Storm impact and blowout activity in grey dunes on Texel

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Storm impact and blowout activity in grey dunes on Texel

The impact of the January 2018 storm on the development of an active and stabilized blowout area in grey dunes in De Nederlande n, Texel

Bachelor thesis Sien Snijder

Future Planet Studies, Earth Sciences, University of Amsterdam 2-7-2018, Amsterdam

First supervisor: A.M. Kooijman Second supervisor: J.H. van Boxel

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Abstract

Blowout activity has proven to lead to positive effects in counteracting soil acidification caused by nitrogen deposition. Blowouts provide fresh nutrient-poor sand for wind transportation. After deposition this sand can buffer the pH, making it more suitable for pioneer species to thrive. Reactivation of blowouts have been used as a strategy against soil acidification and grass-encroachment in species-rich grey dunes in the coastal region of the Netherlands. Storms are thought to have influence on the amount of blowout activity, as wind reaches high velocities which could transport large amounts of sand. In January 2018 a severe storm moved across the

Netherlands with velocities of 120 km/hour. The main goal of this study is to asses the impact of the storm on the development of an active and stabilized blowout area in a grey dune area. A field study was conducted in De Nederlanden on Texel, a grey dune area in which blowout activity occurs naturally. Data of 2017 has been compared to newly obtained data for 2018 and shows that the blowout activity still leads to a higher pH, less nutrients in the soil and lower aboveground biomass. An aerial photo analyses has been done to study the amount of blowout activity over the years and this has been coupled to data on severe storms. The analysis shows that storms are often not the cause for the amount of blowout activity in De Nederlanden. Heavy rainfall could lead to initiation or expansion of blowouts. However, extensive blowout activity has likely taken place and is possibly the cause of an increased pH and bulk density in the stabilized blowout area.

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Content

Abstract ... 2 Content... 3 Introduction ... 4 Theoretical framework... 6 Research area... 7 Methodology... 8 Results ... 12

Comparison of the stable and active area for 2018... 12

Comparison between 2017 and 2018 for the active area ... 14

Comparison between 2017 and 2018 for the stable area ... 14

Aerial photo analysis ... 15

Discussion ... 16

Blowout activity and influence on soil and vegetation ... 16

Development of blowout areas ... 17

Storms and blowout activity in De Nederlanden, Texel ... 18

Implications ... 19

Conclusion ... 20

References ... 21

Appendix A – T-tests and correlations ... 22

Appendix B – Means, standard deviations, minima and maxima. ... 27

Appendix C - ANOVA’s for comparison of the groups ‘stable 17’, ‘stable18’, ‘active17’ and ‘active18’. ... 34

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Introduction

Coastal dunes provide many ecosystem services, such as water catchment, sand mining, recreation, coastal protection and nature conservation (Barbier et al., 2011). The Dutch coast is stretched out over the full length of the country and consequently the country has a long history of floods and coastal management. Climate change and corresponding scenarios of sea level rise along the Dutch coast predict a rise of 0.5 to 1.25 m in 2100 and emphasize the need for flexible coastal management strategies (Katsman et al., 2009; Vellinga et al., 2009). Another aspect that stresses the importance of the Dutch dunes is its function for nature conservation. The Dutch dunes host almost 70% of the species of the country’s flora (Veer & Kooijman, 1997) and consist of habitats with rare and exclusive vegetation communities protected under the Natura 2000 regulation.

However, over the last centuries the dunes in the Netherlands have been suffering from increased inputs of atmospheric nitrogen leading to soil acidification and eutrophication. As a result of the increased nutrient inputs large parts of the coastal dunes became dominated by tall grasses (Van Boxel et al., 1997). Former coastal management has contributed to this as it was focused on stabilizing dunes and preventing wind erosion by planting marram grasses (Jungerius & van der Meulen, 1988; Van der Meulen et al., 1996). This grass-encroachment is associated with a decrease in species diversity and decreasing number of species in dune landscapes (Veer & Kooijman, 1997), eventually leading to a more monotonous and stabilized dune landscape.

Particularly, grey dunes have been undergoing the negative effects of increased nitrogen-deposition and grass encroachment. Grey dunes are habitats protected by the Habitat Directive and consist of more or less fixed, stabilized dunes with herbaceous vegetation, mosses and lichens. These habitats suffer from the decreased pH and the reduction in dynamics, but also from a sharp decline in the rabbit population, as they provide grazing (Kooijman et al., 2005). For the conservation of grey dunes input of fresh, nutrient-poor sand is needed to increase the pH and allow new succession for both soil development and vegetation growth (Witz, 2015).

Nowadays we know that, contradictory to the former management strategy of stabilizing, dunes would not exist without wind action (Kooijman et al., 2005). Processes underlying aeolian activity lead to the rejuvenation of dune landscapes resulting in a more diverse landscape containing different types of vegetation (Kooijman et al., 2005; van Boxel et al., 1997). This understanding has caused coastal dune management to shift towards a more dynamic approach, in which natural processes are stimulated.

A strategy for allowing aeolian activity in the inner dunes of which increasing attention has been paid to last couple of years is the reactivation of blowouts. Blowouts, parts in the dunes where sand is exposed and aeolian activity is high, were formerly seen as a threat to the protective function of the dunes against sea level rise (Kooijman et al., 2005, Van Boxel et al., 1997). Thus, they were not stimulated in their development and this has led to a relatively low number of blowout areas in the coastal dunes of the Netherlands. Nonetheless, studies have shown the benefits of reactivating blowouts and proven their counteracting effects on eutrophication and soil acidification (Van Boxel et al., 1997; Kooijman et al., 2005). Blowouts could provide input of fresh nutrient-poor sand for the preservation of grey dunes.

In January 2018 a storm hit the Netherlands with wind speeds of over 120 km/h. The storm was relatively small (500 km wide) and short (7 hours), but the impact was severe (KNMI, 2018). A storm with the average velocity of the one in January occurs every 8 years (KNMI, 2018). A storm of

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such intensity may have caused high aeolian activity in dune areas and potentially stimulated the formation or reactivation of blowouts. Blowouts can be initiated by high velocity winds by sand burial or removal of vegetation (Hesp, 2002). However, it is still unknown what the exact effect is of a storm on blowout areas.

