SALINISATION OF THE HARINGVLIET AND
ITS EFFECTS ON THE SURROUNDING
AGROSOCIAL SYSTEM
Final version May 22, 2016 Aerial view of the Haringvliet sluices Esther Bos 10543171 Esther Brakkee 10633480 Inger Bij de Vaate 10624562 Course: Interdisciplinary Project 2016 Supervisor: N. van Woerden Expert supervisor: A. Gilbert Word count: 7215 (incl. intext references)Abstract
Salinisation of soils is an increasing problem worldwide. Saline agriculture has potential as a sustainable solution in saltaffected areas. In the Haringvliet, saline intrusion will increase due to the opening of the sea sluices in 2018. In this research, the local area is viewed as an agrosocial system governed by a productivityfocused paradigm. The effect of increased salinisation on this system and its paradigm is investigated. The pressure of salinisation was considered in combination with other pressures on the system to see if they might together drive a transition towards saline agriculture. Saline intrusion from the Haringvliet was found to occur to a significant extent especially close to the water body. Without countermeasures this will substantially affect local farmers. Other pressures on various levels, such as drought, are simultaneously affecting the system. Saline agriculture can reduce several of these pressures, increasing its feasibility in the region. Especially a multifunctional, climateproof form has potential. However, barriers were found to the upscaling of saline agriculture, especially the lockin created by the current water infrastructure and the low willingness of farmers to change. These barriers have to be taken into account when saline agriculture is considered as a solution for salinity problems.
Table of content
Introduction Theoretical framework Methodology Background casestudy area Characteristics of the agrosocial system Characteristics of agriculture Characteristics of the water system Results Section 1. Future extent of salinisation 1.1 Salinity distribution Haringvliet 1.2 Saltwater intrusion 1.3 Consequences of salinisation for agriculture Section 2. Transition to a new agrosocial system 2.1 Challenges current paradigm with increased salinity 2.2 Strategies to cope with salinisation 2.3 Arisen opportunities for Saline Agriculture from the identified pressures on the current regime 2.4 Barriers for saline agriculture implementation on a large scale DiscussionConclusions
Appendices
Introduction
Climate change, irrigation and land subsidence are leading to a spread of salinisation in many areas of the world. This causes salinity problems in the rooting zone of arable lands, decreasing the yield of conventional crops (Rozema & Flowers, 2008). In the past decennia genetic modification has not been able to produce a salt tolerant crop (Ibidem.). However, naturally salttolerant plants, halophytes, have potential for commercial agriculture in saline environments (Rozema & Flowers, 2008). Saline agriculture growing naturally salttolerant crops using a saline irrigation regime is often proposed as a good adaptation to salinity.
The surroundings of the Haringvliet in the southwest of the Netherlands are a typical lowlying, saltaffected area. The Haringvliet (see figure 1) is an estuary that has been enclosed from the sea by sluices since the 1970s, which created a freshwater environment (Visser & Breukelaar, 2015). Agriculture expanded after this, profiting from the low salinity, but biodiversity in the Haringvliet declined. In the decades that followed, international agreements to obtain a good ecological status in all European water bodies (EU Water Framework Directive (2000/60)), and agreements to facilitate fish migration into the Rhine, increased the pressure to restore a link with the sea (Tromp & Bakker, 2009). When a shift occurred at the national level towards more integrated, ecologyfocused water management, the decision, called ‘het Kierbesluit’, was made to partially reopen the sluices in 2018 (Visser & Breukelaar, 2015). This will cause the salinity of the lake to increase, which could aggravate the salinity problems for the surrounding lands.
Figure 1: The Haringvliet sluices are indicated by the red circle.
Protests have been significant among the inhabitants of the region, fearing to lose their farms, identity and income (Marks et al., 2014). The most important fear was that a saline Haringvliet would prevent use of its water for agriculture (Verhorst, pers. Comm., 1 April 2016). Compensation measures will be implemented before 2018 to address this problem. New, more easterly water inlet points are being created to allow the distribution of freshwater to farms to
continue (Wolfert, pers. comm., 6 April 2016). However, the water supply from the Haringvliet is not the only route by which the local community can be affected. As the Haringvliet becomes saline, saline groundwater from the lake may seep upwards and aggravate soil salinity. It is still unclear what effect the sluice opening will have on saline intrusion. This research maps the intrusion to assess its possible effect on the agrosocial system.
If an increase in salinisation occurs and the current counteracting system proves inadequate, farmers will be strongly affected. Therefore, this region needs research into the possible strategies to cope with salinity. Saline agriculture is a potential solution; however, scientific research into saline agriculture has mainly focused on the technical and biological aspects. The potential for saline agriculture in a certain area depends also on social, economic and environmental aspects. In this research, the approach is taken to explore the potential for saline agriculture by researching the local system as a whole.
The research will focus on the agrosocial system surrounding the Haringvliet lake. This system is approached as a socialecological system (SES), which is a collection of social, biological and physical actors that interact in a particular area (Glaeser, 2015). In our research the focus is on the agrosocial system within significant reach of the saline groundwater flows, approximately 5 km from the Haringvliet on both the northerly peninsula VoornePutten and the southerly island GoereeOverflakkee. The following question is addressed: What will be the challenges and opportunities to implement saline agriculture in the surroundings of the Haringvliet, when the sluices will be partially opened in 2018? This question is divided into the sub questions that are given in figure 2.
Figure 2: Sub questions
To understand the consequences and solutions of the sluice opening on the system as a whole, insights from earth science, ecology and social geography are combined. First, the theoretical framework is given. This framework provides a basis for answering the sub questions, which is done in the results section. Second, the methods used within the disciplines, and the way the disciplines have been integrated, are explained. Subsequently, the agrosocial system as it is now is described because the impact of salinisation strongly depends on the specific farming methods and water management that are present. This is followed by a discussion of the extent of salinisation from the Haringvliet and how this will put pressure on the agrosocial system. To deal with these pressures, two strategies flushing and saline farming are given. The second is worked out in detail to assess its feasibility in the Haringvliet area. Finally, the results are integrated to a
conclusion and discussion, including recommendations for policy makers to address the salinity issue around the Haringvliet.
