger and older sediments. It should be noted that Texel has more than doubled in surface area since the

start of the 11th century (Aggenbach et al., 2016). The Koog was furthermore situated in the northern part of a peninsula (figure 2). The research area is furthermore located at the coastal complex at the western part of Texel, beginning at pole 16. It stretches north, up to the Buitenmuy

and contains large geomorphological diversity. furthermore indicates that, compared to other areas at Texel, Eolic processes have been present for a longer period at his location. As the research area is largely situated on younger material, soil profiles indicate no advanced developed features. Therefore, this area can to a large extend be defined as grey dunes with an intermediate to non-calcareous soil (Aggenbach et al., 2016; Van der Meulen et al., 1996).

Figure 1: Air photograph of the research location, active blowout area indicated in red stable area indicated in green.

Figure 2: The Island of Texel, approximately 1200. Current coastline indicated with a dotted line, from Kloosterhuis (1986), (Aggenbach et al., 2016)

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Furthermore, no reactivation measures have been executed at this location. The presence of active and non-activated blowouts enhances, however, fauna diversity

(Aggenbach et al., 2018). Compared to continental dunes, overall Eolic activity is lower at the Wadden Islands. Since 1996 several periods of activity have occurred. At – most abundant – west and southwestern winds, Eolic activity has decreased during the period 1996 – 2015. This phenomenon occurred mostly at the eastern parts of the Wadden Islands, where on-shore wind is mostly absent. Eolic processes needed to maintain dynamic processes take place at wind speeds of 6 Beaufort and higher. Therefore, near the West coast of Texel, blowouts have been proven to be most active (van der Meulen et al., 1996).

At the research area, Dicranum scoparium (broom forkmoss) dominates, while grasses are scarce (Aggenbach et al., 2016). Nonetheless, active blowouts present in the area have reversing effects on local diversity. The mechanisms of blowout succession depend on Eolic activity. At active blowouts, wind provides the transporting mechanism of loose sediments. As a result, dune sand at Texel migrates, removing organic, low pH top soils and exposing fresh sand beneath it. If deeper lime rich material is transported to areas in proximity of the blowout, the buffer capacity of the renewed top soils increases (van der Meulen et al., 1996). The reduced weathering and acidification characteristics of these lower layers provide the basis of pioneering species needed to restore local vegetation. Phleo-Tortuletum ruraliformis, cladonia foliacea and cupressiforme lacunosum, are examples of pioneering species found at the active blowout zones (Aggenbach et al., 2016).

Sustainable dynamic dune systems, require energy from wind speeds of 6 Beaufort and higher (van der Meulen et al., 1996). At the 18th of January 2018 a western storm hit the Netherlands. During this storm wind speeds of over 120 km/h were observed on a time scale of several hours (Haarsma et al., 2018). Therefore the Royal Dutch meteorological institute released a code red for large parts of the Netherlands. In proximity of

Texel, the nearest weather station is located at Vlieland. At this station the

observed maximal hourly-and peak wind speed where subsequently 72 km/h and 112 km/h (KNMI, 2018). The severity of this storm is scaled within the top 10 largest storms of the last 50 years. Indicated is, that an extreme event as the January 2018 storm has a periodicity of 8 Years (Figure 3; Haarsma et al., 2018).

Figure 3 periodicity of the year maximum hourly wind speed over the last 48 years. 2018 storm indicated in red, KNMI (Haarsma et al., 2018)

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Additionally, research suggests a correlation between increased wind speed as a result of an extreme events and blowout activity. Kooijman et al (2005) describes storm events as potential causes of blowout surface area increase. Precipitation events can,

however also reduce mobility of sediments, resulting in less dispersion of sand. Strom driven dispersion could, however, also result in ecosystem disruption. The dune grass Ammophila arenaria, benefits from dispersion, encroaching the environment (Veer & Kooijman, 1997). Moreover, non-mobile species are particularly vulnerable (Kooijman et al., 2005).

Methods

The data was collected during a 7 day fieldwork period at Texel. The was fieldwork layout was based on Witz (2015). This predetermined transect was set out in the field using the Arc-Pad application in the Arg-Gis Trimble. The transect was identical to that of the previous year (figure 4). Subsequently, for every transect point the GPS-location was noted.

Furthermore, vegetation cover and species

abundance was estimated if present. Five types of vegetation were distinguished; herbs, shrubs, mosses lichens and grasses. Vegetation samples were taken by removing all non-moss vegetation at 25x25 plots . At points were a lower vegetation abundance was

observed, 50X50 plots were used. Thereafter 2 pF-rings were used to collect 2 - 100 cm3 soil samples needed to determine further bulk density and C/N content analysis. Additionally an auguring of approximately 80 cm was made, to describe the soil profile (figure 6). At the stable blowout zone an identical transect was established. In total 40 transect points were made, providing 80 soil samples and 40 vegetation samples.

Figure 4: Aerial photograph of the transect layout for the active blowout location, Texel

Figure 5: Aerial photograph of the grid for the active blowout location, Texel

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The grid point data was collected using the grid raster of Kolb (2017); (figure 5). The Arc-Trimble provided the map to establish an identical grid in the field. At both the active and stable blowout, 150 grid points were taken. The GPS-location of each grid point was noted using the Arc-Trimble. Furthermore, the upper 20 cm of the soil was described, taking note of Ah and C layers (figure 7). Equally to the transect data, the vegetation cover and species abundance was described.

Lab analysis

Soil Analysis

The collected samples were separated and ordered in the lab. Of the soil samples, 40 were used to calculate the Bulk density and the other 40 to determine the pH, EC and C/N Content. The 40 vegetation samples were used to determine the dry weight, EC, and C/N content.

Bulk density

First 40 metal containers were weighted and labelled. To determine the bulk density, each of the 40 100cm3-samples was placed in the metal containers. The samples were subsequently dried at 105°C for 24 hours. Afterwards, the samples were weighted. The following formula was thereafter used to calculate the bulk density:

Bulk density = Wd / V V = Soil Volume in cm3 Wd = Dry soil weight in g Bulk density in g/cm3

pH and Electrical conductivity

To determine the pH and the electrical conductivity 15 ml of demineralised water were added to 10 gram subsamples. These suspensions where thereafter put in a container and shaken for 2 hours. After this process the containers were stored undisturbed overnight during a 14 hour period and shaken for 30 minutes the following day. The pH en EC of resulting samples was measured with an electrode.

Figure 7: Layering of a grid point soil profile.