Last couple of years, coastal dune areas consisting of lime-poor and lime-rich grey dunes in the Netherlands have been studied for the effects of blowout activity and reactivation of blowouts (Kooijman et al, 2005; Aggenbach et al, 2016; OBN, 2018, in press). A higher pH, more bare sand coverage, less carbon in the topsoil and a lower C/N-ratio of the soil were observed effects in active blowout areas (OBN, 2018, in press). Studies also emphasized the struggle to keep reactivated blowout areas active on the long-term, particularly in the Waddendistrict (Kooijman et al., 2005). It stresses the importance of extended research in the Waddendistrict to obtain more insight on the underlying processes of blowout activity and blowout reactivation.

During the fieldwork of this study an active blowout area and a stabilized blowout area have been visited again to analyse the impact of the storm on their development. The main question is: What is the effect of the January storm of 2018 on the development of the active and stabilized blowout areas in De Nederlanden? The first sub-question will revise the differences between the two blowout areas for 2018. Other sub-questions will focus on the effect of storm activity on soil and vegetation parameters by comparing the newly obtained data with the data of 2017. Expectations are that differences have remained between the active and the stable blowout areas and that the blowout activity in the active area leads to higher pH and a higher species diversity compared to the stable area. The hypothesis regarding the storm is that the high wind speeds have caused high aeolian activity in the area and consequently led to fresh sand deposits in a large part of the study area. Finally, it is expected that the storm might have increased the active blowout area by initiating new blowouts or expansion of the active blowout.

Figure 1. Geomorphology of a blowout. (Hesp, 2002)

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Theoretical framework

The increase in airborne nitrogen pollutants is one of the major threats for natural and semi-natural ecosystems leading to extensive soil acidification, groundwater pollution and disturbed nutrient balances (Galloway, 1995). Despite the successful reduction of acidifying emissions, the Netherlands is one of the countries with the highest risks of the effects of nitrogen deposition, because of high levels of nitrogen still present (Slootweg et al., 2014). The Dutch government has set up a program called PAS (Programma Aanpak Stikstof) to preserve its nature and protect the Natura 2000 habitats from eutrophication and acidification. 118 out of the 160 Natura 2000 areas in the Netherlands suffer under increased atmospheric nitrogen inputs and are incorporated into PAS.

In coastal dune areas and inland dune grasslands the main effects of increased nitrogen input s are an accelerated succession and increase in biomass (Bobbink et al., 2010). Increased nitrogen deposition is very likely the main driver for grass-encroachment in dunes and the creation of a monotonous dune landscape. Grass-encroachment in dry dunes is associated with a decline in species diversity, particularly mosses and lichens (Veer & Kooijman, 1997). The increase in aboveground biomass also inhibits light availability for small species and may cause their disappearance (Veer & Kooijman, 1997).

The effects of nitrogen deposition and the corresponding measures are different for lime-rich and lime-poor dunes. The Dutch coastal dunes can be divided into two zones with regard to soil chemistry: the Renodunaal district, which is south of Bergen/Egmond, and the Waddendistrict north of this. The main difference is that they differ in primary lime-content: the Renodunaal district contains 2-10%, whereas the Waddendistrict contains 0.5-2% (Kooijman et al., 2005). Another factor characterizing the Waddendistrict is the nutrient-poor sand originating from glacial sands deposited during the Saalian (Eisma, 1968). The study area De Nederlanden is located in the Waddendistrict, hence this study focuses on lime-poor (grey) dunes.

Grey dunes have a high coverage with mosses and lichens leading to their slightly grey colour (Witz, 2015). They are found more land inwards than the white dunes covered with marram grasses and are stabilized. The grey dunes in De Nederlanden are lime-poor and lack the buffer capacity that lime-rich grey dunes have and are therefore more prone to acidification. The effects of eutrophication and acidification could be counteracted when nutrient-poor sand is deposited by the wind (Van Boxel et al., 1997; Van der Meulen et al., 1996). Unfortunately, a negative effect of fresh sand deposition is that it could stimulate the succession of marram grasses (Van Boxel et al., 1997; Kooijman et al., 2005). To trigger aeolian activity and fresh sand deposition blowouts could provide suitable conditions. A blowout can be described as a cup-shaped depression or hollow formed by wind erosion on a pre-existing sand deposit (Hesp, 2002). The blowout makes sand available for transport by wind after which it can be deposited. The geomorphology of a blowout can be described in three components: the depositional lobe, the deflation basin and the erosional walls, as displayed in Figure 1. In the process of wind erosion at the deflation zone and accumulation of sand at the depositional lobe, the position of a blowout can slowly change in upward wind direction (Witz, 2015). A blowout can grow in depth and size, depending on the rate of wind erosion. Reactivation of blowouts have been successful. A study of Van Boxel et al. (1997) showed that after reactivation blowouts grow in size and increased in depth. Deepening of the blowout is fortunate as it reaches nutrient-poor or lime-rich sand. The deposition of this sand can facilitate the succession of pioneer species by locally lowering the pH of the soil (Kooijman et al., 2005).

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Research area

The research is done in the coastal dunes north of De Koog on Texel. Before the Middle Ages Texel was smaller, orientated more to the east and consisted of salt marshes (Aggenbach et al., 2016). West from the former centre of the island there was a long dune complex stretching out towards the North, in between what is now Den Hoorn and De Koog. This was the beginning of the current sand dike. From the parabolic dune complexes that can be clearly seen south of and around De Koog, it is assumed that aeolian activity must have been high in that area, indicating a high potential for successful activation of blowouts (Aggenbach et al., 2016). More south of these parabolic dune complexes, below pole 16, the inner dunes have been stabilized for a long time and have probably decalcified quite deep (Aggenbach et al., 2016), therefore the potential for successful reactivation here is low.