Theoretical framework
Socialecological systemsThis research uses theories on socialecological systems to understand the area around the estuary ‘the Haringvliet’ as a socialecological system (SES). A SES is a collection of social, biological and physical actors that interact in a particular area (Glaeser, 2015). Here, the SES comprises the agrosocial system, including the farmers, farms and their required infrastructure, the society in which they are embedded and their natural environment. First a SES is further explained, followed by estuaria mechanisms which are relevant in the SES under study.
Resilience and transitions
An important characteristic of a SES is its resilience to change. Here, resilience is defined as the capacity of a system to remain in a stable state, or regime, after disturbances, so that the economic and ecological services of the system are maintained. This assumes the presence of alternative stable states which can be entered by the system when critical thresholds are exceeded (Scheffer et al., 2012).
Transitions replace an old regime by a new one which differs from the old one by different assumptions and routines (Bos, 2016). In this research, we link regimes to paradigms (Lohman, 2010): the dominant paradigm of a system is the way of thinking and perceiving that governs the dominant regime. Using this paradigm perspective, a transition is seen as a shift from one paradigm to another.
Lohman (2010), has defined several possible agricultural paradigms in the Netherlands. The Productionist Paradigm (PP) stimulates large scale, monoculture production on highly specialised farms, using technology and chemical additives to maximize production with minimum labour (Lohman, 2010). The Ecology Integrated Paradigm (EIP) is characterised by lowinput practices and uses naturally present characteristics of organisms to adapt to pressures. The Life Sciences Integrated Paradigm (LSIP) is characterised by using genetic modification of organisms to adapt to pressures and is more similar to PP than EIP (Lang & Heasman, 2004; Lohman, 2010; Beus & Dunlap, 1990).
Multilevel perspective and lockin
The transition theory describes transitions between different regimes from a multilevel perspective (Lohman, 2010), as figure 3 shows. Successful transitions develop from radically different, yet fitted niches in the current regime (Schot et al., 1994; Lohman, 2010; Smith, 2006).
Figure 3: Multiple scale levels in a nested hierarchy (Geels, 2002).
Multilevel interconnectedness creates a stable regime with a lockin: the current regime is preferred over all possible others regimes, which inhibits a transition towards a new dominant regime (Lohman, 2010). However, the innovative niche development combined with multilevel pressures on the regime creates a dynamic resilience landscape (Bos, 2016), as figure 4 shows.
Figure 4: Schematic representation of dynamic resilience landscape (Lohman, 2010).
One example of a lockin mechanism arises when actors’ perceptions of the costs and benefits of different strategies are biased towards those strategies that fit into their current paradigm. The effect of such personal perceptions on actor's willingness to choose for a new strategy – that is, to make a transition is described by the protection motivation theory. This theory states that an actor’s willingness to change his practices in the face of a threat is a sum of six factors: how he perceives the benefits of his current practices; the chance that the threat will happen; the severity of the consequences; the ability of the new method to deal with the threat; his ability to implement the new method; and the costs involved in making the shift (Floyd et al, 2000; van Duinen et al., 2015).
Saline intrusion in estuaries
An estuary is defined as a marginal marine environment that has a salinity that is decidedly different from that of the open ocean. Such environments form where salt water undergoes mixing with fresh river or meltwater resulting in brackish bodies of water. However, the actual salinity distribution depends strongly on the morphology of the estuary and the relative influence of tidal dynamics. For this study the approximate salinity distribution will be determined based on the estuarine circulation by means of the flow ratio. The flow ratio has been introduced by Hansen & Rattray (1966) and compares the volume of water entering the estuary during one tidal cycle to the average volume of water in the estuary. The larger the flow ratio, the less significant are the intrusion of seawater in the estuary and the mixing of salt and freshwater.
If a water body salinises, the surrounding land will be impacted by means of saltwater intrusion. A common definition of saltwater intrusion is the movement of saline water into an underground storage space previously containing fresh water (Bruington, 1972), where saline water is perceived as any water containing salt concentrations that are higher than the native freshwater in the area (Bruington). Salt water intrusion occurs naturally in coastal areas due to hydraulic connection between groundwater and seawater. The extent of saltwater intrusion mainly depends on the relative depth of the groundwater table (Essink, 2001; Van Dam, 1976 ). This relation is given by the GhybenHerzberg principle.
Figure 5: Schematic representation of the GhybenHerzberg principle (Lee, 2015).
Equation 1: GhybenHerzberg equation. ρf is the freshwater density and ρs the saltwater density.
According to this principle (see Figure 5 and Equation 1), the extent of saltwater intrusion (z) depends on the difference in density between freshwater and seawater and the difference between the groundwater and seawater level (h) (Van Dam, 1976). Saltwater intrusion happens via seepage: the upwelling of water from the adjacent water bodies into the soil (Essink, 2001). The rate of flow through the soil depends on the conductivity of the soil. This is related to the texture: soils with a very fine texture such as clay have a low conductivity and therefore a relatively slow flow (Essink, 2001).
Integrative approaches
Different parts of the agrosocial system were investigated from the viewpoint of earth science, ecology and social geography. The transition theory is a system approach and acts as an overarching theory to integrate the disciplines. Actors and pressures of the agrosocial system are identified and individual effects are analysed from the multiple disciplines, taking the whole system into account.
Integration techniques were applied to improve the interdisciplinary integration. We use the expansion integration technique with the Transition Theory, see figure 6. Originally, this theory is used in social sciences only. However, we expanded it by adding factors from natural sciences: earth sciences and ecology. Furthermore, expansion is used to assess the feasibility of saline agriculture. We consider this feasibility not only from a technical side, but include also social and natural factors.
Figure 6: Expansion of the Transition Theory
Methodology
The research methodology combines literature review, expert interviews and modelling study using ArcGIS and Matlab. Finally disciplinary findings were combined using integration approaches (see Theoretical framework section).
The literature study focused on describing the characteristics of the agrosocial system. To supplement the literature, interviews were conducted with several experts: an expert of saline agriculture, director of the farmers organisation LTO and a project manager at Water Board Hollandse Delta. In the analysis of the system it was decided not to focus on economic actors beyond agriculture, as industries and market researchers are not much involved in saline agriculture yet (de Kempenaer et al., 2007). The interviews were conducted in a face to face setting. The interviews with Van Bodegom and LTO can be found in the appendix. The interview with Hollandse Delta was recorded, the recordings are available on request.