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Carbon and Nitrogen content

Another 40 Subsamples containing approximately 40 cm3 of were made, dried at 70°C and sieved. Thereafter, these samples were grinded and stored in glass containers. These were subsequently dried again at 70°C. Afterwards subsamples duplicates of 40 and 60 mg were weighted and folded. Resulting in 80 grinded dried and folded packages. Furthermore, 40 packages of sulfuric acid were made. These packages were added to the CHNS analyser. The soil samples have been analysed in runs of 70 soil samples during 10 hour periods. The resulting values of C and N have subsequently been converted to g/m2 using the bulk density data. The following formulas were used:

C content = (BD* Vt)*(%C/100) * N content = (BD* Vt)*(%N/100) * * BD = Bulk Density in g/cm3

Vt = soil volume in the upper 10 cm 100*100*10= 100.000 cm3 % C = Carbon percentage coming from the CNHS-analyser % N = Nitrogen percentage coming from the CNHS-analyser C content = Soil Carbon content in g/m2

N content = Soil Nitrogen content in g/m2

C/N ratio

The soil C/N ratio was determined by dividing the C content by the N content resulting from the carbon and nitrogen content analysis.

Vegetation analysis

Dry weight

The collected vegetation samples were dried at 70°C for 24 hours. Thereafter, each vegetation sample was weighted.

Carbon and Nitrogen content

The dried samples were subsequently grinded and stored in glass containers. After another 24 hour drying period at 70°C, 5-15 mg subsamples were folded in duplicates. The resulting 80 samples were put in the CHNS analyser. The vegetation samples have been analysed in runs of 70 soil samples during 10 hour periods.

C/N ratio

The vegetation C/N ratio was determined by dividing the C content by the N content resulting from the carbon and nitrogen content analysis.

Data analysis

Arc-Gis analysis Aerial photographs

The 15 aerial photographs of De Nederlanden area in Texel were analysed in Arc-Gis. Using the editor tool, bare sand coverage of the years 1996, 2000, 2003, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015 and 2016 was determined.

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Transect data

In Arc-map transect data of vegetation coverage and the sand layer thickness have been processed. Both the Spline interpolation and the spatial analyst tool were used to compose maps.

Statistical analysis Matlab

The data was further analysed using statistical tests in Matlab. Using independent t-tests, soil parameters including pH, EC, Bulk density, bare sand coverage, Ah layer thickness, C content, N content and C/N ratios were compared separately. Thereby, the following data was compared: the active blowout area vs the stable blowout area in 2018, the active blowout area for 2017 and 2018 and the stable blowout area in 2017 and 2018. To conduct further analysis on the C content, N content and C/N ratio, the transects were subdivided into three zones (table 1). This was done using the layout of Kolb (2017). These zones reduce homogeneity throughout the transect and provide a better analysis on the dynamics of the blowout itself. The

vegetation variables were analysed similarly using the dry weight, C content, N content and C/N ratio data.

To compare both the active and stable transect for 2017 and 2018, ANOVA (Analysis of Variance) was used. ANOVA tests were conducted for all soil and vegetation

characteristics. The C content, N content and C/N ratios were analysed in the three zones depicted in table 1. Furthermore, the vegetation coverage was also analysed for mosses, herbs and shrubs. Furthermore, t-tests were conducted to compare the differences observed in the ANOVA tests.

Results

In total 300 grid points and 40 transect points were made (figure 8).

Vegetation characteristics Dry weight

The dry weigh of the vegetation was significantly different between the active and stable blowout area in 2018. Here, the dry weight was higher in the stable area. The 2017-2018 comparisons indicated no significant dry weight differences for the active 2017-2018 comparison and the stable 2017-2018 comparison (appendix A tables 21-23).

N content

The nitrogen content is significantly different between the active and stable area in 2018 for the unaffected and

Table 1: Division of zones, Kolb (2017)

Figure 8: Transects points indicated in green and grid points indicated in red

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accumulation zone. The nitrogen content of the blowout zone is, however not significantly different when comparing the active and stable area in 2018. Furthermore, no significant differences were found for all zones at the active and stable for the active 2017-2018 comparison and the stable 2017-2018 comparison (appendix A tables 17, 19 and 21). C content

The carbon content differences significantly between the stable and active area in 2018 for the unaffected and accumulation zone. The carbon content of the blowout zone is however not significantly different between the active and stable area. Moreover, there was no significant difference found for all zones for the active 2017-2018 comparison and the stable 2017-2018 comparison (appendix A table 16, 18 and 20).

C n ratio

The C/N ratio is not significantly different for all zones at the stable and active area comparison of 2018. Also no significant differences were found for all zones at the active area comparison between 2017 and 2018. Contrary to the accumulation zone, where the C/N ratio is higher in 2018, no significant differences were found at the 2017-2018 stable area comparison for the blowout and unaffected zone (appendix A table 13-15).

Species cover

The 2018 moss, herb and shrub, lichens and grasses occurrence of the stable and active blowout were processed in arc-map (figures 9, 10, 11, 12 and 13). When looking at the ANOVA of moss occurrence between 2017 and 2018 , there seems to be a larger moss occurrence at the stable blowout area in 2018 compared to 2017 (appendix A figure 8). The corresponding t-test confirms a significant difference in moss occurrence at the stable blowout area between 2017 and 2018 (appendix A table 24). The other comparisons show no significant differences (appendix A tables 22, 23). Herb occurrence, on the other hand, seems to differentiate very little between the years 2017 and 2018. Overall, the test

suggests a lower herb occurrence at the active areas (appendix A figure 9). These differences are, however not significant (appendix A tables 22-24). Shrub occurrence implies a division between 2017 and 2018 for both the active and stable blowout areas, where 2018 has a higher shrub occurrence (appendix A figure 10).

These observed divisions are significant according to the corresponding t-tests (appendix A tables 22-24). Lichens and grasses seem to have a larger spread in the stabilized blowout area (appendix A figures 22 and 23). Nevertheless, no significant dissimilarities were found for the within 2018 grasses and lichens comparisons (appendix A table 22).

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Soil characteristics pH

The pH comparison between both the stable and active area for 2017 and 2018 resulted in what appears to be a difference between the active and stable blowout areas for 2018. Accordingly, the active blowout seems to have a higher pH. Moreover, the stable blowout appears to have a higher pH in 2018 (appendix A figure 1). The corresponding t-tests confirms a significant difference between the 2018 active and stable blowout area. Also, significant differences in pH of the stable area in 2017 compared to 2018 were found (appendix A tables 1-3).