The dune area this research is focused on is called De Nederlanden, situated north of De Koog in the area that has high potential for successful reactivation. Since 2000, the number of blowouts has increased in this area and with this blowout activity has been increasing (Aggenbach et al., 2016). Although reactivation potential is high, no measures have been taken in this area yet. De Nederlanden has been studied for its high aeolian activity and its natural active and stabilized blowouts in a lime-poor area. One of the reasons for this high aeolian activity is presumably the favourable position of Texel with respect to the net transport direction. Other factors beneficial about this geographical location is that De Nederlanden is only 350 meters from the foot of the fore dunes, relatively close to the sea, and the large active blowout is approximately 20 meters above NAP (Nationaal Amsterdams Peil). Additionally, the high abundance of rabbits in the period 1996-2016 are favourable for aeolian activity, as rabbits provide grazing and maintain the vegetation (Aggenbach et al., 2016; OBN, 2018, in press).

A recent study showed that De Nederlanden has a relatively high diversity compared to lime-rich dunes (OBN, 2018, in press). This was unexpected as a study before showed that lime-lime-rich dunes in general have a higher species diversity compared to lime-poor dunes (Aggenbach et al., 2016). The highest diversity on Texel is found in the aeolian active areas, such as De Nederlanden (OBN, 2018, in press). This dune area consists mainly of lime-poor grey dunes and is part of the Natura 2000 protected habitats. To conserve this habitat larger blowout areas are necessary of which the deflation zones reach the lime-rich sand that lays deeper (Aggenbach et al., 2016). In this way, small patches of pioneer species that prefer base-rich conditions will be maintained.

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Methodology

An overview of the research is given in Table 1. A large part of the methodology is based on study of Witz (2015), which has focused on open dune grasslands and blowout activity.

Fieldwork

The fieldwork will be conducted in two blowout areas, one with an active blowout and one with a stabilized blowout. For both study areas transects studies and grid point analyses will be performed in order to analyze soil and vegetation. An overview of the types of samples and measurements taken for both analyses can be found in Table 2.

Study Data collection Data analysis

Research proposal • Theoretical framework • Methodology • Expected results Concept report Final report • Results

• Discussion & conclusions

Fieldwork

• Transect analysis • Gridpoint analysis

Laboratory testing

• Bulk density of soil • pH of soil

• EC of soil • C/N content soil • Dry weight vegetation • C/N content vegetation

Statistical analysis

• ANOVA test for more than two groups • T-test for two groups

GIS processing

• Interpolation grid points

Table 1. Overview of research.

Transects Gridpoints

Notations • GPS location

• Type and percentage of vegetation cover • Soil profile description • Two pF-ring soil samples • Vegetation

determination • Vegetation sample

• GPS location

• Type and percentage of vegetation cover

• Depth and type of topsoil layer

Active blowout 15-20 samples 150 measurements

Stable blowout 15-20 samples 150 measurements

Total 30-40 samples 300 measurements

Table 2. Overview of fieldwork measurements.

Transects cover the length of the blowouts with a short transect perpendicular of these and sampling points distributed over blowout zone (deflation zone), accumulation zone (depositional zone) and stable zone (behind erosional edges). On the transects 15 to 20 sampling points will be taken, adding up to a maximum of 40 in total for both blowouts. The exact locations of the sampling points are determined in the field with help of the GPS Trimble. In the study that was conducted in 2017 transects were made for the blowout areas. These transect points have been used to reconstruct the same transects for this study (Fig. 2).

For each sampling point notations were made (Table 2), a soil profile description was done and soil and vegetation samples were taken. The soil sample was done with metal pF-rings in 5 cm depth, which supplies a sample amount of approximately 100 cm3. Afterwards, bulk density, electrical

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conductivity (EC), pH and C and N content have been measured in the laboratory (Table 3). Furthermore, aboveground vegetation was sampled in grids of 25cm x 25 cm when vegetation cover was larger than 20% and in an area of 50cm x 50cm when vegetation cover was smaller than 20%. In the laboratory, aboveground biomass was calculated, and C and N content were determined (Table 3).

For the grid point analyses approximately 150 measurements were taken per blowout area, conducted in a grid in and around the blowouts (Figure 2). At each point the GPS location, type and percentage of vegetation cover and topsoil characteristics have been noted. If present, the thickness of the Ah-layer was measured. Afterwards a map was made from these grid points in ArcGIS to obtain an overview of the soil and vegetation in the area. Maps were created for both areas using inverse distance weighted interpolation in ArcMap.

After fieldwork the samples have been processed and tested in the laboratory at Science Park. A description of the tests can be found in table 3.

Figure 2. Grid points and transects for the active and stable area.

Measurement Laboratory measurements

Bulk density (BD) 20 gr of the sample will be put in the oven for 48hrs at 105°C. This subsample will be weighed after the drying in the oven to obtain the dry weight of the sample. Bulk density can be calculated by dividing this weight by the total Volume, which is 100 m3_.

pH and EC of soil 10 gr of the sample will be mixed with 25 ml of demineralized water. This solution will be shaken for 2hrs, followed by a resting period overnight. The next day it will be shaken for another 20 minutes. The values will be measured using a pH and EC electrode.

C and N content of soil Two subsamples, of which one duplicate, of 20-50 mg are be prepared per soil sample and put in the oven for 48hrs at 70°C. Carbon and nitrogen concentration (in percentages) were measured with a CHNS analyser. C and N content were calculated as follows:

C content = (BD*Volume)*(%C/100) N content = (BD*Volume)*(%N/100)

The calculation for the C/N ratio is:

C/N ratio = Carbon content / Nitrogen content

Dry weight of vegetation The vegetation samples are dried for 24hrs at 40°C and weighed before and after. After weighing the leftover material is ground at rotational speed 8.000 rpm.

C and N content of vegetation

Two subsamples, of which one duplicate, of 10-15 mg are prepared per vegetation sample and put in the oven for 48hrs at 70°C. Carbon and nitrogen concentration (in percentages) are measured with a CHNS analyser. C and N content of the vegetation were calculated as follows:

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C vegetation content = Dry weight per m2_*(%C/100) N vegetation content = Dry weight per m2_*(%N/100)

Moss species and woody plant material will not be collected, as this exclusion might alter the C/N ratio.

C/N ratio = Carbon content / Nitrogen content

Table 3. Overview of laboratory measurements.