The extent and rate of saltwater intrusion is determined by the processing of local data in ArcGIS and subsequent modelling in Matlab. The GhybenHerzberg principle is used to determine the maximum saltwater intrusion at 130x130m grid cell size. Thereafter, twodimensional saltwater flow is calculated based on basic flow equations (see appendix AD for more details). The focus of the model remains solely on the contribution of the Haringvliet to the salinisation of the surroundings. Future uncertainties such as sea level rise due to climate change are therefore not included in the model but will be discussed separately.
Background casestudy area
Characteristics of the agrosocial system
As the first part of the research, the current agrosocial system around the Haringvliet estuary is mapped using elements of the transition theory. This allows us to understand and anticipate where in this system changes will happen after the opening of the Haringvliet sluices. The map in figure 7 includes the most important physical, biological and social components of the system and their interactions (Bodin & Tengö, 2012; Darnhofer et al., 2012).
Figure 7: Current agrosocial system around the Haringvliet. Consumers and supply chains were not looked into due a lack of information.
How the agrosocial system will be affected by salinisation depends on the farming methods, crop use and the water infrastructure that facilitates these methods. The characteristics of the agricultural system and of the water system are described here. It becomes clear that the Productionist paradigm (PP) forms the dominant paradigm in the current agrosocial system (Lohman, 2010).
Characteristics of agriculture
The farms in the study area are designed in accordance with PP (Lohman, 2010). The farming happens on a rather large scale with an average farm size of 47 ha, while the average farm size for the Netherlands as a whole was 26 ha in 2010 (Eurostat, 2012). Farms in the study area are increasing in size: the average farm size increased from 34 to 47 ha between 2000 and 2012, while the total agricultural area decreased by 5 per cent (CBS, 2016b).
Mechanisation has been successful in increasing farmers’ incomes in the past decades (Verhorst, pers. comm., 1 April 2016). Although the turnover of individual farmers in the region is relatively low when compared to the rest of the Netherlands, the yearly returns brought in by farmers in the municipalities surrounding the Haringvliet has consistently increased in the past years (CBS, 2016a). However, the investments in modernisation to remain competitive have forced many farmers into debts (Lohman, 2010; PDC, n.d.) and create a dependence on technology to maintain yields, such as fresh water irrigation, which has been employed since the 1970s (Verhorst, pers. comm., 1 April 2016) and usage of high value crops, or cash crops. Mechanically yielded crops grow in monocultures and fertilizers, herbicides and pesticides are required for economic viability (Coolman, 2002).
Characteristics of the water system
The water system in the region counteracts the natural upwelling of saline groundwater (Jonkhoff et al., 2008). Currently, saline intrusion is a problem in the following areas: the Zuiderdiep, around Dirksland, and around Zuidland (Wolfert, pers. comm., 6 April 2016; see figure 8).
Figure 8: Salinity of the groundwater at 7.5 m NAP in 2000 (Jonkhoff et al., 2008). The red and yellow areas currently face risk of saline intrusion. The areas Zuiderdiep (ZD), Dirksland (DL) and Zuidland (ZL) are indicated.
Most crops grown in the area are highvalue crops that are highly sensitive to salinity. The farming system is therefore strongly dependent on counteracting salinity (Verhorst, pers. comm., 1 April 2016). Currently, this is done with a flushing system. Freshwater from the Haringvliet is pumped into the channels and ditches to flush out saline water, and prevent it from seeping into farmland. In addition, farmers use surface water for irrigation, which also requires channels and ditches to be fresh (Wolfert, pers. comm., 6 April 2016). Most of the land surrounding the Haringvliet is flushed
with freshwater, with the exception of a few nature areas where salt water is brought in (WSHD, 2015). Flushing is especially frequent at VoornePutten, north of the Haringvliet, while at GoereeOverflakkee flushing only happens in summer. This water demand for agriculture takes up to 50% of the total water demand in the 35% of the Netherlands that lies below sea level (Snellen et al., 2015).
The water level in the system is managed by the local water board and the levels are determined in consultation with the farmers (WSHD, 2015; Wolfert, pers. comm., 6 April 2016), who are the main stakeholders. Local and national governance bodies also shape the water management through investments and spatial planning decisions (WSHD, 2015).
The farming system and the water system around the Haringvliet are thus based on lowsalinity water and soils. To what extent this freshwater system will be affected when the Haringvliet becomes saline is discussed in the following section.
Results
Section 1. Future extent of salinisation
This section will go into more depth about the expected extent of salinisation of the Haringvliet due to the opening of the sluices and the consequences for the surrounding (agricultural) lands.
1.1 Salinity distribution Haringvliet
One of the major uncertainties concerning the Kierbesluit is the behaviour of the waterbody itself. According to Philip Wolfert (employee of Waterschap Hollandse Delta, personal communication April 6, 2016) the actual extent of salinisation within the estuary is unpredictable. Nevertheless, a maximum extent has been determined, to which the regulation of the sluices will be adapted (see figure 9).
Figure 9: Maximum extent of salinisation is shaded red (KierHaringvliet, n.d.).
To test whether this maximum of salinisation is realistic, a preliminary prediction can be made based on the flow ratio and the morphology of the estuary. The flow ratio can be calculated by:
Equation 2: Equation for flow ratio of an estuary.
in which Q represents the average discharge (m 3/s), t the duration of a tidal cycle (s) and b, h and l the dimensions of the estuary (m). It is stated when the discharge will become less than 1500m 3/s at Lobith (a measuring point upstream at the German border) or ~100m 3/s in the Haringvliet, the sluices will be shut (Borm & Huijgens, 2011; Rijksoverheid, 2011; Rijkswaterstaat, 2012). The average discharge of ~500m 3/s (Rijkswaterstaat, 2012) in combination with the average dimensions of 30km by 1km by 8m (Canavan, 2006) result in a flow ratio for the Haringvliet of approximately 0.093. According to Hansen & Rattray this would indicate the presence of a wellmixed estuary.
However, using the flow ratio as predictor of the salinity distribution neglects the morphology of the estuary. In the case of the Haringvliet the average cross section is very different in size from the flow area at the mouth of the estuary. Namely, the opening in the sluices will vary from 25m 2
in the case of low discharge to 1200m 2 in the case of high discharge (Kuijken, 2010). Estuaries with
a very narrow mouth go accompanied with decreased circulation and a welldefined vertical salinity gradient (Sumich & Morrissey, 2004). This is also evident when using the sluice opening as flow area. However, Kuijken (2010) did not express low and high discharge in numbers and therefore an estimation of 100m 3/s is used as low discharge and 3000m 3/s as high. For low discharge this results in a flow ratio of 5.96 and 3.73 for high discharge.