Electrical conductivity

Figure 10: Herb cover, 2018

Figure 11: Shrub cover, 2018

Figure 12: Lichens cover, 2018

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The observed differences of electrical conductivity appear to mainly present between the stable blowout areas in 2017 and 2018. This comparison implies a lower electrical

conductivity in 2018. Additionally, some differences can be noticed between the stable and active location in 2018 (appendix A figure 2). The resulting p-values confirm a significant difference in electrical conductivity between the stable blowout areas in 2017 and 2018. The within year difference of 2018 is, however, not significant (appendix A table 1-3).

Bulk density

The bulk density results seems to differentiate on all comparisons. Suggested is here, that all 2018 values are higher. Also the bulk density of the active blowout area was probably larger than that of the active area in 2018 (appendix A figure 3). This is emphasised by the

resulting significance for the within year and between year comparisons (appendix A table 1-3).

Bare sand coverage

The within year bare sand coverage appears to be higher in the active 2018 blowout area. The bare sand coverage seems to differentiate very little for the 2017 and 2018 stable blowout area (appendix A figure 4). The resulting probability values confirm significance for the active-stable comparison in 2018 (appendix A table 1-3).

The spread of bare sand coverage for the active and stable blowout area was processed in Arc-Map for 2018 (figure 14).

The historical bare sand coverage provided possible bare sand differences between years (figure 15). The total bare sand coverage peaks in 2011. The lowest total bare sand coverage was observed in 2005. Furthermore, the areas directly surrounding the blowout seem to maximize in size during the years 2007,2008,2009 and 2011 (appendix A table 34).

Ah layer

The Ah layers of the active areas seem to have a larger spread the than those of the stable blowout areas. Suggested is, furthermore, that the active blowout area has a higher percentage of bare sand for the within year comparisons (appendix A figure 4). The

Figure 14: Bare sand coverage, 2018

Figure 15: Historical aerial photograph analysis for the blowout zone (orange) and total area (blue), bare sand coverage.

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corresponding t-tests do, however not confirm any significant difference (appendix A tables 1-3).

C/N ratio

The C/N ratio of the within 2018 comparison appears to have very little variation for the unaffected and accumulation zone. The blowout zone implies to have a higher C/N ratio at the active area (appendix A figures 5-7). This is emphasized by the significance of the

blowout zone active-stable comparison (appendix A table 4). The between year comparisons imply a higher C/N ratio for the unaffected and accumulation zone at the active blowout area in 2018 (appendix A figures 5-7). The blowout zone appears to have a lower C/N ratio in 2018. The differences are significant for all zones (appendix A table 5). The stable blowout area comparisons suggest a higher C/N ratio for the unaffected and accumulation zone in 2018. Here, the blowout zone seems to differentiate little (appendix A figures 5-7). The differences of the unaffected and accumulation zone are significant (appendix A table 6). Carbon content

At all zones, a higher C content is suggested for the resulting within year comparison in 2018 (appendix A figures 11-13). This is stressed by the significance of all zones (appendix A table 7).For the active area comparison, very little variance seems to be present between all zones. At the blowout zone very little variance can be noted. Furthermore, some

discrepancy can be observed between blowout zones, where the blowout zone seems to have a higher C content (appendix A figures 11-13). This is emphasised by the significant difference between the 2017 and 2018 active blowout zones (appendix A table 9). Some variety appears to be present at the stable 2017-2018 comparison. Of those variances, the C content seems to be a higher in 2018 (appendix A figures 11-13). This is emphasised by the significant difference between the unaffected zones of 2017 and 2018 (appendix A table 11). Nitrogen content

There seems to be a clear difference between the stable and active blowout area for all zones in 2018. Here, the active blowout areas appear to have a lower N content (appendix A figures 14-16). These observations are underlined by the corresponding t-tests (appendix A table 8). For the two year active comparisons, some variance occurs. A possible larger difference is observed at the blowout zone. Here, the N content seems to be higher in 2018 (appendix A figures 14-16). Emphasised is, that this difference is indeed significant

(appendix A table 10). The comparison for the stable blowout area in 2017 and 2018 appears to differentiate somewhat. The spread is however large as well (appendix A figures 14-16). The corresponding p values underlined that the N content between these areas did not differ significantly for all zones.

Discussion

Differences in blowout activity, Soil characteristics

The pH can be a good indicator of soil conditions in the area. Soil acidification is a natural process at stable soils. An increasing pH implies a disruption of this process. A rising pH can indicate fresh sand influx in grey dunes (Aggenbach et al., 2016). The stable blowout area is

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characterized by a lower pH than the active area in 2018. Therefore, a more active – high pH – area can still be distinguished from a more stabilized – lower pH – area. Another indicator of Eolic activity is bare sand coverage (Aggenbach et al., 2016). A higher pH will accordingly be expected at higher bare sand coverage. The significantly higher bare sand coverage and pH of the active blowout area emphasises the higher activity at the active blowout area. The pH of the active area did not change significantly, indicating equal activity in 2017 and 2018. The higher pH in the stable blowout area in 2018 suggests sand dispersion. Contradictory, no differences in bare sand coverage were found, implying little variance between 2017 and 2018.

The electronic conductivity is another factor used to determine the soil nutrient availability and acidity (Smith & Doran 1996). The electronic conductivity depends on texture and particle size of soils (Grisso et al., 2009). The EC found in 2018 indicates a larger spread at the active blowout area. This suggests larger variances in the 2018 active EC values, and a possible indictor of stabilizing processes. The mean differences did, however, not confirm these indications. The significantly larger EC in the stabilized blowout area in 2018 suggests sand influx. The influence of the scale of this process on the total magnitude of the stable blowout area is however not clear.

Bulk density is a measure of the sand content of a soil, where a greater bulk density indicates a higher sand content. A lower bulk density could furthermore be related to a higher organic matter content (Pulleman et al., 2000). This research affirms the higher bulk density in the active area in 2018, where young soils with a lower organic matter content are expected (Aggenbach et al., 2016). Larger bulk density values were also found in 2018 for both the stable and active areas implying a decrease of soil organic matter.

