Water and agriculture: contribution to an analysis of a critical but difficult relationship

Pierre STROSSER (DG XI), Maria PAU VALL, Eva PLötscher (Eurostat)

A publication on the relationship between agriculture and the environment has to include a chapter on both the qualitative and quantitative aspects of the critical relationship between agricultural activity and water. Water management is a traditional practice in numerous regions, with irrigation in the south of Europe and the drainage of wetlands in the north. However, the increase in irrigated or drained areas since the Second World War poses increasingly significant environmental problems. The sound management of water resources is essential to any strategy geared to sustaining growth and preserving biodiversity. This chapter examines, inter alia, the problems connected with water scarcity and the quality issues created by nitrate, phosphate and pesticide pollution. The qualitative aspects of the relationship between agriculture and water are illustrated with the example of the Rhine basin.

Renewable fresh water, a basic component of the water cycle, is a resource essential to life. From the earliest days, the availability of fresh water has determined the emergence and development of living organisms on our planet. It has also determined, and probably still determines, the existence of humans and their activities. Today, economic development goes hand in hand with increasing consumption and problems of availability or quality. 

The relationship between water and agriculture is an ancient one, water having been used for agricultural purposes for several millennia by successive civilisations in the Mediterranean regions. However, recent agricultural policies adopted at national and Community level have altered the state of balance in these countries.

This intensification has led to a significant increase in water abstraction, giving rise to growing environmental problems. 

These include (i) lower ground water and river flow levels as a direct result of water abstractions; (ii) secondary effects, which are much more difficult to measure, such as the disappearance of wetlands (also related to the implementation of drainage systems), oxygen deficits in rivers leading to the possible extinction of species of flora or fauna or the gradual salinisation of ground water in coastal areas; (iii) environmental problems from with the construction of dams and the diversion of water-courses for irrigation purposes; (iv) the effects of water use on agricultural land causing increased nitrate and pesticide leaching and the pollution of ground water and rivers.

Agricultural intensification has also led to a significant geographical extension of irrigation in Northern Europe, particularly in France, Belgium, the United Kingdom and the Netherlands. For example, in 1995 irrigable land accounted for some 29% of the utilised agricultural area (UAA) of the Netherlands. Consequently, the environmental problems associated with the use of water by agriculture nowadays concern a significant part of the UAA in Europe, with quantitative aspects predominating in southern European countries, while the northern regions mostly face problems of water quality and pollution. 

Clearly, agriculture is not the only player disrupting the water cycle. The urbanisation of the areas at risk from flooding, tourism, and the construction of roads or canals blocking natural drainage routes also have a clear environmental impact. Add to this human consumption of water, that of animals, industrial demand, particularly for cooling water, its use as means of transport or as a solvent and human, animal and industrial waste. Frequently, the various sectors in competition are both the cause and the victims of the depleting supply and deteriorating quality of water resources. 

This chapter examines the main factors in the relationship between water and agriculture. The objective is not to conduct an exhaustive study at European level of this relation, but to contribute to the necessary, though already widespread, debate. Analysing this relationship is a difficult task, all the more in view of the plentiful scientific literature on the subject, the numerous but rarely comparable case studies available, and the shortage of statistical data on the various key variables concerning water resource management (box 1). 

Quantitative aspects 

Some figures 

At European Union level, the average annual availability of internal water is in the region of 1 212 km ³, equivalent to 3 326 m ³ per person per year (Eurostat). Adding the water supplied by neighbouring countries sharing a number of catchment areas, total water availability reaches 1 303 km ³ and 3 740 m ³ per person per year. There are considerable differences between Member States however both in terms of the total volume available and of the degree of reliance on water supplies from neighbouring countries. The Netherlands, for example, is an extreme case, with 88% of available water resources originating in neighbouring countries. External supplies are also considerable in Portugal, Luxembourg and Germany, where they account for over 40% of available water. Their significance underscores the need for managing water resources at the drainage basin level, as proposed under the new Framework Directive on Water currently being examined at the European level, rather than the present regional and national scales as is currently the case. 