In other words, it is highly likely that throughout the entire year the salinity distribution of the Haringvliet will be dominated by a salt wedge. This implies that the salinisation of the Haringvliet will not reach far in the estuary and therefore the maximal extent of salinisation (figure 9) is perceived plausible. Moreover, this entails that the surface waters will experience little mixing with
saline water as this will be confined to bottom waters. However, the presence of extremely silt bottom waters that go accompanied by a salt wedge estuary (see figure 10) are likely to cause significant salt water intrusion via the subsoil.
Figure 10: Salinity distribution of a salt wedge estuary (adapted from Wollast & Duinker, 1982).
1.2 Saltwater intrusion
To determine the extent and rate of saltwater intrusion, first the maximum saltwater level was determined according to the GhybenHerzberg principle. The land surrounding the Haringvliet is mostly low lying (see figure 11) and the groundwater level is often below NAP (TNONITG, 2016).
Figure 11: Surface elevation of the surroundings of the Haringvliet (adapted from Algemeen Nederlands Hoogtebestand,
n.d.).
Consequently, almost entire GoereeOverflakkee and VoornePutten are potentially exposed to salt water intrusion. This can be seen in figure 12: all the blue coloured areas have groundwater levels that are lower than the water level of the Haringvliet and will experience saltwater intrusion.
Figure 12: Groundwater level of the surroundings of the Haringvliet with respect to NAP.
The results from the saltwater intrusion simulation are displayed in figure 13. This figure shows the extent of intrusion for four time slices, 1, 10, 50 and 100 years. The yearly extent of intrusion can be viewed via this link 1 to the complete simulation. The results of the simulation show that saltwater intrusion is a relatively slow process. In the first year the saltwater will have traveled approximately 100m land inwards, while in 100 years this will only have been increased to about 1km. The area that will be affected by saline intrusion according to the model is 36.25km 2 after
one year, 49.92km 2 after 10 years and 77.47km 2 after 100 years. This equals respectively 5.8%,
8.0% and 12.4% of the entire area of the surrounding land (GoereeOverflakkee and VoornePutten combined: 622,34km 2). However, it will only be a matter of time for saltwater to intrude in areas further away from the Haringvliet.
Figure 13: Saltwater intrusion for 13A: 1, 13B: 10, 13C: 50 and 13D: 100 years after salinisation of Haringvliet (modelled in MATLAB).
Furthermore, the intrusion appears to have more effect on VoornePutten than on GoereeOverflakkee, as a larger area is affected in the same amount of time, which is the result of different conductivities of the soil. Moreover, it stands out that the rate of intrusion reduces over time. This is especially clear in figure 14 that shows the combined extent of saltwater intrusion after 1, 10 and 100 year(s). On some places, the distance covered in the first year even equals that covered in the subsequent 99 years.
Figure 14: Extent of saltwater intrusion for 1, 10 and 100 years of salinisation of the Haringvliet (modelled in MATLAB).
1.3 Consequences of salinisation for agriculture
Salinity decreases plant osmosis potential (Naheed et al., 2008), but this effect is usually negligible in the face of plant growth performance (van Bodegom, 2016). However, Na+ and Cl inhibit K + uptake at the cell membrane and are toxic to plants (Naheed et al., 2008). Also, nutrient imbalances arise, which cause nitrogen and phosphorus deficits ( Sleimi & Abdelly, 2002). Nitrogen uptake is limited in saline soils (Rahman et al., 1995), because symbionts, which form the main nitrogen source for plant, are salt intolerant (Bala et al., 1990; Bruning et al., 2013).
In figure 15 the extent of the modelled saline intrusion after 10 years (2028) is overlain on a land use map. This gives an indication of the area where crops are affected and farmers’ incomes are at risk. The salinisation as resulting from our model will have affected about 26 km 2 of farmland after 10 years. However, not all farmers in the salinised region will be equally affected. Especially the area around the Zuiderdiep on GoereeOverflakkee (see figure 6) may be at risk. As explained before, the salinity risk is currently already quite high here, while the area is also within reach of saline seepage from the Haringvliet, causing the two problems to add up (Wolfert, pers. comm., 6 April 2016). The damage to farmers is also determined by which crops are grown. At GoereeOverflakkee half of the affected farmland are pastures; at VoornePutten this is 35% (see figure 16); these farmers may be less sensitive to salinity than arable farmers, as grassland is not affected by salinity very fast (FAO, n.d.). Among arable farmers, especially those who grow salinitysensitive and/or highvalue crops such as flower bulbs will lose income.
Figure 15: Outline of salinisation after 10 years shown in red. Base map from Nationaal Georegister (2015). Figure 16: Areas of farmland affected by salinisation from the Haringvliet after 10 years. Areas have been estimated from land use maps.
Section 2. Transition to a new agrosocial system
2.1 Challenges current paradigm with increased salinity
Besides the increased saline seepage due to the sluice opening, other pressures on the PP are identified on multiple system levels (see figure 17). Table 2 lists the pressures on the system and classifies them according to the level on which they affect the system, consistent with the central concepts of transition theory. After table 2, we elaborate on pressures that are pertinent to our research and have not already been discussed. Figure 17: The dominant regime in the Haringvliet is under pressure from all three levels. Table 2: Identified pressures on the current AgroSocial system. The bold pressures are further elaborated below. Landscape pressures Salinisation Haringvliet Policy changes (RVO, 2016; LTO, 2013) Climate change (Kovats et al., 2014) Public opinion usage pesticides and herbicides Environmental concern Regime pressures
Fresh water demand (Snellen et al., 2015) Inadequate flushing design (Snellen et al., 2015) Debts farmers (Lohman, 2010; Melyukhina, 2011) Resilience farms (Agrosocial system) Low salinity tolerance conventional crops (Bodegom, 2016) Summer droughts (van Duinen et al., 2015) Costs subsidizing farmers (Lohman, 2010) Herbicides and pesticides resistance (Pimentel et al., 1992) Environmental degradation (Pimentel et al., 1992) Nitrogen and phosphorus shortages (Bruning et al., 2015) Niche pressures Ecology Integrated Paradigm (EIP) (Lohman, 2010) Life Sciences Integrated Paradigm (LSIP) (Lohman, 2010) Saline agriculture (Lohman, 2010) Landscape pressures Policy changes
Both at the EUlevel and at the national level, some policies relating to agriculture and water are increasingly oriented towards sustainability and ecological values (EC, 2015). Farming subsidies from the EU are increasingly tied to environmental goals, such as enhancing farmland biodiversity (RVO, 2016). Also the national standards for, for example, pesticides and manure use, are being tightened (Verhorst, pers. comm., 1 April 2016). Farmers and local governments are under increased pressure to comply with these policies (LTO, 2013).