The higher nitrogen and carbon contents at the stable blowout area in 2018 were expected. The lower bare sand coverage at the stabilized blowout area reduces sand dispersion. Moreover, the smaller buffer capacity of calcareous poor grey dunes decreases the pH as observed in stabilized area in this study. The conditions favourable to biomass production and reduced organic matter decomposition appear to be present in the stabilized blowout area (Kooijman et al., 2005). As a result soil N and C contents increase, as observed. The timescale of this process and the effects of sand dispersion could have influenced the little, insignificant difference found at the 2017 to 2018 comparison. The differences in N and C content between the active blowout zones are contrary to the other zones

noteworthy here. These values could indicate a smaller activity in the blowout zone in 2018. The stabilized comparisons have resulted in little difference between 2017 and 2018. These results are in line with the inconvenience of natural reactivation (Kooijman et al., 2005). The C content in the unaffected zone in the stabilized area is higher. The N content found in this study does, however not correspond to this difference (Arens et al., 2013). This could be explained by the C and N characteristics of acid soils. These soils could have a larger C content. The microbial N fixation is then presumably smaller, resulting in a significant difference between C contents, but not for N contents in soils (Kooijman et al., 2005).

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The C/N ratio is related to the C and N content of the soil and is expected to become lower when fresh sand is deposited (Aggenbach et al., 2018). In contrast with these expectations, the 2018 comparison did not provide any different C/N ratios indicating no significant difference between the active and stable blowout zone. Moreover, the blowout zone had a larger C/N ratio at the active blowout area. This result is adverse, but can possibly be attributed to microbial activity at the active blowout zone (Kooijman et al., 2005). An indicator of reduced Eolic activity is provided by the higher C/N ratios in 2018 at the active area. This could be explained by reduced wind dispersion or differences in microbial activity. Unexpected here is, however the extreme significantly lower C/N ratio at the 2018 active blowout zone. This could imply a reactivation of the blowout itself, which seems unlikely. These differences are therefore probably based on errors. The stable comparisons are overall in line with the assumption that fresh sand influx in the stabilized areas is more difficult (Kooijman et al., 2005). No indications for increasing C/N ratios were found at the stabilized blowout zone, implying no further stabilization at this zone. Overall, the effects of blowouts zones in lime poor grey dunes could be less influential, as no very calcareous rich material is dispersed. Therefore, conditions favourable to sustainable Aeolic conditions are less likely to appear in lime-poor grey dunes. (Aggenbach et al., 2016)

Differences in vegetation characteristics

Vegetation indicators partially describe blowout activity, as vegetation dynamics are influenced by soil characteristics. Nitrogen rich vegetation indicates dominance in species abundance (Veer & Kooijman, 1997). This research indicates that the difference in

vegetation C and N content between the active and stable blowout area is still present (Kolb, 2017). The stabilized blowout area is characterized by a higher vegetation abundance and more acid conditions (Aggenbach et al., 2016). Long stabilized conditions favour nitrogen fixating vegetation. The resulting monocultures cause an increase of dry mass. According to Kooijman et al (2005), a higher vegetation abundance results in a reduced sand mobility. Furthermore, remobilizing a fixed upper soil layer will be increasingly difficult if vegetation is already present. The effects on the stabilized blowout area are, therefore, in line with the expected abundance and variance in dry weight of the vegetation. Supposed here is,

therefore, that a later succession stage is present in the stable blowout area (Veer, 1997). A higher N content would suggest a lower C/N ratio. Jones et al. (2004) found – however – higher C/N ratios at increasing N availability in soils. As vegetation parameters are influenced by soil nutrients, no changes in nitrogen inputs are suggested. Nevertheless, no differences in C/N ratios were found in this study, indicating little vegetation N variability.

The comparisons between both the active and stabilized areas in 2017 and 2018 did not result in contrasting C and N contents or dry weight differences. Aeolic activity is linked to fresh sand input, resulting in lower C and N concentrations and pioneering species abundance. Lichens are indicators of ecosystems in acid conditions. Lichens thrive in areas with a low Aeolic activity and in stabilized areas. Higher lichens abundance has a positive influence on grey dune diversity. Although no direct lichens comparison was conducted, total moss occurrence was higher in stable blowout 2018. This suggests could suggest

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increased diversity. Grasses, on the other hand, represent high N driven monocultures. No differences occur between the active and stable blowout areas in 2018. This is a possible indicator of previous activation, as ecosystem diversity in grey dunes can still benefit from previous activity (Aggenbach et al., 2016).

Herb cover did not differentiate for all comparisons indicating little to no variability in activity. The herb spread is, however interesting. There appears to be more herb cover in the accumulation zone, suggesting some activity. Shrub occurrence counteracts these

observations. The increasing shrub occurrence for both the stable and active blowout area between 2017 and 2018 could cause a reduction in diversity. Isermann (2008) found

competition advantages for herbs in grey dunes. This research also suggests an increasingly stronger domination of herb species. The effects of these occurrences on future stabilization in The Nederlanden remains, however unclear. Another potential factor of influence is the effect of the vegetation on blowout dynamics. Grey & Barker (2004) relate vegetation and root presence to a higher shear strength. Roots could therefore potentially reduce growing capabilities of the blowout zone. Overall, no extensive stabilization or activation processes seem to have taken place for vegetation characteristics between the spring of 2017 and the spring of 2018.

Storms and blowout activity

The aerial photographs have been analysed to provide historical bare sand coverage data. The most active years – containing the largest bare sand coverage – were found to be 2007,2008,2009 and 2011. These results could be compared with existing storm data of the Royal Dutch Meteorological Institute (KNMI). Interesting here is after comparisons were made, no higher bare sand coverage seems to occur after storms. According to the KNMI, the severest storm in the recorded period occurred in the autumn of 2013. A smaller

magnitude storm was furthermore observed in the early winter of 2013. These storms could have caused increased sand dispersion (Aggenbach et al., 2016). Despite these observations, the 2014 bare sand coverage area did not seem to have expanded. The other severe storms from 2000 (two storms), 2003 and 2016, did all not seem to have positively influenced bare sand coverage. These contradictory results could have been caused by short term storm activity. To sustain dynamic blowout systems yearly averaged wind speeds in excess of 6 Beaufort (10.8-13.8 m/s) have to be present (van der Meulen et al., 1996). At Texel, averaged wind speeds in excess of 6 m/s are recorded most of the year between 1981 and 2010. The Wadden islands including Texel belong to one of the most active areas in the Netherlands (KNMI, 2011). Eolic activity could, however, decrease as soil moisture contents are high (Aggenbach et al., 2016).

The only possible relation was found at the blowout zone. The bare sand coverage seems to have increased after the 2007 storm. The most active years found after the aerial photograph analysis could be the result of larger averaged yearly wind speeds or dry years. Local rodent populations form another potential source of the considerable expansion in those years (Kooijman et al., 2005).