Overall, despite the significant differences between countries, there are sufficient renewable resources at European level, as the difference between renewable resources and abstracted resources shows (Figure 1). However, these overall statistics do not take into account the high spatial and temporal variability of the two variables under consideration and shed no light on the water scarcity problems in many European regions. 

The breakdown of water consumption between the various economic sectors varies considerably from one region to another, depending on natural conditions and economic and demographic structures (Figure 2). 

• In France (64%), Germany (64%) and the Netherlands (55%), for example, most of the water abstracted is used to produce electricity. 
• In Greece (88%), Spain (72%) and Portugal (59%), water is mostly used for irrigation. 
• In northern European countries such as Finland and Sweden, little water is used in agriculture. In contrast, cellulose and paper production, both highly intensive water-consuming industries, are significant activities and water is abstracted mainly for industrial purposes (66% and 28% respectively of total abstractions). 

Electric power stations have the highest water abstractions for cooling. These are followed by agriculture for irrigation, by industry, and by the distribution of drinking water. However, the concept ‘water abstraction’ only partially reflects the impact of the various sectors on the resource. Analysing the water consumed, i.e. water abstracted but not discharged, reflects a quite different reality. Hydro-electric power stations, for example, discharge practically all the water they abstract once it has passed through the turbines. Other power stations consume only a very small proportion, as most of the cooling water is discharged immediately without being polluted.

In the case of irrigation, a more or less significant share of the abstracted water joins ground water or the water-course, either by run-off or by infiltration. The effectiveness of irrigation (defined as the ratio between the water abstracted and the water actually consumed by the plant) varies according to soil characteristics, differences in altitude, irrigation practices and techniques (border, furrow or drip method) and water distribution method (by gravity, under pressure). For example, the effectiveness varies between 50 and 70% in the gravitational systems of the Ebro basin in Spain, but can rise to over 95% in modern drip systems 1 . Nevertheless, the water "lost" by the irrigator and by the irrigated system is not necessarily lost for the catchment basin. Indeed, the lost waters joining water-courses or ground water can be re-used by other users who are located further downstream from the water-course or who pump from the ground waters concerned. However, in absence of water accounts at catchment basin level, the real losses (i.e. the quantities of water returning to the sea surplus to the quantities necessary for ecosystems to function properly and for economic activities) connected with ineffective irrigation cannot be assessed. 

As emphasised in the introduction, excessive abstraction reduces water availability. The consequences are a fall in the level of ground water, water-courses or the volumes contained by the various dams. In some regions, agriculture is the main cause of these falls in ground water levels. That is the case, for example, in the Beauce region in France, the "acuiferos 23 and 24" located under the region of Castilla-La Mancha, and the "Campo de Dalias" in Almeria, Spain. In some regions, major actions involving the agricultural profession have been undertaken to reduce the pressure of agriculture on the environment and to restore ground water levels. That is the case, for example, in the Castilla-La Mancha region, where Spain’s first and main agri-environmental programme was developed with a view to safeguarding water resources and protecting the related ecosystems (Box 2).

Surface water and subsoil water

Surface water is the main source of water abstracted in most countries (figure 3), accounting for over 80% of abstractions in Finland, the Netherlands, the United Kingdom, Belgium, France, Germany and Spain. Only Denmark, Luxembourg and Austria abstract water primarily from the subsoil. These results should be put into perspective, however. Luxembourg, for example, buys its electricity from neighbouring countries and has no power stations (major consumers of surface water for cooling). The figures for Denmark refer to public supplies only and cannot, therefore, be compared with those of other countries. 

Subsoil water is generally of much better quality than surface water, as soil acts as a natural filter for percolating water. Most drinking water is abstracted subsoil, justifying particular care in the protection of subsoil water. The various European water directives (drinking water, nitrates), for example, set out specific actions for protecting water and water catchment areas. 

Whereas in Ireland, Germany, France, Spain and Greece, irrigation is carried out primarily with surface water, subsoil water is the leading source of irrigation water in Denmark, Sweden, the Netherlands, Austria and Portugal (figure 4). 