Climate change
According to the latest report by the International Panel on Climate Change, the Netherlands will experience severe impacts by climate change on water resources in the near future. By 2100, a sea level rise of circa 0.4 – 1.05 meters is expected and the frequency of extreme flood events will increase in coastal zones (Kovats et al., 2014). On the other hand, long periods of drought and low river discharge will become more frequent (Ibidem). The reduced river discharge in combination with higher sea levels will increase the salinity stress on crops (van Minnen et al., 2013). This
climatecaused salinisation is a separate process from the Haringvlietderived salinisation we modelled, but forms an additional pressure on the system.
Regime pressures
Freshwater demand
Overall water demand is expected to increase (Rozema & Flowers, 2010), especially in summer when drought will become more frequent (Utwente, 2015) and flushing is required to limit salinity damage. On Voorneputten and GoereeOverflakkee, the flushing system is inefficient in terms of water use and uses up to 50% of freshwater in the area (Snellen et al., 2015). Already, in summer the water supply is inadequate to maintain both quality and quantity of the required flushing water to meet high surface water quality for agricultural practices and this problem will increase in the future (Ibidem.; Stuyt, 2007; Van Landbouw, n.d.; Utwente, 2015; Jonkhoff et al., 2008). Inadequate flushing system
The current system of flushing, which includes inlet points, channels and ditches, is not sufficient to maintain the required surface water quality demands (Snellen et al., 2015). Current infrastructure is not sufficient to provide all users at all times with water of certain high quality (Snellen et al., 2015). Moreover, when the Haringvliet sluices are opened the number of fresh water inlets will reduce from six to two, meaning that problems with individual inlets have more impact.
Debts farmers
The profitability of many farms in the Netherlands has been threatened in recent years by fluctuating food prices. As a result of this and other factors, Dutch farmers have been under pressure to make large investments in upscaling and modernisation (PDC, n.d.). Debts in all farming sectors have been increasing over the past decades, especially in intensive sectors, and are high compared to other EU countries (Melyukhina, 2011). Debts and problems with profitability may undermine the current farming system.
Niche pressures
At the level of the niche, two paradigms are identified which are altering the resilience landscape and thus put pressure on the PP regime: Life Science Integrated Paradigm (LSIP) and the Ecologically Integrated Paradigm (EIP) (Lohman, 2010).
LSIP requires little change in system and behaviour of the PP (Lohman, 2010), which makes a transition towards LSIP as dominant paradigm relatively easy. EIP is significantly different from PP, since it does not use pesticides and herbicides. Therefore, it is expected that productivity will decline (Coolman, 2002). However, considering the paradoxical relationship between a dominant paradigm and chance of success of a niche to become dominant, EIP has a good opportunity to become dominant.
Saline agriculture can be fitted both in the LSIP and EIP, although EIP is the only paradigm in which it is put into practice today (Lohman, 2010; Bodegom, 2016). Saline agriculture in the EIP will not be able to meet conventional yields (Bodegom, 2016) while having the same costs (Ibidem.), this will force saline agriculture into a niche market (Ibidem.). However, due to complicated genomes
responsible for salt and drought tolerance, GM has not been able to increase salt tolerance (Ibidem.). Additionally, Bodegom (2016) identifies a trend that the niche market in which saline agriculture operates is increasingly adopting organic practices recently, which will make saline agriculture unsuitable in LSIP.
2.2 Strategies to cope with salinisation
Our modelling showed that salinisation will increase due to the opening of the sluices and this will negatively affect crop productivity in the affected area. Therefore coping strategies are required to realise sustainable agriculture. Two methods are identified: continuous flushing of the system to limit increase in soil salinity; and saline agriculture.
Flushing
If saline intrusion increases, the strategy of the water board will probably be to intensify flushing, for example, by bringing in fresh water all year instead of only in summer (Wolfert, pers. comm., 6 April 2016). The costs of flushing the area are, seemingly paradoxically, relatively low: on average flushing one acre on the islands of the province of Zeeland costs €59,71 annually. The costs are low because all the infrastructure is already in place (Snellen et al., 2015). The costs of flushing water vary between €0.15/m3 and €1.50/m3 (Snellen et al., 2015). Despite these low costs, at some point
intensifying pumping will become too expensive. At the moment, for example, the water board does not try to keep the brackish Zuiderdiep fresh, as the costs would be too high (Wolfert, pers. comm., 6 April 2016).
Saline agriculture
Currently saline agriculture is being exploited as a niche on multiple locations in the Netherlands, ranging from a saline experimental garden on Texel to experiments on the Afsluitdijk (a dyke at the Lake IJssel) and in the provinces of Friesland and Zeeland (Ziltperspectief, n.d.; Zeeuwsetong, 2016). The saline experimental garden of Texel started in 2006 and is amongst the first saline agricultural experiment to commercially produce halophytic crops (Ziltperspectief, n.d.). The experiments include cultivation of both halophytes and conventional crops under various salinity levels (De Vos, 2016). The aim of the experiments is to gather physiological information on crops and their salt tolerance, increase practical knowledge on cultivation in saline conditions, raise public awareness and commercialise saline crops (Ibidem.; Bodegom, 2016; De Vos, 2016).
Saline agricultural systems have to compete economically with PP farms in order to be sustainable (Bodegom, 2016). Brandenburg (2009; retrieved from De Vos et al., 2010) identified three main agricultural sustainable systems in which saline agriculture can be exploited. The categories are identified according to different principles: the first system, a mixed saline farm, assumes very limited freshwater availability. The second system, a climateproof arable farm, is designed from a general water availability perspective and lastly the climateproof multifunctional farm has been designed from a societal demand perspective (De Vos et al., 2010).