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The January 2018 storm is the largest of the past 28 years (KNMI, 2018). This research confirms a significant bare sand cover difference between the active and stabilized areas in 2018. This indicates that the active and stabilized area are still distinguishable. The 2017-2018 comparisons describe no differences in dynamic activities of both areas, which could be attributed the previously mentioned mechanisms. A relative high activity in 2017 could also have been attributed to the little observed differences. The highest wind speeds were observed at Hoek van Holland, indicating a slight southwestern wind direction (KNMI, 2018). Despite the severity, the duration and wind direction of this storm could have been reducing factors at the effectiveness of enhancing blowout activity.

Lastly, no recent change in dispersions layers were found in this research, as the Ah layering comparisons did not provide any significant differences. The small effects of a storm event on dispersion layers is a potential cause of the insignificance in this comparison. Implications

The best efforts were taken to conduct a thorough research within the given time frame. However, some potential limitations of this research have to be mentioned.

The blowout zone is often not related to the other zones. This is the most dynamic part of the activate blowout. Still, some of the discrepancies could be the result of

disturbances in lime rich material. This can can be seen at the C/N ratios of the blowout zone comparisons between 2017 and 2018. Furthermore, a small margin of error has to be taken into account when working with laboratory devices. Another potential reducing factor is the effect of the vegetation on blowout dynamics. Other factors such a rodent populations could also influence bare sand coverage. The mechanisms of animals in this area was, however not covered in this research.

Lichens and grasses were not defined separately in 2017. These classes are direct indicators of N content and ecosystem variability. Therefore, no direct comparison between 2017 and 2018 could be made. Also, in 2018 part of the Ah layering observations were incomplete, just as the 2017 Ah layering data (appendix figures 25,26). Therefore, no accurate comparisons could be made between the Ah layers between and within years.

The Statistical tests were conducted between means of groups. Although the C content, N content and C/N ratio were divided in zones, still local differences could have been overseen. This discrepancies could be important in systems as complex and diverse as grey dunes (Aggenbach et al., 2016). Also, bare sand coverage and vegetation were

estimated in the field. Therefore some inconsistencies could occur between this data and the other data. Also estimates could differ between the 2017 and 2018 observations. The ANOVA’s could cause false indications as the scale was enlarged to improve the

observations. Also the ANOVA’s of the C content and N content of the unaffected-and blowout zones were insignificant, indicating no difference between all comparisons.

The aerial photographs provided some adversity as well. The quality of these

photographs was not equal amount years, where some photographs had a higher resolution or contrast. Also, the actual labelling of bare sand was an estimate by looking at colour differences. This was especially complicated by the photograph of 2013, which was

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discoloured. Lastly, the photographs of 1997, 1998, 1999, 2001, 2002 and 2004 were missing. These included potential comparisons between the storms of 1998 Late 2000 and 2002 (KNMI, 2018).

Conclusions

To conclude, the main question: ‘What is the impact of the January 2018 storm on the development of the active and stable blowout in lime poor grey dunes at Texel?’ can be answered. The January 2018 storm has had several positive influences on blowout activity. These indicators including a higher pH and bulk density are potential signals of increased activity. These variables could indicate a higher influx of fresh sand at the stabilized areas in 2018. Other factors, such as the nitrogen and carbon content showed very little difference between the years. Furthermore, some results seemed to have adverse effects. Also, vegetation characteristics indicated very little effects of the 2018 storm. Here, vegetation presence was a potential reducing factor in natural reactivation processes. Lichens indicate more diversity but cannot be significantly confirmed as this year subdivisions were made. Furthermore, plant growth potentially reduces the capabilities of blowout areas to grow through stabilizing characteristics of rooting systems. Stabilized systems seem to benefit less from increased Eolic activity. The aerial photograph analysis provided information about previous Eolic activity. The link with storms was, however, not noticeable. Other factors such as microbial and animal activity also have a large influence on Grey Dune ecosystems. The short duration of the 2018 storm probably caused little differences between the 2017 and 2018 comparisons. The overall scale and effect of the storm is therefore to be assumed little. The many variables included in this research have, however led to some uncertainties. The quantification of the overall effects of these storms is therefore important to assess and eventually predict the inner mechanism of these complex ecosystems. Therefore more research is needed to understand these protected habitats to preserve them and stimulate reactivation at other Grey Dune systems.

References

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Aggenbach C.J.S., Arens S.M., Kooijman A.M. & Lammers W.J. (2016). Beheeradvies activering eolische dynamiek op de Waddeneilanden als PAS-maatregel voor habitattype H2130 Grijze duinen. VBNE, Vereniging van Bos- en Natuurterreineigenaren Advies OBN-11-DK.

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Arens, B. (2007). De zeereep van Groote Keeten. Duin, 30(4), 12.

Arens, S. M., Slings, Q. L., Geelen, L. H., & Van der Hagen, H. G. (2013). Restoration of dune mobility in the Netherlands. In Restoration of coastal dunes (pp. 107-124). Springer, Berlin, Heidelberg.

Bowman, W. D., Cleveland, C. C., Halada, Ĺ., Hreško, J., & Baron, J. S. (2008). Negative impact of nitrogen deposition on soil buffering capacity. Nature Geoscience, 1(11), 767.

Van Boxel JH, Jungerius PD, Kieffer N & Hampele N, 1997. Ecological effects of reactivation of artificially stabilized blowouts in coastal dunes. Journal of Coastal Conservation 3: 57-62. European comission, Environment, nature and biodiverisity, EU nature law. Retrieved at 16-04-2018 from:

http://ec.europa.eu/environment/nature/legislation/habitatsdirective/index_en.htm Erisman, J. W., Domburg, P., De Haan, B. J., De Vries, W., Kros, J., & Sanders, K. (2005). The Dutch nitrogen cascade in the European perspective (No. 05-007). ECN. Chapter 4

Gray, D. H., & Barker, D. (2004). Root-soil mechanics and interactions. In Riparian vegetation and fluvial geomorphology (Vol. 8, pp. 113-123). Water science and Application, American Geophysical Union: Washington, DC.

Grisso, R.B., M. Alley, D. Holshouser and W. Thomason, 2009. Soil electrical conductivity. Virginia Cooperative Extension, Communications and Marketing, College of Agriculture and Life Sciences, Virginia Polytechnic Institute and State University, USA., pp: 442-508.

Haarsma, R., Tijm, S., & van den Brink, H. (2018). Zeer zware storm van 18 januari. KNMI-klimaatbericht. Retrieved from: https://www.knmi.nl/over-het-knmi/nieuws/zeer-zware-storm-van-18-januari at 26-04-2018

Hicks, W. K., Whitfield, C.P., Bealey, W.J., Sutton, M.A. (2011). Nitrogen Deposition and Natura 2000: Science and Practice in Determining Environmental Impacts. COST729/ Nine/ESF/CCW/JNCC/SEI Workshop Proceedings, published by COST. Available at: http:// cost729.ceh.ac.uk/n2kworkshop

Holland, E. A., Braswell, B. H., Sulzman, J., & Lamarque, J. F. (2005). Nitrogen deposition onto the United States and Western Europe: synthesis of observations and models. Ecological applications, 15(1), 38-57.