Development of irrigated areas 

The statistics published by the FAO show a clear upward trend in irrigable areas in the European Union Member States, even if this trend has slowed considerably in recent years. As regards the European Union of 15 Member States, irrigable surfaces rose by +152 000 ha/year between 1961 and 1980, +146 000 ha/year between 1980 and 1996 and +123 000 ha/year in the 1990s. This means that the irrigable area in the European Union rose from 6.5 million hectares in 1961 to 11.6 million hectares in 1996 (figure 5), namely a two-fold increase in overall irrigable land. However, trends vary considerably from one Member State to another:

• France shows the highest increase in irrigable area, totalling +25 000 ha/year between 1961 and 1980, +48 000 ha/year between 1980 and 1996 and even reaching a maximum of +59 000 ha/year in the 1990s. This means that irrigable land increased 4.5 times from 1961 to 1996. The largest increase was in the Poitou-Charentes region, where irrigated areas grew tenfold!
• Since 1961, irrigated areas in Greece have increased steadily at an annual rate of +28 000 ha/year.
• In Italy, there was a statistically significant increase in irrigable areas only in the period 1980-96 (+25 000 ha/year).
• In Portugal, the annual increase in irrigable areas has been limited and remains below 1 000 ha/year.
• The increase in irrigable area in Spain was significant up until 1980 (almost +60 000 ha/year), but has fallen sharply since. Irrigable areas rose by only +34 000 ha/year over the period 1980-1996 and there has been no statistically significant trend in the 1990s. Overall, irrigable area in Spain increased by 80% over the period 1961-1996.
• In the other Member States of the European Union, there was a clear upward trend during the 1960s and 1970s (+41 000 ha/year); since 1980, this figure has fallen to +12 000 ha/year. There has been no change in irrigable areas since 1990 (table 1).

Given the high temperatures and high evapotranspiration, average water consumption per hectare is higher in Southern European countries such as Italy, Portugal, Spain, and Greece. In Italy, the figure is as high as 1.282m ³/ha (figure 6). In the Netherlands, it is high compared with other Northern European countries owing to the significance of intensive agriculture in that country.

The quantity of water used for irrigation depends on various factors, such as climate, as the statistics in figure 6 illustrate, and crop types (box 3), soil characteristics, water quality, cultivation practices, the state of infrastructure and irrigation methods. The implementation and development of techniques such as the drip method improves the effectiveness of irrigation, which can reach 96%. These techniques reduce the volume of water abstracted for irrigation and decrease the investment in infrastructure for storing and gathering new water resources. They also reduce the problems associated with soil erosion and the salinisation of ground water in coastal areas. In the case of soils with high salinity levels or of subsoil irrigation waters with high salt content, the lower water output of these techniques does not, however, allow the quality of the soil to be restored and/or excess salts to be leached.

Agriculture, a non-point source of pollution 

The impact of water pollutants on the environment clearly depends on the quantity of pollutants discharged and on their physicochemical characteristics (Box 4). A distinction is made between point sources of pollution and non-point sources. While the former are fixed sources usually emitting high levels of pollutants, non-point sources are characterised by the emission of substances from mobile sources, by sources covering wide expanses or by a great number of sources of low-pollution emission. For example, discharges of waste water from industrial plants are point sources of nitrogen, whereas agriculture is a non-point source of nitrogen and pesticide pollution. Pollution from point sources is often easier to treat (for example by installing filters in the pipes through which the polluting products are released into the natural environment), while polluting emissions from non-point sources are difficult to calculate, to measure and, therefore, to control. 

Agriculture, the main source of nitrogen in water 

Nitrogen in water in the form of nitrates is a pollutant, since it stimulates eutrophication and can affect human health. Maximum admissible nitrate concentration limits have been set for drinking water. Directive 98/83/EC on the quality of drinking water specifies a compulsory limit of 50 mg/litre, matching the limits recommended by the World Health Organisation. 

Water contamination by nitrates is one of the main problems associated with agricultural activities. That is due among other things to the fact that nitrates are highly soluble and migrate easily into ground water through the soil. It is nonetheless difficult to establish a link between nitrogen supply and water pollution. The leaching of nitrates also depends on geological, climatic and biological factors. It is particularly common in porous rock aquifers and in wet climates. Nitrates can be de-nitrified by microbes, however. Despite these phenomena, over-use of fertilisers always increases the nitrate level of water. 