Bodegom (2016) does not see saline agriculture being implemented on a large scale in the Netherlands, since salinisation is not perceived significant enough and because of consumer behaviour. Therefore the second and third identified system are possible candidates to upscale saline agriculture in The Netherlands. The climateproof arable farm ‘uses available water
throughout the seasons’ (De Vos et al., 2010, p52). In dry summers, the water will be saline and it will be inevitable to use it (Ibidem.). Conventional crops will be cultivated as much as possible, complemented with halophytic crops (Ibidem.). The climateproof multifunctional farm, in addition, will bring together multiple services into one system; for example, a combination of crop production with recreation, housing and/or (mental) health care will be made. This will add additional economic and social value to the farm (De Vos et al., 2010).
Identified arable crops for saline agriculture in the Netherlands are: beet, barley and spelt (table 3). In accordance with the prerequisite that cash crops have to have either high yield per acre or have to have a niche market in which people are willing to pay high prices per kg product, spelt is a good candidate for upscaling saline agriculture (Bodegom, 2016). See table 3 for an inventarisation of saline agriculture cash crop candidates in the Haringvliet area.
Table 3: Evaluation of crops for saline agriculture.
2.3 Arisen opportunities for Saline Agriculture from the identified pressures on the current regime
As explained, in societal transitions regimes are usually under pressure both from small niches and from drivers on the large scale. Niches often manage to grow if they link up to largerscale pressures (Lohman, 2010). In the case of the Haringvliet there is a possibility for this, as saline
agriculture resolves some of the landscape and regime pressures on the current system that were identified in section 2.1 (see table 2).
Landscape pressures
Salinisation
Applying saline agriculture would first of all solve the sensitivity of the system to soil salinity. The system is adapted to salinity, so increased saline intrusion would no longer threaten farmers’ yields.
Policy changes
As argued earlier, saline agriculture around the Haringvliet is most likely to happen within an ecologically integrated paradigm. This means that saline agriculture could make use of the tendency within national and EU scale politics towards more sustainable and ecologically orientated agricultural and water policies. One recently added pillar of the EU farming subsidies, greening, promotes organic farming and biodiversityfriendly areas within agricultural lands (RVO, 2016). These EU policies might support sustainable saline agriculture if it would be given the same status as organic agriculture.
On the national level, there are also support routes for innovations in agriculture. However, there is little specific policy on saline agriculture so far, apart from a subsidy for farmers changing their equipment for a shift to saline agriculture (RVO, 2016). Saline agriculture could also link up with nature conservation. Saline agriculture could be clustered around saline nature areas, as they require the same water management (WSHD, 2015).
Regime pressures
Freshwater demand
Fresh water demand will probably decrease under saline agriculture due to the possibility to use brackish or saline water for irrigation. In addition, less flushing is required because soil salinity does not have to be zero. In addition, summer droughts no longer form a threat but will form a
driver to increase crop diversity.
Resilience farms
The diversity of crops grown is likely to increase under saline agriculture, especially when it is applied under the EIP, which stimulates crop diversity (Lohman, 2010). The climateproof multifunctional type of saline agriculture combines conventional and halophytic crops and also stresses a combination of income sources on farms. With this diversity of crops and activities, yields and incomes may be more resilient to shocks like diseases and market changes (Scheffer et al., 2012).
2.4 Barriers for saline agriculture implementation on a large scale
Profitability
Although conventional crops have shown to be more salt tolerant than generally perceived (Bodegom, 2016), it has shown to be hard to convince the government and breeders that the figures on this are real, which hold back the upscaling of saline agriculture (Ibidem.). In addition,
public opinion determines the success of the saline agriculture experiments and must therefore never be underestimated (Ziltperspectief, n.d.).
Texel has proven to be able to successfully produce commercial crops in saline agriculture. However, the yields are about ½ to ⅔of the yield of conventional agriculture while the costs compared to nonsaline cultivation have been unchanged (Bodegom, 2016). This implies that saline agriculture can only be commercially competitive with conventional agriculture when a niche market can be found to sell the products at higher prices or when salinity is so severe that conventional production experiences higher costs at lower yields.
If halophytes are grown instead of conventional crops, economical barriers also arise. The methods are often labour intensive and so far bring in low profits (Frans, 2011; Grontmij, 2010). The markets for halophyte crops such as samphire and sea aster are very small, which will make upscaling difficult (de Kempenaer et al., 2007). Most farmers in the area are not considering saline agriculture as an economically viable option: they will choose freshwater farming as long as it is possible (Verhorst, pers. comm., 1 April 2016).
Lockin
Hydraulic structures often create a lockin and prevent a system to change; this happens because it is easier to choose a strategy that maintains these structures than to take a totally different track (Pel et al., 2014). In the Haringvliet case, the flushing system is acting as such a lockin, hampering a transition towards a salinebased system.
Over time, a complicated structure of ditches, channels and pumps has been created around the Haringvliet to facilitate flushing. The existing infrastructure makes flushing a relatively easy and attractive approach to salinisation. In addition, large investments have been made recently by the water boards and local governments to update the flushing infrastructure to the post2018 conditions (Wolfert, pers. comm., 2016). Saline farming, however, would need a different water management approach in which saline seeping is not combated; this would mean large renewed adaptations in the water infrastructure and a loss of the previous investments.
In addition to this lockin, the current water system acts as a barrier for smallscale experiments with water management. Interlinkage of all compartments of the flushing infrastructure complicates local adaptation of the system. In addition, the water board manages ditch water levels for aggregated areas containing several farms (WSHD, 2015). It is therefore not possible to allow saline conditions on one farm only without affecting surrounding farms (Wolfert., pers. comm., 6 April 2016). This means that it will be hard for individual farmers to shift to saline farming on their own.
Lack of knowledge
Limited research funds hold back the expensive experimental research required to increase knowledge on saline agriculture (Bodegom, 2016). Knowledge on saline agriculture will increase very slowly, limiting the willingness of breeders and stakeholders to invest in such an ‘uncertain’ farming system (Ibidem.). In previous research in the Haringvliet area, the farmers themselves were also found to be unwilling to adopt practices that involve many uncertainties (van Duinen et al., 2015).
Farmer attitudes
As explained before, the adaptation behaviour of individuals depends on their personal perceptions of the risks and benefits of the new method. Several of these perceptions act as a barrier to saline adaptation in the case study area. These are the farmers’ perception of the ability of saline agriculture to deal with the salinisation threat; and their perception of the chance and severity of salinisation.