Isermann, M. (2008). Expansion of Rosa rugosa and Hippophaë rhamnoides in coastal grey dunes: effects at different spatial scales. Flora-Morphology, Distribution, Functional Ecology of Plants, 203(4), 273-280.

Janssen, G. M. (1993). De eutrofieering van de Noordzee en de Waddenzee, een tussenbalans. Zien we al resultaten van het saneringsbeleid?. H2O, 26, 86-91.

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Jones, M. L. M., Wallace, H. L., Norris, D., Brittain, S. A., Haria, S., Jones, R. E. & Emmett, B. A. (2004). Changes in vegetation and soil characteristics in coastal sand dunes along a gradient of atmospheric nitrogen deposition. Plant Biology, 6(5), 598-605

Daggegevens van het weer in Nederland (18-01-2018). Klimatologie, KNMI retrieved from: http://projects.knmi.nl/klimatologie/daggegevens/index.cgi at 26-04-2018

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https://www.knmi.nl/nederland-nu/klimatologie/lijsten/zwarestormen at 25-06-2018 langjarig gemiddelde 1981-2010 per maand, KNMI retrieved from:

http://www.klimaatatlas.nl/klimaatatlas.php?wel=wind&ws=kaart&wom=Gemiddelde%20w indsnelheid at 26-06-2018

Kolb, E.M. (2017). Active blowouts as management measure for grey dunes on Texel. Bachelor Thesis.

Kooijman, A.M., Besse M. & Haak R. (2005). Effectgerichte maatregelen tegen verzuring en eutrofiering in open droge duinen. Eindrapport fase 2. Directie Kennis, Ministerie van Landbouw, Natuur en Voedselkwaliteit, rapport nr. 2005/dk008-O, 158 pp.

Kooijman, A. M., Noordijk, H., van Hinsberg, A., & Cusell, C. (2009). Stikstofdepositie in de duinen: een analyse van N-depositie, kritische niveaus, erfenissen uit het verleden en stikstofefficiëntie in verschillende duinzones.

Van der Meulen F., Kooijman A.M., Veer M.A.C. & Van Boxel J.H. (1996). Effectgerichte maatregelen tegen verzuring en eutrofiering in open droge duinen. Fysisch Geografisch en Bodemkundig Laboratorium, Universiteit van Amsterdam, 232 pp.

Provoost, S., Jones, M. L. M., & Edmondson, S. E. (2011). Changes in landscape and

vegetation of coastal dunes in northwest Europe: a review. Journal of Coastal Conservation, 15(1), 207-226.

Pulleman, M. M., Bouma, J., Van Essen, E. A., & Meijles, E. W. (2000). Soil organic matter content as a function of different land use history. Soil Science Society of America Journal, 64(2), 689-693.

Robertson, G. P., & Vitousek, P. M. (2009). Nitrogen in agriculture: balancing the cost of an essential resource. Annual review of environment and resources, 34, 97-125.

Smith, J. L., & Doran, J. W. (1996). Measurement and use of pH and electrical conductivity for soil quality analysis. In Methods for assessing soil quality (Vol. 49). Soil Science Society of America Madison, WI.

Veer, M., & Kooijman, A. (1997). Effects of grass-encroachment on vegetation and soil in dutch dry dune grasslands. Plant and Soil, 192(1), 119-128.

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Veer, M. A. C. (1997). Nitrogen availability in relation to vegetation changes resulting from grass encroachment in Dutch dry dunes. Journal of Coastal Conservation, 3(1), 41-48. Wang, Z. B., Hoekstra, P., Burchard, H., Ridderinkhof, H., De Swart, H. E., & Stive, M. J. F. (2012). Morphodynamics of the Wadden Sea and its barrier island system. Ocean & coastal management, 68, 39-57.

Witz L, 2015. The potential of small-scale blowout activity for landscape diversity in the Dutch grey dunes. Master Thesis, University of Amsterdam.

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25 APPENDIX A

Soil parameters P value Significant

pH 0.000005 Yes

EC (mS/cm) 0.1646 No

BD (g/cm3) 0.00006 Yes

Bare sand coverage (%) 0.0051 Yes

Ah-layer thickness (cm) 0.1601 No

C/N-ratio 0.1408 No

pH 0.5197 No

EC (mS/cm) 0.2823 No

BD (g/cm3) 0.0068 Yes

Bare sand coverage (%) 0.8208 No

C/N-ratio 0.2862 No

pH 0.0041 Yes

Table 1 Comparison active vs stable, 2018 (t-tests)

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EC (mS/cm) 0.0027 Yes

BD (g/cm3) 0.0141 Yes

Bare sand coverage (%) 0.7454 No

C/N-ratio 0.00004 Yes

Zones P-value Significant

Unaffected Zone 0.1115 No

Blowout Zone 0.0199 Yes

Accumulation Zone 0.6709 No

Unaffected Zone 0.0279 Yes

Blowout Zone 8.5197e-05 Yes

Accumulation Zone 0.0039 Yes

Blowout Zone 0.1214 No

Table 3 Comparison 2017 vs 2018, stable (t-tests)

Table 4 Comparison C/N ratio Active-Stable 2018 Soil

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Table 6 Comparison C/N ratio Stable 2017-2018 Soil

Table 7 Comparison C content Active-Stable 2018 Soil

Table 8 Comparison N content Active-Stable 2018 Soil

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Table 10 Comparison N content Active 2017-2018 Soil

Table 11 Comparison C content Stable 2017-2018 Soil

Table 12 Comparison N content Stable 2017-2018 Soil

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Unaffected Zone 4.1554e-04 Yes

Table 14 Comparison C/N ratio Active 2017- 2018 Vegetation

Table 15 Comparison C/N ratio Stable 2017- 2018 Vegetation

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Table 17 Comparison N content Active-Stable 2018 Vegetation

Table 18 Comparison C content Active 2017- 2018 Vegetation

Table 19 Comparison N content Active 2017- 2018 Vegetation

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Vegetation parameters P value Significant