Nitrates and ammonium are the most common forms of nitrogen in rivers, with nitrates alone accounting for over 80% of total nitrogen. For the period 1992-1996, over 65% of the rivers in the European Union had average annual nitrate concentrations exceeding 1 mgN/litre. During the same period, concentrations of over 7.5 mgN/l were also found to exist in approximately 15% of cases. The highest concentrations are in Northwest Europe, where agriculture is particularly intensive (Europe's Environment: The Second Assessment). 

Clearly, the nitrogen in water does not come from agriculture alone, even if agriculture remains the largest source of nitrogen (Box 5). Industrial waste water also contains nitrogen, particularly water discharged by manufacturers of fertiliser or explosives, metal-processing industries and food-processing industries.

Domestic waste, the main source of phosphorus 

Phosphorus, an element necessary for plant growth, is the main cause of eutrophication and of water quality deterioration. Even a minimal phosphorus content (some tens of µg/l) can constitute a dangerous pollutant. Thus, according to the ECE (Economic Commission for Europe of the United Nations) classification of surface water, water is considered fairly eutrophic as of 25 µg/l. Phosphorus is analysed as soluble phosphate or as full phosphorus. It quickly develops into such low soluble forms as apatites. Much of the phosphorus is adsorbed into particles and suspended matter. As a result, soil acts as a phosphorus reservoir restricting the impact of excess supplies.

Agriculture produces phosphorus in the form of livestock effluents and mineral fertilisers (calcium or ammonium phosphates). The use of phosphorus in agriculture (see article nitrogen in agriculture), associated with the use of fertilisers, thus contributes to surface water pollution. Nevertheless, the main source of phosphorus in Europe is not agriculture, but domestic and industrial waste water. In France, for example, the phosphorus produced by agriculture accounts for only 23% of the total (figure 7).

The reduction in phosphorus discharges in recent years is in large part the fruit of the major actions undertaken to process domestic waste water and reduce industrial discharges. The agricultural sector, on the other hand, is only at the outset of a stringent phosphorus waste control policy, including, for example, measures designed to improve the storage of animal effluents and the implementation of environmentally friendlier cultivation practices.

Pesticides

Plant-care products can have undesirable side effects on man and the environment. While the toxicity for man and fauna of the various pesticides is relatively well-known, little research has been done into their adverse effect on the environment. Pesticide residues (insecticides, weedkillers, fungicides, etc.) are to be found in water, soil, air and food-stuffs. How they spread to the various parts of the environmental depends on the type of product, its method of application and its physicochemical characteristics. Owing to their high solubility, pesticides are readily transported by run-off and by drainage water or infiltrate into ground water.

Effective monitoring of pesticide residues in water would be a complex and costly affair. For want of adequate analyses it is impossible at present to assess the presence and scope of the residues of numerous pesticides likely to have adverse effects on health. A study in four countries of the European Union (Isenbeck-Scröter et al. 1997) shows that the pesticides most frequently detected in water analyses are atrazine, simazine and bentazone, all three substances being broad-spectrum weedkillers used not only in agriculture, but in industry and the household. Indeed, a considerable proportion of residues from plant-care products comes from the industrial production of plant-care products and from pesticide use by railway companies, road-maintenance/conservation services, private individuals and local communities.

Currently, a limited number of pesticides is being monitored. In many Member States, the pollution level of pesticides in the ground- and surface waters is often unknown. Directive 98/83/EC of 3 November 1998 on the quality of drinking water has set the maximum admissible concentrations of each substance at 0.1 µg/l and the total concentration of all pesticides at 0.5 µg/l. In addition, the Directive sets threshold values at 0.03 µg/l for the most toxic substances, for example aldrin, dieldrin, heptachlor and heptachlor-epoxide. The World Health Organisation also publishes threshold values for concentrations of pesticides in drinking water. These values are based on toxicological considerations and are less strict than the maximum concentrations allowed by the European Union. For example, the threshold value put forward by the World Health Organisation for atrazine is 2 µg/l. Atrazine is one of the most frequently used weedkillers in maize-growing. In view of the widespread pollution of ground water and drinking water in some regions, it also is one of the most frequently monitored molecules.