Statistical analysis

The results have been digitized and cleaned in Microsoft Office Excel after which in MatlabR2017b the calculations and statistical tests have been performed. T-tests have been performed on all variables for the following comparisons:

• Active 2018 – Stable 2018 • Active 2017 – Active 2018 • Stable 2017 – Stable 2018

In this way, it is tested whether there are still significant differences between the active and the stable area and to test if the areas have undergone changes, possibly influenced by the storm. To obtain more insight on the data ANOVA’s have been performed for all variables and to compare the different groups (active 2017, stable 2017, active 2018, stable 2018) with each other.

For the analysis of C and N content, the transects have been subdivided into three zones: the unaffected zone, blowout zone and accumulation zone (Figure 3). This is to reduce the influence of the high C/N-ratios in the blowout zone and because the zones differ in the amount of sand that is deposited (based on the westerly winds). This subdivision has been made in the research of last year for the samples and is used again (Table 4).

Table 4. Different zones and corresponding samples.

Unaffected zone A1-A5 S1-S5

Blowout zone A6,A7,A16,A16 S6,S7,S15,S16 Accumulation zone A8-A14,A17,A20 S8-S14,S17-S20

Figure 3. Different zones: unaffected zone (yellow), blowout zone (blue) and accumulation zone (not in contour).

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Aerial photo analysis

An aerial photo analysis will be conducted to study whether storms might have impacted the study area in the past. Photos are available from 1996, 2000, 2003, 2005-2016. In ArcGIS polygons are drawn around the spots where bare sand is at the surface. The total area of bare sand is calculated which is done for each year. Afterwards, this data will be analysed by comparing it with historical data of severe storms in the Netherlands.

Unfortunately, photos were not available yet from 2017 and 2018, so the impact of the January storm of 2018 cannot be studied in this way. However, this analysis on the aerial photos and storm data gives more insight in storm impact on De Nederlanden, Texel.

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Results

Comparison of the stable and active area for 2018 Soil parameters

For the soil pH a significant difference was found between the stable and the active area for 2018 (Appendix A). The pH in the active area is relatively higher than the pH of the stable area. The bulk density between the areas differs significantly (Appendix A). The mean bulk density in the active area is slightly higher than in the stable area. This could be attributed to the amount of sand in the top soil, which is likely to be higher in the active area with high blowout activity. In electrical conductivity of the soil no significant difference was found between the areas.

The amount of C and N in the soil differs significantly between the active and stable area for all zones (Appendix A). From the means can be derived that nutrient loads are overall higher in the stable area (Table 5). The C/N-ratios of did not show a significant difference between unaffected zone and accumulation zone. Ratios did differ between the blowout zones, but this can be attributed to the high C/N-ratios in the active blowout zone (32.5 maximum), where relatively low concentrations of N are present.

2018 Soil Mean Active C Mean Stable C Mean Active N Mean Stable N

Unaffected zone 838.16 2364.06 62.54 168.90

Blowout zone 381.44 1396.40 16.85 108.58

Accumulation zone 912.45 1850.64 68.87 129.18

Table 5. Mean carbon and nitrogen content in g/m2_{of the soil for all zones in the active and stable area for 2018.}

Bare sand coverage is significantly higher in the active area compared to the stable area (Figure 5; Appendix C). This is mainly due to the large bare sand coverage that represents the large blowout in the active area. Some spots of bare sand are present in the stable area, these were near steep slopes. However, more of these sandy spots occur in the active zone (Figure 5). A positive correlation was found between bare sand coverage and pH (Appendix D).

The thickness of the Ah-layers did not show a significant difference between the areas. In both areas there were often signs of (former) blowout activity in the soil, where the first Ah-layer had formed on a sand deposit which was followed by a second and older Ah-layer (Figure 4). Unfortunately, the amount of these layers could not be compared between the areas, due to missing data from the active area.

Figure 4. Approximately 20 cm of topsoil in which a sand deposit is present. Underneath the light-coloured sand, a second Ah-layer is present.

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Figure 5. Bare sand coverage (%) of the stable blowout area (upper) and the active blowout area (below).

Vegetation parameters

The dry weight of the vegetation differed significantly for the active and the stable blowout area. Dry weight of the vegetation is higher in the stable area, with a mean of 140.5 g/m2_{compared to 79.7} g/m2_{in the active area. C and N content of the vegetation are significantly higher for the stable area} (Table 6). C/N ratios do not show a significant difference, except for the blowout zone. In the active area the C/N ratio of the blowout zone is lower than in the stable area (Appendix B). This could be because in sample A16 the concentration N is relatively high, which has caused the mean concentration N in the active blowout zone to become relatively high in comparison with the other zones (Table 6).

2018 Vegetation Mean Active C Mean Stable C Mean Active N Mean Stable N

Unaffected zone 38.06 64.14 1.13 2.04

Blowout zone 29.48 51.37 1.28 1.61

Accumulation zone 37.53 70.83 1.22 1.98

Table 6. Mean carbon and nitrogen content in g/m2_{of the vegetation for all zones in the active and stable area for 2018.}

Means and maxima of the vegetation coverage indicate that lichens, mosses, shrubs and grasses occur in higher numbers in the stable area (Table 7). However, no significant differences were found for coverage in lichens, mosses, herbs, shrubs and grasses between the active and the stable area for 2018 (Appendix A).

2018

Vegetation coverage 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

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Lichens seem to be more evenly dispersed in the active area, whereas in the stable area lichens seem to be more clustered or isolated (Appendix D). Mosses coverage seem to be higher in the stable zone, but this is not a significant difference (Appendix A & D). This is in contrast to the maps and data of 2017 in which mosses had a higher abundance in the active area.

Comparison between 2017 and 2018 for the active area Soil parameters

No significant differences were found for the pH and electrical conductivity when comparing the data of 2017 with 2018 for the active blowout area. The average and median of the pH is slightly higher for 2018 (Appendix B). Bulk density does differ significantly between the years (Appendix A). It is higher in 2018, with a mean of 1.36 g/m3_{against 1.20 g/m}3_{for 2017. Additionally, the one-way anova for} bulk density shows that the median and the minimum are higher for 2018 (Appendix C). Bare sand coverage and the thickness of the Ah-layer did not differ significantly for the active area.