Dry weight 5.6653e-04 Yes

C content (g/m2) 6.7657e-04 Yes

N content (g/m2) 0.0031 Yes C/N ratio 0.2123 No Lichens (%) 0.1731 No Mosses (%) 0.0782 No Herbs (%) 0.3056 No Shrubs (%) 0.0664 No Grasses (%) 0.1202 No

Dry weight 0.6232 No

C content (g/m2) 0.3109 No

N content (g/m2) 0.8450 No

Table 21 Comparison N content Stable 2017- 2018 Vegetation

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C/N ratio 0.4168 No

Mosses (%) 0.3684 No

Herbs (%) 1.00 No

Shrubs (%) 0.0124 Yes

Dry weight 0.6080 No

C content (g/m2) 0.3321 No

N content (g/m2) 0.9439 No

C/N ratio 0.0012 Yes

Mosses (%) 4.3936e-6 Yes

Herbs (%) 0.9665 No

Shrubs (%) 8.0346e-04 Yes

Soil parameters Mean A 2017 Mean A 2018 Std A 17 Std A 18

pH 6.4945 6.6825 1.0195 0.7968

EC (mS/cm) 76.89 63.715 38.0064 38.3993

BD (g/cm3) 1.1964 1.3610 0.1978 0.1642

Table 23 Comparison active 2017-2018 (t-tests) Vegetation

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33 Bare sand coverage (%) 23.5 25.8 32.48 31.29 C content (g/m2) complete transect 808.79 787.67 515.37 558.30 C content (g/m2) unaffected 937.67 838.16 614.1 628.91 C content (g/m2) blowout 257.16 381.44 89.08 88.25 C content (g/m2) accumulation 950.80 912.45 446.33 589.29 N content (g/m2) complete transect 69.20 56.88 47.71 43.84 N content (g/m2) unaffected 86.68 62.54 51.57 43.42 N content (g/m2) blowout 4.1 16.85 1.51 8.33 N content (g/m2) accumulation 84.92 68.87 33.76 45.41 C/N-ratio complete transect 21.2832 15.8796 21.4914 6.0948 C/N-ratio unaffected 10.7954 13.1410 1.8225 0.7137 C/N-ratio blowout 63.0864 25.3589 1.7406 7.8859 C/N-ratio accumulation 10.8493 13.6774 1.2591 2.5869

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34

Soil parameters Min A 17 Min A 18 Max A 17 Max A 18

pH 5.15 5.50 8.70 7.92 EC (mS/cm) 27.60 19.70 160.40 127.40 BD (g/cm3) 0.8098 1.02 1.5745 1.59 Bare sand coverage (%) 0 0 100 100 C content (g/m2) complete transect 204.68 294.15 1824.18 2101.20 C content (g/m2) unaffected 288.17 390 1824.18 1923.90 C content (g/m2) blowout 204.68 294.15 389.85 504.10 C content (g/m2) accumulation 355.24 433.65 1667.32 2101.20 N content (g/m2) complete transect 3.20 9.06 162.38 153.82 N content (g/m2) unaffected 23.34 31.51 162.38 136.43 N content (g/m2) blowout 3.20 9.06 6.36 27.12

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35 N content (g/m2) accumulation 39.11 21.67 138.71 153.82 C/N-ratio complete transect 7.7661 11.5686 64.7059 32.4561 C/N-ratio unaffected 7.7661 12.3762 12.3494 14.1020 C/N-ratio blowout 61.2903 18.4783 64.7059 32.4561 C/N-ratio accumulation 8.7163 11.5686 12.5676 20.9302

Soil parameters Mean S 17 Mean S 18 Std S 17 Std S 18

pH 5.1330 5.6240 0.5959 0.4015 EC (mS/cm) 78.64 47.875 28.5394 31.9963 BD (g/cm3) 0.9862 1.1325 0.1998 0.1570 Bare sand coverage (%) 4.65 3.6 8.1839 11.7983 C content (g/m2) complete transect 1400.80 1888.15 586.71 921.63 C content (g/m2) unaffected 1298.58 2364.06 461.91 719.23 C content (g/m2) 1037.81 1396.40 833.78 629.57

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36 blowout C content (g/m2) accumulation 1579.25 1850.64 516.88 1037.56 N content (g/m2) complete transect 116.96 135 38.74 62.40 N content (g/m2) unaffected 114.63 168.90 32.42 47.61 N content (g/m2) blowout 92.16 108.58 54.3 51.27 N content (g/m2) accumulation 127.03 129.18 34.44 69.37 C/N-ratio complete transect 11.4816 13.7951 1.9286 1.1283 C/N-ratio unaffected 11.1413 13.9385 1.1287 0.6961 C/N-ratio (blowout) 9.8893 12.9048 3.2711 0.6955 C/N-ratio (accumulation) 12.2153 14.0536 1.2591 2.5869

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Soil parameters Min S 17 Min S 18 Max S 17 Max S 18

pH 4.06 4.6 6.13 6.05 EC (mS/cm) 35.8 19.2 139.1 140.9 BD (g/cm3) 0.6009 0.89 1.3378 1.55 Bare sand coverage (%) 0 0 25 50 C content (g/m2) complete transect 292.69 449.50 2367.86 3261.85 C content (g/m2) unaffected 785.53 1616.50 1910.11 3213.2 C content (g/m2) blowout 292.69 576.20 1920.62 2106.50 C content (g/m2) accumulation 561.86 449.50 2367.86 3261.85 N content (g/m2) complete transect 43.17 34.02 169.31 222.14 N content (g/m2) unaffected 83.16 118.13 159.82 216.92 N content (g/m2) blowout 43.17 45.96 139.23 170.34 N content (g/m2) accumulation 58.13 34.02 169.31 222.14 C/N-ratio complete 6.7797 11.76 14.14 15.87

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38 transect C/N-ratio unaffected 9.2184 12.9966 11.9520 14.8128 C/N-ratio blowout 6.7797 12.3668 13.7942 13.9125 C/N-ratio accumulation 9.6663 11.7585 14.1412 15.8749 Vegetation parameters Mean S 2017 Mean S 2018 Std S 2017 Std S 2018 Dry weight (g) 151.5440 140.5060 72.7472 61.7841 C content (unaffected) (g/m2) 77.8720 64.1395 32.2714 20.9385 C content (blowout) (g/m2) 51.8400 51.3657 27.0649 20.1575 C content (accumulation) (g/m2) 83.5200 70.8252 39.7506 37.7563 N content (unaffected) (g/m2) 1.8998 2.0382 0.8037 0.4722 N content (blowout) (g/m2) 1.4259 1.6125 0.7753 0.5947 N content (accumulation) (g/m2) 2.0788 1.9823 1.0147 0.9293 C/N-ratio (unaffected) 40.8008 31.6809 5.2324 7.4965