A case study: water quality in the Rhine basin

The Rhine basin is one of the largest basins in Europe. Its tributaries cross Switzerland, Austria, Liechtenstein, Italy, France, Germany, Luxembourg, Belgium and the Netherlands. The tributaries, subsoil water flows and waste water discharges introduce a great many substances into the Rhine and the river acts as a storage basin for pollutants of all kinds.

From 1981 to 1995, nitrate levels in the Rhine oscillated between 1.3 mg/l and 4.3 mg/l, reaching their peak in the mid 1980s. Phosphates also reached their peak at 4 mg/l in the same period. The concentration of nutrients increases as you go downstream, underlining the limits of the Rhine’s capacity to self-purify nitrogen and phosphate (map 1). Since 1985, the concentration of nitrates has remained relatively stable, with only a slight fall in concentration recorded at the German-Dutch border (Bimmen/Lobith), showing the limits of the current nitrate pollution control policies.

Compared with a nitrate concentration threshold for drinking water of 25 mg/l, average nitrate concentrations in the Rhine, ranging between 1 and 2 mg/l, are clearly risk-free for drinking purposes. From an ecological viewpoint however, the Rhine’s water quality is far from excellent. With total nitrogen concentrations of 2 mg/l and phosphorus concentrations of 60 m g/l the Rhine's waters are highly eutrophic and polluted (ECE Classification on the quality of fresh water for maintaining aquatic life).

On the other hand, phosphate levels have decreased considerably in the downstream basin. In 1995, the level was below 1 mg/l. This improvement is due to a combination of factors:

• Changes in the composition of detergents with phosphates being replaced by other softening molecules;
• Some sewage treatment plants have been equipped with facilities for eliminating phosphates;
• Industry and sewage treatment plants were forced to treat their effluents and to decrease their discharges into the natural environment;
• Falling consumption of phosphate fertilisers since the 1980s.

Pesticides remain a problem, however. Concentrations of atrazine in the river were between 0.01 m g/l and 0.34 m g/l in 1995 (map 2). At each of the four sampling stations, levels were determined as being above the threshold value of 0.1 m g/l. Nevertheless, atrazine concentrations remain below the threshold recommended by the World Health Organisation. It is worthwhile noting the high temporal variability of atrazine concentrations, which faithfully reflect the seasonal use of the product in agriculture. On account of its high infiltration capacity, peaks in atrazine concentration appear mainly between April and June. So it seems that, much remains to be done to contain the use of pesticides and reduce atrazine concentrations below the 0.1 µg/l mark.

The outlook

Both the quantitative and qualitative aspects of the issues identified in this chapter constitute a significant challenge for agriculture and the agricultural world. Numerous actions have already been implemented to reduce the impact of agriculture on water resources. For example, 20% of arable land is engaged in voluntary agri-environmental actions and over 2 million hectares are devoted to organic farming. These actions need to be expanded and strengthened if there is to be a sound water resource management ensuring better protection of water resources.

There are many possible actions and some have already been initiated or are in the discussion and negotiation phase. These include:

• actions taken at regional, national and European levels with a view to improving the implementation of the Directive on nitrates;
• participation of the agricultural profession in the implementing of water-management plans for catchment basins. In France, for example, such management plans (Water-Planning and Management Plan) are being drawn up for several catchment basins. These plans define objectives for water management and environmental protection, as well as a series of actions involving the various users of the resource in the pursuit of the declared objectives.
• the use of economic tools (taxes, subsidies) to modify the conduct of economic players as regards use of pollutants and water. A tax on pesticides and fertilisers already exists in some northern European countries. The introduction of water prices reflecting the true cost of irrigation is a further component of the Framework Directive on Water debated at European level.

However, these actions clearly need to be adapted at local levels to allow for the physical and hydrological specificities of the natural environment and the social and economic characteristics of the agricultural world.

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