The t-tests for the C and N content in the soil do not show significant differences for the unaffected zone and the accumulation zone (Appendix A). However, C/N ratios for these zones do show significant differences and are relatively higher for 2018. The means suggest a decrease in N content could have led to these higher ratios (Table 8). P-values are significant for both C and N content in the blowout zone (Appendix A). The average C and N content are higher in 2018 for the blowout zone (Table 9). The average N content is much lower in 2017 than in 2018 and because of this the mean C/N ratio for the blowout zone is extremely high in 2017 compared to 2018. (Table 9).

Active 2017 & 2018 Soil Mean C 2017 Mean C 2018 Mean N 2017 Mean N 2018 Unaffected zone 937.67 838.16 86.68 62.54 Accumulation zone 950.80 912.45 84.92 68.87

Table 8. Means of carbon and nitrogen content in g/m2_{of the unaffected and accumulation zone for 2017 and 2018}

Active 2017 & 2018 Blowout zone C content soil g/m2 N content soil g/m2 C/N-ratio soil Mean 2017 257.16 4.1 63.09 Mean 2018 381.44 16.85 25.36

Table 9. Carbon and nitrogen data of active blowout zone for 2017 and 2018. .

Vegetation parameters

No significant differences were found for the vegetation parameters dry weight, mosses and herbs when comparing the active area for 2017 and 2018. Shrubs did show to differ significantly and seems to have increased in the active area (Appendix A).

For C and N content of the vegetation no significant differences were found in all zones. The C/N-ratios of the different zones were not significant.

Comparison between 2017 and 2018 for the stable area Soil parameters

Both pH and electrical conductivity differ significantly for 2017 and 2018 in the stable area. The pH is relatively higher in 2018 for almost the complete transect (Figure 6). Some samples in the accumulation zone show higher pH in 2017 (Figure 6). Electrical conductivity is relatively lower in 2018, which might indicate that there are less nutrients in the soil. However, no significant correlation was found between EC and C or N content for 2018. Only for 2017, a significant correlation was found between EC and N content and EC and C content (Appendix A).

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A significant difference is found for the bulk density when comparing the data of 2017 and 2018 for the stable area. The means show bulk density values to be relatively higher for 2018 compared to 2017 (Appendices B). Bare sand coverage and the thickness of the Ah-layer did not show significant differences between 2017 and 2018 for the stable area.

The C content of the soil differed significantly in the unaffected zone, but not in the blowout and accumulation zone. Average C content of the unaffected zone is much higher compared to the average C content in 2017, respectively 2364.06 g/m2_{against 1298.58 g/m}2_{. This is quite an extreme difference} and has caused the C/N ratio to increase significantly (Appendix A & B). N content did not show any significant differences for 2017 and 2018. C/N ratio showed also significant difference for the accumulation zone, of which the mean indicates the ratio is slightly higher for 2018. When taking into account the means for C and N content of the accumulation zone, it shows the average C content is higher for 2018 although not significant (Appendix B), which probably caused the C/N-ratio to become higher.

Vegetation parameter

Dry weight of the vegetation and herbs coverage did not differ between 2017 and 2018 for the stable area. Mosses and shrubs do differ significantly, and both seem to be relatively higher in 2018 (Appendix C). However, this information must be taken with caution, as the data is based on estimations in the field.

Figure 6. Side and front view of the stable transect showing the pH of the sampling points for 2017 (blue) and 2018 (orange).

Aerial photo analysis

From the aerial photo analysis figure 7 was obtained showing the total area of bare sand for each year and the maximum value of bare sand which represents the large blowout zone in the active area. The largest area covered with bare sand was in 2011, with a total area of 150803.07 m2_{. As visualized in} the graph, this is an enormous increase (93631 m2_{) compared to the year before. Another large} increase in the total area of bare sand is observed for 2006, in which the total bare sand coverage rose with 43474 m2_. 3 3,5 4 4,5 5 5,5 6 6,5 S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 pH Transect points

pH side view stable transect

2017 2018 3 3,5 4 4,5 5 5,5 6 6,5 S15 S16 S17 S18 S19 S20 pH Transect points

pH front view stable

transect

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After the increase of total bare sand coverage between 2005 and 2006, the blowout zone expanded with 3020 m2_{, which is a relatively small increase. However, in 2007 the blowout zone expanded} drastically with 14696 m2_{, which is 96% of the total increase of bare sand coverage for 2007. After} 2008 the blowout zone seems to decrease in size and in 2010 increases again with 11520 m2_{. In} contrast, the total area of bare sand is lower in 2010 relative to 2009. Strikingly, the large increase in total area of bare sand for 2011 does not account for the blowout zone, which increased with only 607 m2_.

Figure 7. Total area of bare sand (blue) and the maximum value of bare sand (orange) in m2 _{for each year}

Discussion

Blowout activity and influence on soil and vegetation

There are still significant differences between the active and the stable blowout areas for 2018. The pH is considerably higher in the active area and this is positively correlated with bare sand coverage. More bare sand at the surface leads to a higher pH as more sand can be transported by the wind. Consequently, bulk density is higher in the active area, because relatively much sand is present in the topsoil. Bulk density is lower for the stable area and the aboveground biomass is higher than the active area. This is consistent as a higher vegetation coverage makes the topsoil less compact as bulk density decreases because of roots and soil organic matter (Adams, 1973). C and N content of the vegetation are higher in the stable area along with the amount of C and N in the soil. This was expected as the amount of nutrients in the vegetation reflects the amount of nutrients that are available in the soil (Witz, 2015).

No significant difference was found for EC values. Electrical conductivity provides information on soil properties such as moisture content, nutrient condition and salinity (Sudduth et al., 2005). Expectation was that EC values would be higher for the stable zone, reflecting the amount of nutrients in the soil. Similar outcome (no difference) was found last year for EC-values. Correlation seems to be lower for EC values and sand content (Sudduth et al., 2005), so assumingly EC relates slightly differently with soil properties for dune soils. Also unexpecting were the C/N ratios of the soil that showed no significant differences between the active and the stable area. C/N ratios were thought to be lower in the active area, as a likely cause of the decrease in carbon concentration of the topsoil, which is an

0 20.000 40.000 60.000 80.000 100.000 120.000 140.000 160.000 1996 2000 2003 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 m ² Years

Aerial photo analysis of bare sand coverage and size of

blowout

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effect of blowout activity (OBN, 2018, in press). C content is considerably lower in the active area, but N content as well, eventually leading to similar ratios as in the stable zone.