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39 C/N-ratio (blowout) 37.9591 31.9611 7.5413 2.8288 C/N-ratio (accumulation) 40.5505 35.3595 7.0017 3.8095 Vegetation parameters Mean A 17 Mean A 18 Std A 17 Std A 18 Dry weight (g) 87.2240 79.6940 56.7096 37.4952 C content (unaffected) (g/m2) 48.7840 38.0598 18.7059 13.9326 C content (blowout) (g/m2) 23.1200 29.4776 19.8802 27.7126 C content (accumulation) (g/m2) 48.7127 37.5298 32.5438 14.1974 N content (unaffected) (g/m2) 1.2216 1.1270 0.3442 0.6375 N content (blowout) (g/m2) 0.9816 1.2754 0.8009 1.2989 N content (accumulation) (g/m2) 1.3630 1.2204 0.8484 0.4020 C/N-ratio (unaffected) 39.8187 7.8574 37.6957 10.6878 C/N-ratio (blowout) 17.2355 11.6079 19.2848 14.0833

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40 C/N-ratio (accumulation) 36.0765 7.5830 30.9015 7.7049 Vegetation parameters

Min S 17 Min S 18 Max S 17 Max S 18

Dry weight (g) 46.5600 61.1200 302.8800 340.8000 C content (unaffected) (g/m2) 28.0800 38.0670 110.8800 89.4159 C content (blowout) (g/m2) 23.2800 28.8517 83.4400 77.4915 C content (accumulation) (g/m2) 33.7600 35.7556 151.4400 167.5373 N content (unaffected) (g/m2) 0.8062 1.2286 2.7315 2.4429 N content (blowout) (g/m2) 0.4930 0.8498 2.3579 2.2459 N content (accumulation) (g/m2) 0.8713 1.0146 4.3421 4.1828 C/N-ratio (unaffected) 34.8286 48.2564 19.5000 39.6797 C/N-ratio (blowout) 29.3288 47.2193 28.4089 34.5034 C/N-ratio 31.1518 53.7534 30.1128 41.9040

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41 (accumulation)

Vegetation parameters

Min A 17 Min A 18 Max A 17 Max A 18

Dry weight (g) 0 0 278.4000 157.7600 C content (unaffected) (g/m2) 27.5200 17.1265 73.8400 52.9576 C content (blowout) (g/m2) 0 0 45.7600 65.4783 C content (accumulation) (g/m2) 22.8000 20.4893 139.2000 60.3075 N content (unaffected) (g/m2) 0.6626 0.4340 1.5370 1.9979 N content (blowout) (g/m2) 0 0 1.8536 2.9479 N content (accumulation) (g/m2) 0.5064 0.7066 3.7286 2.1061 C/N-ratio (unaffected) 28.3924 48.0425 26.5071 54.7141 C/N-ratio (blowout) 0 24.6865 0 33.8183 C/N-ratio (accumulation) 22.8353 48.5452 20.6273 44.6398

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42 Year Bare Sand (m2) Mean (m2) Std (m2) Min (m2) Max (m2)

1996 44.771 243 384 4 3.213 2000 57.468 182 348 0 2.843 2003 42.435 71 181 0 2.781 2005 22.364 97 153 3 1.082 2006 65.838 116 334 0 4.102 2007 81.141 118 755 2 18.798 2008 83.082 130 822 0 19.042 2009 82.322 136 482 0 6.349 2010 57.172 114 813 1 17.869 2011 150.803 218 1.455 0 18.477 2012 50.580 139 403 0 3.686 2013 43.938 85 344 0 5.663 2014 43.102 95 722 0 13.454 2015 48.144 112 496 0 6.918 2016 26.175 93 312 0 3.120 Vegetation coverage 2018 Mean Active Mean Stable Max Active Max Stable Lichens 12.00 21.25 50 70 Mosses 30.75 47.00 80 80 Herbs 11.50 15.50 50 40 Shrubs 18.50 27.50 40 65 Grasses 23.50 33.00 50 80

Table 32 Minima and maxima of active blowout for 2017 and 2018. Vegetation

Table 33 Vegetation coverage 2018

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43 Figure 1 ANOVA pH 2017 2018 stable and active comparison

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44 Figure 2 ANOVA EC 2017 2018 stable and active comparison

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45 Figure 3 ANOVA BD 2017 2018 stable and active comparison

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46 Figure 4 ANOVA bare sand coverage 2017 2018 stable and active comparison

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47 Figure 5 ANOVA C/N ratio unaffected zones 2017 2018 stable and active comparison

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48 Figure 6 ANOVA C/N ratio blowout zones 2017 2018 stable and active comparison

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49 Figure 7 ANOVA C/N ratio accumulation zones 2017 2018 stable and active comparison

(50)

50 Figure 8 ANOVA occurrence of mosses 2017 2018 stable and active comparison

(51)

51 Figure 9 ANOVA occurrence of herbs 2017 2018 stable and active comparison

(52)

52 Figure 10 ANOVA occurrence of shrubs 2017 2018 stable and active comparison

(53)

53 Figure 11 ANOVA C content Unaffected zones 2017 2018 stable and active comparison

(54)

54 Figure 12 ANOVA C content blowout zones 2017 2018 stable and active comparison

(55)

55 Figure 13 ANOVA C content Accumulation zones 2017 2018 stable and active comparison

(56)

56 Figure 14 ANOVA N content Unaffected zones 2017 2018 stable and active comparison

(57)

57 Figure 15 ANOVA N content blowout zones 2017 2018 stable and active comparison

(58)

58 Figure 16 ANOVA N content Accumulation zones 2017 2018 stable and active comparison

(59)

59

Not significant

Figure 17 ANOVA C content Accumulation zones vegetation 2017 2018 stable and active comparison

(60)

60

Not significant

(61)

61 Figure 19 ANOVA C content Accumulation zones vegetation 2017 2018 stable and active

(62)

62

Not significant

(63)

63

Not significant

(64)

64 Figure 22 ANOVA N content Accumulation zones vegetation 2017 2018 stable and active

(65)

65 Figure 23 ANOVA occurrence of grasses active vs stable blowout area, 2018

(66)

66 Figure 24 ANOVA occurrence of lichens active vs stable blowout area, 2018

(67)

67 Figure 25 Depth of the first Ah layer, 2018

Accessing the effects of the January 2018 storm on blowout activity in grey dunes at ‘De Nederlanden’ at Texel. A comparison with 2017 and historical aerial photograph data