Firstly, farmers in the area do not believe in the effectivity of the saline agriculture method, as they generally feel very strongly against letting farmland salinise. This can partly be explained by the 1953 floods, after which salt lowered crop yields strongly for several years. They also have little knowledge about saline farming (Verhorst, pers. comm., 1 April 2016).
Secondly, farmers’ perception of the chance and severity of the salinisation threat is low. Farmers and the Water Board expect that the Kierbesluit compensation measures will take away any additional salinisation threat from the opening of the Haringvliet sluices. Farmers expect the water board will prevent salinisation by flushing, therefore they do not perceive a necessity to shift to saline farming (Verhorst, pers. comm., 1 April 2016; Wolfert, pers. comm., 6 April 2016). The farmers understand there could be an increase in salinisation in the farther future, but they plan on a rather short term compared to the water managers (Verhorst, pers. comm., 1 April 2016; Wolfert, pers. comm., 6 April 2016). This difference in focus on time scales hampers an agricultural transition (Pel et al., 2014; Kemp et al., 2007).
Discussion
Future salinisation extent
As mentioned previously, the modelling of saline intrusion focused solely on the contribution by the Haringvliet estuary and a constant water level was used. However, future prospects indicate that the sea level of the North sea will rise significantly in the coming century which will likely amplify saline intrusion from both the North sea and possibly the Haringvliet (van Minnen et al., 2013). Furthermore, climate change will cause an increase in freshwater demand with 25% in 2050 compared to the current situation (Snellen et al., 2015). Such a buildup of freshwater abstraction will further increase the relative importance of salt water within the estuary and potentially accelerate saline intrusion.
Moreover, seepage (upward flow) is not included in the simulation. However, the variance in soil texture of the subsoil and the presence of hardly permeable layers at some locations influence the behaviour of saltwater intrusion: incorporating this into the model will give more detailed results. Nevertheless, the results from the simulation show correspondence with an earlier performed study on the effect of salinisation of the groundwaters of GoereeOverflakkee (van der Hoog, 2007) concerning the rates of salinisation and the decrease in rate over time.
The salinity thresholds of crops (table 3) have been retrieved from the FAO on (semi) arid areas. It is possible that the thresholds in nonarid climates are at higher salinity concentrations, since the described threshold might be influenced by drought stress (Bodegom, 2016). Furthermore, the impact of nutrient status on salt tolerance has not been taken into account. Salinity tolerance can be improved by tackling the nutrient imbalance by adding limiting minerals (mostly N and P, see also appendix F) (Naheed et al., 2008) and by breeding for increase in soil/root contact area by selecting for large root hairs (Schleiff, 2008).
Feasibility of saline farming
Flushing will decrease under saline agriculture, increasing soil salinity. However, this has longterm consequences (van Bodegom, pers. comm., 1 April 2016). We expect significant resistance against this among locals and farmers. Conducting in situ longterm experiments will have to point out the extent and consequences of adapting these farming strategies.
We have found that the general view on the shortterm implementation of saline agriculture is rather negative. However, farmers who are strongly affected by salinity do show interest in saline farming on the short term. There are already more experiments with saline farming on some islands in Zeeland that have no external freshwater supply, as there is more pressure on the water system here (Verhorst, pers. comm., 1 April 2016; Provincie Zeeland, 2006). Therefore, if the salinity pressure in the Haringvliet area increases in the future, farmers may be willing to implement saline farming here as well.
More research could help to overcome the current barriers to saline agriculture. The dominant view among stakeholders is that saline agriculture is not economically viable and its workings very uncertain. Knowledge about needed investments and market possibilities for saline agriculture is lacking. Further research into the uncertainties surrounding saline agriculture, such as the salt tolerance of crops and its economic feasibility, can reduce this barrier of lacking knowledge. In addition, research results should be better communicated to stakeholders, as they are little aware of the knowledge that is available.
Interdisciplinary integration
We described and analysed the whole agrosocial system from the transition theory perspective. All three disciplines have been successfully integrated in the analysis and all are equally important to understand the system and the processes that are occurring in the system. It has appeared relatively easy to combine disciplinary findings by means of interdisciplinary integration. Mainly the transition theory proved to be of use. However, the integration could be improved by having more regular meetings along the way of writing the report.
Conclusions
The agrosocial system around the Haringvliet is currently governed by the productionist paradigm. The farming system is sensitive to salinity, and depends on the present flushing system to keep functioning.
The area of the Haringvliet that will cause saltwater intrusion will probably be the area between the mouth and the middle of the estuary. The initial contribution of the Haringvliet to salinisation is small, because the process takes a long time due to low conductivity of the surrounding soils. However, almost the entire surroundings are sensitive for saltwater intrusion due to a low surface elevation and negative groundwater level. Salinisation of the agricultural soils will have varying effects on crops and farmers.
Besides salinisation, the productionist paradigm in the casestudy area is under several other pressures, such as an increasing freshwater shortage and climate change. The latter has not been included in the modelling due to its great uncertainty but could very likely lead to increased salinisation. Saline agriculture could be an answer to most of the identified pressures. However, it is not likely it will be broadly accepted and applied as a solution due to large cultural and economic barriers. Few signs show that an alternative farming approach will be implemented as long as conventional farming is possible.
The insights are directly applicable in the Haringvliet area: saline intrusion due to the sluice opening must be seen by stakeholders as a real issue, with potential effects on the farming and water systems. Our findings on the feasibility of saline agriculture have wider relevance for other saltaffected places where saline agriculture is considered. Saline agriculture is theoretically a good solution in such areas. However, our research has made clear that social and economic barriers, such as lockin and perceptions of farmers, have to be taken into account when saline agriculture is applied in a practical situation.
References
Actueel Hoogtebestand Nederland (n.d.). AHN Viewer. Retrieved on march 10, 2016 from http://ahn.maps.arcgis.com/apps/webappviewer/index.html?id=c3c98b8a4ff84ff4938fafe7c c106e88
Bala, N., Sharma, P. K., & Lakshminarayana, K. (1990). Nodulation and nitrogen fixation by salinitytolerant rhizobia in symbiosis with tree legumes. Agriculture, ecosystems & environment, 33(1), 3346.
Berner, E. K., & Berner, R. A. (2012). Global environment: water, air, and geochemical cycles . Princeton University Press.