The high C and N content in the stable area are an indicator of grass-encroachment. The averages of lichens, mosses, shrubs and grasses indicate higher abundances in the stable blowout area. Only the mean of herbs coverage seemed higher in the active area. However, all comparisons showed no significant differences between the areas.

Overall, the active blowout area shows positive effects of blowout activity, a higher pH, lower nutrient concentrations in the soil and less aboveground biomass.

Development of blowout areas

The newly obtained data of 2018 has been compared with the data of 2017 for both active and stable blowout areas. The comparison gives insight on the short-term development (duration of one year) of the blowout areas and the effects on soil and vegetation.

No significant changes were observed for bare sand coverage in both areas relative to 2017. Nonetheless, bulk density seems to have increased in both areas, which indicates that the amount of sand in the topsoil has likely increased. This could indicate that aeolian activity has led to sand depositions in both areas. For the active area this sand is likely originating from the active blowout, whereas for the stable area this could have been caused by high wind speeds which can have transported sand from the beach.

Expectation was that C/N ratios would decrease for the active area, as carbon was expected to decrease as an effect of blowout activity (OBN, 2018, in press). In contrast, C/N ratios increased for the unaffected zone and accumulation zone of the active area. The means assume this was caused by a decrease in the N content of these zones. Unfortunately, both C and N content showed no significant difference for the unaffected zone and the accumulation zone comparing 2017 and 2018, so no evident conclusion can be drawn on the N content. The C/N ratio of the active blowout zone decreased, and a significant increase is shown in the C and N content for this zone in 2018. It is not certain what caused this increase in nutrients for the active blowout zone. In the samples taken from the large active blowout some organic matter might crumbled off from the edges of the blowout and rolled into the blowout. Samples A15 and A16 might have been taken from a spot with more slightly more developed topsoil than in 2017, as many transect points were reconstructed. No significant changes have occurred for the vegetation coverage in the active area. Only shrub coverage did seem to differ significantly, and the averages indicate an increase for 2018.

For the stable area no significant changes were observed for the C and N content of the soil, except in the unaffected zone of the stable area where C content was found to be higher for 2018. In two samples of this subset relatively high nutrient loads were found and have caused the mean C content of 2018 for this zone to be much higher than 2017. C/N ratio of the accumulation zone was higher for 2018 and this is possibly caused by a higher C content. However, no significant differences are found for C and N content of the vegetation.

The percentages of mosses and shrubs coverage seem to have increased in the stable area for 2018. The increase in mosses, particularly lichens, could be a positive effect of blowout activity (OBN, 2018, in press). It is unfortunately not clear whether lichens have increased or not, because no estimations were made in the field for these in 2017. Shrubs such as Rosa pimpinellifolia, which was found throughout the study area, is maintained by rabbit grazing (Aggenbach et al., 2016). In the period 1996-2016 the rabbit population has been relatively high in De Nederlanden (OBN, 2018, in press). During the fieldwork many burrows were observed in the study area, however most of these seemed empty. Entries were almost grown with vegetation or covered with cobwebs. Further research should be done on the rabbit population in this area and the impact of rabbit grazing on the vegetation.

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Storms and blowout activity in De Nederlanden, Texel

The aerial photo analysis showed that the increase in the area of the active blowout zone does not seem to follow increase in total area of bare sand. A sharp increase in the total area of bare sand was observed for 2011, however the blowout zone of the active area did barely increase that year. No severe storm (wind velocity of at least 10 Beaufort) has taken place in in 2010 or 2011 (KNMI, 2018), so this could not have been the initiator of the increase in bare sand coverage. The other relatively large increase in the total area of bare sand was between 2005 and 2006, but also for this period no severe storm has taken place (KNMI, 2018).

A large increase in the area of the active blowout zone is observed for 2007, which accounts for 96% of the increase in total area of bare sand coverage of that year. An event must have taken place to have caused this large expansion of the blowout zone. A possible cause might be the storm on January 18 of 2007, in which wind speeds were measured of 120 to 130 km/hour (KNMI, De zware storm Kyrill van 18 januari 2007, 2007). The amount of precipitation during this storm was exceptional. On many locations 50 to 60 mm of precipitation was measured within 36 hours (KNMI, De zware storm Kyrill van 18 januari 2007, 2007). Comparing the storm number (a unit developed by KNMI researcher Sander Tijm) of this storm with the storm number of the January storm of 2018, the 2007 storm was more severe (Table 10). One of the reasons the storm of 2018 was less severe than the storm of 2007 is that it was not characterized with heavy precipitation.

Dune soils containing organic matter can resist wind erosion, but are prone to rain erosion as the organic matter makes it water-repellent (Jungerius & van der Meulen, 1988). This makes grey dunes overall more sensitive to erosion by heavy rainfall than erosion by wind, because of the soil organic matter in the topsoil. A wet storm such as the January storm of 2007 could have initiated the blowout zone to expand by washing away topsoil. A factor, however, that resists the large blowout from expanding is the extensive root network that makes up the edges of the blowout (Figure 8). In 2010, the active blowout zone also showed high activity and increased in size relative to 2009. No severe storm has taken place in 2009 or 2010 (KNMI, 2018), so this increase is more likely initiated by other factors. Top ten severe storms NL Date Storm number 1 25 January 1990 78.7 2 3 January 1976 56.2 3 26 February 1990 48.6 4 13 November 1972 43.8 5 18 January 2007 40.6 6 27 October 2002 38.5 7 2 April 1973 31.1 8 18 January 2018 24.4 9 13 January 1993 24.3 10 27 November 1983 19.8

The January storm of 2018 was not characterized by heavy precipitation, so probably there was no rain wash erosion during this event. It is not known how much precipitation exactly fell during this storm, but rainfall intensity has a stronger causal effect to this erosion than the total amount of precipitation (Jungerius & ten Harkel, 1994). This could also be the reason why there was no significant change in the bare sand coverage of both areas relative to 2017. For the formation of such spots or small blowouts the topsoil must be removed, and this might not be possible by only high wind

Table 10. Top ten severe storms in the Netherlands since 1970 (KNMI, 2018).