Beus, C., Dunlap, R., (1999) “Conventional versus Alternative Agriculture: The Paradigmatic Roots of the Debate”, Rural Sociology 55(4), pp. 590616.
Van Bodegom, P. (2016). personal communication, April 1st.
Bodin, Ö., & Tengö, M. (2012). Disentangling intangible social–ecological systems. Global Environmental Change, 22(2), 430439.
Borm, W. & Huijgens, C. (2011). Is het experiment de Kier achterhaald?. Retrieved on April 11, 2016 from http://www.adviesgroepbormenhuijgens.nl/zddekier.php
Bruning, B., van Logtestijn, R., Broekman, R., de Vos, A., González, A. P., & Rozema, J. (2015). Growth and nitrogen fixation of legumes at increased salinity under field conditions: implications for the use of green manures in saline environments. AoB plants, 7, plv010 Bruning, B., & Rozema, J. (2013). Symbiotic nitrogen fixation in legumes: Perspectives for saline
agriculture. Environmental and experimental botany,92, 134143
Canavan, R. W. (2006). Biogeochemical cycling of nutrients and trace metals in the sediment of Haringvliet Lake: Response to salinization (Vol. 264). Utrecht University.
CBS (2016a). Standaardopbrengst land en tuinbouwbedrijven per gemeente in 2011 en 2015.
Retrieved from
https://www.cbs.nl/nlnl/maatwerk/2016/08/standaardopbrengstlandentuinbouwbedrijv enpergemeentein2011en2015
CBS (2016b). Retrieved from CBS StatLine: http://statline.cbs.nl/Statweb/dome/?TH=51870&LA=nl Coolman, I. F. (2002). Developments in Dutch farm mechanization: Past and future. Agricultural
Engineering International: CIGR Journal.
Conway,G. 1993. Sustainable agriculture: tradeoffs with productivity, stability and equitability.
Economics and ecology 5768
Darnhofer, I., Gibbon, D., & Dedieu, B. (2012). Farming systems research: an approach to inquiry (pp. 331). Springer Netherlands.
De Vos, A., Rozema, J., Rijsselberghe van, M., Duin van, W., & Brandenburg, W. (2010). Zilte Landbouw Texel, een voorbeeld transitieproject 20062010 Eindrapport. Project Leven met Water, Leven met Zout Water, 2057, 191.
Du Laing, G., Rinklebe, J., Vandecasteele, B., Meers, E., & Tack, F. M. G. (2009). Trace metal behaviour in estuarine and riverine floodplain soils and sediments: a review. Science of the Total Environment, 407(13), 39723985.
van Duinen, R., Filatova, T., Geurts, P., & van der Veen, A. (2015). Coping with drought risk: empirical analysis of farmers’ drought adaptation in the southwest Netherlands. Regional Environmental Change, 15(6), 10811093.
Eisa, S., Hussin, S., Geissler, N., & Koyro, H. W. (2012). Effect of NaCl salinity on water relations, photosynthesis and chemical composition of Quinoa (Chenopodium quinoa Willd.) as a potential cash crop halophyte. Australian Journal of Crop Science, 6(2), 357.
Essink, G. H. O. (2001). Salt water intrusion in a threedimensional groundwater system in the Netherlands: a numerical study. Transport in porous media, 43(1), 137158.
Eurostat. (2012). Agriculural census in the Netherlands. Obtained on April 2, 2016 via http://ec.europa.eu/eurostat/statisticsexplained/index.php/Agricultural_census_in_the_Ne therlands.
Evans, Forney & GuidoDiBrito. (1998). Student Development in College: Theory, Research, and Practice. JosseyBass: San Francisco, CA, 111114.
FAO. (n.d.). Agricultural drainage water management in arid and semiarid areas. FAO irrigation and drainage paper. 61. ISSN 60545264.
Floyd, D. L., Prentice‐Dunn, S., & Rogers, R. W. (2000). A meta‐analysis of research on protection motivation theory. Journal of applied social psychology, 30(2), 407429.
Frans, P. (2011, December 13). Lange weg te gaan voor zilte teelten. Opgehaald van http://www.boerderij.nl/Home/Achtergrond/2011/12/Langewegtegaanvoorzilteteelten AGD577844W/
Glaeser, B. (2015). From global sustainability research matrix to typology: a tool to analyze coastal and marine socialecological systems. Regional Environmental Change, 16(2), 367383. Grattan, S. R., & Grieve, C. M. (1998). Salinity–mineral nutrient relations in horticultural crops.
Scientia Horticulturae, 78(1), 127157.
Gunderson, L. H. (2000). Ecological resiliencein theory and application. Annual review of ecology and systematics, 425439.
Hansen, D. V., & Rattray, M. (1966). New dimensions in estuary classification. Limnology and Oceanography, 11(3), 319326.
Hollandse Delta. (2016). Interview
Hoog, van der, J. (2007). Effect Kierbesluit op grondwater van GoereeOverflakkee . Retrieved on April 21, 2016 from http://www.citg.tudelft.nl
Jonkhoff, W., Koops, O., Krogt, van der R.A.A., Oude Essink, G.H.P., & Rietveld, E. (2008). Economische effecten van klimaatverandering. Overstromingen en verzilting in scenario’s, modellen en cases. TNO Rapport 2008DR0711/A, 1128.
Kemp, R., Rotmans, J., (2001) “The management of the coevolution of technical, environmental and social systems” in Towards Environmental Innovation Systems.
Kemp, R., Loorbach, D., & Rotmans, J. (2007). Transition management as a model for managing processes of coevolution towards sustainable development. The International Journal of Sustainable Development & World Ecology, 14(1), 7891.
De Kempenaer, J. G., Brandenburg, W. A., & van Hoof, L. J. W. (2007). Het zout en de pap: een verkenning bij marktexperts naar langeretermijnmogelijkheden voor zilte landbouw (No. 07.2. 154, p. 93). InnovatieNetwerk.
Kovats, R.S., R. Valentini, L.M. Bouwer, E. Georgopoulou, D. Jacob, E. Martin, M. Rounsevell, and J.F. Soussana, (2014). Europe. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 12671326.
Kuijken, W. J. (2010). Analyse uitvoering Besluit beheer Haringvlietsluizen. Deltacommissaris. Lang, T., Heasman, M., (2004) Food Wars. Global Battle for Mouths, Minds and Markets, Londen:
Earthscan Publication.