Figure 8. Large blowout in the active zone. Sharp edges are formed by plant roots holding the topsoil together.

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velocities. High wind speeds could have led to blowout activity, transporting fresh sand to the surrounding areas, but this is not very affective in the winter season, as soil moisture content of the surface sand is high (Pluis, 1992). Overall, it seems the January storm of 2018 did not have the characteristics and suitable conditions to initiate blowouts or lead to extensive blowout activity. Although, the storm is not the likely cause for widespread blowout activity, the soil data suggests by the increased pH and bulk density in the stable area that blowout activity has taken place there. Implications

Some implications were experienced during this study. The results of the soil and vegetation data is based on a total of 40 samples. More samples would increase the statistical power. For the estimations on the vegetation coverage the same accounts. There were estimations of the vegetation coverage for all 300 grid points which can provide a more representative vivew of the vegetation coverage in both areas. Recommended for future research is to digitize these grid points.

Moreover, these estimations remain arbitrary and data based on these estimations should always be taken with caution when drawing conclusions.

Not a good comparison could have been made of the thickness of the Ah-layer and the blowout deposits for the areas, because notes of these observations lack for the first half of the active transect. Some findings regarding change of the C and N content of the soil are not clearified in this study, particularly some indications that C content migth have increased for 2018. Therefore, further research must be conducted in these blowout areas of De Nederlanden, to study whether these developments are part of a trend or event.

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Conclusion

This study has shown the positive effects of an active blowout area on soil and vegetation in counteracting soil acidification caused by nitrogen deposition. The pH, bulk density and bare sand coverage are higher in the active blowout area than the stabilized blowout area. The coverage of bare sand and pH are positively correlated, supporting the expectation that fresh nutrient-poor sand deposits buffer soil acidification. Both aboveground biomass and C/N content of the soil were higher for the stable area, where soils are more developed and thus have a lower pH. Consequently, C and N content were found to be higher in the stable area.

Positive effects have been observed for 2018 particularly for the stable area, where the pH and bulk density increased significantly compared to 2017. The January storm of 2018 is a likely cause for these effects in the stable area, as the high wind speeds were possibly able to transport sand from the beach or active blowout area. However, the hypothesis that the storm would have initiated blowout formation or expanded the large blowout in the active zone is not supported, because coverage of bare sand does not seem to differ between 2017 and 2018. Historical analysis of storm data and the aerial photo analysis suggest that formation or expansion of blowouts is more likely caused by storms with heavy precipitation in which rain wash erosion removes the topsoil. Yet, the increase in bare sand coverage for the total area does not match the severe storm data, so other factors are more likely to play a role in the maintenance of bare sand spots in the area, such as rabbit grazing.

The findings on the C and N content of the soil showed often insignificant when comparing 2017 and 2018 and seem to variate largely. Further research should be conducted on active and stabilized blowout areas to obtain more insight on these variations in the nutrient concentrations of the topsoil.

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References

Adams, W. (1973, March). The effect of organic matter on the bulk and true densities of some uncultivat ed podzolic soils.

Journal of Soil Science, 24(1), 1-144.

Van Boxel, J. H., Jungerius, P. D., Kieffer, N., & Hampele, N. (1997). Ecological effects of reactivation of artificially stabilized blowouts in coastal dunes. Journal of coastal conservation, 3(1), 57-62.

Hesp, P. (2002). Foredunes and blowouts: initiation, geomorphology and dynamics. Geomorphology, 48(1), 245-268.

Jungerius, P. D., & ten Harkel, M. J. (1994). The effect of rainfall intensity on surface runoff and sediment yield in the grey dunes along the Dutch coast under conditions of limited rainfall acceptance. Catena, 23(3–4), 269–279.

Jungerius, P. D., & van der Meulen, F. (1988). Erosion processes in a dune landscape along the Dutch coast. Catena, 15(3– 4), 217–228.

KNMI. (2007, 01 18). De zware storm Kyrill van 18 januari 2007.

KNMI. (2018, 01 18). Code rood voor zeer zware windstoten op 18 januari 2018.

KNMI. (2018). Zware stormen in Nederland sinds 1910. Opgehaald van Koninklijk Nederlands Meterologisch Instituut:

https://www.knmi.nl/nederland-nu/klimatologie/lijsten/zwarestormen

Kooijman, A., Besse, M., Haak, R., Van Boxtel, J., Esselink, H., ten Haaf, C., et al. (2005). Effectgerichte maatregelen tegen verzuring en eutrofiering in open droge duinen. Eindrapport Fase, 2.

Van der Meulen F, Kooijman AM, Veer MAC & Van Boxel JH, 1996. Effectgerichte maatregelen tegen verzuring en eutrofiering in open droge duinen. Fysisch Geografisch en Bodemkundig Laboratorium, Universiteit van Amsterdam, 232 pp.

OBN report. (2018) in press.

Pluis, J. (1992, November). Relationships between deflation and near surface wind velocity in coastal dune blowout. Earth

Surface Processes and Landforms, 17(7), 663-673.

Provoost, S., Ampe, C., Bonte, D., Cosyns, E., & Hoffmann, M. (2002). Ecology, management and monitoring of dune grasslands in flanders, belgium. Littoral 2002.the Changing Coast, , 11-22.

Slootweg, J., Posch, M., Hettelingh, J. -., & Mathijssen, L. (2014). Modelling and mapping the impacts of atmospheric deposition on plant species diversity in europe - CCE status report 2014 No. 2014- 0075) Coordination Centre for Effects. Sudduth, K., Kitchen, N., Weibold, W., Batchelor, W., Bollero, G., Bullock, D., . . . Thelen, K. (2005, March). Relating apparent electrical conductivity to soil properties across the north-central USA. Computers and Electronics in Agriculture,

46(1-3), 263-283.

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.

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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Appendix A – T-tests and correlations

Comparison active vs stable, 2018 (t-tests)

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

Comparison 2017 vs 2018, active (t-tests)

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

Comparison 2017 vs 2018, stable (t-tests)

pH 0.0041 Yes

EC (mS/cm) 0.0027 Yes

BD (g/cm3) 0.0141 Yes

C/N-ratio 0.00004 Yes

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Comparison active vs stable, 2018 (t-tests) Vegetation

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

Comparison active 2017-2018 (t-tests) Vegetation

Dry weight 0.6232 No

C content (g/m2) 0.3109 No

N content (g/m2) 0.8450 No

C/N ratio 0.4168 No

Mosses (%) 0.3684 No

Herbs (%) 1.00 No

Shrubs (%) 0.0124 Yes

Comparison stable 2017-2018 (t-tests) Vegetation

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

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Mosses (%) 4.3936e-06 Yes

Herbs (%) 0.9665 No

Shrubs (%) 8.0346e-04 Yes

Comparison C/N ratio Active-Stable 2018 Soil

Zones P-value Significant

Unaffected Zone 0.1115 No

Blowout Zone 0.0199 Yes

Accumulation Zone 0.6709 No

Comparison C/N ratio Active 2017- 2018 Soil

Unaffected Zone 0.0279 Yes

Blowout Zone 8.5197e-05 Yes

Accumulation Zone 0.0039 Yes

Comparison C/N ratio Stable 2017-2018 Soil

Blowout Zone 0.1214 No

Comparison C content Active-Stable 2018 Soil

Comparison N content Active-Stable 2018 Soil

Comparison C content Active 2017-2018 Soil

Comparison N content Active 2017-2018 Soil

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Comparison C content Stable 2017-2018 Soil

Comparison N content Stable 2017-2018 Soil

Comparison C/N ratio Active-Stable 2018 Vegetation

Comparison C/N ratio Active 2017- 2018 Vegetation

Comparison C/N ratio Stable 2017- 2018 Vegetation

Comparison C content Active-Stable 2018 Vegetation

Comparison N content Active-Stable 2018 Vegetation

Unaffected Zone 4.1554e-04 Yes

Comparison C content Active 2017- 2018 Vegetation

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Accumulation Zone 0.3087 No Comparison N content Active 2017- 2018 Vegetation

Comparison C content Stable 2017- 2018 Vegetation

Comparison N content Stable 2017- 2018 Vegetation

Pearson correlation p-values

Variables P-value

EC 2017 & N content 2017 5.66e-04 EC 2018 & N content 2018 0.4578

EC & N content 0.2666

EC 2017 & C content 2017 7.88e-05 EC 2018 & C content 2018 0.5032

EC & C content 0.3832

Bare sand 2018 & pH 2018 8.54e-08

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Appendix B – Means, standard deviations, minima and maxima.

Means and standard deviations of active blowout for 2017 and 2018. Soil

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 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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Minima and maxima of active blowout for 2017 and 2018. Soil

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 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

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Means and standard deviations stable blowout for 2017 and 2018.Soil

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) blowout 1037.81 1396.40 833.78 629.57 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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Minima and maxima of stable blowout for 2017 and 2018. Soil

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 transect 6.7797 11.76 14.14 15.87 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

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Means and standard deviations stable blowout for 2017 and 2018. Vegetation 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 (g/m2) unaffected 77.8720 64.1395 32.2714 20.9385 C content (g/m2) blowout 51.8400 51.3657 27.0649 20.1575 C content (g/m2) accumulation 83.5200 70.8252 39.7506 37.7563 N content (g/m2) unaffected 1.8998 2.0382 0.8037 0.4722 N content (g/m2) blowout 1.4259 1.6125 0.7753 0.5947 N content (g/m2) accumulation 2.0788 1.9823 1.0147 0.9293 C/N-ratio unaffected 40.8008 31.6809 5.2324 7.4965 C/N-ratio blowout 37.9591 31.9611 7.5413 2.8288 C/N-ratio accumulation 40.5505 35.3595 7.0017 3.8095

Means and standard deviations active blowout for 2017 and 2018. Vegetation 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 (g/m2) unaffected 48.7840 38.0598 18.7059 13.9326 C content (g/m2) blowout 23.1200 29.4776 19.8802 27.7126 C content (g/m2) accumulation 48.7127 37.5298 32.5438 14.1974 N content (g/m2) unaffected 1.2216 1.1270 0.3442 0.6375 N content (g/m2) blowout 0.9816 1.2754 0.8009 1.2989 N content (g/m2) accumulation 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 C/N-ratio accumulation 36.0765 7.5830 30.9015 7.7049

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Minima and maxima of stable blowout for 2017 and 2018. Vegetation 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 (g/m2) unaffected 28.0800 38.0670 110.8800 89.4159 C content (g/m2) blowout 23.2800 28.8517 83.4400 77.4915 C content (g/m2) accumulation 33.7600 35.7556 151.4400 167.5373 N content (g/m2) unaffected 0.8062 1.2286 2.7315 2.4429 N content (g/m2) blowout 0.4930 0.8498 2.3579 2.2459 N content (g/m2) accumulation 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 accumulation 31.1518 53.7534 30.1128 41.9040

Minima and maxima of active blowout for 2017 and 2018. Vegetation 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 (g/m2) unaffected 27.5200 17.1265 73.8400 52.9576 C content (g/m2) blowout 0 0 45.7600 65.4783 C content (g/m2) accumulation 22.8000 20.4893 139.2000 60.3075 N content (g/m2) unaffected 0.6626 0.4340 1.5370 1.9979 N content (g/m2) blowout 0 0 1.8536 2.9479

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N content (g/m2) accumulation 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

Means and maxima of vegetation coverage in 2018. 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

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Appendix C - ANOVA’s for comparison of the groups ‘stable 17’, ‘stable18’,

‘active17’ and ‘active18’.

pH Electrical conductivity

Bare sand coverage Bulk density

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C/N unaffected zone (soil) C/N blowout zone (soil)

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Herbs Shrubs

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C content - Unaffected Zone C content - Blowout Zone

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N content - Unaffected Zone N content - Blowout Zone

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C vegetation content - Unaffected Zone C vegetation content - Blowout Zone

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N vegetation content - Accumulation Zone

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